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  • Using X-ray Computed Tomography to Investigate Mortar Subjected to Freeze-Thaw Cycles
    Cement Concrete Comp. (IF 5.172) Pub Date : 2020-01-16
    Ghazal Sokhansefat; Masoud Moradian; Mark Finnell; Amir Behravan; M. Tyler Ley; Catherine Lucero; Jason Weiss

    This work uses X-ray computed micro tomography (XCT) to investigate the role of the critical degree of saturation (DOS) and air void system on the crack propagation of portland cement mortar subjected to freeze-thaw cycles. Three-dimensional imaging before and after freezing allow quantitative measurements on the location and volume of the formation of new cracks and the infilling of air voids. Cracks present before freeze-thaw cycles are observed to extend and new cracks initiate from the paste-aggregate interface. In addition, calcium-rich products were observed to fill > 20% of the volume of the air voids with a diameter < 50 μm. These observations provide insights into the freeze-thaw performance of mortar and are a step in understanding the damage in concrete.

  • In situ-Grown Carbon Nanotubes Enhanced Cement-Based Materials with Multifunctionality
    Cement Concrete Comp. (IF 5.172) Pub Date : 2020-01-15
    Mimi Zhan; Ganghua Pan; Feifei Zhou; Renjie Mi; Surendra P. Shah

    Smart cementitious materials integrated with carbon nanotubes (CNTs) have potential applications as sensors in structural health monitoring (SHM). The sensitivity to strain (gauge factor) and strength of such materials are limited by the difficulty in dispersing CNTs. Here we synthesized CNTs in situ on the surface of fly ash (FA) to significantly improve the CNT dispersibility and enable the cement mortar to exhibit an outstanding strain-sensing capability. The mortar with CNT-coated FA ([email protected]) at 2.0 wt.% CNT concentration had a gauge factor of 6544, about one order of magnitude higher than that of mortar with commercial CNTs under the same condition. Its electrical resistivity can reversely vary as high as 69% upon cyclic compressive loading. The great self-sensing ability of cement mortars reinforced with in situ-grown CNTs was explained by two mechanisms: 1) the high possibility of the breakup/formation of CNT conductive paths provided by the unique morphology of [email protected]; 2) high ratio of tunneling resistance with respect to the total resistance caused by the good dispersion of CNTs, which is demonstrated by optical microscopy measurements. The compressive and flexural strength values of the mortars with [email protected] are also higher than those of the plain mortar at an age of 28 days. The [email protected] mortars with enhanced electrical and mechanical properties have potential applications in assessing the conditions of civil engineering structures.

  • Improved Toughness and Delamination Resistance in Continuous Fiber Reinforced Geopolymer Composites via Incorporation of Nano-Fillers
    Cement Concrete Comp. (IF 5.172) Pub Date : 2020-01-13
    Akm Samsur Rahman; Patrick Jackson; Donald W. Radford

    Geopolymer matrix composites (GMC) have the potential to bridge the processing performance gap between polymer matrix and ceramic matrix composites. Yet one drawback of GMCs is their extreme brittleness and weak inter-laminar shear strength. The aim of this study was to evaluate the effectiveness of Silicon Carbide Whisker (SCW) nano-filler on the mechanical performance of neat unreinforced geopolymer and unidirectional fiber reinforced GMCs containing variations in fiber surface chemistry. In order to evaluate, neat and SCW populated geopolymer matrices were fabricated for comparison. Nextel 610 fiber reinforced GMCs were also fabricated with SCW for comparison to GMCs without the SCW nano-filler. The effect of the nano-filler was evaluated using three-point flexural methods to obtain strength and fracture toughness (KIC). Results indicate that the addition of SCWs up to 4 vol% improved Mode-I fracture toughness of the baseline geopolymer matrix by 113%. The improvements to the neat matrix also resulted in improved flexural strength, inter-laminar shear strength, and delamination resistance of the continuous fiber reinforced composites.

  • Engineering of high specific strength and low thermal conductivity cementitious composites with hollow glass microspheres for high-temperature high-pressure applications
    Cement Concrete Comp. (IF 5.172) Pub Date : 2020-01-10
    Konrad J. Krakowiak; Raj Gopal Nannapaneni; Amir Moshiri; Tejasree Phatak; Damian Stefaniuk; Lukasz Sadowski; Mohammad Javad Abdolhosseini Qomi

    Lightweight cement-based composites with high specific strength and low thermal conductivity are highly sought in the energy and construction industries. These characteristics are important in designing cement liners for high-temperature, high-pressure (HTHP) wells, in addition to those operating in permafrost. Similar attributes are also desirable in designing cementitious composites for energy efficient building envelopes. This work reports the results of an experimental campaign focused on engineering lightweight cementitious composites with hollow glass microspheres. It is demonstrated that the chemical stability of microspheres at HTHP conditions can be directly controlled by modulating the specific surface area and dissolution rate constant of supplementary siliceous additives. In addition to the stabilizing effect, such additives lead to the pore structure refinement and the enhancement of interfacial transition zone (ITZ). Introduced lightweight composites are capable of delivering significant load bearing capacity when normally cured, which is greatly increased by hydrothermal curing. Such high specific strength composites possess thermal conductivity below 0.3 W/mK at the oven dry density <1000 kg/m3 and cement dosage <400 kg/m3. This class of cementitious composites bears potential to enhance zonal insulation and well integrity, as well as increasing energy efficiency of building envelopes.

  • The role of limestone and calcined clay on the rheological properties of LC3
    Cement Concrete Comp. (IF 5.172) Pub Date : 2020-01-10
    Tafadzwa Ronald Muzenda; Pengkun Hou; Shiho Kawashima; Tongbo Sui; Xin Cheng

    Understanding the rheological properties of cementitious materials is important for controlling their fresh properties and for improving the practical applications. In this study, the rheological properties of pastes made from ordinary Portland cement blended with different amounts of calcined clay and limestone were investigated in order to understand the combined and independent effects of limestone and calcined clay on the rheological properties of limestone calcined clay cement (LC3). Large Amplitude Oscillation Strain was applied and the subsequent harmonic distortion was used to evaluate nonlinear response for the first time for cementitious materials. The results showed that calcined clay leads to increased static and dynamic yield stress, initial thixotropic index, plastic viscosity and cohesion, as well as decreased harmonic distortion, while limestone has an opposite effect. It is believed that these results will aid in understanding the viscoelasticity of this blended cement.

  • Synthesis, design and piezo-resistive characteristics of cementitious smart nanocomposites with different types of functionalised MWCNTs under long cyclic loading
    Cement Concrete Comp. (IF 5.172) Pub Date : 2020-01-10
    Rajanikant Rao; B.S. Sindu; Saptarshi Sasmal

    In recent years, carbon nanotubes (CNTs) incorporated smart cement composites have attracted significant attention as it opens up a new avenue to develop new class of sensors, in general, and uniquely enables the structural materials to reflect the internal stress state, in particular. However, dispersion of CNTs, threshold limit, polarization effect, type and design of electrode, effect of functionalization of CNTs etc. on piezo-resistive properties of cementitious nanocomposites need further investigations. The present study describes the systematic approach for developing cement based smart nanocomposites exploiting the unique capabilities of functionalised MWCNTs and comprehensive studies on performance under monotonic- and long reverse cyclic-loading. Three different types of multiwalled carbon nanotubes (MWCNTs) like pristine MWCNTs, hydroxyl (-OH) MWCNTs and carboxyl acid (-COOH) MWCNTs are considered. The response of cement based smart nanocomposites under cyclic compression load was measured in terms of fractional change in resistivity (FCR) where type and dosage of CNT, type of electrode are the parameters. The test results indicate that the performance of the smart composite with COOH-MWCNTs is superior compared to other types and the gauge factor of the composite is found to be as high as 451. The study also emphasizes the role of stabilization, tunneling effects and formation of conductive paths in imparting the piezo-resistive properties in porous, nonconductive materials like cement composites.

  • Experimental Investigation of Fatigue Bond Behavior between Deformed Steel Bar and Concrete
    Cement Concrete Comp. (IF 5.172) Pub Date : 2020-01-10
    Weiping Zhang; Yunpeng Zhang; Hao Li; Xianglin Gu

    Bond degradation induced by fatigue loading may affect the serviceability and even safety of reinforced concrete (RC) structures. To investigate fatigue bond behavior between rebar and concrete, three sets of eccentric pull-out tests were carried out, especially on specimens with a thinner concrete cover. Based on monotonic tests of nine specimens with different cover thicknesses, a bond stress-slip model was developed for specimens with splitting failure. According to the tested monotonic bond strength, repeated loadings with different amplitudes and cycles were applied to 15 specimens to fail. Failure mechanism of different fatigue bond failure modes was analyzed. Relative slip develops in three stages under repeated loading and it can be well predicted by a power function model. To investigate the effects of fatigue loading history, five specimens were subjected to a certain number cycles of repeated loading before undergoing monotonic tests. Test results show that fatigue loading history has little influence on bond strength but leads to increased bond stiffness and peak slip. An empirical unified model for splitting failure was finally proposed to describe the bond stress-slip relationship of specimens under monotonic and repeated loading.

  • Effects of Strain Rate on the Tensile Behavior of Cementitious Composites made with Amorphous Metallic Fiber
    Cement Concrete Comp. (IF 5.172) Pub Date : 2020-01-10
    Hongseop Kim; Gyuyong Kim; Sangkyu Lee; Gyeongcheol Choe; Jeongsoo Nam; Takafumi Noguchi; Viktor Mechtcherine

    Amorphous metallic fiber has higher tensile strength as well as corrosion and wear resistance than common, crystalline steel fibers. Its utilization as reinforcement improves the crack resistance and flexural and tensile performance of concrete. In the study at hand, the tensile behavior of thin plate amorphous metallic fiber-reinforced cementitious composites (AFRCC) is compared with that of hooked steel fiber-reinforced cementitious composites (HSFRCC) for both quasi-static and dynamic loading regimes. AFRCC exhibites a high stress distribution effect and higher tensile strength, strain capacity, and peak toughness than HSFRCC, but lower tensile toughness and lower dynamic increase factor values for tensile strength, strain capacity, and toughness.

  • Investigating the effect of carbon nanotube on early age hydration of cementitious composites with isothermal calorimetry and Fourier transform infrared spectroscopy
    Cement Concrete Comp. (IF 5.172) Pub Date : 2020-01-07
    Zhen Li; David J. Corr; Baoguo Han; Surendra P. Shah

    The effects of a range of carbon nanotube (CNT) additions (0.1 to 0.5% by weight of cement) on the early hydration processes (0-24h) of cementitious composites were investigated by isothermal calorimetry, Fourier transform infrared spectroscopy (FTIR), X-Ray powder diffraction (XRD) analysis and scanning electron microscope (SEM) observation. The addition of CNT can improve the rate of hydration heat of cementitious composites. However, 0.1 wt.% CNT obviously decreased the total cumulative hydration heat of cementitious composites. Additionally, the peaks corresponding toSV4iO44− vibrations were shifted from 496 cm-1 to higher frequencies (534 cm-1, 534 cm-1 and 546 cm-1) at 24h due to the inclusion of CNT (0.1%, 0.3% and 0.5%). It is hypothesized that CNT with high surface energy can improve the energy of cementitious composites and increase the polymerization of C-S-H. According to the XRD test, CNT didn’t affect the types of cement hydration products, but can reduce the orientation index of calcium hydroxide crystal. The microstructure observations demonstrated that CNT can also change the morphologies of hydration products and modify the microstructure of cementitious composites. Such behaviors could be associated with the case that CNT can increase the polymerization degree of C-S-H which was verified by the isothermal calorimetry and FTIR test.

  • The rotation speed-torque transformation equation of the Robertson-Stiff model in wide gap coaxial cylinders rheometer and its applications for fresh concrete
    Cement Concrete Comp. (IF 5.172) Pub Date : 2020-01-03
    Yu Liu; Caijun Shi; Qiang Yuan; Xiaopeng An; Lingli Zhu; Bin Wu

    The rheological properties of fresh concrete can be characterized by the function between shear rate and shear stress. However, neither shear rate nor shear stress can be measured directly, but transformed from the rotation speed and torque logged by the rheometer. Therefore, the relationship between the rheological model and the torque-rotation speed function needs to be established. In order to describe the nonlinear rheological behavior of fresh concrete, the Robertson-Stiff model was proposed in this paper, and the relationship between rotation speed-torque and rheological parameters measured by the coaxial cylindrical rheometer was derived. Eight concrete mixtures were made, and its rheological properties were tested with ConTec 5 viscometer. Then raw data was utilized to validate the model. The results showed that the Robertson-Stiff model could be used to describe the rheological behavior of fresh concrete.

  • Effect of natural fibers on thermal spalling resistance of ultra-high performance concrete
    Cement Concrete Comp. (IF 5.172) Pub Date : 2020-01-03
    Dong Zhang; Kang Hai Tan; Aravind Dasari; Yiwei Weng

    It has been established that the addition of synthetic fibers like polypropylene (PP) to ultra-high performance concrete (UHPC) enhances the latter’s thermal spalling resistance. The key for this is the thermal mismatch between embedded fibers and matrix as a result of the expansion of PP fibers with temperature. This manuscript explores the effect of natural fibers (replacing traditional PP fibers) on compressive strength, hot permeability, and spalling resistance of UHPC. Different dosages (3, 5 and 10 kg/m3) of jute fibers are used for this purpose. The findings are critical as they oppose the mechanism of thermal spalling resistance established for synthetic fibers in UHPC. Natural fibers swell by absorbing water (during the casting of UHPC and during their service life) and shrink upon exposure to warm and high temperatures. The deswelling and shrinkage of natural fibers at high temperatures create spaces between fibers and matrix, which could influence permeability at those temperatures. This suggests that percolation of fibers is critical in the case of jute as opposed to PP fibers. It was found that a dosage of 10 kg/m3 of jute fibers is required for eliminating spalling of UHPC as opposed to 3 kg/m3 for PP fibers. Additionally, preliminary efforts are put in to investigate the short-term durability of the samples and changes in properties of UHPC with jute fibers.

  • Micromechanics-guided Development of a Slag/Fly ash-based Strain-hardening Geopolymer Composite (SHGC)
    Cement Concrete Comp. (IF 5.172) Pub Date : 2020-01-03
    Shizhe Zhang; Victor C. Li; Guang Ye

    Strain-hardening geopolymer composite (SHGC) lately emerged as a promising alternative to traditional strain-hardening cementitious composite with added advantage of industrial by-product utilization and enhanced sustainability. However, as the design of SHGC requires multi-factor optimization, application of the traditional trial-and error method is inefficient and hinders the development of this material. This paper aims at the development of a slag-fly ash based SHGC with low slag content using micromechanical model to guide the composite mixture design. To this end, experimentally characterized physical properties of fiber, matrix and interface are used as input for the micromechanical model, which serves as a predictive tool for the tensile performance of SHGC. Following the guidance, a slag/fly ash based SHGC with tensile strain capacity of 4.8% and ultimate tensile strength above 3.8 MPa was systematically developed. The feasibility and effectiveness of using micromechanics as the design basis of SHGC are demonstrated and experimentally verified.

  • On the origins of Transient Thermal Deformation of Concrete
    Cement Concrete Comp. (IF 5.172) Pub Date : 2019-12-31
    Florent Manzoni; Thierry Vidal; Alain Sellier; Xavier Bourbon; Guillaume Camps

    The conditions that lead to Transient Thermal Deformation (TTD), also called Thermal Transient Creep (TTC), of concrete subjected to various temperatures and compressive loads in sealed conditions are analysed and a model based on a two-scale porosity is proposed. In this model, water expands in the smaller pores and diffuses progressively to the capillary pores at the upper scale. It is then shown that the water overpressure in smaller pores and the duration of the diffusion process between the two scales of porosity control the TTD. It is also shown that creep or shrinkage before the temperature transition mitigates TTD. The aim is to provide a model able to predict the conditions for TTD to appear and the amplitude of the TTD under various thermo-mechanical conditions. The TTD model is implemented in an existing basic creep model, fitted and compared with different experimental results.

  • Using particle composition of fly ash to predict concrete strength and electrical resistivity
    Cement Concrete Comp. (IF 5.172) Pub Date : 2019-12-31
    Taehwan Kim; M. Tyler Ley; Shinhyu Kang; Jeffrey M. Davis; Seokhyeon Kim; Pouya Amrollahi

    This paper uses a new approach where fly ash is characterized on a particle-by-particle basis using automated scanning electron microscopy. The particle data is then analyzed with principal component analysis (PCA) to find interrelationships among the particle chemical composition for 20 different fly ashes. Consistent trends were observed in 20 fly ashes. These trends from PCA were verified by making comparisons of these trends for individual particles. One application is introduced using this particle data. Each particle is categorized into four broad groups with a limited chemical composition. These four groups were found in different proportions in the different fly ashes investigated. Compressive strength and surface electrical resistivity were measured from concrete mixtures made with these fly ashes and the four groups correlated with the performance in concrete. This finding is an important step to develop a more general classification of fly ash based on the individual particle make-up, which helps to optimize the mixture design and also benefits the sustainable concrete by increasing the effectiveness of industrial by-waste usage.

  • Reinforcement effects of multi-scale hybrid fiber on flexural and fracture behavior of ultra-low-weight foamed cement-based composites
    Cement Concrete Comp. (IF 5.172) Pub Date : 2019-12-31
    Yuanyi Yang; Qi Zhou; Yi Deng; Jinhui Lin

    The flexural behavior and fracture parameters of ultra-low-weight foamed cement-based composites (FCC) reinforced by a novel fiber hybridization containing short PP fiber and CaCO3 whisker was investigated. The flexural behavior, fracture failure, fracture toughness and fracture energy of FCC with multi-scale fibers has been comprehensively evaluated. The fiber hybridization performed better fracture performances than that of incorporation of either mono PP fiber or CaCO3 whisker, which has provided a grading crack resistance in the ultra-low-weight FCC, and achieved the synergistic reinforcing effect. This work is helpful towards the foundation of optimal design for fracture toughness analysis in fiber-reinforced lightweight cement elements.

  • Visco-elastic behavior of blended cement pastes at early ages
    Cement Concrete Comp. (IF 5.172) Pub Date : 2019-12-31
    Zhangli Hu; Adrien Hilaire; Mateusz Wyrzykowski; Pietro Lura; Karen Scrivener

    This study aims at elucidating the visco-elastic behavior of hardening blended cement pastes, focusing on uniaxial basic compressive creep tests at early loading ages. Cement pastes with Portland cement only or blended with quartz or fly ash (both at a substitution level of 49 % by volume of the total solids) were subjected to different loading scenarios. The results show that both blended systems had higher creep than pure cement paste at early ages and that the creep compliance of the blended system with fly ash was higher than with quartz. While this difference is in part due to the restraining effect of the elastic phases, the amount of C-S-H and the porosity, dissolution creep may also play a role. A numerical algorithm with generalized Kelvin-Voigt chain model was developed and it was capable of predicting with good accuracy the strain evolution of the blended cementitious materials at early ages.

  • Tailoring sodium-based fly ash geopolymers with variegated thermal performance
    Cement Concrete Comp. (IF 5.172) Pub Date : 2019-12-31
    Mukund Lahoti; Stephen Fransceda Wijaya; Kang Hai Tan; En-Hua Yang

    Sodium-based fly ash geopolymers show great fire resistance potential and commercial advantage for structural applications. Hence, in current research, tailoring of sodium-based geopolymer mix design without changing the fly ash source has been studied. It was found that a wide variety of residual compressive strength ranging from significant reduction (∼80%) to maintaining significant enhancement (∼150%) after being exposed to 900°C was observed. The contributory mechanisms were discovered by investigating their chemical stability, pore structures, volume stability, and strength endurance prior to and after exposure to high-temperature using different microstructure characterization techniques including XRD, FTIR, MIP, dilatometry, and SEM. Crack formation due to moisture migration, pore shrinkage, and re-crystallization of nepheline adversely affected compressive strength. Matrix densification due to shrinkage of pore and stronger inter-particle bonding due to viscous sintering, favored compressive strength gain. This work discusses at length these competing mechanisms influencing the residual compressive strength.

  • Water Permeability of Eco-Friendly Ductile Cementitious Composites (EDCC) under an Applied Compressive Stress
    Cement Concrete Comp. (IF 5.172) Pub Date : 2019-12-28
    Qiannan Wang; Nemkumar Banthia; Wei Sun; Chunping Gu

    Permeability of concrete is one of its most important characteristics determining the durability. In this study, water permeability of a new class of fiber reinforced concrete materials called Eco-Friendly Ductile Cementitious Composites (EDCC) was studied, with and without an applied compressive stress. Hollow-core specimens were used and permeability tests were performed under full flow-equilibrium conditions. Four applied stress levels of 0.3fu, 0.4fu, 0.5fu and 0.6fu were investigated, where fu is the compressive strength of the EDCC in question. Permeability tests under identical conditions were carried out on plain control specimens without fiber reinforcement (termed Plain Cementitious Composites, PCC). The results indicated that the permeability of unstressed specimens declined over time due to the continuous hydration. A ‘critical’ compressive stress level (fcc) was identified and defined, which when exceeded, a dramatic increase in the coefficient of permeability occurred. The ‘critical’ compressive stress level (fcc) was noted to be between 0.5fu ∼ 0.6fu for EDCC and 0.4fu ∼ 0.5fu for PCC. In other words, EDCC was more damage tolerant than PCC, and even when fcc was exceeded, the impact of stress on the permeability of EDCC was far less pronounced compared to PCC.

  • Strategic use of steel fibers and stirrups on enhancing impact resistance of ultra-high-performance fiber-reinforced concrete beams
    Cement Concrete Comp. (IF 5.172) Pub Date : 2019-12-28
    Jin-Young Lee; Tianfeng Yuan; Hyun-Oh Shin; Young-Soo Yoon

    In order to investigate the static and dynamic flexural behavior of ultra-high-performance fiber-reinforced concrete (UHPFRC) beams, twelve half-scale beams (125 × 250 × 2438 mm) were fabricated and tested under quasi-static and drop-weight impact loading conditions. Four different volume fractions (vf) of steel fibers, i.e., 0, 0.5, 1.0, and 1.5%, and shear reinforcements were considered as test variables. Force-displacement relations and energy dissipating capacity were derived to evaluate and compare the impact resistance of the UHPFRC beams. The force-displacement curves, excluding inertial effects, were obtained by a proposed process using D’Alembert’s dynamic equilibrium principle, and energy dissipating capacity was calculated by integrating the overlapped force-displacement curves of sequential impact tests. Furthermore, the equivalent blast load was converted from the impact force to extend the utilization of impact test results for substituting difficult blast tests on structural specimens. Lastly, the test results indicate that the addition of steel fibers and stirrups enhanced the static and impact resistances of the UHPFRC beams in terms of higher load carrying capacity, higher energy dissipating capacity, and lower maximum and residual displacements. As for specimens without steel fibers and stirrups, brittle shear failure occurred under static and impact loading conditions.

  • Fiber reinforced geopolymer composites: A review
    Cement Concrete Comp. (IF 5.172) Pub Date : 2019-12-27
    Navid Ranjbar; Mingzhong Zhang

    There is a burgeoning interest in the development of geopolymers as sustainable construction materials and incombustible inorganic polymers. However, geopolymers show high quasi-brittle behavior. To overcome such weakness, hundreds of research have been focused on development, characterization, and implementation of fiber reinforced geopolymers for a wide range of applications. This paper discusses the rapidly developing state-of-the-art of fiber reinforced geopolymer composites, focusing on material and geometrical properties of construction fibers, and underlying mechanisms on fiber-binder interaction at fresh and hardened states, mechanical properties, toughening mechanisms, thermal characteristics, and environmental durability. It is intended to build a strong conceptual and technical background for what is currently understood on fiber reinforced geopolymers by tying the subject together with knowns for other similar cementitious composites rather than a historical report of literature.

  • Assessment and prediction of concrete flow and pumping pressure in pipeline
    Cement Concrete Comp. (IF 5.172) Pub Date : 2019-12-26
    Egor Secrieru; Wesam Mohamed; Shirin Fataei; Viktor Mechtcherine

    In work at hand, an onsite-suitable, scientifically-based methodology to characterise and predict fresh concrete pumping behaviour was developed and verified. The properties of the lubricating layer (LL) formed during pumping and consequently reducing the friction at the pipe wall-to-concrete interface were investigated and quantified. The flow pattern of fresh concrete was modelled experimentally and numerically. Instrumented full-scale pumping experiments were performed simultaneously with rheological tests on fresh concrete before and after pumping. The comparison of predicted and actual pressure-flow rate curves showed for these methods a highly accurate predictive capacity. Hence, the authors strongly advocate the application of the scientifically based, ready-to-use methodology developed here in construction practice as a part of the future in situ rheology monitoring concept.

  • The microstructural evolution of cementitious, flexible waterproofing membranes during deformation with special focus on the role of crazing
    Cement Concrete Comp. (IF 5.172) Pub Date : 2019-12-24
    Marius Waldvogel; Roger Zurbriggen; Alfons Berger; Marco Herwegh

    The initiation and evolution of deformation-induced (micro)structures in one-component, cementitious, flexible waterproofing membranes is investigated combining normed crack-bridging (EN14891) with image analysis of in-situ photos acquired by optical and scanning electron microscopy. The permanent deformation of the polymer matrix concentrates in a trapezoidal deformation volume and subdivides into an active and a passive part. During the active part, the polymer matrix stretches and fibril-void microstructures (FVM) form. The ubiquitously present heterogeneities (quartz grains, cement particles and air pores) act as stress concentrators. After FVMs reach their maximum density inside the deformation volume, straining by passive stretching until final rupturing takes over. Starting at the substrate-membrane interface, the cracking propagates through the membrane along aforementioned heterogeneities and the spatially distributed FVMs. Linking mechanical behaviour and deformation structures is therefore crucial to (i) understand the complex elasto-plastic deformation and to (ii) develop new products increasing the durability of the protective system.

  • Effect of waste glass incorporation on the properties of geopolymers formulated with low purity metakaolin
    Cement Concrete Comp. (IF 5.172) Pub Date : 2019-12-23
    O. Burciaga-Díaz; M. Durón-Sifuentes; J.A. Díaz-Guillen; J.I. Escalante-Garcia

    Given the worldwide abundant resources of low purity kaolin and urban waste glass, their use to produce alkali activated cements seem to be a promising area in the search for alternative sustainable cements with environmental advantages over Portland cement. Under this perspective, the properties of silicate activated low purity metakaolin (MK) and flat soda lime silicate waste glass (WG) at MK/WG mass ratios of 100/0, 85/15 and 70/30 were investigated. The chemical composition of the pastes was varied in terms of modulus (Ms=0.8-1.2) SiO2/Na2O of the activating solution with additions of 12 and 16 wt.% Na2O. Cubic samples dry cured at 20°C were used to follow the compressive strength from 1 to 90 days, which reached from 17 to 56 MPa; the highest values were attained by samples activated with Ms= 0.8- 1 and 12%Na2O. The products of the reactions were evaluated by X-ray diffraction, infrared spectroscopy, scanning electronic microscopy and nuclear magnetic resonance. The microstructures included unreacted MK, WG and N-A-S-H, while the incorporation of WG favored the formation of a more complex reaction product similar to a (N,C)-A-S-H type gel.

  • Development of Relationships between Electrical Testing and Water Permeability of Concrete
    Cement Concrete Comp. (IF 5.172) Pub Date : 2019-12-23
    Caitlin M. Tibbetts; Jerry M. Paris; Christopher C. Ferraro; Kyle A. Riding; Timothy G. Townsend

    Electrical test methods for predicting concrete penetrability have been widely accepted for use in assessing quality and durability of concrete; however, these methods are indirect and have not been related to concrete water permeability. This research compares three standardized electrical test methods, AASHTO T 358, AASHTO TP 119, and ASTM C1202, to physical water permeability. As no consensus standardized water permeability test method is available, a uniaxial, steady-flow permeameter test that has generally been used within the research community was employed for this research. The results demonstrate that the electrical test methods investigated for predicting concrete penetrability are not appropriate for all concrete mixtures. Materials with electrically conductive components in pore solution or bulk matrix perform poorly in electrical testing such as surface or bulk resistivity, or chloride ion penetrability testing, although physical water permeability indicates comparable performance to traditional supplementary cementitious materials.

  • Polymer-cement composites with adhesion and re-adhesion (healing) to casing capability for geothermal wellbore applications
    Cement Concrete Comp. (IF 5.172) Pub Date : 2019-12-20
    Kenton A. Rod; Carlos A. Fernandez; Manh-Thuong Nguyen; James B. Gardiner; Nicolas J. Huerta; Vassiliki-Alexandra Glezakou; Tamas Varga; Roger Rousseau; Phillip K. Koech

    Deterioration of cement/casing adhesion in wellbore scenarios can result in unwanted and potentially harmful leakage with the potential of serious repair costs. In this work, the authors explore the use of self-healing polymers added to conventional wellbore cements as a way to bring about self-healing and readhering (to casing) properties to the composite. Self-healing capability was demonstrated by permeability analysis showing that polymer-cement composites reduce flow by 50-70% at cement bulk and at the cement/steel interface. Use of atomistic simulations imply that these polymers have good wetting properties on the steel surfaces. Interactions between steel/polymer and cement/polymer are complementary, resulting in a wider range of bonding patterns. Cracks seem to expose under-coordinated sites that result in more bonding interactions, which agrees well with the permeability measurements showing high degree of healed cracks and cement-steel interfacial gaps together with an overall increased in structural integrity of these advanced polymer-cement composite materials.

  • Water Transport Mechanisms In Concretes Bearing Mixed Recycled Aggregates
    Cement Concrete Comp. (IF 5.172) Pub Date : 2019-12-17
    B. Cantero; I.F. Sáez del Bosque; M.I. Sánchez de Rojas; C. Medina

    Aggressive agents present in the environment that penetrate concrete through its pore structure induce deterioration, compromising the service life of concrete members. Determining the viability of using recycled materials in structural concrete calls for a prior understanding of their effect on water transport, the primary vehicle for external agent ingress. This article describes durability indicators such as electrical resistivity, water permeability (pressure testing), total water absorption, effective porosity and sorptivity that directly or indirectly measure water penetration and consequently performance across the service life of concrete bearing 20 % to 100 % mixed recycled aggregate (MRA). The 28 d concretes studied here with up to 75 % MRA exhibited <7 % weight gain due to water absorption, <15 vol.% porosity and <30 mm maximum depth of water penetration under pressure, all indicative of high quality concrete. In 90 d materials, the values of the aforementioned parameters were 40 % lower. Even in concrete with up to 100 % MRA (with 28 d readings of 50 Ω·m to 100 Ω·m), electrical resistivity remained unaffected, The present findings reveal that high quality high durability structural concrete can be viably manufactured with up to 75 % MRA.

  • Dispersion of graphene oxide–silica nanohybrids in alkaline environment for improving ordinary Portland cement composites
    Cement Concrete Comp. (IF 5.172) Pub Date : 2019-12-12
    Junlin Lin; Ezzatollah Shamsaei; Felipe Basquiroto de Souza; Kwesi Sagoe-Crentsil; Wen Hui Duan

    2D nanomaterials such as graphene oxide (GO) nanosheets have demonstrated marked potential for reinforcing and functionalizing ordinary Portland cement (OPC) composites. Yet despite its excellent intrinsic properties, the poor dispersion of GO in cement matrix hampers its effectiveness in enhancing the performance of OPC composites. In this study, GO was modified by tetraethylorthosilicate (TEOS) to synthesize thin hybrid GO-SiO2 nanohybrids (GOS). The GOS was characterized and its dispersion behaviour in cement pore solution was compared to that of GO. The results demonstrated that GOS had significantly longer dispersion stability than GO. We propose that the formation of a thin silica coating on GOS prevented cross-linking between Ca2+ ions from solution and carboxylate groups from GO. The thin silica coating also functioned as a spacer and minimized agglomeration caused by van der Waals forces. The effects of GOS on the workability and mechanical properties of cement mix were also investigated. Compared to batches with GO, GOS nanohybrids provided additional 26% and 22% enhancements of compressive strength and 21% and 31% enhancements of tensile strength at 7 and 28 days respectively. These results demonstrate the strong potential of our novel method for improving GO dispersion in a cement environment and for increasing the strength of OPC composites reinforced by nanomaterials.

  • Water desorption characteristics of saturated lightweight fine aggregate in ultra-high performance concrete
    Cement Concrete Comp. (IF 5.172) Pub Date : 2019-11-12
    Peiliang Shen, Linnu Lu, Fazhou Wang, Yongjia He, Shuguang Hu, Jianxin Lu, Haibing Zheng

    In this study, the water desorption behavior of saturated lightweight fine aggregate (LWA) in ultra-high performance concrete (UHPC) was systemmically investigated using isothermal calorimetry, relative humidity (RH), mercury intrusion porosimetry, X-ray microtomography methods, etc. The LWA with high porosity and coarse pore structure exhibited high absorption and easy desorption at high RH. The results indicate that a large amount of water in LWA was released before setting, resulting in an increase of water to binder ratio, which had an adverse effect on the performance. However, the water absorbed in LWA released fast after 6 h, inducing an internal curing effect. Mechanism on a "four-stage desorption" driven by capillary pressure and RH gradient was proposed. The water desorption that is beneficial for the internal curing is calculated. The results indicated that the internal curing efficiency could be enhanced by increasing LWA content and reducing its pore size.

  • Microstructure of cement paste incorporating high volume of low-grade metakaolin
    Cement Concrete Comp. (IF 5.172) Pub Date : 2019-11-09
    Diandian Zhao, Rahil Khoshnazar

    The influence of low-grade metakaolin (MK) on the mechanical and microstructural properties of cement paste was studied through compressive strength test and microstructural analyses, including thermogravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) and X-ray photoelectron spectroscopy (XPS). The results indicated that cement paste incorporating MK with around 40 wt.% kaolinite content in raw clays achieved comparable 28-day strength to that of the reference even at 40 wt.% replacement level. Microstructural studies showed a considerable amount of portlandite consumption after 3 d and a refinement of pore structure in backscattered micrographs. The Al/Ca ratio of calcium-aluminosilicate-hydrate (C-A-S-H) increased upon the increased replacement levels, while Ca/Si decreased due to the introduction of MK, but it did not further reduce with the increased MK content. The binding energy of Si 2p, Al 2p and Ca 2p spectra increased due to the incorporation of MK.

  • Modeling the effect of temperature gradient on moisture and ionic transport in concrete
    Cement Concrete Comp. (IF 5.172) Pub Date : 2019-11-12
    Yu Bai, Yao Wang, Yunping Xi

    Most reinforced concrete structures are under the influence of environmental conditions, such as temperature fluctuations, moisture and chloride variations simultaneously. Thus, the moisture transfer in concrete is driven by the moisture gradient as well as the temperature gradient. Similarly, the ionic transfer in concrete is driven by the concentration gradient of the ion as well as the temperature gradient. This paper developed an analytical solution that can be used for the moisture or the chloride transport in concrete considering the effect of temperature gradient. The effect of mass transfer on the thermal conduction was not considered, so the problem is simplified as a one-way coupled problem. The analytical model was validated by using two CASE studies, in which realistic material parameters of concrete were used, the parameters were obtained from experiments in the literature. The comparisons between analytical results and experimental results showed good agreement. It indicated that the present model can successfully characterize the effect of temperature gradient on moisture transfer and the effect of temperature gradient on chloride transport in concrete.

  • A nonlinear rate-dependent model for predicting the depth of penetration in ultra-high performance fiber reinforced concrete (UHPFRC)
    Cement Concrete Comp. (IF 5.172) Pub Date : 2019-11-08
    Y.Y.Y. Cao, Q.H. Tan, Z.G. Jiang, H.J.H. Brouwers, Q.L. Yu

    Ultra-high performance fiber reinforced concrete (UHPFRC) is increasingly utilized in protective structures because of its ultra-high compressive strength and excellent toughness. Nevertheless, there is still a lack of model for predicting the depth of penetration (DOP) in UHPFRC against projectile penetrations. This study proposes an analytical predicting model for UHPFRC on the basis of the dynamic cavity expansion theory. The Hoek-Brown criterion is utilized to account for the nonlinear response of UHPFRC, and its rate dependency is also addressed in the model. The developed predicting model is validated against penetration experimental data, and its effectiveness is further compared with previous predicting formulae. The comparison results indicate that the proposed model can achieve more reasonable DOP predictions in UHPFRC targets. Finally, a number of influential parameters are discussed based on the proposed model. It is observed that the DOP is affected by the target compressive strength, while the tensile strength influences the cracked region radius. The developed DOP predicting model provides an accurate estimation of the UHPFRC impact resistance and promotes an effective approach to design UHPFRC protective structures.

  • Calcium sulphoaluminate cement used as mineral accelerator to improve the property of Portland cement at sub-zero temperature
    Cement Concrete Comp. (IF 5.172) Pub Date : 2019-11-12
    Ge Zhang, Yingzi Yang, Hualong Yang, Huaming Li

    To avoid the harmful effect of inorganic salt antifreeze admixture on concrete in winter construction, high early strength calcium sulphoaluminite cement (CSA) used as the mineral accelerator was added in Portland cement (PC). The effects of CSA content and pre-curing time on the compressive strength, setting time, freezing point and frozen water, hydration heat, hydration products, and pore structures and microstructure were investigated. The results showed that the compressive strength of PC at sub-zero temperature was enhanced about 300% by the addition of CSA at appropriate dosage and pre-curing time (5 wt % CSA with 2 h pre-curing and 20 wt % without pre-curing). The freezing point and the amount of frozen water of paste were decreased by the addition of CSA and pre-curing. In addition, the hydration process, hydration products, and the microstructures were significantly affected by the amount of CSA and pre-curing time.

  • A robust time-dependent model of alkali-silica reaction at different temperatures
    Cement Concrete Comp. (IF 5.172) Pub Date : 2019-11-16
    Hamed Allahyari, Amin Heidarpour, Ahmad Shayan, Vinh Phu Nguyen

    Alkali-Silica-Reaction (ASR) is one of the most deteriorating phenomena in concrete structures. This study uses a machine learning approach (i.e. Artificial Neural Network) to provide further insight into ASR. The approach combines chemo-mechanical and kinetics-based approaches to develop a time- and temperature-dependent model of ASR, which is eventually used in generating user-friendly charts to conveniently assess existing concrete structures. To reach a higher degree of confidence in the precision of the model, an experimental dataset was developed from the laboratory and was combined with a dataset from the literature. A comparison between the developed model and a chemo-mechanical one (Gao's model) showed higher accuracy for the developed model. This higher accuracy was more obvious regarding the specimen with fine single-size aggregate grading. This study also reveals a varying thickness of connected porosity (tc) for fine single-size aggregate. Based on the results, aggregate size and tc have a coupled effect on the ASR-induced expansion.

  • Enhancing the tensile capacity of no-slump high-strength high-ductility concrete
    Cement Concrete Comp. (IF 5.172) Pub Date : 2019-11-15
    Tian-Feng Yuan, Jin-Young Lee, Young-Soo Yoon

    The high shape-holding ability of no-slump concretes (NSC) allows is widely used in roller-compacted and prefabricated concrete. However, it is limited by its low strength properties, and low tensile properties, which lead to potential durability problem in prefabricated concrete. Therefore, this paper aims to investigate the synergy effect in tensile properties of no-slump high-strength high-ductility concrete (NSHSDC) based on polyethylene (PE) and steel fibers (SF). The compressive, flexural, and tensile strength of NSHSDC with three different water-to-binder ratios (w/b) reinforced by 0.0, 1.5 vol% of PE fiber were evaluated. The composites with 16.8% w/b were filtered out due to its poor mechanical properties. The reinforcement characteristics of compressive, flexural, and tensile strength between 16.2% and 17.2% w/b were then compared and analyzed. All composites exhibited a similar compressive strength (>120 MPa), NSHSDC hybrids with different fiber lengths exhibited a flexural strength, tensile strength, and tensile energy absorbing capacity higher than other composites at approximately 18.4%, 14.5%, and 5.4%, respectively. The composites with 17.2% w/b exhibited great mechanical properties than composites with 16.4% w/b; thus, the need for further analysis of its synergy assessment. The composites with 17.2% w/b exhibited a positive synergy and composite hybrids with different fiber lengths established a perfect synergy.

  • Energy dissipation characteristics of all-grade polyethylene fiber-reinforced engineered cementitious composites (PE-ECC)
    Cement Concrete Comp. (IF 5.172) Pub Date : 2019-11-15
    Kequan Yu, Yao Ding, Jiepeng Liu, Yulei Bai

    Systematical research was implemented to explore the impacts of fiber reinforcement index VfLf/df (i.e., the product of fiber volume Vf and fiber aspect ratio Lf/df) on the energy dissipation characteristics including strain energy density and fracture energy, of polyethylene fiber-reinforced engineered cementitious composites (PE-ECC) with compressive strength varying from normal to high. Six VfLf/df values (i.e., 5, 7.5, 9, 10, 15, and 18) and five water/binder ratios (i.e., 0.14, 0.16, 0.18, 0.22, and 0.32) were considered in total. Strain energy density and fracture energy reflect the crack resistance capacity during the strain-hardening and softening processes of PE-ECC, respectively. The strain energy density of PE-ECC increased significantly with the increase of VfLf/df and the decrease of water/binder ratio. The fracture energy increased noticeably with the growth of VfLf/df, while it attained the maximum value at the water/binder ratio of 0.16. For ECC including both the strain-hardening and softening processes, neither the strain energy density nor fracture energy alone can reflect its crack resistance capacity and energy dissipation capacity comprehensively. Thus, in the design and simulation processes of ECC, both energy parameters need to be considered in the constitutive model.

  • Influence of coarse aggregate shape on optimum fine to total aggregate ratio using a virtual voids-ratio diagram in concrete compaction
    Cement Concrete Comp. (IF 5.172) Pub Date : 2019-11-18
    Atsushi Ueno, Yuko Ogawa

    The optimal percentage of fine aggregate in concrete obtained from a virtual voids-ratio diagram does not always remain optimal in a dynamic condition of the aggregate particles, such as during the casting or the compacting stages of concrete. The reasons for this discrepancy lay in the assumption of packing state in the calculation from the virtual voids-ratio diagram and the difference in movement of the aggregate particles. This study investigates the influence of the particle shape of coarse aggregates on two optimal fine to total aggregate ratio values based on the virtual voids-ratio diagram as well as obtained in an actual concrete compaction experiment. A suitable index to express average coarse aggregate shape was also examined at the beginning of the study. Finally, a method was suggested for adjusting the optimum fine to total aggregate ratio obtained from a virtual voids-ratio diagram using the quantified average particle shape of the coarse aggregates.

  • Potential of sodium sulfate solution for promoting the crack-healing performance for strain-hardening cementitious composites
    Cement Concrete Comp. (IF 5.172) Pub Date : 2019-11-16
    Chung-Chan Hung, Hsuan-Hui Hung

    Strain hardening cementitious composites (SHCCs) have been shown to have promising self-healing ability. Nevertheless, reliable healing performance only occurs for micro-cracks in relatively young SHCCs and requires several months of moisture exposure. To overcome these criteria for effective healing, this study explored the feasibility of using sodium sulfate solution to promote the healing performance of medium-term SHCCs. For this purpose, cracks were induced in SHCC specimens at the age of 180 days followed by a 28-day exposure to high sulfate ion concentrations. Four SHCC mixtures with different ratios of cement replaced by pozzolans were tested. In particular, the performance of the SHCCs containing an extremely high volume of granulated blast-furnace slag (GGBS) was studied. The healing behavior of the SHCCs was evaluated via multiple means, including uniaxial tensile tests, monitoring of the crack width, scanning electron microscopy, and energy dispersive x-rays. The results indicated that short-term exposure to sodium sulfate solution effectively promoted the healing performance of cracked SHCCs, especially for cracks with relatively larger widths. It was found that the newly formed healing precipitation within the cracks primarily consisted of calcium carbonate, calcium silicate hydrates, and ettringite. In addition, the SHCCs with 71% replacement of cement by GGBS had the highest recovery in terms of crack width and tensile response.

  • Thermal behavior of alkali-activated fly ash/slag with the addition of an aerogel as an aggregate replacement
    Cement Concrete Comp. (IF 5.172) Pub Date : 2019-11-18
    Joonho Seo, S.J. Bae, D.I. Jang, Solmoi Park, Beomjoo Yang, H.K. Lee

    The present study investigated the thermal behavior of alkali-activated fly ash/slag with the addition of an aerogel as an aggregate replacement. Samples having aggregate-to-aerogel replacement ratios of 25, 50, and 75% by volume were fabricated and were exposed to temperatures of 200 °C, 400 °C, 600 °C or 800 °C. Water contact angle and thermal conductivity tests were carried out to assess the dispersion of the aerogel in an alkaline environment. X-ray diffractometry, mercury intrusion porosimetry, compressive strength test and thermogravimetry were conducted to investigate the thermal evolution of the reaction products, the pore structures and the mechanical strength. The results revealed that the incorporated aerogel mitigated thermal expansion up to 600 °C while also inducing rapid thermal shrinkage above 600 °C. Meanwhile, the pore structures of the samples with high aerogel contents were scarcely altered upon exposure to high temperatures, showing a level similar to those observed at 25 °C.

  • Effects of heating and drying on the strength and stiffness of high-early-strength Portland cement pastes
    Cement Concrete Comp. (IF 5.172) Pub Date : 2019-11-12
    Ryo Kurihara, Ippei Maruyama

    Changes in the bending strength and Young's modulus after drying and heating up to 90 °C of high-early-strength Portland cement paste with water to cement ratios (W/C) of 0.30 and 0.55 were measured. The bending strength decreased until 40% RH and then increased below 40% RH in the case where the W/C equaled 0.55. For a W/C of 0.30, the bending strength only changed minorly for relative humidity above 70%, while the strength increased significantly below 70% RH. Based on microstructural characterizations, for a W/C of 0.30 the strength change of the paste can be evaluated by a combination of changes in the strength of a solid skeleton composed of C–S–H agglomerations and the macropores, which is related to the strength characteristics of porous materials. When the W/C equals 0.55, changes in the solid strength and macropores or mesopores influence the strength variation, but the mesopores have more impact on the strength than macropores. Since the increase in the solid strength becomes predominant from higher RHs for lower W/C paste, the starting point of strength increase (SPSI) of lower W/C paste appears at higher RH values than in higher W/C cases. Despite the relatively large scatter in the experimental results – the bending strength and Young's modulus standard deviation of HCP were 16% (W/C = 0.55) and 10% (W/C = 0.30) – consistent and reliable tendencies were found.

  • Changes of pore structure and chloride content in cement pastes after pore solution expression
    Cement Concrete Comp. (IF 5.172) Pub Date : 2019-11-19
    Xiang Hu, Caijun Shi, Qiang Yuan, Jian Zhang, Geert De Schutter

    Pore solution expression is a widely accepted approach to extract pore solution of cement-based materials by appllying high pressure. In this study, the variations of pore solution distribution and chloride content in cement pastes before and after pore solution expression were examined. The results showed that the value of chloride concentration index Nc were mostly higher than 1.0 for cement pastes immersed in NaCl solution, and decreased with the chloride concentration of soaking solution and water-to-binder (w/b) ratio. During the pore solution expression, the pores larger than 40 nm were totally removed and the porosity of smaller pore was decreased. Based on a proposed physical model on structure of cement paste, the value of Nc was calculated according to the variations of pore structure and chloride content during pore solution expression. The calculated results showed similar trend as the experimental results obtained by pore solution expression method.

  • Multiphysics Lattice Discrete Particle Model for the simulation of concrete thermal spalling
    Cement Concrete Comp. (IF 5.172) Pub Date : 2019-11-18
    Lei Shen, Weixin Li, Xinwei Zhou, Jun Feng, Giovanni Di Luzio, Qingwen Ren, Gianluca Cusatis

    Explosive thermal spalling behavior during fire exposure is one of the major issues in the design of modern reinforced concrete structures. Previous experience on fire disasters indicates that spalling of concrete can have serious structural and economic consequences and must be taken into account in the design for fire. However, spalling mechanisms and their interaction still remain in dispute in the scientific community. In order to shed some light on this phenomenon, a discrete hygro-thermal model of concrete at high temperature called DTemPor3 is proposed and a full coupling scheme between DTemPor3 and the Lattice Discrete Particle Model (LDPM) is performed. The proposed multi-physical coupled model features the effect of pore pressure and temperature on the mechanical response as well as the impact of cracking on moisture mass transport and heat transfer. Simulations of typical spalling experiments show good agreements with data gathered from the literature for both high-performance concrete and ordinary concrete, demonstrating the accuracy of the proposed approach. Cracking localization is found to significantly impede the local pore pressure build-up due to the increase of pore or crack volume. The numerical simulations demonstrate that the spalling phenomenon can be successfully reproduced, only when the effect of thermal stresses is taken in account along with the effect of pore pressure on crack initiation.

  • Laboratory production of calcium sulfoaluminate cements with high industrial waste content
    Cement Concrete Comp. (IF 5.172) Pub Date : 2019-11-22
    Oğulcan Canbek, Sahra Shakouri, Sinan T. Erdoğan

    A drawback of conventional calcium sulfoaluminate (CS̄A) cement production is the use of the costly raw material bauxite as a source of alumina to form the main clinker phase ye'elimite. Replacement of bauxite with industrial wastes can benefit CS̄A cements economically and environmentally. This study demonstrates the use of high amounts of red mud, a sulfate-rich/high-lime fly ash, and desulfogypsum as raw materials in producing CS̄A clinkers and cements with better mechanical performances than an all-natural raw material CS̄A reference cement. Mineralogical compositions of the clinkers and hydrated cement pastes were investigated using x-ray diffraction, isothermal calorimetry, thermogravimetric analysis and scanning electron microscopy. Compressive strength development of mortars, made with citric acid, were studied up to 28 d. It was found that increasing fly ash increases the belitic nature, and increasing red mud increases the ferritic nature of the clinkers. Mortars with 28-d strengths exceeding 40 MPa could be made with cements containing ~38% waste and only half the bauxite in the reference. Medium early and ultimate strength mortars could be made with a ~55% waste cement when bauxite was reduced to a quarter of the reference, with small additions of Ca(NO3)2·4H2O or Li2CO3. Desulfogypsum, as a source of sulfates, was more beneficial to strength development than natural gypsum. Ye'elimite reactivity was enhanced in red-mud containing cements. Cements with both fly ash and red mud experienced lower carbonation than those made with only one of the two wastes.

  • Improvement in corrosion resistance of recycled aggregate concrete by nano silica suspension modification on recycled aggregates
    Cement Concrete Comp. (IF 5.172) Pub Date : 2019-11-22
    Weilai Zeng, Yuxi Zhao, Haibing Zheng, Chi sun Poon

    This work modified recycled aggregates (RAs) by soaking them in a nano-silica (NS) suspension and evaluated the modification effects on recycled aggregate concrete (RAC). Firstly, different soaking times were studied based on the surface microhardness and the penetration depth of NS particles in the RA. Secondly, mechanical properties (e.g., compressive strength and microhardness of interfacial transition zones) and durability properties (e.g., steel corrosion and corrosion-induced cracking) were tested. The 1-h soaking modification was selected as the optimal soaking time. The nano-modification improved the protection of steel and the resistance to corrosion-induced cracking, which was believed to be related to the improvement of the ITZ properties according to the microhardness test results.

  • The use of palm oil clinker as a sustainable construction material: A review
    Cement Concrete Comp. (IF 5.172) Pub Date : 2019-11-14
    Hussein M. Hamada, Gul A. Jokhio, Alyaa A. Al-Attar, Fadzil M. Yahaya, Khairunisa Muthusamy, Ali M. Humada, Yasmeen Gul

    Waste byproducts of palm oil can potentially help preserve non-renewable resources and enhance the sustainable, environmental, and economic characteristics of the construction industry if used as alternative construction materials. Palm oil clinker (POC) is a waste byproduct of palm oil mills, which is obtained after burning the solid palm oil waste for producing electricity. Recently, significant research has focused on the usage of POC as lightweight concrete aggregate. The present paper presents and examines the physical and chemical properties of POC as well as the mechanical properties of palm oil clinker concrete (POCC). POC has a lower specific gravity than the conventional weight aggregates, thus it has low density that enables the weight of the resulting concrete to reduce. The concrete containing POC would have a lower density as well as compressive strength than the normal aggregate concrete. The present review is significant for the future studies to identify the knowledge gaps and address the shortfalls in other aspects. In addition, this paper could be a base knowledge for researchers to encourage them to use green and sustainable materials that have great benefits to the environment and cost less if compared with the conventional materials.

  • Composites based on Juncus maritimus fibers for building insulation
    Cement Concrete Comp. (IF 5.172) Pub Date : 2019-11-22
    Zahia Saghrouni, Dominique Baillis, Abdelmajid Jemni

    Juncus maritimus fibers present an interesting cellular porous microstructure useful for thermal insulating properties. The elaboration and experimental characterization of composite materials based on different Juncus maritimus fibers content (0, 2, 5, 7 and 10 by mass) are investigated. We show that optimized composite materials can be elaborated from a simple chemically treatment of fibers. The thermo-physical properties (thermal conductivity, thermal diffusivity, and density) of both mortar composites with the raw and chemically treated fibers, were evaluated experimentally. Also, the water absorption uptake and mechanical strengths were performed to evaluate the chemical surface modification effects on the performances of the composites. As a result, due to their porous cellular microstructure, the use of Juncus maritimus fibers enhances the thermal insulating and lightness performances of reference mortar but affects negatively its mechanical strengths. The moisture effect tests reveal that thermal conductivity and density of the saturated composites are two times higher than that in a dry state. The chemical surface modification of used Juncus maritimus fibers improves the flexural and compressive strengths, decreases the water uptake of resulting composites with a low water diffusion coefficient. Thus, these new treated bio-cellular fibers composites can be used as structural and insulating lightweight concrete.

  • Nanostructural evolution of alkali-activated mineral wools
    Cement Concrete Comp. (IF 5.172) Pub Date : 2019-11-21
    J. Yliniemi, B. Walkley, J.L. Provis, P. Kinnunen, M. Illikainen

    Mineral wools are the most widely used building insulation material worldwide. Annually, 2.5 million tonnes of mineral wool waste are generated in the EU alone, and this is a largely unutilised material that is landfilled or incinerated. However, mineral wool wastes are promising precursors for production of alkali-activated cementitious binders due to their favourable chemical and mineralogical composition and high surface area. Alkali-activation is therefore a valuable route for valorisation of large quantities of mineral wool waste. This study resolves the phase assemblage and nanostructure of reaction products formed upon alkali activation of stone wool and glass wool by sodium hydroxide and sodium silicate solutions with X-ray diffraction, electron microscopy and solid state nuclear magnetic resonance spectroscopy experiments probing 27Al and 29Si. The stone wool-based alkali-activated binder comprises an amorphous sodium- and aluminium-substituted calcium silicate hydrate (C-(N-)A-S-H) gel, an amorphous sodium aluminosilicate hydrate (N-A-S-H) gel and small amounts of the layered double hydroxide phase quintinite and zeolite F. The glass wool-based alkali-activated binder comprises an amorphous Ca- and Al-substituted sodium silicate (N-(C-)(A-)S–H) gel. Gel chemical composition and reaction kinetics of alkali-activated mineral wools are shown to be dependent on the activating solution chemistry, with reaction rate and extent promoted by inclusion of a source of soluble Si in the reaction mixture. This work provides the most advanced description of the chemistry and structure of alkali-activated mineral wools to date, yielding new insight that is essential in developing valorisation pathways for mineral wools by alkali activation and providing significant impetus for development of sustainable construction materials.

  • Mechanism of long-term capillary water uptake in cementitious materials
    Cement Concrete Comp. (IF 5.172) Pub Date : 2019-11-06
    N.M. Alderete, Y.A. Villagrán Zaccardi, N. De Belie

    Capillary imbibition or water uptake tests are practical and they satisfactorily describe the performance of cementitious materials. Most of these tests are performed for a short period (<1 week), however, additional water uptake has been documented after the water front has covered the total height of samples. This process occurs at a very low rate and it could provide further information about the pore structure. We investigated long-term capillary imbibition in mortar and concrete with and without supplementary cementitious materials. This paper reports our results and results from literature, and proposes a phenomenological description of the process. The trends observed from long-term tests are consistent across different water to cementitious material ratios, binder types, fine and coarse aggregates, curing ages, and conditioning regimes. Long-term measurements reveal primary and secondary periods of capillary imbibition that are well described by a bi-linear relationship with the fourth root of time.

  • Multi-scale characterisation of recycled aggregate concrete and prediction of its performance
    Cement Concrete Comp. (IF 5.172) Pub Date : 2019-11-30
    Subhasis Pradhan, Shailendra Kumar, Sudhirkumar V. Barai

    The inherent inferior quality of recycled coarse aggregate (RCA) influences the microstructural characteristics and consequently, the macro-mechanical properties of recycled aggregate concrete (RAC). The present paper investigates the influence of aggregate properties, degree of hydration (α), and micro and meso level characteristics of concrete on its compressive strength. Moreover, the influence of different mix design methods (conventional and Particle Packing Method) and mixing approaches (normal mixing approach and two stage mixing approach) on α, and micro and meso level properties of concrete are analysed. In addition to the crushing value and water absorption of coarse aggregate, thermogravimetric analysis, nanoindentation and image analysis of back-scattered electrons images and X-ray microtomography images are performed to measure α, interfacial transition zone (ITZ) thickness, voids content in the ITZ and interface of concrete, respectively. However, none of these parameters can be singled out to demonstrate its major or significant contribution to the compressive strength of concrete. Hence, the influence of each parameter must be appreciated. An expression is proposed by accounting each of these parameters and also the cement content and coarse aggregate fraction to predict the compressive strength of concrete, which exhibits good correlation with the experimental results.

  • Experiments on drying shrinkage and creep of high performance hybrid-fiber-reinforced concrete
    Cement Concrete Comp. (IF 5.172) Pub Date : 2019-11-29
    Vahid Afroughsabet, Susanto Teng

    Drying shrinkage can cause high performance concrete (HPC) to crack, resulting in a reduction of its overall strength and durability. Creep behavior is also an important property of HPC and it should also be considered in applications. This paper evaluates the time-dependent creep and shrinkage properties of HPC as well as high performance hybrid-fiber-reinforced concretes (HPHyFRC) through experimental programs and the results will be compared with some common prediction models. The authors’ HPC were developed by using certain percentages of silica fume (SF) and ground granulated blast-furnace slag (GGBS) as cement replacement materials. Double hooked-end steel fibers, single hooked-end steel fibers, and polyvinyl alcohol fibers were mixed in different proportions in the concrete to get HPHyFRC. The total combined volume fractions of the fibers were 0%, 0.6%, and 1.2%. The results indicate that the substitution of ordinary Portland cement (OPC) with SF or GGBS improved the properties of concrete. The addition of fibers significantly reduced the drying shrinkage and creep coefficient of HPHyFRC. While the fiber volume fraction had an insignificant influence on the drying shrinkage of HPHyFRC, hybridization of polyvinyl alcohol fiber with steel fibers resulted in the minimum shrinkage strain. The least creep coefficient was attained by the concrete mix containing 1.2% double hooked-end steel fibers. The CEB-FIP 2010 model predicts the time-dependent behaviors of concretes with the best accuracy among different models compared in this study.

  • Quantifying the freeze-thaw performance of air-entrained concrete using the time to reach critical saturation modelling approach
    Cement Concrete Comp. (IF 5.172) Pub Date : 2019-11-29
    Mehdi Khanzadeh Moradllo, Chunyu Qiao, Rita Maria Ghantous, Myo Zaw, Hope Hall, M. Tyler Ley, W. Jason Weiss

    Many State Highway Agencies have been working to develop performance-based specifications for concrete pavements and concrete bridge decks in freeze-thaw environments. A time to reach critical saturation (TTRCS) model has been proposed to estimate the freeze-thaw performance of concrete. This study evaluates the TTRCS model for thirty different concrete mixtures with varying w/c, air volumes, and quality of air void (size and spacing). Simple quality control test procedures are used to determine the input parameters for the TTRCS model. The estimated time to reach critical saturation is compared with the measured durability factor using ASTM C 666–15. Results indicate that 86% of the mixtures with air volume above 4.5% and a Sequential Air Method (SAM) Number below 0.30 have a normalized time to reach critical saturation of greater than 20, and a durability factor that is greater than 75%. The mixtures with a high range water reducer require a higher volume fraction of entrained air to satisfy the recommended limit for the durability factor. This appears to be due to an interaction between the high range water reducer and air entraining admixture which results in greater air void spacing (i.e., larger air voids). However, the addition of high range water reducer was also found to increase the time to reach critical saturation in the mixtures with a low w/c due to a refined pore structure with a reduction in the connectivity of the matrix pores. Reducing the w/c improves the freeze-thaw performance due to a reduction in the pore volume, connectivity, and absorption rate of the concrete. A relationship is developed to estimate the time to reach critical saturation based on SAM Number and apparent formation factor. In addition, a relationship is proposed to estimate the critical degree of saturation based on air void content and quality.

  • 4D characterisation of damage and fracture mechanisms of ultra high performance fibre reinforced concrete by in-situ micro X-Ray computed tomography tests
    Cement Concrete Comp. (IF 5.172) Pub Date : 2019-11-21
    Z.J. Yang, A. Qsymah, Y.Z. Peng, L. Margetts, R. Sharma

    In-situ microscale X-ray computed tomography (μXCT) tests of ultra high performance fibre reinforced concrete (UHPFRC) specimens were conducted under progressive wedge-split loading for the first time. A sequence of μXCT images of two 40 × 20 × 25 mm notched specimens were obtained at different loads with a voxel resolution of 16.9 μm. Through 3D image processing, the UHPFRC's internal microstructures are characterised and the complicated damage and fracture mechanisms are visualised, including bridging, bending and pull-out of fibres, spalling and fracture of matrix, and evolution of micro-cracks into macro-cracks. The deformed μXCT images clearly show the significant effects of steel fibres: suppressing microcracks from propagation, leading to dispersed multiple cracks, and contributing to deviate the originally vertical crack towards the overall fibre orientation across the cracks. It is concluded the in-situ μXCT tests provide an unrivalled tool for elucidation of complicated damage and fracture evolution in UHPFRC with high-resolution 3D images that will be invaluable for validation of numerical models and optimisation of the material's micro-structures.

  • Effects of the strain rate and fiber blending ratio on the tensile behavior of hooked steel fiber and polyvinyl alcohol fiber hybrid reinforced cementitious composites
    Cement Concrete Comp. (IF 5.172) Pub Date : 2019-12-05
    Minjae Son, Gyuyong Kim, Hongseop Kim, Sangkyu Lee, Jeongsoo Nam, Koichi Kobayashi

    The strain rate effect on the tensile behavior of high performance hybrid fiber reinforced cementitious composites was evaluated according to the blending ratio of hooked steel fiber (HSF) and polyvinyl alcohol fiber (PVA). The tensile strength, strain capacity, peak toughness, and softening toughness were investigated. In the experimental result, specimen with 1.5 vol% HSF and 0.5 vol% PVA (HSF1.5PVA0.5) exhibited the highest tensile strength and softening toughness. However, the strain capacity and peak toughness were less than those of the specimen with 2.0 vol% HSF (HSF2.0). Nevertheless, HSF1.5PVA0.5 exhibited the highest dynamic increase factors (DIFs) for the tensile strength, strain capacity, and softening toughness. HSF2.0 showed a higher DIF for the peak toughness than HSF1.5PVA0.5. But HSF1.5PVA0.5 is expected to exhibit a higher DIF for the peak toughness than HSF2.0 at high strain rates (>101 s−1), because it have highest strain rate sensitivity of tensile strength and strain capacity.

  • Study of seawater mixed one-part alkali activated GGBFS-fly ash
    Cement Concrete Comp. (IF 5.172) Pub Date : 2019-12-09
    Wei Lv, Zengqing Sun, Zijian Su

    This work tests the suitability of seawater for the synthesis of one-part alkali-activated material. The setting time, strength development, reaction product and steel corrosion of seawater mixed one-part alkali-activated ground granulated blast furnace slag-fly ash are investigated. Compared with freshwater, seawater can accelerate the alkali activation process, reflecting as shortened setting times. The obtained material possesses high early and long-term strength; the 3 d and one-year compressive strength are over 25 MPa and 73 MPa, respectively. In addition, the seawater mixed material has very slight negative influence on the reinforcement steel. Apart from the alkali activation process, chloride-binding property by synthesized material was also studied. Formation of chloride-bearing reaction product was detected, which might contribute to retard chloride and minimise the corrosion risk. All these results contribute to better understand the chemistry of alkali-activated materials and promote its application.

  • Spalling behavior of metakaolin-fly ash based geopolymer concrete under elevated temperature exposure
    Cement Concrete Comp. (IF 5.172) Pub Date : 2019-12-09
    Hai Yan Zhang, Guang Hong Qiu, Venkatesh Kodur, Zhen Sheng Yuan

    Fire-induced spalling is a serious risk to concrete structures, especially for high strength concrete structures. This paper presents results from high temperature spalling tests on geopolymer concrete. The effect of moisture content, concrete strength, heating rate and temperature level on the spalling behavior of geopolymer concrete is studied. The temperature-induced spalling mechanism in geopolymer concrete is investigated through the measurement of residual compressive and splitting tensile strength, variation in permeability (by sorptivity test) and chemical composition (by X-ray diffraction test) of geopolymer concrete after elevated temperature exposure up to 700 °C. The test results indicate that geopolymer concrete exhibit a good spalling resistance as compared to that of OPC concrete. The lower spalling risk in geopolymer concrete under high temperature exposure is facilitated from the highly connected pore structures and lower strength degradation with temperatures. Further results indicate that the pore structure (permeability) of geopolymer concrete gets a significant evolution with the exposure temperature, especially above 500 °C range. This is related to the sintering reaction in geopolymer binders at high temperatures.

  • Interfacial fracture toughness between aggregates and injected quick-hardening mortar
    Cement Concrete Comp. (IF 5.172) Pub Date : 2019-12-10
    Il-Wha Lee, Rahwan Hwang, Dong Joo Kim, Sukhoon Pyo

    This study investigated the interfacial fracture toughness (IFT) between injected quick-hardening mortar and coarse aggregate to increase the strength of quick-converting track concrete. The effects of different maximum grain size of sand and different additives (two types of polymer, silica fume, ground granulated blast-furnace slag and fly ash) on the IFT were investigated by using three-point fracture toughness tests to suggest an effective method to omit the cleaning process of contaminated aggregates in the quick-converting track concrete. The silica sand with the maximum grain size of 0.5 mm produced higher IFT than that with smaller particle size; consequently, the strength of quick-converting track concrete using silica sand with coarser particle size was 43.3 MPa, while the IFT was 10.10 MPa∙mm1/2. Silica fume among the various additives produced the highest strength of quick-converting track concrete (51.9 MPa). Furthermore, the effect of abraded fine particles (attached to aggregates) on IFT was evaluated. As the content of abraded fine particles increased from 0.00 to 0.10 wt%, the value of IFT decreased from 10.39 to 9.29 MPa∙mm1/2. The experimental findings suggest that the use of silica sand with the maximum grain size of 0.5 mm and silica fume enables an efficient quick-converting track method without a thorough cleaning process of contaminated aggregates.

  • Visualized tracing of capillary absorption process in cementitious material based on X ray computed tomography
    Cement Concrete Comp. (IF 5.172) Pub Date : 2019-12-09
    Shuxian Hong, Shaofeng Qin, Wanqiong Yao, Bangwen Guo, Dongshuai Hou, Yuxin Zhang, Wei Liu, Weiwen Li, Biqin Dong

    Moisture is one of the major deterioration factors of concrete. In this study, the capillary absorption process, which is one of the major transportation mechanism in cement paste, is non-destructively investigated by using X-ray computed tomography (XCT). A novel image processing procedure is proposed to correct the XCT image artifacts and calibrate the results of different measurements. The proposed image processing procedure allows for 3D visualization of the absorption process and additional information can be obtained, including the height of the water absorption front and the water content gradient.

  • Internal curing effect of saturated recycled fine aggregates in early-age mortar
    Cement Concrete Comp. (IF 5.172) Pub Date : 2019-12-05
    Zhen Li, Jiaping Liu, Jianzhuang Xiao, Peihua Zhong

    This paper explored the potential for internal curing of saturated recycled fine aggregate (RFA) in mortar. Water release from saturated RFAs at various relative humidity (RH) values was investigated using desorption isotherms. Capillary pressure measurements and autogenous shrinkage tests for mortar (W/C= 0.30) with RFA at an early age were used to evaluate water release. The influences of the RFA particle size, water absorption capacity, and dosage were analyzed. Desorption isotherms of the RFAs showed that only 16%–36% of the water they absorbed in 24 h was released at RH > 93%. Retardation of self-desiccation and reduction of early autogenous shrinkage of mortar were observed with saturated RFAs. RFAs with finer particle sizes and higher water absorption capacities gave greater reductions in autogenous shrinkages at the first three days, which could be attributed to the RFA pore structure. Internal curing with the RFA was observed clearly in a mixture with a high aggregate content.

  • Influence of expansive calcium sulfoaluminate agent dosage on properties and microstructure of expansive self-compacting concretes
    Cement Concrete Comp. (IF 5.172) Pub Date : 2019-11-19
    P. Carballosa, J.L. García Calvo, D. Revuelta

    Expansive concretes based on the formation of ettringite from calcium sulfoaluminate agents are presented as an effective alternative to minimize the problems derived from shrinkage and low tensile strength at the early ages of the concrete. However, determining the mechanism responsible for the expansion is still a controversial issue today. In this study, the influence of three doses of expansive agent on fresh state and on compressive strength and magnitude of free expansion under two curing environments was evaluated on a reference mixture of self-compacting concrete (SCC). The microstructural evolution of the hydrates and anhydrous related with the expansive phenomena was also studied. From our observations it seems that microcrystalline/X-Ray amorphous ettringite is formed and that this ettringite would be strongly related to expansion. As a result, the influence of the ratio w/cementitious material and curing environment on the magnitude of the expansion as well as the influence of this on the mechanical properties of the SCCs was identified.

  • Metakaolin based geopolymers with high limestone contents – statistical modeling of strength and environmental and cost analyses
    Cement Concrete Comp. (IF 5.172) Pub Date : 2019-11-07
    P. Perez-Cortes, J.Ivan Escalante-Garcia

    The mechanical properties of alkaline binders of precursors of metakaolin with up to 80% limestone and molar ratios of Na/Al=0.5-1.86 and Si/Al=1.81-3.13 were modelled and optimized using the surface response method. A quadratic model (R-squared=94.31%) indicated an optimal formulation of 32.32%LS, Na/Al=1.34 and Si/Al=2.96 with a predicted 28-day strength of 70±3.9MPa, experimentally corroborated at 69MPa; that was higher than references of 100%MK and blended Portland cement (BPC). Other optimized blends of 0 and 60%LS reached 51 and 62MPa, respectively, were successfully corroborated experimentally. The microstructural features were in agreement with the high strength. The analyses of cost, CO2-emissions and energy demand indicated that pastes of 100% metakaolin are better than BPC only regarding CO2 emissions, while blends with %LS>32.12% were better in all indicators relative to both of the former. As limestone is abundant, cheap, reduces the demand of alkalis and do not require calcination, these binders are actually sustainable.

  • The Influence of Calcium Chloride Deicing Salt on Phase Changes and Damage Development in Cementitious Materials.
    Cement Concrete Comp. (IF 5.172) Pub Date : 2015-12-23
    Yaghoob Farnam,Sarah Dick,Andrew Wiese,Jeffrey Davis,Dale Bentz,Jason Weiss

    The conventional CaCl2-H2O phase diagram is often used to describe how calcium chloride behaves when it is used on a concrete pavement undergoing freeze-thaw damage. However, the chemistry of the concrete can alter the appropriateness of using the CaCl2-H2O phase diagram. This study shows that the Ca(OH)2 present in a hydrated portland cement can interact with CaCl2 solution creating a behavior that is similar to that observed in isoplethal sections of a ternary phase diagram for a Ca(OH)2-CaCl2-H2O system. As such, it is suggested that such isoplethal sections provide a reasonable model that can be used to describe the behavior of concrete exposed to CaCl2 solution as the temperature changes. Specifically, the Ca(OH)2 can react with CaCl2 and H2O resulting in the formation of calcium oxychloride. The formation of the calcium oxychloride is expansive and can produce damage in concrete at temperatures above freezing. Its formation can also cause a significant decrease in fluid ingress into concrete. For solutions with CaCl2 concentrations greater than about 11.3 % (by mass), it is found that calcium oxychloride forms rapidly and is stable at room temperature (23 °C).

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