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  • 更新日期:2018-03-14
  • 更新日期:2018-03-13
  • Identification of similar seismic events using a phase-only correlation technique
    Constr. Build. Mater. (IF 3.169) Pub Date : 2018-03-12
    Hirokazu Moriya

    Identification and clustering of similar acoustic emission (AE) events are important to determine source locations precisely and to evaluate subsurface cracks. An AE cluster analysis method using phase-only correlation (POC) is proposed to identify and hierarchically classify similar AE waveforms. The POC of time-varying spectral representations is used to evaluate the similarity between two waveform images in the time–frequency domain, and cluster analysis is used to classify the waveforms into groups according to a distance measure. The method is applied to waveforms from local earthquakes in Japan to assess its ability to identify similar waveforms perturbed by white noise.

  • Deterioration mechanism of CA mortar due to simulated acid rain ☆
    Constr. Build. Mater. (IF 3.169) Pub Date : 2018-03-07
    Xiaohui Zeng, Yirui Li, Yuzhou Ran, Kai Yang, Fulin Qu, Ping Wang

    In acid rain regions of Southwest China, cement-emulsified asphalt mortar (CA mortar), a key structure component in China Railway Track System (CRTS), is reported with more serious damaged signs than other locations. To investigate the effects of acid rain on its durability, the CA mortar specimens were immersed in acid solutions with pH values of 3.0, 4.0, and 5.0 for 21 months. Scanning electron microscope (SEM), energy dispersive spectrometer (EDS), differential thermal analyzer (DTA) and biological microscope were applied to evaluate the deterioration mechanism. Cracking, desquamation, pulverization, and decreased compressive strength were observed in them. The results of SEM and EDS show that a large number of crystals, rich in Ca, S and O, deposited on surfaces of the specimen soaking in the solutions, which is related to gypsum as shown in DTA pattern. Also, DTA patterns show that the decomposition peak of calcium silicate hydrate (C–S–H) gel in CA mortar specimens decreased gradually from the internal to the external surface. The analysis of acid solution based on the biological microscope indicates that large amounts of filamentous fungi and yeast existed in the solution during the long-term soaking, which corresponds to the investigation of the seriously damaged CA mortar in the field. In conclusion, deterioration mechanisms of CA mortar by acid rain includes CaSO4·2H2O crystalline expansion damage, decomposition and dissolution of C–S–H gel and biological corrosion when the alkaline environment was damaged.

  • Comparison of the retarding mechanisms of sodium gluconate and amino trimethylene phosphonic acid on cement hydration and the influence on cement performance
    Constr. Build. Mater. (IF 3.169) Pub Date : 2018-03-07
    Beixing Li, Xingdong Lv, Yun Dong, Shihua Zhou, Jianfeng Zhang

    ATMP and SG were effective hydration retarders of cement. The goal of this study was to provide the comparison of the influence of ATMP and SG on the performance and hydration of Portland cement. The setting time at 20 °C and 35 °C, compressive strength and fluidity of cement pastes containing either ATMP or SG at different dosages from 0.02% to 0.10% were tested respectively. The hydration behaviors of Portland cement with ATMP and SG were investigated by the means of isothermal calorimetry measurements, X-ray diffraction (XRD), thermogravimetric analysis (TGA) and scanning electron microscope (SEM). The results showed that the retarding effect of ATMP was much intensive than SG, especially in the case of a higher temperature; the “dispersion loss resistant” of ATMP were superior to SG; The limitation dosage of ATMP and SG was 0.15%; Although SG could reduce cement hydration cumulative heat and hydration evolution rate at some degrees, the effect was much weaker than ATMP. ATMP continued to inhibiting the hydration of C3S effectively during the whole hydration period. SG was also inhibiting the hydration of C3S during the hydration of 1d, but it promoted the hydration of C3S beyond 1d at some degrees.

  • Characterization of air voids and frost resistance of concrete based on industrial computerized tomographical technology
    Constr. Build. Mater. (IF 3.169) Pub Date : 2018-03-05
    Jie Yuan, Yue Wu, Jiake Zhang

    Air voids structure is the key parameter that affects the frost resistance of concrete, but traditional approaches of measuring the air voids of concrete are all destructive. This work utilizes the industrial computerized tomography to visualize the microstructure change during cyclic freeze/thaw test. The results indicate that the combination of industrial computerized tomography with subsequent image processing program can precisely measure the morphology and position of air voids in concrete. The air content measured by computerized tomography is slightly higher than that of traditional pore structure analyzer. The air content and spacing factor increase after cyclic freeze-thaw for both air-entrained and non-air-entrained concrete, and the variation rate of non-air-entrained concrete is several times that of air-entrained concrete. Besides, it can be directly observed from the reconstruction model that he air voids in air-entrained concrete experience no obvious expansion after cyclic freeze/thaw test, which increases the frost resistance of concrete.

  • Effect of calcined Czech claystone on the properties of high performance concrete: Microstructure, strength and durability
    Constr. Build. Mater. (IF 3.169) Pub Date : 2018-03-03
    Eva Vejmelková, Dana Koňáková, Magdalena Doleželová, Lenka Scheinherrová, Petr Svora, Martin Keppert, Pavel Reiterman, Robert Černý

    Most supplementary cementitious materials (SCM) have been only rarely used in high performance concrete (HPC) design to date, silica fume being one of the very few exceptions in that respect. The content of many SCMs in blended cements was also often low because at higher dosage they were not capable to replace Portland cement effectively. Their environmental and economical advantages could thus be utilized in a limited extent only. In this paper, the effect of calcined Czech claystone (CCC) on the properties of HPC based on a binary binder containing Portland cement and silica fume was analyzed over a 10–60% range of Portland cement replacement in the mix. The material characterization experiments carried out using mercury intrusion porosimetry and scanning electron microscopy showed that an up to 30% presence of CCC in the blend resulted in a formation of closer packed HPC microstructures than if only silica fume was used as SCM. The highest compressive and bending strengths were achieved for the 30% Portland cement replacement level over the whole one year testing period. The best durability properties expressed in terms of water and water vapor transport parameters were observed for the same mix with 30% of CCC used instead of Portland cement.

  • Measurement of radioactivity in building materials – Problems encountered caused by possible disequilibrium in natural decay series
    Constr. Build. Mater. (IF 3.169) Pub Date : 2018-03-02
    Boguslaw Michalik, Govert de With, Wouter Schroeyers

    The determination of the activity concentration of naturally occurring radionuclides in construction materials is based on the principles of gamma-spectrometry. Gamma spectrometry is a comparative method and therefore includes many parameters that are specific to the test sample and measurement circumstances. Consequently, several of the testing conditions must be verified prior to testing and/or require correction to obtain accurate results. Besides problems encountered during the measurement, the interpretation of the results and calculation of the activity indices, needed for material classification, may lead to significant mistakes. Current regulation in the European Union requires to calculate an activity concentration index (index I) using the activity concentration of 226Ra, 232Th and 40K. Not all of these radionuclides are directly measurable by gamma spectrometry and, to determine the index, additional assumptions have to be made about secular equilibrium in uranium and thorium decay series. These assumptions are often not valid in case of NORM (Naturally Occurring Radioactive Materials) where long term lack of secular equilibrium in the uranium and/or thorium decay series is often observed. As a consequence, this may result in an underestimation or overestimation of the index. The article discusses specific disequilibrium situations in building materials. Sources for potential inaccurate determinations and misinterpretation are identified and practical mitigation options are proposed.

  • Zeolitized bottom ashes from biomass combustion as cement replacing components
    Constr. Build. Mater. (IF 3.169) Pub Date : 2018-02-21
    Danutė Vaičiukynienė, Boguslaw Michalik, Michał Bonczyk, Vilimantas Vaičiukynas, Aras Kantautas, Jūratė Krulikauskaitė

    In power plants biomass combustion produces large quantities of biomass bottom ash wastes. During the combustion process, the produced ashes are enriched in the radionuclides. The different enrichment of the various radionuclides within a radioactive series, such as that of 226Ra, 228Ra, 228Th, 40K, 210Pb and 137Cs results in the disturbance of radioactive secular equilibrium. The production of energy from renewable resources, such as biomass, is increasing rapidly. As the demand for bioenergy production increases, waste products from biomass combustion will increase too and will become a relevant environmental and economic problem. Therefore, environmentally friendly, and economic solutions to recycle the resulting by-products are essential. This research provides a real opportunity to save cement thus disposing the waste by using zeolitized biomass bottom ash as supplementary cementitious materials. The zeolitized products were examined by X-ray diffraction (XRD), X-ray fluorescence spectrometer (XRF) spectroscopy and high-resolution gamma spectrometry. In all investigated cases, compressive strength in hardened cement pastes and concrete samples slightly increases by replacing from 3% to 5% of Portland cement with zeolitized ashes. The results showed that natural radionuclides as 226Ra, 228Ra, 228Th, 40K are concentrated in similar way as in case of ashes obtained from combustion. However, addition of biomass leads to concentration of artificial radionuclide 137Cs that is still commonly present in biomass due to Chernobyl disaster. The observed activity concentration of 137Cs reaches the level of natural radionuclides concentration. Taking into consideration the contribution of 137Cs to gamma dose (usage of expanded activity index formula) may lead to exceeding the value of 1 in some cases. Calculated differences between activity indexes reach 13%.

  • Using RESRAD-BUILD to assess the external dose from the natural radioactivity of building materials
    Constr. Build. Mater. (IF 3.169) Pub Date : 2018-02-17
    S. Pepin

    RESRAD-BUILD is a code developed by Argonne US National Laboratory for assessing the radiological doses resulting from the occupancy of buildings contaminated with radioactive material. This freely downloadable software allows to consider multiple sources of contamination and to assess not only the external exposure pathway but also the dose resulting from inhalation or ingestion of contaminated dust as well as the dose from inhalation of radon. The software offers the possibility to assess in a flexible way the external dose from the natural radioactivity of building materials. A room model similar to the one used for deriving the activity concentration index of the 2013/59/euratom directive may easily be implemented and gives consistent results. A comparison is made with the calculations performed in the CEN technical report on dose-assessment of gamma radiation from building materials. An example of assessment of the external dose resulting from multiple layers of building materials is given where measurements data are used for the activity concentrations. The assessment allows demonstrating compliance with the reference level set up in the directive.

  • Identifying CFRP strip width influence on fracture of RC beams by acoustic emission
    Constr. Build. Mater. (IF 3.169) Pub Date : 2018-02-13
    Sena Tayfur, Ninel Alver, H. Murat Tanarslan, Emre Ercan

    Carbon fiber-reinforced polymer (CFRP) is a widely used material to strengthen deficient structures externally. While CFRP has numerous advantages, debonding is the main problem of CFRP-strengthened reinforced concrete (RC) beams as it causes sudden failure. Thus, to circumvent this problem, failure modes of an RC beam strengthened with CFRP need to be understood. There are various application types of CFRP strips and plates depending on their ease of application and contribution as a strengthening material such as side bonding and wrapping. Using CFRP as a strip is a cost effective way and is widely preferred. Strip width and spacing have a firsthand effect on the mechanical behavior of the strengthened element. Accordingly, in this study, AE parameter analysis and SiGMA analysis were applied for identification of CFRP strip width effect on fracture of RC beams having different CFRP widths. Within the scope of the experimental study, a reference beam and two CFRP-strengthened beams were tested under cyclic loading and monitored by AE. Both mechanical and AE results show that the behavior is not enhanced by increasing the strip width.

  • An experimental-based model for the assessment of the mechanical properties of road pavements using ground-penetrating radar
    Constr. Build. Mater. (IF 3.169) Pub Date : 2018-02-09
    Fabio Tosti, Luca Bianchini Ciampoli, Fabrizio D'Amico, Amir M. Alani, Andrea Benedetto

    This work proposes an experimental-based model for the assessment of the stiffness of a road flexible pavement using ground-penetrating radar (GPR – 2 GHz horn antenna) and light falling weight deflectometer (LFWD) non-destructive testing (NDT) methods. It is known that the identification of early decay and loss of bearing capacity is a major challenge for effective maintenance of roads and the implementation of pavement management systems (PMSs). To this effect, a time-efficient methodology based on quantitative and qualitative modelling of road stiffness is developed. The viability of using a GPR system in combination with LFWD equipment is also proven.

  • Polarization behavior of activated reinforcing steel bars in concrete under chloride environments
    Constr. Build. Mater. (IF 3.169) Pub Date : 2018-02-07
    Binbin Zhou, Xianglin Gu, Hongyuan Guo, Weiping Zhang, Qinghua Huang

    Polarization behavior of activated reinforcing steel bars (rebars) in concrete was investigated by use of measured cathodic polarization curves. Five factors thought to contribute to the polarization behavior of rebars in concrete were examined, including relative humidity, Cl− content, rebar diameter, water-cement ratio and corrosion duration. The Levenberg-Marquardt curve-fitting algorithm made it possible to determine the corrosion rate and electrochemical parameters of underlying anodic and cathodic sub-process simultaneously. Degrees of activation polarization and concentration polarization related to cathodic reaction were quantified. A prediction model for the average value of corrosion rate in regard to the whole surface of a corroded rebar was proposed based on the electrochemical corrosion theory. Finally, the accuracy of this model was testified by comparing the predictions of this model with published corrosion test results.

  • Efficient damage inspection of deteriorated RC bridge deck with rain-induced elastic wave
    Constr. Build. Mater. (IF 3.169) Pub Date : 2018-02-01
    Hidefumi Takamine, Kazuo Watabe, Hirokazu Miyata, Hisafumi Asaue, Takahiro Nishida, Tomoki Shiotani

    To maintain a large number of bridges, efficient inspection methods are needed. We have developed a new and efficient method for inspecting reinforced concrete bridge decks by using acoustic emission (AE) monitoring. Notably, we use AE signals acquired during heavy rain, which have generally been considered to be noise in the past. Analysis of rain-induced AE signals reveals severe cracks deep inside a deck, which would have been difficult to recognize by conventional passive non-destructive testing. Our method is also quite efficient with measurements able to be completed in a very short period of time.

  • Effect of coarse aggregate type on chloride ion penetration in concrete
    Constr. Build. Mater. (IF 3.169) Pub Date : 2018-02-01
    Hani H. Titi, Habib Tabatabai

    Long-term durability and sustainability of crucial infrastructure systems such as bridges and pavements are of utmost importance for the economic health of any society. Understanding factors that affect long-term deterioration of reinforced concrete structures can help enhance durability and sustainability of these systems. This paper investigates the effect of the type of coarse aggregate used in concrete on chloride ions penetrability. Twelve coarse aggregate types of different geologic formations (sedimentary, igneous, and metamorphic) were used to prepare fresh concrete in which silica fume and class C fly ash were used. All mix parameters including gradation and volumes of different aggregates were held constant in different mixes with the only variable being the aggregate type. The Rapid Chloride Penetration Tests were conducted on concrete specimens made with various aggregate types at ages of 28, 56, 91 and 365 days. Analysis of test results showed that the aggregate type as well as aggregate absorption rates have significant influence on the electrical charges passed through concrete, especially in early ages of concrete containing aggregates with sedimentary rock origin and relatively high absorption. These specimens exhibited the highest RCPT results indicating higher capacity to allow chloride ion penetration when compared to specimens with igneous and metamorphic rock aggregate of lower absorption values. This influence (discrepancy) diminishes with time for both aggregate type and absorption rates in terms of the magnitude of measured total charge passed.

  • A nondestructive evaluation method for semi-rigid base cracking condition of asphalt pavement
    Constr. Build. Mater. (IF 3.169) Pub Date : 2018-02-01
    Guoshuai Zang, Lijun Sun, Zhang Chen, Li Li

    The evaluation of semi-rigid base cracking condition is one of the most important elements of project-level pavement evaluation, and has been a key challenge facing pavement engineers for many years. This is because that the semi-rigid base cracking condition cannot be obtained through visual surveys unless the asphalt course is milled off, therefore the nondestructive detection and evaluation method is a better choice. This paper develops a nondestructive FWD-based evaluation model to evaluate the semi-rigid base cracking condition. It was found that the normalized base modulus (ratio between back-calculated and initial modulus) and the semi-rigid base cracking condition had good relationship on log-log scales, therefore the normalized base modulus was considered to be a reasonable indicator for the evaluation of semi-rigid base damage (cracking) condition. Based on the comparison of measured data and back-calculated modulus in freeway pavements, the evaluation criterion is established.

  • Crack monitoring in historical masonry with distributed strain and acoustic emission sensing techniques
    Constr. Build. Mater. (IF 3.169) Pub Date : 2018-02-01
    Els Verstrynge, Kristof De Wilder, Anastasios Drougkas, Eli Voet, Koen Van Balen, Martine Wevers

    The analysis of crack patterns and crack growth is one of the most important steps in the assessment of structural damage in historical masonry. In a search for integrated and accurate monitoring techniques for crack measurements in masonry, several novel techniques based on distributed strain monitoring and acoustic emission (AE) sensing have been investigated in an experimental test campaign. Aim of the test program was to develop integration procedures for the strain and AE sensors, analyse their use for crack monitoring specifically in historical masonry and assess their robustness and efficiency with respect to the experimentally observed crack pattern. The applied techniques were integrated optical fibres with distributed fibre Bragg grating sensors (FBGs), stereo-vision digital image correlation (DIC) without the use of a speckle pattern, optical fibre sensors for acoustic emission sensing (AE-FOS), piezo-electric transducers for acoustic emission sensing (AE-PZT) and LVDTs. While the latter two were applied as reference techniques, the former three were under investigation as novel application. This paper discusses the efficiency of the monitoring techniques with respect to their use in masonry, explains the developed integration procedures, and relates the obtained data sets with the deformations and crack pattern obtained in a full-scale masonry wall test. Additionally, the effects of temperature fluctuations are investigated. The configurations that were developed proved effective for crack monitoring in historical masonry. The highest sensitivity and robustness was observed for the integrated optical fibres with FBGs.

  • High temperature durability of fiber reinforced high alumina cement composites
    Constr. Build. Mater. (IF 3.169) Pub Date : 2018-02-01
    Eva Vejmelková, Dana Koňáková, Lenka Scheinherrová, Magdaléna Doleželová, Martin Keppert, Robert Černý

    The effect of high temperature exposure on the durability of fiber-reinforced composite materials based on high alumina cement is studied. A combination of X-ray diffraction- and thermal analyses of hydrated phases shows a simultaneous presence of all principal hydrates (CAH10, C2AH8, C3AH6, AH3) in significant amounts during the whole 2–28 days hydration period. The application of basalt aggregates and basalt fibers is found to improve significantly the high-temperature durability, in a comparison with the cement paste. The residual values of compressive and bending strength of the most successful mix with the combination of longer and shorter basalt fibers in a 90:10 ratio are 50% and 34%, respectively, after 1000 °C exposure. The fiber reinforced composite material with the most favorable mechanical properties exhibits also the highest resistance to water and water vapor transport and the lowest water vapor adsorption after 1000 °C pre-heating, which correlates well with its lowest amount of pores bigger than 100 nm. The thermal conductivity and specific heat capacity of all analyzed composites show a significant increase with the increasing moisture content; the differences between the values in dry and water saturated state are up to 100% and 65%, respectively. The thermal strain of all studied materials is almost linear within the whole 20–1000 °C range, with the basalt fibers being able to decrease it by up to 7% at 1000 °C.

  • Acoustic emission characteristics of fracture modes in masonry materials
    Constr. Build. Mater. (IF 3.169) Pub Date : 2018-01-19
    G. Livitsanos, N. Shetty, D. Hündgen, E. Verstrynge, M. Wevers, D. Van Hemelrijck, D.G. Aggelis

    Acoustic emission (AE) is a powerful technique for detection and analysis of the elastic waves produced by the failure mechanisms in construction materials such as masonry. In this study, the different fracture mechanisms are studied in relation to the properties of bricks and mortars. The fracture process is being evaluated using the combination of AE and Digital Image Correlations (DIC) techniques. The isolation of the AE signatures of different types of failure mechanisms is done by testing bricks in flexure and brickwork couplets in compression. AE data are analyzed with a simplified AE parameter-based approach aiming to characterize the fracture mode. This is one of the first times where the relation between the shear and the longitudinal strain field is correlated in masonry with AE. This offers new insight in the material's behavior especially in relation to complicated structural geometries where the dominant stress mode is not known a priori.

  • VOCs characteristics and their relation with rheological properties of base and modified bitumens at different temperatures
    Constr. Build. Mater. (IF 3.169) Pub Date : 2018-01-10
    Min Lei, Shaopeng Wu, Gang Liu, Serji Amirkhanian

    During heating process of bituminous materials, volatile organic compounds (VOCs) will be released, and it is harmful to the skin, the respiratory and nervous system of the human body, especially increasing its carcinogenic tendency. In this study, the VOCs emission of base and modified binder was characterized as the function of typical temperatures by gas chromatography coupled with mass spectrometry (GC/MS). The rheological behavior of each binder before and after the emission of VOCs was compared. The relation between the VOCs emission of bitumen and its rheological properties was researched. The results indicated that a higher temperature can lead to increase of VOCs components of binder. The addition of SBS modifier can reduce VOCs components of its base binder. However, the degradation of the SBS modifier decreased its inhibition effect on the VOCs emission of bitumen at 220 °C. Naphthalene release and carcinogenic index of polycyclic aromatic hydrocarbons (PAHs) increased with the increase of temperature. The complex-flow activation energy Ea E a increased after VOCs emission. Naphthalene content exhibited a better linear relation with Ea E a .

  • Research on properties of bio-asphalt binders based on time and frequency sweep test
    Constr. Build. Mater. (IF 3.169) Pub Date : 2018-01-09
    Junfeng Gao, Hainian Wang, Zhanping You, Mohd Rosli Mohd Hasan

    Bio-asphalt is a binding agent that is made of bio-oil and petroleum asphalt, or bio-oil modified with incorporations of some other additives under certain conditions. This study was carried out to evaluate the properties of bio-asphalt binder-based in terms of the value of complex shear modulus (G∗) and the phase angle (δ) tested by dynamic shear rheometer (DSR). Four bio-oil dosages of 5, 10, 15, and 20% based on the weight of asphalt (S100) were used to alter the SBS-modified binder. Whereby, the SBS content is approximately 1% of the weight of the virgin asphalt. The complex shear modulus and frequencies of virgin and short-term aged binders were tested. The master curves of rutting factor (G∗/sinδ) of different bio-asphalt were then generated to survey its rheological properties in a broad range of frequencies and temperatures. Based on the results, it was found that the addition of bio-oil extracted from sawdust has significantly increased the complex shear modulus of asphalt binder at the same frequency conditions after going through rolling thin film oven (RTFO), which is desirable for rutting prevention of asphalt mixtures. The rheological properties of bio-binders are more susceptible to the RTFO aging condition compared to the reference binder. The master curve of rutting factor of bio-binder indicated that the rutting factor of bio-asphalt increased with the increase of frequency before and after RTFO. Additionally, incorporations of bio-oil into the SBS modified asphalt, has greatly increased the rutting factor (G∗/sinδ) after RTFO, regardless of the loading frequency. However, the degree of enhancement was dominated by the percentage of bio-oil and aging condition.

  • Further evidence of interfacial adhesive bond strength enhancement through fiber reinforcement in repairs
    Constr. Build. Mater. (IF 3.169) Pub Date : 2018-01-08
    Cristina Zanotti, Giulia Rostagno, Brian Tingley
  • Temperature predictions for asphalt pavement with thick asphalt layer
    Constr. Build. Mater. (IF 3.169) Pub Date : 2018-01-08
    Yi Li, Liping Liu, Lijun Sun

    Temperature is one of the most important factors affecting functional as well as structural performance of asphalt pavements with thick asphalt layer (>30 cm). For a successful pavement design, it is vital to accurately predict the pavement temperatures at various depths. However, most previous researches focused on the temperature predictions for conventional asphalt pavements, of which the asphalt thickness is less than 30 cm. This suggests their proposed models are applicable in top layers, but may not be so effective for temperature predictions at deeper depths. As a result, the primary objective of this research was to develop a statistical model to predict temperatures at deep depths. Three test sites were selected, and they were instrumented with a number of sensors and a data logger to record the pavement temperature hourly. Also, all test sections can provide meteorological monitoring to collect hourly air temperatures and hourly total solar radiation. The recorded meteorological conditions were found to have cumulative effect on the measured pavement temperatures at various depths. On basis of their relationship, a statistical regression was performed, and the temperature prediction model was determined as a function of depth, average air temperature and total solar radiation calculated in the cumulative time. For an improvement in applicability, historical mean monthly air temperatures were also incorporated into the mode. The accuracy and applicability of the improved model were validated by applying it to additional sites for which the measured pavement temperatures and meteorological data were available. Also, by comparing with existing models, the developed model was testified to be more effective for asphalt pavements with thick asphalt layer, promising the model’s potential use.

  • Replacement of steel with GFRP for sustainable reinforced concrete
    Constr. Build. Mater. (IF 3.169) Pub Date : 2017-12-28
    Shamim A. Sheikh, Zahra Kharal

    Corrosion of steel in reinforced concrete structures has cost a significant amount of resources globally over the past few decades. Glass fiber reinforcement polymer (GFRP) bars present a feasible and cost-effective solution to the problem of steel corrosion. The aim of this paper is to let engineers gain a better understanding of the overall behavior of GFRP as internal reinforcement so that they have more confidence using it as a sustainable material. This paper provides a few significant outcomes from an extensive experimental program underway at the University of Toronto. The work discussed here provides a summary of the tests on 24 GFRP reinforced beams, 60 GFRP direct tension specimens and 20 GFRP confined columns, and evaluates the behavior of GFRP-RC in flexure, shear, tension and compression. A recently proposed tension-stiffening model has been incorporated in analytical modeling of GFRP-RC beams and the results show significant improvement in the prediction of deflection and stiffness of the beams. Results from column tests show that GFRP bars used as longitudinal reinforcement can resist compressive stresses in excess of 700 MPa and GFRP lateral reinforcement can confine concrete core more effectively than steel.

  • Effect of graphene nano-sheets on the chloride penetration and microstructure of the cement based composite
    Constr. Build. Mater. (IF 3.169) Pub Date : 2017-12-13
    Baomin Wang, Ruying Zhao

    In this work, the effects of the non covalent surface modification method on the dispersion of graphene nano-sheets (GNS) in water and chloride diffusion of the cement paste incorporating these dispersions were investigated. Results showed that stable and homogeneous suspensions of graphene nano-sheets were prepared using polyoxyethylene (40) nonylphenylether (CO890) as a dispersant. In this research, water to cement ration is kept 0.30, the addition of GNS is ranging from 0.02% to 0.15% by weight of cement. It is found that introduction small quantities of GNS as little as 0.02% can decrease the chloride penetration depth and coefficient by as much as ∼37% and ∼42%, respectively. This improvement could be attributed to the enhanced degree of cement hydration, filling effect, barrier effect and crack-arresting effect of GNS in cement matrix. This work provides a new way to further understand the improvement of GNS in cement composites.

  • Effects of the incorporation of recycled aggregate in the durability of the concrete submitted to freeze-thaw cycles
    Constr. Build. Mater. (IF 3.169) Pub Date : 2017-12-13
    N.S. Amorim Júnior, G.A.O. Silva, D.V. Ribeiro

    Recycled concrete aggregates have been extensively studied in recent years. However, the studies that have addressed the use of the recycled aggregate in concrete subjected to freeze-thaw cycles are divergent. Thus, the present work suggests the use of recycled coarse aggregate (RCA), derived from civil construction waste, in concrete as a substitution to the natural coarse aggregate (NCA). To this end, concrete specimens were molded with replacement levels equal to 15%, 25% and 50% of the NCA for RCA, being the specimens evaluated according to the ASTM C 666-15 norm. In addition, the samples were characterized for apparent porosity and density, water absorption by capillarity, axial compression strength and dynamic modulus of elasticity. The use of recycled aggregates proved to be efficient as a possible alternative to the incorporation of air in the concretes, presenting a durability factor at the end of the cycle higher than presented by the reference mixture.

  • Hybrid fiber reinforced self compacting concrete with fly ash and colloidal nano silica: A systematic study
    Constr. Build. Mater. (IF 3.169) Pub Date : 2017-12-11
    Chinmaya Kumar Mahapatra, Sudhirkumar V. Barai

    The current systematic study investigates properties of hybrid fiber reinforced self compacting concrete (HyFRSCC) with crimped steel fibers (CSF) and polypropylene fibers (PPF) along with class F fly ash (FA) and colloidal nano silica (CNS). Optimization of HyFRC mix is conducted using L16 Taguchi Orthogonal Array where additive has four levels. Combination of 10% FA, 0.4% CNS, 1.25% CSF and 0.167% PPF found to be optimal recommendation. Multiple linear regression analysis predicts equations of tensile strength as the function of cylinder compressive strength, for combination of FA, CNS, CSF and PPF. A good correlation between tested and predicted values is obtained.

  • Solidification/stabilization mechanism of Pb(II), Cd(II), Mn(II) and Cr(III) in fly ash based geopolymers
    Constr. Build. Mater. (IF 3.169) Pub Date : 2017-12-11
    Yaguang Wang, Fenglan Han, Jingqiu Mu

    Geopolymers are new cementitious materials, which can effectively solidify/stabilize heavy metal ions. Fly ash is an industrial waste from the coal-consumed power plant. With thermal power projects continuously building in the world and the emissions and accumulation quantities of fly ash are increasing yearly. At the same time, with the development of modern industry, waste and waste water containing heavy metals are continuously discharged, so that heavy metal pollution has been the very serious world environmental problems. Aiming at the problem of fly ash and heavy metal pollution, this study referred to solidification/stabilization (S/S) of Pb (II), Cd (II), Mn (II) and Cr (III) in fly ash based geopolymers prepared using composite activator of sodium silicate and sodium hydroxide. The solidification (S/S) results had been explained by means of the leaching and compressive strength of the solidification (S/S) geopolymers (solidified bodies) acquired. The analysis was performed through chemical analysis, X-ray Diffraction (XRD), Fourier Transform Infrared Spectrometer (FTIR), Scanning Electron Microscope (SEM), Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES) and compressive strength tests. The results indicated that heavy metal ions could be effectively solidified in fly ash based geopolymers with a replacement of safe metal ions like Na (I) and Ca (II). Heavy metal ions had different effects on the compressive strength of geopolymers. (1.5 wt%) Pb (II) was beneficial to improve the compressive strength of geopolymers, and reached 49.34 MPa at 28 d. The XRD patterns indicated an amorphous structure and zeolite-like structure of aluminosilicate. The FTIR patterns study suggested changes of the Si-O-T (T = Si or Al) peak in the geopolymers. The SEM analysis revealed almost condensed homogenous surface of geopolymers. ICP-AES results showed that the geopolymer showed a high degree of solidification (S/S) of the heavy metal ions; in all samples, the solidification rates reached 99.9%. The mechanism of heavy metal ions being solidified was the interaction of physical fixation, adsorption and ion exchange. Finally, the pilot-scale test can achieve the same result on the basis of this study and made preparations for the future of industrialization.

  • Control of radon emanation at determination of activity concentration index for building materials
    Constr. Build. Mater. (IF 3.169) Pub Date : 2017-12-08
    Andrey Tsapalov, Konstantin Kovler

    Radon emanation is a well-known source of uncertainty at determination of activity concentration index for building materials and NORM. To reduce this uncertainty both radon emanation coefficient of the sample material and radon leakage from the measuring container should be considered. Two different methods (the rapid method and precise method, which requires to keep the sample sealed for at least three weeks), which are based on the use of only gamma-ray spectrometer, are proposed for testing radon emanation. Both methods also allow simultaneous determination of the specific activity of radium and an assessment of radon exhalation rate from the surface of the finished building products. In addition, the method for determination of radon leakage from the container is proposed. The reliability of the sealing methods of containers is compared and standard PET-flasks with a high radon-tightness are offered. The criteria to control radon leakage and radon emanation coefficient are given for three types of test samples: (a) building materials, (b) natural materials of mineral origin (sands, clays, rocks etc.), and (c) artificial materials, such as absorbents, filters, radioactive wastes. A simplified screening test to control activity concentration index for building materials without a need to keep the sample sealed before the measurement is proposed.

  • Integrated GPR and laboratory water content measures of sandy soils: From laboratory to field scale
    Constr. Build. Mater. (IF 3.169) Pub Date : 2017-12-06
    M. Ercoli, L. Di Matteo, C. Pauselli, P. Mancinelli, S. Frapiccini, L. Talegalli, A. Cannata

    In this study, laboratory and GPR water content measurements on two sandy soils are compared. A robust procedure to constrain GPR surveys is provided, aiming to obtain accurate and reliable soil moisture information at the field scale. The application of the well-known Topp’s equation, provided good results only for water contents (θv) from 5 to 17%. Therefore, integrated analyses are mandatory to better understand the subsurface structures and the water content pattern in unsaturated zones. Data and results here presented represent the first reference for typical sandy soils outcropping in Central Italy, providing solid constraints for engineering and hydrogeological applications.

  • Radioactivity and Pb and Ni immobilization in SCM-bearing alkali-activated matrices
    Constr. Build. Mater. (IF 3.169) Pub Date : 2017-12-01
    M.M. Alonso, A. Pasko, C. Gascó, J.A. Suarez, O. Kovalchuk, P. Krivenko, F. Puertas

    Partial or total replacement of Portland cement clinker by SCMs (Supplementary Cementitious Materials) is a priority for the cement industry in its pursuit of global sustainable development and eco-friendly binder manufacture. The most widely used SCMs include industrial by-products such as blast furnace slag, fly ash and red mud. Alkali-activated cements manufactured with SCMs may reduce the need for Portland clinker by up to 90 wt%–100 wt% with no significant decline in material strength. The trade-off, however, is the risk of higher than legally allowable levels of radioactivity and unbound heavy metals (Cd, Hg, Ni, Pb, Cr), which may leach into the soil with the concomitant adverse implications for human health and the environment. This study assessed the mechanical strength, leachability and natural radioactivity of alkali-activated cement paste containing industrial waste-based SCMs (blast furnace slag, fly ash and red mud) and Pb and Ni compounds. Strength was highest in alkali-activated slag and slag/fly ash pastes and lowest in the red mud-containing materials. The addition of Pb or Ni sulphates had no adverse effect on this parameter. Alkaline and OPC pastes showed a high level of immobilization of both lead and nickel ions. According to the radiological findings, the Activity Concentration Index (I) was higher in red mud than in OPC, blast furnace slag or fly ash. With (I) values lower than 1, however, all the hydrated/activated materials studied would be EU directive-compliant. Nonetheless, the use of these new materials will depend not only on the activity concentration index, but also on their physical and chemical properties and the quality tests that must be passed to conform to legal requirements.

  • Coupling effect of temperature and relative humidity diffusion in concrete under ambient conditions
    Constr. Build. Mater. (IF 3.169) Pub Date : 2017-11-20
    Ye Tian, Nanguo Jin, Xianyu Jin

    To accurately analyze the temperature and relative humidity (RH) distribution in concrete structures under ambient conditions, based on Krstulovic-Dabic hydration kinetics, an improved hydration model is proposed to geometrically bridge the relationship between hydration degree and microstructure of cementitious materials. Both the water content and hydration heat can be individually extracted from the model to evaluate the influence of ambient conditions variation. And the adsorption curve of concrete is acquired based on the microstructure obtained from hydration model and a redistribution of moisture content in pores is applied to evaluate the hydration process accordingly. Thus, the coupling effect of RH and temperature diffusion in concrete is decoupled in terms of hydration degree. An engineering verification indicates that the model can accurately predict the development of relative and temperature in concrete structures, and the construction procedure has significant influence on moisture and heat diffusion in concrete under ambient conditions.

  • The NORM4Building database, a tool for radiological assessment when using by-products in building materials
    Constr. Build. Mater. (IF 3.169) Pub Date : 2017-11-15
    Wouter Schroeyers, Zoltan Sas, Gergo Bator, Rosabianca Trevisi, Cristina Nuccetelli, Federica Leonardi, Sonja Schreurs, Tibor Kovacs

    Scientific data on natural occurring radioactive materials (NORMs) is available in unknown quantities and the data is fragmented over several different sources. The new EU-BSS is regulating the use of NORM in building materials, however a large scale database with country specific information that can support legislators and industry in the assessment of the radiological impact of the use of by-products in construction is missing. Currently the COST Action ‘NORM4BUILDING’ (2014–2017) is creating such a database using a semi-automated datamining approach. In this paper radiological aspects on by-products that can find application in concrete are discussed based on the database.

  • Time-varying relative displacement field on the surface of concrete cover caused by reinforcement corrosion based on DIC measurement
    Constr. Build. Mater. (IF 3.169) Pub Date : 2017-11-14
    Xianyu Jin, Jing Tong, Ye Tian, Nanguo Jin

    To investigate the cracking process of concrete cover due to corrosion of reinforcement for concrete specimens subjected to semi-immersed accelerated corrosion, digital image correlation (DIC) was applied to quantitatively and visually characterize the development of relative displacement on the viewed surface. The impacts of stirrups and concrete cover thickness on the evolution of relative displacement were interpreted. And a detailed analysis covered the initial cracking time, position and relative displacement distribution on the surface during the cracking procedure. The study indicates that the corrosion of stirrups is prior to longitudinal reinforcement as the longitudinal reinforcement is cathodic protected by stirrups. The full-scale monitoring on the relative displacement reveals that a thicker concrete cover can retard the initial cracking but will promote the propagation speed of corrosion cracks. The investigation on the initial cracking zone implies that the initial cracking has high probability to appear within a region and its width is approximately close to the concrete cover thickness.

  • Gamma exposure from building materials – A dose model with expanded gamma lines from naturally occurring radionuclides applicable in non-standard rooms
    Constr. Build. Mater. (IF 3.169) Pub Date : 2017-11-12
    Tom Croymans, Federica Leonardi, Rosabianca Trevisi, Cristina Nuccetelli, Sonja Schreurs, Wouter Schroeyers

    Building materials are a significant source of gamma rays exposure due to the presence of naturally occurring radionuclides. In order to protect the public from harmful radiation, the European Basic Safety Standards (Council directive 2013/59/Euratom) (European Council, 2014) introduced a one-size-fits-all building(s) (materials) activity concentration index (ACI) based on a limited set of gamma lines. The ACI is considered “as a conservative screening tool for identifying materials that may cause the reference level (i.e. 1 mSv/y) laid down in article 75(1) to be exceeded”. Regarding calculation of dose, many factors such as density and thickness of the building material, as well as factors relating to the type of building, and the gamma emission data need to be taking into account to ensure accurate radiation protection. In this study the implementation of an expanded set of 1845 gamma lines, related to the decay series of 238U, 235U and 232Th as well as to 40K, into the calculation method of Markkanen (1995), is discussed. The expanded calculation method is called the Expanded Gamma Dose Assessment (EGDA) model. The total gamma emission intensity increased from 2.12 to 2.41 and from 2.41 to 3.04 for respectively the 238U and 232Th decay series. In case of 40K a decrease from 0.107 to 0.106 is observed. The 235U decay series is added, having a gamma emission intensity of 3.1. In a standard concrete room, the absorbed dose rates in air (DA) per unit of activity concentration of 0.849, 0.256, 1.08, 0.0767 nGy/h per Bq/kg are observed. The use of weighted average gamma lines increased the DA with 6.5% and 1% for respectively the 238U and 232Th decay series. A decrease of 4.5% is observed in the DA of 235U decay series when using the weighted average gamma lines in comparison to its non-averaged variant. The sensitivity of the EGDA model for density, wall thickness, presence of windows and doors and room size is investigated. Finally, a comparison of the index and dose calculations relevant for the dose assessment within the European legislative framework applicable towards building materials is performed. In cases where the ACI and density and thickness corrected dose calculation of Nuccetelli et al. (2015) cannot provide guidance, the EGDA allows performing more accurate dose assessment calculations leading to effective doses which can be several 100 µSv/y lower.

  • Use of water reducer to enhance the mechanical and durability properties of cement-treated soil
    Constr. Build. Mater. (IF 3.169) Pub Date : 2017-11-04
    Liangxing Jin, Weimin Song, Xiang Shu, Baoshan Huang

    This study investigated the potential of using water reducer (WR) to enhance the mechanical and durability properties of cement-treated soil. WRs have long been used in Portland cement concrete (PCC) to increase the properties of PCC. When added at a small dosage, WR helps improve the dispersion of cement particles and release the water otherwise entrapped in cement clusters, thus reducing the water demand for the same consistency or increase the consistency of PCC without adding more water. Cement-treated soil uses similar raw materials and has similar chemical compositions to PCC. However, little research has been conducted to explore the potential of using WR in cement-treated soil to improve its compaction and thus its mechanical and durability properties. In this study, a laboratory experiment was conducted to examine the effects of WR on the compaction characteristics and engineering properties of cement-treated soil. As expected, similar benefits of water reduction and improved properties could be achieved by adding WR in cement-treated soil. The improved mechanical and durability properties of cement-treated soil were due to the fact that WR could improve the compaction behavior of cement-treated soil through reduced optimum moisture content and increased maximum dry density. Further studies are recommended for the interaction among WR, soil particles, and cement particles to achieve an optimal effect for engineering applications.

  • Thermal and mechanical properties of alkali-activated slag paste, mortar and concrete utilising seawater and sea sand
    Constr. Build. Mater. (IF 3.169) Pub Date : 2017-11-04
    Ying-Lei Li, Xiao-Ling Zhao, R.K. Singh Raman, Saad Al-Saadi

    This paper presents an experimental study on the thermal properties of alkali-activated slag paste, mortar and concrete utilising seawater and sea sand exposed to elevated temperature. The thermal properties of paste and concrete utilising cement, fresh water and river sand were also investigated for comparison purpose. The samples were heated to different target temperatures up to 1000 °C at a heating rate of 5 °C/min, and tested both under hot and cooled conditions. The thermal properties, including temperature gradient, visual observation, mass loss, thermal strain and mechanical properties (i.e. strength, Young’s modulus and stress-strain curve) were investigated. X-ray CT scanning and scanning electron microscopy (SEM) were conducted to understand the macro/microscopic changes of the paste and concrete in response to heating. Degradation in mechanical properties of slag paste is attributed mainly to the cracks induced by temperature gradient, pore pressure and phase change. The degradation of concrete is caused by thermal mismatch between paste matrix and aggregates regardless of the use of cement or slag, freshwater or seawater, and river sand or sea sand.

  • Discussion and experiments on the limits of chloride, sulphate and shell content in marine fine aggregates for concrete
    Constr. Build. Mater. (IF 3.169) Pub Date : 2017-11-04
    Wei Liu, Ruihua Huang, Jiyang Fu, Waiching Tang, Zhijun Dong, Hongzhi Cui

    Concrete is the most consumable building material in the world. Marine aggregates are the natural sand and gravels available in the sea or dredged from seabed. Contents of chloride, sulphate and shell in the marine aggregates can influence the properties of concrete and corresponding performance of the concrete structures. However, the limitations of chloride, sulphate and shell contents are set as different threshold values in different countries and/or regions. Some of them are inconsistent or puzzling for user. This paper presents a comprehensive review on the limit values of these contents used in different countries and provides a better understanding on the rationale behind these limit values thorough analysis on the limits of chloride, sulphate and shell content in marine fine aggregates for concrete. Except discussion, in this paper, an experimental study was carried out to evaluate the corrosion of reinforcing steel in concrete mixed with DMS as well. The experimental results of corrosion potential and corrosion current density showed that the rebar in DMS concrete should be safe from corrosion when the chloride content in DMS is less than 0.18% or the total chloride content in concrete is less than 0.34%. This study can contribute to fill the knowledge gap on concrete applications on dredged marine sand (DMS) and relative research.

  • Utilization of circulating fluidized bed combustion ash in producing controlled low-strength materials with cement or sodium carbonate as activator
    Constr. Build. Mater. (IF 3.169) Pub Date : 2017-10-06
    Jeong Gook Jang, Sol-Moi Park, Sangho Chung, Ji-Whan Ahn, Hyeong-Ki Kim

    The present study investigates the fresh and hardened properties of controlled low-strength materials (CLSM) utilizing circulating fluidized bed combustion (CFBC) ashes, activated with cement or sodium carbonate. Engineering properties such as flowability, settlement, setting behavior, compressive strength, and hydration characteristics were evaluated. The results provided new insights, demonstrating that CFBC ashes can be effectively utilized in producing CLSM with suitable material design as the CLSM could achieve the required performances specified in the ACI 299R-13. The CLSM mixtures showed a self-destruction characteristic due to the formation of ettringite, while it showed stable strength development in a dry condition.

  • Concrete cover cracking and service life prediction of reinforced concrete structures in corrosive environments
    Constr. Build. Mater. (IF 3.169) Pub Date : 2017-09-14
    Zhen Cui, Alice Alipour

    Crack initiation of concrete cover due to corrosion defines the end of functional service life where repair or replacement is required for corroded reinforced concrete (RC) structures. This study provides a comprehensive and critical analysis for the analytical and numerical models of corrosion-induced cover crack initiation for both uniform and non-uniform corrosion. Parametric studies are conducted to investigate the effects of different factors on crack initiation time and crack propagation patterns using a thermal analogy approach defined in three dimensional nonlinear finite element (FE) models. The results show that the type of corrosion products, thickness of interfacial transition zone and rate of corrosion are the parameters that affect crack initiation time the most significantly. The developed FE models are able to study crack initiation and propagation for both uniform and non-uniform corrosion and quantify the extent of concrete damage due to cracks. The FE results show that crack patterns under uniform and non-uniform corrosion differ. Under uniform corrosion, the major crack occurs vertically in the cover. But under non-uniform corrosion, major cracks form diagonally at the location of the pit in the cover. The vertical crack appears later and then becomes the third major crack. The results also show that non-uniform corrosion causes high concentrated pressure at the pits which would lead to earlier cover cracking. It is shown that assuming uniform corrosion may result in non-conservative service life estimation. The efficiency and applicability of the existing empirical models have been analyzed using the outcomes from the finite element models. Recommendations on how to select proper models to estimate crack initiation time have been provided. The outcome of the research provides a reliable approach to predict corrosion-induced cover crack initiation and propagation for RC structures.

  • The Diplomatic Hall of the Royal Palace of Naples: Structural characterization of the timber roof by in situ ND investigations
    Constr. Build. Mater. (IF 3.169) Pub Date : 2015-08-11
    Beatrice Faggiano, Anna Marzo, Federico M. Mazzolani

    Especially in monumental buildings the preservation is compulsory for perpetuating the history of the construction technologies and of the past used materials. Therefore, the evaluation of the residual bearing capacity of existing structures is necessary, in order to detect any structural deficiency and to select proper restoration interventions. First of all a comprehensive knowledge of the structures should be acquired through in depth surveys, aiming at the structural identification. In this context, the paper exemplifies the structural identification procedure with reference to the complex covering timber structure of the Diplomatic Hall of the Royal Palace of Naples. The focus is specially on the in situ investigation phase, as the first essential step prior to the structural analysis of stress and deformation. Both geometrical and visual surveys are presented, in addition to in situ ND tests, the latter being performed by the CNR IVALSA Institute according to the current Italian Rules. As a result, the geometrical and static schemes were identified, the wooden species distinguished, the moisture content assessed, defects and degradations due to both aging and biological attacks detected, the effective transversal section determined and the effectiveness of the connections evaluated.

Some contents have been Reproduced with permission of the American Chemical Society.
Some contents have been Reproduced by permission of The Royal Society of Chemistry.
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