Journal of Materials in Civil Engineering

This investigation studied the retempering technique of remediation to mitigate the influence of combined transportation time and extreme hot and cold temperatures on plastic self-consolidating concrete (SCC). This method of remediation consisted of adjusting admixture dosage at the end of hauling to produce a matrix with similar fresh properties as those of the control concrete prepared at the temperature of 21°C and transportation duration of 10 minutes. Seven different temperatures (43, 36, 28, 21, 14, 7, and $-0.5°\mathrm{C}$ ) and five different hauling times (10, 20, 40, 60, and 80 minutes) were adopted. Polycarboxylate-based high-range water-reducing admixture (HRWRA) and viscosity-modifying admixture (VMA) were used to produce the selected matrices with slump flow of $635\pm 25\mathrm{mm}$ or $711\pm 25\mathrm{mm}$ , visual stability index (VSI) of 0 (highly stable concrete) and $T_{50}$ of 2 to 5 s. Laboratory test results revealed that the retempering method of remediation was successful in mitigating the adverse effect of combined hauling time and temperature on the flow characteristics of self-consolidating concrete.

A mechanistic-empirical pavement design guide (MEPDG) for portland cement concrete pavement (PCCP) has been developed recently and, within it, the coefficient of thermal expansion (CoTE) of concrete is considered as a crucial variable. Previous research has suggested that the concrete CoTE is affected by the availability of moisture in capillary and gel pores. The capillary pores are filled with hydration products, and their volume decreases at an early age of the concrete. However, the variation of the concrete CoTE due to hydration and moisture has not been quantified completely. The results have varied mainly due to the development of measurement techniques. The age and moisture effects on the CoTE of concrete were investigated by measuring the temperature, humidity, and strain of a cylinder specimen at both the initial and later ages. Drying shrinkage and autogenous shrinkage were considered in the calculation of the CoTE, particularly at early concrete ages. This investigation was facilitated by moving a concrete test specimen periodically from a 60°C environment to a 10°C environment over a 6-month period. Dilatometer testing and composite modeling were also conducted to verify the age and moisture effects on the concrete CoTE. Results show a close resemblance between the CoTEs determined by these different approaches. According to finite-element (FE) analysis, the behavior of the pavement slab was significantly affected by the variation of the concrete CoTE.

This research aims to study the effect of water to binder (W/B) ratio and ground fly ash on properties of recycled aggregate concrete. Normal concretes were designed by using Portland cement type I with W/B ratios of 0.45, 0.55, and 0.65. Recycled aggregate concretes were made by using recycled aggregate to fully replace crushed limestone in the mix proportion of the normal concretes. Ground fly ash was also used as a partial replacement of Portland cement type I at 20, 35, and 50% by weight of binder in order to improve the properties of recycled aggregate concrete. Compressive strength and water permeability of recycled aggregate concretes were determined at 28 and 90 days. In addition, the modulus of elasticity of concrete was investigated. The results showed that the use of ground fly ash to replace cement in recycled aggregate concrete could improve the compressive strength to be higher than that of concrete without ground fly ash at the same W/B ratio. Ground fly ash could be used throughout to replace cement up to 35% by weight of binder for recycled aggregate concrete with W/B ratio of 0.45 and should not exceed 20% for recycled aggregate concretes with W/B ratios of 0.55 and 0.65. For the same compressive strength, the modulus of elasticity of recycled aggregate concrete with and without ground fly ash was lower than that of normal concrete by about 16–20%. Moreover, the use of ground fly ash to replace cement in recycled aggregate concrete was more effective for reducing the water permeability coefficient than the reduction of the W/B ratio.

A material exhibits thixotropic behavior if its apparent viscosity decreases under stress and if it recovers its initial viscosity when unloaded. This thixotropy is well defined for fluids, but it is not well understood for viscoelastic materials. For bituminous binders, it a priori corresponds to a decrease in material stiffness under cyclic loading and a recovery of this stiffness after rest. Rheological tests, in which the stress distribution in the material is simple and controlled, appear interesting to gain relevant observations concerning the thixotropic behavior of bitumens. The materials were tested under simple shear flows with the help of a controlled stress rheometer, and the influence of temperature, frequency, and conditioning time were studied. This paper proposes a new experimental procedure for studying binder thixotropy in cyclic mode by means of shear tests. The procedure relies on the observation of the breakdown curves in the nonlinear domain and modulus recovery curves at different frequencies and temperatures. Stiffness variations are demonstrated to be linked to a rearrangement of molecular structure and not to crack formation and healing. Moreover, fatigue performance appears better for the binder that shows the most important capacity to be destructured.

The paper summarizes the relative influence of different pavement thermophysical properties on the thermal response of pavement cross sections and how their relative behavior changes in different climatic regions. A simplified one-dimensional (1D) heat-flow modeling tool was developed to achieve this by using a finite difference solution method for studying the dynamic temperature profile within pavement constructions. This approach allows for a wide variety and for daily varying climatic conditions to be applied, where limited or historic thermophysical material properties are available, and permits the thermal behavior of the pavement layers to be accurately modeled and modified. The model was used with available thermal pavement materials properties and with properties determined specifically for the study reported in this paper. The pavement materials included in the study comprised both conventional bituminous and cementicious mixes and unconventional mixtures that allowed a wide range of densities, thermal conductivities, specific heat capacities, and thermal diffusivities to be investigated. Initially, the model was validated against in situ pavement data collected in the United States in five widely differing climatic regions. It was found to give results at least as good as others available from more computationally expensive approaches such as two-dimensional (2D) and three-dimensional (3D) finite-element (FE) commercial packages. The model was then used to compute the response for the same locations where the thermal properties had been changed by using some of the unconventional pavement materials. This revealed that reduction of the temperature range by several degrees was easily possible (with implications for reduction of rutting, fatigue, and the urban heat island effect) and that depth of penetration of peak temperatures was also achievable (with implications for winter freeze and thaw). However, the results showed that there was little opportunity to displace the peak temperatures in time.

The objective of this study was to evaluate the laboratory moisture susceptibility of low-volume hot mix asphalt (HMA) and warm mix asphalt (WMA) mixtures containing moist aggregates and recycled materials, such as manufactured roofing shingles and coal ash material. These materials were tested after short- and long-term aging procedures. The test properties of these mixtures included indirect tensile strength (ITS), the tensile strength ratio (TSR), and the flow value of virgin and aged specimens. The experimental design included two percentages of coal ash (10 and 5% by weight of the aggregate), two roofing shingle contents (5 and 3% by weight of the aggregate), three WMA additives (Asphamin, Sasobit, and Evotherm), two antistripping agents (hydrated lime and one liquid antistripping agent), and two aggregate sources. A total of 72 mixtures were designed and a total of 416 ITS specimens were tested for short- and long-term aged procedures in this study. The test results indicated that the dry and wet ITS values of low-volume mixtures containing moist aggregate generally satisfied the demand of pavement without requiring additional treatment. Mixtures containing hydrated lime, in general, showed a better moisture resistance than liquid ASA for WMA mixtures. Moreover, the addition of WMA additives in the low-volume mixture was effective and generally showed a similar moisture resistance to HMA, except for when using Asphamin and liquid ASA simultaneously. Research results also indicated that the utilization of recycled coal ash and roofing shingles significantly improved moisture resistance of HMA and WMA mixtures.

In the summer of 2008, a field trial project using Sasobit-modified warm-mix asphalt (WMA) was established in Alaska, which was Alaska’s first experience with a WMA technology. Previous studies conducted by writers identified a number of engineering benefits of Sasobit-modified WMAs over conventional hot-mix asphalt (HMA). This paper presents a further assessment focusing on low temperature performance of both Sasobit-modified WMA binders and mixes. A series of binder tests including bending beam rheometer (BBR), direct tension test (DTT), and asphalt binder cracking device (ABCD) tests were conducted. Indirect tension tests (IDT) of mixtures along with a thermal cracking analysis were performed to obtain a more definitive answer regarding the WMA application for cold-weather conditions. Results showed a decrease of tensile strength for both WMA binders and mixtures at low temperatures, and the cracking temperatures of both WMA binders and mixtures increased with the increase of Sasobit content. However, the increase in cracking temperature was very slight, which indicated that Sasobit addition had an insignificant effect on resistance to low temperature cracking. Therefore, Sasobit-modified WMA should be suitable for the Northern Region of the Alaska Department of Transportation and Public Facilities (AKDOT&PF) without compromising the resistance to low temperature cracking.

Although the opportunity to replace prescriptive codes and specifications with those based on performance has been widely discussed, currently only limited tools are capable of providing performance-based description of concrete behavior. This paper introduces a stochastic approach to relate the free shrinkage of concrete with anticipated cracking performance. This method proposes that shrinkage performance grades could be established to allow the designer to limit the probability of cracking based on free shrinkage as a first step. The probabilistic assessment of concrete cracking performance is further obtained from Monte Carlo simulations in which material properties (e.g., shrinkage, modulus, and strength) are treated as random variables with assigned predefined distributions. As a result of these simulations, user-friendly diagrams are obtained that can be further used by transportation agencies and contractors to predict field performance of concrete.

This research evaluated the benefits of geogrid reinforcement of granular base specimens and studied the effect of different factors contributing to their performance. This includes geometry, tensile modulus, arrangement/location of geogrids, the moisture content of specimen, and stress state. Five geogrids of different tensile modulus and aperture geometries (three rectangle or biaxial and two triangle or triaxial) were used. The study was experimentally carried out by conducting repeated load triaxial (RLT) tests to evaluate the resilient and permanent deformations of the specimens. The test results demonstrated the potential benefit in placing the geogrid within the granular base specimens. Less permanent deformations were measured under cyclic loading for geogrid-reinforced base specimens compared to unreinforced specimens. The geogrid geometry and tensile modulus had noticeable effects on the specimens’ performance. Of the five geogrids used, the triaxial geogrid (TX1) with triangle geometry and the highest tensile modulus performed consistently better than the other four geogrids. For geogrids with the same geometry, the higher the tensile modulus, the lower was the accumulated permanent deformation. The test results also showed obvious effects of the geogrid arrangement/location on the specimens’ performance, with the double geogrid location consistently yielding the largest improvement. The test results did not show any appreciable improvement in the resilient deformation or resilient modulus of the geogrid-reinforced granular specimens. The effect of moisture content on the performance of geogrid-reinforced specimens was evident, with higher improvement observed for specimens prepared at the optimum and dry of optimum than those prepared at wet of optimum.

This paper discusses the effect of multiwalled carbon nanotubes (CNT) on strength characteristics of hydrated portland cement paste. Various cement-CNT composites and an equivalent control mix were prepared by mixing 0.5, 0.75, and 1.0 percent CNTs (by weight of cement) to check the strength gain in portland cement composite material. Cylindrical specimens of size approximately $15.8\mathrm{mm}\times 31.6\mathrm{mm}$ were prepared for compressive strength and splitting-tensile strength tests to measure mechanical strength of composites. The specimens were tested at 7, 28, 60, 90, and 180 days of curing, and at least three samples were tested at each curing age. Results show an increase in compressive and splitting-tensile strengths in portland cement–CNT composites having CNT content of 0.5% by weight of portland cement. The increase in compressive and tensile strengths with respect to control mix were 15% and 36%, respectively, at 28 days curing age. Above 0.5% CNT content, the strength decreases. Scanning electron microscopy and transmission electron microscopy have also been carried out to check the microstructure bonding of the cement-CNT paste.

The effect of calcium hydroxide on the mechanical and microstructural characteristics of geopolymer produced from alkaline activation of aluminosilicate wastes produced from demolition works were investigated. Demolition wastes are coarse aggregates, including waste concrete and demolished walls with cementing binder, both passing a sieve of 90 µm. A trial was carried out by making a mix containing demolished walls/waste concrete in the ratio of $60/40$ % by weight and other mixes having a hydrated lime content of 0–25% of the dry weight as a partial replacement for demolished walls. Half of the waste concrete was substituted with metakaolin, produced by firing kaolin at 800°C for 3 h. The alkaline activators used were sodium hydroxide and sodium silicate in the ratio of $3:3\%$ by weight of the dry weight. Curing of the geopolymer mixes was performed at ambient temperature (23°C) in tap water and under a mild temperature of 40°C [100% relative humidity (RH)]. Drying treatment at 80°C for 24 h was carried out on each specimen mix before subjecting it to compressive strength so as to improve the mechanical properties, and the resulting properties of dried and saturated samples were compared. Addition of the calcium compound improved the mechanical and microstructural properties of the specimens with the increase of hydrated lime up to 10 % by weight for mix specimens that were water-cured under ambient temperature, whereas the properties slightly decreased for those specimens cured in 100% RH at 40°C.

This paper presents methods to predict quantities of absorbed, inert, and effective bituminous material in reclaimed asphalt pavement (RAP) for particular sets of conditions; three RAP sources were investigated. The approach couples a data set of properties for 568 asphalt mix designs spanning five years of practice and testing of 100% RAP with added virgin binder; 394 compacted specimens and 68 loose specimens of 100% RAP were tested. A method to predict RAP absorbed asphalt was developed requiring two inputs: (1) total asphalt content; and (2) RAP effective specific gravity when coated with virgin binder. The method, was shown to yield more reasonable results than conventional methods, which were shown to very likely give incorrect absorbed asphalt estimates in some conditions. The relative effectiveness of RAP surface asphalt was evaluated, and estimates of inert and effective RAP asphalt were made for a variety of temperature, compactive effort, and warm mix additive conditions. Results showed different behaviors between RAP sources and between hot and warm mix temperatures.

The aim of this study is to develop structural foamed concretes by using silica fume, fly ash, and polypropylene fiber. The study presents the use of fly ash for fully replacing sand to produce foamed concrete. Fine silica fume and polypropylene (PP) fiber were used to improve properties of foamed concrete. Lightweight foamed concretes with a wide range of concrete densities ( $800–1,500\mathrm{kg}/{\mathrm{m}}^3$ ) were studied mainly for compressive strength, splitting tensile strength, and drying shrinkage. The results indicate that foamed concrete with a density of $800–1,500\mathrm{kg}/{\mathrm{m}}^3$ and compressive strength of $10–50\mathrm{MPa}$ can be made by using silica fume and PP fiber. Fine silica fume and PP fiber greatly improved the compressive strength of foamed concrete. In addition, adding PP fiber significantly improved the splitting tensile strength and drying shrinkage resistance.

This paper summarizes major findings from a laboratory study based on stress-controlled cyclic uniaxial compression tests with initial deviator stress conducted on expanded polystyrene (EPS) geofoam. The experiments involved nonelasticized EPS cylinders of various densities subjected to various static deviator stresses and cyclic loading conditions to provide a detailed description of the geofoam cyclic stress-strain response in the viscoelastic and visco-elasto-plastic domains. Experimental results characterizing the viscoelastic behavior were compiled into a normalized Young’s modulus and damping ratio versus cyclic axial strain amplitude relationships. A unified formulation that can be used to determine the normalized modulus degradation curve for a given static deviator stress level and geofoam density (within $15–25\mathrm{kg}/{\mathrm{m}}^3$ ) was developed. Examination of the yielding behavior of EPS geofoam under cyclic loading revealed a nonlinear increase in the accumulated plastic axial strain with the increasing number of applied loading cycles. Additionally, larger cyclic deviator stress amplitudes and lower loading frequencies resulted in larger plastic axial strains accumulated under the same number of cycles.

Owing to its importance in the design and assessment of steel-reinforced concrete structures, the bond behavior of reinforcing bars embedded in concrete has been widely investigated. In this paper, 91 specimens were cast and tested to study the effect of lateral pressure on the bond behavior of plain and deformed round bars. On the basis of the experimental results, it is found that, for plain round bars, the bond capacity increases significantly with an increase in lateral pressure, whereas the slip corresponding to the peak bond stress reduces dramatically once the lateral pressure is applied. Through using the deformed reinforcing bars with noncentrosymmetric surface configuration, it is found that the bond behavior is closely related to the direction and magnitude of the lateral pressure. When the lateral pressure is applied parallel to the transverse rib, the bond capacity increases with an increase in lateral pressure. When the lateral pressure is perpendicular to the transverse rib, the bond capacity basically remains constant. Finally, a theoretical explanation of the experimental phenomena is given.

The impact characteristics of wood-cement particleboard (WCPB) made with wood particles produced from the waste stream are investigated. With a view toward sustainable practices, the potential application of WCPB to enhance concrete crash barriers is explored. Laboratory experiments using a drop-weight test and compression tests on ring-shaped WCPB specimens were conducted. Both tests indicated that WCPB has the capability of absorbing large amounts of energy. Finite-element simulations of the experimental tests were conducted using the LS-DYNA software. Subsequently, crash simulations of a vehicle frontally impacting a concrete crash barrier enhanced with WCPB facades having a variety of geometric shapes were conducted. The simulations show that the concrete barrier enhanced with a facade consisting of a bundle of WCPB tubes minimizes impact vehicle decelerations and reduces the potential for passenger injuries.