Journal of Materials in Civil Engineering

Design of structures made using silica fume (SF) concrete to an acceptable level of safety requires the probabilistic evaluation of its mechanical properties. An extensive experimental program was carried out on compressive strength, flexural strength, and tensile splitting strength of SF concrete. Seven concrete mixes with different proportions of SF were designed to produce 490 concrete samples. The probabilistic models to describe the variability of the mechanical properties of SF concrete were proposed. Two-parameter probability models such as Weibull, normal, lognormal, and gamma distribution were considered for the representation of variability. The probability distribution models were selected based on goodness-of-fit tests such as the Kolmogorov-Sminrov (KS), chi-square (CS), and log-likelihood (LK) tests. The results obtained from the models are useful for description of the variability of selected mechanical properties of SF-incorporated concrete. This study proposes the lognormal distribution function as the distribution model that most closely describes the variations of different mechanical properties of SF concrete from a practical point of view. Further, the performance of typically selected buildings using SF concrete was evaluated through fragility curves and reliability indices incorporating the proposed probability distributions and variability of compressive strength property. It was found that 15%–25% of partial replacement of cement with SF may yield better performance of the frames.

In this paper, the spatial and time-variant chloride distribution in RC beams subjected to combined sustained flexural loads and cyclic drying–wetting action is studied. By means of the digital image correlation (DIC) technique, the distribution and evolution of load-induced damage and cracks in beam specimens during four-point bending are mapped and quantified using a damage factor. The influence of damage and cracks on the chloride resistance of beams is elucidated and a numerical model to reproduce the chloride penetration in precracked beams is proposed. The results show that the concrete in the pure bending zone of the beam has the highest rates of chloride ingress and reinforcement corrosion activity, followed by those in the support zone and combined shear-flexure zone. The regression analysis suggests that the apparent chloride diffusion coefficient of concrete increases exponentially, while the corrosion current density increases linearly, with the increasing magnitude of loads applied on the beams. The proposed model can reasonably predict the chloride profiles across the entire RC beams.

One of the most important concerns in using different additives for improving fatigue and low-temperature cracking resistance is the diminishing rutting resistance of pavement. In this research, saturates, aromatics, resins, and asphaltenes (SARA)-separation, dynamic shear rheometer (DSR), multiple stress creep recovery (MSCR), and bending beam rheometer (BBR) tests were conducted to study the interaction between chemical components and rheological behavior of binders with 25, 50, and 100 percentages of reclaimed asphalt pavement (RAP) binder modified with a softer binder and rejuvenator. The results show that the use of general guidelines for RAP content that do not consider the specific properties of all component materials in use has major limitations. The parameters obtained from rheological tests correlate positively with the asphaltene content. Using just asphaltene content as an index is more reliable than using Gastel and Asphaltene indices for investigating the effect of aging or adding an aged binder because its correlation with MSCR parameters is stronger. In this research, it also discovered that 100% of RAP content could be replaced in the case of an oil rejuvenator addition.

The flow number test is widely utilized as a routine test for assessing the rutting resistance of asphalt mixtures. The objective of this study is to propose a novel method of determining the flow number of asphalt mixtures with better accuracy. The Dynamic Testing System (DTS) was employed to perform the flow number tests on four types of asphalt mixtures at multiple temperatures. With respect to the test data, the existing flow number calculation methods are firstly evaluated in terms of the accuracy of the determined flow number values. It is demonstrated that none of the existing methods are recommended to determine the flow number of asphalt mixtures. The two-step secant method is then developed based on the curve shape of the permanent strain versus load cycles graph. The characteristics of concavity and convexity shown in such a graph are utilized to determine the onset of the secondary stage and that of the tertiary stage. As the kernel of the two-step secant method, the secant method is employed twice to determine the load cycle at the minimum slope of secant line for selected permanent strain data. The two load cycles determined by the second step of the two-step secant method are demonstrated to be the onset of the secondary stage and tertiary stage. The termination criterion of flow number tests is then established based on the test data of four asphalt mixtures so that the two-step secant method can be applicable. In conclusion, the proposed two-step secant method is capable of determining the initiation points of the secondary stage and tertiary stage with better accuracy for different types of asphalt mixtures.

This study experimentally investigates the effects of edge-oxidized graphene oxide (EOGO), which is a low-cost carbon-based nanomaterial, on fresh and hardened properties of normal portland cement concrete (PCC) and fiber-reinforced concrete (FRC). Interestingly, adding EOGO to normal concrete mixtures improves the workability of concrete. In this regard, EOGOs as an additive were applied to FRCs in order to improve FRCs’ low workability without losing mechanical enhancement due to EOGOs. Two fiber types of basalt fiber (BF) and steel fiber (SF) were used in this study. First, 0.05% of EOGO by the cement weight was mixed in basalt FRC (BFRC) mixture, which is 0.1% of the BF by the concrete volume. Second, considering the results of BFRC, 0.1% of EOGO was employed in steel FRC (SFRC) mixture with 1.0% of SF by the concrete volume. Testing was aimed at investigating the effects of EOGO on the workability and mechanical strengths of the FRC mixtures. The test results illustrate that the EOGO improves workability more than 100% in the SFRC mixture but about 20% in the BFRC mixture. The EOGO provides a slight increase of both compressive and flexural strengths for normal concrete and SFRC mixtures. In contrast, it was observed that the EOGO increases the flexural strength of SFRC in terms of initial crack generation and range of elastic behavior. The EOGO-SFRC required more than 30% of energy to reach the initial crack point than the SFRC mixture.

The influence of mill scale and steel type on the passivation capability and impressed current-induced accelerated corrosion behavior of reinforcing steels in concrete was studied using electrochemical impedance spectroscopy (EIS) and backscattered electron (BSE) images. Conventional low-carbon (LC) reinforcing steel and Cr-bearing low-alloy (LA) reinforcing steel with and without mill scale were prepared. After natural passivation and accelerated corrosion, it was confirmed that the initial passivation capability of steels and the corrosion-induced concrete cracking were significantly affected by the mill scale on steel surface. Also, the steel type played an important role on the characteristics of the corrosion layers as well as the long-term passivation capability. Furthermore, the corrosion pattern of steels induced by this accelerated corrosion was compared with that after long-term natural exposure to chloride solution.

Biological induced calcite precipitation is a potential method being investigated for improved soil stabilization. In terms of the associated urea hydrolysis concept, three main strategies have been developed over the last 2 decades: (1) using live urease-producing bacteria, (2) using plant-extracted urease, and (3) using bacterial-extracted urease. This paper focused on evaluating the comparative benefits of two of these methods (i.e., live bacterial cell or extracted bacterial urease methods for induced calcium precipitation) in terms of their biocementation performance. Cell-based induced carbonate precipitation (ICP) (i.e., MICP) testing was completed on standard Ottawa coarse-grained sand (#20/30), and bacterial-enzyme-based (i.e., BEICP) testing was conducted individually on both coarse-grained and fine-grained (#50/70) sands. Distinctly higher unconfined compressive strength (UCS) was achieved with the BEICP method when evaluated at similar levels of calcium precipitation. Residual permeability levels remained markedly higher after BEICP testing versus MICP. The UCS of BEICP coarse-grained treated sand was approximately 450–1,500 kPa, whereas that of fine-grained treated sand had a notably lower range (i.e., 250–900 kPa) when evaluated at similar levels of ${\mathrm{CaCO}}_3$ production. These results indicate that calcium carbonate content is not the sole factor which impacts the strength of biocemented sand. Additional test-tube investigation of ICP-derived ${\mathrm{CaCO}}_3$ precipitation was used to evaluate the chemical conversion efficiency for each method, i.e., live cells (i.e., Sporosarcina pasteurii) or bacterial-extracted urease. The calcite precipitation ratio declined at higher substrate chemical concentrations. However, this ratio increased with higher rates of enzymatic activity.

This paper presents an energy-controlled fracture model to simulate mechanical behavior of cemented granular material (CGM). A modified mixed-mode cohesive zone model is developed to describe the damage behavior of the cementitious bond, which consists of Mohr-Coulomb yield criterion and strain-softening formula controlled by fracture energy. This developed constitutive model is implemented in a three-dimensional discrete element method (DEM) simulation. Three-point bending tests are used to calibrate model parameters. A group of uniaxial compression tests are carried out to study the mechanical behavior and fracture propagation. The study investigates how cementation can influence the strength parameters at the peak and postpeak states that govern softening behavior of CGMs. Strong agreement between experimental and numerical stress-strain curves was achieved. The numerical simulation presents strong and weak force chains and quantifies the bond damage process as well as the damage distribution. A comprehensive sensitivity analysis is provided by varying parameters in the mixed-mode cohesive zone model, and their influence on the stress-strain behavior of CGM is also illustrated.

Based on the room-temperature and high-temperature test method (steady state and transient state), a series of mechanical property tensile tests was carried out on S30408 (AISI304) austenitic stainless-steel materials. There were 72 specimens in total, including 8 specimens at room temperature, 28 specimens for a high-temperature steady-state test, and 36 specimens for a high-temperature transient-state test. Through the experimental investigation, the mechanical properties of stainless steel at room and elevated temperatures were obtained. The stress-strain curves of stainless steel at elevated temperatures were given and the development laws in a large range of strain were revealed. The tensile test results show that (1) with increasing temperature, the mechanical properties (elastic modulus, yield strength, and ultimate strength) of stainless steel continuously decrease; (2) the nominal yield strength of stainless steel in corner areas is higher than that in flat areas at the same temperature; and (3) the test loading rate has a significant effect on the stress-strain curve of stainless steel at elevated temperatures; with a higher loading rate, all strength indexes of stainless steel at elevated temperatures are improved. In this paper, a theoretical model for stress-strain curves of stainless steel at elevated temperatures, containing five mechanical property parameters, was developed by theoretical derivation, and the accuracy of the theoretical model was verified by experimental results. Next, the high-temperature reduction coefficients of the five mechanical property parameters in the theoretical model were analyzed by numerical simulation, their calculation formulas were fitted, and a reliability analysis was carried out on the five parameters using SPSS. Finally, a complete theoretical model of the stress-strain curve of stainless steel at elevated temperatures was proposed that can accurately predict the mechanical properties of austenitic stainless steel at elevated temperatures.

Chloride transport is an important subject for the durability of steel-reinforced concrete structures in chloride-laden environments. There are several different types of tests for determination of the chloride-transport properties of concretes. The understanding of the differences between these tests is critical for choosing the most suitable type of test. Besides, there are different factors affecting the chloride transport in concrete, such as the water/binder (w/b) ratio, cement type or mineral additives, and the stress levels (since concrete structures are designed to withstand different loads). This work aims to evaluate the applicability and feasibility of different chloride-transport tests on concretes predamaged by compression. Moreover, the combined effect of predamage caused by different stress levels and the concrete mix design (w/b ratio, mineral additives) on chloride transport in concrete were investigated. The results show that the chloride profiles and the chloride diffusion coefficients in the chloride sorption + diffusion tests are much higher than those in the chloride diffusion tests, especially for the concretes subjected to higher stress levels. This indicates that the effect of sorption on the increase of chloride ingress into concrete is more significant when the concrete has more microcracks. Sorption was found to have minimum influence on the surface chloride content. The chloride migration coefficients were found to be higher than the chloride diffusion coefficients, especially for the concretes with a higher stress level. The partial replacement of ordinary Portland cement (OPC) with ground granulated blast-furnace slag (GGBS) can significantly reduce the detrimental effects caused by the high stress levels on chloride transport in all three methods.

A Cr-bearing low-alloy (LA) reinforcing steel with two different surface conditions (polished surface and as-received ribbed surface) was investigated using various electrochemical measurements and microstructural characterization techniques for their corrosion resistance when exposed to alkaline solutions containing low chloride concentration (0.1 M NaCl) and high chloride concentration (3.0 M NaCl). Low-alkaline saturated ${\mathrm{Ca}(\mathrm{OH})}_2$ solution (CH solution) and high-alkaline solution (CP solution) were used to simulate the electrolytic environments of concrete. It was confirmed that, due to the presence of defective mill scale and ribs on the steel surface, which are susceptible to chloride-induced corrosion, the ribbed LA steel exhibited much lower corrosion resistance than the polished LA steel exposed to the two alkaline solutions with chlorides. In the low-chloride condition (0.1 M), both steels in CP solution had higher corrosion resistance than in CH solution. However, in the presence of 3.0 M NaCl, CH solution provided unexpectedly higher protection to both ribbed and polished LA steels than did CP solution, which was attributed mainly to the formation of Ca-containing precipitates on the surface of the corroded steel exposed to CH solution, thereby suppressing the cathodic reaction by delaying the oxygen diffusion.

This paper examines the fatigue behavior of steel/glass fiber reinforced polymer (GFRP) double-strap joints under a variation of cyclic shear loading at different given temperatures. Initial experiments were performed at a constant amplitude force, which demonstrated a reduction in fatigue strength at increasing temperatures. The results were used for cumulative relative damage calculation purposes. Subsequent tests were then performed under two-stress level fatigue (TSLF) tests with a given temperature. The TSLF tests demonstrated the following: (1) relative to results at 20°C, the damage was retarded at lower temperatures ($-10°\mathrm{C}$ and 0°C), and the damage accelerated at higher temperatures (40°C); and (2) linear damage accumulation models, such as the Palmgren-Miner model, are not appropriate and tend to overpredict fatigue life. By using the nonlinear strength wearout and linear cycle mix models for bonded joints, an improved prediction method is proposed, and the fatigue results of the TSLF tests were discussed in which it was found that the proposed method can accurately predict the fatigue lifetime.

A key requirement for performance-based specification for pavement materials is the selection of laboratory tests that can predict their response under conditions similar to those encountered in the field. This paper presents the results of a study that was conducted to evaluate the capability of different laboratory tests to predict the behavior of unbound granular base course materials under cyclic traffic loading. To achieve this objective, a laboratory testing program was conducted on three types of unbound granular base course materials, namely limestone, sandstone, and granite. The laboratory testing program included conducting a static triaxial test as well as three types of repeated load triaxial (RLT) tests on the materials considered at their optimum field compaction conditions. The three types of RLT tests considered included: resilient modulus, single-stage, and multistage RLT tests. The results of the static triaxial tests showed that the considered materials had similar shear strength properties. However, the RLT test results showed a distinct behavior between those materials, such that the limestone and sandstone exhibited the highest and lowest resilient modulus values, respectively, in the resilient modulus test. In addition, the granite and sandstone accumulated the highest and lowest permanent strain, respectively, in both single-stage and multistage RLT tests. The multistage showed that the granite and limestone experienced the unstable collapse behavior at higher cyclic deviatoric stress than sandstone. In addition, the results demonstrated that the resilient strain behavior was distinct from that of the permanent strain, which indicates that the resilient modulus test cannot be solely used to evaluate the performance of base course materials under cyclic traffic loading. Finally, this study demonstrated that the multistage RLT test provides an important tool to characterize the long-term behavior of a base course material at varying stress conditions. Therefore, it is recommended to use this test in future performance-based specification.

An alternative carbonation technique was studied with normal concrete (NC) and concrete blended with natural zeolite (ZC) samples under an artificial environment with the help of carbonated-water curing. The effect of carbonated-water curing on concrete mixes incorporating natural zeolite powder as a partial replacement for cement was examined in this study. Accelerated carbonation was carried out by immersing concrete specimens in a 0.352-M sodium bicarbonate solution. The experimental program consisted of the evaluation of compressive strength, pH profiling, measurement of carbonation depth, X-ray diffraction (XRD), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), and chemical composition measurements in order to study the extent of carbonation. ZC specimens cured in carbonated water had higher compressive strength development, greater extent of ${\mathrm{CaCO}}_3$ formation, and lower pH values than concrete cured in normal water for same curing period. Results obtained from XRD, TGA, FTIR, and chemical composition measurements showed that the amount of calcium carbonate increased in the carbonated concrete, which is closely associated with carbonation.

Early-age carbonation for concrete curing has gained increasing attention due to the remarkably enhanced material performance and substantial ${\mathrm{CO}}_2$ storage capability. However, carbonation curing leads to reductions in concrete pH and may weaken concrete’s ability to resist weathering carbonation–induced corrosion during service. This study examines the atmospheric weathering carbonation behavior of portland cement–based concretes after carbonation curing. Two types of concrete mixtures representing normal and high-strength concretes were cured with carbonation at two different durations of high-pressure ${\mathrm{CO}}_2$ exposure. Compressive strength and water absorption of concrete were measured upon the completion of carbonation curing and the 28-day subsequent moisture curing. An accelerated weathering carbonation test (AWCT) was consecutively performed for 12 weeks, and concrete carbonation depth, pH distribution, and compressive strength were measured. It was found that the coefficients of ${\mathrm{CO}}_2$ diffusion due to weathering carbonation were significantly reduced in concrete subject to carbonation curing. The ultimate carbonation depth was attributed to both carbonation curing and weathering carbonation. The normal strength concrete with a higher water-to-cement (w/c) ratio showed a larger ultimate carbonation depth because of the more intensive carbonation curing but was found to substantially slow down the rate of weathering carbonation. With sufficient rebar depth, reinforced concretes made with this mix design could potentially develop a more robust resistance to weathering carbonation–induced corrosion through carbonation curing. With a lower w/c ratio, high-strength concrete cured by carbonation appeared less vulnerable to weathering carbonation due to the lower intensity of carbonation curing and hence proved to be viable for this curing approach. On exposure to 12-week AWCT, concrete made with $0.4\mathrm{w}/\mathrm{c}$ ratio exhibited comparable carbonation depths and pH profiles regardless of curing methods. It is inferred that carbonation curing could potentially be applied to normal-strength reinforced concretes with large rebar depths or general high-strength concrete formulations without accentuating the risk of carbonation-induced corrosion.

Bridges constructed with adjacent precast concrete box beams have been in service for many years. A recurring problem with this type of bridge is cracking in the longitudinal joints between adjacent beams. Many research results have indicated that efficient joint material should have small or zero shrinkage at an early age and achieve sufficient bond strength at the interface between the joint and the box beam. As the first part of a comprehensive study, two phases of material properties tests were conducted to select the best material for the joint between adjacent box beams to resist cracking. During Phase I work, four potential joint materials were tested and evaluated based on shrinkage, flexural tensile strength, and normal bond strength. During Phase II work, time-dependent material testing was conducted on the materials selected from Phase I to characterize the nonlinear changes in bond, compressive, and tensile strength with time. In addition, three-dimensional (3D) finite-element models (FEMs) were developed to calculate the early-age joint stress distribution and evaluate the structural performance of a Type IV joint grouted with epoxy grout and a Type V joint filled with shrinkage-compensated concrete. A finite-element modeling approach that is capable of simulating early-age joint behavior was illustrated, and models were developed for beam-joint-beam structures that were 1.2 m (4 ft) long. The analytical results indicated that a Type V joint filled with shrinkage-compensated concrete is expected to better resist joint cracking than a Type IV joint filled with epoxy. Although the FEM results indicated that a Type V joint filled with shrinkage-compensated concrete still induces tensile stress near the exterior of the interface, placing reinforcement near the edge will provide sufficient capacity to resist debonding at the interface during the early-age period when initial cracking has been found to occur.

Skid resistance has long been recognized as one of the most important pavement surface characteristics for safer roads. Evaluation of skid resistance of pavement is crucial but it is not an easy task. Moreover, it depends on numerous parameters such as pavement type, materials and tire properties, and environmental conditions. Aggregate texture changes significantly according to its origin and affects the skid resistance performance of the road surfaces. In the current study, chip seal samples were produced with different aggregate types at different polishing levels to evaluate the effect of aggregate microtexture on skid resistance performance. The Micro-Deval (MD) test device was utilized to obtain polished aggregates. Different polishing levels were provided by distinct revolutions of the MD drum. To monitor the change in aggregate surface with the polishing process, aggregates were monitored by scanning electron and optical microscopes at each level. Mean texture depths (MTDs) of chip seals were determined with outflow meter test. On the other hand, dynamic friction tester (DFT) and British pendulum tester (BPT) were implemented for assessment of skid resistance according to the relevant ASTM standards. Skid resistance and texture measurements were further used to identify the International Friction Index (IFI) for each sample. In addition, a correlational analysis was conducted between DFT and BPT results, and variable relationships were set for different speeds. Consequently, better skid resistance values were observed for chip seals produced by slags than the ones with natural aggregates at each polishing level. After fulfilling the economic and environmental requirements, using metallurgical by-products is recommended for long-lasting skid-resistant pavement surfaces. Additionally, it can be concluded that MD apparatus may be considered an easier, more cost-effective, and faster way to assess the polishing resistance of aggregates.

Given the application characteristics and shortcomings of basalt fiber in road engineering, improvements to its reinforcing effect in asphalt mixture, such as reinforcing, toughening, and bridging, are needed. A silane-coupling agent (ammonia propyl triethoxysilane, or KH550) is used to pretreat and modify the surface of basalt fiber. A comprehensive series of tests, including heat resistance, basalt fiber absorption asphalt capacity, segregation and dispersion performance, and micromorphology of a drawing fracture surface, is conducted to examine the road performance of the modified basalt fiber. Furthermore, the modification mechanism of the KH550 solution on the basalt fiber interface is analyzed using infrared spectrometry, scanning electron microscopy, and X-ray energy spectroscopy. The results show that the KH550 solution can significantly improve the interfacial properties of the basalt fiber, form convexities with stable chemical bonds on the basalt fiber surface, and significantly enhance its cohesive force with asphalt. Overall, the KH550 solution significantly enhances the effect of the basalt fibers in an asphalt mixture.

The surface morphology of fibers influence the global performance of fiber-reinforced cementitious composites. Commercially available polypropylene fibers may be coated with polyglycol ester to facilitate the fiber production process; this coating cannot be detected easily. In this study, it was demonstrated that, although the coating does not change the mechanical strength and elongation at break of a single polypropylene fiber, the interface bonding characteristics of polypropylene fibers with the cement matrix are modified by the coating; this leads to changes in global mechanical performance (which are characterized by the tensile and flexural response) of the composite.

Thermally tempered glass fails into small and blunt pieces upon fracture, and therefore is the product of choice when a degree of safety is required from a monolithic glass panel. The characteristic fracture pattern is the result of residual stresses in the glass that are induced during the tempering process and released during fracture. Previous research sought to correlate residual stress with the size of the fragments. In this paper, the two salient models (Barsom’s and Gulati’s) were described and validated against new experimental data. The experimental data were obtained by inducing fracture in specially prepared thermally tempered glass panels. The glass panels consisted of an unprecedented wide range of residual stress, obtained by a carefully executed thermal relaxation process. The residual stress of the specimens was measured with a scattered light polariscope that was calibrated by means of a specially devised experimental approach. It was shown that Barsom’s model is the more accurate of the two and is appropriate for predicting the fragmentation of glass with a surface residual compression larger than 60 MPa. The accuracy and precision of the scattered light polariscope were found to be ±4.7 MPa and ±3.9 MPa, respectively. The findings from this study provide a basis for a nondestructive safety evaluation of thermally tempered glass.

A computational modeling procedure for generating a random aggregate structure (RAS) for recycled concrete aggregate (RCA) materials is proposed in this paper. The two-dimensional aggregate generation was based on a convex hull algorithm to randomize arbitrary planar shapes of RCA particles. During the generation of RAS, randomizations of the maximum aggregate size and spatial distribution of RCA particles were considered. Finite-element models for RCA systems were generated based on an extensive image analysis procedure. Numerical analyses were performed for 12 different RCA systems including crushed-shape and rounded-shape aggregates by varying the morphological parameters of the RCA particles. The mechanical performance of RCA systems with different particle shapes, maximum aggregate sizes, adhered mortar content levels, and aggregate ratios were used as factors to evaluate the mechanical performance of RCA systems under simulated compressive loading. Numerical results were compared with experimental studies from a large statistical database. The numerical simulation results for the mechanical properties of RCA systems showed represented experimental behavior such as the simulated elastic moduli and compressive strengths were within one and two standard deviations, respectively, of experimental results from a robust data set obtained through a detailed literature investigation. The proposed aggregate generation approach and numerical simulation procedure can be used by researchers to better understand how aggregate morphological properties influence the mechanical behavior of concrete made with recycled aggregates.

This paper discusses the effect of the particle packing method (PPM) of mix design on the fracture behavior of concrete. A three-point bending (TPB) test was performed on single-edge notched beam for three different sizes. The fracture energy is estimated from the load (P)–crack mouth opening displacement (CMOD) relationship obtained from the TPB test. By truncating the end of the P–CMOD curve at different lengths, the sensitivity of fracture energy is analyzed, and eventually it is recommended to be at 2% of the depth of the beam. The fracture toughness parameters are calculated analytically using a double-$K$ fracture model. The size effect on the fracture energy and fracture toughness parameters is studied. The PPM mix design provides improved fracture energy and fracture toughness parameters of concrete with respect to the conventional mix design approach.

Since fly ash is an industrial by-product, its properties are not controlled and, as such, are highly variable, leading to a high degree of variability in the performance of concrete. The feasibility of the blending of fly ashes in order to homogenize their properties was investigated by studying the variability in the heat of hydration and compressive strength of mortar mixes. All the mixes, including control mixes as well as blends, were prepared by replacing 30% ordinary portland cement (OPC) with either one fly ash or a blend of fly ashes. Blends of various fly ashes were prepared to homogenize their Blaine fineness, reactive silica content, and alumina content, the main parameters that influence the properties of concrete. It was found that blending the fly ashes, obtained from different sources, reduces the variability in the heat of hydration and the compressive strength. Single and double parameter blends were prepared to homogenize either a single or two parameters of fly ash by blending two or more fly ashes. It was observed that all the blends effectively reduced the variations in the hydration of cement and strength of cement mortars. Additionally, it was also found that homogenizing the Blaine fineness was the most effective means to reduce the variation in the performance of the mortars.

The rotational failure of backfills and embankments is known to be involved with inhering anisotropic effects resulting from different stress paths along the rotational shear plane. The granulated rubber–sand mixtures have been lately used in embankments and backfills as light additives while their anisotropic effects are not well understood. This paper investigates the effect of stress rotation angle ($\alpha$) and intermediate stress ratio ($b$) on shear strength and excess pore-water pressure (PWP) variations of granulated rubber–sand mixtures (GRSM) under undrained conditions using a hollow cylinder apparatus (HCA). Specimens are prepared using different percentages (by weight) of granulated rubber. The experimental results show that for a specific granulated rubber percentage, increasing $\alpha$ from 0° to 60° and/or $b$ from 0 to 1 reduces the shear strength and increases PWP of GRSM. Moreover, by increasing granulated rubber percentage (up to 20%), the mixture becomes more isotropic, and the effects of $\alpha$ and/or $b$ on shear strength degradations and PWP variations are reduced. The reducing effect of anisotropy is further investigated quantitatively through evaluating the rotational shear strength and failure potential of an embankment resting on a granulated rubber–sand mixture layer.

The current study aims at examining the effect of different calcium-based stabilizers {calcium hydroxide [$\mathrm{Ca}{(\mathrm{OH})}_2$], calcium carbonate [${\mathrm{CaCO}}_3$], and calcium chloride [${\mathrm{CaCl}}_2$]} on the geotechnical properties and lime-leaching behavior of expansive clay. The lime-leaching tests were conducted on clay samples that were compacted at maximum Proctor dry density values relying on specially fabricated molds and subjected to water flow conditions for a specific period (up to 7 days). In order to study the effect of pore fluid on the lime-leachability patterns, the pH of the leaching solution was kept at 7 (pH of deionized double-distilled water) and at 4 (adjusted using 0.1 N ${\mathrm{HNO}}_3$). The effect of curing period (1, 7, 14, and 28 days) on the lime-leaching pattern and unconfined compression strength (UCS) behavior were also studied. One-dimensional fixed-ring consolidation tests were performed to quantify the effect of various stabilizers (at fixed dosage of 4% by weight of dry sample) on the swell and deformation characteristics. The results of the study indicate that with an increase in curing period, irrespective of the type of stabilizer, the calcium concentration in the leachate reduced. The flow duration (7 days was adopted in the study) had an insignificant effect on the resultant lime-leaching values. When acidic water was used as flushing solution, relatively higher concentrations of calcium were noticed, which further establishes the fact that amorphous pozzolanic compounds formed in the early hydration reaction stages are easily soluble. Furthermore, the associated anions in respective stabilizers have a direct bearing on the resultant UCS and consolidation behavior.

This paper focuses on the effect of supplementary cementitious materials on early-age mechanical and viscoelastic properties of concrete, restrained shrinkage-induced cracking, and time to cracking. Compressive strength, indirect tensile strength, and the elastic modulus were measured with different percentage of ordinary portland cement (OPC) replacement using either fly ash, ground-granulated blast-furnace slag (GGBFS), or ferronickel slag (FNS). Tensile creep and drying shrinkage were measured on dog-bone–shaped specimens. Restrained shrinkage-induced stresses and concrete cracking age were assessed by using the ring test. Results revealed that early-age strength development of fly ash–, GGBFS-, and FNS-blended concrete is lower than that of the corresponding OPC concrete. Similar tensile creep coefficients were observed for fly ash–blended concrete and OPC reference concrete whereas GGBFS- and FNS-blended concretes showed significantly higher tensile creep. Drying shrinkage was not altered to a great extent when OPC was replaced by fly ash. However, concrete containing GGBFS and FNS showed more shrinkage than OPC concrete. Partial replacement of OPC by supplementary cementitious materials resulted in a shorter time to cracking. 30% OPC replacement by FNS had the lowest influence on time to cracking with only 20% reduction compared to the reference OPC concrete. 20% replacement by fly ash and 30% replacement by GGBFS led to a reduction in time to cracking of about 33% and 40%, respectively, compared to the reference OPC concrete.

The microstructural, mechanical, and shrinkage characteristics of cement mortar containing 100% fine reclaimed asphalt pavement (RAP-mortar) were revealed through an extensive experimental program in this study. The work utilized petrographic technology and isothermal microcalorimetry to investigate microstructural features and cement heat of hydration. Mechanical properties were determined, and shrinkage properties and cracking potential under restrained drying condition were characterized through the shrinkage test and a customized ring test, respectively. Despite significant strength loss and high shrinkage, the RAP-mortar exhibited higher ductility, toughness, and crack resistance compared with the plain mortar. A potential material application for the RAP-mortar could be the structures whose strength requirement is low but are vulnerable to cracking problems. The RAP-mortar material might also be used for attenuation of high energy thanks to its improved ductility and toughness.

Fly ash–based geopolymers are being developed as sustainable alternate binders for producing concrete. The consistent production of a stable geopolymeric binder suitable for use in structural applications from alkaline activation of low-calcium fly ash was explored in this paper. The role of working solution and total reactive oxide ratios in consistently achieving high compressive strength in fly ash–based geopolymers were evaluated using different source fly ashes. The primary source variability was identified with the reactive silica and alumina contents in the fly ash. The maximum strength achieved from the activated fly ash was determined by the reactive alumina content in the fly ash. Due to source variability of reactive species contributed by fly ash, maintaining a constant composition of the activating solution resulted in varying compressive strength from the activated fly ash. Keeping constant reactive oxide contents in the activated system produced consistent strength from the fly ash–based geopolymers. The composition of the aluminosilicate gel depended on the reactive oxide ratios, and it varied with the fly ash composition for identical solution ratios. Global reactive oxide ratios, which are calculated based on the reactive oxide contents of the fly ash and the alkaline solution, were established. The link between strength and product formation was established, and the global reactive oxide ratios resulted in a larger reaction product content.

This work studied the influence of pores of different scales on the strength of cementitious materials. A method to make pores in cementitious materials with particles of soft materials was developed and proved. With this method, mortar specimens with different porosity and pore-size distributions were prepared. The results of static and dynamic strength tests showed that the static and dynamic compressive strength decreases with the increase of porosity and average pore radius, whereas the strain rate sensitivity increases. Predictive models of static strength, dynamic strength, dynamic increase factor, and their respective relationships with multiscale porosity were proposed. The influence of multiscale pores on strength and strain rate sensitivity was calculated quantitatively. It indicated that when the pore radius is larger than 100 nm, at the same pore volume the effect of pores on static strength, dynamic strength, and strain rate sensitivity increases with the pore radius.

The importance of selecting suitable aggregates in very-high-strength concrete (VHSC) ($>100\mathrm{MPa}$) and high-strength concrete (HSC) (50–100 MPa) formulations and quantifying their influence on the mechanical properties is the focus of this study. The effect of two aggregate types, basalt and granite, on hardened properties was investigated. The study showed that selecting suitable aggregate is vital to produce VHSC with compressive strengths up to 150 MPa or more, and suitable aggregate types are proposed. The currently available models cannot predict the properties of HSC and VHSC accurately considering the aggregate effects. Finally, using results of present experimental program and the literature, new expressions including aggregate density as the aggregate parameter are proposed to formulate and predict elastic modulus of HSC and VHSC.

The use of steel fiber–reinforced (SFR) cement based materials for semistructural applications is expected to increase because some design codes propose such methods for design. The first step for the steel fiber–reinforced concrete (SFRC) design is using correct parameters for material properties. The behavior of concrete under compression and tension is evaluated by using standards. The tension behavior of concrete materials is evaluated, most of the time, via bending tests because these tests are relatively less cumbersome when compared to direct tensile tests. The existing standards/codes suggest using different geometries and set-ups for evaluating bending performance because very different geometries are being used in the structural design. Studies have been conducted by researchers to understand the parameters affecting the results obtained from the bending tests. In this study, the effects of varying shear span-to-depth ratios ($a/d$) and specimen depth to steel fiber length ratios ($d/f_L$) on the most used design parameters [i.e., the equivalent bending strength (EBS) and bending strength ratio (EBR)] were studied with different steel fiber types and amounts, and the results were discussed based on current standards limitations on size and the $d/f_L$ ratio. A thorough evaluation of the fresh and hardened state properties was carried out for a full understanding of material properties, and a detailed fiber orientation density analysis was also done for the correct evaluation of the flexural test results.

Incorporation of high contents of reclaimed asphalt pavement (RAP) in asphalt mixes produced at warm-mix asphalt (WMA) temperatures raises questions about the interaction between the RAP and the WMA additives and the performance of these mixes. In this study, a two-phase experimental program was devised to examine the effect of six factors, including mixing/compaction temperatures, RAP content and source, WMA type, binder grade, and conditioning duration, on the volumetric properties, compaction, and cracking performance of RAP-WMA mixes. The results showed that mixing/compaction temperatures, RAP content, and RAP source have statistically significant effects on the compaction of the mixes. Semicircular bend (SCB) results showed that RAP content overwhelms the effect of all other factors. More importantly, the experimental program revealed that some mixes passed the volumetric requirements but failed the cracking test. This is a critical finding given the increased production of unconventional mixes that came into use after the development of current specifications. The current state of practice needs to be upgraded to incorporate performance as part of the mix design process.

The aim of this study was to test the isotropic behavior hypothesis for concrete by means of wave propagation tests. The elastic properties of the concrete were determined using ultrasound tests with 1.0 MHz longitudinal and transversal transducers in polyhedral specimens with 26 faces. The concrete was analyzed using the theoretical aspects of three types of elastic behavior, namely isotropy, transverse isotropy, and orthotropy, in concretes with different compressive strengths and coarse aggregate size distributions. The results show that there were no statistically significant differences in the elastic parameters on the three symmetry axes. The constitutive relation between the shear modulus and longitudinal modulus, which involves Poisson’s ratio, was as expected for isotropic materials, and the elastic properties of the concrete differed equally as a function of the compressive strength. Considering the results, the isotropic behavior of the concrete was validated regardless of the elastic behavior adopted in the analyses.

An experimental investigation was carried out to evaluate the influence of fines content on the hysteretic behavior of water-retention characteristic curves (WRCCs) of reconstituted soil subjected to wetting and drying cycles. The red soil fines were collected from the Indian Institute of Technology Hyderabad, Kandi, Sangareddy. An Indian Standard Grade-II sand (i.e., Ennore sand) was reconstituted including red soil fines content of varying percentages (30%, 40%, 50%, 60%, 70%, 80%, 90%, and 100%) by dry weight of sand to produce different soil mixes. The filter paper method was adopted to measure the effect of the fines content on the WRCCs for both drying and wetting cycles. Experimental results revealed that the presence of fines influences the shape of the WRCC. The results further revealed that the WRCC of soil is hysteretic in nature as the water content is less in the wetting path compared to that in the drying path at a constant suction value. Nonlinear regression equations are proposed for the fitting parameters of the WRCC in terms of the liquid and plastic limits for the drying WRCC based on the experimental results. The present study also proposes nonlinear regression equations to predict fitting parameters of the wetting WRCC in terms of the fitting parameters of the drying WRCC. The proposed nonlinear equations are validated for soil collected from Padakal village, Mahbubnagar district, Telangana state, India. A formulation is presented to predict the degree of hysteresis based on the uniform slice method to evaluate the effect of fines content on the hysteretic behavior of WRCCs. The proposed regression fits were compared to existing fits in the literature to validate their authenticity.

Thermal conductivity, $k$, is one of the key factors that control heat transfer in concrete. This paper presents the results of an experimental study conducted to analyze the effects of modern concrete materials, such as supplementary cementitious materials (SCMs), normal-weight, lightweight, and recycled aggregates, and steel and polypropylene (PP) fibers, on the thermal conductivity of concrete. The thermal conductivity tests were performed on cylindrical specimens of concrete mixes containing various amounts of these materials. The results indicate that $k$ values of concrete reduced with the amount of SCM (slag and fly ash) replacement for cement. The mineralogy and absorption of normal weight aggregate considerably affect $k$ value of concrete. Replacing normal weight coarse aggregate by lightweight or recycled aggregate reduced the $k$ value of concrete. Addition of steel fiber at a dosage higher than 0.25% (by volume) increased $k$ value of concrete noticeably, whereas the addition of up to 2% PP fiber showed little effect.

This study aims to test the effects of aggregate properties on the features of aggregate-paste interphase in portland cement concrete mixtures. The microstructural, chemical, and nanomechanical properties of the interphase region, formed because of the interaction of two commonly used chemically-distinctive aggregates (i.e., limestone as a calcite aggregate and quartzite as a siliceous aggregate) with ordinary portland cement paste, were examined through multiscale measurements. More specifically, the microstructural, chemical, and nanomechanical properties at the interphase zone were characterized using laser scanning microscopy, scanning electron microscopy coupled with energy dispersive spectroscopy, and nanoindentation. Furthermore, a three-point bending test was used to evaluate the bond between the aggregate and paste on single edge notched beam specimen where a thin aggregate sheet was inserted. A coupled microstructural, mechanical, and chemical examination can provide integrated characterization of an interphase region formed by different aggregate properties. It was found that the thickness of interfacial debonding between aggregate and paste is more dominantly influenced by moisture absorption capacity, while the surface chemistry of the aggregates did not significantly affect the characteristics of the interphase. It was also observed that when there is a good bonding between aggregate and paste, ample calcium silicate hydrate (C─ S─ H) gel is formed close to the aggregate surface, which is demonstrated by similar Ca/Si ratios between the interphase region and adjacent paste region. On the other hand, poor interphase and resulting interfacial debonding was associated with more involvement of CH crystals at the interphase region, which was observed by greater Ca/Si ratios.

There has been a rapid increase in the use of ultrahigh-performance concrete (UHPC) in bridge connections and in bridge rehabilitation. When using UHPC in bridge construction, one common recommendation is that UHPC reach a compressive strength of at least 97 MPa before allowing traffic loads. However, bridges are subject to other loads prior to being open to traffic, such as load due to construction equipment, shrinkage, and temperature. The interface bond strength and interfacial parameters, such as adhesion/cohesion and the shear friction coefficients at early ages, are important in determining the ability of connections to resist these types of loads early on after casting. In this study, the interfacial bond strength between high-strength concrete (HSC) and UHPC was determined using pull-off, bi-shear, and slant-shear test methods at different ages. These test methods provide values of bond strength for different stress scenarios at interfaces, and the resulting values of bond strength vary by the test used. The adhesion/cohesion coefficients were calculated using experimental data, and the mean values were found to be in the range of 1.9–3.6 MPa and 3.2–6.5 MPa under tension and shear, respectively. The friction coefficients were found to be in the range of 1.37–1.52 due to tension and 1.07–1.37 due to shear. This research found that the adhesion/cohesion and friction coefficients are much higher than the values reported in AASHTO for initially roughened surfaces.

Microbial-induced calcium carbonate precipitation (MICP) technique takes advantage of the metabolic process of bacteria bonding soil particles together with an environmentally-friendly and sustainable manner. In this study, powder of activated carbon-fiber felt (ACFF) scrap was utilized together with MICP to improve soil strength, and six different ACFF ratios (0%, 0.2%, 0.6%, 1%, 1.4%, and 2% by weight) were adopted. Unconfined compressive strength (UCS) and splitting tensile strength (TS) tests were carried out for evaluating the effect of ACFF on the dry and saturated strength of MICP-treated sand. It was found that the bacterial immobilization extent increases in the presence of ACFF, subsequently resulting in a greater yield of calcium carbonate. UCS and TS are remarkably enhanced with a small quantity of ACFF, and softening degree caused by water can also be improved by ACFF. However, only strength rather than ductility could be enhanced by ACFF. On the whole, wasted ACFF scrap could be effectively reused in the MICP technique because of the better behavior of ACFF reinforced MICP-treated sand.

High-early-strength concrete (HESC) made of Type III cement attains approximately 60%–70% of its design compressive strength at ambient temperature in 1 day. A numerical method incorporating a rate-constant model was developed to optimize curing regimes for HESC at preassigned maximum temperatures of 40°C, 50°C, and 60°C with design concrete compressive strengths of 30, 40, and 50 MPa. The use of HESC after optimization resulted in 36%–55% savings in terms of energy index, compared with the curing regime typically applied for concrete with Type I cement. Experimental verification was performed by compression tests for HESC that were cured according to the optimum regimes. Compared with conventional trial-and-error mix methods, the developed numerical model contributes to a significant reduction of the number of trial mixes and provides in a systematic way the effects of design variables on optimum curing regimes.

This article presents mass stabilization studies performed on very soft organic clay, with very high water content, very low pH value, and high clay activity, treated with high early strength dry portland cement. The specimens were prepared in a laboratory with differing cement contents and subjected to unconfined compression tests under different preloading conditions and curing times. Undisturbed samples of the mass stabilized soil were collected in situ and subjected to unconfined compression tests. The results showed that the preloading during the curing period and the amount of cement directly influenced the strength and the secant modulus of the organic clay stabilized in the laboratory, reducing the porosity of the specific blends studied. The strength measured in the laboratory specimens was about twice as high as the strength measured in the field specimens, which, in turn, was about five times higher than the strength of unstabilized soil. Finally, it can be concluded that for the highly organic clay and cement blend conditions studied in this paper, the porosity controls the mechanical properties of the blends.

The recycling of cement-stabilized macadam (CSM) is beneficial from the effective utilization of resources and the viewpoint of environmental preservation. For the effective utilization of CSM, it is useful to use CSM as recycled aggregates for hot-mix asphalt (HMA) productions as aggregates. In order to make this technology feasible, mixture design, chemical and physical properties, and durability of recycled aggregate hot-mix asphalt (RAHMA) should be engaged in the processing of demolished CSM. The objective of this study is to develop one RAHMA by recycling the base layer of semirigid pavements, and to assess the performance of natural and methanesiliconic acid sodium salt solution (MASS) enhanced RAHMA. Initial laboratory results find that the MASS treatments were beneficial to the performance of RAHMA; however, moisture resistance was found to be unsatisfactory. To improve moisture resistance, cement and hydrated lime fillers were applied in this study. The combined 1.75% by weight cement/ hydrated lime (1:1) was found to perform the best of the cases utilizing improved moisture resistance of RAHMA. Also, all of the residue Marshall stability ratio ($M{S}_0$) and the splitting tensile strength ratio (TSR) were found to meet specifications. However, although the unaging and short-term aging performance of RAHMA were successful, all of the moisture resistance indicators of long-term aged RAHMA fell below standard rirements. Therefore, the long-term performance of the proposed RAHMA rires further improvement and study. While the particular use for RAHMA needs improvement concerning moisture durability, the enhancement methods mentioned in this study should be considered in the application of recycling CSM in hot-mix asphalt productions.

Concrete creep is related to not only loading age and holding time but also curing temperature and humidity. To investigate the influences of curing temperature and humidity on creep performance, tensile creep tests of hydraulic concrete were conducted under different curing conditions (wrapped, exposed, and water). First, based on the measured strains in the compensation specimens, strain statistical models were established to separate the thermal strain, autogenous volume strain, dry shrinkage strain, and wet expansion strain under different curing conditions. Then, the measured strains in the loaded specimens and compensation specimens were investigated. Analogous to the dry shrinkage strain and drying creep, the concept of wet expansion creep, which corresponds to the wet expansion strain, was proposed. Hence, the total creep strain, basic creep strain, drying creep strain, and wet expansion creep strain results were obtained under different curing conditions. Finally, based on the equivalent-age theory, a fractional-order creep model that considers the coupling effects of temperature and humidity was proposed for hydraulic concrete, and the parameters of the new model were determined using the tensile creep test data and a complex optimization method. The results show that the fractional-order creep model can describe the growth rule of the tensile creep of concrete under different curing conditions.