Journal of Materials in Civil Engineering

Biocementation or microbially induced calcium carbonate precipitation (MICCP) is a research domain explored by many researchers in the field of civil engineering. It has a significant potential to improve the mechanical properties of a wide range of construction materials. It can be an effective tool to increase the durability of structures. MICCP uses metabolic pathways of bacteria to form calcium carbonate, the crystals of which get deposited in the pores of the matrices of construction materials resulting in the improvement of matrix properties of construction materials. This article presents a review of the basics of biocementation by the ureolysis pathway. Major and minor influencing factors and techniques to practically apply biocementation to improve the properties of cement-based materials are presented and discussed in this article. Furthermore, advantages and limitations of biocementation from a practicability point of view are briefly discussed. An effort has been made to discuss most aspects of biocementation so that it can benefit the researchers to explore further possibilities of this technique for its field applications.

This study compared the performance of asphalt concrete mixes containing five different wastes fillers [carbide lime (CL), copper tailings (CT), glass powder (GP), red mud (RM), and rice straw ash (RSA)] to a conventional mix containing stone dust (SD). The comparison was made using a novel ranking methodology, which is based on the various engineering properties of the asphalt mixes, and the priority assigned by the designer to each property. Various physical and chemical properties of the fillers were initially determined. Subsequently, the asphalt mixes were designed at their optimal binder contents and their stability, volumetric properties, cracking resistance, moisture susceptibility, rutting resistance, and active and passive adhesion were assessed based on various accepted standards. All mixes displayed satisfactory stability and volumetric properties, and the fillers having finer particles (RM, CT, CL, and GP) formed mixes with superior cracking and rutting resistance. Mixes containing calcium-based fillers (CL and SD) showed excellent adhesion and moisture resistance, while the GP mixes showed very poor moisture resistance. RM and RSA were determined as the best- and worst-performing fillers, respectively, based on the proposed ranking methodology.

This investigation is focused on the evaluation of the fresh and hardened states of a distinctive and novel self-compacting concrete (SCC) with two distinct nonpozzolanic contents, i.e., gray phyllite (PLT) and marble + granite powders. Although the phyllite is commonly commercialized in SCC preparation, a distinctive mixture using the phyllite and marble + granite contents is used. Marble and granite beneficiation residues (MGBR) come from an ornamental stone industry, and their inappropriate discard drastically damage the environment. To characterize the starting additions and SCC specimens, SEM (scanning electron microscope) and XRD (x-ray diffraction) techniques are used. The resulting mechanical behavior favors the SCC with the MGBR content, which is $\sim 40\%$ higher than the SCC with the PLT content. Additionally, when the mechanical strength-to-relative cost ratio is determined, the SCC with the MGBR content shows a value between 1.1 and 1.3 times higher than the SCC containing phyllite. This suggests that an economical aspect concatenated with mechanical performance and environmentally friendly aspect is induced. The SCC with the MGBR represents a promising alternative for the traditional self-compacting concrete.

This paper investigates the development of compressive strength ($f_c^{\prime }$), flexural strength ($f_r$), and static elastic modulus ($E_c$) in relation to the dynamic modulus ($E_d$) for portland concrete cement (PCC) pavement and patch mixtures. The study in this paper was motivated by the need to establish the less commonly known $f_r-E_d$ relationship in comparison with the more established $f_c^{\prime }-E_d$ models. A total of 399 cylinders and 144 beams were cast and cured under laboratory (23°C) and cold (7.22°C) regimes. Experiments were conducted at concrete ages ranging from 12 h to 28 days. Cylinder specimens were subjected to $f_c^{\prime }$, $E_c$, and transverse dynamic modulus ($E_{dc}^T$) tests. Beam specimens were subjected to $f_r$, transverse ($E_{dp}^T$), and longitudinal ($E_{dp}^L$) dynamic modulus tests. Early opening to traffic (EOT) concrete strength criteria were accurately predicted as most $f_c^{\prime }$ and $f_r$ estimates fell within 10% of relative error when respectively using $E_{dc}^T$ and $E_{dp}^T$. Overall, the normalized development of $f_c^{\prime }-E_{dc}^T$ and $f_r-E_{dp}^T$ relationships reveals distinct growth trends as $f_r$ developed at a higher power factor.

This paper aims to evaluate and optimize a number of semilightweight self-consolidating concrete (SLWSCC) mixtures containing coarse and fine aggregates, lightweight expanded slate, and reinforced with different types of polymeric fiber. The fibers used were 8 and 12 mm polyvinyl alcohol (PVA8 and PVA12), and 19 mm polypropylene (PP19). The developed mixtures included different binder contents (550 and $600\mathrm{kg}/{\mathrm{m}}^3$), fiber volumes (0.3% and 0.5%), and coarse-to-fine (C/F) aggregate ratios (0.7 and 1.0). Two normal-weight self-consolidating concrete (NWSCC) mixtures made with fine and coarse crushed granite aggregates also were tested in this investigation for comparison. Although the use of polymeric fibers negatively affected the fresh properties of the mixture, it was possible to develop successful SLWSCC mixtures with significantly improved flexural strength using up to 0.5% fibers. SLWSCC mixtures with shorter fibers (PVA8) had better fresh properties and strengths compared to mixtures with longer fibers (PVA12 and PP19). A minimum of $550\mathrm{kg}/{\mathrm{m}}^3$ binder content was required to develop SLWSCC mixtures with acceptable self-compactability. However, using $600\mathrm{kg}/{\mathrm{m}}^3$ binder content contributed to improving the fresh properties of the mixture, which allowed using a higher content of lightweight expanded slate aggregate, achieving a further reduction of the mixture density. The results also showed that unlike the lightweight coarse aggregates, the use of lightweight fine aggregates helped to develop mixtures with higher flowability, passing ability, and strengths.

Specifications limits and tolerances are crucial in the relationships among contractor, road agency, and citizens because they influence profits, acceptance procedures, and pavement durability. They mainly depend on processes involved, and, unfortunately, their relationship with durability is mainly empirical and calls for further investigation. In the light of these issues, the study described in this paper deals with assessing how durability and pay adjustment (PA) are affected by variations in the main explanatory variables [e.g., air-void content (AV)] within specification limits. A model was set up in order to assess the impact on the modulus of a bituminous mixture, which is a crucial factor for the expected life (EXL). The model was applied to a well-known set of contract specifications in order to check for their suitability and rationale. Results demonstrate that usually, air void–related consequences are worse than penetration-related consequences, which, in turn, outrank aggregate gradation–related and asphalt content–related consequences. An exception is the maximum size of aggregates. Furthermore, when pay adjustments build on empirical algorithms, they have to be layer-specific because the same error implies more severe consequences in deeper layers. Results can benefit both researchers and practitioners.

Graphene oxide (GO)–modified magnesium phosphate cement (MPC) is used as an adhesive to bond carbon fiber–reinforced polymer (CFRP) composites in the formation of MPC-CFRP strengthening materials. The performance of GO-modified MPC paste and the mechanical performance of MPC-CFRP–strengthened concrete prisms are investigated in this paper. Workability and mechanical properties of MPC with different dosages of GO (0.035 wt% and 0.07 wt% by MgO) are tested. The results indicate that GO has negative effects on the fluidity and setting time of MPC. Mechanical properties of MPC are improved by a proper addition of GO. Compared with unstrengthened prisms, bearing capacity and stiffness of strengthened concrete prisms increase with the layers of MPC-CFRP: maximum bearing capacity increased by 372.08%, and stiffness increased by 130.15%, respectively. MPC with the optimal mechanical properties (MPC-GO1) is used as the adhesive to bond CFRP, which forms a new type of strengthening composite and greatly improves the bearing capacity and ductility of plain concrete prisms.

Clays and clay minerals are widely used as raw materials in different industrial processes due to their abundance. Generally, in road construction projects, clays are considered waste materials because they have some undesirable engineering properties (e.g., plasticity and swelling properties). For this reason, this material is generally discarded in landfills or dumps. However, taking advantage of its abundance, this material could be used as a substitute for natural aggregates of hot mix asphalt (HMA) production as long as their undesirable properties are eliminated. In this study, a bentonite was thermally treated (subjected to high temperatures) in order to be used as replacement for the total filler content of a natural aggregate in HMA. X-ray diffractometry (XRD), X-ray fluorescence (XRF), Atterberg limits, and free swelling index tests were carried out on bentonite (with and without thermal treatment). Marshall, indirect tensile strength (ITS) (under dry and wet conditions), resilient modulus, permanent deformation, resistance to fatigue, and Cantabro tests were carried out on HMA mixtures using thermally treated bentonite (BT) as filler. On all test results an ANOVA test was carried out. When BT replaced the total fraction of the natural filler, its resistance under monotonic load, stiffness under cyclic loading, and resistance to moisture damage increased remarkably. A similar resistance to fatigue and abrasion in the Cantabro test was observed. Based on the results obtained, BT could be considered a technically viable alternative as a substitute material for natural fillers in HMAs.

Biocementation catalyzed by ureolytic bacteria or enzyme urease is a promising technique for the treatment of liquefiable soil. Silty sand is often encountered in natural conditions and is often prone to earthquake liquefaction. However, the applicability of the biocementation to silty sand is still a challenge. In this study, we proposed and tested a new method of applying the biocementation to silty sand. In this method, crude urease obtained from the lysis of ureolytic bacteria was used for the soil treatment instead of using live bacteria directly. It was found that crude urease could be successfully obtained from bacteria using the ultrasonic cell lysis method. The activity of the crude urease was relatively high in $0.01–1\mathrm{mol}/\mathrm{L}$ of urea concentrations and 5–11 pH values and increased in temperature in the tested range (10°C–50°C). The results of the ${\mathrm{CaCO}}_3$ precipitation reaction tests showed that crude urease was capable of hydrolyzing urea and could be used in the biocementation treatment when the initial urea concentration was not higher than $0.5\mathrm{mol}/\mathrm{L}$. Triaxial consolidated undrained tests and ${\mathrm{CaCO}}_3$ content measurements were conducted on the silty sand samples treated by either urease or live bacteria. Silty sand samples treated by urease had higher shear strengths and more dilative stress-strain responses during the undrained shear as compared with the samples treated by live bacteria. In the bacteria-treated samples, ${\mathrm{CaCO}}_3$ was prone to accumulating at the injection side of the samples, while the treatment using crude urease can alleviate such a problem by showing higher ${\mathrm{CaCO}}_3$ contents at farther locations of the samples.

The role of cement and lime used in combination with enzymes in enhancing stabilization effect on soil in rammed earth construction has been explored. There were 144 cylindrical rammed earth specimens prepared with six different combinations of stabilizers tested for their engineering properties at four aging periods. Cement was found to be a better stabilizer than cement and lime used in combination for the gradation of the reconstituted soil used in this study. TerraZyme has enhanced the stabilization effect of conventional stabilizers. The macrolevel changes in the engineering properties of test specimens were supported by microlevel changes observed by scanning electron microscope (SEM) images. Based on the results from the laboratory study, it is possible to reduce the cement content used for the construction of rammed earth walls of the proposed residential building. This combined laboratory study and field implementation presents the advantages of using stabilizers in combination and the need for proper grading of soil to be used for rammed earth construction to obtain smooth finish and good texture of rammed earth walls.

Ten types of nano ${\mathrm{TiO}}_2$ (NT) were used to endow cementitious composites with the electromagnetic absorbing property. The influences caused by sample thickness, the size, and surface treatment of NT on the electromagnetic absorbing performance of cementitious composites in the frequency of 2–18 GHz were compared. Results showed that the electromagnetic wave-absorbing property of NT-modified cementitious composites increases with the increasing thickness of the sample. When the sample thickness is 20 mm, the cementitious composite incorporated with 1,500- nm rutile NT exhibits the best absorbing performance with a reflectivity of $-29.29\mathrm{dB}$ in Ku (12.5–18 GHz) band, which is 242.97% higher than that of control cementitious composites. Compared with untreated NT, mixed crystal NT, ${\mathrm{TiO}}_2{@\mathrm{SiO}}_2$, and ${\mathrm{TiO}}_2{@\mathrm{Al}}_2{\mathrm{O}}_3{@\mathrm{SiO}}_2$ have a better enhancement effect on the electromagnetic wave-absorbing properties of cementitious composites. Through analyzing the dielectric constant and magnetic permeability of cementitious composites, it can be proved that the electromagnetic-absorbing properties of cementitious composites with NT are governed by dielectric loss rather than magnetic loss.

To study the effects that healing conditions have on the fatigue-healing properties of asphalt materials, we conducted a fatigue-healing-fatigue test on asphalt materials using a dynamic shear rheometer and four-point bending-fatigue-testing machine. We analyzed the changes in the fatigue-healing properties of the asphalt materials with exposure to different healing conditions. The results showed that the fatigue-healing performance of the styrene butadiene styrene (SBS)-modified asphalt and asphalt mixture was better than those of the #70 asphalt and asphalt mixture. Increases in the healing temperature, within a certain range, promoted the healing of the asphalt mixture. Excessive temperatures led to asphalt aging and inhibited healing. The optimal healing temperatures for the #70 asphalt and SBS-modified asphalt mixtures were 50°C and 60°C, respectively. Extending the healing time was beneficial to healing. The healing efficiency decreased with an increase in the healing time. The most effective healing times for the asphalt binder and asphalt mixture were approximately 30 min and 12 h, respectively. We do not advise the excessive prolongation of the healing time to pursue a 100% healing recovery.

This work improved the low-temperature rheological properties of asphalt modified with styrene butadiene styrene (SBS) using an acid modifier, namely polyphosphoric acid (PPA), and investigated the microstructural changes induced by such a modification. Four mass fractions of acid modifier were added into SBS modified asphalt (polymer-modified asphalt, PG 64-28). A bending beam rheometer (BBR) and Fourier-transform infrared spectroscopy (FTIR) were used to obtain the creep stiffness, the $m$-value, and the microstructure distribution of the modified asphalt binders. Then the fractional viscoelasticity model was used to calculate the damping ratio, $\xi$, and the dissipation energy ratio, $\omega$, of the modified composite asphalt. The creep stiffness and the $m$-value of the composite asphalt increased, compared with those of SBS-modified asphalt, but this trend was largely affected by temperature. The differences in the calculated results suggest that the addition of the acid modifier to the SBS-modified asphalt enhanced the viscous properties at low temperatures ($-30\mathrm{°C}\le T\le 0\mathrm{°C}$).

In fires, concrete structures sometimes suffer blasting loads. This paper investigated the effect of high temperature on the dynamic mechanical properties of concrete. The specimens were cored from 10-year-old concrete beams and exposed to room temperature (20°C), 200°C, 400°C, and 600°C. The split Hopkinson pressure bar (SHPB) was used to study the dynamic mechanical behavior. The results showed that the dynamic compressive stress–strain curve of concrete after exposure to high temperature can be divided into three stages: elastic growth, slow decline, and rapid decline. Furthermore, at the same temperature, as the strain rate increased, the dynamic strength increased. When the strain rate was constant, high temperature resulted in low dynamic strength. A dynamic constitutive model is proposed. The calculation results were in good agreement with the experimental data. Therefore, this model can provide a theoretical basis for the simulation of the dynamic mechanical behavior of concrete after exposure to high temperature.

High early strength (HES) portland cement concrete (PCC) is widely used in pavement preservation because it permits a quick reopening to traffic. However, these repairs often deteriorate faster than normal paving concrete, prompting a need to investigate the mechanisms leading to poor performance. In this study, six HES concrete mixtures with varying cement factors and accelerator dosages were subjected to isothermal calorimetry, strength testing, drying shrinkage, and various durability-related tests. The effects of the cement content and accelerator dosage on concrete strength and durability were then investigated. It is hypothesized that mixtures containing high cement contents and large dosages of accelerators will demonstrate poor performance. Testing results indicate that a target minimum compressive strength of 1,800 psi in 6 h, as required by certain state highway agencies, can be obtained using any of the studied mixtures, regardless of the cement content or accelerator dosage. Only one mixture successfully achieved all durability-related testing targets; however, only one of the mixtures catastrophically failed, and the remaining four mixtures all performed reasonably well. Thus, it cannot be concluded that HES portland cement concrete is inherently nondurable and that high cement content and accelerator dosage are incongruent with durable concrete. Possible explanations for the anecdotal poor field durability are explored.

The effects of the application of elastomeric construction adhesives on the wind uplift resistance of light-frame wood connections were investigated and are presented in this paper. Previous research has revealed that proper roof-to-wall connections play a critical role in mitigating structural damage during severe winds by providing a continuous load transfer path from the roof down to the foundation. Monotonic uplift tests of 30 rafter-to-top-plates connections of six configurations were conducted. Two specimen groups, standard ring shank nails alone and strengthened with hurricane ties, were constructed with and without elastomeric adhesive application, and their wind uplift resistances were compared to explore the effectiveness of the two adhesives (i.e., polyurethane and polyether) when applied to the roof connections. Experimental results show that the addition of adhesives allowed both groups to resist higher uplift loads (approximately 200%–460%) and dissipate considerably more energy (approximately 200%–750%). Replacing hurricane ties with the adhesives approximately doubles the uplift capacity but reduces the energy dissipation by nearly half owing to reduced deformation capacity. Failure modes were also examined to provide reasonable explanations for the observed performance of the connections.

Based on the superelasticity of shape memory alloy (SMA) and the electrodeformation of a piezoelectric transition (PZT) ceramic, a novel SMA/PZT composite control device (SPCCD) was designed and its energy dissipation performance and neural network constitutive model investigated. The composite control device is composed of a variable friction unit that contains four rectangular PZT actuators and an SMA unit that includes energy-dissipation and resettable wires. The friction force can be adjusted in real time by applying the voltage to the PZT actuators and the SMA wires can dissipate energy via hysteresis and provide a reset force. This composite control device’s different components participate in energy dissipation at different seismic intensities. Electro-mechanical tests are conducted to evaluate the performance of the SPCCD with different displacement amplitudes, loading/unloading frequencies, and excitation voltages. Correspondingly, the force-displacement curves are acquired, and the influences of the lap hysteretic energy dissipation, equivalent stiffness, and equivalent damping ratio on the energy dissipation capacity of the SPCCD are analyzed. Then, the excitation voltage and loading history are considered as neuronal input to establish a back-propagation (BP) neural network model of the SPCCD. The experimental results show that the hysteresis curves of the SPCCD are approximately symmetrical and the loading/unloading frequency has little effect on the mechanical properties. The maximum control force of the SPCCD linearly increases with an increase in the excitation voltage, and its semiactive PZT unit has a large adjustable range for energy dissipation. Thus, the SPCCD is reasonably designed. Moreover, the BP network constitutive model is able to accurately track the output of the SPCCD, providing an effective means for the establishment and application of the constitutive model to SMA-based composite control devices.

This study investigates the performance of sustainable use of recycled-glass powder (GP) in soil improvement. The porosity/cement ratio ($\eta /C_{\mathrm{iv}}$) and curing time are employed to study the evolution of unconfined compressive strength (${\mathrm{q}}_{\mathrm{u}}$) and durability against wet–dry cycles (measuring of loss of mass) of a sedimentary silty soil of Guabirotuba formation, stabilized with GP and cement, in Southern Brazil. Three dry unit weights of molding (${\gamma }_{\mathrm{d}}$), three cement contents ($C$) between 3% and 9%, and curing times of 7, 28, and 90 days are used to study the influence of GP content (i.e., 5%, 15%, and 30% by weight) and $\eta /{\mathrm{C}}_{\mathrm{iv}}$ index on ${\mathrm{q}}_{\mathrm{u}}$ and accumulated loss of mass (ALM) of the compacted blends. The long-term strength improvement and durability are observed and well-fitted to a power function depending on the $\eta /{\mathrm{C}}_{\mathrm{iv}}$ ratio. When ${\gamma }_{\mathrm{d}}$, GP, and $C$ are increased and the initial porosity ($\eta$) is reduced, ${\mathrm{q}}_{\mathrm{u}}$ strength and durability increase for all GP contents. The $\eta /{\mathrm{C}}_{\mathrm{iv}}$ ratio can also establish the empirical ratios between ${\mathrm{q}}_{\mathrm{u}}$-ALM dependent on the GP contents used during compaction of the specimens. Finally, equations for dosing and estimating ${\mathrm{q}}_{\mathrm{u}}$ and ALM are obtained and set to 96.5% with a 6% error. Thus, all strengths and ALM percentages show the same normalized (i.e., divided) potential trend as the functions of GP, $C$, and ${\gamma }_{\mathrm{d}}$, compatible for the value of $\eta /{\mathrm{C}}_{\mathrm{iv}}^{0.20}=37.5\%$ by volume, and it may be possible to extend it to other compacted blends proposed in the recent literature, such as soil-lime and soil-cement-roof tile waste.

The performance of an asphalt binder is closely related to its microstructure. Understanding the properties of asphalt binders at the nano/microscale may help to improve knowledge of their macroperformance. The emergence of atomic force microscopy (AFM) technology makes it possible to distinguish the microstructural and micromechanical properties of asphalt binder. In this paper, the effects of aging and modifiers on the micromechanical properties of asphalt binder were investigated by using AFM peak force quantitative nanomechanical mapping (PFQNM) mode. Four different virgin asphalt binders and one styrene-butadiene-styrene (SBS)-modified asphalt binder subjected to different aging conditions were considered. It is found that the variation of morphology of bee structures relates to the penetration grade. The Derjaguin-Muller-Toporov (DMT) modulus fluctuates violently inside the bee structure. With the increasing aging degree of asphalt binders, the DMT modulus for three phases (catana, peri, and para phases) all increase correspondingly. Moreover, the addition of modifier improves the microscopic properties of asphalt binder.

The embedment behavior of plybamboo panels under dowel-type connections used for glued, laminated bamboo (GluBam) structures, was experimentally studied, following the half-hole loading method suggested by ASTM standards, further improved to deal with small-diameter connections. Embedment stress curves were obtained under six different loading directions, with three types of metal connectors, from 2-mm-diameter nails to 14-mm-diameter bolts. The corresponding compression tests in the same six directions were also performed as reference. Based on the original test data, embedment strength values were calculated as defined by ASTM standards. The maximum embedment strength observed from the tests was about 80 MPa when the nail was placed orthogonal to layers and orthogonal to fibers, and the minimum embedment strength was about 20 MPa when the nail was placed parallel to layers and parallel to fibers. Moreover, the compression curves were always below the corresponding embedment stress curves. Semiempirical regression-based capacity equations for the embedment strengths under different loading directions were given as a function of the plybamboo density and the connectors’ diameters. The 5% characteristic values and the design values of the embedment strength were estimated from test data, based on the design-by-testing method suggested in European standards. Results from this research can be used to predict the ultimate strength of GluBam connections, as well as to obtain reliable design values for engineering applications.

In order to study the effect of different structural parameters on the connection performances of a tapered head sleeve (THS) and the calculation method of the bond strength, a three-dimensional finite-element model was established. Seventeen THS specimens with different specifications were designed and simulated. Considering the inner cavity radius, sleeve thickness, sleeve length, and anchorage length of reinforcing bar, the influence law of each parameter on THS deformation was analyzed. According to the restraint mechanism and the law of circumferential strain distribution, the calculation methods of bond strength between the grouting material and the inner cavity of the grouting sleeve and between the steel bar and the grouting material are put forward. The results show that the longitudinal strain of the sleeve increases with decreasing the radius of the sleeve and the thickness of the sleeve; the decreases of sleeve lengths and anchorage lengths affect the strain distribution trend of the whole sleeve, but have no obvious effect on the peak value of the longitudinal strain and circumferential strain; the formulas well express the bond strength between each part.

The disposal of copper mine tailings (CMT) in finite containment facilities near mine sites is a serious human safety and environmental management challenge in most copper-producing countries of the world. Therefore, this study evaluates the reuse potential of the CMT as a 0%–30% partial substitute material for cement in paste, mortar, and concrete mixtures. The CMT was characterized first, and thereafter its effects on the performance of cement paste and mortar were evaluated via normal consistency, setting time, strength activity index (SAI), X-ray diffraction (XRD), scanning electron microscopy analysis, and autoclave expansion tests. Mechanical strength evolution of CMT-blended concrete mixtures exposed to water-curing and a sulfate-rich environment was also monitored for about a year. Cement paste and mortar test results indicate that while the CMT led to a slight increase in water demand and set retardation, all the CMT-modified mortar mixtures met the minimum SAI requirement of 75% at the 28th and 90th days. Moreover, free lime induced longitudinal expansion generally decreased with increasing content of the CMT in pastes. These improved performances engendered by the CMT were also replicated in concrete. Whereas only the mechanical strengths of concrete incorporating 5%–20% CMT were higher than that of the plain reference concrete, the sulfate resistance of all the CMT-blended mixtures was superior to that of the reference concrete. XRD results also confirmed that the potentials of the CMT as a cement replacement material is high. All in all, the environmental and material sustainability benefits arising from the use of the CMT in cement composites are enormous.

To investigate the roles of nonisometric flaws in rock failure behaviors, uniaxial compression tests with the combined monitoring of acoustic emission (AE) and digital imaging were conducted on sandstone specimens containing two preexisting flaws with a variety of flaw length ratios. The AE rate-process theory was used to analyze fracture-related AE event rate characteristics. Acoustical observations suggest that soon before macrofracturing, the AE event rate rapidly increases, while the AE event rate rapidly decreases after macrocracks initiate, propagate, and coalesce with each other. Optical inspections imply that the strain localizes around the flaw tips prior to the formation of macrocracks, the strain releases at the moment of the macrofracturing, and the first crack initiation is always induced by tensile cracking, while the ultimate failure is triggered by shear fracturing. Combined acousto-optic-mechanical (AOM) inspections imply that the cracking processes of sandstone specimens with relatively large flaw length ratios are more progressive than those with small flaw length ratios. For isometric flaw configurations, the stress fields interact with a stress buildup pattern, while for nonisometric flaw configurations, the stress buildup pattern and the stress shadow pattern coexist. Finally, the microscopic tensile and shear failure mechanisms are revealed by parametric analysis of the AE signals.

The present investigation is mainly focused on the effect of copper slag (CS) on micro, macro, and flexural characteristics of geopolymer concrete (GPC). In this study, copper slag was used as a partial replacement of fine aggregates at different levels (0%, 20%, 40%, and 60%) by weight. Fly ash and ground granulated blast furnace slag (GGBS) were used as binders and a combination of sodium hydroxide (8 M) and sodium silicate solution were used for activating the binders. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) analyses were conducted to examine the microstructure of the GPC. In macrolevel studies, a compressive strength of GPC was determined, and prediction models were developed to assess the compressive strength using nondestructive testing (NDT) techniques. The load and moment characteristics of reinforced geopolymer concrete (RGPC) beams were also studied. From the results, it is concluded that the incorporation of CS shows better performance in the micro, macro, and flexural properties of GPC.

Conventional building materials like fired clay brick (FCB) and concrete blocks are expensive and, in some cases, have detrimental effect on environment. Compressed stabilized earth block (CSEB) can be an effective alternative that can be easily prepared from locally available clays with little addition of stabilizers. This study is carried out to assess the performance of CSEBs prepared of highly fine-grained soils as a suitable construction material. As such, both stabilized and unstabilized earth blocks were tested and a comparative assessment is made in terms of compressive strength, unit weight, durability, and load-deformation characteristics. Varying proportions of cement, coarse sand (CS), and fine sand (FS) were used in a quest to find an optimum combination for producing CSEB that meet the design criteria outlined in several standards. Inclusion of 50%–60% CS is found to provide maximum density and compressive strength, and beyond 60% CS content, strength begins to drop. CSEBs made with cement $\ge 6\%$ with proper amount of sand showed better durability. Although addition of mixed sand (CS and FS) was found to be more effective in increasing strength; however, durability was poor. With the increase of cement, water absorption was found to decrease. CSEBs with cement content $\ge 6\%$ and coarse sand $>40\%$ showed water absorption of less than 15%. Moreover, with the increase of cement content, peak stress increases and failure strain decreases, resulting in brittle nature of the material. Some interesting stress–strain response was observed for different cement content at a constant CS content, directing to a conclusive solution. Taking the aforementioned parameters into consideration, optimum proportions of cement, CS, and FS to achieve considerable strength and durability was suggested. Finally, a cost analysis was performed and the prospect of CSEBs as an eco-friendly, and sustainable alternative to conventional masonry units like FCBs was presented.

In this paper, the cyclic response of plastic concrete material used in cutoff walls of embankment dams has been studied. To investigate the dynamic behavior of such a material, an extensive series of triaxial monotonic and cyclic compression tests were performed on plastic concrete specimens. The effects of confining pressure, mix design, age, anisotropy, and various loading conditions on the cyclic behavior of the material as well as the variation of the shear modulus and damping ratio have been assessed. Moreover, an empirical equation was derived by which the maximum shear modulus of the plastic concrete material can be estimated based on the stress level. Furthermore, to evaluate the degradation of the material due to cyclic loadings, the postcyclic monotonic stress–strain curves were compared with the corresponding curves for the specimens not subjected to cyclic loadings. It was concluded that in the high-cement- or low-bentonite-content specimens especially at the higher ages, the cyclic loading has little effect on the postcyclic monotonic behavior of the material.

The dynamic modulus of asphalt concrete (AC) mixtures is commonly measured using cylindrical specimens having a 100-mm diameter and a 150-mm height (full-size specimens). Testing as-built AC mixtures using this geometry is rarely possible because the required specimen height is greater than the typical AC lift thickness. In this study, the feasibility of using small-scale cylindrical specimens to measure the dynamic modulus of AC mixtures was investigated. Dynamic modulus tests were conducted on full-size and two small-scale (common height of 110 mm and two diameters of 38 and 50 mm) geometries extracted from gyratory-compacted samples. Both small geometries showed similar performances to full-size specimens except at high temperature of 37.8°C, where they resulted in greater dynamic modulus values. Second, field cores were collected from highways to perform the dynamic modulus and Hamburg wheel tracker tests, and the two test results were correlated. The findings showed that small-scale specimens are capable of measuring the as-built dynamic modulus of AC mixtures and predicting their rutting performance in the laboratory.

An experimental investigation on the deformation behaviors of the aluminum alloy Al5052-H32 is presented under tensile, compressive, and flexure loads at different strain rates and temperatures. Quasi-static tests on tension and compression are performed using an electromechanical universal testing machine in the strain rate range $0.0001–0.1{\mathrm{s}}^{-1}$ at a room temperature of 25°C. Flexural tests (three-point bending) are conducted using the same universal testing machine at different crosshead speeds ($1–200\mathrm{mm}/\min$) for different span lengths (90, 120, and 150 mm) and orientations (flat and transverse). Split Hopkinson tensile bar and split Hopkinson pressure bar setups are used for dynamic tests on tension ($650–\mathrm{1,300}{\mathrm{s}}^{-1}$) and compression ($450–\mathrm{2,500}{\mathrm{s}}^{-1}$), respectively. The compression tests are conducted at three different aspect ratios (0.5, 1, and 1.5) of specimens to study the effects of their geometry on the compressive behavior of the alloy. The quasi-static tensile tests are repeated at different elevated temperatures (250, 350, and 450°C) at a constant strain rate of $0.001{\mathrm{s}}^{-1}$ and a mixed brittle–ductile fracture mode is observed. The mechanism of the fracture surfaces of the broken tensile specimens at different temperatures are determined using a scanning electron microscope. The aforementioned aluminum alloy is found to be negatively sensitive to strain rates at different loads. Typical stress–strain curves of serration phenomenon are presented and it is found that the alloy is susceptible to Portevin–Le Chatelier effects.

Enzyme-based soil stabilizers have been successfully used in ground applications for the last 30 years. However, the successful application of a given enzyme-based additive is case specific and depends on soil type, soil condition, and operational loads. As a result, contractors incur a substantial cost in terms of time and money for preliminary lab tests, which may determine the suitable mix proportions to utilize in the field application. A sound understanding of the stabilization mechanism of these additives can minimize these costs and yield optimum benefits from the stabilization process. This paper investigates the stabilization effects of a novel enzyme-based additive, commercially known as Eko Soil, that is being applied to construct unpaved roads in Australia and worldwide. The aim of this research is to identify the optimized mix proportions of the additive by unveiling its mechanism of stabilization for a fine-grained field soil, which is dominant in Victoria, Australia. A series of experiments were conducted under a 4-stage test program that included macroscale mechanical tests and microscale imaging tests to unveil stabilization effects and the mechanism of stabilization. The identified mechanism has facilitated enhancement in the efficiency of enzyme-based soil stabilization significantly compared to the strength of nonstabilized soil. The research will substantially benefit the road construction industry by not only replacing traditional construction methods with economical/reliable approaches, but also providing insight on the optimum additive amount required to stabilize road pavements based on this stabilization mechanism.

Most studies on the bolted extended end-plate (BEEP) moment connection have focused on the rotation capacity of the connection before the yielding of the connection members takes place, and effects of seismic low-cycle fatigue (LCF) and ultralow-cycle fatigue (ULCF) in this type of connection have received little attention. This study focused on the effects of LCF and ULCF in BEEP-moment connections in steel moment frames. In this regard, four steel moment-frame structures of 3, 7, 12, and 15 stories with BEEP connections were selected for this study. All four structures, constructed from Grade St-37 steel material, were subjected to 11 earthquake records for investigation. Also, the effects of ULCF were evaluated by ABAQUS Finite Element Software using a cyclic-void growth model (CVGM). The results revealed that the effect of LCF in BEEP connections was more notable in beams than in columns. The results also showed that in high-rise structures, higher modes of vibration play an important role in increasing the damage due to LCF. Also, in BEEP connections under ULCF, the maximum rotation capacity of the connection was achieved by preventing both the yielding of the end-plate and the failure of the bolts.

In this study, different percentages of silicafume (SF) were replaced with natural zeolite (NZ) (25%, 50%, 75%, and 100%), in order to mitigate autogenous shrinkage of ultrahigh-performance concrete (UHPC) with almost equivalent mechanical properties. The results showed that replacement of SF with NZ had a positive effect on maintaining internal relative humidity (RH) in the higher range and consequently reducing the autogenous shrinkage of UHPC. The mixtures with 25%, 50%, 75%, and 100% replacing SF by NZ had lower autogenous shrinkage compared to reference mixtures with 100% SF. The results of microstructure and thermogravimetric analysis showed that NZ had a good pozzolanic activity. The results of the compressive strength indicated showed that by replacing 50% SF with NZ, the 90 days compressive strength was only slightly lower than the reference mix. The relative cost analysis of the samples indicated that replacing SF with NZ yields a cost-effective solution. By replacing SF with NZ, UHPC mix with appropriate compressive strength, low autogenous shrinkage and relatively low cost, can be produced.

ASTM A240/A240M 304 structural stainless steel is a widely used structural material in civil engineering. In this study, by using the split Hopkinson pressure bar (SHPB) technique, the dynamic compressive mechanical behavior of this material was experimentally investigated at four different temperatures of 25°C, 300°C, 500°C, and 700°C and three strain rates of 1,000, 3,000, and $\mathrm{5,000}{\mathrm{s}}^{-1}$. Quasi-static compressive test under the strain rate of $0.001{\mathrm{s}}^{-1}$ was also carried out in the material test system at temperatures of 25°C, 300°C, 500°C, and 700°C. Test results showed that flow stress of ASTM A240/A240M 304 stainless steel decreases with temperature increase but increases with increase of strain rate. Moreover, temperature becomes the main factor affecting material performance at 700°C. Based on the measured stress–strain curves, the modified Johnson-Cook model was proposed as the constitutive stress–strain model for ASTM A240/A240M 304 stainless steel. It was shown that the proposed modified Johnson-Cook model is in good agreement with the experimental results. According to the proposed modified Johnson-Cook model, a user subroutine (VUMAT for Abaqus/Explicit) for ASTM A240/A240M 304 written in Fortran was developed and verified. The proposed constitutive model and user subroutine of ASTM A240/A240M 304 stainless steel can be used for structural analysis and finite-element analysis under high strain rates and elevated temperature.

Macroperformance, i.e., skid resistance, high-temperature, and compaction performance, are related to the functional performance, safety, and durability of asphalt pavement. Currently, the research on such influencing factors focuses on the properties of asphalt, gradation composition, pavement structure, and so forth, whereas the geometrical characteristics of coarse aggregate, especially its angularity, has not gained due attention from researchers. This paper investigated the effects of coarse-aggregate angularity on the skid resistance, high-temperature performance, and compaction performance of asphalt mixtures. Three-dimensional angularity (3DA) computed by X-ray computed tomography (XCT) was employed to characterize coarse-aggregate angularity. Texture depth (TD) and British pendulum number (BPN) were evaluated through the sand patch test and the British pendulum test (BPT), respectively. The dynamic stability and rutting depth of mixtures with different coarse-aggregate angularities were examined with the wheel tracking test. The variation in height of the specimen with different angularity asphalt mixtures during the compaction process was tested through the Superpave gyratory compactor (SGC). The dynamic modulus ($|E^{*}|$) of the asphalt mixtures was analyzed with the asphalt mixture performance tester (AMPT) and the generation of master curves. The results showed that three-dimensional (3D) angularity is able to characterize the angularity of the coarse aggregate. A lower coarse-aggregate angularity leads to a smaller skid resistance of the asphalt mixture. The angularity greatly influences the high-temperature and compaction performance of asphalt mixtures. Higher angularity leads to better high-temperature stability but causes difficulty in compaction. The angularity has a significant influence on the $|E^{*}|$ values of SMA-16 asphalt mixture. The results revealed that the decrease in coarse-aggregate angularity translated into a decrease in $|E^{*}|$ values on average. This study provides support for further research into and application of macroscopic properties of asphalt mixtures.

The lack of universal design standards for cold mix asphalt (CMA) has led to the use of laboratory–field correlation techniques to predict its strength. Such techniques disregard the gradual strength increase in CMA with curing time and temperature. This study developed strength–maturity functions to predict CMA strength. Virgin and recycled aggregates from reclaimed asphalt pavement (RAP) were considered. Specimens 100 mm in diameter and 63.5 mm in thickness were produced using the Marshall method. These were subjected to isothermal curing regimes and measured for indirect tensile strength. The early-age strength of the RAP mix cured at low temperatures of 25°C was lower than that of the virgin mix. However, after curing for 18 days, there was no significant difference in strength between the virgin and RAP mixes for all temperature regimes. Asphalt made from RAP mix had a higher temperature sensitivity factor ($B$) than that of the virgin mix. A linear–parabolic strength–maturity function predicted the strength of cold asphalt emulsion mixtures (CAEMs) with an accuracy greater than 95%. Thus, the proposed maturity method effectively predicts the strength of CAEMs.

The crack propagation of a large-size asphalt mixture (LSAM) with three temperatures, three asphalt aggregate ratios, three displacements, and short-term and long-term aging is investigated by an improved overlay test (OT). Based on the concept of pseudodisplacement and finite element simulation, a method for evaluating the fracture performance and crack propagation of LSAM is proposed in this paper. The crack propagation length can be obtained by calculating the relative pseudosecant stiffness. The results show that: (1) a power function can describe the crack growth of LSAM, and the rate of crack growth is larger at the initial stage of loading and gradually decreases with an increase in load cycles; (2) increasing the displacement, decreasing the temperature, and increasing the aging time significantly increases the crack growth rate of LSAM, but the variation in asphalt aggregate ratios does not have a significant effect on the crack growth rate of LSAM; and (3) the stress intensity factor decreases with an increase in crack length, and the stress intensity factor and the fracture properties parameters ($n$) increase with an increase in displacement, a decrease in temperature, and an increase in aging time.

Smectite-bearing, expansive clayey soils are common in many areas of Texas, causing damage to pavements and building foundations by cyclic shrinking and swelling. The mechanism of shrinking and swelling has been widely studied, but there is limited research on geochemical modeling of the impact of chemical modifiers on shrink-swell soils. Two thermodynamic equilibrium models (Visual MINTEQ and Geochemist’s Workbench) based on Gibbs free energy minimization were used to model the interaction of a hydrogen ion stabilizer (HIS) with a smectite clay. The models describe the release of ${\mathrm{Al}}^{3+}$ ions from the octahedral layer of smectite and molecular structural changes by dissolution. X-ray diffraction and Fourier transform infrared spectroscopy were used to validate structural changes indicated by both models. Smectite was treated with concentrated HIS (no added water) and chemical stabilizer HIS (diluted with 20 parts water to 1 part stabilizer). Partial dissolution of smectite layers was observed when the clay was treated with the 20-to-1 dilution. Reduced d-spacing of 2 Å was recorded at 95% relative humidity for the sample treated with 20-to-1 diluted chemical stabilizer. One-dimensional cyclic swell testing indicated a reduction in swelling of up to 46% following the third swell cycle for smectite treated with 20-to-1 diluted HIS compared to untreated smectite.

The friction at the steel pipe–flowing concrete interface plays an important role in concrete pumpability. To reduce the friction or improve pumpability, in this paper, various ultrafine powders (nanoclay, $\mathrm{nano}\text{-}{\mathrm{CaCO}}_3$, and microsized marble powder) are incorporated into a highly flowable concrete mixture with a low water-binder ratio ($\mathrm{w}/\mathrm{b}=0.35$) at a dosage of 1% (by weight) as a cement replacement. The effects of these ultrafine powders on rheology of the concrete and the properties of the lubrication layer, near the steel pipe–concrete interface, are studied by a portable rheometer and tribometer. The thickness of the lubrication layer of each concrete mixture is determined using a microindentation test method. The results show that 1% nanoclay and $\mathrm{nano}\text{-}{\mathrm{CaCO}}_3$ replacement increases the rheological parameter values (e.g., yield stress, viscosity) of both bulk concrete and the lubrication layer. However, 1% marble powder replacement largely reduces the viscosity of the lubrication layer as well as the pumping pressure. The thickness of the lubrication layer of the concrete mixtures studied is about 1–2 mm.

Increasing crude oil prices and environmental concerns demand an alternative petroleum-based bitumen binder for Indian road construction industry. In this study, viscosity grade (VG)10 bitumen was modified by adding pyro-oil obtained from municipal plastic waste. The calorific value ($\mathrm{10,745}\mathrm{kcal}/\mathrm{kg}$) and the Fourier transform infrared spectra of the specimen pyro-oil were identical to those of diesel and bitumen respectively. This study investigated the use of this specimen as a substitute for diesel to prepare modified cutback bitumen, which acts as a tack coat between two layers of bituminous pavement. All empirical results of the modified cutback were within ASTM limits. Furthermore, using a newly developed attachment to the Marshall stability apparatus, the shear strength of the tack coat was tested at various temperatures. At the rate of application of tack coat as $0.20\mathrm{kg}/{\mathrm{m}}^2$ and with 20% addition of pyro-oil, the optimal shear strength reached was 331.21 kPa. Dynamic shear rheometer testing determined the complex shear modulus ($G^{*}$) value to be 1.975 kPa. Due to its adequate performance and green synthesis, the modified cutback bitumen can be a potential solution for use in flexible pavement.

The objective of this study was to compare the effectiveness of rejuvenators and determine how the methods of adding rejuvenators into recycled asphalt mixtures could affect their performance. In this study, five different rejuvenators (three bio-oils, one aromatic extract, and one rerefined engine oil bottom), three recycled asphalt mixtures (30% RAP mix, 40% RAP mix, and 25% RAP/5% RAS mix), and four methods of adding rejuvenators (terminal blend, belt spray, 48-h marination, and 14-day marination) were included in the experimental plan. Performance grading of the binders extracted from the mixtures and mixture performance tests to characterize the resistance of the recycled asphalt mixtures to raveling and cracking were conducted and analyzed. The results of this study indicated that tall oil could be more effective in improving binder performance grades than the other rejuvenators evaluated in this study, and the four methods of adding rejuvenators into the recycled asphalt mixtures showed statistically similar effects on the mix performance. The findings in the study are drawn based on the limited types and dosages of rejuvenators, and the conclusions could be different when other rejuvenators and dosages are used.

This paper investigates the process of selecting the aggregate gradation according to the Superpave mix design specifications and evaluates the volumetric properties and mechanical performance of mixtures with perturbed aggregate gradations. The mix design information and pavement materials for two typical Superpave mix designs with a 12.5-mm nominal maximum aggregate size were collected for this study. The volumetric properties of the mixtures were judged mainly by the voids in mineral aggregates, whereas the rutting potential and strength of the mixtures were assessed with the Hamburg wheel-tracking and indirect tension tests, respectively. Bailey ratios and corresponding acceptance criteria were used to evaluate the impact that aggregate gradation has on the engineering behavior of mixtures. Although design variables such as binder content and characteristics can be adjusted to improve the performance of mixtures, balanced volumetric and mechanical properties can be achieved by selecting the aggregate gradation in a rational manner.

The skeleton structure has a strong influence on the uncured and cured performances of the epoxy asphalt mixture. Based on the Bailey method, the different skeletal structures of the mixture have been obtained by varying the chosen unit weight ($CUW$), coarse aggregate ($CA$) ratio, and fine aggregate coarse fraction ($F{A}_c$) ratio. The performance experiments of these mixtures have been conducted in this paper. The results indicate that as the $CUW$ decreases from 105% to 80%, the epoxy asphalt mixture gradually changes from a skeleton dense structure to a suspended dense structure, and the strength and moisture resistance of the cured mixture gradually increase. The uncured strength of the mixture reaches a maximum at the $CUW$ of 95%. The skeleton structure of the mixture is gradually destroyed as the $CA$ ratio increases from 0.4 to 1.0, which also leads to a decrease in water stability given the difficulty in compaction. As the $CA$ ratio increases, the uncured stability of the mixture gradually reduces, but the stability and low-temperature performance of the cured mixture gradually increases. As the $F{A}_c$ ratio increases from 0.35 to 0.55, the fine aggregate fully fills into the skeleton, and the high-temperature performance, low-temperature performance, and moisture stability performance of the mixture improve. A dense gradation structure with a $CUW$ of 95%, $CA$ ratio of 0.4, and $F{A}_c$ ratio of 0.35 is recommended for an epoxy asphalt mixture applied in runway overlay or pavement maintenance without interrupting traffic.

This study aims to adopt the acoustic emission (AE) technique to evaluate the reinforcing effect of basalt and steel fibers on the fracture resistance of asphalt concrete (AC) under indirect tension (IDT) testing at low temperature. Control asphalt concrete (CAC) with no fibers was also tested for comparison. The AE counts and durations were recorded and analyzed to characterize the fracture processes of basalt fiber reinforced asphalt concretes (BFRAC) and steel fiber reinforced asphalt concretes (SFRAC), which were compared with the results from static displacement and strain data obtained through digital image correlation (DIC). The results revealed that the low-temperature fracture processes of BFRAC and SFRAC could be effectively divided into four stages according to the evolutions of AE parameters and corresponding cumulative AE parameters. AE properties could effectively evaluate the reinforcing effects of basalt and steel fibers on the low-temperature fracture resistance of AC, whereas static displacement and strain failed to identify the effects. BFRAC with a fiber length of 12 mm (BFRAC-12) had favorable ductile property at the final failure stage, whereas BFRAC with a fiber length of 6 mm (BFRAC-6), SFRAC with a fiber length of 6 mm (SFRAC-6), and SFRAC with a fiber length of 12 mm (SFRAC-12) exhibited brittle characteristics based on variations of AE parameters. Good correlations between the curve characteristics of AE parameters and the failure loads of AC specimens can be observed. The AE technique demonstrated great potential for the damage fracture characterization of asphalt materials.

Cellulose fiber is commonly used to improve the properties of asphalt pavement. However, its production process is complex and costly, consumes valuable forest resources, and pollutes the environment. Cotton straw is a waste of cotton production. Large quantities of cotton straw have not yet been reasonably used. In this study, cotton straw was processed into straw fibers by a simple mechanical pulverization method with a self-made planetary blade crusher. The processing parameters of the cotton straw fibers were selected, and the performance of the cotton straw fiber asphalt mixtures was investigated. Results show, as a potential substitution for cellulose fibers, cotton straw fibers can improve the high-temperature stability, low-temperature properties, and water stability of asphalt mixtures; processing cotton straw into fibers and using them in asphalt mixtures can make better use of waste materials of cotton production and has the advantages of energy conservation, environmental protection, and abundant resources.

In this article, a comparative analysis of the sulfate resistance (${\mathrm{Na}}_2{\mathrm{SO}}_4$ and ${\mathrm{MgSO}}_4$) of an alkali-activated binary concrete (AABC) (70% natural volcanic pozzolan and 30% granulated blast-furnace slag) and a concrete based on ordinary portland cement (OPC) is performed. The AABC and OPC concrete were cured for 28 days prior to their immersion in solutions of sulfates (5% by weight) for a period of up to 730 days. Dimensional changes, compressive strength, absorption, and porosity properties were evaluated at different test ages. Additionally, the level of concrete deterioration was monitored by visual inspection, scanning electron microscopy, and X-ray diffraction (DRX). The results show that the AABC presents resistance to sulfate attack greater than that of OPC. The percentage of expansion to 730-day exposure for AABC was 0.0985% in ${\mathrm{Na}}_2{\mathrm{SO}}_4$ with a compressive strength index of $-0.58\%$; in ${\mathrm{MgSO}}_4$, these values were 0.1471% and $-20.85\%$, respectively. AABC complies with the expansion limit specified by ASTM C1012 for the most severe class of exposure (S3). This finding allows for the classification of the AABC as a high-${\mathrm{Na}}_2{\mathrm{SO}}_4$-resistant concrete.

Lightweight aggregate concrete (LWAC) is a widely used material in civil engineering. This paper aims to evaluate the macro- and microcharacteristics of lightweight aggregate concrete which has served as the deck in the Nanjing Yangtze River Bridge for 50 years. The average compressive strength and the stress-strain curves were obtained from limited-size core specimens. The interfacial transition zone (ITZ) between lightweight aggregate and bulk cement paste was characterized by scanning electron microscopy (SEM), backscattered electron microscopy (BSEM), and nanoindentation to determine the morphological, mineralogical, and mechanical features. The results show that the average compressive strength, obtained from limited-size core specimens, is 76% of the initial compressive strength after 50 years of service in a real condition, including freeze/thaw and dynamic load. The ITZ of LWAC is not apparent in SEM and BSEM micrography owing to the long-term hydration of cement around the lightweight aggregate. The ITZ is around 100 μm thick according to the micromechanical properties, including indentation modulus and hardness by nanoindentation.

The potential of using amorphous aluminosilicate as a modifying agent for the adhesive dry mixes was explored. The technology of preparation of the additive based on amorphous aluminosilicates was investigated. This paper presents experimental data on the influence of amorphous aluminosilicate–based additives on the topological structure and strength of cement paste.

Modification of aged binders by the use of recycling agents is significantly influenced by the chemical compositions of these agents. Despite the widespread use of recycling agents, the effect of their chemical properties on the modification process of aged binders cannot be fully found by referencing the reported studies. Recently, the National Center for Asphalt Technology (NCAT) categorized the recycling agents in five main groups. This paper addresses the chemical characteristics of recycling agents in each group by employing saturate, aromatic, resin, and asphaltene (SARA) analysis, Fourier-transform infrared spectroscopy (FT-IR), and elemental analysis. The test results and analyses revealed that the aromatic extracts were similar in chemical composition and bond with virgin unmodified binders. In addition, the results showed that the chemical nature of triglycerides/fatty acids and tall oils might increase the moisture susceptibility and accelerate the degradation of the asphalt binder. The SARA analysis indicated that the compatibility between paraffinic and naphthenic oils with the binder might be a concern; however, the level of oxygen content was low, and these agents did not contain chemical bonds sensitive to moisture and aging.