Abstracts:This paper reports the results of 120 low-cycle fatigue tests on steel reinforcing bars with varying slenderness ratios at varying strain amplitudes. The failure modes of the fractured bars were investigated through analysis of the fracture mechanisms of bars. The results of experimental testing were used to update empirical models of low-cycle fatigue life for such bars. The newly improved empirical models were then incorporated into a recently developed constitutive material model that accounts for bar buckling and fatigue. The experimental results show that the size effect is significant for short steel reinforcing bars where there is no buckling. The results also show that as the slenderness ratio of the steel reinforcing bars increases, the influence of the bar diameter on low-cycle fatigue reduces.

Abstracts:In this study, the effect of thermal shock (TS) on the mechanical properties of granite is investigated. Two schemes are performed to provide different cooling rates for the TS processes. Decreasing trend of dry density and P-wave velocity with ascending TS temperatures are observed. The porosity has an increasing trend with ascending TS temperatures. The effects of TS on the mechanical responses are investigated through Brazilian tests on the granite specimens of the cracked straight through Brazilian disc (CSTBD) under Mode I and Mode II loading. Mode I and Mode II fracture toughness values are obtained according to the mechanical tests, and a power relation is proposed to fit the fracture toughness values with respect to TS temperatures. Scanning electron microscope (SEM) is adopted to observe the fracture surfaces of the TS-treated specimens after the tests. Distinct features such as intergranular fracture are identified on the fracture surface of a water-cooled specimen, which indicates material deterioration to a greater extent as compared with that of an air-cooled specimen.

Abstracts:Limited research has been reported on strength improvement of biocemented soils in relation to crystal patterns of microbially induced calcite ( ${\mathrm{CaCO}}_3$) precipitation (MICP). In this study, sand samples were treated under the coeffect of different bacterial culture (BC) and cementation solution (CS) concentrations to evaluate the optimum BC and CS combination that yields the highest soil strength. It was found that for lower CS conditions (0.25 M), higher BC produced stronger samples, whereas for higher CS conditions (0.5 M or 1 M), lower BC was more dominant in improving the soil strength. This can be attributed to the effectively precipitated ${\mathrm{CaCO}}_3$ crystals, which were in rhombohedral shape and large size and were concentrated at the soil pore throat rather than deposited on the individual sand grain surface. This finding was confirmed with the scanning electron microscopy (SEM) analysis. The strength and permeability of the optimized biocemented samples were also compared with sand samples treated with ordinary portland cement (OPC). The optimized biocemented sand provided higher strength and permeability than those obtained from the samples treated with similar content of OPC at a curing period of 28 days.

Abstracts:In order to evaluate the influence of filler type on the moisture susceptibility of asphalt mixtures, this study examined the thermodynamic properties of mastic and the mechanical properties of hot-mix asphalt subjected to multiple freeze-thaw cycles. Furthermore, the potential of using waste concrete aggregates as filler material was particularly evaluated using the moisture damage properties of asphalt mixtures. To fulfill these objectives, recycled concrete aggregates, limestone filler, and portland cement were used as filler materials in asphalt mixtures and siliceous stone powder was used as filler in control samples. The indirect tensile strength and resilient modulus tests were performed as commonly used experiments to assess the moisture sensitivity of asphalt mixtures. Furthermore, the surface free-energy components of mastics as well as the cohesion and adhesion of the mixtures were determined. The results of mechanical and thermodynamic experiments suggest that asphalt mixtures containing the portland cement filler outperform those containing other types of filler at all freeze-thaw cycles in terms of moisture susceptibility. However, recycled concrete aggregates are a sustainable alternative for the aggregate filler and, based on results, they can improve the moisture resistance of asphalt mixtures, particularly at increased freeze-thaw cycles.

Abstracts:Recently, various types of additives are being used to enhance the properties of bitumen. Until now, few researchers have handled the utilization of different additives in the same binder. In this study, styrene-butadiene-styrene (SBS) and Evotherm were used both separately and in the same blend. Dynamic shear rheometer (DSR) and bending beam rheometer (BBR) tests were applied to SBS and Evotherm modified binders. SBS and Evotherm were added to pure bitumen in three different ratios. Sixteen different combinations were produced using the two additives, and a pure binder in the same binder was evaluated in the DSR test. Eight different combinations were evaluated in the BBR test. The conclusion reached was that the maximum usage of Evotherm (0.9%) induces a 20% reduction in the rutting parameter of both the 5% and 6% SBS modified binders. The 0.5% Evotherm with 4% and 5% SBS modification does not have an adverse effect on rutting performance. Evotherm modification could prevent the stiffness increment that originates from using the SBS additive, especially at high content. Using 0.7% Evotherm with 4% SBS can acquire the pure binder’s low temperature performance.

Abstracts:For comprehensive utilization of the coal gangue from different locations, coal gangues were calcined at temperatures of 800°C, 900°C, and 1,000°C for 2 h, respectively, and then blended in cement with a replacement level of 10%, 20%, 30%, and 40% by weight to fabricate the blended cement mortars. By means of Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscope (SEM), and an ion solubility test, the thermal-activation mechanism and pozzolanic activity evaluation for coal gangue was investigated, and the effect of coal gangue on mechanical properties and the hydration process of cement mixture was also studied. Results show that the optimum thermal-activation temperature of coal gangue is 800°C: the coal gangues in Yangquan, Huozhou, and Xinzhi, China, had higher activity and the replacement level of coal gangue in the cement can reach 40% by weight, but the coal gangues in Yanzhou, Zhengzhou, and Qitaihe, China, showed lower activity. The replacement level of coal gangue in the cement should not exceed 20% by weight. The active ${\mathrm{SiO}}_2$ and ${\mathrm{Al}}_2{\mathrm{O}}_3$ in the thermal-activated coal gangue are able to react with the $\mathrm{Ca}(\mathrm{OH}{)}_2$, which was produced by cement hydration, and form hydrated calcium silicate and hydrated calcium aluminate gel to enhance the compressive strength of cement.

Abstracts:The aim of this paper is to implement a numerical model to reproduce the nonlinear behavior of cob walls under shear loading. Axial compression, pull-off, and diagonal compression tests were carried out to derive the mechanical parameters. In addition, the stress-strain relationships, the nonlinear behavior, and the failure modes were defined. The experimental results were then used to calibrate a finite-element model. The material behavior was simulated through a macromodeling approach adopting the total strain rotating crack model. A sensitivity analysis was conducted to assess the effects of varying the parameters with higher uncertainty on the structural behavior. The numerical model achieved good correspondence with the experimental results in terms of simulation of the shear stress–shear strain relationship and of damage pattern.

Abstracts:The corrosion risk in reinforced mortar slabs containing untreated sugarcane bagasse ash (UtSCBA) (0%, 10%, and 20% replacement of cement) was analyzed for 75 months. The mortars were prepared with a constant 0.63 water/cementitious-materials ratio. Cylinders and reinforced slabs were cast with the mortars. Two galvanized wire meshes were used as reinforcement for the slabs. Curing regimes of 0, 7, and 28 days were applied to the samples. The cylinders were used to obtain the compressive strength (CS) and the chloride diffusion coefficient ( $D_{eff}$) of the mortars. To evaluate the corrosion risk, the slabs were exposed to wet-dry cycles of 12 h each in a 3% NaCl solution. Corrosion potential measurements and linear polarization resistance tests were taken every 28 days for that purpose. It was found that the addition of 10% and 20% UtSCBA reduces the workability of the mortar binders and leads to a slight decrease in the CS of hardened mortars. However, it significantly reduced the $D_{eff}$ of the mortars by 50% and 65% ( $p\ll 0.05$), respectively, and also decreased the corrosion risk of mortar slabs over time.

Abstracts:Hydrated lime has been recognized as an effective additive used to improve asphalt concrete properties in pavement applications. However, further work is still needed to quantify the effect of hydrated lime on asphaltic concrete performance under varied weather, temperature, and environmental conditions and in the application of different pavement courses. A research project was conducted using hydrated lime to modify the asphalt concretes used for the applications of wearing (surface), leveling (binder), and base courses. A previous publication reported the experimental study on the resistance to Marshall stability and the volumetric properties, the resilient modulus, and permanent deformation at three different weather temperatures. This paper reports the second phase of the experimental study for material durability, which investigated the effect of hydrated lime content on moisture susceptibility when exposed to a freeze-thaw cycle, and fatigue life. The experimental results showed an improvement in the durability of the modified asphalt concrete mixtures. Optimum hydrated lime contents for different course applications are suggested based on the series experimental studies. Finally, the advantage of using the optimum mixtures for a pavement application is demonstrated.

Abstracts:Studies on shredded waste tires mixed with sand for fill applications are well documented. In this study, a new composite material from mixture of shredded tires and fly ash as fill material is explored. Shredded waste tires with nominal size equal to 9.5 mm (granulated rubber), and fly ash generated from two thermal power plants are used in the study. The composite material is obtained by mixing different proportions of granulated rubber and fly ash. Granulated rubber content equal to 0%, 10%, 30%, and 60% (by weight of fly ash) in the mixture are tested. Compaction characteristics, optimum mixing ratio, and shear strength properties of the mixtures are determined. The maximum dry unit weight and the optimum water content values ranged between 15%–22.5% and $12.6–14.6\mathrm{kN}/{\mathrm{m}}^3$, and 10%–27% and $10.5–11.6\mathrm{kN}/{\mathrm{m}}^3$ for mixtures prepared with fly ashes from two sources. Large-size direct shear apparatus is used to obtain the angle of shearing resistance and apparent cohesion of mixtures at both peak state and at near end-of-test. The shear strength of fly ash and granulated rubber mixture is found to be higher than that of fly ash alone or granulated rubber alone, and the maximum shear strength of the composite material is observed for granulated rubber contents equal to about 60% (by weight of fly ash). The peak shear strength parameters of mixtures, apparent cohesion and friction angle, are found to be in the range 14.9–46.0 kPa and 37.5°–50.1°, respectively. Based on minimum void ratio, optimum mix proportions of granulated rubber and fly ash from two sources ranges between 54%–100% and 81%–185% (by weight of fly ash). Based on shear strength testing, fly ash-granulated rubber mixtures are found to perform better than sand-granulated rubber mixtures.