Construction and Building Materials(2024 - 2024)
Enhancing fire resistance in geopolymer concrete containing crumb rubber with graphene nanoplatelets
Iqbal H.W.; Hamcumpai K.; Nuaklong P.; Jongvivatsakul P.; Likitlersuang S.; Pothisiri T.; Chintanapakdee C.; Wijeyewickrema A.C.
Construction and Building Materials, Elsevier Ltd., Vol.426, 2024, MAY.
(https://doi.org/10.1016/j.conbuildmat.2024.136115)
Abstract
Geopolymer concrete (GPC) has a tendency to spall and lose its strength at high temperatures, rendering it brittle. This research incorporates graphene nanoplatelets (GNPs) to enhance the fire resistance of GPC. A comprehensive experimental framework, comprising 20 distinct mix designs, was developed. Crumb rubber (CR) was substituted for natural sand in the mixture proportions, ranging from 10% to 30% by volume, while GNPs were incorporated in quantities ranging from 0.1% to 0.4% by weight of fly ash. The objective of this study is to assess the mechanical properties of these mixtures after exposure to 30, 60, and 90 min of ISO 834 standard fire. The properties of GPC were analyzed both before and after exposure to fire. The attributes and properties investigated include spalling, mass loss, stress-strain behavior under compression, compressive strength, compressive toughness, modulus of elasticity, and porosity. Furthermore, the study examined the interfacial interaction between the aggregates and the geopolymer matrix, as well as microstructural and morphological changes due to fire exposure, utilizing field emission scanning electron microscopy (FESEM). The results indicated that GNPs significantly mitigated the loss of post-fire compressive strengths of GPC. The Response Surface Methodology (RSM) was employed to develop statistical models and optimize the mixture proportions of CR and GNPs, aiming to maximize the compressive strength and the modulus of elasticity while minimizing the mass loss of GPC after exposure to fire. The optimization outcomes suggested that a mixture containing 10% CR and 0.3% GNPs represented the optimal composition for enhancing the fire resistance of GNP modified rubberized GPC. c 2024 Elsevier Ltd
Impacts of synthesis variables on spectroscopics evaluation of biobased fatty amide as alkylammonium salt's precursor for perovskite
Mustafa N.M.; Jumaah F.N.; Yoshizawa-Fujita M.; Ludin N.A.; Akhtaruzzaman M.; Hassan N.H.; Ahmad A.; Chan K.M.; Su'ait M.S.
Construction and Building Materials, Elsevier Ltd., Vol.428, 2024, MAY.
(https://doi.org/10.1016/j.conbuildmat.2024.136283)
Abstract
Ammonium salts are widely used in chemical industries as additives in cement industries, phase change materials in thermal cooling, ionic materials in electrochromic window and multifunction medium/precursor/catalyst in solar cells to improve the efficiency and stability. This work introduces a procedural enhancement by incorporating a liquid-liquid extraction purification process, resulting in a high-purity biobased fatty amide (FA) with tri-substitution and high-purity biobased tetraalkylammonium ammonium salt (TAS). Biobased FA derived from renewable sources was synthesized via an amidation reaction between fatty acids from vegetable oil with tris(3-aminopropyl)amine under reflux conditions, producing a precursor for TAS used in perovskite solar cell (PSC). This study aimed to optimize and determine the reaction condition of biobased FA at various key synthesis variables by investigating the effects of solvent selection, reaction and crystallization, temperature, catalyst, mole ratio, and dehydrating agent on synthesis yield. A multiple liquid-liquid extraction process was employed to enhance the purity of biobased FA by tunning the selection of solvent based on its relative polarity of the reactant and products. Response surface methodology (RSM) and central composite design (CCD) were utilized to optimize the total yield and the three key variables (reaction time, crystallization time, catalyst amount) respectively. The experimental model developed in this study demonstrated a high degree of fitness with the experimental data (F-value = 27.34), p-value < 0.05) and nonsignificant lack of fit. The model predicted a maximum synthesis yield percentage of 52.62 % under optimal conditions (reaction and crystallization time of 12 and 28 hours), respectively with 4.47 % catalyst). The coefficient of determination of R2 = 0.98 shows a high correlation with the predicted values and in good agreement with the experimental values. Physicochemical properties analysis using spectroscopies techniques, confirmed improved purity with 100% abundance yield of tri-substitution biobased FA and enhanced TAS's purity up to 60%. The optimization study sheds light on the impact of key synthesis variables on the synthesis yield and percentage abundance (purity), advancing the development of more efficient and tailored sustainable construction materials. These findings highlight the potential of using biobased FA as a sustainable source for TAS production, contributing to a more environmentally friendly approach in PSC development. c 2024 Elsevier Ltd
Underwater fatigue behavior of cementitious mortar and a countermeasure using a water-dispersible polyurethane ether?Portland cement composite
Takahashi K.; Matsuda Y.; Miura S.; Akitou T.; Kuraoka M.; Kono I.
Construction and Building Materials, Elsevier Ltd., Vol.428, 2024, MAY.
(https://doi.org/10.1016/j.conbuildmat.2024.136296)
Abstract
The underwater fatigue behaviors of cementitious mortars are investigated with a focus on the mechanisms contributing to the deterioration of bridge foundations and possible countermeasures. This study analyzes the effects of water penetration during repetitive loading and unloading on the underwater fatigue lives of cementitious materials, highlighting the importance of considering dynamic water motion, in addition to the surface energy mechanism. Water penetration during underwater fatigue occurs even in water-saturated specimens, and water in- and egress within a few millimeters of the specimen surface can significantly reduce the fatigue life. This study proposes a novel approach using a water-dispersible polyurethane ether?Portland cement composite as a countermeasure to improve underwater fatigue resistance. Based on experimental analysis of fatigue in water and microstructural investigations of the composite, the presence of polyurethane compounds within the nano-to-micron-sized microstructures may mitigate water penetration and contribute to a corresponding increase in underwater fatigue life. c 2024 Elsevier Ltd
Experimental study on the mechanical behavior and failure characteristics of rock analogs with filled internal fractures: A new method by sand powder 3D printing
Wang X.; Jiang L.; Li Y.; Zhang L.; Sainoki A.; Mitri S H.; Yang Y.; Peng X.
Construction and Building Materials, Elsevier Ltd., Vol.427, 2024, MAY.
(https://doi.org/10.1016/j.conbuildmat.2024.136261)
Abstract
Rock formations naturally contain intricate internal fractures due to various environmental factors. Such fractures result in significant weakening of the mechanical properties of the rock mass. As factures have different geometric features and fill material characteristics, it is difficult to replicate their complex behavior in the laboratory. This poses a serious limitation on the experimental investigation of the mechanical properties of fractured rocks. Sand powder 3D printing (3DP) can overcome the limitations of casting methods in preparing samples with complex fractures and thus is widely applied in soft rock mechanics experiments. This paper utilizes Computer Tomography (CT) scanning to obtain the probability distribution patterns of fractures in fractured rock samples. Additionally, it combines sand powder 3DP technology to generate soft rock-like samples with internal networks of filled fractures. Uniaxial compression experiments employing digital image correlation (DIC) and acoustic emission (AE) techniques are used to investigate the mechanical properties, deformation characteristics, and fracture evolution patterns of samples with different fracture densities. By increasing the fracture density, the peak strength of the soft rock-like samples exponentially decreases, and the deformation characteristics linearly decrease. Crack propagation paths mostly follow the prefabricated fracture trajectories and loading direction. An RA-AF analysis suggests that the failure mode of the soft rock-like samples transitions from diagonal shear failure to block-shaped shear failure with increasing fracture density. These research findings represent a novel sand powder 3DP approach for studying the complex mechanics of complex fractured rocks. c 2024 Elsevier Ltd
Vertical stiffness reduction of rubber bearings under lateral displacement considering different shape factors
Yang Y.; Li T.; Dai K.; Xu J.; Ge Q.; Ikago K.
Construction and Building Materials, Elsevier Ltd., Vol.426, 2024, MAY.
(https://doi.org/10.1016/j.conbuildmat.2024.136168)
Abstract
Rubber bearings are composite components consisting of rubber layers and steel shims, which have been widely used in seismic isolation structures. The vertical stiffness of rubber bearings reduces significantly under lateral displacement. Previous studies have not clarified the vertical stiffness reduction for bearings with different dimensions. The focus of this study is to comprehensively explore the influence of the first and second shape factors (S1 and S2) on the vertical stiffness reduction of bearings with different shapes and to develop a prediction method. On the basis of the two-spring model, an improved theoretical formula for predicting the vertical stiffness of bearings under a lateral displacement was derived considering the influence of the S1. Subsequently, a series of finite element (FE) models were developed. The parameters of rubber material were calibrated using experimental data. A parametric FE study was conducted to investigate the influence of different S1 and S2 on the vertical stiffness reduction of bearings under lateral displacements. The effectiveness of the proposed formula was evaluated by comparing the results with those obtained from the FE analyses. Finally, based on the improved formula, an empirical formula for vertical stiffness reduction that can consider the influence of both S1 and S2 was developed. The predicted results of the empirical formula showed good agreement with the experimental and numerical results. c 2024 Elsevier Ltd
Mechanical properties and microstructural discrepancies of concrete with flotation-modified fly ash from circulating fluidized bed and pulverized coal furnaces
Yu R.; Jiang J.; Li S.; Zhou A.; Geng R.; Wan J.; Gao W.
Construction and Building Materials, Elsevier Ltd., Vol.428, 2024, MAY.
(https://doi.org/10.1016/j.conbuildmat.2024.136320)
Abstract
Fly ash (FA) is a by-product of coal-fired power generation in thermal power plants. Disparities in coal types and combustion furnaces result in varying levels of unburned carbon in FA, hindering its effective utilization. In this study, FA from a circulating fluidized bed furnace (CFBFA) and pulverized coal furnace (PCFFA) was modified using froth flotation technology, and the influence of the modified FA from the froth flotation process on the mechanical properties and microstructural discrepancy of concrete was analyzed through the preparation of mortar and cement paste specimens. The results indicated that the flotation process proved effective in reducing the unburned carbon content in FA, with modified PCFFA showing higher surface area and fluidity, opposite to CFBFA. Notably, the flotation process altered CFBFA's mineral content, reducing CaSO4E2 H2O from 26.6% to 7.5% and increasing CaSO4, enhancing hydration and strength in concrete applications. The optimal FA dosage was found to be 20%, with CFBFA specimens displaying superior compressive strength across all tests. Conversely, the modified PCFFA exhibited low activity, making it challenging to reach the desired strength after 28-d. This study serves as a theoretical foundation for the application of highly unburned carbon FA in construction engineering and promotes the circular development of FA resources. c 2024 Elsevier Ltd
Mechanical behavior of self-compacting recycled concrete reinforced with recycled disposable medical mask fiber
Zhang F.; Li X.; Wang D.
Construction and Building Materials, Elsevier Ltd., Vol.429, 2024, MAY.
(https://doi.org/10.1016/j.conbuildmat.2024.136314)
Abstract
The outbreak of the COVID-19 epidemic has led to a large number of waste disposable medical face masks (DMFMs) worldwide, which seriously pollute the environment and threaten human health. In this paper, waste DMFMs were recycled as mask fiber and mixed into self-compacting recycled aggregates concrete (SCRAC) to form a mask fiber reinforced self-compacting recycled aggregates concrete (FRSCRAC). The effects of recycled coarse aggregate (RCA) replacement ratio, DMFM fiber content, and length on the working and mechanical properties of FRSCRAC were investigated. The results show that the specimens meet the requirements of self-compacting concrete (SCC) in terms of working and mechanical performance, but the RCA and DMFM fiber could reduce the workability of the FRSCRAC, and the higher the amount of RCA and DMFM fiber, the more obvious the reduction. At the same time, the mechanical properties of FRSCRAC increased as the decreasing RCA replacement ratio and growing DMFM fiber content. Compared with specimens without DMFM fiber reinforcement, the compressive strength, split tensile strength, flexural strength, and elastic modulus were increased by 1.3%-9.6%, 1.46%-8.6%, 24.4%-54.69%, and 0.65%-4.73%, respectively. Moreover, the reduction of the DMFM fiber length is favorable to the mechanical properties of FRSCRAC as well. Furthermore, the X-ray CT and scanning electron microscope (SEM-EDS) techniques were applied to analyze the microstructure of typical specimens. The results showed that the DMFM fiber and surrounding mortar could form a multiphase composite, which reduces the porosity and improves interfacial stress transfer efficiency, thus enhancing the mechanical properties of FRSCRAC. In addition, based on the experimental results, the mechanical strength index of FRSCRAC and the calculation formula of its mutual conversion relationship were proposed. The research conclusions of this paper can provide a reference for the application of waste DMFM fibers in FRSCRAC. c 2024 Elsevier Ltd
Investigation of vibration on rheological behavior of fresh concrete using CFD-DEM coupling method
Cao G.; Bai Y.; Shi Y.; Li Z.; Deng D.; Jiang S.; Xie S.; Wang H.
Construction and Building Materials, Elsevier Ltd., Vol.425, 2024, APR.
(https://doi.org/10.1016/j.conbuildmat.2024.135908)
Abstract
Vibration can increase the flow ability of fresh concrete and may cause segregation. The rheology behavior of fresh concrete after vibration is different from that in the unvibrated state. In this paper, a CFD-DEM coupling method was developed to investigate the rheological behavior of fresh concrete before and after vibration. The Bingham model and Hershcel-Bulkley were respectively used as the constitutive relationship of fresh concrete in unvibrated and vibrated state. The Hertz-Mindlin with bonding bond is employed to describe the interaction between coarse aggregate. To analyze the effect of vibration on the rheological behavior of fresh concrete, the rheometer test was conducted. The relationship of shear stress and shear strain rate is linear before vibration and is nonlinear after vibration. Vibration reduces the yield stress and plastic viscosity of concrete. The shear zone decreases when fresh concrete is vibrated. c 2024 Elsevier Ltd
Effect of expansive additives and external restraint on the early age mechanical properties and microstructure of cement paste
Gupta M.; Igarashi G.; Takahashi Y.; Granja J.; Azenha M.; Ishida T.
Construction and Building Materials, Elsevier Ltd., Vol.422, 2024, APR.
(https://doi.org/10.1016/j.conbuildmat.2024.135655)
Abstract
The early age expansion of cement paste/concrete due to expansive additives (EA) has a significant impact on the microstructure and early-age mechanical properties of cement paste and concrete. Moreover, external restraints owing to reinforcement and supports play a crucial role in reducing concrete expansion and may also affect the microstructure. In this study, a measurement technique to monitor the development of early age elastic modulus of paste (from casting to hardened stage) focusing on the effect of external restraints was established. The influence of external restraint on the microstructure and elastic modulus was examined using the Elastic Modulus Measurement Ambient Response Method (EMM-ARM) and mercury intrusion porosimetry (MIP). This study also focuses on the effect of water-to-binder (w/b) ratios and amount of EA on the early-age mechanical properties of cement paste. The experimental results revealed that under unrestrained conditions, the addition of EA caused the microstructure of the paste to become porous, resulting in a decrease in mechanical properties. Conversely, under restrained conditions, the elastic modulus of the paste with EA and the level of porosity were comparable to the paste without EA. These findings have significant implications for the utilisation of EA in concrete construction and provide potential avenues for enhancing the durability and performance of concrete structures. c 2024 Elsevier Ltd
Hardening characteristics of granulated blast furnace slag with different degrees of saturation
Hara H.; Nasu E.
Construction and Building Materials, Elsevier Ltd., Vol.424, 2024, APR.
(https://doi.org/10.1016/j.conbuildmat.2024.135942)
Abstract
Field test embankments constructed using granulated blast furnace slag (GBFS) have been confirmed to harden within a few months and exhibit high strength. In contrast, a laboratory test wherein the hardening behavior was investigated by immersing in fresh water indicated that the structure was not self-supporting for over a year. The water content of GBFS differed greatly between the field and laboratory tests, and the degree of saturation affected the discrepancy between the two results. In this study, we clarified the usefulness of GBFS as a geomaterial in land construction by conducting unconfined compression tests, pH tests, and three types of instrumental analyses (X-ray computed tomography imaging, scanning electron microscopy, and thermogravimetric analysis) on GBFS that were cured at various degrees of saturation. The increase in strength for degree of saturation of 20?80 % was more prominent than in under saturated conditions. However, at a degree of saturation of 10 %, the water content was low with low strength. The amount of hydrate produced depends on the degree of saturation. At the early stage of curing, a lower degree of saturation resulted in greater hydrate formation. Whereas, after 56 days of curing, a higher degree of saturation yielded the same result. Further, the unconfined compressive strength and progress of the hydration reaction were not necessarily proportional in GBFS under different degrees of saturation. This was attributed to the difference in the density of the hydrate produced depending on the degree of saturation. c 2024 Elsevier Ltd
Headed coupling behavior of large diameter Cu-Al-Mn shape memory alloy bars: Mechanical testing and microstructural analyses
Hong H.; Gencturk B.; Kise S.; Araki Y.; Jain A.; Saiidi M.S.; Uruma K.
Construction and Building Materials, Elsevier Ltd., Vol.424, 2024, APR.
(https://doi.org/10.1016/j.conbuildmat.2024.135862)
Abstract
Cu-Al-Mn (CAM) superelastic alloy bars (SEAs) have received increasing attention in bridge applications. To take full advantage of their strain recovery and energy dissipation capacity, CAM SEAs are usually only applied in the plastic hinge regions of columns as part of the longitudinal reinforcement and coupled with steel rebar through mechanical splices. In this study, the feasibility of using headed coupling to connect large diameter CAM SEAs with steel rebar was investigated. Five large diameter CAM SEAs with headed ends were prepared: one 30 mm diameter and four 20 mm diameter samples. First, mechanical tests were performed on the five headed samples where each sample was coupled with one steel rebar at each end. Monotonic, incremental and constant strain cyclic loading was applied to simulate earthquake loading. The key mechanical properties were extracted and discussed. Second, microstructural analyses including electron backscatter diffraction (EBSD), metallographic imaging, Vickers hardness testing and fractographic evaluation were performed. The crystal orientation, phase composition and fracture surfaces were investigated to understand the effect of heading process on the stress induced martensitic transformation (SIMT), phase composition and failure of the headed CAM SEAs. It was found that the heading process only affects the near end portion of the specimen and it has no influence in the middle portion of the bars. Therefore, the strain recovery capacity of the CAM SEAs after heading was not reduced. Heading process led to high density of bainite phase precipitation at the end portions, which strengthened the sample. In order to uniformly strengthen the headed end of large diameter CAM SEAs, the key is to ensure a consistent cooling rate in the central and peripheral regions of the headed end after the heading process. c 2024 Elsevier Ltd
Multiscale computational modelling of nano-silica reinforced cement paste: Bridging microstructure and mechanical performance
Nithurshan M.; Elakneswaran Y.; Yoda Y.; Kitagaki R.; Hiroyoshi N.
Construction and Building Materials, Elsevier Ltd., Vol.425, 2024, APR.
(https://doi.org/10.1016/j.conbuildmat.2024.136047)
Abstract
This study presents a systematic model to optimise nano-silica utilisation in cement paste and predict its nonlinear behaviour. The model integrates a hydration model, which calculates the dissolution rate of each clinker mineral, with a thermodynamic model that simulates the hydration reaction and interaction between hydrates and nano-silica. The investigation considered different replacement levels of nano-silica (2 and 4% by weight of cement) to analyse the phase assemblages and porosity of nano-silica reinforced cement paste. The reaction between nano-silica and the hydrate (portlandite) was meticulously accounted for by incorporating the formation of calcium-silica-hydrate (C-S-H) with a realistic transition from jennite-type C-S-H (Si/Ca ratio of 0.58) to tobermorite C-S-H (Si/Ca ratio of 0.67). The coupled model was validated against the experimental results obtained from thermogravimetric analysis, X-ray diffraction, and scanning electron microscopy, ensuring its reliability. Subsequently, the model was used to compute the volume fractions of various phases including hydrates, unhydrated clinkers, pores, and unreacted nano-silica. A representative volume element (RVE) was formulated for the cement pastes with and without nano-silica using MATLAB. The RVE was further evaluated through finite element analysis using COMSOL Multiphysics, enabling the computation of homogenised material properties such as compressive strength, and this aligned well with experimental findings. In summary, the proposed systematic model provides a realistic prediction of the nonlinear behaviour of cement pastes with different nano-silica replacement levels. Its applicability extends to the optimisation of cement-based composites for diverse engineering applications. c 2024 Elsevier Ltd
A review of mechanical properties of deteriorated concrete due to delayed ettringite formation and its influence on the structural behavior of reinforced concrete members
Sanjeewa H.V.A.N.; Asamoto S.
Construction and Building Materials, Elsevier Ltd., Vol.422, 2024, APR.
(https://doi.org/10.1016/j.conbuildmat.2024.135795)
Abstract
Reinforced concrete (RC) members are subject to map cracking owing to the delayed ettringite formation (DEF) by excessive core temperature during the first few days of hydration. Studies on the mechanical properties of concrete with DEF expansion have been conducted to identify the variation in moduli and strength of the material. This paper provides a comprehensive review of the mechanical properties of plain concrete with DEF expansion to examine the degradation characteristics compared to the experimental conditions. The dynamic moduli, static moduli, and compressive strength of the plain concrete decreased up to 60%, 85%, and 65%, respectively, owing to large swelling, where the damage process showed colossal expansion. The reduction amount depends on the aggregate-to-cement ratio, chemical composition of the cement, aggregate type, water-to-cement ratio, and the mix. The static moduli is more sensitive to expansion in the initial expansion stage than other mechanical properties. The structural performance of DEF-affected RC members was also investigated, reviewing the relevant studies to include the structural performance of alkali-silica reaction (ASR) affected structures. The structural performance cannot be appraised using the mechanical properties of plain concrete. It was indicated that the DEF expansion of concrete core can be significantly confined by surrounding reinforcement in RC members. This inhibits the reduction in mechanical properties of concrete and results in maintaining the load-carrying capacity of RC members. Chemical prestress developed in concrete due to the swelling restraint by reinforcement, and anisotropic damage improves the stiffness of the RC members. c 2024 Elsevier Ltd
Material design of geopolymers using calcined allophane
Sato K.; Saito T.; Miyashita A.
Construction and Building Materials, Elsevier Ltd., Vol.422, 2024, APR.
(https://doi.org/10.1016/j.conbuildmat.2024.135706)
Abstract
As kaolinite, the main material of geopolymers, is not produced in East Asia and elsewhere, it is necessary to find alternative materials to replace kaolinite. The authors therefore investigated the preparation conditions and optimum curing temperature of geopolymers using allophane, which is not used as a cementitious material. Based on compressive strength and internal temperature history results, specimens were prepared by mixing allophane calcined at 800 ‹C for 3 h with an alkaline solution adjusted to a Na2O/SiO2 ratio of one at a water-to-powder ratio of two. Powder X-ray diffraction and nuclear magnetic resonance spectral analyses of specimens indicated that amorphous geopolymers with a three-dimensional structure were produced from calcined allophane. As for the optimum curing temperature, the samples cured at 20 ‹C showed the best strength development properties. On the other hand, specimens cured at 80 ‹C showed a temporary decrease in compressive strength as zeolite formation progressed with increasing curing time. Since 20 ‹C is the optimal curing condition, we conclude that geopolymers that can be used for on-site curing can be produced by using calcined allophane. c 2024 Elsevier Ltd
Forecasting and characterization of composite pipeline based on experimental modal analysis and YUKI-gradient boosting
Seguini M.; Khatir S.; Boutchicha D.; Brahim A.O.; Benaissa B.; Le Thanh C.; Noori M.; Fantuzzi N.
Construction and Building Materials, Elsevier Ltd., Vol.425, 2024, APR.
(https://doi.org/10.1016/j.conbuildmat.2024.135625)
Abstract
The surging demand for fiberglass pipe materials in the Oil and Gas transportation sectors are driven by their exceptional durability and ease of use. This study combined improved experimental and numerical analyses to assess the behavior of composite pipe and focused on characterizing it, especially in terms of identifying the frequency based on different crack lengths. Various tests, such as impact hammer tests and modal analysis, determine the pipe properties and natural frequencies. The study also investigates the impact of varying fiber volume fractions to refine material properties. To understand crack effects behavior, different crack lengths have been introduced into the pipes and analyzing the modal analysis using frequency and mode shapes. The effect of cracks into frequency based on experimental and developed numerical models is investigated. A predective model is developed based on YUKI-Gradient Boosting algorithms and Deep Artificial Neural Networks. To test the robustness of developed algorithm several tests are provided and the results show the effectiveness of YUKI-Gradient Boosting outperforms YUKI-Deep-ANN in accuracy and consistency. c 2024
Influences of hybrid fiber-reinforcement using wollastonite and cellulose nanofibers on strength and microstructure characterization of ultra-high-performance mortar
Supit S.W.M.; Nishiwaki T.; Shaikh F.U.A.; Boonserm K.; Rahman S.A.
Construction and Building Materials, Elsevier Ltd., Vol.423, 2024, APR.
(https://doi.org/10.1016/j.conbuildmat.2024.135802)
Abstract
This paper presents the effect of incorporating wollastonite microfibers and cellulose nanofibers on mechanical properties and microstructure of ultra-high-performance mortar (UHPM). Cellulose nanofibers of 0.005%, 0.015%, and 0.030% are combined with 4.8% wollastonite microfiber by weight of binder, which consists of 10% silica fume and 90% cement. Compressive and flexural strengths of the UHPM specimens are measured at 7 days. The microstructure is characterized in terms of SEM/EDX, XRD, FTIR, and nanoindentation. The results show the effectiveness of the fiber hybridization in enhancing the compressive and flexural strength of ultra-high-performance mortar with the improvement in flexural toughness and fracture energy by as much as 10% than control mortar. Moreover, hybrid fiber-reinforcement based on the microstructural analysis provided more synergic effect and uniform distribution of the fibers, thus developing an efficient micro crack bridging mechanism as well as resulting in enhanced toughening properties and an increased load carrying capacity. Additionally, the combination of wollastonite microfibers and cellulose nanofibers promoted the hydration reaction products and contributed a denser matrix between the fibers and cement matrix, resulting in an increase of the microstructure and interface area between the fibers and cement matrix. Nano indentation analysis also confirmed the increase of UHD C-S-H from 65% to 84% and lower percentage of anhydrous phase in ultra-high-performance matrix after combining wollastonite microfibers and cellulose nanofibers. c 2024 Elsevier Ltd
Electrochemical Corrosion Kinetics of Steel Bars in Pseudo-Transparent Concrete under Different Alkaline Properties and Chloride Contamination Levels
Bui H.T.; Maekawa K.; Tan K.H.
Construction and Building Materials, Elsevier Ltd., Vol.421, 2024, MAR.
(https://doi.org/10.1016/j.conbuildmat.2024.135636)
Abstract
Electrochemical kinetics of corroded steel bars is of importance in evaluating corrosion process and subsequent structural deterioration under different aggressive environments. This paper presents an experimental programme to investigate corrosion kinetics of steel bars in pseudo-transparent concrete subjected to different levels of chloride contamination and alkalinity in pore solution. The results show that corrosion current density increased with the rise of chloride content in simulated pore solution until Cl?/[OH?] ratio reached around 10. However, further chloride contamination with Cl?/OH?=12.5,15or20 tended to reduce current density. The phenomenon of decreasing corrosion rate and increasing corrosion potential when concrete was severely contaminated by chloride ions has not been widely reported in previous publications. An electrochemical mechanism was proposed based on the concepts of thermodynamics, anodic and cathodic polarisation kinetics to explain this extraordinary phenomenon, in which the decrease of corrosion current density when Cl?/[OH?] ratio increased from 10 to 20 was due to the rises of both anodic and cathodic Tafel slopes. On the other hand, a more neutralised pore solution in pseudo-transparent concrete induced a greater corrosion current density. When pH value was larger than 13, corrosion current density was negligible, while it substantially increased once pH value decreased to lower than 12.5. c 2024 Elsevier Ltd
Physicochemical properties of carbonized grass (CG): Implications for soft clay improvement
Li J.; Zhang Z.; Omine K.; Shi S.; Fujii T.; Du N.
Construction and Building Materials, Elsevier Ltd., Vol.419, 2024, MAR.
(https://doi.org/10.1016/j.conbuildmat.2024.135553)
Abstract
In global environmental governance, effectively and sustainably treating soft clay remains a key challenge. The production of traditional soil stabilizers, like cement, not only consumes vast non-renewable resources but also poses issues related to high energy consumption and environmental burdens. Hence, there is an urgent need to identify sustainable alternatives. This study introduces carbonized grass (CG) prepared from waste cutting grass as a sustainable material, experiments on soft clay and research on its physical and chemical properties, and adds wood charcoal (WC) and carbonized cow dung compost (CC) as controls. The study assesses the impact of carbonization temperature (500?1000 ‹C) on the water absorption properties of WC, CC, and CG. Using CG produced by a homemade dry distillation gasifier (SDDG) as raw material, it is added directly or together with calcined oyster shell waste (COS) into the soft clay, and a cone penetration test is conducted. The impact of different initial moisture contents (30%, 50% and 70%) of soft clay and the blending amounts of CG and CG-COS on the strength of the samples was studied, and an evaluation formula was proposed. Test results showed that CG exhibited a significant advantage in stabilizing high-moisture clay compared to CC and WC. After 28 days, the incorporation of CG significantly reduces the amount of COS (about 40%). Employing Scanning Electron Microscopy (SEM) and Energy-Dispersive X-ray Spectroscopy (EDS), the physical and chemical properties of the samples were analyzed. The analysis confirmed CG's unique honeycomb structure, acting as nucleation sites between particles. Additionally, its strong water absorbency aided in shortening the distance between particles, promoting the bonding of hydrated calcium silicate (C-S-H) with soil particles, leading to an improvement in sample strength. The results showed that improving soft clay with CG-COS significantly reduces the use of traditional stabilizers while leading to a substantial increase in soil strength. Additionally, this approach contributes to a noteworthy reduction in greenhouse gas emissions. Therefore, recycling cutting grass for CG preparation as a substitute for conventional soil stabilizers emerges as a green and viable method. c 2024 Elsevier Ltd
Flexural performance enhancement of modified gypsum-based composite boards using basalt fiber braids
Li Z.; Wang X.; Wijeyewickrema A.C.; Wu Z.
Construction and Building Materials, Elsevier Ltd., Vol.418, 2024, MAR.
(https://doi.org/10.1016/j.conbuildmat.2024.135430)
Abstract
In conventional fiber-reinforced gypsum boards, while the integration of fibers curtails crack propagation and moderately increases the flexural strength, the phenomenon of strain-softening is inevitably induced, which restricts the wider application of gypsum boards. The present study primarily focuses on evaluating the influence of basalt fiber (BF) braids on the flexural performance of fiber-reinforced modified gypsum matrix composite boards. The investigation considers factors such as the types of modified gypsum-based matrix, the number of BF braid layers, and the placement of fibers. During the experiments, the failure modes of various structural gypsum boards were observed, and comparisons were made regarding the changes in flexural stress-strain behavior, flexural strength, and displacement. Moreover, a reasonable explanation of the entire flexural stress process was provided based on the internal forces of the gypsum boards. Furthermore, a comparative analysis is conducted to examine the variations in ductility indices among different structural configurations of gypsum boards. The research results indicate that the combined action of fibers and BF braids effectively restricts the development of cracks, preventing a sudden decrease in stress during the growth stage. Additionally, BF braids fulfill their role, ensuring stress strengthening occurs within the gypsum board. Furthermore, the configuration of modified gypsum with fibers and two layers of BF braids (MG-BF-B-L2) exhibits the most significant improvement in flexural performance. Compared to modified gypsum group (MG), the flexural strength, entire ductility, and post-peak ductility have increased to 3.39 times, 7.66 times, and 1.58 times, respectively. c 2024
Effects of spatial corrosion distribution and prestressing levels on the structural performance of deteriorated PC beams
Wu T.; Akiyama M.; Lim S.; Wu L.; Xu Z.; Srivaranun S.; Frangopol D.M.; Chen W.
Construction and Building Materials, Elsevier Ltd., Vol.421, 2024, MAR.
(https://doi.org/10.1016/j.conbuildmat.2024.135650)
Abstract
This paper aims to study the effects of spatial corrosion distribution and prestressing levels on the structural performance of corroded prestressed concrete (PC) beams via experimental studies. X-ray and digital image processing techniques are developed to visualize and quantify the spatial corrosion of strands in PC beams. The spatial characteristics of strand corrosion and its effect on the structural performance of PC beams are compared with those of reinforced concrete (RC) beams. Unlike RC beams showing more ductile behavior, the load-bearing capacity and ductility of the corroded PC beams are determined by the maximum local steel weight loss of an individual steel wire in the maximum bending moment region. The prestress force induces larger local maxima of steel corrosion and widens corrosion-induced cracks by elevating the concrete tensile strain in the transverse direction. c 2024 The Authors
Tensile and cracking behaviour of crimped textile reinforced mortar (TRM) based on digital image correlation
Junaid K.; Zyed M.; Nonna A.; Gaochuang C.; Amir S.L.
Construction and Building Materials, Elsevier Ltd., Vol.417, 2024, FEB.
(https://doi.org/10.1016/j.conbuildmat.2024.135321)
Abstract
The tensile behaviour of textile reinforced mortar (TRM) is sensitive to the adopted matrix, textile, and their interfacial bonding. The matrix?textile bond varies with the nature of the adopted textile. In this study, the influence of textile crimp and orientation on the tensile and cracking responses of cement matrix-based TRM was studied for coated and noncoated (uncoated) carbon textiles using digital image correlation. This study also examined the behaviour of a hybrid TRM incorporating layers of coated and noncoated carbon. The results showed that the presence of load-aligned crimped yarns influenced the deformation, damage mode, cracking evolution, and crack opening of the TRMs. Finally, based on the observed deformations of the load-oriented crimped-yarn TRMs, a simple modification term for the second phase strains of the ACK model was proposed based on the textile geometry. The modified term produced strain values within 9.7?15% of the experimental strain. c 2024 The Authors
Bond behavior between bundled composite bars and concrete using beam-end pullout tests
Sun Y.; Zheng Y.; Sun Z.; Miao Z.; Wei Y.; Wu G.; Ge H.
Construction and Building Materials, Elsevier Ltd., Vol.414, 2024, FEB.
(https://doi.org/10.1016/j.conbuildmat.2024.134963)
Abstract
Bundled reinforcement can improve construction efficiency by reducing the number of connectors required. The steel-fiber reinforced polymer (FRP) composite bar (SFCB) is a novel reinforcement with high strength, moderate modulus of elasticity and good durability. Four groups of pullout tests were carried out, with parameters including the number of bars within each bundle, bonded length, and rebar type (steel bar, BFRP bar, SFCB). The failure modes of bar pullout without or after yielding, rebar fracture, and concrete splitting were observed. Compared to the single-bar specimen, the two-bar and three-bar bundled specimens resulted in approximately 30% and 40% decrease in average bond strength. The yielding slip sy of the three-bar bundled SFCB specimen is 3.8 times that of the single-bar specimen, indicating that bundled reinforcement can effectively control sy. A simplified bond strength prediction method and a bond stress-slip constitutive model based on the equivalent effective area approach are proposed. Finite element (FE) models were established and verified, and the failure modes of bar fracture are obtained by varying the bonded lengths for different bundled reinforcements, the ultimate slip of four-bar bundled BFRP bars increased by 127%. Recommendations for the development length of bundled SFCBs are proposed based on the FE results, which provide enough safety redundancy. c 2024 Elsevier Ltd
Influence of acetic acid treatment on microstructure of interfacial transition zone and performance of recycled aggregate concrete
Thaue W.; Iwanami M.; Nakayama K.; Yodsudjai W.
Construction and Building Materials, Elsevier Ltd., Vol.417, 2024, FEB.
(https://doi.org/10.1016/j.conbuildmat.2024.135355)
Abstract
Utilization of acetic acid treatment to enhance the quality of recycled aggregate (RA) has exhibited environmentally friendly and cost-effective method. This study aims to investigate the effect of acetic acid treatment on the change of microstructure properties and performance of recycled aggregate concrete (RAC). The treatment process involved treating low-quality RA with acetic acid, followed by removal of the old attached mortar by mechanical rubbing. The experimental investigation was conducted in three parts. First, the physical properties, including the water absorption, specific gravity, and bulk density of acetic acid treated RA, were determined. Then, the mercury intrusion porosimetry (MIP), Vickers microhardness, and scanning electron microscopy (SEM) tests were conducted to study the effect of acetic acid treatment on the microproperties of RAC. In addition, the compressive strength, splitting tensile strength, and chloride ion penetration resistance of the RAC prepared with treated RA were evaluated. The results showed that the interfacial transition zone (ITZ) Vickers microhardness increased, while the total pore volume of RAC and the width of the new ITZ decreased when the treated RA was used. The effects of acetic acid treatment on the microproperties of RAC were in agreement with the results of macroproperties. Compared to natural aggregate concrete (NAC), there was only a 6.2 % reduction in compressive strength when 50 % treated RA was incorporated. The effect of acetic acid treatment on the performance of RAC was more pronounced on RAC prepared with a low W/C ratio than a high W/C ratio. Based on the findings, the study holds significant potential in promoting the wider use of higher replacement percentage of natural aggregate (NA) with low-quality RA in durable and sustainable concrete construction. c 2024 Elsevier Ltd
Investigation on bonding behavior between CFRP patch and corrosion-damaged steel associated with surface preparation techniques
Cai L.; Yang M.; Kainuma S.; Liu Y.
Construction and Building Materials, Elsevier Ltd., Vol.411, 2024, JAN.
(https://doi.org/10.1016/j.conbuildmat.2023.134279)
Abstract
To assess the impact of corrosion on steel and the effectiveness of surface preparation techniques on the bonding behavior between carbon fiber reinforced polymer (CFRP) and steel, thirty bonded joint specimens were examined. These specimens were based on three distinct corrosion levels of steel and three conventional surface preparation techniques. Furthermore, various evaluation methods were employed to understand the steel surface characteristics, encompassing macro and microscale observations, analysis of topographical structures, and quantification of surface evaluation indices. These were performed to determine their correlations with the interfacial stress behavior. The findings revealed that when the target for repair shifted from a new steel substrate to a corroded one, the synergistic performance at the steel-adhesive interface decreased. This led to a decrease in the maximum shear stress at the plate end, and there was also an undesirable shift in the mode of failure. Both test parameters (i.e., the corrosion level and surface preparation), synergistically determined the surface cleanliness, topography, and bonding defects, all three of which directly influenced the bonding behavior. Finally, an improved model for predicting the debonding capacity of CFRP-corroded steel bonded joints was introduced, incorporating surface damage (k1) and surface topography (k2) coefficients. This model's applicability was also verified by collecting other test data from available literature. c 2023 Elsevier Ltd
Mechanical activation of coal gasification slag for one-part geopolymer synthesis by alkali fusion and component additive method
Chen C.; Shenoy S.; Pan Y.; Sasaki K.; Tian Q.; Zhang H.
Construction and Building Materials, Elsevier Ltd., Vol.411, 2024, JAN.
(https://doi.org/10.1016/j.conbuildmat.2023.134585)
Abstract
Coal gasification slag is an industrial by-product obtained after valuable gas production from coal gasification. There is little research concentrating on geopolymer synthesis using coal gasification slag. In this study, the suitability of mechanical activation for coal gasification slag-based one-part geopolymer synthesis has been investigated by alkali fusion and component additive method. The results showed that coal gasification slag ground at 20 min (S-20) presented the finest particle size, and the corresponding geopolymer (G-20) had the highest compressive strength. The reaction degree test proved that mechanical activation improved the reaction degree of geopolymers. However, different mechanical activation times had little influence on the reaction degree of geopolymers. It can be concluded that the particle size of the coal gasification slag was the primary reason for the compressive strength in geopolymers, and finer coal gasification slag led to higher compressive strength. Fine coal gasification slag additive particles could fill the pores of the geopolymer or be connected by the newly formed hydration products. This helped to form a dense, uniform, and compact matrix and increased the compressive strength of the geopolymers. As the mechanical activation time went up, the coal gasification slag particles got bigger, and the coal gasification slag additive's filling effect got weaker, which decreased the compressive strength of geopolymers. Furthermore, this study gave a new explanation of the role of the coal gasification slag additive in one-part geopolymer, which improved the feasibility of the other materials for one-part geopolymer synthesis by the alkali fusion and component additive method. c 2023 Elsevier Ltd
Effect of the strength grade of parent concrete on the performance of recycled aggregate treated by cement-fly ash slurry under prolonged soaking duration
Dao X.H.; Bui P.T.; Ogawa Y.; Kawai K.
Construction and Building Materials, Elsevier Ltd., Vol.411, 2024, JAN.
(https://doi.org/10.1016/j.conbuildmat.2023.134528)
Abstract
The detrimental effects of quarrying natural resources have contributed to large-scale environmental pollution. Utilizing recycled concrete aggregate (RCA) obtained from construction and demolition waste as a replacement for natural aggregates has become an effective solution for environmental sustainability. However, the inevitably diminished characteristics of the adhered mortar and the existence of an additional interfacial transition zone (ITZ) have negatively suppressed the widespread use of these materials in production lines. The present study aims to comprehensively investigate the effects of a cement-fly ash slurry with a mass ratio of 50% of the total weight of RCA on the microstructure and engineering properties of RCA derived from three different parent concretes with strength grades of 20, 30, and 60 MPa. The RCAs were soaked for 24 h, 48 h, and 72 h to evaluate the long-term effects of the pozzolanic slurry. A sequence of laboratory tests was conducted, including mercury intrusion porosimetry (MIP) test, thermal gravimetric?differential thermal analysis (TG-DTA), X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses, and measurements of water absorption and crushing value. The MIP results demonstrated a significant increase in medium capillary and gel pores, and a reduction in large capillary pores in the RCA with an increase in soaking time. TG-DTA results indicated an increase in Ca(OH)2 content during the first 24 h and 48 h of treatment. However, after 72 h of treatment, the Ca(OH)2 content of the treated RCA decreased in all cases. XRD analysis revealed the appearance of a few additional ettringite peaks among the treated RCAs in all cases. SEM images demonstrated the presence of additional hydration products after treatment, which filled the pores and improved the surface texture. Furthermore, after treatment, the crushing value of all treated RCA decreased by 6.0?27.1%, whereas the water absorption decreased by 12.0?30.9% compared to the untreated RCA. Based on several experimental results, the formation of hydration products and the improvement mechanism of RCA from three different parent concretes by slurry treatment with different soaking durations were discussed. In conclusion, a prolonged impregnation time of 72 h yielded a dominant performance, effectively intensifying their inferior properties, regardless of the initial strength grade of parent concrete. c 2023 Elsevier Ltd
Effects of the shape, size, and surface roughness of glass coarse aggregate on the mechanical properties of two-stage concrete
Ichino H.; Kuwahara N.; Beppu M.; Williamson E.B.; Himi A.
Construction and Building Materials, Elsevier Ltd., Vol.411, 2024, JAN.
(https://doi.org/10.1016/j.conbuildmat.2023.134296)
Abstract
Because two-stage concrete (TSC) is obtained by placing coarse aggregate in formwork and then filling the gaps with flowable grout, the properties of the coarse aggregate can notably affect the mechanical properties of TSC. In this study, uniaxial compressive and splitting tensile tests were conducted on TSC with eleven types of glass coarse aggregate of different shapes, sizes, and surface roughness for coarse aggregate. Two types of spherical glass aggregate with diameters of 17 and 30 mm, irregular shape of crushed glass plate classified into two size groups (20?30 mm and 10?20 mm) were used. Surfaces of spherical glass aggregates were two types; those were smooth and rough. The compressive strength of grout matrices used in specimens was 44.6 N/mm2 in the normal-strength mixture and 129.8 N/mm2 in the high-strength one. The relationship between the compressive and tensile strengths and the size of the coarse aggregate changed depending on the grout matrix strength and roughness of the coarse aggregate surface. The tensile strength for crushed glass aggregate were larger than those for spherical glass aggregate. Increasing roughness of the coarse aggregate surface led to an increase in the tensile and compressive strengths. The modulus of elasticity was affected by not only the solid content aggregate but also the shape and roughness. Moreover, the mechanical properties of TSC were compared with those of conventional concrete with the same coarse aggregate and same water-cement ratio as TSC. Observations from the test program indicate the design parameters that most strongly influence the strength and stiffness of TSC specimens. c 2023 Elsevier Ltd
Combined effect of internal curing and hydration promotion on concrete performances: Contributions of roof-tile waste aggregate and chloride-based accelerator
Khuat D.D.; Yamanaka S.; Nguyen M.H.; Nakarai K.
Construction and Building Materials, Elsevier Ltd., Vol.411, 2024, JAN.
(https://doi.org/10.1016/j.conbuildmat.2023.134527)
Abstract
Internal curing (IC) of concrete has recently been the subject of research due to its advantages, particularly in long-term performance. However, IC often decreases early-age strength and requires sufficient external curing time to be most effective. On the contrary, a chloride-based accelerator (CA) is well-known for accelerating early-age cement hydration and strength development. Therefore, this study aimed to investigate the combined effect of IC using roof-tile waste aggregate and CA using sea salt on concrete performance. Several concrete mixtures were cast with single or combined effects under poor and standard curing conditions. Roof-tile waste was used to partially replace normal coarse or fine aggregate to provide IC for concrete. Subsequently, the compressive strength and carbonation rate, as mechanical and durability indices, respectively, were measured until approximately 8 years of age. The combined effect resulted in significant strength improvement compared with the single effects under the same curing conditions. At approximately 8 years, under standard curing conditions, the IC effect increased the compressive strength by 40%, while the combined effect increased it by 60% compared to normal concrete. Concrete with combined effects also performed better in terms of durability tests but with a smaller magnitude than the strength index. c 2023 Elsevier Ltd
Impact of interatomic structural characteristics of aluminosilicate hydrate on the mechanical properties of metakaolin-based geopolymer
Kim G.; Cho S.; Im S.; Suh H.; Morooka S.; Shobu T.; Kanematsu M.; Machida A.; Bae S.
Construction and Building Materials, Elsevier Ltd., Vol.411, 2024, JAN.
(https://doi.org/10.1016/j.conbuildmat.2023.134529)
Abstract
This study explores the influence of the interatomic structure of sodium aluminosilicate hydrate (N-A-S-H) with varying silica contents on the mechanical properties of metakaolin-based geopolymer. Geopolymer pastes comprising Si/Al ratios between 2.0 and 3.0 were synthesized. A larger number of Si-O-Si linkages compared to Si-O-Al linkages and a higher atomic number density were found in the geopolymers with higher silica contents, which enhanced the compressive strength of the geopolymer pastes up to the optimal Si/Al ratio of 2.5. The paste with a Si/Al = 2.5 exhibited a greater portion of Q4(1Al and 2Al) and denser morphology compared to the other geopolymer pastes. Furthermore, in-situ high-energy synchrotron X-ray scattering experiments were conducted to assess the elastic modulus of the aluminosilicate structure at a local atomic scale. The modulus value in real space decreases with increasing silica contents up to Si/Al = 2.5 and increases with the presence of excessive unreacted silica fume. The modulus value in reciprocal space for the axial and lateral directions both presented a positive value at the geopolymer comprising a Si/Al ratio higher than 2.5, indicating that the load-bearing property of N-A-S-H changed at higher Si/Al ratios. Moreover, the smallest difference between the strains along the axial and lateral directions was detected for the geopolymer with Si/Al = 2.5 in both the real and reciprocal space, owing to the most interconnected and flexible nanostructure, which led to the highest mechanical strength. c 2023 Elsevier Ltd
Evaluating tensile strength of cement paste using multiscale modeling and in-situ splitting tests with micro-CT
Kim S.-Y.; Eum D.; Lee H.; Park K.; Terada K.; Han T.-S.
Construction and Building Materials, Elsevier Ltd., Vol.411, 2024, JAN.
(https://doi.org/10.1016/j.conbuildmat.2023.134642)
Abstract
This study investigated a strategy to simulate splitting tests to evaluate the tensile strength of cement paste within a multiscale framework, and validated the approach with in-situ micro-CT measurements. Phase-field fracture model was used to simulate the splitting test using virtual microstructures reconstructed from the macroscale micro-CT measurements. Among the modeling parameters, the range of the diffusive crack width, which is an internal parameter for phase-field fracture model, was further investigated. The cracks propagated through the weaker solid phase, and the predicted strengths and standard deviations were comparable to those obtained from the experiments. It was found that the diffusive crack width should be smaller than the characteristic length of the weaker phase to predict the crack pattern accurately. These findings confirm the effectiveness of the proposed multiscale modeling approach in predicting the tensile strength of cement paste. c 2023 Elsevier Ltd
Time-varying damage detection in beam structures using variational mode decomposition and continuous wavelet transform
Liu J.-L.; Wang S.-F.; Li Y.-Z.; Yu A.-H.
Construction and Building Materials, Elsevier Ltd., Vol.411, 2024, JAN.
(https://doi.org/10.1016/j.conbuildmat.2023.134416)
Abstract
Civil engineering structures in operation are likely to suffer damage. During the service life, structural damage evolves gradually from minor to severe. However, most current studies focus on damage localization and quantification of damage severity, and hence little attention has been paid to the detection of time-varying damage. This paper aims to propose a new approach for tracking the damage evolution of beam structures. In this approach, the wavelet threshold method is used at first to denoise the response signal. After that, the variational mode decomposition (VMD) is introduced to decompose the denoised response signal into several mono-components adaptively. A proposed index of wavelet total energy change (WTEC) is then applied to the new decomposed signals to localize damages of beam structures. On a basis of this, a time-varying damage index called wavelet energy change ratio (WECR) is established via the continuous wavelet transform and time window techniques and then applied to the response at the damaged position for tracking damage evolution. The proposed method is verified via a numerical example of a simply supported beam (its length and area of cross section are 5 m and 0.04 m2, respectively) with a sudden and a linear stiffness reduction under 1940 El Centro ground acceleration record. In addition, an experiment on a 10-meters-long steel bridge with abrupt stiffness reduction under a moving load is investigated to demonstrate the effectiveness and accuracy of the proposed time-varying damage detection method. The results show that the index of WTEC is able to localize damages of beam structures effectively whatever they are a single damage position or multiple damage positions. Moreover, the damage evolution can be tracked by the proposed index of WECR accurately even though random noises and end effects pose a great impact on the time-varying damage detection results. c 2023 Elsevier Ltd
Evaluation of the diffusion coefficient of cement paste from pore size distribution using three-dimensional simulation
Sakai Y.
Construction and Building Materials, Elsevier Ltd., Vol.411, 2024, JAN.
(https://doi.org/10.1016/j.conbuildmat.2023.134451)
Abstract
A three-dimensional diffusion simulation was performed to evaluate the diffusion coefficient (D) of cementitious materials based on the pore structure determined by mercury intrusion porosimetry (MIP). In the numerical simulation, a simple cubic lattice was assumed. As a result, the simulated D agreed better with the measured D than in previous studies without adjusting the parameters. The quantitative evaluation of D was possible with a certain accuracy based on the numerical simulation using the pore structure information evaluated by MIP, even though the MIP results include the ink-bottle effect, which causes an underestimation of the pore size. c 2023 Elsevier Ltd
Effect of multiaxial strain amplitudes on the cyclic behavior for SN490B steel under proportional loading
Teramae U.; Hiyoshi N.; Hirata H.; Teranishi M.; Kaneko K.
Construction and Building Materials, Elsevier Ltd., Vol.411, 2024, JAN.
(https://doi.org/10.1016/j.conbuildmat.2023.134696)
Abstract
SN490B is used in main steel members of high-rise buildings. In this study, multiaxial cyclic tests were conducted on SN490B under a combination of axial tension, compression, and torsion. For a strain amplitude of ƒÃa = 0.3%, cyclic softening behavior was observed regardless of multiaxiality. The cyclic softening converged after approximately 100 cycles. However, no significant cyclic softening was observed at ƒÃa = 0.5%. The stress variation is expressed as a function of plastic strain. The stress variation equation developed for the cyclic softening and hardening behavior of SN490B accurately approximated the test results. c 2023 Elsevier Ltd
Engineered geopolymer composite (EGC) with ultra-low fiber content of 0.2%
Wang F.; Ma J.; Ding Y.; Yu J.; Yu K.
Construction and Building Materials, Elsevier Ltd., Vol.411, 2024, JAN.
(https://doi.org/10.1016/j.conbuildmat.2023.134626)
Abstract
Engineered cementitious composite (ECC) features with excellent tensile performance. However, two major drawbacks, including the high environmental impacts associated with high content of cement and the high cost caused by high fiber content, impede the wide application of ECC. This study designs and successfully develops a high ductile cement-free engineered geopolymer composite (EGC) with ultra-low content of fibers (0.2% by volume, EGC-0.2%). EGC-0.2% exhibits a tensile strain capacity above 4% and a controllable crack width around 200 ƒÊm. The compressive strength reaches 39 MPa and the density is below 1200 kg/m3, showing an excellent specific strength (the ratio of the compressive strength-to-density) of 37 kPa/(kg/m3). The matrix fracture toughness of the developed EGC is low to facilitate the high ductility of the EGC-0.2% by such low fiber content. In addition, EGC-0.2% presents extremely low environmental impacts and cost. The embodied energy and embodied carbon decrease by 23% and 67% than conventional concrete, respectively, and the cost is only 21% of the classic M45-ECC with similar mechanical performance. The current findings provide valuable references for the future advancement of ECC towards high sustainability and cost effectiveness. c 2023
Evaluation of BFRP strengthening and repairing effects on concrete beams using DIC and YOLO-v5 object detection algorithm
Zhou K.; Lei D.; Chun P.-J.; She Z.; He J.; Du W.; Hong M.
Construction and Building Materials, Elsevier Ltd., Vol.411, 2024, JAN.
(https://doi.org/10.1016/j.conbuildmat.2023.134594)
Abstract
In this study the effectiveness of using Basalt Fiber Reinforced Polymer (BFRP) for strengthening and repairing concrete beams after pre-damage was investigated. Four-point bending tests were conducted on concrete beams, and their strain nephograms were analyzed using 3D-DIC (Digital Image Correlation) to assess the BFRP reinforcement and repair effects on concrete. A damage indicator model based on stress-displacement curves was proposed to quantify concrete damage and evaluate the BFRP strengthening effect. Additionally, the YOLO-v5 object detection algorithm was employed to detect surface damage on concrete specimens, and its results were cross-verified with the damage indicator. The study reveals that BFRP reinforcement primarily affects the concrete beams beyond the elastic limit, enhancing their load-bearing capacity by 37.91% and improving ductility. The proposed damage indicator proves successful in quantifying damage in BFRP-reinforced concrete beams, distinguishing the transition points between elastic, cracking, and failure stages. The YOLO-v5 algorithm accurately detects damage in strain nephograms, providing sensitive and timely identification of concrete damage. Results proves that the offset ratio between the damage identification results of YOLO-v5 and the experimental stress-displacement curve data is between ? 3.03% and 8.66%. The proposed damage indicator and YOLO-v5 detection offer valuable tools for evaluating damage and monitoring the health of concrete structures in engineering applications. c 2023