Journal of Materials in Civil Engineering

Geopolymers and alkali-activated materials (AAM) have emerged as a promising sustainable alternative to ordinary Portland cement (OPC). Although much effort has recently been devoted to a wide range of research on the self-healing of cracks in OPC-based composites, little is known about the self-healing potential of AAMs. Therefore, this study explores the crack self-healing capability of NaOH-activated slag composites using a portfolio of testing methods, including electrical conductivity, mercury intrusion porosimetry, inductively coupled plasma optical emission spectroscopy, scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy, and X-ray microcomputed tomography. Experimental results indicate that alkali-activated slag-based composites incorporating calcium hydroxide achieved higher levels of self-healing than control specimens without calcium hydroxide. X-ray micro-computed tomography coupled with three-dimensional image analysis demonstrated that the observed self-healing was a surface mechanism that only occurred at surface cracks. Calcium carbonate was found to be the main self-healing product in all test specimens. Leaching experimental results indicated that the concentration of ${\mathrm{Ca}}^{2+}$ ions in the AAM matrix plays a critical role in calcium carbonate precipitation and, thus, in the self-healing potential.

Hydraulic asphalt concrete (HAC) used as upstream facing of embankment dams is subjected to different temperatures and loading conditions. The main goal of this paper is to investigate the compressive behavior of HAC under different temperatures ($-20°\mathrm{C}$–30°C) and strain rates (${10}^{-5}$–${10}^{-2}{\mathrm{s}}^{-1}$). The results showed that temperature and strain rate had significant impact not only on the stress–strain characteristics of HAC, but also on its failure modes. The dynamic compressive strength, elastic modulus, and energy absorption capacity increased with increasing strain rate, while they decreased with increasing temperature. The failure mode at a temperature range of 10°C–30°C was mainly in binder failure, whereas that at a range of $-20°\mathrm{C}$–5°C was in binder failure and transaggregate failure, and the ratio of aggregate cracking increased with increasing strain rate from ${10}^{-5}$–${10}^{-2}{\mathrm{s}}^{-1}$. Moreover, empirical formulas for temperature influence factors (TIFs) and dynamic increase factors (DIFs) of the compressive strength and elastic modulus of HAC were proposed and found to be in good agreement with test results. Finally, the calculation model of the compressive strength and elastic modulus, considering the interactions between temperature and strain rate, were successfully established based on the time–temperature superposition principle.

Pavement foundations supported on expanded polystyrene (EPS) geofoam blocks are vulnerable to excessive deformation or even failure owing to truck passage during construction. To investigate this, a series of large-scale static plate load tests, accompanied by numerical analyses, were carried out to determine the effects of overlying soil thickness, EPS geofoam density, and the gap between EPS blocks. Furthermore, the effect of geocell reinforcement on the performance of such pavement systems was evaluated. Test results showed that as the soil thickness increased from 300 to 600 mm, the surface settlement of unreinforced pavement decreased by up to 65%. Low-density EPS geofoam can double or triple surface settlements or cause premature failure in a system. Additionally, reinforcing the overlying soil layer with geocell causes up to a 54% reduction in surface settlements. A series of verified numerical analyses demonstrated that as long as the pressure transferred to geofoam blocks remains below the compressive strength of EPS geofoam, the increase in pavement surface settlement is limited. Furthermore, increasing the gap between EPS geofoam blocks can increase the surface settlement of unreinforced pavements, while geocell reinforcement can help to moderate these settlements. The results of this study can be used to develop solutions to some of the limitations encountered during the construction of EPS geofoam embankments and under static loading conditions.

In this study, the effect was investigated of side chain length changes of polycarboxylate-ether–based high-range water–reducing (HRWR) admixture on fresh properties, compressive strength, and water adsorption capacity of cementitious systems. For this aim, three HRWR admixtures having same raw materials, anionic/nonionic group ratio, free nonionic group content, and main chain length but different side chain length and molecular weight were synthesized. The effect was investigated of the mentioned admixtures on the properties of mixtures containing 0%, 15%, 30%, and 45% of fly ash. According to the test results, regardless of fly ash utilization ratio, the flowability of the mixtures was positively affected with the increase of the water-reducing admixture side chain length to a certain value. However, utilization of admixtures having the longer side chain length than a certain value adversely affected the flow properties of the mixtures. It is thought that this situation is due to the reduction of the admixture efficiency (steric effect) by increasing the possibility of intertwining of polymers of admixture having higher side chain length. The admixture with $\mathrm{2,400}\mathrm{g}/\mathrm{mol}$ of side chain molecular weight (length) showed the best performance in terms of fresh properties. The change of HRWR admixture properties had no significant effect on the strength and water adsorption capacity of the mixtures. Moreover, regardless of HRWR admixture properties, the time-dependent flowability of the mixtures was adversely affected and the water adsorption capacity was decreased with the utilization of fly ash. This effect was more pronounced with increasing replacement ratio of fly ash.

This study investigates the acoustic emission (AE) and physicomechanical properties of concrete under three sulfate attack conditions: continuous immersion, wetting–drying cycles, and cyclic loading coupled with wetting–drying cycles. The characteristics of AE absolute energy during the concrete compression process were statistically analyzed by the histogram method and maximum likelihood (ML) method. The results from this study showed that the concrete specimens experienced two stages: an enhancement stage and a subsequent deterioration stage. Both wetting–drying cycles and cyclic loading accelerated the sulfate attack process. The probability density distribution of AE absolute energy satisfied a power law, and the distribution exponent was related to the degree of sulfate attack. The filling of expansion products during the enhancement stage led to the ML curves displaying a good plateau with lower exponents. Conversely, the cracking occurring during the deterioration stage created upturned ML curves with higher exponents. The results indicate that the exponent can accurately characterize the degree of concrete degradation under sulfate attack.

The efforts toward sustainability of natural resources promote the use unexploited natural resources and raw materials. Beach sand, unsuitable as filler in concrete due to its salinity and generally uniform grain size, was tested as an alternative filler in geopolymer composites. The processability of the mixture determined the minimum and maximum amounts of beach sand (70 and 75 wt%, respectively). Geopolymer solids with the limit of sand content were studied in terms of stability and mechanical properties. Laboratory results corroborated the tendency of flexural and compressive strength to increase over time, with the maxima being 9.95 MPa for flexural and 64.1 MPa for compressive. Infrared analysis showed formation of geopolymer bonds even after the addition of beach sand. These findings offer a new potential for the use of beach sand in coastal areas as a local source of material for less demanding construction, such as seawalls.

Effects of synthetic and neutralized vinsol resin (NVR) air-entraining admixtures (AEAs) were compared through air-content measurements of freshly mixed concrete, hardened cylinders, and cores from field and laboratory concrete, and through a modified foam drainage test. The results show that air bubbles entrained with synthetic AEAs are less likely to survive during concrete sampling procedures than those entrained with NVR-based AEAs, leading to larger discrepancies between air-content measurements using the pressure method and the air content established from pavement cores. These discrepancies in turn can prompt imposition of contractor penalties, delays in construction, and controversy with potential longer-term impacts on concrete pavement longevity.

Fatigue changes the mechanical behavior of reinforcing bars, significantly reducing the performance of aging concrete structures. This study performed a fatigue loading test on post-tensioned prestressed concrete (PC) beams with various corrosion levels of prestressed tendon. The effect of corrosion on fatigue life and failure modes of test beams were discussed. Steel bars at different distances from the fracture location in beams were removed for static tensile tests. The mechanical properties of the steel bars after fatigue in different locations relative to the failure point were analyzed. A quantitatively constitutive relationship was proposed to characterize the mechanical behavior of steel bars after fatigue. This model can consider the effects of fatigue stress range, fatigue cycles, and fatigue fracture location of steel bars. The experimental results showed that the failure of corroded post-tensioned PC beams initiated from the brittle fracture of prestressed tendon, promoting the fatigue fracture of steel bars. The proposed models were verified by the test data in the literature. The theoretical values were in good agreement with the experimental results. The proposed constitutive relation model considering the location effect can be used to model the uncertain effect caused by fatigue.

Autoclaved aerated concrete (AAC) is an energy-saving and environmentally friendly building material. However, ordinary portland cement (OPC) mortar is prone to cracking and spall when it is used for surface plastering of AAC. To resolve this situation, this research proposes a novel plastering mortar appropriate for AAC based on magnesium phosphate cement (MPC) incorporating fly ash (FA) and cenospheres. Two series of mortar mixtures were formulated with different FA and cenosphere dosages. Firstly, MPC was partially replaced with FA by weight. Then, in the case of fixed FA content, sand was replaced with an equal volume of cenospheres at different percentages. The mechanical strength, water retention, drying shrinkage, and thermal conductivity of the MPC mortar was investigated. The hydration products and microscopic properties of the MPC mortar were examined by scanning electron microscope (SEM) and X-ray diffraction (XRD). The results show that FA greatly improves the water retention of MPC mortar. The water retention of MPC mortar is 97.5% at FA replacement of 40%. Although cenospheres replacing sand slightly reduced mechanical strength of MPC mortar, they can significantly decrease the thermal conductivity and drying shrinkage of mortar. When sand was completely replaced with cenospheres, the bond strength, drying shrinkage rate, and thermal conductivity were 0.6 MPa, $0.08\mathrm{mm}/\mathrm{m}$, and $0.26\mathrm{W}/\mathrm{m}·\mathrm{K}$, respectively. Finally, XRD and SEM tests of MPC mortar also indicated that cenospheres inhibited the hydration of MPC and reduced the strength of MPC mortar. In conclusion, the developed MPC mortar has excellent bond strength as well as low drying shrinkage rate and thermal conductivity, which can effectively deal with the problem of cracking and spall in traditional plaster mortar and is also an eco-friendly building material.

The modern deep cement mixing wall requires a thinner wall thickness due to limited space in urban areas. A soil–cement column can have the characteristics of a brittle failure pattern and low tensile and flexural strength due to the high cement content (10%–20%); thus, to ensure the serviceability and stability of a restricted wall when subjected to horizontal loads, jute fiber and polyvinyl alcohol (PVA) fiber are utilized as reinforcement to improve the flexural and fracture performance of the soil–cement column. In this research, the effect of fiber addition on the flexural performance and fracture mechanics of cemented soil were evaluated by the indicators of peak flexural strength, residual flexural tensile strength, crack mouth opening displacement (CMOD), and energy absorbing capacity. In addition, the durabilities of unreinforced and fiber-reinforced specimens were studied by comparing the flexural strength under wet–dry cycles and observing the plastic shrinkage cracks in the early age. The results showed that the inclusion of fibers significantly improved the flexural performance and fracture energy of soil–cement, and it was shown that the fiber reinforcement effectively restrained the formation and propagation of plastic shrinkage cracks in the early age and reduced the flexural strength loss under wet–dry cycles.

This study explored the relationship between air voids and permeability, and investigated the correlation between air void type, coefficient of permeability, mechanical properties, and moisture damage in hot-mix asphalt (HMA). Six asphalt mixtures were prepared with air voids ranging from 4% to 19% in increments of 3%. Major tests, including two air void tests, a penetration test, and a dynamic water scouring test, were conducted to assess the moisture damage by measuring and comparing the difference in air voids and permeability before and after the dynamic water scouring. A compressive test was conducted to evaluate the residual strength of HMA with different porosities. Results indicated that the effective voids and coefficient of permeability had a strong correlation. There was an obvious increase of effective voids and permeability for specimens with air voids from 10% to 13% after dynamic water scouring tests. In terms of compressive strength, specimens with air voids from 7% to 13% had greater strength loss and deformation than other specimens, indicating that moisture damage occurred and developed rapidly in asphalt mixtures within a certain porosity range.

Welded-wire reinforcement (WWR) is widely used as the main reinforcement in bridge decks and vertical shear reinforcement in concrete bridge girders. Previous studies on concrete members reinforced with WWR have indicated that the reduced ductility of the cold-drawn wires leads to lower member ductility and rupture of shear reinforcing steel at failure. Additionally, the influence of the heat-affected zones created at the electric-resistance welds raises concerns regarding the mechanical behavior at the welded connections. To evaluate the fracture behavior of WWR meshes, an experimental program was developed involving tensile and Charpy V-notch (CVN) specimens sampled from straight bars and welded intersections. Due to size constraints, both full and subsized CVN specimens were tested, and a variety of size correction methods were trialed for degree of accuracy in comparing the two sizes of specimens tested. Tensile tests showed that the cross-welds decreased ultimate strain by an average of 10% without significantly altering yield stress, ultimate strength, or elongation at fracture. CVN tests indicated that the cross-weld tended to increase impact toughness by up to $30\mathrm{J}$ ($22\mathrm{ft}\text{-}\mathrm{lbf}$) as the longitudinal and transverse bars became closer in size. Experimental values are evaluated using statistical methods and compared to specification minimums in American and European standards.

Organic acids, such as acetic and lactic acids, are prevalent in agricultural and food effluents. They pose a considerable pollution threat and must be collected and stored safely before treatment and release. They cause significant damage to cementitious materials, reducing the service life of structures. In this study, the resistance of alkali-activated fly ash and slag-blended binders to organic acids was studied, and a comparison with ordinary portland cement binders was carried out. The findings demonstrate that alkali-activated binders with increased fly ash content have marginally better resistance to acetic acid, but mixes with increased slag content have better resistance to lactic acid. This is due to the solubility of the calcium and aluminum salts of acetic and lactic acids. Overall, the performance of the alkali-activated binders was better than that of the ordinary portland cement binder, with a lower mass and strength losses observed. This was attributed to their lower calcium content with less vulnerable phases, such as calcium hydroxide and ettringite. Instead, the calcium-silicate-hydrate (C-S-H) type gels in alkali-activated binders suffered decalcification and dealumination but left behind a silicon-rich gel, which helped to resist further acid attack.

Early-age carbonation curing of concrete is considered an alternative curing method that efficiently utilizes carbon dioxide to improve the performance of concrete and reduce carbon emission. Carbonation curing is commonly implemented in a pressure chamber at high pressure. The application is therefore limited only to special products such as concrete masonry units. To promote wider applications of the technology for general precast concrete with any shapes and sizes, an ambient pressure carbonation system in a flexible enclosure is needed. This paper presents a study on developing a new carbonation curing system at a curing pressure of 1.4 kPa (0.014 bar), which is considered as ambient pressure. The system includes a flexible enclosure made from a plastic sheet with a pressure-resistant zipper that can accommodate any shape and size of precast concrete products and can be made either in a factory or on a job site. Compared to the traditional high-pressure carbonation at 0.5 MPa (5 bars), which generates 12% ${\mathrm{CO}}_2$ uptake, carbonation in the ambient-pressure system at 1.4 kPa (0.014 bar), can achieve a carbon dioxide uptake of 11% with a comparable strength at both the early and late ages. Besides, the ambient pressure carbonation has shown less pH reduction and smaller carbonation depth than high pressure, which would have the advantage of protecting the reinforcing steel in concrete from carbonation-induced corrosion. Furthermore, ambient pressure carbonation-cured concretes were found to have higher compressive strength, higher surface electrical resistivity, lower porosity, and faster ultrasonic pulse velocity than normal hydration concretes at both the early and late hydration stage. Microstructure analysis indicated that carbonates were intermingled with C─ S─ H, contributing to the strength gain and performance improvement of concretes subject to ambient pressure carbonation curing.

This paper presents an innovative study on the partial replacement of lime binder with foam glass dust to explore a new application of this waste dust as a lime mortar additive. Standard air lime mortars and natural hydraulic lime (NHL) mortars were made by incorporating from 0% to 40% of foam glass dust in replacement to lime, and their mechanical performances, microstructure, and durability were determined. The waste foam glass dust showed an unusually high pozzolanic activity, predicting an improvement in the mechanical properties and durability of lime mortars. As the replacement level in air lime mortars increased, the performance properties of the mortars improved. The pozzolanic reaction of foam glass dust did not compensate for the loss of hydraulic binder in NHL mortars; therefore, these mortars have gradually lost their strength. The progress in mortars carbonation, as well as the pozzolanic reaction of foam glass dust, led to the formation of denser and more frost-resistant structure in air lime mortars, whereas the partial binder replacement in NHL mortars with foam glass dust had no significant effect on their frost resistance. The highly effective use of foam glass dust as a supplementary material was assessed to air lime mortars.

The objective of this paper is to examine the orientation dependence of plasticity and fracture in single-crystal superelastic Cu-Al-Mn shape memory alloy (SMA) bars. For this purpose, we prepared 14 single-crystal superelastic Cu-Al-Mn SMA bars of 15-mm diameter and 140-mm length. The crystal orientation was measured using electron backscatter diffraction. This work involved cyclic tension tests up to 10% strain and consecutive monotonic tension tests up to fracture. From these results, strong orientation dependence was observed in plasticity and fracture. Ductility was poor or moderate when the orientation of the specimen was close to the $<\begin{array}{ccc}1& 0& 1\end{array}>$ direction. On the other hand, a highly ductile response was observed when the orientation was close to the $<\begin{array}{ccc}1& 1& 2\end{array}>$, $<\begin{array}{ccc}1& 1& 3\end{array}>$, or $<\begin{array}{ccc}0& 0& 1\end{array}>$ direction. In these specimens, the fracture strain ranged from 47% to 92%. The large rotation of crystal lattice and the propagation of slip band along the long distance in the longitudinal direction are the reasons for the highly ductile response. Such a highly ductile response is desirable in structural materials, especially in seismic applications for civil structures like buildings and bridges.

Corroded steel bars frequently exist in concrete structures under chloride exposure conditions. Tensile behaviors of corroded steel bars at high temperatures are important in the fire-resistance evaluation of corroded reinforced concrete structures. This paper presents an experimental investigation on the tensile behavior of corroded steel bars at elevated temperatures. Corroded steel bars with different corrosion degrees are obtained by using the impressed current method. Then, a three-dimensional (3D) laser-scanning technique is applied to geometrically modeled corroded steel bars to quantify the corrosion degree. To investigate the influence of corrosion degree and temperature on the mechanical properties of steel bars, steady-state tensile tests were conducted at elevated temperatures. According to test results, the fracture initiation of an uncorroded steel bar occurs at the center of the fracture surface, whereas for a corroded steel bar, it moves to a corrosion pit on the surface. The effective elastic stiffness decreases significantly with the increase of temperature, whereas the influence of corrosion on the elastic stiffness could be ignored. The yield and ultimate strength in terms of the average cross-sectional area decrease with the increase of both the temperature and corrosion degree, and corrosion shows a decreased impact at a higher temperature. For a steel bar with a corrosion degree of 0.15, the yield and ultimate strength reduce by 11% and 17% at room temperature and by 9% and 10% at 500°C, respectively. However, the influence of corrosion on the yield and ultimate strength in terms of minimum cross-sectional area can be neglected. The yield plateau shortens with the increasing temperature and disappears at the critical temperature, which is around 300°C for uncorroded steel bars, and decreases linearly with the increase of corrosion degree. As temperature increases, the ultimate strain firstly decreases to the lowest value at about 400°C, and then increases, and it further decreases with the development of corrosion at a certain temperature.

This paper summarizes the results of a research study that was conducted to evaluate the effects of asphalt binder and aggregate gradation on the rutting and cracking resistance of asphalt mixtures used in construction of airport pavements. Different asphalt binders were considered, including polymer-modified asphalt binders, a highly polymer modified binder (HiMA), and a ground tire rubber (GTR)-modified binder. In addition, Bailey method was employed to select the aggregate gradation for optimal rutting resistance. A comprehensive laboratory testing program was performed on the considered airport asphalt mixes, which included conducting the flow number, asphalt pavement analyzer (APA), Hamburg wheel-tracking device (HWTD), indirect tensile strength (ITS), and semicircular bending (SCB) tests. Statistical analysis was conducted on the test results to provide ranking of the evaluated mixtures. The results indicated that Bailey method was effective in improving the rutting resistance of the considered airport asphalt mixes. Furthermore, the asphalt binder type had a significant effect on the rutting and cracking resistance of considered airport asphalt mixes.

Cold recycled materials (CRMs) are products of modern recycling techniques that are used in maintenance and rehabilitation of pavement structures with significant economical and environmental benefits. CRM mixes are produced at ambient temperature using bitumen emulsion or foamed bitumen as a binding agent, and the aggregate phase is composed mainly of reclaimed asphalt pavement (RAP). This paper investigated the compactability of two RAP sources and their effects on the behavior of CRM mixtures tested in the small strain domain. The compactability was studied using experimental results and the compressible packing model (CPM). Complex modulus tests of CRM mixtures were conducted, and the results were modeled using the Di Benedetto–Neifar (DBN) model. Findings showed that in CRM mixtures with the same gradation and formulation, one RAP source required almost half of the compaction energy of the other source to reach the design air voids content. The rheological analysis results highlighted the impact of the RAP source on the behavior of the CRM mixes in the small strain domain.

Concrete specimens of varying compressive strengths were subjected to impact from fragments with relatively common width-to-thickness, or aspect, ratios. The influence of material characteristics on penetration and perforation response and the ability of existing penetration depth prediction methodologies to forecast protective structural member performance when impacted by these fragments were evaluated. The structural element response was assessed using a cylindrical target specimen designed with a circumferential steel ring to provide radial confinement. The general relationships between concrete compressive strength and impact response, mass loss, and the benefits of fiber reinforcement in structural element protective performance were found to be similar regardless of fragment aspect ratio. Compressive strength was found to have a greater effect on impact performance, and penetration depth was found to be of greater concern as the fragment aspect ratio decreased. Some existing penetration methodologies were found to be fairly accurate when predicting impact response from lower-aspect-ratio fragments; this was not the case for high-aspect-ratio fragment impacts on the same concrete materials.

Sulfate exposure at low temperatures is known to accelerate chemical deterioration in limestone cement concrete by promoting thaumasite formation. Carbonation curing as an emerging ${\mathrm{CO}}_2$ sequestration strategy converts gaseous ${\mathrm{CO}}_2$ into mineral calcite, a key species that incurs thaumasite formation in conventional limestone cements. To clarify the risk of thaumasite sulfate attack after carbonation curing, this paper presents a laboratory characterization of carbonation-cured mortars stored in a ${\mathrm{MgSO}}_4$ solution at 6°C for up to 900 days. It was found that carbonation curing suppressed mortar swelling and enhanced material mechanical integrity and dimensional stability. The mineral thaumasite and gypsum were significantly lessened after carbonation curing. The maximum longitudinal expansion of mortar bars during ${\mathrm{MgSO}}_4$ exposure was lowered from $\sim 0.9\%$ to less than 0.06% by carbonation curing. The compressive strength of carbonation-cured mortars remained higher than 60 MPa whereas the noncarbonated control decreased to less than 2 MPa. Moreover, mortar critical pore diameter after ${\mathrm{MgSO}}_4$ storage decreased from $52.3\mathrm{nm}$ (noncarbonated) to $12.5–15.8\mathrm{nm}$ (carbonation-cured), with the total pore volume lowered by $9\%–11\%$ resulting from carbonation curing. The pore densification led by calcium carbonate precipitation tends to limit ${\mathrm{MgSO}}_4$ ingress and prevent mortar interior damage. It was concluded that the calcium carbonate converted from ${\mathrm{CO}}_2$ through carbonation curing did not promote thaumasite formation, and material durability with respect to thaumasite sulfate attack could be further enhanced after carbonation curing.

In asphalt mixtures, external loading transfer paths can be deemed as force chains. The force chains difference can be used to evaluate skeleton structure. In this study, various asphalt mixture virtual specimens were established via discrete-element method (DEM) to investigate force chains length distribution and skeleton composition. Results indicate that, although dense-graded asphalt mixtures (AC) generate a large number of force chains compared with stone mastic asphalt (SMA) and open-graded asphalt friction course (OGFC), most of them are shorter length force chains that are not conductive to transfer external loading. When asphalt mixtures were penetrated to the same depth, asphalt mixtures with smaller nominal maximum aggregate size (NMAS) need more force chains to transfer external loading. In asphalt mixtures, the increase of NMAS can help to form longer length force chains. The passing percentage of 2.36 mm (P2.36) increase can lead to form more short length force chains. In asphalt mixtures, less than 50% quantity aggregates participate in skeleton composition. The aggregates within 2.36 mm participate in skeleton composition for AC16. Skeleton composition difference between AC and skeleton type asphalt mixtures is mainly affected by P2.36.

To explore the compression behavior of confined high-performance concrete (HPC) and high-performance fiber-reinforced concrete (HPFRC), 24 HPC and HRFRC (steel fiber in 2% volume ratio) circular columns confined with spiral stirrups with compressive strengths up to 116.21 and 138.24 MPa were tested under axial compression. The investigated parameters included concrete strength in the range of 100–120 MPa, stirrups volumetric ratios in the range of 0%–2%, and steel fiber contents in the range of 0%–2%. The results indicated that all specimens fell into two damaged patterns, expansion failure and shear failure, and the stress-strain curves of the specimens had three stages: the linear, nonlinear, and descending branch. Besides, concrete strength and the volumetric ratio of stirrups mainly influenced both the load capacity and the ductility, while steel fibers mainly affected the ductility. Moreover, the Baduage model can be applied to predict the peak stress and the peak strain of confined HPC and HPFRC.

The hydration process of cementitious materials involves a thermally activated reaction that depends on the composition of the mixture and the curing temperature. The main parameter affecting the temperature variation of cast-in-place concrete is the apparent activation energy, which can be used for the efficient prediction of the temperature evolution and maturity index of hardening concrete. This paper discusses two methods to determine the activation energy of mortar specimens, whose mixture proportions are based on standards. The first approach is based on isothermal calorimetry measurements, and the second involves compression tests of mortar samples stored under four different temperature conditions. Mortar mixtures with ordinary portland cement and two rates of cement substitution with siliceous fly ash (10% and 20%) are investigated. The values of the activation energy obtained using the two approaches are compared. Finally, the effectiveness of different tests in determining the activation energy, and thus, maturity index is highlighted.

To improve the durability of cracked concrete structures in a marine environment by self-healing of cracks, the efficiency and speed of self-healing need to be increased. In this study, the interactions between organic chelation agents, i.e., tetrasodium ethylenediaminetetraacetic acid (EDTA-4Na), triethanolamine (TEA), and sodium hexametaphosphate (SHMP), and ions in seawater for accelerating crack self-healing were investigated. After self-healing for 1 day, the closure ratio of cracks of an initial width of $400\mathrm{\mu m}$ increased from 5% to 80%, 65%, and 90% when 1.5% (by weight of cement) EDTA-4Na, SHMP, and TEA were admixed, respectively. However, the distribution of self-healing products in surface cracks of specimens with organic chelation agents was nonuniform in the early stages of healing, resulting in the large scatter—in terms of the standard deviation and range—of the values of the crack closure ratio. As the self-healing products gradually formed and accumulated in surface cracks, the standard deviation and range gradually decreased. Furthermore, in specimens with 1.5% triethanolamine, after seawater immersion for 1 day, a thin about $250\text{-}\mathrm{\mu m}$-thick layer of $\mathrm{Mg}(\mathrm{OH}{)}_2$ formed at the crack mouths. During self-healing for 28 days, this thin layer extended inward up to a depth of 3 mm. To investigate the accelerator mechanism, the mineralogy of the self-healing products was characterized. When EDTA-4Na and SHMP were used, the main minerals were portlandite, brucite, aragonite, and calcite, while there was no portlandite when TEA was used.

Despite the awareness of the alkali–silica reaction (ASR) since 1940, the need for an efficient and reliable method of evaluating the potential reactivity of aggregates for use in concrete still exists. Current standards to assess the ASR susceptibility of aggregates have limitations due to inherent problems with accelerated testing conditions. This paper introduces a novel chemical reactivity index (RI) to evaluate the alkali–silica reactivity of coarse aggregates or concrete mixtures by exposing samples to a simulated pore solution with composition mimicking that expected in the concrete. Based on the mix design to be evaluated, aggregate samples are exposed to an alkaline solution of appropriate concentration and fixed amounts of CaO. The newly proposed alkali–silica RI is calculated based on the concentrations of silicon, aluminum, and calcium in solution after 21 days of exposure at 55°C. This RI, sensitive to alkali concentration and aggregate mineralogy, exhibited strong agreement with physical expansion.

The casting process creates a significant amount of waste foundry sand (WFS). Using WFS as a concrete ingredient reduces the problems associated with the dumping process of these types of wastes, removes/reduces carbon dioxide, and is also considered economical in terms of overall concrete production cost. Besides, WFS has been reported to be a critical parameter affecting the mechanical properties and workability of concrete. Hence, predicting the behavior of concrete using the development of models based on artificial intelligence (AI) algorithms derived from the laboratory data can remarkably improve the project’s efficiency in terms of cost and time. This paper assessed the performance of artificial neural networks (ANNs) to predict the strength parameters of concrete containing WFS (CCWFS). In this regard, a comprehensive laboratory database consisting of 102, 397, 146, 346, and 169 data for the slump, compressive strength, elasticity modulus, splitting tensile strength, and flexural strength of CCWFS were collected from literature, respectively. Seven different variables including waste foundry sand to cement ratio (WFS/C), water to cement ratio (W/C), fine aggregate to the total aggregate ratio (FA/TA), coarse aggregate to cement (CA/C), waste foundry sand to the fine aggregate ratio (WFS/FA), 1,000 superplasticizer to cement ratio (1,000SP/C), and age (except for slump), were selected as input. The accuracy of the models was verified by examining 11 different performance indicators. Comparing the predicted and observed data’s overlap percentage indicated that the ANN models are less error-prone than those obtained using multiple linear regression (MLR). Also, the models’ validation and uncertainty analyses showed that all models were within the permissible range. Given the performance evaluation results, it can be concluded that ANNs can be used as a reliable and accurate method for predicting the mechanical properties of CCWFS.

In the framework of recycling techniques employed in maintenance and rehabilitation projects for the road industry, cement bitumen–treated materials (CBTMs) provide good performance as well as economic and environmental benefits. Because these materials are produced with bitumen emulsion at atmospheric temperature, the environmental factors during production are extremely important to guarantee the quality of the final product. This paper focuses on the stiffness of CBTMs produced and conditioned at low temperatures, and cured in two different conditions (sealed and unsealed). The mixtures were evaluated in terms of rheological properties using complex modulus ($E^{*}$) tests performed 1 year after production. Results were modeled with an adapted version of the Di Benedetto-Neifar (DBN) model for plastic dissipation for small cycles (PDSC), accordingly called ${\mathrm{DBN}}_{\mathrm{PDSC}}$. Results showed that the curing conditions, as well as the low production temperatures, significantly changed the rheological properties of the material. In fact, mixing or compacting the mixtures at 5°C compared with 25°C resulted in a loss in stiffness of around 30% in the small strain domain. This model is a good tool to describe, in the small strain domain, such material behavior, which shows plastic nonviscous phenomena.

A new mechanical model of polyvinyl alcohol fiber–reinforced ferrocement cementitious composite (PVA-RFCC) was proposed with excellent integrated mechanical properties, which was reinforced with both PVA fiber and steel wire mesh (SWM). A series of experiments were conducted to study their mechanical properties, and a comparative analysis was also performed to evaluate their flexural toughness. The specimens of the PVA-RFCC thin plates were subjected to 4-point flexural experiments until their ultimate failure. The experimental results showed that the flexural properties of the PVA-RFCC specimens can be markedly improved compared with PVA-ECC (PVA-engineered cementitious composites) specimens. The highest increments in the initial stiffness, cracking strength, displacement ductility coefficient, and toughness of the PVA-RFCC specimens were improved by 62.4%, 174.7%, 251.0%, and 192.5%, respectively. The comparative analysis indicated that the method based on recent Chinese standards was suitable for the flexural toughness evaluation of the PVA-RFCC thin plates. A mechanical model of the PVA-RFCC thin plates was proposed. The PVA fibers had excellent prepeak behavior and the SWM had excellent postpeak behavior in the proposed mechanical model of the PVA-RFCC specimens.

Residual hydrated cement powder (HCP) produced from recovering recycled concrete is usually restricted from being directly reused in concrete due to its high water absorption and porous structure. This study aims to enhance the properties of HCP via ${\mathrm{CO}}_2$ treatment. The simultaneous impacts of ${\mathrm{CO}}_2$ treatment and water-to-cement ($\mathrm{w}/\mathrm{c}$) ratio on physical properties and microstructure of HCP were studied. The findings showed that carbonation can effectively reduce the porosity of HCP owing to the formation of calcite, and the calcite content increases with increasing $\mathrm{w}/\mathrm{c}$ ratio. Furthermore, there was a reduction in the 28-day compressive strength of paste specimens containing uncarbonated HCP, while paste containing 5%–20% of carbonated HCP (CHCP) achieved higher strength than the control paste. It is believed that the presence of calcite in CHCP leads to the formation of more stable calcium aluminate monocarbonate. The mass ratio of highly crystalline to poorly crystalline ${\mathrm{CaCO}}_3$ increased with an increase in the replacement level of CHCP, and the $\mathrm{w}/\mathrm{c}$ ratio exhibited no significant influence at a given replacement ratio.

In this study, coarse aggregates extracted from waste concrete were used as recycled coarse aggregates in a concrete mixture. Such durability properties of concrete samples as water absorption, porosity, and electrical resistance as corrosion evaluation indicators were assessed. First, estimation models for the mechanical and durability parameters of concrete were obtained using the kriging surrogate model; then, these models were evaluated using a metaheuristic optimization algorithm coupled with a simple and fast new method of reliability evaluation. Ultimately, the probabilistic optimal values of using recycled coarse aggregates to achieve an environmentally friendly concrete were calculated. The probabilistic single-objective optimization results revealed that in an environment with 70% humidity, a temperature of 23°C, and chloride ion concentrations of 0%, 3%, 5%, and 8%, the replacement ratio of recycled coarse aggregates for the different chloride ion concentrations listed above is limited to 39.12%, 38.08%, 37.21%, and 22.68%, respectively, in a water-to-cement ratio of 0.40.

The anchorage of a cable-stayed bridge failed and was subsequently replaced by another anchorage made of SAE/AISI 1045 steel. The new structural component has been assessed by using different options of failure assessment diagrams. Tensile tests were performed on both the base metal and weld metal of a welded coupon composed of SAE/AISI 1045 and ASTM A572 steels. The fracture toughness was estimated from the results of Charpy tests performed on the heat-affected zone (HAZ) of SAE/AISI 1045 steel. In addition, finite element analysis was used to determine the stress state caused by four heavy vehicles (T3-S2-R4 type) localized on one side of the column. Based on two types of postulated defects, the stress state of the tie rods, and the material fracture toughness, the failure assessment diagrams were constructed to predict the critical load that can be withstood by the anchorage and the weld metal. The results indicate that both the SAE/AISI 1045 steel and the weld metal could work safely under typical operating conditions of the bridge, even when there is a detachment of one of the anchorages. The weld metal is susceptible to plastic collapse failure, while the HAZ of the steel is susceptible to a combination of fracture and plastic collapse. It is also noted that the critical stress predicted by Option 1 on the HAZ of SAE/AISI 1045 tends to be more conservative than that predicted by Option 2. The degree of conservatism ranges from 7.8% up to 12% for a superficial flaw and from 6.2% to 15.5% for an embedded flaw.

Due to budget constraints, highway agencies tend to use thin lifts as a primary rehabilitation strategy. The construction of a thin lift requires a small nominal maximum aggregate size (NMAS), e.g., 9.5 mm or smaller. However, hot-mix asphalt (HMA) with a small NMAS is prone to rutting and/or studded tire wear. Stone matrix asphalt (SMA) is a gap-graded asphalt mixture with interlocking aggregate that enhances the mixture’s mechanical properties compared with HMA, especially with regard to resistance to both rutting and studded tire wear. Therefore, SMA mixes with a small NMAS may provide a viable solution to these distress types. Few studies have evaluated the performance of small NMAS SMA for thin overlays, especially for high levels of studded tire traffic. To address this gap in the literature, this study assessed the laboratory performance of 9.5-mm NMAS SMA compared with that of commonly used 12.5-mm NMAS SMA and 9.5-mm NMAS HMA mixtures to determine the feasibility of using 9.5-mm NMAS SMA in thin lift overlays subjected to heavy traffic in the State of Washington, where the use of studded tires is widespread in winter. Three types of mixtures were tested for their resistance to bottom-up fatigue cracking, top-down fatigue cracking, thermal cracking, rutting and moisture susceptibility, and studded tire wear. The resistance to top-down fatigue cracking of the 9.5-mm SMA was comparable to that of the 9.5-mm HMA and the 12.5-mm SMA. The 9.5-mm HMA and 9.5-mm SMA had comparable resistance to bottom-up fatigue cracking and performed better than the 12.5-mm SMA. Both the 9.5-mm HMA and the 9.5-mm SMA had better thermal cracking resistance than the 12.5-mm SMA. The 12.5-mm SMA had better rutting and moisture susceptibility resistance than the 9.5-mm SMA and 9.5-mm HMA. Both the 9.5-mm SMA and 12.5-mm SMA had comparable resistance to studded tire wear and performed better than the 9.5-mm HMA. Overall, the results showed that 9.5-mm NMAS SMA is a viable material for thin-lift overlays, outperforming 9.5-mm NMAS HMA in terms of resistance to rutting, moisture, and studded tire wear. Further studies are needed to assess the field performance, constructability, and life-cycle costs of 9.5-mm SMA.

Studies on the characterization and performance of residual sugarcane bagasse ash (SCBA) obtained from high-temperature cogeneration boilers in concrete are highly limited. This study investigated the pretreatment process and optimization of SCBA collected from high-temperature boilers by various physicochemical methods. The effect of recalcination and grinding on the physical and mineralogical properties of SCBA were also examined. The percentage replacement of cement with SCBA was optimized using packing density and flow. The performance of optimized binder with combinations of cement and SCBA was validated through compressive strength of mortar specimens. From the results, it was observed that SCBA from high-temperature boilers can be used as a supplementary cementitious material with minimal processing efforts, and a 15% level of replacement is suggested as the optimum level for SCBA-blended cement. Based on the investigation, a framework with a step-by-step procedure including pretreatment and optimization methods is suggested for the use of SCBA.

Ultrafine nanosilica particles have the potential to produce concrete under low temperatures. In this study, nanomodified concrete was cured under freezing temperatures ($-10°\mathrm{C}$ and $-20°\mathrm{C}$) using insulation blankets without or with phase change material as conventional and hybrid protection methods, respectively. Six mixtures, incorporating general use and high early strength cements, fly ash (20%), nanosilica (6%), and cold weather admixture system (antifreeze/accelerator), were tested. The mixtures were assessed based on setting times, compressive strength, fluid absorption, and resistance to frost damage in water and salt solution. Moreover, thermogravimetric and mercury intrusion porosimetry were conducted to assess the hydration and microstructural development of concrete under these freezing temperatures. The nanomodified concrete protected by the hybrid system, even with the presence of 20% Class F fly ash, indicated improved hardening, mechanical, and durability performance; thus, such a mix design and protection method might present a viable option for concrete applications in cold conditions down to $-20°\mathrm{C}$.

Fiber-reinforced foamed lightweight soil is a new type of material that is mixed with cement, foam, polypropylene fiber, and water, and has been applied in the reinforcement of soft soil subgrade. However, it has not yet formed a complete theoretical system. Currently, it is imperative to explore the fiber-reinforced foamed lightweight soil. In this paper, the shear strength characteristics of polypropylene fiber-reinforced foamed lightweight soil with different reinforcement ratios and confining pressures are compared using the global digital systems (GDS) triaxial shear test. It is found that the triaxial shear strength and cohesion first increases, then decreases with the increase of reinforcement ratio, the maximum of which occurs at 0.75% reinforcement rate. The internal friction angle of fiber-reinforced foamed lightweight soil is less affected by the reinforcement ratio. This indicates that the cohesive force of the material is the main factor that affects the strength of the polypropylene fiber-reinforced foamed lightweight soil. The strength reduction rate presents an obvious downward trend with the increase of the reinforcement rate. It reaches from about 40% to 10%, and keeps stable at 10%. From investigating the influence of reinforcement ratio and confining pressure on strength parameters, the research obtains the law of crack propagation of fiber-reinforced foamed lightweight soil and establishes the stress–strain relationship equation. The constitutive equations for the strength parameters of foamed lightweight soil in terms of reinforcement ratio and confining pressure are proposed. After normalizing the experimental data of different reinforcement ratios, the study obtains the stress–strain equation of fiber-reinforced foamed lightweight soil and variation of equation parameters with the influence of stiffening rate and confining pressure.

The objective of this research was to investigate the effect of degree of blending on the rutting and fatigue performance of 100% reclaimed asphalt pavement (RAP) content mixtures. Recycled asphalt binders were extracted from the mixtures using a stage-extraction technique and evaluated. Five commercially available rejuvenators were evaluated based on a homogeneity index and the aging rate to select the best (RA1) and the worst (RA2) performing rejuvenator, respectively. Five mixtures were designed and tested at three aging levels to evaluate the selected rejuvenators. Mixtures were tested using the loaded wheel tester (LWT) and the Florida indirect tensile test (IDT) for high- and intermediate-temperature performance characterization, respectively. The LWT showed that the short-term aged recycled mix exhibited a better rutting resistance and less moisture susceptibility than the virgin mix when its high-temperature performance grade (HTPG) was 6°C higher than the virgin mix. However, the level of diffusion, as measured by the homogeneity index ($I_h$), did not seem to be a determining factor in moisture susceptibility or rutting depth. Also, the applied aging levels did not seem to affect the rut depths for RAP mixtures at lower rejuvenator dosage levels (RAP + 7.9% RA1 and $\mathrm{RAP}+6.5\%\mathrm{RA}2$). IDT results showed that the virgin and 100% RAP mixtures exhibited average energy ratio (ER) values higher than the critical value of 1, indicating satisfactory crack initiation resistance behavior. Mixture R1 (100% RAP mixtures recycled with a low dose of RA1), with the highest $I_h$, exhibited the best cracking performance compared to the virgin mixture. It is recommended that cracking and rutting performance be plotted against the HTPG to determine the target HTPG of the recycled mix. The target HTPG of the recycled mix can then be obtained by adjusting the rejuvenator amount. In this research, the target HTPG of the recycled mix was 75°C or higher. It should be noted that this type of analysis is mix- and rejuvenator-specific and should be conducted during the mix design until a sufficient degree of confidence and familiarity with the rejuvenator is reached.

Steel slag accumulation is one of the major issues for steel manufacturing companies, because it occupies a large portion of a company’s yard. Investigators have suggested various applications for using slag in other industries. There is great potential for using slag as an aggregate in road and railway construction. Evidence demonstrates the compatibility of slag for road base and subbase construction. However, the use of slag as a subballast for railway construction has not been investigated thoroughly. This research studied the application of slag to subballast railway construction. A railway subballast layer requires a high shear strength, which is greater than slag’s shear strength. Therefore, the authors modified the slag with 1%, 2%, and 3% gilsonite, or natural binder, and performed Los Angeles abrasion, direct shear, and California bearing ratio tests on the modified slag. The results of all experiments indicated significant improvement in the modified slag’s shear strength properties, which makes gilsonite-modified slag a potential replacement for traditional subballast material.

Foamed asphalt cold-recycled mixtures have been increasingly used in China. However, the interlayer shear performance between the foamed asphalt cold-recycled layer and its top and bottom layers is still not clear. In this study, we explored factors affecting the interlayer shear performance of foamed asphalt cold-recycled layers (FACRL). Regarding the interlayer performance between the foamed asphalt cold-recycled layer and cement-treated base (CTB), the optimal content of the prime coat asphalt was $0.8\mathrm{kg}/{\mathrm{m}}^2$, and the prime coat asphalt was recommended to be applied on the surface of the base as soon as the base was paved. Styrene-butadiene-styrene (SBS)-rubber modified asphalt with a content of $2.3\mathrm{kg}/{\mathrm{m}}^2$ and aggregates with a size range of $4.74–9.5\mathrm{mm}$ was recommended for use in the seal coats. The aggregates used in the seal coat were recommended to be premixed with a 0.3% asphalt binder to improve the adhesion and to be paved with a spreading area of 65%. Regarding the interlayer performance between the foamed asphalt cold-recycled layer and top hot-mix asphalt (HMA), the interlayer shear strength and fracture energy increased and then decreased with the added tack coat asphalt. The shear strength and fracture energy of the interlayer at 50°C was only 20% and 8% of that at 25°C, respectively. The optimum usage percent of the tack coat binder is $0.4\mathrm{kg}/{\mathrm{m}}^2$.

An ultrathin wearing course (UTWC) is a preventive maintenance treatment method for a road surface which can improve the safety and comfort of driving by providing superior skid resistance. However, the skid resistance is a concern after multiple years of loading cycles. The role of coarse aggregate in preventing the skid resistance deterioration of an UTWC is not fully understood. This study determined the effect of coarse aggregate types and nominal maximum aggregate size (NMAS) on the skid resistance deterioration of an UTWC. Different types of stone mastic asphalt (SMA), which are used in three kinds of coarse aggregates (diabase, limestone, and basalt) and three kinds of NMAS coarse aggregate (SMA-5, SMA-8, and SMA-10), were prepared for the test. A Model Mobile Load Simulator 3 (MMLS3) was used to simulate repeated vehicle loading and abrasion. After specific loading cycles, the skid resistance of an UTWC was measured by the British pendulum number (BPN) test and the sand patch test. The BPN and mean texture depth (MTD) were chosen to evaluate the skid resistance of the UTWC. The results showed that the BPN value of an UTWC is sensitive to the type of coarse aggregate. The skid resistance of SMA-8 with diabase and basalt is better than the performance of SMA-8 with limestone. The results of grey relational analysis (GRA) showed that the loss polishing stone value (LPSV) index should be used to evaluate the coarse aggregate of the UTWC. The MTD value of an UTWC is sensitive to the NMAS. The skid resistance of SMA-8 and SMA-10 is better than that of SMA-5. The skid resistance deterioration (BPN and MTD) of UTWC was fitted by an exponential model. The measured data of the Guangxi Nanyou expressway for 5 years showed that the exponential fitting equation can describe the attenuation process of the skid resistance of an UTWC in actual engineering. The findings will play an essential role in selecting coarse aggregates in an UTWC.

Foamed concrete backfill has been proved to be an ideal material to improve the bearing capacity of underground engineering structures with the exception of buried pipelines. In order to study the role of foamed concrete backfill in improving the antiexplosion performance of buried pipelines, ANSYS/LS-DYNA finite-element software is used to analyze the dynamic response of buried pipelines under explosion load. The stress, velocity, acceleration, and displacement responses of the elements and nodes at the specified position on the pipe cross section and pipe shaft are investigated. The results show that after adding foamed concrete backfill, the effective stress, velocity, acceleration, and displacement peak attenuation reach 3%–8%, 4%–20%, 3%–22%, and 10% respectively, indicating that foamed concrete backfill can effectively improve the antiexplosion performance of buried pipelines. In this paper, the influence of physical and mechanical parameters of backfill on the dynamic response of pipelines is investigated as well.

Concrete compositions demand products in order to meet certain requirements and specific properties. For the production of self-compacting concrete, a certain amount of fine materials and/or chemical products should be added to the mix as viscosity modifying agents that will enable a mixture with enough flowability, and that should show stability. This paper presents preliminary results of a novel viscosity modifying agent based on a biopolymer (chitosan) found in the residues of the fishing industry. The effects of the product were tested in cement pastes by means of typical flow tests and rheological measurements. The new admixture promotes an increase in the plastic viscosity and yield stress of fluid cement pastes resulting in stable and fluid mixtures.