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Highlights • Effects of content and size of CRT glass aggregate on the concrete were studied. • Finer CRT glass aggregates generally increased the strength and elastic modulus. • CRT glass aggregate content had a limited impact on the damping ratio of concrete. • Reducing the size of CRT glass aggregate generally lowered the damping ratio. Abstract This paper investigates the influences of the content and particle size of recycled cathode ray tube (CRT) glass on the damping ratio of the CRT glass concrete by free vibration attenuation method. The density, water absorption, strength, and elastic modulus were also evaluated. The results show that the water absorption, elastic modulus, compressive strength and tensile strength decreased monotonously with CRT glass content, while the CRT glass content had a limited impact on the damping ratio. In general, hardened density, water absorption and damping ratio would decrease when the maximum particle size reduces from 4.75 mm to 0.60 mm, while the compressive strength, tensile strength and elastic modulus would increase. However, an unexpected decrease in the compressive strength and increase in the damping ratio of CRT glass concrete comes out when the maximum particle size decreases from 1.18 mm to 0.60 mm. The tensile strength of CRT glass concrete is underestimated by most of the existing concrete specifications when using compressive strength to estimate tensile strength. These specifications provide a conservative estimation that allows for the safe application of recycled CRT glass concrete in engineering designs. [ABSTRACT FROM AUTHOR]

Piezoceramic-based smart aggregate has been widely used to evaluate early-age concrete strength and to detect damage in concrete structures. In these structural health monitoring systems, they are generally verified and calibrated through experiments under load-free condition. However, the stress levels of actual concrete members are different. The microstructures of concrete will change with the variation of external load, and the high-frequency waves used in the monitoring system may be highly sensitive to these changes. In this study, the effects of axial compressive loading on the monitoring results are investigated. Specifically, three loading cases, that is, single cycle load, cyclic load, and step-by-step load, are employed to stress the concrete specimens embedded with smart aggregates. The amplitude and velocity of monitoring signals were measured before, during, and after each loading case. The test results show that the axial load lower than 30% of failure load still have a significant impact on the received signals. The amplitude attenuation is dependent on both frequency and load history, while the velocity is highly stress-dependent. The results indicate that the baselines of monitoring signals obtained from the same concrete structure in its healthy state can vary under different stress levels. The axial load variation should be carefully considered during the monitoring process. This study also provides a potential method to assess stress state in concrete structures using smart aggregates. [ABSTRACT FROM AUTHOR]

• Engineering sediment waste can be converted into beneficial supplementary cementitious material. • The optimal calcination condition for engineering sediment waste is determined. • Use of calcined engineering sediment improves environmental performance of concrete. • The overall performance of recycled concrete is evaluated by multi-criteria analysis. The extensive use of underground space has led to an increasing amount of engineering sediment waste, which occupies about 60% of construction waste in China. At present, most of the engineering sediment waste is randomly dumped, occupying a lot of land resources and hindering sustainability of built environment. To solve these problems, this work proposes the recycling of engineering sediment waste via calcination and subsequent use as a cement substitute in concrete for construction. The optimal calcination condition is evaluated through strength activity index method. The mechanical properties, environmental and economic benefit of the concrete prepared with various substitution rates of calcined engineering sediment waste are determined using mechanical tests and the life cycle assessment. A multi-criteria analysis method is employed to comprehensively estimate the performance of concrete in terms of compressive and flexural strengths, global warming potential, energy consumption, and economic cost. The effect of calcined engineering sediment on the pozzolanic activity, cement hydration, CH content and microstructure of concrete has been quantitatively evaluated to reveal the mechanism behind the variation of mechanical properties. The concrete with 50% substitution of calcined engineering sediment showed superior environmental performance and economic benefit than those of reference concrete. This work contributes to an effective method for converting sediment waste into valuable resources to prepare concrete with low environmental impact and good mechanical performance, thereby promoting resource conservation and contributing to sustainability of built environment. [ABSTRACT FROM AUTHOR]

Great autogenous shrinkage has become a common problem in cement-based materials with a low water-to-binder ratio (w/b). To limit the autogenous shrinkage in ultra-high performance concrete (UHPC) during the process of hydration and curing, sustainable use of recycled micropowder (RMP) made from autoclaved aerated concrete waste (AACW) to cure UHPC internally is proposed in this paper. The influence of RMP (at the levels 5%, 10%, and 15% by mass) with three particle size classes ranging from 0 to 600 μm on the autogenous shrinkage, hydration reaction, internal relative humidity, and compressive strength of UHPC were investigated. The results show that mixtures with different dosages and particle sizes improve the fluidity of UHPC, and its internal curing effect can effectively inhibit the early-age autogenous shrinkage of UHPC and maintain a higher internal humidity compared with the control group. The incorporation of RMP can advance the appearance of a hydration peak and increase the cumulative heat of hydration. Microscale analyses show that the curing water released from RMP promotes the hydration of the unhydrated cement around RMP. The generated hydration product filled the surface pores of RMP and weakened the negative effect of the pores introduced by RMP on the compressive strength of UHPC. Thus, RMP can be utilized as internal curing materials for UHPC to reduce autogenous shrinkage. • The potential for internal curing of RMP in UHPC is investigated. • Autogenous shrinkage of UHPC with RMP is reduced by 65%. • The underlying mechanism behind internal curing of RMP has been explored. • Compressive strength of UHPC with RMP can still exceed 160 MPa at 28 days. [ABSTRACT FROM AUTHOR]

Abstract: Concrete structures in service may be suffer from sulfate attack, which may lead to the deterioration of both static and dynamic properties of concrete, and therefore jeopardize their performance in earthquake events. To predict the seismic performance of sulfate-damaged concrete structures, the rate-dependent strength, deformation behavior and energy absorption capacity of concrete specimens under sulfate attack were investigated. First, half of the specimens were initially cured under sulfate attack for 4months and the other half of the specimens were cured in a room environment for comparison. Then axial compressive experiments for concrete specimens with different strain rates were carried out. Experimental results show that sulfate attack had a significant impact on the dynamic properties of concrete. Sulfate attack makes concrete strength more sensitive to strain rate. With increasing strain rates, the peak strain and energy absorption capacity of control and sulfate attacked concrete tend to increase, but they are greatly decreased by disruptive expansion and chemical deterioration induced by sulfate attack. Finally, the failure phenomenon was shown and the damage mechanism of specimens was discussed. [Copyright &y& Elsevier]

[Display omitted] • Influence of PCT and additives on the compressive strength and permeability was investigated. • Low strength ratios of permeable concrete to cement paste results from the low bonding area. • Enhanced bonding ratio can produce the greatest benefit in terms of strength. • Loss of permeability is the result of both reduced connected porosity and increased tortuosity. • Cement paste thickness distribution and pore size distribution were predicted by lognormal function. The macro performance and mesostructure of permeable concrete are largely determined by the paste coating thickness (PCT) on aggregates within the fresh mixture. Accordingly, in the present study, the strength and permeability of permeable concrete with different paste coating thicknesses were measured. The mesostructure characteristics of cement paste and pore were subsequently quantified by X-ray CT images and image processing techniques. As a result, the influence of PCT on the compressive strength and permeability, the characteristics of cement paste and pore was determined. The distribution of cement paste thickness and total pore size were used as functions of paste coating thickness, which coud be used to predict these mesostructure characteristics at the design stage of permeable concrete. The significance of this paper includes providing a deeper understanding of the relationship between macro performance and mesostructure from the perspective of paste coating thickness within mixtures. [ABSTRACT FROM AUTHOR]

• Silane emulsion modification was used to improve the compressive strength of RA permeable concrete. • Silane emulsion modification was used to improve freeze–thaw durability of RA permeable concrete. • Mechanism of silane modification and freeze–thaw failure were verified. • Microstructure of cement matrix and ITZ were investigated based on BSE-IA technology. Currently, there are few effective methods for improving the freeze–thaw durability of recycled aggregate (RA) permeable concrete without reducing the strength or permeability. Thus, this study aims to improve the freeze–thaw durability of recycled aggregate permeable concrete without the degradation of strength and permeability. Accordingly, two silane emulsion modification methods, namely the surface modification of recycled aggregate and integral modification of cement matrix, were used to raise the freeze–thaw durability. The compressive strength, permeability coefficient, freeze–thaw durability of recycled aggregate permeable concrete were measured. The characteristics of interfacial transition zone (ITZ) and cement matrix were investigated to analyse the modification mechanism. The results indicate that surface modification of recycled aggregate can increase both the compressive strength and freeze–thaw durability of recycled aggregate permeable concrete more effectively than the integral modification of cement matrix. This study provides an effective method to improve the comprehensive performance of recycled aggregate permeable concrete. [ABSTRACT FROM AUTHOR]

The work reports on an experimental programme, conducted to validate comprehensively our previously proposed coupled chemo-transport model for external sulfate attack on concrete. Specifically, the effects of the concentration of sulfate solution and temperature on the distribution of sulfate ions in concrete are experimentally investigated and used to demonstrate the accuracy of the modeling framework. Further, the profile of aluminate depletion and the leaching depth numerically are investigated. For all cases the model predictions are in good agreement with the experimental results, showing increases of the concentration of sulfate ions in concrete with higher concentrations of sulfate solution and higher temperatures. It is concluded that higher sulfate solution concentration and temperature enhance the processes involved in the external sulfate attack on concrete, namely diffusion of sulfate ions and their chemical reactions with concrete. It is found that these parameters affect the external sulfate attack predominantly via the chemical reaction process. [ABSTRACT FROM AUTHOR]

Assessing the long-term durability of concrete structures subjected to external sulfate attack (ESA) poses a significant challenge, primarily due to the lack of a well-defined quantitative metric for durability limit states. Traditional performance indicators such as compressive strength, mass loss, and expansion strain are insufficient for providing a comprehensive understanding of the extent of damage and are often difficult to measure accurately in practice. The primary objective of this study is to introduce a novel durability failure indicator, namely the failure thickness of concrete under ESA exposure, designed to quantitatively assess the ultimate limit state of concrete durability. Experiments were conducted and the results confirmed that the failure thickness can reliably reflect changes in both the elastic modulus and compressive strength of concrete exposed to ESA. A prediction model for estimating the failure thickness was subsequently developed, integrating key influencing factors like sulfate concentration, initial aluminate content, and sulfate ion diffusion coefficient. The established model exhibited a high degree of correlation between the predicted and experimental failure thickness values, with a low margin of error. The findings of this research contribute to serve as a foundation for both lifespan prediction and durability design of concrete structures exposed to sulfate-rich environments. • We propose a durability failure indicator based on critical sulfate concentration. • Concrete performance deterioration can be well characterized by failure thickness. • The validity of the prediction model of failure thickness was confirmed. [ABSTRACT FROM AUTHOR]

Highlights • Actual coarse aggregate shapes were statistically analyzed based on CT technology. • A Polygon aggregate modeling method was proposed considering statistical features. • Proposed polygon aggregate models were verified by an experimental test. • Several meso-scale models with various sizes and cross-section shapes were provided. Abstract Few efforts have been made to study actual coarse aggregate shapes in mesoscopic simulation analysis, whereas it has a significant impact on stress distribution and micro-crack propagation during the failure process of concrete. In this study, the true characteristics of aggregates (i.e. edge number, area, equivalent radius, elongation ratio and size distribution) were statistically analyzed by processing the real 2D slice images of concrete obtained from X-ray computed tomography technology. A polygon random aggregate modeling method, considering above statistical features of aggregate, is proposed and verified by an experimental investigation. The test results show that the established model can give an accurate description of the stress-strain behavior and damage evolution of concrete. Moreover, several representative meso-scale concrete models were established, which provides a reference in building meso-scale models with various sizes and cross-sectional shapes, especially for large-scale concrete members that are unable to undergo CT testing due to limitation of operational space. [ABSTRACT FROM AUTHOR]

Cathode ray tube (CRT) funnel glass has been used to partially or totally replace natural sand as fine aggregate in concrete. It is an effective and environmentally friendly method of recycling the increasing number of discarded CRT in the electronic industry. However, little research has been performed on its durability performance under environmental attacks, in particular in the areas of chloride ion penetration and sulfate attack, the two major environmental attacks on reinforced concrete structures. This study presents an experimental investigation on the durability performances of concrete using CRT funnel glass as fine aggregate in 8% sodium chloride solution, 5% sodium sulfate solution and 10% sodium sulfate solution. Four volume replacement ratios (the ratio of CRT glass to natural sand), i.e. 0%, 30%, 60%, 100%, are considered. The chloride ion content along concrete depth direction, compressive strength and elastic modulus of concrete was measured with attack time. The test results show that although the compressive strength and elastic modulus decrease with increasing content of CRT funnel glass in concrete, the long-term resistance to chloride ion penetration is enhanced by using CRT funnel glass as fine aggregate. Furthermore, the compressive strength, rather than dynamic elastic modulus of concrete containing CRT glass, is more sensitive to sulfate attack. The relative increase in strength of CRT glass concrete is obviously larger than that of control concrete under sulfate attack. This study also provides a reference for the durability design of concrete structures using CRT funnel glass as fine aggregate. [ABSTRACT FROM AUTHOR]

• The effect of seawater and sea sand at different stages of preparation on the performance of AWC mortar was systematically studied. • The adverse effect of seawater on the properties of AWC mortar at the molding stage was found for the first time. • The mechanism of the influence of seawater on AWC properties at the molding stage was revealed. Seawater and sea sand are widely used in marine concrete to overcome the shortage of freshwater and river sand. However, the effect of the various salts in seawater and sea sand on the performance of anti-washout underwater concrete (AWC) is unclear. In this study, the influence of seawater and sea sand, as well as the aggressive ions in seawater, on the anti-washout ability, mechanical performance, and microscopic structure of AWC mortar are studied systematically. The AWC mortar molded in seawater has a lower compressive strength even though its indicators of anti-washout ability perform better than that in freshwater. This is because Mg2+ in seawater chemically binds with OH– in cement to form Mg(OH) 2 film absorbed by anti-washout admixture(AWA), which inhibits the release of substances in AWC while also introducing more defects in AWC. This study lays the foundation for promoting the application of seawater and sea sand AWC in marine engineering. [ABSTRACT FROM AUTHOR]

With the increasing height of high-rise buildings, adverse effects caused by differential axial shortening become significant. Most of the calculation methods that have been developed to analyze the axial shortening of high-rise buildings are based on a common assumption that creep is linearly proportional to stress and conforms to the superposition principle. However, this assumption is rarely verified when it is used to describe the time-dependent deformation development of early age concrete in construction process. This paper presents an experimental study to examine the validity of this assumption in this use. A step-by-step load was employed to approximately simulate the load history of axial components experienced in the construction process and the strain developments were monitored. A comparative analysis between test results and numerical simulations shows that, the strain development of early age concrete under a step-by-step load is substantially affected by the loading age and stress amplitude, which verifies that the assumption, on which previous methods are based, may lead to inaccurate prediction of strain development in axially loaded concrete components. The time-dependent strain is overestimated with the larger step-by-step stress amplitude and shorter loading history. [ABSTRACT FROM AUTHOR]

The anti-washout concrete (AWC) made with seawater and sea sand has a limited marine infrastructure application due to its unfavorable properties. Our study proposes an effective performance enhancement method for AWC using silica fume. A comprehensive examination was carried out to investigate the effects of silica fume on AWC's flowability, anti-washout ability, compressive strength, microstructure, permeability, and abrasion resistance, with the AWC prepared with seawater and sea sand, and molded in seawater. It was discovered that 10 % silica fume can most effectively improve the performance of AWC. This enhancement is due to the pore structure refinement realized with C-S-H gel generated from pozzolanic reaction. Exceeding 10 % silica fume content can have a detrimental effect on the slump-flow of mixtures, while only providing marginal improvements in impermeability and compressive strength. The study lays a fundamental groundwork for the wide use of sea-based resources and the application of AWC in marine engineering. • The science behind modification of AWC mortar molded in seawater using silica fume was revealed. • The effects of silica fume on the performance of AWC molded in seawater were thoroughly explored. • The optimal content of silica fume to improve performance of AWC molded in seawater was identified. [ABSTRACT FROM AUTHOR]

• The performance of concrete under sulfate attack and dry-wet cycles is investigated. • A newly defined index is proposed to describe the progress of sulfate attack. • A novel method is proposed to assess the performance of sulfate-attacked concrete. Sulfate attack is a major cause of concrete durability deteriorations. Mass loss, strength reductions, and expansive strain of concrete specimens are generally used in laboratory testing to identify the resistance of concrete materials to sulfate attack. However, these indicators cannot be directly used to quantitatively predict the bearing capacity of actual concrete structures under sulfate attack. There exists a significant size effect between laboratory and engineering size concrete components. In this study, the durability performance of concrete specimens, exposed to sulfate attack and dry–wet cycles, was investigated. Mass loss, dynamic elastic modulus, compressive strength, and sulfate ions distributions of deteriorated concrete were measured over time. Test results indicate that the newly defined integral area of sulfate ions distributions is a suitable index to describe the non-uniform deteriorations behavior of sulfate–attacked concrete; and a novel method based on the homogenizations theory is proposed to predict the deteriorations level of components of attacked concrete structures, which provides a potential use in assessing the loading capacity of actual concrete structures based on accelerated test results in a laboratory. [ABSTRACT FROM AUTHOR]

• The influences of moisture variations on ion transport and physical crystallization were discussed. • The respective contributions of chemical and physical attack to crystallization pressure were distinguished. • The deterioration in concrete performance was considered under the combined impacts of external sulfate attack and drying–wetting cycles. • A transport-chemical-physical–mechanical model was developed to evaluate and predict damage progression to concrete. When coupled with drying–wetting cycles, the deterioration process of concrete subjected to external sulfate attack (ESA) is significantly accelerated. The impact of moisture variations on ion transport was considered to establish a mass conservation equation with pore solution concentration as the variable. The contributions of chemical and physical attack to crystallization pressure were distinguished, and a bulk modulus reduction function was introduced to ascertain the stiffness deterioration. An ESA model was proposed and verified by comparing it to published experimental data, which could accurately predict the deterioration process of concrete under ESA and drying–wetting cycles. [ABSTRACT FROM AUTHOR]

This study investigates the effects of lime-saturated water and water–CO 2 cyclic recuring on strength recovery of thermally damaged high-performance concretes (HPC). The HPC samples were subjected to elevated temperatures up to 1000 °C in 200 °C increments and underwent recuring. Phase assemblage and distribution, microstructure evolution, and pore structure of the HPC samples were identified. According to the results, recovered compressive strength of the HPC samples with low silica content can surpass their original strength after 600 and 800 °C exposure and recuring. In contrast, HPC with high silica content is unfavorable for strength recovery at temperatures above 800 °C because the low-calcium phases formed have low reactivity. After 1000 °C exposure, only water–CO 2 cyclic recuring coalesces the disintegrated microstructure and recovers the compressive strength. Strength recovery primarily depends on healing the microcracks and large pores rather than the coarsened cement paste. [ABSTRACT FROM AUTHOR]