Journal of Materials in Civil Engineering

Over the years, there has been mounting interest in the use of recycled tire rubbers in highway construction. Tire rubber-filled concrete, a rubberized Portland cement concrete with a portion of aggregates replaced by tire rubber particles, represents an alternative of using recycled tire rubbers. It is found that rubberized concrete has very high toughness. However, its strength decreases significantly as the rubber content increases. This limits its application to secondary structural components only. Very little progress has been made in increasing the strength of rubberized concrete due to the lack of understanding of the toughing mechanism. In this study, rubberized concrete was treated as a multiphase particulate-filled composite material. A modified three-layer built-in composite model was proposed based on a previous study on ordinary concrete. Finite element analysis was conducted on the developed composite model. Cylindrical rubberized concrete samples and ordinary concrete samples were prepared and tested to provide basic physical/mechanical properties in the analysis. The effect of various design parameters on the composite strength was evaluated. The finite element analysis validated the test results.

This paper presents a microscopic approach to model the yield condition of high fluidity concrete in the fresh state for the rheological evaluation and the numerical flow simulation to optimize its workability and composition. Based on considering fresh concrete as a type of particle assembly containing water, cohesive particles (cement grains), and cohesionless particles (aggregate grains), the directions and magnitudes of inter-particle forces are examined, the shear deformation resistance of fresh concrete is investigated. Then, an equation of yield condition is derived, and a yield model is proposed for high fluidity concrete in fresh concrete. Furthermore, the dependence of the yield stress on interparticle friction, temperature, normal stress on the shear plane, etc., is clarified on the basis of the obtained yield condition equation.

An experimental study is reported to evaluate corrugated metal ties for attaching brick veneer walls to wood framing, subjected to lateral loads in the in-plane and out-of-plane directions. Typical residential and light commercial brick veneer construction in the central and southeastern U.S. was characterized, and subassemblies comprising two bricks, a wood stud, and a corrugated metal wall tie were tested to capture the local performance of overall wall systems rather than of just the tie itself. Test parameters included tie thickness, initial offset displacement, attaching method of ties to wood studs, and type of loading (including cyclic). Reduced eccentricity (with sheathing), as well as embedment length, were also evaluated. Typical failure modes included nail pullout from the wood stud, tie pullout from the mortar joint, and tie buckling. Tie thickness and eccentricity affected tension stiffness, whereas embedment length affected tension strength. Experiments on full-scale wall systems over wood framing on a shake table are underway.

The linearity limits of various unmodified and modified bituminous binders, as well as asphalt mixtures incorporating these binders, have been investigated using a dynamic shear rheometer and a purpose-built, dynamic, direct tension–compression, servohydraulic testing apparatus. Both continuously graded, as well as gap-graded, asphalt mixtures have been tested together with a fines/filler mortar (mastic). Cylindrical specimens of these mixtures were subjected to sinusoidal loading at temperatures between 10 and $40°C\text{,}$ first, under stress sweep conditions and, second, under frequency sweep conditions. The results show that there are binder and bulk strain dependent linearity criteria for both binders and asphalt mixtures at high complex modulus values as well, as a high-temperature binder strain dependent linearity criterion for elastomeric modified binders. The linearity bulk strain criterion for the asphalt mixtures was found to be in the order of 100 microstrain with the binder strain criterion for the binders being at least 100 times greater at just over 10,000 microstrain and the polymer network binder strain criterion at 1,000,000 microstrain. In general, the linear viscoelastic rheological characteristics of the asphalt mixtures were similar with differences in the complex modulus and phase angle only being found at intermediate temperatures and frequencies and are attributed to the rheological characteristics of the binders. However, the extra stiffening effect of the aggregate skeleton did increase the elastic response of the asphalt mixtures relative to that of the binders, particularly at high temperatures and low frequencies.

Short fiber reinforced cement composites with large volumes of perlite have been investigated for their resistance to high temperature exposures. The composites were manufactured by the extrusion technique. The extruded products, thin plates and cylinders, were subjected to different thermal treatments with the maximal exposure temperatures, $T_m\text{,}$ of 200, 300, 450, and $600°C\text{,}$ and exposure periods, $T_h\text{,}$ of 1 and 10 h. After that, the residual mechanical properties of those extrudates, such as flexural strength, $f_t\text{,}$ compressive strength, $f_c\text{,}$ and modulus of elasticity, $E$ were measured and normalized to the corresponding values obtained from specimens without thermal treatments. The weight loss ratios, ω, of the composites were also monitored during the thermal treatment process. In addition, the microstructure of these composites was studied using a scanning electron microscope and the pore structure was examined by mercury intrusion porosimetry. It was found that $f_t\text{,}$ $f_c\text{,}$ and $E$ significantly decreased as $T_m\text{,}$ $T_h\text{,}$ or both increased. The property deterioration could be attributed to fiber melting or softening, dehydration of cement hydrates, and porosity increasing during the heating process. Flexural strength, $f_t\text{,}$ decreased more remarkably than compressive strength, $f_c\text{,}$ and modulus of elasticity, $E\text{.}$ The thin sheets reinforced by polyvinyl acetate (PVA) fibers showed more significant reduction in flexural strength than those reinforced by glass fibers due to the much lower melting point of PVA fiber. The composites, incorporating silica sand as aggregates, showed greater degeneration of mechanical properties than those using perlite as aggregates. The improvement of thermal resistance of perlite specimens could be attributed to the greater specific heat, lower thermal conduction coefficient, and the better thermal insulation property of perlite.

Steel slag is a byproduct from either the conversion of iron to steel in a basic oxygen furnace, or the melting of scrap to make steel in an electric arc furnace. This paper reviews the production, processing, and characteristics of steel slag, and its use as a cementing component in different cementing systems. The chemical composition and cooling of molten steel slag have a great effect on the physical and chemical properties of solidified steel slag. Steel slag with high basicity and being cooled properly can exhibit cementing property. Ground steel slag has been used in several different cementing systems. The use of steel slag in these cementing systems results in some advantages over conventional cements. At the moment, most steel slag is being used as unbound aggregate for ashphalt concrete pavement in many countries. However, the use of steel slag as a cementing component should be given a priority from technical, economical, and environmental considerations.

The current ASTM Standard Guide G101 has a method for estimating the atmospheric corrosion resistance of low-alloy steels from the content of five elements: Cu, Ni, Cr, Si, and P. The ASTM method was developed by fitting a quadratic model to thickness loss data from specimens that were made from 270 different steel compositions and were exposed to the atmosphere for 15.5 years. The quadratic structure resulted in a model that provides an irrational measure of the effect of the most important alloying element. Additionally, the use of the correlation coefficient as the single criterion for selecting predictor variables led to inaccurate coefficients. The reanalysis of the writers, using multiple criteria for selecting the best predictor variables, yields more accurate coefficients and a level of explained variance of nearly 80%. While the multiple criteria analysis of the writers does not sacrifice prediction accuracy to achieve rationality, the problem inherent to the quadratic model cannot be overcome altogether in low-alloy steels containing more than about 0.40% copper. The corrosion index of Guide 101 should not be used to decide whether a low-alloy steel qualifies as a weathering steel.

This paper deals with the time dependence of fluidity and thixotropy of high fluidity concrete containing polycarboxylate-based superplasticizer. Taking the effects of both hydration and physical flocculation of cement particles into consideration, the increases in apparent viscosity and Bingham constants with the elapsed time of the stationary state, and the time dependence of the apparent viscosity in agitated state, are theoretically investigated. Moreover, the effects of the number, peak value, and durations of applied stepwise stresses, etc., on the shape and the area surrounded by the hysteresis loop of shear rate versus shear stress are discussed quantitatively.

The uniaxial compressive strength of concrete is the most widely used criterion in producing concrete. Although testing of the uniaxial compressive strength of concrete specimens is done routinely, it is performed on the 28th day after concrete placement. At this point, it is too late to make improvements if the test result does not satisfy the required strength. Therefore, the strength estimation before the placement of concrete is highly desirable. This study presents the first effort in applying neural network-based system identification techniques to predict the compressive strength of concrete based on concrete mix proportions. Back-propagation neural networks were developed, trained, and tested using actual data sets of concrete mix proportions provided by two ready-mixed concrete companies. The compressive strengths estimated by the neural networks were verified by laboratory testing results. This study demonstrated that the neural network techniques are effective in estimating the compressive strength of concrete based on the mix proportions. Application of these techniques will contribute significantly to the concrete quality assurance.

An experimental investigation of the use of polymers dissolved in aqueous solutions to enhance the resistance of clay-based barrier materials to freeze-thaw action and desiccation was performed. The polymers considered included a nonionic polysaccharide (guar gum) and a cationic polyacrylamide (PAM). Concentrations ranging from 0.25 to 8.00 g/L were used and mixed with three barrier materials, namely, 100% Na-montmorillonite clay, a mixture of 70% sand, 30% clay, and a mixture of 90% sand, 10% clay (by weight). Freeze-thaw and desiccation tests were used to investigate material durability. The effects of freeze-thaw action on the materials were assessed in terms of crack measurements, while the drying rates as well as crack measurements were used to assess the influence of desiccation. The extent to which crack formation was mitigated by polymer amendment varied according to polymer type, mode of crack initiation, and clay fraction. In particular, unmodified mixtures of 70% sand and 30% clay exposed to desiccation stress resulted in crack area density values as high as 11.9% while modification with guar or PAM reduced this to 2.7 and 3.4%, respectively, as revealed by analysis of the computed tomography-generated images. Increases or reductions in performance are attributed to polymer–clay interactions and relative hydration between clay and polymer phases.

The purpose of this study was to evaluate the pavement distress associated with moisture and cracks. A feedback-controlled test was developed to generate a crack with a controlled width in asphalt concrete specimens. Three different mixtures, i.e., dense graded, stone mastic asphalt (SMA), and porous asphalt (PA), were tested for moisture-induced damage aggravated by cracking and high void contents. An exponential relationship was found to exist between permeability and air voids. The intrusion of water can be greatly reduced when the asphalt mixture is properly compacted to an air void level of 7% or less. As water penetrated into the mixtures, PA and SMA coated by a thicker asphalt film showed more resistance to water damage than the dense mixture by a thinner one. The test results indicated that voids in these three types of mixtures could be categorized as impervious, semieffective, and effective, respectively. The corresponding permeability was found to be ${10}^{-2}\mathrm{cm}/s$ or higher, ${10}^{-2}$ to ${10}^{-4}\mathrm{cm}/s\text{,}$ and ${10}^{-4}\mathrm{cm}/s$ or lower, respectively. When cracks became wider than 0.2 cm, the indirect tensile strength of all three mixtures reduced significantly in the presence of water. The effect of cracks on a pavement was similar to an increase in voids in a mixture regarding water damage. A pavement showing 0.2 cm cracking is recommended to have immediate maintenance. The present research may provide insight into establishing criteria for a durable asphalt pavement.

A prefabricated fiber-reinforced polymer (FRP) composite shield or jacket was developed to repair wood piles in the field. Cylindrical E-glass/vinyl ester composite shells were bonded underwater to encase damaged wood piles. The resistance to freeze–thaw cycles of an underwater curing epoxy adhesive was evaluated. The standard test procedure for single-lap shear adhesion for FRP composite bonding, ASTM D5868, was selected. A standard procedure for freeze–thaw cycling exposure was adopted. The effect of freeze–thaw cycling exposure on the performance of the adhesive bond was discriminated by comparing the lap shear strength and the mode of failure of control and exposed samples. It was found that the lap shear strength is substantially reduced by exposure to freezing and thawing cycles. A change in the mode of failure from predominantly adhesive type to combined adhesive/cohesive type was noticed after exposure.