Journal of Materials in Civil Engineering

This paper introduces two types of laminates, double-layer reformed bamboo (cross-ply) laminate and fiber-reinforced cementitious (FRC) plate-reformed bamboo laminate. The second laminate is made of reformed bamboo and extruded FRC plates. The reformed bamboo is ductile and tough and has a high tensile strength, while the FRC plate has higher compressive strength. The FRC plate-reformed bamboo laminate fully utilizes the advantages of each component to achieve superior mechanical properties. A series of flexural, impact, and compression after impact (CAI) tests have been conducted to evaluate the performance of both laminates. It is found that the newly developed FRC plate-reformed bamboo laminate has a high flexural strength (up to 96 MPa), excellent impact resistance, good ductility, and outstanding toughness. Hence, it has good potential in engineering applications.

This paper deals with the behavior of roller compacted concrete (RCC) cores in uniaxial tension cored from a practical RCC dam. Properties included are tensile strength, peak strain, modulus of elasticity, fracture energy, brittleness, complete stress-deformation curve, and stress-crack width curve both for the RCC matrix and the interface. Two categories of compressive strengths of RCC, 15 and 20 MPa, respectively, were tested in order to investigate the effect of RCC compressive strength on their behaviors. Two categories of specimen sizes of RCC, $150\times 300$ mm and $250\times 500$ mm cylindrical specimens, were also tested in order to investigate the effect of specimen size on their behaviors. The complete stress-deformation curves for RCC specimens were achieved by using a servohydraulic closed-loop testing system and four extensometers, of which the extensometer indicating maximum deformation is employed as feedback signal. Based on the stress-deformation curves, their stress-crack width curves were also obtained and theoretically modeled. The present results support the following conclusions. The uniaxial tensile strength of the RCC matrix is related to both the square root of its nominal compressive strength and the ratio of the maximum size of aggregate to the characteristic dimension of the specimen, but the uniaxial tensile strength of the interface is related only to the later. The modulus of elasticity both for the RCC matrix and for the interface are related to the square root of their nominal compressive strength and the ratio of the maximum size of the aggregate to the characteristic dimension of the specimen. The ultimate crack width of the RCC matrix is governed by the maximum size of the aggregate, but the ultimate crack width of the RCC interface is governed by the ratio of the maximum size of aggregate to the characteristic dimension of the specimen. The fracture energy of the RCC matrix is related to the square root of its nominal compressive strength and the ratio of the maximum size of the aggregate to the characteristic dimension of the specimen, whereas the fracture energy of the RCC interface is related to the square root of its nominal compressive strength and the maximum size of aggregate. The characteristic length of the RCC matrix and interface is related to both the square root of their nominal compressive strength and the ratio of the maximum size of the aggregate to the characteristic dimension of the specimen.

The mechanical behavior of many bound granular materials such as asphalt mixtures is anisotropic in nature. However, the majority of the current mechanical tests and analytical models for asphalt mixtures are based on the assumption of isotropic material properties. This study investigates the stiffness anisotropy of asphalt mixtures using micromechanics-based models. The models’ parameters are obtained by quantifying the internal structure anisotropy in terms of the preferred orientation of longest axes and contact normals of aggregates. Image analysis techniques are used to conduct the internal structure measurements. The orientations of the longest axes are found to be easier to measure, and better descriptors of anisotropy, than the contact normals. Finite-element analyses of the internal structure are also used to provide insight into the mixture stiffness anisotropy. The mixture properties are selected to represent a wide range of temperatures. The stiffness in the horizontal direction is shown to be as high as 30% more than the stiffness in the vertical direction. The stiffness anisotropy decreases with a decrease in the mixture temperature. The finite-element results are shown to have very good correlation with the results of the micromechanics model derived based on the orientation of the longest axes of aggregates.

An investigation into the reinforcing behavior of microdiameter fibers in cement composites, with an emphasis on their behavior in the frontal process zone (FPZ) ahead of the crack tip, is presented. Fracture toughness tests were conducted on thin sheet cement composites reinforced with polypropylene (PP), polyvinyl alcohol (PVA), and refined cellulose (RC) fibers under air-dry conditions. Fracture toughness in the absence of microscopic damage was quantified for these composites, as was fracture toughness that included the energy absorbed in the microcracked region prior to failure crack localization. These tests revealed that the PVA and RC fibers were able to effectively postpone microcrack formation, thereby delaying the localization of the failure crack. The PP fibers were not able to provide the same level of reinforcement. An optical microscope was used to monitor the progression of damage during testing. In addition, the acoustic emission technique was used to confirm the accuracy of the fracture toughness values.

The large amounts of industrial sludge generated from the wastewater treatment of a copper slag recycling plant and the marine clay dredged out from excavation and tunneling works create problems of disposal. In this study, the potential use of the industrial sludge mixed with marine clay as concrete aggregate material was examined. Properties of the sintered aggregates, their performances in concrete, and their leaching characteristics were discussed. The results indicate that the incorporation of marine clay reduces the specific gravity and strength of the aggregates. The aggregates containing up to 50% by weight of clay demonstrated better aggregate impact resistance, with values ranging from 2 to 8% over the regular granite aggregates. The concrete test specimens with sludge-clay pellets as coarse aggregates yield 28-day compressive strengths ranging between 31.0 and 38.5 N/mm², which is comparable to concrete cast with regular granite aggregates. The contaminants leached from the sludge-clay aggregates were found to be below World Health Organization drinking water limits after 109 days, indicating no long-term adverse impact of leaching of the contaminants on the environment.

This paper presents the results of pullout bond tests on fiber-reinforced polymer (FRP) tendons embedded in cement mortar filled steel tubes. The pullout test program involved four types of FRP bars, three types of grouts, and two types of bond lengths. The experimental results have shown that the pullout behavior of grouted FRP tendons are influenced by the material properties and surface conditioning of the tendon. The bond length, surface geometry and manufacturing of the tendon, grout properties, and anchorage radial stiffness have an effect on the bond strength of the tendon to the grout. An analytical model of bond stress–slip relationships for grouted FRP tendons has been proposed, and its effectiveness to represent the entire bond-slip curve has been demonstrated.

Standard repeated load triaxial tests commonly performed in the laboratory do not always apply the most damaging field loading conditions for predicting resilient and permanent deformation (rutting) responses of unbound aggregate layers due to moving wheel loads. An advanced triaxial testing machine, named the University of Illinois FastCell (UI-FastCell), was used in this study for determining the loading related directional dependency of granular material properties. Since stresses can be cycled independently in the axial and radial directions, UI-FastCell is ideally suited for simulating dynamic field stresses on the sample and for studying the effects of stress-induced anisotropy. Thirteen aggregates with varying material properties were obtained from eight different states in the United States and tested using the UI-FastCell under both vertical and horizontal dynamic loads. Anisotropic modular ratios were established as aggregate performance indicators, relating these ratios to the quality and strength properties. In general, much lower modular ratios were obtained for the “good quality” materials than for the “poor quality” ones at some representative low, intermediate, and high stress states. A shear stress ratio, which gives the level of applied shear stress as a fraction of the shear strength of the material, was also defined and successfully linked to the modular ratios of the 13 aggregates. A limiting value of this shear stress ratio is believed to control the permanent deformation behavior of aggregates.

This investigation was performed to establish the effects of the source and amount of fly ash on abrasion resistance of concrete. A reference concrete was proportioned to have a 28-day age strength of 41 MPa. Three sources of Class C fly ash were used in this research. From each source, three levels of fly ash to total cementitious materials content (40, 50, and 60%) were used in producing the concrete mixtures. The water to cementitious materials ratio was kept constant at 0.30 for all mixtures. An accelerated abrasion testing method, a modified ASTM C 944 test, was used to measure the abrasion resistance of this high-strength concrete. The effects of both the source and the amount of fly ash on abrasion resistance of concrete were noticeable. All concrete mixtures with and without fly ash exhibited high abrasion resistance in accordance with the ASTM requirement. Concrete abrasion resistance was not greatly influenced by inclusion of Class C fly ash up to 40% of total cementitious materials. However, a slight decrease in abrasion resistance of high-volume fly ash (HVFA) concrete (especially at fly ash content above 50%) was noted as compared to the reference mixture without fly ash.

Three different aggregate types were treated with water and two commercially available dust palliatives and tested in the laboratory to quantify their resistance to erosion by wind and traffic. Treated and untreated specimens were subjected to a simulated wind velocity of 32 km/h in a wind tunnel to examine resistance to wind erosion. In a second test, different specimens were subjected to up to 1,500 simulated traffic applications to measure resistance to traffic erosion. Material and environmental variables considered in the testing program include curing temperature, curing period, palliative concentration, and application rate. Results obtained confirm that dust palliatives can significantly reduce erosion of low-volume unpaved roads and that the effectiveness of a particular palliative depends on soil type, traffic loads, and environmental conditions. A parametric study was also conducted to establish palliative selection criteria. The laboratory testing program developed and the selection criteria identified can be used as a decision-making tool to select an effective dust palliative for a particular soil type and environment.

The experimental program is designed to verify and calibrate the size effect theory. Test specimens made of notched beams are tested under four-point bending. The beams are geometrically similar in two dimensions, and the thickness of all beams is 40 mm. Beams with three different heights (40, 80, and 160 mm) with length/height ratios of 5 and size ranges 1:2:4 are tested. Maximum aggregate size is 15 mm. To start the fracture band, the beams are notched with a depth of 25% of the beam height. Additionally, fracture energy $G_f\text{,}$ process zone length $c_f\text{,}$ and crack tip opening displacement ${\delta }_c$ are defined by the size effect law that has been obtained.

Thermal properties of soils are of great importance in view of the subsurface transmission of either heated fluids or high power currents. Fine-grained soils, in particular clays, pose a serious problem for conduction of heat due to very high thermal resistivity. As such, it becomes mandatory to devise a mechanism by which thermal resistivity of fine-grained soils may be reduced. An engineered backfill, with suitable thermal properties, is adopted frequently to reduce thermal resistivity of these soils. The potential of coal ash (i.e., in the form of either fly ash or lagoon ash) as a suitable backfill material, when mixed with cement, sand, and aggregates, has been explored by several researchers and is well established. However, with increasing amounts of lagoon ash being disposed of at thermal power plants, it is important to study its effectiveness as a fluidizing agent and its use in designing a proper fluidized thermal bed (FTB). Based on laboratory tests on different soils, generalized equations for estimating soil thermal resistivity have been developed in the recent past. These equations have been used for obtaining the optimum quantity of the lagoon ash for designing a fluidized thermal bed. Effect of moisture content and compaction density on thermal resistivity of different FTB compositions has also been studied.