Journal of Materials in Civil Engineering

Steel–concrete composite structures are widely used in modern buildings and bridges for their great rigidity, light weight, and simple construction. However, the mechanical behaviors of steel–concrete composite structures degrade over time because of environmental corrosion and long-term load. The existing research on structural durability has often focused on concrete or steel structures. Few studies have been conducted on steel–concrete composite structures, especially on structures under the coupled impact of corrosion and load. To investigate the coupled impact of corrosion and load on the performance of steel–concrete composite structures, a long-term test of 200 days was carried out on eight connectors. The corrosion of the studs was accelerated by DC current, and the test connectors were submerged in a salt solution with a concentration of 5% NaCl. Deformations including the concrete strain and relative slippage between the concrete slab and the steel beam were measured in the long-term test. The experimental results showed that at the end of the long-term test, the deformations induced by shrinkage were about three times larger than those induced by creep for the steel–concrete composite structures. Notably, the stiffness of the connectors degraded substantially with the aggravation of the corrosion of the studs, whereas the concrete strain was only slightly affected by the studs’ corrosion. The measured deformations were also obviously larger than those calculated by the current specifications. As a reference, a suitable formula for the long-term elastic modulus is proposed to enhance the applicability of specifications.

In the present work, the dynamic stress-strain responses of three types of rock, compact basalt, metadolerite, and granite, are tested under high loading rates using the 38-mm-diameter split Hopkinson pressure bar (SHPB) device for the first time in the literature. The static characterization of the rocks, i.e., the physical and static mechanical properties of the three types of rock, was also determined. Petrological studies of the rocks were carried out through scanning electron microscope and X-ray diffraction tests. In the dynamic tests using the SHPB device, the stress-strain response, dynamic peak stress, and dynamic elastic modulus were studied. The effect of the mineralogy of the rock on peak stress and the dynamic elastic modulus was also studied under varying strain rates. Two correlation equations for the dynamic strength increase factor of compact basalt and granite are proposed herein.

Pavement engineers are continually attempting to resolve the problems associated with the disposal of highway construction materials and conserve the natural resources in line with producing a more economically and environmentally friendly asphalt mixture. This study presents a novel methodology to investigate and obtain a complete blending in the laboratory using a nanomechanical approach so that designers can be more confident in estimating the performance of asphalt mixtures incorporating reclaimed asphalt pavement (RAP) materials. The study also presents an effect of warm additives, Sasobit and Rediset LQ, on the level of blending between RAP and virgin materials. Images obtained from nanoindentation were validated using a scanning electron microscope (SEM), while the level of blending was linked to the overall fatigue cracking of asphalt mixtures, which was measured using dynamic shear rheometer (DSR). It was revealed that although Rediset LQ improved the fatigue life and nanomechanical properties of the virgin interfacial transition zone (ITZ) and mastic phases, it has no effect on the diffusion of virgin binder into aged binder (binder surrounding RAP aggregate) or rejuvenating of aged binder, whereas Sasobit decreased the viscosity of binder and has a great influence in accelerating complete blending between RAP and virgin materials. In summary, nanoindentation integrated with an optical microscopy is a powerful technique to investigate and obtain complete blending between RAP and virgin materials.

The strength reduction associated with the replacement of the virgin coarse aggregate in concrete with recycled asphalt pavement (RAP) limits the use of the RAP concrete to nonstructural applications. Recent research has suggested that RAP concrete might retain sufficient strength for structural applications if high-strength concrete mixture designs were used. Before these high-strength RAP concrete mixtures can be used in transportation infrastructure applications, their durability must be proven. This study evaluated the chloride permeability, the freeze-thaw durability, and the coefficient of thermal expansion of high-strength RAP concrete mixtures. The results indicated that the chloride permeability of the high-strength concrete, as measured by the surface resistivity, was unaffected by the replacement of up to 50% of virgin coarse aggregate with RAP. Furthermore, the freeze-thaw durability of high-strength RAP concrete was improved over high-strength concrete with 100% virgin coarse aggregate. The optimal RAP fraction in terms of the freeze/thaw durability was 35% by mass. Finally, the coefficient of thermal expansion was minimally affected by the replacement of up to 50% of virgin coarse aggregate with RAP. On the basis of these results, the durability of high-strength concrete with RAP coarse aggregate was deemed sufficient for transportation infrastructure applications.

High-strength steels are finding wide applications in steel-framed buildings. Therefore, fire resistance design of high-strength steel structures has gained more attention in recent years. Rapid reduction in mechanical properties, together with high creep deformations, are the most significant factors influencing the fire behavior of high-strength steel structures. A comprehensive experimental investigation was carried out to evaluate temperature-dependent mechanical properties and creep deformation of high-strength Q690 steel with nominal yield strength of 690 MPa. Standard tensile tests were conducted to obtain the mechanical properties of Q690 steel at temperatures ranging from 20 to 900°C. Test data on strength and elastic modulus properties show that the reduction factors developed for carbon (mild) steel are not applicable to high-strength Q690 steels. Therefore, new reduction factors for temperature-dependent yield strength and elastic modulus, as well as the stress-strain relationship, were developed. Creep tests were also carried out to quantify the creep deformation of Q690 steel at temperatures ranging from 450 to 900°C. Data from creep tests are used to develop relations for expressing creep as a function of temperature and stress. These relations, which are based on the Fields and Fields model, can be used to account for creep effects in modeling the response of Q690 steel structures exposed to fire.

Bioasphalt could replace petroleum-based asphalt due to its renewability and environmental friendliness. However, bioasphalt made from different raw materials or processing technologies has different properties and performance. This study investigates and compares the performance of two bioasphalts made from corn (DC) and castor (SH). Elemental analysis shows that both DC and SH have very high oxygen content. Fourier-transform infrared spectroscopy (FTIR) analysis indicates that a certain amount of alcohols and fatty acids exists in DC and SH, respectively. Thermogravimetry–differential scanning calorimetry (TG-DSC) analysis shows that SH exhibits excellent thermal stability whereas that of DC is poor. Moreover, it is found bioasphalt can reduce the viscosity of asphalt binder but has poor aging resistance, especially for DC. The viscosity temperature susceptibility (VTS) demonstrates that bioasphalt can increase the temperature susceptibility of base asphalt. Rheological tests using a dynamic shear rheometer (DSR) illustrate that DC can improve the high-temperature performance whereas SH can improve low-temperature performance. Mixture performance tests indicate that the addition of DC improves rutting resistance whereas SH causes the opposite trend. The addition of DC and SH reduce the low-temperature cracking resistance of mixtures to different extents. In addition, moisture damage resistance tests show that DC increases the moisture susceptibility whereas SH does not have adverse effects on moisture damage resistance. In summary, using differently sourced bioasphalt as an alternative binder to partially replace petroleum-based asphalt is feasible but caution is needed to evaluate the effect of bioasphalt on the dominant pavement failure mechanism.

In this study, the surface electrical properties of calcium silicate hydrate (C-S-H) and their influence on ionic adsorption have been investigated to be able to predict chloride binding in slag-containing cementitious materials. The experimental data showed that the electrokinetic potential of slag cement paste (SCP) is intermediate between hydrated cement paste (HCP) and C-S-H with Ca/Si of 1.0 (C-S-H:1.0) or slag calcium hydroxide paste (SCHP). Two types of C-S-H available in the hydrated SCP for ionic adsorption are considered: one is similar to the C-S-H of HCP and other is like C-S-H:1.0. The surface complexation modeling parameters for ionic adsorption on C-S-H:1.0 were estimated by fitting the experimental data to simulation results. The estimated parameters for C-S-H:1.0 together with surface complexation modeling parameters for HCP were used to predict the adsorption of chloride on SCP. The simulation results show good agreement with experimental data and follow a Freundlich isotherm. When portland cement is partially replaced by slag, it modifies the surface electrical properties of C-S-H in addition to mineralogy and pore structure and leads to change in the chloride adsorption behavior.

Concrete specimens used in this study as artificial rock samples were created to investigate the effects of grain size and specimen size on the mechanical properties of cementitious material. For this purpose, three concrete blocks were produced in which grain sizes of 12, 20, and 25 mm were used. The cylindrical specimens of diameter 56, 68, 72, and 94 mm were prepared. Nine concrete beams were created to determine the fracture toughness of the specimens. Results showed that enhancement in the uniaxial compressive strength of the specimens with diameter 56, 68, and 72 mm was monotonic as a result of the increased grain size, whereas it took a monotonic but decreasing trend in those 94 mm in diameter. Moreover, the results of bending tests indicated that fracture toughness and toughness factor increased with increasing grain size from 12 to 20 mm, whereas fracture toughness was found to decrease slightly when grain size increased from 20 to 25 mm. The findings presented here suggest that the SEL-I model predicted robust increases in strength with increasing size in specimens with a grain size of 12 mm, resulting in a fit of good quality for a grain size of 12 mm ($R^2=0.90$), whereas the coefficients of determination of $R^2=0.69$ and $R^2=0.43$ were reasonably obtained for specimens with grain sizes of 20 and 25 mm, respectively. Moreover, tensile strength decreased monotonically with increasing length-to-diameter ratio, whereas an opposite trend was observed with increasing grain size.

Improvement in rheological performance of asphalt binder with the addition of crumb rubber (CR) depends on the interaction between CR and the asphalt binder matrix. Overall, the change in any rheological property of asphalt binder with the addition of CR can be attributed to two factors: the chemical interaction between CR and the asphalt binder matrix, termed the interaction effect (IE); and the filler nature of CR particles, termed the particle effect (PE). The present research was undertaken to quantify the relative contribution of IE and PE to various parameters responsible for changes in mixing and compaction temperature, high-temperature properties, and intermediate-temperature properties through various rheological approaches. Accordingly, viscosity, $G^{*}/\mathrm{Sin}\delta$, multiple stress creep recovery (MSCR), and linear amplitude sweep (LAS) were tested using base binder modified with two CR particle sizes (ASTM# 30-40 and ASTM# 60-80) and keeping the amount of CR constant at 15% by base binder weight. In order to understand the contribution of IE and PE on different rheological parameters, three sets of samples for each CR size were prepared: (1) base binder, (2) undrained CR-modified binder, and (3) drained CR-modified binder. The effect of CR particle filler nature (through PE) was found to be significantly greater than the effect of chemical interaction (through IE) on viscosity, $G^{*}/\mathrm{Sin}\delta$, recovery, and fatigue life. On the other hand, along with PE, the chemical interaction between CR and asphalt binder matrix (IE) was found to play a significant role in improving nonrecoverable creep compliance response. Additionally, based on comparative analysis of IE and PE in various performance-related parameters, the filler effect produced with the addition of 30-40CR particles was found to be more than the filler effect produced with the addition of 60-80CR particles. This indicates that increased CR particle size may cause changes in the filler nature of the CR–asphalt binder composite. Additionally, high-temperature storage stability was evaluated. Base binder with 60-80CR particles exhibited better stability than base binder with 30-40CR particles.

A three-dimensional discrete element model of an asphalt mixture is developed based on discrete element method (DEM) software to investigate the cracking mechanism of the asphalt mixture, which is validated by the results of an indirect tensile test. Then, the model is applied to study the displacement field and fracture fragment distribution in terms of the micromechanical behavior. The results indicate that the failure process can be divided into three periods, namely, elastic growth of tensile stress, rapid expansion of the cracks, and crack coalescence. The fracture fragment initially forms near the loading bar and develops gradually until coalescence. Displacement circulation arises during the loading period, and the location depends largely on the crack development. Further, parameter-sensitive analysis revealed the effects of various loading speeds, different friction coefficients, and normal-to-shear stiffness ratios of the asphalt binder on the mechanical behavior of the asphalt mixture.

Drop-weight tests are conducted to study the dynamic flexural properties of alkali-activated concrete (AAC) under four different impact velocities, corresponding to strain rates of 15, 35, 55, and $75{\mathrm{s}}^{-1}$. The effect of low temperature ($-30°\mathrm{C}$) is also observed at the strain rate of $35{\mathrm{s}}^{-1}$. The replacement ratio of fly ash with slag, alkali concentration, modulus of alkali activator, and water:binder ratio are selected as parameters to study the strain rate effect of AAC. The quasi-static compressive strength, flexural strength, and elastic modulus are evaluated. For comparison, one mixture of ordinary portland cement concrete (OPCC) is also studied. The results show that, similar to OPCC, AAC is a strain rate–sensitive material; the flexural strength, energy consumption, and deformation at failure increase with the loading rate; the dynamic increase factor (DIF) of flexural strength is related to its quasi-static strength, and a lower quasi-static strength leads to a higher DIF; and the energy dissipation capacity of AAC increases almost linearly with the strain rate regardless of its quasi-static strength. In addition, different from OPCC, alkali-activated slag concrete (AASC) is found to exhibit less sensitivity to low temperature in terms of the flexural property, which might be attributed to the refinement of the microstructure, high proportion of micropores, and high concentration of pore solution in AASC.

This study explores the development of eco-friendly burnt clay bricks incorporating recycled waste marble powder (WMP). Waste marble powder was collected from the local marble industry and used to manufacture brick specimens at a local brick manufacturing facility with dosages ranging from 5 to 25% by clay weight. The mechanical and durability performance of bricks incorporating WMP were investigated. The WMP produced lighter weight bricks with reduced linear shrinkage. It also decreased the compressive strength of bricks because of enhanced porosity, as shown by scanning electron microscopy (SEM) analysis. However, bricks incorporating up to 10% of WMP achieved compressive strength values within the specified limits of the local building code. All tested bricks satisfied the minimum standard flexural strength requirements. Using 5% WMP in fired clay bricks yielded similar efflorescence and resistance to sulfate attack compared with control bricks without WMP. Leaching tests on brick specimens indicated that leached species from WMP-modified bricks were well below regulatory thresholds. Full-scale implementation of WMP in burnt clay brick manufacturing could mitigate the landfilling of this by-product and lead to the development of eco-friendly, nonhazardous and economical masonry construction.

This study presents a comparison between different testing procedures to determine the tensile strength of reactive powder concrete (RPC). The tensile strength test methods include a direct tensile test and two indirect tensile tests, the splitting test and the double punch test (DPT). In this study, the RPC was designed to obtain a nominal compressive strength of 100 MPa at the age of 28 days. Macro steel fibers were used to reinforce the RPC by volumetric percentages of 0, 1, 2, and 3%. Mechanical properties of RPC were obtained at 28 days such as compressive, tensile, and flexural strengths; compressive stress-strain relationship; and tensile stress-strain behavior. By comparing the experimental results of the two indirect tensile tests with the uniaxial direct tensile test (DTT), it was shown that the DPT presents more accurate results of the RPC tensile strength than the splitting test. The experimental results were verified with the existing model to predict the tensile strength of the RPC. In addition, considering the low cost and the ease of conducting the DPT, this test can be used as an alternative to the DTT to obtain the tensile strength of the RPC.

This paper proposes a design for a testing program for accelerated life testing of reinforced concrete in the sulfite saline soil area. According to the situation of saline soil area, a constant current was used to accelerate the corrosion of steel rebar, and the wet sand with complex salt solution was used as electrolyte. The accelerated life testing was carried out, and a certain amount of accelerated life data was collected using electrochemical technique. By using scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), and X-ray photoelectron spectroscopy (XPS), the microstructure and composition of corrosion products were analyzed. According to present codes, the critical corrosion current density of reinforced concrete was obtained. The linear model and exponential model were used to fit the average value of data corresponding to each time point respectively. Furthermore, based on the Wiener stochastic process, a reliability model for the degradation of reinforced concrete was established, and the accelerated life of reinforced concrete specimens was predicted. The results showed that the experimental scheme can effectively simulate the natural corrosion state of steel rebar in the sulfite saline soil area of western China. Corrosion current density can be used as the key factor for the durability deterioration of reinforced concrete specimens, and it can be used to judge the corrosion state of the reinforced concrete. Wiener stochastic process can effectively describe the durability degradation process of reinforced concrete specimens. By integrating the life data of the degradation process, the accelerated life reliability function established by this method can directly reflect the accelerated life of the specimen. The method is simple in calculation, and has certain value of popularization and application.

Magnetorheological (MR) fluids are suspensions of microparticles or nanoparticles dispersed in carrier fluids, which contain iron particles, carrier fluids and additives. In this study, a novel kind of composite iron particle—graphene oxide (GO)-coated magnetic particles was adopted to prepare MR fluids together with surfactants-modified iron particles. The influence of dosage proportions of the two composite iron particles, volume fraction of iron particles, and the dosage of liquid paraffin on the performances of MR fluids was investigated through sedimentation stability, viscosity, and shear yield stress tests. The test results presented that GO-coated iron particles with low density and high-saturation magnetization were beneficial to the improvement of stability and adjustability. Additionally, dosage proportions of the two composite iron particles, volume fraction of iron particles, and the dosage of liquid paraffin all had significant influence on the performances of MR fluids. Finally, the mathematical model of shear yield stress of the MR fluid was deduced, and the calculated results were compared with the tested data, which had verified the correctness of the mathematical model.

When cured in the field, unsaturated lime-treated expansive soils will undergo concurrent development of lime cementation and suction stress. This study aims to assess the relative roles of lime cementation and suction stress in the swelling potential of two lime-treated expansive soils cured under different curing environments. To this end, a series of tests were conducted to evaluate the one-dimensional swelling potential of statically compacted lime-treated expansive soils cured under controlled curing (CC), in-laboratory curing (ILC), and field-simulated curing (FSC) conditions. The characteristics of curing environment in terms of temperature, relative humidity, and imposed total suction are presented. For each curing environment, the swelling potential and total suction of lime-treated expansive soils as a function of lime content (2, 4, and 6%) and curing period (7, 14, and 28 days) were measured. The results reveal that curing environment had a significant effect on the swelling potential of the lime-treated soils considered. Different trends in the variation of swelling potential with curing period were observed to depend on soil type, lime content, and curing conditions. These swelling potential trends were interpreted in view of two mechanisms, namely, development of lime cementation bonds and suction stress emergence in specimens caused by desiccation, especially under ILC and FSC environments. Finally, a rational approach was proposed to visualize the effects of suction and lime cementation on swelling behavior of lime-treated expansive soils. This approach may be used to define the cementation-suction equilibrium stress, which can be used to quantify the magnitude of lime cementation bonds.

This paper presents a finite-element model of pullout test specimens using a nonlinear spring element. The model simulates the bond-slip behavior between three-dimensional crescent ribbed bars and concrete. A total of 180 spring elements were created between the ribbed bar and concrete. This model simulates the gradational deformation from the loading end to the free end of the ribbed bar as closely as possible to the real situation. The displacements and stresses of the ribbed bars obtained were compared to experimental results. Good agreement was achieved from the comparison of the numerical and experimental results. The results indicate the feasibility of simulating the bond-slip behavior between three-dimensional ribbed bars and concrete by using a nonlinear spring.

The interfacial interaction between asphalt binder and mineral aggregate makes different components have different concentration distributions. It influences the performance of the interface and consequently that of the mix. An asphalt binder–mineral aggregate interface model was built by molecular dynamics (MD) simulation. Four asphalt components and five mineral components were selected to analyze the concentration distribution at the interface. Results show that the concentration peak distribution of asphalt components was dependent on directions. The concentration peak perpendicular to the surface of minerals was higher than that parallel to the surface of minerals. Increasing temperature accelerated the movement of four asphalt components, resulting in reduction and widening of concentration peaks. Increasing temperature made four asphalt components disperse more homogeneously. The resin and asphaltene had similar concentration distribution curve forms, but the peaks of resin lagged behind asphaltene. In contrast, the concentration distribution of aromatics and saturates was more random and homogeneous.

The purpose of this study was to investigate the effects of warm mix additive Sasobit and Deurex on the properties of amorphous poly alpha olefin (APAO) modified asphalt (AMB) mixture. Marshall stability (MS) and indirect tensile strength (ITS) tests were used to measure and characterize the mechanical properties of mixtures. Air voids (Va), void in mineral aggregate (VMA), and void filled with asphalt (VFA) tests were carried out to evaluate the volumetric properties. Additionally, index of retained strength (IRS), tensile strength ratio (TRS), and retained Marshall stability ratio (RMSR) were obtained by moisture damage, freeze-thaw damage, and long-term aging tests, respectively. Analysis of variance (ANOVA) was performed to verify if Sasobit and Deurex affected the mixture statistically. The results showed that the appropriate amount of warm mix additive (such as 4% Sasobit and 2% Deurex) had outstanding effects on construction temperatures and temperature sensitivity for AMB in terms of decreased viscosity and viscosity temperature susceptibility (VTS). Marshall stability tests showed that warm AMB mixture had higher carrying capacity and resistance to deformation than the control AMB mixture, and Deurex performed better than Sasobit at the same dosage. Volumetric properties tests showed that Sasobit or Deurex could increase the Va and VMA value of AMB mixtures and decrease the VFA value. Also, Deurex had more positive effects on compaction and effective asphalt ratio for the AMB mixture than Sasobit at the same dosage. The results of indirect tensile strength tests indicated that an appropriate amount of Sasobit (4%) improved the low-temperature performance of the AMB mixture, whereas Deurex had a positive effect on it. The durability test analysis concluded that the addition of Sasobit or Deurex to the AMB mixture could slightly reduce the durability of its water damage but positively affect its long-term aging performance. The statistical analysis results also confirmed that there was a significant difference in the experimental performance between different dosages of warm-mix additives. In summary, 4% Sasobit and 2% Deurex were the optimal dosages for the AMB mixture in this research concerning the construction workability, mechanical properties, volumetric properties, durability, and economic benefits.

The bond development between the masonry materials is influenced by the characteristics of the masonry unit and the mortar. The mortar, sandwiched between the masonry units, undergoes shrinkage. The paper is focused on understanding the role of mortar shrinkage on the flexure bond strength of cement-stabilized soil brick (CSSB) masonry using cement-lime mortar (CLM). The mortar shrinkage was varied by varying the consistency/flow. Flexure bond strength of CSSB masonry prisms using CLM mortar having different flow values was measured. Relationships between the mortar flow and the drying shrinkage as well as between the mortar drying shrinkage and the masonry flexure bond strength were established. The results reveal that the mortar drying shrinkage increases with the increase in the flow or consistency of the mortar, and the relationship is linear. Also, the flexure bond strength of the CSSB masonry increases with an increase in the drying shrinkage of CLM mortar and the relationship is linear. The results suggest that it is better to use higher flow value mortars, for achieving better bond strength for CSSB masonry.

Most of the existing soil-water characteristic curve (SWCC) prediction models do not have a high level of prediction accuracy. The $R^2$ values of these model predictions range from 0.1 to 0.6 when applying them to a large data set. The inaccurate prediction of SWCC diminishes the prediction accuracy of engineering properties of unbound material. To overcome this issue, the goal of this study was to improve the prediction accuracy of SWCC using an artificial neural network (ANN) approach. Two three-layer ANN models were constructed for plastic and nonplastic soils separately, which consisted of one input layer, one hidden layer, and one output layer. The input variables included soil gradation indicators, particle diameter indicators, Atterberg limits, saturated volumetric water content, and climatic factors. The hidden layer, including a total of 20 neurons, used a log-sigmoidal function as a transfer function and the Levenberg–Marquardt back propagation method as the training algorithm. The output layer variables were the fitting parameters of the Fredlund–Xing equation. The SWCC database from the NCHRP 9-23A project was used to develop ANN models with 80% of the data set for training and 20% of the data set for validation. The developed ANN models had $R^2$ values between 0.91 and 0.95 for predicting the SWCCs of unbound material, which are significantly higher than other regression models. Finally, the developed ANN models were validated by comparing a new data set collected from both the NCHRP 9-23A project and other literature sources to the model predictions.