Journal of Materials in Civil Engineering

A literature review of the latest advancements in recycled aggregate concretes with regards to identifying properties, improving performance, and numerical modeling is presented in this paper. Although the properties of recycled aggregate concrete are widely considered to be inferior to those of natural aggregate concrete, research in the field still is of merit due to growing awareness of environmental concerns relating to the concrete construction and demolition industry. In addition, some methods have been proposed to improve the properties of recycled aggregate concrete, with the use of geopolymer binders in place of portland cement showing the most potential. In addition to further research regarding the improvement of properties of concrete made with recycled aggregates, the development of numerical models that accurately represent the behavior of recycled aggregate concrete under loading are essential to the industrial implementation of the technology.

Cement-stabilized macadam is an important highway construction material. To fully understand the reinforcing and toughening functions of fibers in cement-stabilized macadam, the influence of the concentration and length of polyvinyl alcohol (PVA) fibers on the performance of cement-stabilized macadam was investigated. Through indoor compressive tests and splitting tests, the changes in the splitting and compressive strengths of cement-stabilized macadam with different fiber lengths and contents were compared, and the influence of fiber length and content on the compressive and splitting strengths was determined. The results showed that the compressive and splitting strengths of cement-stabilized macadam were considerably improved by PVA fiber addition; fibers of varied lengths and contents had different effects on the compressive and splitting strengths. The increase in the compressive and splitting strengths of cement-stabilized macadam was the greatest with a fiber length of 12–24 mm and concentration of $0.6–0.9\mathrm{kg}/{\mathrm{m}}^3$. The experimental results can provide a theoretical basis for the application of PVA fibers in cement-stabilized macadam.

The loss of strength and durability because of the presence of moisture leads to moisture damage in asphalt mixtures. Differences in the drinking water characteristics, used in moisture sensitivity tests, and runoff water, which causes moisture damage in the asphalt pavements, motivated the present study on the effect of air pollutants, dust, and soot on pavement surface (as the surface contamination) on the acidity (pH) of rainfall-runoff. In addition, the effect of a change in the pH of runoff was investigated on the moisture damage of HMA samples. In this study, the modified Lottman method was employed as the common test of moisture damage in HMA and concepts of the thermodynamic theory were used to investigate the mechanism of changes in the process of stripping. Based on the results, the pH of the rainfall-runoff was acidic in areas with heavy traffic in which the accumulation of soot was dominant, and basic in areas with light traffic in which the accumulation of dust particles was more probable. The results of mechanical tests revealed that pH fluctuations reduced the asphalt mixture’s strength in wet conditions and increased the potential for moisture sensitivity. Also, more differences could be observed in the performance of asphalt mixtures at neutral pH and higher and lower values of pH during higher freeze–thaw cycles, which can be very important in areas with more rainfall cycles. The surface free energy (SFE) method results showed that the acidic and basic runoff increased the energy released at the asphalt–aggregate interface and the tendency of both acidic and basic aggregates to moisture, which led to decreasing the moisture strength of asphalt mixtures. In addition, the nonpolar properties of surface free energy of runoff were increased in both acidic and basic environments. Variation in water properties, in addition to the change in the runoff acidity and weakening of the aggregate-bitumen adhesion, also caused a weakening in the bitumen film and increased the cohesion failure. Also, statistical analysis results showed that in addition to the type of contamination, the type of aggregate affects the characteristics of runoff and consequently the performance of an asphalt mixture against moisture damage in different chemical conditions.

This study investigated the influence of preconditioning on the strength and microstructural development of carbonated reactive MgO cement (RMC)-based concrete mixes. The hydration mechanisms of the prepared formulations were studied via isothermal calorimetry. Compressive strength and porosity measurements were conducted to assess sample performance. X-ray diffraction (XRD), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM) were used for the microstructural analysis and quantifications of phases within each sample. Subjecting RMC samples to moderately elevated temperatures (50°C–60°C) for 1–2 days before the start of the curing process enhanced the hydration process. This increase in the degree and rate of the hydration reaction increased the amount of phases available for the subsequent carbonation reaction. The increase in the content and size of hydromagnesite [$4{\mathrm{MgCO}}_3{·\mathrm{Mg}(\mathrm{OH})}_2{·4\mathrm{H}}_2\mathrm{O}$] crystals led to denser microstructures, thereby facilitating higher strengths in samples subjected to preconditioning. The obtained results showed that the application of this practical approach to the preparation of RMC-based samples can not only present a more efficient use of the binder component, but also enable the increased sequestration of ${\mathrm{CO}}_2$ within these samples.

Textile concrete was modified to create eco-friendly, low-shrinkage material with higher density, compressive and tensile strength, and freeze–thaw resistance characteristics. Shrinkage characteristics of the cement paste and textile concrete based on it were established in the early stages of curing using a specially assembled device, and the pozzolanic activity of mineral additives was carried out by the absorption of lime from a solution. In addition, the microstructural, morphological, and thermal properties of such concrete at 28 and 72 days of curing were determined. When analyzing the microstructure of the composite binder specimens, there was a significant decrease in the number of microcracks formed and their sizes compared with the ordinary cement paste. Developed polymineral composite binders demonstrate a tendency to reduce the aggressive influence, which is also confirmed by microscopic examination of the surface of fiberglass located in the cement paste of composite binders for 72 days. The nature of the influence of various types and dispersion of superabsorbent polymers on plastic shrinkage in cement paste has been established, which consists of reducing the negative capillary pressure through the loss of superabsorbent polymers, which helps to reduce shrinkage deformations of a fresh system and, as a result, reduce the number of destructive processes at the initial stage of structure formation.

With the continuing increase in the use of recycled asphalt pavement (RAP) and recycled asphalt shingle (RAS) for highway construction, there is a concern over how much of the aged asphalt binder inside RAP/RAS can be blended into virgin asphalt binder. In this study, the RAP/RAS binder mobilization rates of 13 different mixtures produced by three different types of asphalt plants in Tennessee were determined using fluorescence microscopy and gel permeation chromatography (GPC). A multiple regression model was developed to explore the factors critical to enhancing the mobilization rate of the RAP/RAS binder. Results showed that the RAP/RAS binder mobilization rate was significantly lower than 100% for most mixtures, indicating that only part of the RAP/RAS binder was mobilized during the production process. The mixing and delivery temperatures had significant influence on the mobilization rate of RAP/RAS binder. In addition, the aging degree of RAP/RAS binder also significantly affected the mobilization rate.

This study developed a high-strength and high-ductility engineered cementitious composite (HSHD-ECC) using coarse river sand (RS) for the first time. Within this newly developed ECC, saturated multiple cracking was achieved based on the flaw effect of coarse RS. The maximum size ($\mathrm{4,750}\mathrm{\mu m}$) of RS was almost 20 times that of ultrafine silica sand (USS) in conventional ECC. The compressive strength of river sand HSHD-ECCs exceeded 115 MPa. Moreover, the tensile strength and strain were more than 12 MPa and 9%, respectively. More importantly, fully distributed microcracks with spacing less than 1.3 mm could be observed on the RS-HSHD-ECCs. The pseudo-strain-hardening (PSH) index and PSH intensity were calculated to theoretically explain saturated multiple cracking and high ductility behavior. Also, it was found that coarse RS can be regarded as a flaw in HSHD-ECC and thus tailor the pre-existing flaw in the matrix. The agreement between theory analysis and experiments showed that coarse RS was preferable for application in HSHD-ECC to achieve the saturated multiple cracking and high ductility.

In this study, the fatigue performance of cement-stabilized crushed gravel (CSCG) is examined. The mechanical strength of CSCG specimens formed using the vertical vibration compaction method (VVCM) or quasi-static compaction method (QSCM) is compared with that of field core samples (FCS). Cylindrical specimens formed using VVCM are used to study the splitting fatigue performance, and a fatigue equation is established using Weibull distribution. The factors that influence the fatigue performance, namely gradation and cement content, are also analyzed. The results show that the correlation of mechanical strength between FCS and CSCG formed using VVCM is as high as 90%, whereas that between FCS and CSCG formed using QSCM is $<50\%$. The splitting fatigue life of CSCG obeys the two-parameter Weibull distribution. The results also show that gradation and cement content have significant effects on the fatigue performance of CSCG. For a stress level of 0.65 and reliability of 50%, compared with the fatigue life of CSCG with suspended dense gradation, those with skeleton dense gradation improved by 22.4% and 9%, and the fatigue life of CSCG significantly increased by 44.5% and 28.6% when the cement content was 3% and 5%, respectively.

To develop a new modification method with environmentally friendly and seismically resistant characteristics for saturated loess foundations, lignin extracted from paper industrial wastes was selected for mixing into the loess. Mixtures with different lignin contents were prepared under static pressure. A series of dynamic triaxial tests were performed by applying sine loads after the lignin-modified loess specimens were saturated and consolidated on the dynamic triaxial apparatus. The microstructural images and the mineral components of the modified loess with different lignin contents were investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Based on the test results, the variation regularity of the dynamic residual deformation and the dynamic pore water pressure of the lignin-modified loess was analyzed. The microstructural characteristic parameters of the lignin-modified loess were extracted, and the relationship between these parameters and the lignin contents was obtained. Based on the dynamic triaxial test, the SEM, and the XRD results, the mechanical mechanism of the liquefaction resistance of the lignin-modified loess is discussed. The results show that lignin can significantly improve the resistance of cyclic shear deformation of the saturated loess and can effectively control the increase of the pore water pressure. When the lignin content was 4%, the liquefaction resistance of the lignin-modified loess was the most significant. Compared with the unsaturated compacted loess, the number of small and micropores in the lignin-modified loess increased significantly, and the apparent pore ratio decreased. Additionally, the arrangement sequence of pores deteriorated, the pore structure became more complex, and the pores were more compactly arranged. However, when the lignin content was higher than 4%, the microstructural characteristic parameters reflected a reduction in compactness of the lignin-modified loess. No other new minerals were formed in the lignin-modified loess except for a small amount of albite (${\mathrm{NaAlSi}}_3{\mathrm{O}}_8$), which was generated by the ion exchange between the lignin and loess. Furthermore, the liquefaction resistance mechanism of the lignin-modified saturated loess mainly included the filling and cementation of the lignin, thinning of the electric double layer in the modified loess, reinforcement of the lignin fiber, adsorption of fine particles and water by the fiber, and ion exchange between the lignin and loess.

The employment of cold plasma surface treatment on crumb rubber (CR) particles is expected to improve the performance of rubberized binders. In this study, the viscoelastic properties of plasma-treated rubberized binders were characterized by the multiple stress creep recovery (MSCR) test. The test results of two response parameters, namely, nonrecoverable creep compliance and percent recovery, indicated a positive effect of plasma treatment on the rutting resistance and stress sensitivity of rubberized binders. The rutting resistance of most rubberized binders met the criteria of the specification, and a nonlinear viscoelastic behavior of binders was observed during MSCR testing. Also, the modeling of the creep and recovery response was satisfactorily conducted using the Burgers model and modified power law model, respectively. However, the Burgers model lacked accuracy in predicting the strain response in the recovery phase, while the modified power model was indeed better with the consideration of nonlinearity. Further studies reported some pronounced correlations between the model parameters and response parameters. Finally, the creep and recovery behavior of the rubberized binder was fairly related to its large molecular size (LMS) fraction quantified by a gel permeation chromatography (GPC) test.

Excessive surface temperature of asphalt pavement in summer is one of the main causes of urban heat islands (UHIs), so reducing pavement temperature is a potential research perspective for alleviating the UHI effect. This paper proposes a new type of asphalt-mix design. The thermal diffusivity of asphalt pavement is effectively enhanced by replacing the limestone coarse aggregate (LCA) of traditional asphalt mixture with quartzite coarse aggregate (QCA) with high thermal conductivity, which accelerates the heat diffusion of pavements to reduce the pavement temperature and the air temperature near the ground. By designing the material composition of high thermal diffusivity asphalt concrete (HTD-AC) with different replacement ratios of QCA, the asphalt concrete achieves a higher thermal diffusivity than traditional asphalt concrete. In addition, the mechanical properties of QCA and its adhesion to asphalt were tested. It was proved that the QCA meets road requirements, and QCA can be used in the preparation of HTD-AC. Moreover, asphalt pavement with high thermal diffusivity was verified to have good service performance, which effectively guarantees the quality and safety of urban traffic.

Adobe has been used as an economic building material since ancient times and continues to be used today, particularly in developing countries. Due to its sustainability credentials, interest in adobe as an alternative to traditional fired masonry has gathered pace. In order to develop guidance on the design of new adobe structures and the strengthening of existing ones, a detailed understanding of the material’s properties is required. Currently available studies on adobe material often concentrate on one particular property. Due to the differences in adobe makeup, correlation of the existing results can be problematic. To address this, a detailed experimental study using one consistent, reproducible and realistic adobe mix is presented here. The material behavior in compression (including strength gain with time), tension, and shear is studied. For the first time, the interface between the adobe units and mud mortar is investigated in direct tension and in shear, including the effects of coexisting compression. Crucially, parameters such as tensile and shear fracture energy, often excluded from existing experimental work, are evaluated. The data provided herein will enable development of accurate numerical and analytical models to describe adobe masonry structural behavior.

Graphene oxide (GO) is a nanomaterial that is characterized by a two-dimensional, atomically thin, honey-combed lattice. Studies over the years have indicated potential applications of GO for improving performance characteristics of asphalt binder. This study attempts to explore the impact of GO on various chemical and rheological characteristics of unmodified asphalt binder (AC30). GO was added to AC30 over varying dosages of 1%, 2%, and 3% by weight. Carbon (C), hydrogen (H), and nitrogen (N) determinations and Fourier-transform infrared (FTIR) spectroscopy aided in understanding the chemical interaction of GO with AC30. Further, the effect of GO on dynamic viscosity was also evaluated. Rutting performance of GO-modified AC30 was studied using the multiple stress creep recovery (MSCR) test, whereas fatigue performance was evaluated based on the linear amplitude sweep (LAS) test. Additionally, yield energy GO-modified AC30 was comprehended using the binder yield energy test (BYET). CHN determination and FTIR spectroscopy indicated that modification of GO is mostly physical in nature. An improvement in aging resistivity was observed due to incorporation of GO. GO was observed to increase dynamic viscosity. Improvement in both rutting and fatigue performance of AC30 was observed but different optimum dosages of GO were obtained: 1% for maximum rutting performance and 2% for maximum fatigue performance. Enhancement in yield energy and recovery potential was also observed.

This study evaluated the impact resistance and mechanical properties of a number of optimized self-consolidating concrete mixtures developed with lightweight expanded slate aggregate. The investigated parameters included different lightweight expanded slate types (fine and coarse), different aggregate volumes, and various binder contents (500, 550, and $600\mathrm{kg}/{\mathrm{m}}^3$). The mechanical properties of all developed mixtures were assessed using the compressive strength, splitting tensile strength, flexural strength, and modulus of elasticity. On the other hand, the impact resistance for the tested mixtures was evaluated by a drop-weight test conducted on both cylinders and small-scale prism beams. The results showed that despite the relatively low strength of lightweight aggregates, using a ternary binder material system (cement, metakaolin, and fly ash) helped to develop successful lightweight self-consolidating concrete mixtures with a density ranging from 1,850 to ${\mathrm{2,000}\mathrm{kg}/\mathrm{m}}^3$ and a strength of at least 50 MPa. Expanded slate fine aggregate showed better mechanical properties and impact resistance when compared to expanded slate coarse aggregate. The results also indicated that with the absence of self-compactability restrictions, it was possible to develop LWVC mixtures, with a density of up to $\mathrm{1,784}\mathrm{kg}/{\mathrm{m}}^3$ and compressive strength of around 40 MPa.

Thermal or low-temperature cracking is caused by extremely cold weather or temperature cycles in cold climates. This distress can be controlled by, among others, bitumen modification. In light of the positive performance of natural and synthetic fibers in previous studies, this study investigated the effect of ceramic fiber, a low-cost and available mineral fiber, as a bitumen modifier on the low-temperature cracking potential of asphalt mixtures. Bending beam rheometer (BBR) and semicircular bending (SCB) tests were performed to evaluate the rheological properties of bitumen and low-temperature performance of asphalt mixture, respectively. In addition, direct tensile strength tests using the pull-off method for cohesive failure and adhesive failure conditions, as well as thermodynamic theory based on the surface free energy (SFE) method were used to determine the mechanism of impact of ceramic fibers on bitumen and asphalt mixture properties at low temperature. The results indicated that the application of ceramic fibers up to 0.4% by weight of bitumen reduced creep stiffness and increased $m$-value, thereby making the rheological properties of bitumen suitable for one grade lower than the control bitumen. The results of the SFE method demonstrated that the application of ceramic fibers increased the acidic component and decreased the total SFE of the control bitumen, thus increasing the free energy of adhesion in samples with both acidic and basic aggregates. Also, bitumen modification increased the nonpolar SFE, and consequently increased the total SFE, thereby improving bitumen resistance to cohesive failure. The results of the pull-off test at the thick and thin bitumen film conditions indicated that the application of ceramic fiber enhanced the resistance to cohesive and adhesive failure. Statistical analysis also revealed that thermodynamic variables played an effective role in the type of failure. Based on the results of the SCB test parameters, the use of ceramic fiber, especially up to 0.4% by weight of bitumen, improved all three parameters of load peak, fracture energy, and fracture toughness, thus decreasing the potential of low-temperature cracking in samples made with the modified bitumen. Also, based on the statistical analysis, the performance parameters of the asphalt mixture against low-temperature cracking were efficiently dependent on the thermodynamic variables obtained from the SFE components of bitumen and aggregate.

Crumb rubber modifier (CRM) has been applied widely in modified asphalt production in the pavement industry and demonstrates many performance advantages. Further, its use makes it possible to recycle scrap tires and reduce the consumption of raw materials. However, CRM asphalt mixtures demand higher construction temperatures than do conventional asphalt mixtures because the CRM asphalt binder has higher viscosity, which increases energy consumption, emission of greenhouse gases, and disintegration of the crumb rubber. In this study, sodium hypochlorite (NaClO) was introduced to functionalize the CRM particles’ surface to alleviate these associated problems. The CRM particles’ surface was activated using different amounts of NaClO, and the microscopic morphology of the activated CRM was measured using scanning electron microscopy (SEM). The size characteristics of the two types of CRM (activated and inactivated) were measured using the Brunauer, Emmett, and Teller (BET) test. The Brookfield viscosity at $180°\mathrm{C}$ and rheological properties of CRM asphalt binders with different activated CRM were measured. In addition, the correlation between pore size characteristic and rheological properties was calculated statistically. Subsequently, a rougher surface microscopic morphology was observed for CRM activated with NaClO solution than without. The pore characteristics’ indices (cumulative pore volume, cumulative pore area, most probable pore size, and mean pore size) decreased generally with lower amounts of NaClO and then increased when the NaClO exceeded a certain amount. Using NaClO solution to produce activated CRM can improve both the workability and rutting resistance issues associated with the application of CRM asphalt binder. The test results and correlation analysis indicated that the pore characteristics are a key factor for activated CRM to reduce viscosity values and increase the rutting factor significantly.

The dispersibility of graphene is one of the determining factors which affect its efficacy in practice. In the present work, highly dispersed graphene [namely, titanium dioxide (${\mathrm{TiO}}_2$)-reduced graphene oxide (RGO) nanocomposites] was fabricated by a novel ${\mathrm{TiO}}_2$ intercalation method to the RGO. Such a highly dispersed graphene with a marginal doping amount of the solid aluminosilicate precursors (i.e., 0.01% and 0.02% by weight of geopolymer paste) was used to modify geopolymer pastes. Experimental results showed that such ${\mathrm{TiO}}_2$-RGO nanocomposites can effectively improve mechanical properties of geopolymer matrix, especially the flexural strength, which increased 85%–125% with 0.02% by weight graphene. The graphene enabled the reduction of concentrated stress, which prevents the development of cracks in geopolymer matrix. Compared with the control specimens, the graphene-modified geopolymers are more compact and denser due to the refined pore structures of graphene/geopolymer composites, which is confirmed by the scanning electron microscopy and mercury intrusion porosimetry results.

Expansive soils are liable to cause damages to engineering structures and subsequent yearly repairs worth billions of dollars worldwide. Given the extensive global occurrence of expansive soils, it is imperative to restrain the natural expansive and compressibility behavior of such soils to a controllable extent. Consequently, the present study examined the expansive and compressibility behavior of lime-stabilized marine clays reinforced with 0.5%, 1%, 1.5%, and 2% natural coir fibers (CF) and synthetic polypropylene fibers (PPF). Accordingly, a series of one-dimensional (1D) swell-consolidation and linear shrinkage tests were conducted on untreated and treated 7-day cured clay samples to examine their volume-change behavior. Results indicated an optial reduction in the swelling potential of the lime-stabilized clay upon the addition of 1% CF or 1.5% PPF and a maximum reduction in the linear shrinkage of the clay upon the addition of 2% CF or 1.5% PPF, respectively. Similarly, an optimal reduction in the compressibility of the lime-stabilized clay was achieved upon the addition of 2% CF or 1% PPF. The microstructural analysis showed the formation of cementation compounds (C-S-H and C-A-H) owing to the clay-lime interaction. The reported findings engaged the concurrent application of lime and natural/synthetic fibers to improve the expansive and compressibility behavior of soft marine clayey deposits.

Phosphogypsum (PG) is an industrial solid waste which is difficult to dispose of and can cause environmental pollution. This paper investigated a low-energy-consumption preparation from PG of an environmentally friendly building material. PG was converted to $\alpha$ hemihydrate gypsum ($\alpha \text{-}\mathrm{HH}$) using the nonautoclaved method. Then the $\alpha \text{-}\mathrm{HH}$ from PG (PGHH) was mixed with different dosages of fly ash and/or cement to obtain PGHH–fly ash–cement (PFC) cementitious materials, enhancing the water resistance of the corresponding hardened material. Results showed that the optimal mix proportion (by weight) of PGHH:fly ash:cement was $70:24:6$ when the water resistance and mechanical strength properties of the corresponding hardened materials were comprehensively compared. With this proportion, the 3-, 28-, and 90-day softening coefficients were more than 25%, 50%, and 70% higher than those of the control group (PGHH alone). It was demonstrated that the ${\mathrm{Ca}(\mathrm{OH})}_2$ from hydration of cement can activate the pozzolanic reaction of fly ash, thus forming ettringite and C─ S─ H gel and making the hardened materials denser and more waterproof. The prepared PFC cementitious material has application as a building material which can provide a low-energy-consumption and environmentally friendly method for utilizing PG.

The kinetics of subcritical crack growth (SCG) in hardened cement pastes attacked simultaneously by mechanical damage and calcium leaching was experimentally investigated by a novel test approach in a recent study. Anchored at the experimental benchmarks obtained in the macro- and microcharacterization, material modeling and numerical simulation for SCG under calcium leaching were performed. To utilize the unique physical or chemical laws involved in each individual deterioration process, a two-dimensional (2D) discrete model consisting of two orthotropic lattice systems was constructed to approximate mesostructures of the hardened cement pastes. The two lattice systems were interlinked by the physical variable—the porosity of hardened cement pastes—which evolves with the interaction of matrix cracking and cement dissolution. The proposed material model was implemented in Abaqus through user subroutine VUMAT. The artificial time scale, which allows coarse temporal discretization, was used in the numerical framework and served as the basis for a hybrid of implicit and explicit formulation. This discrete model can realistically describe SCG in hardened cement pastes subject to coupled chemomechanical deterioration.

Large quantities of waste toner (WT) are generated annually either due to the incessant manufacturing process or from copying machines. Disposal of WT is primarily in landfills, which deteriorates the environment. This study attempts to overcome this predicament by utilizing WT for asphalt pavement construction by means of incorporating it in asphalt binder. The effect of WT on rheological properties of asphalt binder was explored in this research. An unmodified asphalt binder AC30 was adopted and modified with three contents of WT (7%, 14%, and 21% by weight). Tests including high-temperature performance grade (PG), temperature sweep, frequency sweep, and multiple stress creep and recovery (MSCR) were performed in this study. Mixing and compaction temperature was observed to marginally increase on introduction of WT. The addition of WT was perceived to cause a bump in high-temperature PG of AC30 binder. Improvement in rutting resistivity of AC30 binder was recorded. However, a degradation of fatigue resistance was observed. Master curves indicated an enhancement in complex shear modulus ($|G^{*}|$) and reduction in phase angle ($\delta$) at low frequencies due to incorporation of WT. However, at higher frequencies, convergence of the curves was observed. MSCR analysis indicated that WT addition enhanced percent recovery ($R$) and decreased nonrecoverable creep compliance ($J_{nr}$). Overall, the addition of WT was observed to cause changes in the rheological behavior of AC30 binder and an improved resistance to rutting at high temperature.

This study investigated the engineering properties and durability of high-performance recycled aggregate concrete (HPRAC) specimens. The specimens were prepared using alkali-activated slag with varying proportions of fly ash (FA) (Category 1) and reactive MgO (Category 2). The first category included specimens in four subcategories in which FA replaced ground granulated blast furnace slag (GGBFS) in the binder at ratios of 0%, 15%, 30%, and 45% by weight. The second category included specimens in three categories in which a group mixture containing 15% FA and 85% GGBFS was modified by 2.5%, 5%, and 7.5% reactive MgO (based on the total weight of FA and GGBFS). The engineering properties of HPRAC specimens were assessed using tests for slump, compressive strength, splitting tensile strength, water absorption test, ultrasonic pulse velocity (UPV), electrical surface resistivity (ESR), thermal conductivity, and rapid chloride ion penetration (RCPT). All the HPRAC specimens exhibited good strength and durability at 91 days of curing. However, the engineering properties of the concrete samples were significantly affected by the levels of added FA and MgO. Although the CF15M5 mixture exhibited the highest compressive strength and best attributes of the HPRAC specimens, its performance in terms of the tested variables still was inferior to that of natural aggregate concrete.

The objective of this paper is to investigate the effect and mechanism of three types of fibers—basalt fiber (BF), polyester fiber (PF), and lignin fiber (LF)—on the pavement performances of asphalt mixtures containing basic oxygen steel making furnace slag (BOF). The dynamic modulus test, low-temperature bend test, and three-point fatigue bending test were conducted, and the antislide performance and attenuation law were analyzed. The reinforcement mechanisms of the three types of fiber in the steel slag asphalt mixture were studied. The results reveal that there are differences in pavement performance after the addition of fibers; fibers could result in increasing the dynamic modulus of steel slag mixtures, especially at lower frequency area; fiber can improve low-temperature crack resistance of steel slag asphalt mixtures; the antislide performance is enhanced after the addition of fibers; fibers can also improve the resistance to repeated bending tensile load to enhance the antifatigue performance of steel slag asphalt mixtures; moreover, BF offers the optimal pavement performance. This research can provide a useful reference for practical applications of BF, PF, and LF in road engineering.

This paper investigates the dynamic behavior of local Barak River sand mixed with different sizes of commercially available crumb rubber at low strain conditions. A series of torsional resonant column tests are conducted to determine the dynamic properties of local Barak River sand and sand–crumb rubber mixture (SCRM). It is aimed to study the effect of different influencing parameters such as confining pressure, relative density, and particle size of crumb rubber on the dynamic behavior of local Barak River sand. All the tests have been conducted under three different confining pressures of 50, 100, and 200 kPa. In this study, two types of crumb rubber with different ranges of particle sizes are mixed with the locally available Barak River sand in different percentages by weight. The test result confirms that the shear modulus is directly proportional to relative density and confining pressure. Higher values of shear modulus have been observed for the samples prepared using larger-sized crumb rubber particles. Moreover, the maximum shear modulus value for the larger crumb rubber is observed at a lower percentage of crumb rubber content compared to that for smaller-sized crumb rubber.

The goal of this paper is to reveal the influence of temperatures on the triaxial strength of asphalt mixtures. The triaxial compression and triaxial tensile tests, as well as plane tensile and compression/axial tensile tests, which were developed by the self-developed triaxial test equipment to carry out the complex stress state under different temperatures (5°C, 10°C, 15°C, 20°C, and 25°C), were performed on the asphalt mixture. The ultimate failure strength of the material shows that the temperature and stress state significantly affect the triaxial strength characteristics of the asphalt mixture, and the three-dimensional strength decreases by the increase in temperature. Under the triaxial compression and triaxial tensile stress state, the resistance of the octahedral shear stress increases with the hydrostatic stress. A three-dimensional strength calculation model is established based on the influence of temperature and characterization by the tensile meridian, compression meridian, and failure strength envelope. It reveals the change of failure strength envelope with increasing temperatures and decreasing hydrostatic stress under complex stress state. It provides experimental and theoretical references to the design of asphalt pavement structure of different temperature conditions according to the three-dimensional stress state.

An experimental investigation on the mechanical properties of AZ61 magnesium alloy is presented under tensile, compressive, and flexural loads. Quasi-static experiments under tension and compression are performed at strain rates of $0.0001–0.1{\mathrm{s}}^{-1}$, while flexural (three-point bending) tests are conducted at cross-head speeds $1–100\mathrm{mm}/\min$ for different span lengths (80–160 mm) and orientations (flat and transverse) of flexure specimens at room temperature 25°C. Experiments at 100°C, 150°C, and 200°C are carried out under tension. The heating rate and soaking time of the specimens are $8°\mathrm{C}/\min$ and 15 min, respectively. Dynamic tests on tension ($700–\mathrm{1,150}{\mathrm{s}}^{-1}$) and compression ($\mathrm{1,600}–\mathrm{4,000}{\mathrm{s}}^{-1}$) are performed at room temperature. It is found that the alloy is positively sensitive to tensile, compressive, and flexural loads and negatively sensitive to thermal loads. The effects of specimen geometry are observed on the compressive properties of the alloy. The mechanisms of material failure are studied by scanning electron microscope (SEM), and it is found that the propensity of dimple pattern fracture increases with increasing temperature. Also, the suitability of the existing Cowper-Symonds and Johnson-Cook models are discussed in connection with the aforementioned loading conditions.

This research investigated the effect of loading rates or implicit creep on the strength and deformation capacities of single shear-bolted lap joints subjected to elevated temperatures. To address this issue, 16 bolted lap joints were tested under two different loading rates at temperatures ranging from 400°C to 700°C. The rate- and temperature-dependent retention factors for the bolt shear capacities were compared with those from previous studies in the literature. The effects of loading rate and temperature on the bolt pretension force also were examined. The results showed that all tested bolted lap joints failed in bolt shear. The results of the slow loading rate tests indicated a larger reduction in bolt shear capacities compared with the fast tests for temperatures greater than 400°C. That is, the effect of loading rate on the bolt shear capacity ranged from 18% to 36% difference for temperatures ranging from 450°C to 700°C, respectively. Finally, a strength reduction coefficient was introduced in the bolt shear capacity equation to account for the loading rate effect when designing bolted connections in fire.

Mechanical deterioration of concrete structures by freeze–thaw cycles has been widely spotted, mainly in temperate zones. In order to incorporate the icing-induced microdefects into global damage, a poromechanical model (PM) was integrated into the latest microplane model (M7) to build a holistic model (M7p) for simultaneous evaluation of both freeze–thaw behavior and external loadings. Aligning with the PM, which associates icing-induced strain with temperature and the spacing factor, M7p extends its capability beyond conventional semistatic or dynamic simulation. The features of the M7p are as follows: (1) through a four-stage procedure, the accumulated residual icing-induced strain is evaluated; (2) by calibration of parameters with one single existing freeze–thaw cycle data, a satisfying agreement on the degradation of elastic modulus and strength with experimental data is met; and (3) after calibration, deterioration of concrete structures is reasonably captured, by which cracks were initiated and formed. Hence the stability and durability of concrete structures in freezing and thawing environments are computationally predicted and discussed.

Sulfate attack and accelerated carbonation tests were conducted on five concrete mixes made with 50% recycled concrete aggregate (RCA) and 30% fly ash (FA) blended with 70% ordinary portland cement (OPC). The graphene oxide (GO) and graphene oxide ball-milled (GObm) added in the concrete mixes varied by 0.05% and 0.1% by weight of binders. The 28-day cured specimens of the mixes were exposed to sodium sulfate solution and accelerated carbonation chamber under a controlled environment. The change in mass increased but the residual compressive strength reduced with progressing exposure to sulfate solution. The carbonation depth decreased with an increase in graphene oxide inclusion in the mixes but with increasing exposure to ${\mathrm{CO}}_2$, the carbonation depth increased. The X-ray diffraction analysis (XRD) was conducted on samples after 28-day exposure to sulfate solution to confirm the delayed ettringite formation and gypsums. The thermogravimetric analysis (TGA) was performed on 28-day exposure to accelerated carbonation in order to understand the variation in the degradation process. The porosity and pore size distribution for the mixes with GO and GObm addition showed lesser porous compared to the mix without graphene oxide, which was confirmed from the mercury intrusion porosimeter (MIP) analysis conducted on 28-day cured specimens.

In this research, to study the effect of a high-speed shearing method on asphalt aging, based on SK-70# matrix asphalt, the influences of the shear time, shear rate, shear temperature, shear ring, and air on asphalt aging were investigated by using penetration, a 5°C force ductility value, and a softening point as indexes and a high-shear emulsifier as the shear preparation instrument. The results show that oxygen aging in air is the main factor causing asphalt aging during high-speed shearing in laboratory experiments. A device that prevents asphalt from aging during high-speed shearing was invented. The device and method can effectively eliminate the contact between asphalt and oxygen in the preparation of asphalt and remove the heat generated inside the asphalt. A nitrogen layer is formed on top of the asphalt sample, which can prevent oxidation and reduce the temperature of asphalt to solve the asphalt aging problem in high-speed shear preparation. Subsequently, styrene-butadiene-styrene triblock copolymer (SBS)-modified asphalt was used to carry out relevant tests to verify the equipment and method, which proved the reliability of its preventive effect. This study has important reference significance for reducing the influence of thermal oxidation aging and accurately evaluating the properties of modifiers in the preparation of modified asphalt by a high-speed shear machine, providing important technological measures for the preparation of modified asphalt in the future.

Bacteria-induced calcium carbonate precipitation has been considered as an intelligent and environment friendly technology to repair cracks in cement-based materials. However, because of the high alkalinity and harsh physical and chemical environment inside the cement-based materials, even alkali-tolerant microbial spores can hardly survive for a long time in this environment, which affects the self-healing effect of later age cracks of cement-based materials. Two low alkaline materials, potassium magnesium phosphate (MKPC) and sulphoaluminate cement (SC) were screened to protect microbial spores in this paper, and the protective effects of the two materials on spores were compared within 180 days. The results showed that SC had a better protection effect than MKPC in simulated porous solution of cement-based materials because of its compact porosity. The area repair rate and resistance to water permeability repair rate were used to characterize the self-healing effects of cracks. After 180 days, the area repair rate of the specimens with unencapsulated spores, MKPC encapsulated spores and SC encapsulated spores were 18%, 92%, and 96%, respectively, and the corresponding resistance to water permeability repair rate were 14%, 78%, and 85%, respectively. The mineral precipitations at the crack area were analyzed by Scanning Electron Microscope (SEM) equipped with an Energy Dispersive X-ray Spectrometry (EDS) and X-ray diffraction (XRD). These results indicated that the filling materials at the crack area were ${\mathrm{CaCO}}_3$ with compound polymorph of calcite and vaterite. The research suggests the carrier technology can enhance the self-healing effects of later age cracks of cement-based materials, which provides a new idea and method for the long-term self-healing ability of concrete.

The exploration of biodeposition treatment for the surface consolidation of natural stones is limited by thus-far used study-specific treatment conditions. This study explores the surface consolidation performance of Bacillus sphaericus in varying treatment conditions and compares the results with the application of a tetraethyl orthosilicate (TEOS)-based chemical consolidant to suggest a more standardized treatment procedure. Initially, the biodeposition medium was optimized for maximal ureolytic activity. Then, consolidation procedures with different times and numbers of applications were conducted on sound (no aging) Maastricht limestone. Consolidation performances were evaluated by comparing the changes in the ultrasonic pulse velocity ($P$-wave) through the specimens and the drilling resistance of the specimens. Upon two or more subsequent biotreatments, the transmitting velocity of the $P\text{-}\text{wave}$ increased by up to 25% in the first 20 mm of the specimen. The drilling resistance of the specimen increased by 100% up to a depth of 35 mm from the surface. A minimum of two subsequent biotreatments are suggested for a decent consolidation of Maastricht limestone, and a minimum of four subsequent treatments are suggested to replace TEOS.

Many pavement field distresses are caused by moisture damage. However, hydrodynamic pressure is not taken into account by a common laboratorial moisture test of asphalt mixture. Furthermore, aggregate morphology was not considered as an influence factor of moisture susceptibility by most researchers. In this study, the morphologies of aggregate were quantified and used as fundamental backup and moisture susceptibility of a mixture was evaluated by the original and improved moisture test. The relationship between moisture susceptibility and morphological features was then established. Recommendation scopes of aggregate morphologies were concluded. Results show that moisture susceptibility of asphalt mixture has a rising trend with the increase of angularity, texture, coarse aggregate angularity texture value (CAAT), and decrease of sphericity. It was found that texture, sphericity, and CAAT are closely related to moisture sensitivity of the asphalt mixture, while the correlation of angularity is relatively weak. Recommendation scopes of morphological characteristics can be used to initially evaluate moisture stability, guide the aggregate production of quarry, and provide reference for the design of aggregate crusher and shaping machines.

For patch repairs of chloride contaminated RC structures, the use of discrete sacrificial anodes (DSAs) is indispensable. Without DSAs embedded, due to the ring effect, the failure of the RC around the patch area is accelerated. DSAs are increasingly being used, but few studies have evaluated the effectiveness of different DSAs and effects of the surrounding environment on the performance of different DSAs. This study employed four electrical parameters and electrochemical impedance spectroscopy (EIS) to evaluate three types of DSAs embedded in chloride-contaminated concrete through wet–dry and freeze–thaw cycles. The corrosion of the reinforcements is a stochastic process and the bound chloride ions play an important role in determining the corrosion state of the reinforcement. Most of the DSAs provided effective cathodic protection, but the effectiveness of DSAs could be influenced by the corrosion state of the reinforcement. The wet–dry and freeze–thaw cycles had significant influence on the performance of two types of the DSAs. Current DSA designs do not fully utilize the embedded Zn alloy.

Spiral strands, galvanized steel wires, galvanized semiparallel wire strands, and steel tie rods in large-span building structures are inevitably corroded due to long-term exposure to corrosive atmospheres. However, research on different structural cables is rare, and lifetime safety evaluation of large-span building structures is urgently required. Therefore, three corrosion tests and static tensile tests after corrosion of four types of structural cables were conducted to determine the effects on corrosion behavior caused by plating, coating, twisting, and the environment. The corrosion behavior of a cable had different characteristics. A calculation method for the uniform corrosion depth of semiparallel wire strands and a three-parameter power function that effectively expresses the relationship between corrosion depth and exposure time were proposed and verified. The equivalent conversion relationship between the atmospheric exposure test and the standard laboratory accelerated corrosion test was established. The recommended 50-year corrosion depth for different structural cables was calculated, based on two corrosive environments in which long-span building structures often exist.

The service life of mechanically stabilized earth (MSE) walls depends on the rate of corrosion of the metallic reinforcements used in their construction. A methodology was designed to monitor and estimate the corrosion rate of galvanized steel in MSE walls with a conductivity sensor coupled with laboratory electrochemical techniques. The fluid conductivity of six coarse-grained backfill soils undergoing either wet-dry cycles or under submerged conditions were measured regularly for up to $120\mathrm{weeks}$. The corrosion rates of the galvanized steel were determined indirectly by measuring the conductivities of the leachates from the six backfills. The conductivity of the leach-liquor appears promising to monitor the corrosion rate even though the predicted corroded thickness was less than the actual corroded thickness measured with a scanning electron microscope.

The Addis Ababa–Djibouti Railway in Ethiopia extends across the Rift Valley, where cinder gravels (scoria) occur widely. Considering its abundance and environmental benefits, these cinder gravels are an enormous resource for earth structure fill. However, the gravels usually fail to comply with aggregate specifications for ballasted railways, primarily due to the high vesicularity of their particles. Nineteen cinder gravel samples from different locations were tested for their grain-size range, porosity, specific gravity, dry density, morphology, Los Angeles abrasion loss, and geochemistry. The results confirmed that the high void ratios of the gravels limit their direct use in railway construction. The cinder gravels therefore were blended with local silty sands to improve their suitability as aggregates. The blended material was assessed for consolidated undrained shear strength, breakage potential, and California bearing ratio. The field compaction performance of a trial railway section was evaluated and combined with the laboratory test results to produce a guideline for applying the cinder gravels as railway earth structure. Adopting interparticle porosity as a replacement for the original porosity in evaluating the quality of the compacted cinder gravel is recommended. Field dynamic measurements performed at two railway subgrade sections constructed using the stabilized cinder gravel or traditional geomaterials demonstrated that the stabilized-aggregate subgrade performed better under various train speed conditions. This study improves knowledge of aggregate stabilization techniques and facilitates wider use of cinder gravel in railway construction.

Reclaimed asphalt pavement (RAP) in rigid pavements has been used for pavement quality course (PQC), but there are very few investigations available on assessing the effect of RAP gradation in dry-lean concrete (DLC) layers. RAP poses various environmental concerns including disposal and hence it becomes imperative to incorporate this waste material in the construction of subbase layers such as DLC. This paper reports the influence of RAP on the density and strength properties of DLC. In this study, RAP was proportioned on the basis of black curve gradation (BCG) and true curve gradation (TCG). Mix parameters such as density and compressive strength were studied to quantify the effect of RAP using the fractionation method. Fractionated reclaimed asphalt pavement (FRAP) was found to be significant in influencing the behavior of DLC. The first fraction to achieve the benchmark of 7-day DLC compressive strength was 60% fractionated RAP (FRAP), followed by lower percentages. Statistical inferences indicated that, along with moisture content, RAP significantly influences the structural behavior of DLC composites. However, the effect of RAP was insignificant with respect to density. Additionally, a simple economic analysis was adopted, which indicated that FRAP is economically feasible for the construction of DLC layers in rigid pavements.

This study intends to examine the impact of successive wetting and drying cycles on the strength and hydraulic conductivity of lime- and cement-treated soil, with a special emphasis on the protocol that is employed to impose the cycles. Compacted specimens were cured for 90 days before being exposed to different numbers of wetting and drying cycles. These cycles were imposed on treated samples with two protocols, the first one based on oven drying and full saturation, and the second based on control of the relative humidity of the samples at room temperature to thus obtain more realistic conditions for the wetting and drying cycles. The unconfined compressive strength and saturated hydraulic conductivity were monitored as a function of the number of cycles. The results highlight the role of the imposed wetting and drying cycle technique for a better assessment of the long-term performances of treated soils. Special attention was also taken to evaluate the relationship between the alteration of hydraulic conductivity and mechanical strength as a function of the number of applied wetting and drying cycles. The results showed that the degradation of the strength of the treated samples is associated with a significant increase of their hydraulic conductivity as a function of the number of cycles.

This article focuses particularly on the improvement of peatland in the Northeast (NE)-Indian region by using a chemical treatment process. Cement is used as a binding agent to the peat at different percentages (by dry weight of peat) which improves its mechanical, chemical, and microstructural characteristics. The organic content plays a vital role in the densification process, which ultimately reduces the density of peat. Further, the amendment of cement brings a notable strength improvement to peat, as well as nullifies the effect of organic content, reduces the influence of acidity, and finally renders a conducive change to its electrical conductance. Moreover, the principal mechanisms that contributed to this improvement process are supported by using some morphological studies such as field emission scanning electron microscopy (FESEM) with energy dispersive X-ray spectrometry (EDX), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). A significant change in the morphology of cement-treated peat has been noticed in the FESEM micrographs, which yields a reduced porous structure and densifies the entire soil fabric. The formation of the calcium silicate hydrate (CSH), calcium aluminate hydrate (CAH), calcium aluminum silicate hydrate (CASH), and ettringite is confirmed by XRD analysis which is actually responsible for the hardening process. Further, FTIR analysis gives additional support to the observed results where an increase in the spectral intensity throughout the entire range after the treatment process indicates the formation of a new strength-enhancing gel. However, the adverse effect caused by the organic substances (such as carboxylic groups and polysaccharides) to the overall improvement has also been confirmed through FTIR analysis.

The search for innovative solutions that reduce the need for exploitation of natural resources and make use of residues to produce alternative construction materials is a necessity. Eggshell residues are a solid waste material rich in calcium carbonate (${\mathrm{CaCO}}_3$). The present research investigates quicklime and hydrated lime produced from eggshell residues and blended with ground waste glass, analyzing their possible usage as a binder material for soil stabilization. The quicklime and hydrated lime studied herein are produced from the calcination of eggshell residue. Eggshell quicklime (EQL) and eggshell hydrated lime (EHL) were characterized for their physical properties (grain-size distribution, specific surface area, photo microscopy, and X-ray spectroscopy), mineralogy (X-ray diffraction and thermogravimetric analysis), and chemical composition (X-ray fluorescence spectrometry). EQL and EHL consist predominantly of calcium oxide (CaO) and calcium hydroxide [$\mathrm{Ca}(\mathrm{OH}{)}_2$], respectively. Increasing the amount of eggshell quicklime/hydrated lime resulted in the increase of the blend’s mechanical properties, such as strength and stiffness. In general, the results show that both EQL and EHL retain outstanding physical, mineralogical, and chemical characteristics suitable for soil stabilization with an alternative pozzolanic material.