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  • Combined effect of binder type and target mix-design parameters in delaying corrosion initiation time of concrete
    Constr. Build. Mater. (IF 4.046) Pub Date : 2020-01-17
    Bayezid Baten; Tanvir Manzur; Ishtiaque Ahmed

    Ingress of chloride ions is the prime determinant for inducing corrosion damage to marine Reinforced Concrete (RC) structures and subsequent lowered service life. Being attributable to high inherent permeability of concrete, chloride ions ingress can be hindered by appropriate selection of binder types and mix design parameters as means of safeguarding durability concerns while ensuring desired target strength and workability. Commercially available Portland Composite Cement (PCC) consists of general blends of different Supplementary Cementitious Materials (SCM) without any particular regard for durability and there is no proper guideline available to determine the ideal proportion or type of SCM for different mix design requirements. Hence, a comprehensive study is essential in inferring the ideal type and proportion of SCM for a range of common mix design parameters in marine environment. A study has, thereby, been conducted on local concrete mixes, designed for different strengths, with different proportions of fly-ash or slag as SCM for a wide range of water cement (w/c) ratios and target slump values. An overall comparison of both Corrosion Initiation Time (CIT) and compressive strength of each mix has also been evaluated. It has been evident that fly-ash, as SCM, has been significantly effective in enhancing CIT values of concrete mixes, although it affects compressive strength. A considerable effect of target slump range on CIT values has also been observed in the study. Furthermore, generalized graphs have been generated with CIT and strength values for each of the mix parameters with an aim to develop a quantitative guideline to tailor mix designs with ideal SCM selection while maintaining an optimum balance between desired strength, workability and durability concerns in marine environment.

    更新日期:2020-01-17
  • Experimental study on effect of resin matrix in basalt fiber reinforced polymer composites under static and fatigue loading
    Constr. Build. Mater. (IF 4.046) Pub Date : 2020-01-17
    Xing Zhao; Xin Wang; Zhishen Wu; Jin Wu

    To reveal the effect of resin matrix on the behavior and damage mechanism of basalt fiber reinforced polymers (BFRPs), the static and fatigue properties of different resin matrixes based BFRP composites were experimentally investigated. Four types of resins were adopted in this paper. They were normal and toughened vinyl ester resins, and epoxy systems curing at room temperature and at elevated temperature. In parallel to the static and fatigue tests, the damage observation were conducted using in-situ scanning electron microscopy (SEM) observation system embedded in the fatigue test equipment. The results showed that the resins played important roles in both of the static and fatigue behavior of BFRP composites. The static tensile strength of the normal vinyl ester resin based BFRP was similar to that of the BFRP with elevated temperature cured epoxy. However, the fatigue life of the former was significantly lower than that of the latter for more matrix cracking and fiber peeling occurred on the surface of the vinyl ester resin based BFRP. Although the static strength of the BFRP was lower with more ductile matrix like toughened vinyl ester or room temperature cured epoxy, the long-term fatigue strength level of BFRP increased with an increase in fracture elongation of the resins.

    更新日期:2020-01-17
  • Determining the water to cement ratio of fresh concrete by evaporation
    Constr. Build. Mater. (IF 4.046) Pub Date : 2020-01-17
    J. Bret Robertson; M. Tyler Ley

    The water-cement ratio (w/cm) is one of the most influential parameters to determine the quality of concrete. A new test method has been developed that uses external heat to evaporate the water from the concrete before it has hardened. Data are presented for 258 mixtures with 23 aggregates, 9 cements, 5 supplementary cementitious materials, and 15 different admixtures. For the laboratory testing, the average measured w/cm is within 0.01 from the batched w/cm with a coefficient of variation (COV) of 3.2%. A subset of these mixes was evaluated with the AASHTO T 318 microwave test and the measured w/cm is 0.05 higher than the expected value and the COV is almost three times higher (8.9%). Field data is also presented from 27 mixtures and the measured w/cm shows good agreement with the batched values. The method, calculation, and practical applications of this new test method are presented.

    更新日期:2020-01-17
  • Behaviors of GFRP-steel bonded joints under cyclic loading after hygrothermal aging
    Constr. Build. Mater. (IF 4.046) Pub Date : 2020-01-16
    Jie Liu; Tong Guo; Matthew H. Hebdon; Xiaming Yu; Libin Wang

    This paper presents experimental results of double-lap steel Glass Fiber Reinforced Polymer (GFRP) bonded joints which were subjected to fatigue loading after different harsh environmental aging. Bonded joints were manufactured, cured, and tested to study the fatigue behaviors of the GFRP-steel bonded specimens after hygrothermal aging. Experimental results indicated that the hygrothermal environment could negatively affect the fatigue performance of the bonded specimens. In particular, in comparison with the reference specimens, the most significant reduction of fatigue life for harsh cured specimens was 61.2% when the load level was 70% of the ultimate tensile strength. Finally, based on the analysis of the energy dissipation in each load cycle, relative energy dissipation Ere of each specimen was proposed, by which the accelerating point of Nac was obtained to quantify the damage evolution of the bonding joints under cyclic load after being cured in a certain hygrothermal environment.

    更新日期:2020-01-17
  • Comparative analysis of HMA aggregate variability based on impacting and gyratory compaction
    Constr. Build. Mater. (IF 4.046) Pub Date : 2020-01-17
    Haitao Zhang; Tengjiang Yu; Yingli Huang

    In proportion design of hot mix asphalt (HMA), the aggregate gradation in HMA is one of the most important influencing factors on HMA mechanical behavior. During the process of aggregate compaction, the gradation of the aggregate will change at some extent, namely, the aggregate gradation after compaction will be different from the original design gradation, it will influence the HMA design results. Therefore, study on the variability of aggregate gradation at different compaction conditions has a theoretical and practical value. The objective of the project is to explore the influence of different compacting methods on aggregate gradation between Marshall and Superpave methods. Different compaction methods are used to compact different aggregates, then the variability of aggregate gradation under different compaction conditions is analyzed. The research results have shown that although the method of Superpave gyratory compaction generally has the less influence on aggregate gradation than that of Marshall impacting compaction, the detailed influence on the gradation of coarse, medium and fine aggregates between two methods is different. The findings can provide a technical reference for aggregate gradation in HMA proportion design.

    更新日期:2020-01-17
  • 更新日期:2020-01-17
  • The use of non-destructive testing to evaluate the compressive strength of a lime-stabilised rammed-earth wall: Rebound index and ultrasonic pulse velocity
    Constr. Build. Mater. (IF 4.046) Pub Date : 2020-01-17
    Juan Jesús Martín-del-Rio; Jacinto Canivell; Raúl M. Falcón

    The non-standardization of rammed earth construction involves the quality control of such a technique to be so troublesome that it is generally avoided. As a possible approach to improve the mentioned quality control, this paper deals with a series of univariate and multivariate statistical analyses concerning the correlation between a pair of non-destructive testings (rebound index and ultrasonic pulse velocity) and the compressive strength of a specific composition of rammed earth. Both non-linear (univariate) and linear (multivariate) regression models are established so that the variability of the compressive strength is accurately explained by means of both kind of non-destructive testings.

    更新日期:2020-01-17
  • The influence of steel fiber on water permeability of concrete under sustained compressive load
    Constr. Build. Mater. (IF 4.046) Pub Date : 2020-01-16
    Dong Li; Shi Liu

    In order to investigate the influence of steel fibers on the water permeability of concrete at serviceability stage, a self-designed device was adopted and the permeability test was conducted on hollow cylindrical specimens under a sustained compressive load. The combined effect of steel fiber and compressive load on water permeability of concrete was analyzed. Ultrasonic pulse velocity was also measured to verify the damage of the concrete caused by the compressive load. The results demonstrated that the water permeability of the concrete was affected by the compressive load, a significant increment in the permeability coefficient occurred when the applied load exceeded the threshold value. The addition of steel fiber demonstrated positive effects on permeability of concrete under compressive load. The threshold value corresponding to permeability properties of the concrete under compressive load was improved with the increasing of fiber content. The ultrasonic pulse velocity of the concrete under compressive load was also influenced by addition of steel fiber. The variation of the ultrasonic pulse velocity has a certain similarity with the variation of the permeability coefficient of the specimen under compressive load. Ultrasonic pulse velocity test may be an efficient method to evaluate the permeability of concrete at service load.

    更新日期:2020-01-17
  • Establishment of linkages between empirical and mechanical models for asphalt mixtures through relaxation spectra determination
    Constr. Build. Mater. (IF 4.046) Pub Date : 2020-01-17
    Dier Yu; Xin Yu; Yanxia Gu

    Empirical algebraic models as Generalized Sigmoidal model (GSM) and Havriliak-Negami model (HNM) are selected as the pre-smoothing models for comparison. Asphalt mixtures with raw, modified and resin blended binders are tested for original dynamic moduli and phase angles within the linear viscoelastic region by the simple performance test. Three approaches of GSM are evaluated to enhance the accuracy of constructing master curves. The results indicate that modulus master curves are asymmetric with shape parameters less than 1 for thermo-plastic mixtures, and larger than 1 for thermo-setting mixtures, while the most accurate modeling phase angles are from HNM due to its exact Kramer-Kronig relations. The discrete relaxation spectra are derived from pre-smoothed data through the Windowing methods (WMs) with Generalized Maxwell model (GMM) based Storage Algorithm and Loss Algorithm (GM-SA and GM-LA). Windows regions of algorithms are modified to be suitable for iterations. Continuous spectra are determined to verify the accuracy of obtained discrete spectra through inverse Fourier transforms. The results indicate that the discrete spectra with high spectrum points density r = 2 from HNM are more consistent with the discretized continuous spectra than those from GSM with low density r = 1. Moreover, the WMs with empirical pre-smoothing models take obvious advantages in parameters adjustments and relaxation times distribution selections. GM-LA rather than GM-SA exhibit higher accuracy and convergence rate in spectra determinations, since the kernel functions. In addition, the comparisons between the GMM recovered and GSM or HNM measured modulus with fit goodness statistics show that low density of spectrum points per decade is the main reason in the GMM loss modulus oscillations. However, the deviations are less obvious between HNM pre-smoothed moduli and GMM generated moduli than those between GMM-GSM moduli. Therefore, the linkages between empirical and mechanical models are established on relaxation spectra determination by modified WM using GM-LA with denser spectrum distribution r = 2.

    更新日期:2020-01-17
  • Use of bacteria for repairing cracks and improving properties of concrete containing limestone powder and natural zeolite
    Constr. Build. Mater. (IF 4.046) Pub Date : 2020-01-17
    Maedeh Sadat Jafarnia; Mehdi Khodadad Saryazdi; Seyed Mohammad Moshtaghioun

    Precipitation of calcium carbonate crystals caused by the metabolic activities of certain microorganisms is a relatively new method which can improve the properties of concrete and repair concrete cracks. The present study investigated the effects of Sporosarcina pasteurii bacteria on healing cracks, compressive strength, tensile strength, ultrasonic pulse velocity, electrical resistivity and microstructure of concrete containing various percentages of limestone powder and natural zeolite. Experimental results show that the microbial calcite precipitations enhanced compressive strength, tensile strength, ultrasonic pulse velocity and electrical resistivity of all specimens at all ages. The maximum values of these parameters are related to the bacterial specimen containing 10% zeolite without limestone powder. The SEM images of the specimens show that the amount of calcite crystals in the bacterial treated specimen containing limestone powder is more than the specimen without that. In addition, crack healing of the specimen containing limestone powder was also slightly better than the specimen without that. The results of Fourier-Transform Infrared spectroscopy show that the precipitation formed at crack surfaces of specimens is CaCO3.

    更新日期:2020-01-17
  • Flexural strength and failure trend of bamboo and coir reinforced cement stabilized rammed earth wallettes
    Constr. Build. Mater. (IF 4.046) Pub Date : 2020-01-17
    Deb Dulal Tripura; Satish Gupta; Bandana Debbarma; Raavi Satya Sai Deep

    Present study investigates the flexural strength and failure trend of unstabilized and cement stabilized rammed earth (CSRE) wallette with and without bamboo and coconut fiber reinforcement. Twenty four wallettes were prepared and tested under lateral load applied parallel and perpendicular to the compacted layers. Test results shows that the wallette loaded perpendicular to compacted layers/bed joints possesses higher flexural strength. CSRE wallette reinforced with bamboo and fiber shows 139% to 167% higher flexural strength than that of unstabilized rammed earth and shows improved ductility property. Flexural strength obtained in the current study ranges from 0.54 MPa to 2.11 MPa which is comparable to good quality burnt clay bricks masonry wallette strength. Initial failure cracks was observed at bed joint and mid-span for unreinforced samples and shear cracks was observed for bamboo and fiber reinforced samples. Lastly, the reinforced walls can be used for strengthening single leaf internal and external load bearing walls of single or two storey houses depending upon area seismicity.

    更新日期:2020-01-17
  • Study on the fire resistance performance of cementitious composites containing recycled glass cullets (RGCs)
    Constr. Build. Mater. (IF 4.046) Pub Date : 2020-01-17
    Binmeng Chen; Honggang Zhu; Bo Li; Manlung Sham; Zongjin Li

    Glass manufacturing involves abundant amount of natural resources including thermal energy and it is important to explore various ways to ultilize the used glass instead of direct disposal to landfill. One way to recycle the glass products is to crush them into cullets and mix the cullets into cement as filler/aggregate. In this study, the effects of recycled glass cullets (RGCs) with different sizes on the fire resistance performance of cementitious composite were studied. Cementitious composite samples were prepared with RGCs at 4 different sizes, i.e. below 0.6 mm, 0.6–1.18 mm, 1.18–2.36 mm and 2.36–4.75 mm. In order to evaluate the fire resistance of the composites with RGC, the composites samples were heated at different temperatures, and their residual strength, integrity and thermal conductivity were measured accordingly. Moreover, a specially designed furnace in accordance with modified BS 476-22 was employed to observe the thermal insulation and integrity of mortar panels under testing. The microstructure of RGCs mortar was observed under microscope and it was found that adding RGCs inside the composite improved the fire resistance of mortar. The beneficial effect of RGCs on fire resistance was found to reduce with increasing RGCs size, where RGCs finer than 0.6 mm showed the most significant beneficial effect. This is presumably attributed to the softening and state transformation of fine glass cullet at high temperature.

    更新日期:2020-01-17
  • Study of surface microscopic properties of asphalt based on atomic force microscopy
    Constr. Build. Mater. (IF 4.046) Pub Date : 2020-01-16
    Xiaoping Ji; Yueqin Hou; Haiwei Zou; Bo Chen; Yingjun Jiang

    In this paper, atomic force microscopy (AFM) was utilized to investigate the surface microscopic morphology (SMM) and bee structure (BS) of several asphalts and quantitatively evaluate them via roughness theory. The effects of asphalt properties, aging, moisture and anti-stripping agents on the SMM and BS were studied comprehensively. Five types of asphalts were investigated, and each asphalt was prepared with four different conditions. The results showed that the oil source was the only factor among the asphalt properties that influenced the presence of BS, and the BS changed the SMM. The larger the asphalt grade was, the rougher the asphalt SMM, the larger the BS number and the smaller the BS size. The SMM of SBS-modified asphalt was flatter than that of the original asphalt. After aging, the SMM of matrix asphalt became smooth, while the SMM of SBS-modified asphalt became rough. Compared to the original asphalt, the BS number and size of the aged asphalt increased and decreased, respectively. After immersion in water, the phenomenon of water piercing occurred on the asphalt surface, which further changed the SMM and BS; specifically, the roughness of the SMM increased, the BS size decreased, the BS peak increased, and the BS valley decreased. After being blended with the anti-stripping agent, the SMM of the matrix asphalts became smooth, and the SBS-modified asphalts became rough; the BS number increased, the BS size decreased, and both the BS peak and the maximum valley decreased.

    更新日期:2020-01-17
  • Production of new electromagnetic wave shielder mortar using waste mill scales
    Constr. Build. Mater. (IF 4.046) Pub Date : 2020-01-16
    Murat Ozturk; Tolga Depci; Ersin Bahceci; Muharrem Karaaslan; Oguzhan Akgol; Umur Korkut Sevim

    Electromagnetic (EM) wave shielder mortar can be produced by mixing cement, natural limestone, tap water with mill scale (mill scale-I and mill scale-II) which is one of the biggest disposal area problems of the iron-steel sector in Iskenderun, Hatay. In this paper, the detail analysis and information were presented on the influence of electromagnetic properties of mortars including iron steel industry waste mill scales to contribute the solving waste problems. The mortar samples were prepared using different volume of mill scales (5, 10, 15 and 30%) which were substituted with the natural fine aggregate. The mechanical properties (flexural and compressive strength) and the EM shielding properties (using the free space test method) of the mortars were compared with each other and also a control mortar samples. Our results indicated that the obtained mortars containing 15% mill scale had nearly same mechanical properties with the control mortar and they provided better solution for EM shielding. Especially, the mortar containing mill scale-II might be used to create novel construction material with shielding characteristics in entire wireless communication bands due to the cubic crystal structure and ferromagnetic properties of the mill scale-II. The mortar prepared using mill scale-I might be utilized to fabricate novel high strength radomes that behave as air in transmission respect. All experimental results point out that the waste mill scales are viable candidates for EM wave shielder for the buildings and will gain added value as well as solve the scale storage problem of the iron and steel industry.

    更新日期:2020-01-17
  • Rheology, shrinkage and pore structure of alkali-activated slag-fly ash mortar incorporating copper slag as fine aggregate
    Constr. Build. Mater. (IF 4.046) Pub Date : 2020-01-16
    Nanqiao You; Yongchao Liu; Dawei Gu; Togay Ozbakkaloglu; Jinlong Pan; Yamei Zhang

    his study was conducted to investigate the effect of the use of copper slag (CS) as fine aggregate to replace natural sand (NS) at different volume replacement levels (namely, 0%, 20%, 40% and 60%) on the properties of alkali-activated slag-fly ash (AASF) mortars. In addition, both low calcium (LC) and high calcium (HC) alkali-activated slag-fly ash (AASF) mortars were used to studied the influence of the mass ratio of fly ash to fly ash and slag on the properties of mortars. The workability, mechanical properties, autogenous and drying shrinkage and pore structure of mortars were investigated. Results show that using CS to replace NS in AASF mortars at appropriate levels (i.e. 20% and 40%) slightly increases the fluidity, yield stress, consistency, and mechanical strength, while restraining the drying shrinkage and refining the pore structure of mortars. However, when the replacement ratio is increased to 60%, the mortar becomes inhomogeneous due to the high density of CS particles, leading to poor performance of mortars. The use of CS as fine aggregate at a suitable level in AASF mortars can reduce NS consumption while also providing an avenue for value added use of CS.

    更新日期:2020-01-17
  • Assessment of wave modulus of elasticity of concrete with surface-bonded piezoelectric transducers
    Constr. Build. Mater. (IF 4.046) Pub Date : 2020-01-17
    Haifan Yu; Linjun Lu; Pizhong Qiao

    Measurement of the modulus of elasticity of concrete based on wave propagation technique is a critical method to assess condition and performance of concrete materials and structures. In this study, a combined numerical and experimental study is conducted for assessment of wave modulus of elasticity (WMoE) of the fully-cured concrete using surface-bonded PZT (lead zirconate titanate) transducers, also so called smart piezoelectric modules (SPMs). Rayleigh wave (R-wave) acquired from the surface-bonded PZT transducers is selected as the main target signal, and the explicit physical relationship between R-wave and WMoE is applied in signal processing. Piezoelectric solid element and electric load are applied to model the PZT transducers and actuate stress waves in numerical simulation, respectively. The numerical analysis provides a better understanding of surface wave propagation in concrete and sheds light on physical experiment. Effects of excitation frequency, excitation waveform, and size of PZT transducers are first examined in numerical simulation and then validated by physical experiment. Good agreements between the numerical and experimental results show that the Hanning windowed 5-peak or 7-peak sinusoidal tone burst at the frequency range of 40 kHz to 100 kHz is recommended as the excitation signals; while the width-to-thickness ratio of square transducers ranging from 10 to 15 is suggested for selection and design of surface-bonded PZT transducers. Effective measurement of WMoE using the surface-bonded PZT transducers shows great potential for nondestructive evaluation of concrete, and it can be used for condition assessment and health monitoring of concrete structures.

    更新日期:2020-01-17
  • The influence of double-layered distribution of fire retardants on the fire retardancy and mechanical properties of wood fiber polypropylene composites
    Constr. Build. Mater. (IF 4.046) Pub Date : 2020-01-17
    Lichao Sun; Yanjun Xie; Rongxian Ou; Chuigen Guo; Xiaolong Hao; Qinglin Wu; Qingwen Wang
    更新日期:2020-01-17
  • Performance of geopolymer mortar cured under ambient temperature
    Constr. Build. Mater. (IF 4.046) Pub Date : 2020-01-17
    Mohamed G. Khalil; Fareed Elgabbas; Mohamed S. El-Feky; Hany El-Shafie

    Recently, the application of green concrete as an alternative for conventional concrete has become popular worldwide. The innovative green concrete can be produced using waste materials as one of its components. Therefore, recent years witnessed a huge increase in the studies that investigate geopolymer’s fresh and hardened properties. The previous studies show that workability loss, rapid setting time and the need for heat curing are the main constraints that restrict the production of cast in place geopolymer concrete. This study aims to reach the optimum activator modulus which achieves the maximum compressive strength with acceptable workability. Nine different mixtures were blended using industrial by-products, such as Ground Granulated Blast Furnace Slag (GGBS) and Metakaolin (MK). Two main materials mixtures were used; either slag or 50/50 slag/MK. Sodium hydroxide and sodium silicate were used as an activator. The main variables were the base material (GGBS and MK), water/binder ratio (0.0, and 15.0%), and modulus of silicate (1.1, 1.3, 1.5, and 1.7). Fresh and hardened properties were examined using the flow table test, and compressive strength test, respectively. It has been observed that by increasing the modulus of silicate, the workability increased and the compressive strength decreased. Adding water decreased compressive strength significantly, as well. Based on the statistical analysis, it was concluded that the mixture of 1.7 modulus of silicate is the optimum mixture. It worth mentioning that the compressive strength of the optimum mixture after 7, 28 and 90 days of water curing were 19.6, 33.4 and 35.6 MPa, respectively, and its flowability was about 150%.

    更新日期:2020-01-17
  • Strength and ultrasonic properties of cemented waste rock backfill considering confining pressure, dosage and particle size effects
    Constr. Build. Mater. (IF 4.046) Pub Date : 2020-01-17
    Jiangyu Wu; Hongwen Jing; Qian Yin; Bo Meng; Guansheng Han

    It is of great significance to study the material properties of cemented waste rock backfill (CWRB) for preventing mining damages, solving environmental problems and ensuring engineering security. Consequently, this paper carried out the comprehensively factorial tests to investigate the effects of the confining pressure, dosage of cementitious material and particle size distribution (PSD) of aggregate particles on the strength and ultrasonic properties of CWRB, for which the PSD of aggregate particles obeyed Talbot gradation theory. The results show that the relations between the confining pressure and dosage of cementitious material and the compressive strength and ultrasonic pulse velocity (UPV) of CWRB present the positively linear functions. However, the relations between the PSD of aggregate particles and the UPV, compressive strength, cohesive force and internal friction angle of CWRB perform the quadratic functions. It is considered that there is an optimal PSD of aggregate particles in the CWRB for characterizing its optimum material properties, and using the gradation Talbot index for describing that optimal PSD is between 0.4 and 0.6. The microstructure characteristics show that the CWRB with finer PSD of aggregate particles produces more distributions of microvoids and microcracks, while the CWRB with coarser PSD of aggregate particles contains coarser microvoids and microcracks that cannot be completely filled by hydration products and secondary hydration products. However, the dense hydration products can be formed among the particles in the CWRB with a suitable PSD of aggregate particles to reduce these defects. Its mechanism is considered that the superior PSD of aggregate particles can improve the microstructure of CWRB including the scale and distribution of defects, thereby resulting in the improvements of its strength and ultrasonic properties.

    更新日期:2020-01-17
  • Promotion on self-healing of cracked cement paste by triethanolamine in a marine environment
    Constr. Build. Mater. (IF 4.046) Pub Date : 2020-01-17
    Hao Liu; Haoliang Huang; Xintong Wu; Xiaobo Wang; Jie Hu; Jiangxiong Wei; Qijun Yu

    In order to hinder ingress of aggressive ions from sea water via cracks efficiently, it is of great significance to realize rapid self-healing in concrete. In this study, the feasibility to promote self-healing of cracked cement paste in sea water by using triethanolamine (TEA) was investigated. To enlarge the effects of TEA, 0.5–2% (by mass of cement) TEA was added into cement pastes and it was found that TEA can dramatically enhance the self-healing efficiency in sea water conditions. In cement pastes with TEA more than 1% (by the mass of cement), the crack closure ratio can reach 100% at a healing period of 1 d in sea water, 20 times faster than a cement paste without TEA. The permeability of cracked specimen with TEA decreased by about 90% after a healing period of 2 days. At the early stage of self-healing promoted by TEA, large amounts of Mg(OH)2 was formed, accounting for about 70 wt% of the reaction products of self-healing. It is well known that TEA can not chelate with Mg2+ ions. Therefore, the large amounts of Mg(OH)2 leading to complete self-healing of cracks in a short time indicates that the promotion on self-healing by TEA was not mainly caused by the chelating action. Experimental results show that in sea water with the high concentration of Mg2+, the property of TEA to increase its surrounding OH− concentration induces the formation of Mg(OH)2. This is the main mechanism of the promotion on self-healing of cracks by TEA in cement paste in sea water.

    更新日期:2020-01-17
  • Correlate aggregate angularity characteristics to the skid resistance of asphalt pavement based on image analysis technology
    Constr. Build. Mater. (IF 4.046) Pub Date : 2020-01-17
    Hainian Wang; Chonghui Wang; Yin Bu; Zhanping You; Xu Yang; Markus Oeser

    The impact of aggregate morphological characteristics plays a key role in the skid resistance of road surface due to driving safety and cost benefits. The 2nd generation of the Aggregate Imaging Measurement System (AIMS II) and X-ray Computed Tomography (CT) were utilized to evaluate the shape of particles and capture the change in their morphological characteristics. The Los Angeles Abrasion (LAA) Test was also conducted in this paper to investigate the influence of variations in aggregate angularity on the resistant performance of asphalt mixtures. Before and after 100, 300, 500, and 1000 rotations of LAA polishing process, 48 particles from each different size were adopted and measured using AIMS II and XCT to obtain the value of their morphological properties. The parameter gradient angularity (GA) with AIMS II and three-dimensional angularity (3DA) with XCT of aggregate surface area were proposed from these tests. Analysis of Variance (ANOVA) was employed to compare these two image analysis systems. Conventional experiments including the sand patch test and British pendulum test, were applied using the prepared aggregates to establish a correlation between the morphological properties of grains and the parameters related to the skid resistance of asphalt mixtures. It was found that the resistance performance of asphalt mixtures can be well described with a function using the value of morphological properties through regression analysis. The efficacy of the X-ray CT analyzing system was verified to evaluate the performance of asphalt mixture pavement precisely. The changes in morphological characteristics of particles are the main causes for degradation in the skid resistance of asphalt pavement.

    更新日期:2020-01-17
  • Healing fine cracks in concrete with bacterial cement for an advanced non-destructive monitoring
    Constr. Build. Mater. (IF 4.046) Pub Date : 2020-01-17
    Nimrat Pal Kaur; Subhra Majhi; Navdeep Kaur Dhami; Abhijit Mukherjee

    Cracks in concrete are inevitable and they can adversely affect the service life of structures. An efficient method to heal the cracks coupled with a reliable monitoring technique is of paramount importance. Standard crack healing materials are unable to penetrate thin cracks [1]. This paper presents an experimental demonstration of healing of fine cracks of around 0.6 mm using the bacterial based healing technique. Simultaneously, the evidence and efficiency of bacterial healing is investigated using advanced monitoring techniques. Ultrasonic signals passing through the healing area have been recorded and the waveform has been studied to interpret the condition of the crack. It has been validated through a series of water-tightness tests. The bacterial technique was able to heal the crack to the extent that no water was seen to permeate through the crack. The evidence of bacterial healing was confirmed through scanning electron microscopy and X-ray dispersion spectrum. It was found that the ultrasonic technique is able to monitor the progression of healing.

    更新日期:2020-01-17
  • Use of expanded polystyrene in developing solid brick masonry units
    Constr. Build. Mater. (IF 4.046) Pub Date : 2020-01-16
    Youmna A.Y. Ali; Ezzat H.A. Fahmy; Mohamed N. AbouZeid; Yoursy B.I. Shaheen; Mohamed N. Abdel Mooty

    This paper presents the results of an experimental program aimed at using expanded polystyrene (EPS) wastes in developing lightweight mortar and masonry solid brick units of adequate mechanical and thermal characteristics for use in building and construction applications. Five dosages of EPS were used to partially substitute the sand in the mix, namely; 0, 10, 15, 20 and 26 kg/m3. The results showed that the density, compressive strength, tensile strength, static modulus of elasticity, and coefficient of thermal conductivity decrease with the increase of the EPS dosage in the mix. The results showed also that the proposed EPS solid bricks possess adequate strength for non-loadbearing applications have superior thermal properties.

    更新日期:2020-01-16
  • The feasibility of properly raising temperature for preparing high-volume fly ash or slag steam-cured concrete: An evaluation on DEF, 4-year strength and durability
    Constr. Build. Mater. (IF 4.046) Pub Date : 2020-01-16
    Shiyu Zhuang; Jianwei Sun

    Properly raising steam-curing temperature may aggravate the delayed ettringite formation (DEF) and be adverse to the long-term performance of concrete while adding fly ash or slag may alleviate the DEF and be beneficial to the long-term performance of concrete. However, their comprehensive effect is still unclear. In this paper, the feasibility of properly raising temperature from 60 °C to 80 °C for preparing high-volume fly ash or slag steam-cured concrete (HFC-80 or HSC-80) is investigated by evaluating the comprehensive effect of properly raising steam-curing temperature and adding fly ash or slag on the DEF, 4-year strength and durability. Plain cement concrete with 60 °C and 90 °C (PC-60 and PC-90) steam curing is used as the reference. The results show that DEF in HFC-80 is significantly delayed compared with that in PC-90 while DEF does not occur in HSC-80. The expansion of HFC-80 at 4 years is significantly larger than that of PC-60 while the expansion of HSC-80 is as small as that of PC-60. The compressive strength of HFC-80 or HSC-80 at 4 years is 12%-18% smaller than that of PC-60 while the resistance to chloride ion permeability of HFC-80 or HSC-80 at 4 years is better than that of PC-60. Therefore, it can be preliminarily judged that properly raising steam-curing temperature may be unfeasible for HFC but feasible for HSC in terms of in terms of the above results.

    更新日期:2020-01-16
  • The influence of steel fibre properties on the shrinkage of ultra-high performance fibre reinforced concrete
    Constr. Build. Mater. (IF 4.046) Pub Date : 2020-01-16
    Chengfeng Fang; Mohamed Ali; Tianyu Xie; Phillip Visintin; Abdul H. Sheikh

    In this study, the effects of fibre volume fraction, fibre type, and aspect ratio on various shrinkages of the ultra-high performance fibre reinforced concretes (UHPFRCs) were experimentally investigated. Single fibre pull-out tests were conducted and the corresponding results were incorporated to explore the underlying mechanism governing the magnitudes of both autogenous and drying shrinkages. In general, the presence of randomly distributed steel fibres was found to reduce both the total and autogenous shrinkage, and more specifically, an increase in fibre volume fraction or fibre aspect ratio results in significant mitigation in both total and autogenous shrinkages. Hook-end fibres were found to be more effective in restraining autogenous shrinkage compared to straight fibres and consequently blended fibre mixes that include straight fibres were less effective at restraining shrinkage than only hooked-end fibres.

    更新日期:2020-01-16
  • Influence of low-grade bauxite on the properties of magnesium phosphate cement
    Constr. Build. Mater. (IF 4.046) Pub Date : 2020-01-15
    Yuantao Liu; Zhaohui Qin; Bing Chen

    This article investigated the influence of low-grade bauxite (LG-bauxite) on the properties of magnesium phosphate cement (MPC), which were explored by testing the properties of the fresh mixture (fluidity, setting time, and temperature evolution), measuring the strengths, analyzing the hydrates and observing the microstructure. With the successive additions of LG-bauxite, the fluidity continued to increase to a value of 267 mm, and the setting time was prolonged from 13 min to 26 min. The use of LG-bauxite also improved the mechanical properties of hardened MPC samples, and the group containing 10% LG-bauxite yielded the highest compressive strength of 91.2 MPa at 28 days. In addition, by the technique of X-ray diffraction (XRD), thermogravimetric analysis (DTA-TGA), scanning electron microscopy (SEM) and backscattered electron image (BSE) equipped with energy dispersive spectrometer (EDS), the micro-analyses for the MPC pastes was carried out. The obtained results all confirmed the pore-filling effect of LG-bauxite in MPC system and illustrated the formation of new phases, which was thought to be the alumina phosphate hydrate and some aluminosilicate gels. The fresh MPC slurry blended with LG-bauxite exhibited a lower exothermic reaction intensity and a slower hardening stage, which showed that it could be used as a kind of quick repair material.

    更新日期:2020-01-15
  • Residual performance of HPFRCC exposed to fire – Effects of matrix strength, synthetic fiber, and fire duration
    Constr. Build. Mater. (IF 4.046) Pub Date : 2020-01-13
    Doo-Yeol Yoo; Soonho Kim; Gi-Joon Park; Jung-Jun Park

    This study investigates the effects of matrix strength, synthetic fiber content, and heating duration on the explosive spalling resistance and residual compressive and flexural properties of high-performance fiber-reinforced cementitious composites (HPFRCCs). Three different matrix strengths, ranging from 100 to 180 MPa; four different volume fractions of synthetic fibers, i.e., polypropylene (PP) and nylon (Ny) fibers, ranging from 0% to 0.6%; and three different fire durations of 1, 2, and 3 h under the ISO standard fire curve were adopted. Scanning electron microscope (SEM) images were obtained to evaluate the microstructural states of HPFRCCs and a mercury intrusion porosimetry (MIP) analysis was conducted to determine pore size distribution characteristics before and after fire exposure. The test results indicate that the addition of PP and Ny fibers is effective at enhancing the explosive spalling resistance, and higher amounts are required for higher strength matrices. The compressive strength of HPFRCCs decreased by more than 75% after the fire (≥950 °C), and higher residual compressive strengths were obtained with shorter fire durations and higher amounts of added PP and Ny fibers. The toughness was decreased by the fire more than the flexural strength, and the residual flexural performance were enhanced with higher amounts of synthetic fibers and matrix strengths. In particular, the residual flexural performance significantly decreased when the fire duration increased from 1 to 2 h, and only a minor change was observed thereafter. The effectiveness of higher amounts of synthetic fibers at improving the residual performance diminished with longer fire durations.

    更新日期:2020-01-14
  • Dispersion of different carbon-based nanofillers in aqueous suspension by polycarboxylate comb-type copolymers and their influence on the early age properties of cementitious matrices
    Constr. Build. Mater. (IF 4.046) Pub Date : 2020-01-10
    Marco Liebscher; Tin Trong Dinh; Christof Schröfl; Viktor Mechtcherine

    The dispersion behaviour of different carbon-based nanofillers in deionized (DI) water was investigated in the study at hand by using polycarboxylates as surfactants. Carbon nanotubes (CNTs), carbon black (CB) and expanded graphite (EG) were firstly characterized in respect of their morphology. Subsequently, they were dispersed in DI water using two polycarboxylate (PCE) comb-type copolymers which differed in length of their chemical backbones. Optical microscopy and light transmission analysis during centrifugation disclosed a clear difference in the dispersibility among the nanofillers under investigation. Small CB particles showed excellent dispersion in DI water even with no surfactant. CNT was dispersed significantly better than EG, whereby the PCE with the longer backbone yielded better filler dispersion in both cases. After incorporating the carbon nanofillers into a cementitious matrix, interestingly, the highest compressive and flexural strengths at an early age were measured for the CNT samples with worse filler dispersion. This effect is explained by the role of the PCE and the aspect ratio of the carbon nanofiller, both of which determine the microstructure in the hardened cement-based matrix collaboratively.

    更新日期:2020-01-11
  • A review on performance of polyester fibers in alkaline and cementitious composites environments
    Constr. Build. Mater. (IF 4.046) Pub Date : 2020-01-10
    Rouhollah Rostami; Mohammad Zarrebini; Mansoor Mandegari; Davood Mostofinejad; Sayyed Mahdi Abtahi

    The performance of various fibers as a reinforcement in cementitious composites has been studied by many researchers. The point of paramount importance is that cement-based materials are highly alkaline environment. Polyethylene terephthalate (PET) as a man-made fibers in alkaline environment can be subjected to degradation. The available information on stability of PET fibers in cement-based materials is insufficient and inconsistent. Although some researches have rejected the use of these fibers as a suitable reinforcing element in cementitious composites, there are others that have positively advocated the use of such fibers in concretes. This review paper aims to thoroughly investigate the performance of PET fibers in alkaline environment of cementitious composites. Thus chemical degradation of PET fibers and their subsequent behavior when used in alkaline environment of cementitious composites is well documented. The paper encompasses an up to date critical evaluation of the so far conducted research works and additional future research requirements in this field. The overall conclusion that can be drawn is related to the fact that, despite degradation of the added PET fibers, in most applications properties of the cementitious composites can be enhanced. This phenomenon can be attributed to improvement resulted from other properties of the PET fibers in alkaline environment.

    更新日期:2020-01-11
  • Effect of superplasticizers on properties of one-part Ca(OH)2/Na2SO4 activated geopolymer pastes
    Constr. Build. Mater. (IF 4.046) Pub Date : 2020-01-10
    Yazan Alrefaei; Yan-Shuai Wang; Jian-Guo Dai; Qing-Feng Xu

    This paper investigates the effect of three different superplasticizers (SPs), Naphthalene (N), Melamine (M) and Polycarboxylate (PC), on the properties of one-part fly ash/slag geopolymer pastes activated by Ca(OH)2/Na2SO4 powder combination. The flowability, setting time, and compressive strength of the achieved geopolymer pastes were assessed. It was found that the superplasticizers significantly improved the flowability, retarded the setting time, and increased the compressive strength of the one-part Ca(OH)2/Na2SO4 geopolymer pastes. The most recommended superplasticizer was found to be polycarboxylate. The use of polycarboxylate SP for decreasing the water content (i.e. w/b) in Ca(OH)2/Na2SO4 geopolymer pastes has resulted in reducing the porosity and enhancing the compactness of the aluminosilicate gel, therefore, improved the compressive strength. It was found that the excessive use of polycarboxylate (i.e. 3%) for additional water reduction in Ca(OH)2/Na2SO4 geopolymer pastes had an adverse effect; it extended the induction period and delayed the participation of reaction products, thus significantly prolonged the setting time. Furthermore, a comparison between the achieved Ca(OH)2/Na2SO4 geopolymer pastes and the conventional Na2SiO3-anhydrous one-part geopolymer pastes was carried out. It was found that Ca(OH)2/Na2SO4 geopolymer exhibited significantly lower compressive strength, higher flowability and considerably longer setting time compared to Na2SiO3 geopolymer. Hence, such binder can be implemented as a green non-structural material.

    更新日期:2020-01-11
  • Characterization of the mechanical properties and microcosmic mechanism of Portland cement prepared with soda residue
    Constr. Build. Mater. (IF 4.046) Pub Date : 2020-01-10
    Qiang Wang; Jingjing Li; Geng Yao; Xiangnan Zhu; Shugang Hu; Jun Qiu; Ping Chen; Xianjun Lyu

    This work studies the feasibility of the application of soda residue (SR) to the preparation of cement. SR was added to the cement raw materials at 0, 5, 10, and 15 wt%, and four types of cements were synthesized. The free CaO and Cl− contents in the cement clinker, the flexural and compressive strengths, setting times, consistency, fineness, soundness, permeability coefficients, and freeze–thaw resistance of the produced cements were tested. Meanwhile, X-ray diffraction (XRD), thermogravimetric (TG) analysis, and scanning electron microscopy (SEM) were used to study the phases and hydration products of the clinkers and the cements, respectively. The results showed that SR addition could decrease the calcination temperature for clinker preparation. With increased SR content, the initial and final setting times of the produced cements clearly decreased, whereas their water demand and volume expansion continuously increased. When the SR addition was 5 wt%, the flexural and compressive strengths of the produced cement were 4.1 and 23.4 MPa at three days, and 7.5 and 53.1 MPa at 28 days, satisfying the requirements for a 52.5 grade cement. The XRD results demonstrated that the phases of clinkers prepared with SR were alinite, calcium chloroaluminate, and calcium chlorosilicate, as well as alite, belite, aluminate, and ferrite. The Cl− content analysis of clinkers revealed that although a mass of Cl− would be introduced into the cement raw mix due to the SR addition, its contents in all clinker samples was less than 0.06 wt%. Additionally, the XRD, TG, and SEM results showed that the petal-like Friedel’s salt and layered calcium chloride silicate sulfate formed in the hydration products of cements prepared with SR, compared with that of ordinary Portland cement. Finally, the impermeability and freeze–thaw resistance of cement pastes were weakened due to the addition of SR.

    更新日期:2020-01-11
  • Stress-strain behaviour and pore structure of microcapsule-based self-healing cementitious composite under triaxial tests
    Constr. Build. Mater. (IF 4.046) Pub Date : 2020-01-10
    Tielin Han; Xianfeng Wang; Dawang Li; Dongfeng Li; Feng Xing; Jun Ren; Ningxu Han

    In this study, the physical triggered self-healing cementitious composites were prepared by mixing the epoxy resin based microcapsules with the cement, and its mechanical properties and microstructure were investigated as well. The effects of the different content of the microcapsules, proportion of prepressing stress, confining pressure and curing days on the mechanical parameters and microstructure of cementitious composite were carried out by the triaxial compression test and the mercury intrusion porosimetry (MIP) tests. The results indicated that the strength, cohesion, internal friction angle of specimens gradually decreased with an increase in microcapsules content or with an increasing of preloading stress, and the deterioration degree gradually increased with an increase in the microcapsule content or the preloading stress, but peak strain increased to vary degree. The mechanical parameters of the healed samples were repaired to different degrees compared with damaged samples. Microcapsules have significant and positive influences on the healing rates and recovery rates of mechanical properties, pore structure. The healing effect of cementitious materials was improved with increasing microcapsule content. However, the effects of microcapsules on microstructure of sound samples has to be considered.

    更新日期:2020-01-11
  • Effect of soda-lime glass powder on alkali-activated binders: Rheology, strength and microstructure characterization
    Constr. Build. Mater. (IF 4.046) Pub Date : 2020-01-10
    M.H. Samarakoon; P.G. Ranjith; V.R.S. De Silva

    Alkali-activated binders (AABs) have the potential to consume various types of cementitious waste materials, including coal ashes, municipal solid waste incinerator ash, palm-oil fuel ash, steel slags, mine tailings, cement kiln dust, ceramic tile residue, rice husk ash, and waste glass. This paper presents a study of alkali-activated cement paste produced with the substitution of the cementitious waste material soda-lime glass, which makes up the major proportion of the general glass waste stream. In the alkali-activated cement paste, crushed soda-lime glass powder (CG) was used as a replacement for class F fly ash (FA) from 0 to 30% by total solid weight, keeping the ground granulated blast furnace slag (GGBFS) content constant at 50%. The influence of activator molarity (4–8 M), alkaline liquid/solid binder (L/S) ratio (0.4–0.5) and different curing conditions (ambient air curing, wet curing, and short-term heat curing) on the rheology, strength, and microstructure of CG-substituted AABs was investigated and optimum conditions are suggested. According to the experimental results, both the workability and strength (compressive and tensile) of the AAB gradually increased with increasing level of substitution of FA by CG. Significant improvement in flow and setting time was seen with the addition of CG, even in mixtures with a low L/S ratio of 0.4. Both ambient and wet curing had more influence on the strength gain of AABs, especially after 28 days. Short-term heat curing resulted in high early strength gain. The dissolution of CG increased with increasing molarity (from 4 to 8 M) of the alkaline solution, which improved both strength and microstructure with curing time. Morphological and elemental analysis indicated an improvement of the microstructure of AABs due to the increased formation of calcium-dominant hydration products and hence reduced porosity with the substitution of CG. However, undissolved large-sized CG particles agglomerated in the binder without participating in the alkaline reactions. These agglomerated particles may induce micro-cracks due to weak bonding between the cement matrix and the smooth CG interface, which reduces the durability of AABs. Therefore, the inclusion of waste soda-lime glass powder with a mean diameter of 10–15 µm as a precursor in FA/GGBFS-based AAB as a replacement for FA is feasible and provides a good solution for waste material recycling.

    更新日期:2020-01-11
  • A mechanical-diffusive peridynamics coupling model for meso-scale simulation of chloride penetration in concrete under loadings
    Constr. Build. Mater. (IF 4.046) Pub Date : 2020-01-10
    Wanjin Li; Li Guo

    A coupled mechanical-diffusive peridynamics (PD) model is developed to simulate chloride penetration in saturated concrete under various loadings at meso-scale. PD is implemented in the architecture of finite element method (FEM) and truss elements are used to substitute for the PD bonds. In the coupled model, damage evolution and crack growth in concrete under loadings and chloride penetration into concrete with updated diffusivity caused by cracks can be investigated simultaneously. At each coupling step, the quasi-static mechanical analysis is conducted by solving the equilibrium equations, while the forward differencing method is adopted for chloride diffusion. Several numerical examples are carried out to validate the proposed PD models in terms of addressing mechanical-diffusive problems. The numerical results coincide with the test findings and clearly indicate that the width and depth of cracks can influence the chloride diffusivity when “threshold crack width” is reached. Additionally, the chloride diffusivity increases with the increase of stress level under high compressive, tensile and flexural stress levels.

    更新日期:2020-01-11
  • Mechanical properties of recycled aggregate concrete modified by nano-particles
    Constr. Build. Mater. (IF 4.046) Pub Date : 2020-01-10
    Chang Gao; Liang Huang; Libo Yan; Ruoyu Jin; Haoze Chen

    In this study, different nano-particles were used to modify recycled aggregates concrete (RAC) containing recycled clay brick aggregates (RCBAs) to improve the RAC properties. Two stages of experimental works were performed. In the first stage, various nano-particle mixtures produced by different mixing methods, i.e. the use of surfactant and ultrasonication, were examined by optical microscope to evaluate the dispersion of the nano-particles in water liquid. The nano-particles modified cement mortar specimens were further evaluated by flexural tensile test to check how these mixing methods affect the properties of the nano-particle modified cement mortar. In the second experimental stage, the effects of four replacement ratios of recycled aggregates, three type of nano-particles, two mixing methods of RAC, additional surfactant and ultrasonication process used in the mix of nano-particle liquid, and the dosages of the nano-particles on the workability, compressive and split tensile properties of the nano-particle modified RAC were investigated.

    更新日期:2020-01-11
  • Effect of moderately elevated temperatures on bond behaviour of CFRP-to-steel bonded joints using different adhesives
    Constr. Build. Mater. (IF 4.046) Pub Date : 2020-01-10
    Jun He; Guijun Xian; Y.X. Zhang

    The bond behaviour of CFRP-to-steel bonded joint considerably depends on the properties of adhesives, and is significantly influenced by temperature. Meanwhile, different adhesives behave differently at elevated temperatures. Therefore, an in-depth understanding of the effect of temperature on CFRP-to-steel bonded joints with different adhesives is crucial. In this study, a total of 24 single-lap shear joints with four different types of adhesives, were investigated to examine the bond behaviour of CFRP-to-steel bonded joints at a temperature of 23 °C, at 15 °C below the glass transition temperature Tg-15 °C, and at 15 °C above the glass transition temperature Tg + 15 °C. The results indicate that 1) the failure mode of specimens was transformed from cohesive failure or CFRP delamination failure at room temperature to adhesive-steel interface failure with an increase in temperature, 2) the bond strength of all specimens was reduced by approximately 10% at Tg-15 °C, and 70% at Tg + 15 °C. Based on a literature review, an analytical model was proposed to predict the bond strength of the CFRP-to-steel bonded joints at elevated temperatures, 3) the bond-slip relationship of the joints with linear adhesive was changed from a trapezoidal to a triangular with an increase in temperature; However, the bond-slip relationship of the joints with a nonlinear adhesive didn’t change, and 4) the stiffness of the joints decreased with temperature owning to the degradation of the elastic modulus of adhesive.

    更新日期:2020-01-11
  • Development of chemical-physical treatment of cement paste for reduction of dismantled radioactive concrete volume
    Constr. Build. Mater. (IF 4.046) Pub Date : 2020-01-10
    Sunghak Kim; Indong Jang; Chongku Yi

    To reduce the amount of radioactive concrete produced during the dismantling of nuclear power plants, it is essential to remove cement paste attached to aggregates. In this study, the effectiveness of a chemical and physical treatment for cement paste removal was evaluated. Cement-paste specimens having similar size to fine aggregate were treated in a sulfuric acid solution with ultrasonication. The weight loss of the specimens was measured to quantify the degree of decomposition of the cement paste. Scanning electron microscopy, surface hardness test, and inductively coupled plasma analysis were performed to identify the effect of acid treatment on the cement-paste specimens. The results indicated that the cement paste removal is associated with progressive degradation of near-surface layer, and the process can be accurately controlled as a function of water-cement ratio and specimen dimension. The findings are expected to be of great use to disposal of radioactive concrete.

    更新日期:2020-01-11
  • Research into the use of marble waste as mineral filler in soil pigment-based paints and as an active pigment in waterborne paints
    Constr. Build. Mater. (IF 4.046) Pub Date : 2020-01-10
    Deise Mara Garcia Alves Tressmann; Leonardo Gonçalves Pedroti; Anôr Fiorini de Carvalho; José Carlos Lopes Ribeiro; Fernando de Paula Cardoso; Márcia Maria Salgado Lopes; André Fernando de Oliveira; Sukarno Olavo Ferreira

    Producing paint using waste and soil is an efficient way of contributing to sustainable development and reducing costs in the finishing and protection of buildings. Although there are numerous studies related to paints of natural land base, there remain certain technical limitations to be overcome. Moreover, no research has been found in the literature on the use of marble waste as an active or inert pigment in the production of paint, although this waste has several pertinent properties and basic constituents. Thus, the aim of this study was to evaluate whether the use of untreated marble waste as an active pigment in building paint enables a product to be developed which meets specifications and whether the performance of soil pigment-based paints can be improved by incorporating marble waste as a mineral filler. The only preparation for using the waste and the soils as pigments was to sieve them to remove coarser impurities. The samples were formulated based on mix planning using the simplex network and consisted of: marble waste pigment (MWP), soil pigment (SP) and polyvinyl acetate resin (PVA). The amount of water varied according to the ideal viscosity range for paint application. The formulas were analyzed for hiding power (HP), abrasion resistance (AR), microbiological attack and resistance to weathering. The results showed that, for paints produced with MWP as the only pigment, the performance set out in ABNT NBR 15079:2011 was achieved above a percentage of 30% resin in solution. Furthermore, the addition of MWP to SP-based paints provided a film with higher HP and, together with the increased resin content, increased the AR of the samples. Five formulas met both HP and AR performance specifications. The percentages in the mixture were as follows: 0.3 PVA and 0.7 MWP; and 0.4 PVA and 0.6 MWP, with MWP as the sole pigment; 0.25 PVA, 0.175 YSP (yellow soil pigment) and 0.575 MWP; and 0.35 PVA, 0.175 YSP and 0.475 MWP, of YSP and MWP; and 0.25 PVA, 0.175 RSP (red soil pigment) and 0.575 MWP, of RSP and MWP. The weatherability test showed that MWP addition to the paint formula contributed to increased paint durability and improved photolytic stability. Thus, the results indicate that marble waste, as an active pigment or mineral filler, is a promising alternative for producing building paint.

    更新日期:2020-01-11
  • Application of bacterial nanocellulose fibers as reinforcement in cement composites
    Constr. Build. Mater. (IF 4.046) Pub Date : 2020-01-10
    Mohammad Amir Akhlaghi; Raheb Bagherpour; Hamid Kalhori

    In this study, the potential effect of bacterial nano-cellulose on mechanical properties of cement mortar was evaluated. For this purpose, bacterial nano-cellulose (BNC) directly as powder and gel (0.1, 0.3, and 0.5 wt%), and indirectly as coated onto the polypropylene fibers were used in the preparation of cement paste in order to investigate the effect of each method on the flexural strength, compressive strength and water absorption of specimens. Results indicated that samples containing BNC gel and powder enhanced mechanical properties. However, BNC-gel indicated inferior properties compared to powder. The maximum increase in flexural strength between all samples was observed in the specimens containing 0.5% of BNC powder, which was 104%, compared to the control sample. In addition, utilizing nanofibers decreased the water absorption of cement mortar. The water absorption of specimens containing 0.1% of the gel fibers and 0.3% of powder was decreased by 26% and 37%, respectively. According to scanning electron microscopy (SEM) analysis, the roughness and specific surface of polypropylene fibers coated with BNC were increased. This can improve the interaction of these fibers with the cement matrix. The results show clearly that the application of BNC nanofibers improves the mechanical properties of cement paste and workability of polypropylene fibers.

    更新日期:2020-01-11
  • Fresh and hardened properties of an eco-friendly fiber reinforced self-consolidated concrete composed of polyolefin fiber and natural zeolite
    Constr. Build. Mater. (IF 4.046) Pub Date : 2020-01-10
    Mostafa Zaroudi; Rahmat Madandoust; Kamran Aghaee

    This experimental study discuss the fresh and hardened properties of an eco-friendly fiber reinforced self-consolidated concrete (FRSCC). In this research 10% of cement was replaced by natural zeolite (NZ), and polyolefin fiber in different volumetric contents (0.25, 0.5, 0.75, 1, and 1.25 percent) were utilized to improve the hardened properties of concrete. Twelve concrete mixtures with two different water to binder ratios of 0.33 and 0.38 were cast. Workability and viscosity of the modified FRSCC were explored by T50, V-Funnel and L-Box flow tests. The hardened concrete properties were assessed by compressive and splitting tensile tests. The results indicated a significant drop in workability characteristics by using over 1% polyolefin fiber. In terms of hardened concrete properties maximum compressive and tensile strength both obtained by FRSCC containing 0.5 percent polyolefin fiber with water to binder ratio of 0.33.

    更新日期:2020-01-11
  • Multifactorial behavior of the elastic modulus and compressive strength in masonry prisms of hollow concrete blocks
    Constr. Build. Mater. (IF 4.046) Pub Date : 2020-01-10
    José Álvarez-Pérez; Jorge H. Chávez-Gómez; Bernardo T. Terán-Torres; Milena Mesa-Lavista; Ramón Balandrano-Vázquez
    更新日期:2020-01-11
  • Multi-response optimization using Taguchi-Grey relational analysis for composition of fly ash-ground granulated blast furnace slag based geopolymer concrete
    Constr. Build. Mater. (IF 4.046) Pub Date : 2020-01-10
    Jnyanendra Kumar Prusty; Bulu Pradhan

    In this study, Taguchi-Grey relational analysis was used to investigate and optimize the effect of ground granulated blast furnace slag (GGBS) replacement, water to geopolymer solids (W/GPS) ratio, molarity of NaOH solution, binder content and Na2SiO3 to NaOH solution ratio on setting time, workability and compressive strength of fly ash - GGBS based geopolymer concrete (GPC). After arriving at the optimal combination of mix parameters, verification experiments were conducted on the proposed optimized GPC mix with respect to fresh (setting time and workability) and hardened (compressive strength, flexural strength and splitting tensile strength) properties. The microstructural studies on selected fly ash-GGBS based GPC mixes at each GGBS replacement level and the proposed optimized GPC mix were conducted through X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and Field emission scanning electron microscopy (FESEM) analyses. The obtained results showed that GGBS replacement had dominant effect on setting time and compressive strength whereas W/GPS ratio significantly influenced workability of GPC. Variations in formations of N-(C)-A-S-H and C-S-H gels in GPC were confirmed from the results of microstructure analyses. The obtained results of the verification experiment on the proposed optimized GPC mix confirmed the effectiveness of Taguchi-GRA approach for determining the optimal combination of mix parameters for the production of geopolymer concrete.

    更新日期:2020-01-11
  • The molecular structures and the application properties of sulfonated acetone-formaldehyde superplasticizers at different synthetic methods
    Constr. Build. Mater. (IF 4.046) Pub Date : 2020-01-10
    Hui Zhao; Ming Deng; Mingshu Tang

    Nowadays, Superplasticizers (SPs) are the basic component to produce the concrete. In this study, the water-soluble sulfonated acetone-formaldehyde (SAF) SP was prepared at different synthetic methods (SAF-1, SAF-2). The molecular structures and the application behaviors of SAF-1, SAF-2 SPs in the concrete were evaluated. The molecules of SAF-1, SAF-2 SPs have the same OH, CH2, CO, SO3 groups. However, SAF-1 SP has the larger weight-average molecular weight (Mn), the number-average molecular weight (Mw), the polydispersity index (PDI) and the higher sulfonic group content than SAF-2 SP. The larger water-reducing ratio, the better fluidity preservation, the longer setting times, the larger bleeding water rate, wet density and mechanical behaviors of the concrete than those with SAF-2 SP can be found in the SAF-1 SP-blended concrete mixtures. The differences in the air content of the SAF-1, SAF-2 SPs series concrete are insignificant. Therefore, it is an effective method to prepare SAF SP using sodium pyrosulfite as sulfonating agent at four-step processes.

    更新日期:2020-01-11
  • The impact mechanical characteristics of steam-cured concrete under different curing temperature conditions
    Constr. Build. Mater. (IF 4.046) Pub Date : 2020-01-10
    Meng Wang; Youjun Xie; Guangcheng Long; Cong Ma; Xiaohui Zeng; Fu Qiang

    In order to clarify the influence of curing temperature on the dynamic properties of steam-cured concrete, series of SHPB tests were conducted to investigate the impact mechanical characteristics of a typical steam-cured concrete applied in prefabricated components of high-speed railway in China. The index of fineness modulus was proposed to evaluate the degree of concrete breakage under different strain rates. The results showed that the peak stress of steam cured concrete increased with increasing the strain rate, while the peak strain showed a decreasing trend, the fineness modulus of broken concrete particles decreased, and the degree of fracture increased obviously. As curing temperature increases, the peak stress of steam-cured concrete decreased significantly, and the concrete specimens showed a stronger strain rate sensitivity. A statistical damage constitutive model considering the strain rate was established and agreed well with the experimental stress–strain curves. Higher temperatures lead to an increase in internal defects of concrete, which makes the impact mechanical properties different from that of normal temperature cured concrete.

    更新日期:2020-01-11
  • An intensive review on the role of graphene oxide in cement-based materials
    Constr. Build. Mater. (IF 4.046) Pub Date : 2020-01-08
    Li Zhao; Xinli Guo; Luguang Song; Yang Song; Guozhong Dai; Jiaping Liu

    Graphene oxide (GO) has been given a great interest for the use as nano-reinforcement in cement composites due to its exceptional mechanical properties and active functional groups. However, the role of GO in cement-based materials has not been elucidated in the literature because of some inconsistent results. This paper aims at providing an intensive review on the reinforcing effects and mechanisms of GO on cement composites by consulting a lot of correlative literature, mainly focusing on the following aspects: (I) the dispersion issue of GO in the alkaline cement paste; (II) the effects of GO on the macro-performance (workability, mechanical strength, and durability) of cement composites; (III) the reinforcing mechanisms of GO including hydration kinetics, C-S-H structure, pore structure, and interfacial bonding with cement matrix. At last, the novel studies on the hybrid of GO with other materials towards further reinforcement and multifunctionality in cement composites are shared. This review may present a clear understanding of the reinforcing role of GO in cement-based materials and arouse new ideas to promote its practical application in construction materials.

    更新日期:2020-01-09
  • Investigation on vibration induced segregation behaviour of crushed GMZ bentonite pellet mixtures
    Constr. Build. Mater. (IF 4.046) Pub Date : 2020-01-09
    Zhang-Rong Liu; Yu-Jun Cui; Wei-Min Ye; Zhao Zhang; Qiong Wang; Bao Chen

    Mixture of high-density bentonite pellets are considered as a potential buffer/backfill material for high-level radioactive wastes (HLW) repository. One of the outstanding problems of this material is the particle segregation induced by vibration during transportation and emplacement. In this work, the vibration-induced segregation behavior of crushed GMZ (Gaomiaozi) bentonite pellet mixtures with different size distributions was experimentally investigated using a cylindrical container under vertical vibrations. The degree of segregation was evaluated by a weighted coefficient of variation (WCV) reflecting the changes in particle size distribution before and after vibration. Results show that generally the WCV increases with decreases of particle size ratio, the mass fraction of the fine size class and the number of size classes of the mixture. The influences of particle size ratio and distribution were interpreted by two dominant mechanisms including percolation and convection, and could be incorporated into a particle characteristic index (PCI). Further analysis shows that the WCV monotonously increases with the increase of PCI and the relationship between them can be well described using a sigmoid function. Finally, based on the analyses of the experimental results, strategies for reducing segregation were proposed.

    更新日期:2020-01-09
  • Evaluation of epoxy asphalt rubber with silane coupling agent used as tack coat for seasonally frozen orthotropic steel bridge decks
    Constr. Build. Mater. (IF 4.046) Pub Date : 2020-01-08
    Qibo Huang; Zhendong Qian; Leilei Chen; Meng Zhang; Xiaorui Zhang; Jian Sun; Jing Hu

    To improve the durability of tack coat applied to orthotropic steel bridge decks against freeze-thaw cycle in seasonally frozen regions, an epoxy asphalt (EA) tack coat modified by silane coupling agent surface-treated rubber particles (ARP) is proposed. In comparison with epoxy asphalt and epoxy asphalt rubber (EAR), the performance of ARP modified epoxy asphalt (EAAR) and EAAR tack coat were evaluated by conducting an experimental program in the laboratory. The properties of studied tack coat binders were first evaluated by viscosity, direct tensile and bending beam rheometer tests. Furthermore, the steel-asphalt interface performance including pull-off, shear and freeze-thaw damage resistance were evaluated as well. Results show that the incorporation of ARP can improve the mechanical properties and freeze-thaw damage resistance of EAAR, but it had shown a negative effect on the allowable construction time. When EAAR tack coat was used, the low temperature pull-off and shear strength can be improved to approximately 1.2 times that of EA tack coat, and the average interface fracture energy of the EAAR tack coat was about twice higher than EA tack coat. Moreover, EAAR tack coat had shown higher freeze-thaw damage resistance than EA tack coat, regardless of the higher nominal seepage pressure ratio, higher shear strength ratio and lower freeze-thaw damage ratio at the same freeze-thaw cycle periods. All the above findings indicate that the EAAR is of great potential to be applied as tack coat for seasonally frozen orthotropic steel bridge decks.

    更新日期:2020-01-09
  • Effect of silica fume and waste marble powder on the mechanical and durability properties of cellular concrete
    Constr. Build. Mater. (IF 4.046) Pub Date : 2020-01-08
    Sherong Zhang; Kelei Cao; Chao Wang; Xiaohua Wang; Jiaxin Wang; Benbo Sun

    Waste marble powder (WMP) is industrial waste characterized by serious environmental pollution and a low recycling rate. To determine if WMP can be used for partial cement replacement in concrete production, more in-depth and comprehensive research is needed. Moreover, cellular concrete has deficient strength, durability and environmental friendliness, which could be improved by incorporating both silica fume (SF) and WMP. Hence, this study investigated the effects of SF (0%, 2.5%, 5% and 10%) and WMP (0%, 5%, 10%, 15% and 20%) on the mechanical and durability properties of cellular concrete. The slump, density, water absorption and mechanical properties of cellular concrete were discussed. The resistance of cellular concrete containing SF and WMP to MgSO4 and H2SO4 attack was evaluated by changes in compressive strength, splitting tensile strength, mass and microstructure. The cellular concrete with 10% SF and 5–20% WMP exhibited the optimal mechanical and durability properties. After H2SO4 attack, this concrete exhibited significantly higher mechanical properties than the control group and substantially less concrete deterioration and mass (0.20–1.49%), compressive strength (27.40–40.20%) and splitting tensile strength (37.26–46.04%) losses. Moreover, scanning electron microscopy (SEM) images showed that specimens containing SF and WMP (especially SF10 and SF10M5) exhibited better resistance to MgSO4 and H2SO4 attack. Overall, appropriate SF and WMP replacements of cement significantly improved the mechanical and durability properties of cellular concrete, especially after sulfate acid attack.

    更新日期:2020-01-09
  • Real-time quantification of fresh and hardened mechanical property for 3D printing material by intellectualization with piezoelectric transducers
    Constr. Build. Mater. (IF 4.046) Pub Date : 2020-01-08
    Guowei Ma; Yanfeng Li; Li Wang; Junfei Zhang; Zhijian Li

    This study is a pilot exploration to develop rigorous, green, intellectualized approach for optimal controlling the 3D concrete printing. The mechanical performances of 3D printed samples during super-early age, early age, and hardened state are tested and monitored using piezoelectric zirconate titanate (PZT) patches. EMI sensing technique is applied to quantify stiffness gain of printed concrete to evaluate the structural build-up behaviour by establishing the instant correlation between the stiffness of concrete and the EMI signatures. An optimization method for printing process based on EMI detection is proposed. In this way, the PZT signals can be feedback to the digital control system of printer in real time to adjust the printing setting. Instant intellectualization for the 3D printing technique is then realized and the buildability of the printed concrete is expected to be improved. The different early age properties of both printed and casted composites are elaborated. Thereafter, changes of frequency and amplitude in the conductance spectrum acquired by mounted PZT patches are employed to characterize and quantify the mechanical behaviours of the 3D printed samples exposed to orthogonal loadings, which contribute to the understanding of damage accumulation and failure process of concrete materials.

    更新日期:2020-01-09
  • Degradation of cast-in-situ concrete subjected to sulphate-chloride combined attack
    Constr. Build. Mater. (IF 4.046) Pub Date : 2020-01-09
    Gaowen Zhao; Jingpei Li; Mei Shi; Jifei Cui; Feng Xie

    The main aim of the present research is to determine the degradation mechanisms of cast-in-situ concrete subjected to sulphate-chloride combined attack. Concrete specimens were prepared and then put into sulfate or sulfate-chloride mixed solutions. The sample dimension, mass, compressive strength, and sulfate concentration of the specimens were continuously monitored. The microstructures and the complex mineral composition of the concrete were analysed after 12 months of exposure to the corrosive environments. The results show that cast-in-situ concrete suffers more severe damage and greater strength loss when subjected to sulfate-chloride combined attack than when subjected to sulfate only. The diffusion and accumulation of sulfates are accelerated by the coexisting chlorides, especially in the early stages. The coexistence of chlorides in sulfate environments accelerates the degradation of cast-in-situ concrete induced by sulfate attack. The different performances against sulfate-chloride combined attack between cast-in-situ and precast concrete were mainly due to the degradation behaviour at the early stage.

    更新日期:2020-01-09
  • Multi-technical characterization and correlations between properties of standard cured alkali-activated high-calcium FA binders with GGBS as additive
    Constr. Build. Mater. (IF 4.046) Pub Date : 2020-01-08
    Weilong Song; Zhiduo Zhu; Shaoyun Pu; Yu Wan; Xiaoyu Xu; Shigong Song; Jun Zhang; Kai Yao; Lele Hu

    In this study, ground granulated blast-furnace slag (GGBS) was introduced as an additive to improve the setting and hardened properties of alkali-activated high-calcium FA binders at standard curing condition. FA was partially replaced by GGBS with contents of 0, 10%, 20%, 30%, 40% and 50% by mass to form a binary blends, which were then activated by an alkaline solution consisting of Na2SiO3 and NaOH to produce alkali-activated binders. The performance of alkali-activated high-calcium FA binders modified by GGBS were evaluated by multi-technical characterization. Moreover, the correlations between multiple properties were also analysed. The results show that adding GGBS as an additive could accelerate the setting times of alkali-activated high-calcium FA binders. The viscosity increases with an increase in GGBS content and is closely related to the flowability. Increasing GGBS content significantly improves the compressive strength of the paste sample, especially its early compressive strength, but makes the material more brittle. The sorptivity coefficient of hardened paste has a strong correlation with its compressive strength. In addition, the microcosmic improvement mechanism of GGBS as an additive was also discussed. The improvement in strength is owing to the generation of additional C-(A)-S-H gel in the presence of GGBS, which fills the pores in the matrix, transforming the large capillary pores into small gel pores, resulting in a denser and more uniform structure. The resulting decrease of threshold and critical diameters may be the main reason for the decrease of sorptivity coefficient.

    更新日期:2020-01-09
  • Experimental investigation on the tensile behavior of hybrid steel-PVA fiber reinforced concrete containing fly ash and slag powder
    Constr. Build. Mater. (IF 4.046) Pub Date : 2020-01-08
    Fangyu Liu; Wenqi Ding; Yafei Qiao

    A series of direct tensile tests are performed to investigate the tensile behavior of hybrid steel-PVA fiber reinforced concrete containing fly ash and slag powder. Digital image correlation (DIC) measurement is also utilized to capture the formation and propagation of cracks during the test. Different hybrid ratios (steel: PVA = 1:3 ~ 3:1) and fiber volume contents (1%–3%) are investigated to highlight their effects on the tensile behavior. The test results reveal the following: (i) the tensile strength of hybrid fiber reinforced concrete (HFRC) increases with the increase in steel fiber content, while it decreases as the PVA fiber content increases; (ii) the engineering tensile strength (tensile stress at a crack width of 0.2 mm) and the toughness, T0.5 and T1.0, are introduced and proved to be more suitable to describe the tensile behavior of HFRC during the post-peak stage; (iii) adding fly ash and slag powder has no effect on the hybridization of the steel and PVA fibers and their enhanced effects on tensile behavior when compared with HFRC containing different kinds of cementitious material; and (iv) the tensile behavior of HFRC is a combined result of the PVA fiber effect and the steel fiber effect, and their contributions vary with loading.

    更新日期:2020-01-09
  • Effect of waste rubber particles on the mechanical performance and deformation properties of epoxy concrete for repair
    Constr. Build. Mater. (IF 4.046) Pub Date : 2020-01-09
    Jianwen Shao; Han Zhu; Xian Zuo; Wolong Lei; Said Mirgan Borito; Jian Liang; Fuqiang Duan

    The article conducts the compressive, flexural, spilt, deflection and strain experiments on epoxy concrete with added fine, medium and coarse rubber particles respectively at 5%, 10%, 15%, 20% and 25%. Medium sized rubber particle is selected for further study in a composite beam test in which rubber epoxy concrete serves as a repair material to “glue” two ordinary concrete short beams, as well as a bond tensile strength test. A deformation compatibility parameter is introduced to measure two strains for indicting the composite beam’s deformability. It is found that, meanwhile keeping an adequate interfacial strength needed as a repair material, rubber in epoxy concrete help increase deformability, which is beneficial to compensate the rigidness of epoxy concrete.

    更新日期:2020-01-09
  • Application of electromagnetism method to characterize the degradation behavior in structural mild steel within the elastic range
    Constr. Build. Mater. (IF 4.046) Pub Date : 2020-01-09
    Xiao Wang; Jian-Guo Chen; Guo-feng Su; Chong Cui; Hua-Ying Li

    This paper reports a novel use of magnetic technique to characterize the degradation in mild steel within the elastic range. Firstly, the mild steel specimens were stretched to several different kinds of stress within the elasticity. After the tensile test, a shift of hysteresis loop was observed in the tensile specimen, and the variations of magnetic parameters such as Coercivity (Hc), Remanence (Br), maximum permeability (µm), and hysteresis loop area (S) were also evident. When the tensile stress increases to the elastic limit (310 MPa), the Hc increased 16.44% compared with the original specimen, which manifested the variation of the magnetic property in mild steel. The magnetic property variation in material are closely interrelated with its microstructure change. The existence of internal residual stress/strain as well as the dislocation structure change are the main factors affect the magnetic property. The experiment results revealed that the magnetic technique was sensitive to the microstructural change in the mild steel, which has the promising potential to characterize the material degradation at the early stage.

    更新日期:2020-01-09
  • Improvement of bond performance between concrete and CFRP bars with optimized additional aluminum ribs anchorage
    Constr. Build. Mater. (IF 4.046) Pub Date : 2020-01-08
    Bai Zhang; Hong Zhu; Gang Wu; Qiang Wang; Ting Li

    The slippage of fiber-reinforced polymer (FRP) bars in concrete occurs frequently because of the insufficient anchorage capacity of FRP bars in concrete, and it considerably affects the reliable application of FRP bars as reinforcing steel bars in civil engineering structures, especially in prestressed structures. In this paper, an optimized additional rib (AR) anchorage system was applied to the carbon-FRP (CFRP) bars to improve this weak anchorage characteristic of CFRP bars. The extrusion technology of the additional ribs was optimized, and only a slight deterioration of approximately 1.85% in the tensile strength of the CFRP bars was noted, compared to that corresponding to our previous extrusion technology (a loss of approximately 7.84%). Subsequently, pull-out tests were performed to investigate the influence of the number of additional ribs and bond length on the bond performance between the CFRP bars and concrete. The experimental results demonstrated that the existence of additional ribs, which produced an end pressure, transformed the bond stress transferring mechanism and reduced the radial force exerted on the surrounding concrete, thereby delaying the occurrence of the concrete splitting failure. In addition, the CFRP bars anchored with the additional ribs exhibited a remarkable enhancement in the pull-out strength, whereas this improvement was influenced by the embedment length of the CFRP bars and the ratio of the additional rib length to the bond length (lar/L). Finally, an empirical expression to calculate the development length of the CFRP bars with and without an AR anchorage was proposed and compared with the expressions provided in the existing design standards. It was concluded that the applied AR anchorage system could effectively reduce the development length of the CFRP bars. Compared to that of the control specimens, there was approximately 16.7% decrease in the development length for the specimens anchored with one additional rib.

    更新日期:2020-01-09
  • Influence of various bentonites on the mechanical properties and impermeability of cement mortars
    Constr. Build. Mater. (IF 4.046) Pub Date : 2020-01-08
    Mengliang Liu; Yang Hu; Zhenyu Lai; Tao Yan; Xin He; Jie Wu; Zhongyuan Lu; Shuzhen Lv

    The durability of cement mortar depends mainly on its impermeability properties. In this study, three different types of bentonite—sodium bentonite (Na-bent), calcium bentonite (Ca-bent), and magnesium bentonite (Mg-bent)—were added to a cement mortar at different proportions to investigate their effect on the mortar strength and impermeability. The results show that the three types of bentonite provide a significant improvement in the performance of cement mortar, and with increasing bentonite content, this effect is increasingly obvious. For samples with a bentonite content of 10 wt%, the improvement in compressive strength, flexural strength, and permeability with Na-bent can reach 77.5%, 54.5%, and 115.7%, respectively; the corresponding improvements with Ca-bent can reach 62.2%, 47.9%, and 101.9%, while those with Mg-bent can reach 71.6%, 52.2%, and 137.3%, respectively. The waterproofing performance of cement mortar containing Mg-bent is the best, with a maximum impermeability pressure 2.37 times that of the reference group, followed by Na-bent, and finally Ca-bent; however, the lowest impermeability pressure is also 2.02 times that of the reference group. In general, the addition of bentonite improved the strength and impermeability of the cement mortar and has potential application value for improving the durability of cement mortars.

    更新日期:2020-01-09
  • Performance evaluation of new warm mix asphalt and water stability of its mixture based on laboratory tests
    Constr. Build. Mater. (IF 4.046) Pub Date : 2020-01-08
    Ke Zhang; Yaofei Luo; Fei Chen; Feifei Han

    To confirm the reliability of self-developed ZYF-1 warm mix additive and provide some references for the promotion and application of ZYF-1, the conventional performance test and Strategic Highway Research Program (SHRP) test of SK90# asphalt and SBS modified asphalt containing ZYF-1 were conducted. The commonly used warm mix additives of Sasobit and Aspha-min were also tested. Meanwhile, the splitting test and Cantabro test of warm mix asphalt mixture before and after freeze-thaw cycles were conducted to evaluate the long-term water stability. The beam fatigue test and Wheel Tracking test were also carried out to verify other road performance of asphalt mixture with ZYF-1. The results show that ZYF-1 greatly improves the low temperature property of asphalt and has little adverse effect on high temperature performance. After mixed with Sasobit and Aspha-min additive, the high temperature property of asphalt is improved, but the low temperature performance is weakened. ZYF-1 and Sasobit significantly reduces the high temperature viscosity of asphalt binder, while Aspha-min makes the viscosity slightly increase. 4% by the weight of asphalt is recommended as the reasonable dosage for ZYF-1 based on the variation of asphalt performance. Freeze-thaw cycle simulation obviously influences the water stability of warm mix asphalt mixture, and 15 freeze-thaw cycles are recommended for the evaluation of water stability. Among tested additives, the deterioration range of water stability for asphalt mixture caused by ZYF-1 is the smallest. The warm mix asphalt mixture containing ZYF-1 effectively reduce the construction temperature while ensuring the road performance.

    更新日期:2020-01-09
  • Experimental study of the effect of a slow-cooling heat treatment on the mechanical properties of high strength steels
    Constr. Build. Mater. (IF 4.046) Pub Date : 2020-01-08
    F.X. Ding; L.F Lan; Y.J Yu; M.K. Man

    This paper investigated a novel technique that uses a slow-cooling heat treatment to reduce the strength of existing steels to produce a regional soft area for energy dissipation. This research investigated the performance and affecting mechanism of the slow-cooling heat-treatment on the mechanical properties of high strength steels. A total of 18 heat-treating cases were applied to Q420 and Q690 steels. The relation of critical strengths and ductility of the materials versus the heat-treating parameters, such as peak temperature, cooling rate, holding time and terminate temperature, were investigated and discussed. The strength reduction from the slow-cooling heat treatment process in high strength steels and normal strength steels was discussed. The results indicated that the slow-cooling heat treatment can effectively reduce the yield and ultimate strengths of high strength steels. The Q690 steel displayed a more prominent strength reduction than the Q420 steel, especially for the yield strength. The heat treatment also improved the material ductility, especially for the Q690 steels. The peak temperature and cooling rate were two determining factors for the strength reduction performance. A heat treatment process with a 900–1000 °C peak temperature and a 1–2 °C/min cooling rate was suggested for the strength reduction of Q420 steel.

    更新日期:2020-01-09
  • Effect of thermal aging on high viscosity modified asphalt binder: Rheological property, chemical composition and phase morphology
    Constr. Build. Mater. (IF 4.046) Pub Date : 2020-01-09
    Mingjun Hu; Guoqiang Sun; Daquan Sun; Yi Zhang; Jianmin Ma; Tong Lu
    更新日期:2020-01-09
  • Study of bridge-subgrade longitudinal constraint range for high-speed railway simply-supported beam bridge with CRTSII ballastless track under earthquake excitation
    Constr. Build. Mater. (IF 4.046) Pub Date : 2020-01-08
    Yuntai Zhang; Lizhong Jiang; Wangbao Zhou; Yulin Feng; Zhihua Tan; Xilin Chai

    Owing to widespread applications of continuous welded rail (CWR) in high-speed railway bridges, the studies on the seismic response of high-speed railway simply-supported beam bridges (HSRSSBB) considering track constraint is of greatest importance. In order to ensure the high efficiency and high precision of calculations under the consideration of constraint of a long track system, based on the consideration of longitudinal constraint and beam-track interaction, an equivalent model for the HSRSSBB was established, which can simultaneously achieve high calculation efficiency and calculation precision. Also, the sensitivity for seismic response of the HSRSSBB had been proposed, and a judging formula to rapidly determine the bridge-subgrade longitudinal constraint range for the HSRSSBB was established. Finally, after an analysis of a large number of cases, the relationship between the equivalent boundary characteristics and the bridge-subgrade longitudinal constraint range was studied, indicating that the subgrade length of 90 m can be used as the reasonable subgrade length in the longitudinal seismic analysis for the HSRSSBB.

    更新日期:2020-01-09
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