Journal of Materials in Civil Engineering

Materials for housing construction in developing countries are usually too expensive because most materials must be imported. In the hotter climates, especially of Africa and south Asia, coping with the heat creates another problem for designing functional housing. Construction with blocks and bricks made from a local soil has proved beneficial in the case under investigation. Previous work has shown that firing of earth blocks give the materials high crushing strengths, and the addition of cement, lime, and slag further improves the load‐bearing capacity of the blocks. The potential for enhanced thermal comfort by the addition of these additives is investigated in this paper. Thermal conductivity of plain bricks decreases with increasing firing temperature. Also, the addition of cement, lime, or slag further decreases the thermal conductivity of the bricks. The results further show that minimum thermal conductivity coincides with the condition of maximum crushing strength. Thus, the strength achievable is not compromised to obtain minimum thermal conductivity.

Some of the concrete works on the Dadin Kowa Dam project in Bauchi State, Nigeria, from 1982 to 1987 are discussed. Admixtures were used during the concreting, and the relative advantages of using such admixtures are examined in terms of strength and other properties. The data collected show that strength development of concrete with admixtures is a function of the quantity of admixture used per weight of cement. For all classes of admixture used, the strength gained at the end of the seventh day is high and in agreement with the manufacturers' standards. The effect of concreting in a hot environment without the use of any set retarder will increase the cement content by about 19%.

Proper introduction of silica fume in concrete improves both the mechanical and durability characteristics of the concrete. This paper presents the results of research effort conducted at the American University in Cairo using Egyptian silica fume in concrete. The program investigated various characteristics of silica‐fume concrete. It emphasized the effect of silica fume on workability level and its maintenance of fresh concrete; strength development, strength optimization and elastic modulus of hardened concrete; and chemical and mechanical durability of mortar. The experimental program comprised six levels of silica‐fume contents (as partial replacement of cement by weight) at 0% (control mix), 5%, 10%, 15%, 20%, and 25%, with and without superplasticizer. It also included two mixes with 15% silica fume added to cement in normal concrete. Durability of silica‐fume mortar was tested in chemical environments of sulfate compounds, ammonium nitrate, calcium chloride, and various kinds of acids. It was found that there was an optimal value of silica‐fume content at which concrete strength improved significantly. Due to the slow development of pozzolanic effect, there was a drop in early strength up to seven days and late significant gains up to 56 days upon introducing silica fume to concrete. Elastic modulus, toughness, and steel‐concrete bond increased at the optimum silica‐fume content in concrete. Silica‐fume mortar exhibited significant improvement in durability against chemical attacks of most salts and acids. The improvement was moderate in the case of sulfate compounds. Mechanical erosion resistance increased moderately in silica‐fume concrete.

This paper examines the relationship between the gel permeation Chromatographic (GPC) profile and the physical properties of an asphalt cement. This problem was approached from a nontraditional perspective in that a regression‐based model for predicting GPC profiles from the physical properties of the asphalt was developed. Such a model provides an alternative way of investigating the relationship between a specific physical property and the GPC profiles of asphalts. The idea is to better understand how we can use GPC to characterize the behavior of asphalts. We used data for asphalts from a wide variety of sources in developing the regression model. The model was validated by using it to accurately predict the GPC profiles of 11 new asphalts [from the Strategic Highway Research Program (SHRP)]. The validation of the model shows that there is a strong relationship between GPC profiles and the physical properties of asphalts. This relationship is complex, however, the model clearly shows that the GPC profile is largely determined by the rheological type of the asphalt.

An analytical model has been developed for the flexural strength of fiber‐reinforced cement‐based materials. The proposed model adopts the fictitious crack concept to relate the flexural strength of these fiber composites to their tension‐softening properties and to specimen geometry. For the case of a cementitious matrix reinforced with discontinuous randomly distributed fibers, the flexural strength can be related to the micromechanical parameters and specimen geometry. A reasonable agreement has been observed between the model prediction and experimental data reported in literature, supporting the validity of the proposed model. This model led to conclude that the flexural strength of fiber cementitious composites is dependent on specimen geometry and is also strongly influenced by the stress acting across the process zone. In addition, the flexural strength is always higher than the tensile strength and it is reached when the fracture process zone is only partially developed. The model can be used to design fiber cementitious composites for optimum flexural strength.

This study investigates the fatigue behavior of corroded rolled beams made of A588 steel. The beams were weathered under two conditions: One set was boldly exposed to the environment; the other was exposed under a metal deck that simulated the shelter provided by highway bridge decks and lightly sprayed with a salt solution during the winter months. Bold exposure for 62 months and stress cycling in a moist freshwater environment decreased the fatigue strength from category A to B. Sheltered exposure for 67 months and stress cycling in a moist saltwater environment decreased the fatigue strength from category A to E. The one‐category reduction in fatigue strength, from A to B, adopted in the latest specifications from the American Association of State Highway and Transportation Officials may be adequate for ideally and boldly exposed weathering‐steel base metal, but it does not represent the loss in fatigue strength that can be expected of weathering‐steel base metal exposed to the variety of conditions typically found in service.

As part of a larger investigation in steel‐fiber‐reinforced wet‐mix shotcrete, companion specimens were cast using the shotcrete mixes for a direct comparison with shotcrete after hardening. Deformed steel fibers with five different geometries were investigated. Mixes were first shot on wooden forms and then cast using external vibration. Comparisons were made between shotcrete and cast concrete on the basis of compressive and flexural strengths and the flexural toughness. For a given mix, the average compressive strength of cast concrete was found to be significantly higher than that of the shotcrete. Flexural strengths, however, witnessed a reversal in the trend. In the case of flexural toughness, although the results for cast concrete were decisively different from that of shotcrete, no clear trend became apparent. The paper concludes that care should be exercised in predicting the behavior of shotcrete on the basis of the performance of cast concretes of similar proportions.