Journal of Materials in Civil Engineering

An experimental investigation is conducted on the use of a newly developed aramid fiber for the reinforcement of Portland cement‐based concrete and slurry. The fiber is produced by chopping a bundle made of epoxy‐impregnated, braided aramid filaments. Its appearance and handling are more similar to those of steel fibers than to any other synthetic fiber. Aramid‐fiber performance was compared to that of steel and collated‐fibrillated polypropylene fibers under static flexure and drop‐weight impact. Specimens consisted of conventionally cast concrete beams, layered beams using SIFCON construction technique, and thin SIFCON plates. Given the fiber geometries and types used, static and impact results indicate that this aramid fiber acts similarly to steel fiber and is superior to polypropylene fiber.

The capacity to bind chloride ions in hydrated cement paste, with and without fly ash, is studied. Free chloride ions remaining in the pore solution are determined. The hardened pastes are exposed to continuous fog curing, moderate or ${\mathrm{CO}}_2$ polluted environments. Long initial curing of fly‐ash cement pastes, which were to be subjected to moderate environment of negligible carbonation, are found essential in order to make use of the fly‐ash capacity to trap chloride ions. However, fly‐ash pastes that are to be eventually subjected to a ${\mathrm{CO}}_2$ polluted environment show a much lower capacity to trap the chloride ions than the pastes that do not incorporate fly ash. In these fly‐ash cement pastes, larger release of the chloride ions to the pore solution is associated with longer initial curing periods. In elements of structures where chloride contamination is anticipated and where carbonation is likely to proceed rather quickly, the corrosion of steel reinforcement is expected. The results found in this research indicate that due caution must be exercised when setting the minimum cover to reinforcement, curing conditions, and coating measures in the event of using fly‐ash concrete in structural elements.

Water‐permeability measurements were made on 50 mm diameter and 100 mm long cored cylinders obtained from a roller compacted concrete pavement that was 160 mm in average thickness. A triaxial permeability cell was used. The effect of water‐cement ratio, silica fume addition, use of a finer cement, curing technique, etc. on coefficients of permeability were investigated. Roller compacted concrete was found to be considerably more permeable than conventionally proportioned and placed concrete and somewhat more permeable than conventional mass concrete. The use of silica fume and finer cement appeared to reduce the coefficient of permeability to some extent. However, the method of curing did not make any appreciable difference. When observed under a microscope, roller compacted concrete was found to have a number of interconnected compaction voids, hollow aggregate‐paste boundaries, and interfaces that were porous and undeveloped.

The prepeak and postpeak stress‐displacement relations are derived for the bridging mechanism associated with randomly oriented discontinuous flexible fibers in cement‐based composites. The postcrack strength and fracture energy are examined in light of the scaling micromechanical parameters, including fiber snubbing coefficient, diameter, aspect ratio, volume fraction, and interface bond strength. Comparisons of theoretically derived postcracking stress‐displacement relation and pullout fracture energy with experimental data of both steel‐fiber and synthetic‐fiber reinforced cementitious composites of widely varying micromechanical parametric values suggest that the simple model approximates the bridging behavior in this type of composite.

Inadequate understanding of the factors that control the strength and durability of concretionary laterite gravels constitutes a major constraint in the development of practical quality‐control specifications. This results in improper use of these aggregates in road construction, causing poor service performance. To remedy this situation concretionary laterite gravels from across Nigeria were subjected to several physical, mechanical, and chemical tests in the laboratory. The relationships between these tests and the major factors influencing the test results were determined by factor (R‐mode) analysis. The results of the study revealed that four principal component factors control the measured properties of laterite gravels. They are, in decreasing order of importance; (1) iron oxide content (degree of lateritization); (2) porosity and pore‐size distribution; (3) micropores; and (4) adsorbed water. These factors explain 79% of the total variance observed in the measured properties. The degree of lateritization accounts for 51% of the variance, and this indicates its dominating influence on the physical and mechanical properties of laterite gravel aggregates. The results of cluster analysis show that the parent material rock types also have considerable influence on the physicomechanical properties of laterite gravel aggregates and on the relative contribution of each factor group to the property variance.

A thin elastomeric interlayer called polyvinyl butyral (PVB) is used to bond two or more thin glass plates to form a composite commonly called a laminated glass unit. Even though experiments have been performed to determine the load‐deformation characteristics, efforts to create a mathematical model for the stress analysis fall short of the nonlinear shear stress‐strain behavior of the PVB interlayer. Specially made laminated‐glass specimens $50\mathrm{mm}\times 50\mathrm{mm}\times 9.5\mathrm{mm}\text{,}$ with two interlayer thicknesses, 0.76 mm and 1.52 mm, are tested in a direct shear box testing apparatus. The average shear stress versus average shear strain are plotted. Variations of tangent and secant modulii are also plotted as a function of average shear strain. All tests are performed at very low strain rates, because the objective was to study the static behavior of laminated‐glass units.

Typical nonperformance conditions of wall construction in Kuwait are heat penetration, cracking due to high ambient temperature, and changes in moisture content of the building materials. To investigate the causes of cracking and the impact of local construction practices and environmental conditions, a 1,125 unit housing project was selected as a case study. A field survey and laboratory tests were carried out. Construction specifications and practices along with the properties of materials used in the project were studied. Crack location, direction, and pattern were recorded and studied. Laboratory tests were conducted to assess the properties of the masonry blocks and mortars used. The study showed that the main causes of wall cracking in Kuwait are poor design and workmanship, inadequate attention to construction details, and excessive drying shrinkage and wetting expansion of construction materials. The study recommended specific construction practices to prevent wall cracking in Kuwait. These recommendations were applied in a new housing project. Preliminary results of a field survey indicate a significant reduction in wall cracking.

The effect of polymer content and glass‐fiber content on the compressive behavior of polyester polymer concrete is investigated at room temperature. The polymer content varies between 10% and 18% of the total weight of polymer concrete, and the glass‐fiber content varies up to 6% (by weight). The addition of fibers increases the toughness and failure strain (strain at peak stress), but decreases the compressive modulus and the initial Poisson's ratio. In general, the fibers confine the material and delay the crack propagation, thus, increasing the failure strain and postpeak ductility. The compressive strength shows that there is an optimum fiber content for a given polymer content. Simple relationships are used to predict the compressive strength, modulus, failure strain, and Poisson's ratio from the test parameters. The toughness of the fiber‐reinforced polymer concrete is quantified using ASTM recommendations. A stress‐strain model is proposed to predict the complete compressive stress‐strain curves and the toughness indexes, $I_5\text{,}$ $I_{10}\text{,}$ and their ratio. The analytical model favorably predicts the measured stress‐strain relationships and toughness parameters.

This paper reports results of an investigation evaluating the strength development and long-term corrosion resistance of concrete mixes incorporating a superplasticizer, two fly ashes, and a natural pozzolan. The compressive strength was determined up to 90 days. Reinforced concrete specimens were immersed in sodium chloride solution for more than five years. The corrosion rate of reinforcing steel was monitored using electrochemical techniques. Results indicate that the compressive strength of concretes incorporating both a superplasticizer and pozzolans is lower than that of plain superplasticized concrete up to 90 days. However, there is marked improvement in the long-term corrosion resistance of these concretes over plain concrete. This indicates that where durability of concrete (against chloride ingress) is the primary criterion, pozzolans and chloride-free superplasticizers can be used as admixtures to produce impermeable and corrosion-resistant concrete.