Journal of Materials in Civil Engineering

In the regions where temperature fluctuations are large ranging from below freezing in winter to high temperatures in summer, concrete highway pavements fail because of poor durability rather than lack of strength. The effect of fly ash replacement of Portland cement and the use of dense aggregate gradation on the durability of concrete mixtures is studied in this research. Eight concrete mixtures were cast, four of them using the aggregates as per current specifications and the other four mixtures using dense graded aggregates. For each of these two gradations, different fly ash replacement amounts of 30, 35, 40, and 45% for Portland cement were used. All mixtures were designed for 6% air content, and $25–38\mathrm{mm}$ $(1\text{to}11∕2\mathrm{in.})$ slump for the freshly mixed concrete. The study shows that the increase of fly ash content from 30 to 45% increased the durability of concrete mixtures without the loss of compressive and flexural strengths. The concrete mixtures containing dense graded aggregates, and higher percentage of fly ash required less water content indicating the beneficial effects of fly ash and dense graded aggregates. When the fly ash content was increased from 30 to 45% in the concrete mixtures, the permeable pore space decreased in the specific gravity, absorption, and voids in hardened concrete tests; the electric charge passing through the layers reduced in the rapid chloride ion permeability tests; and the spacing factors were smaller in the microscopical determination of air-void tests indicating greater durability. These experimental results proved the benefit of using higher content of fly ash in concrete. The use of dense graded aggregates also proved beneficial.

Rejuvenator is not a commonly used softening agent to be used in recycling of reclaimed asphalt pavement (RAP). In this study, Superpave mixtures containing RAP were designed using rejuvenating agents, including a rejuvenator and a softer binder, and subsequently evaluated in terms of the volumetric results, obtained the indirect tensile strength (ITS) of samples as well as evaluating the mixtures for rutting using the asphalt pavement analyzer (APA). The content of the rejuvenator used for those mixtures containing the rejuvenator was determined from the blending charts of RAP binders containing the rejuvenator. A total of 12 Superpave mixtures including 10 containing RAP and two virgin were designed. The results indicated, for the mixtures tested for this project, that: (1) properties of the recycled mixtures using the rejuvenator, such as ITS and APA, were better than those containing the softer binder; (2) 10% more RAP could be incorporated in the Superpave mixtures by using the rejuvenator than using the softer binder; and (3) the blending charts established under the Superpave binder specifications can be used to determine the content of the rejuvenator for the recycling.

This paper presents the results from an experimental program and an analytical assessment of the influence of addition of fibers on mechanical properties of concrete. Models derived based on the regression analysis of 60 test data for various mechanical properties of steel fiber-reinforced concrete have been presented. The various strength properties studied are cube and cylinder compressive strength, split tensile strength, modulus of rupture and postcracking performance, modulus of elasticity, Poisson’s ratio, and strain corresponding to peak compressive stress. The variables considered are grade of concrete, namely, normal strength $\left(35\mathrm{MPa}\right)$ , moderately high strength $\left(65\mathrm{MPa}\right)$ , and high-strength concrete $\left(85\mathrm{MPa}\right)$ , and the volume fraction of the fiber ( $V_f=0.0$ , 0.5, 1.0, and 1.5%). The strength of steel fiber-reinforced concrete predicted using the proposed models have been compared with the test data from the present study and with various other test data reported in the literature. The proposed model predicted the test data quite accurately. The study indicates that the fiber matrix interaction contributes significantly to enhancement of mechanical properties caused by the introduction of fibers, which is at variance with both existing models and formulations based on the law of mixtures.

The strength of rock mass probably is the first engineering parameter that a geotechnical engineer may be keen to establish before the start of any mining and civil engineering project. The strength of a rock mass at site is generally influenced by joint geometry and the stress state that it experiences. Field studies show that stress conditions around underground structures will be generally true triaxial or polyaxial, i.e., ${\sigma }_1>{\sigma }_2>{\sigma }_3$ . The rock mass behavior in such field conditions can effectively be simulated in laboratory by conducting large-scale physical modeling. In this study the most commonly occurring joint configurations (three joint sets) were created on rock mass models in the laboratory and tested under polyaxial stress compression. The model rock was a sand-lime block with low strength and medium deformability. The joint configurations were varied to assess the influence of joint geometry on the stress-strain curve, failure mechanism, and strength anisotropy. Similarly, on each type of geometry, ${\sigma }_2∕{\sigma }_3$ ratio was also varied to study the effect of intermediate principal stress on engineering behavior of rock mass. The maximum enhancement of 310% in strength due to an increase in the ${\sigma }_2∕{\sigma }_3$ ratio was observed, which corresponded to joint inclination, $\theta =60°$ . Based on testing results, the polyaxial strength criterion was evolved similar to the von-Mises failure envelope.

The properties of red sandstone, such as structures and compositions and disintegration characteristics, were investigated through a series of tests including laboratory tests, a large-scale simulated experimental test, and tests in a section of a highway in China. With the disintegration tests, red sandstone was classified according to its engineering properties. With the understanding of the properties of red sandstone, the filling methods, and the construction techniques of roadbeds and embankments, including quality control and quality examination with associated criteria, were developed. This paper confirmed that these techniques can be successfully applied to solve a series of difficult problems in highway construction in red sandstone regions with considerable potential economical benefits and significant technological and engineering values.

In this study, binder-aggregate adhesion and mechanistic characteristics of neat and polymer modified asphalt mixtures were investigated at low temperatures. The lap-shear test and environmental scanning electron microscope (ESEM) in situ tensile test were conducted to examine the adhesion and fracture morphology of neat and modified binders. The mechanistic properties were obtained from indirect tensile strength test and indirect tensile cyclic load test. It was found that lap-shear strength and toughness energy were functions of temperature and polymer concentration. The ESEM in situ tensile test indicated that the modified binders exhibited improved adhesion properties and had higher number of asphalt fibrils with longer lengths relative to the neat asphalt. In general, the improvements in the mechanistic properties were due to the improvements in the binder-aggregate adhesion behavior at low temperatures. It was found that the horizontal plastic deformation rates of modified mixtures were lower than the neat ones and were related to the lap-shear strength and toughness energy.

The hydration process of fresh concretes with different proportions was studied using electrical resistivity measurement. The minimum point $\left(P_m\right)$ and the transition point $\left(P_t\right)$ were identified on the electrical resistivity development curves. The time $t_m$ at which $P_m$ occurred, represented the time when the curve dropped to a minimum and before increasing as a result of the onset of hydration. The time $t_t$ at which $P_t$ occurred, marked the time when the kinetics of hydration transition changed from the setting to the hardening stage. To evaluate the significance of $t_m$ and $t_t$ in terms of the setting process, they were compared to the initial setting time $\left(t_i\right)$ and final setting time $\left(t_f\right)$ measured with the traditional penetration resistance method. The quantitative relationships between the setting time of concrete and the electrical resistivity critical points were developed. The equations can be used to estimate the setting times of concrete as an alternative method.

An experimental program is reported in which the mechanical properties of high-damping natural rubber were measured. Rubber specimens were tested using a custom-designed mechanical apparatus that is equipped with a temperature chamber as well as displacement and force transducers. Each specimen was subjected to a wide range of carefully controlled dynamic loading tests. Variables studied include the strain, strain rate, and temperature of the material. Results from laboratory testing were used to formulate a fuzzy model of mechanical behavior for shear of the rubber compound. Instead of a mathematical representation of the high-damping rubber material, a Takagi-Sugeno-Kang fuzzy inference system is used to relate three input variables with the shear stress. Parameters of seven membership functions are determined through the use of an (adaptive neurofuzzy inference system). Experimental data applied for training and checking of the model are concatenated sets. The resulting fuzzy inference system is shown graphically and analytically to represent accurately the behavior of the high-damping rubber while minimizing computational requirements.

The microporosity of granite stones has been studied in both the untreated condition as well as after being treated with a consolidation treatment using two commercial products. A decrease in the specific surface area and pore size distribution (especially micropores) has been found in samples treated with an organic silicate consolidant. Treatment with a consolidant containing polysiloxane (a water repellent agent) leads to variable results, depending on the precise pore structure of the untreated stone. The use of consolidation treatments may restrict flow of fluids (e.g., water, saline solutions, etc.) through the pores of the stones, which may decrease degradation.

Five different configurations of carbon fiber-reinforced polymer (FRP) grids were tested for the control of plastic shrinkage cracking of concrete using carbon FRP rods with two different spacings, two configurations of conventional steel wire meshes, and fiber reinforced concrete with two different fiber volume fractions. The experimental program followed the standard acceptance criteria test method for concrete with synthetic fibers. Test results showed that carbon FRP grids meet or exceed the acceptance criteria of minimum 40% reduction in shrinkage cracking of concrete. Introducing a crack reduction efficiency factor as the ratio of crack reduction to the equivalent area of steel reinforcement, carbon grids proved to be the most efficient type of reinforcement tested in this study.