Journal of Materials in Civil Engineering

The experimental technique described below makes it possible to preserve the compressive stress-induced microcracks in concrete as they exist under applied loads. The results can be used to better understand and quantify the general relationship between stress level and crack development, as well as the effect of confinement on crack behavior. Also, it allows observations into the way small cracks are formed and then propagate in concrete, thereby making the application of fracture mechanics to concrete more accurate. Cylindrical specimens of concrete were subjected to testing under uniaxial and confined compression utilizing special testing equipment designed and developed specifically for this experimental study. An alloy with a low melting point was used as a pore fluid. At a specific stress, this alloy was solidified to preserve the stress-induced microcracks as they exist under load. Scanning electron microscopy was employed to capture images from the cross sections of normal and high-strength concrete specimens.

A newly developed digital image-analysis method was used to characterize the morphological characteristics of coarse aggregates. Regression analyses found that the imaging morphological characteristics of coarse aggregates correlated well with results of other indirect characterization tests such as the test method for index of particle shape and texture (ASTM D 3398); the test method for uncompacted void content of coarse aggregate as influenced by particle shape, surface texture, and grading (modified ASTM C 1252); and the test method for unit weight and voids in aggregate test (ASTM C 29). The imaging morphological characteristics of coarse aggregates also correlated well to the effects of coarse-aggregate properties on hot-mix asphalt concrete mixtures. This research offers a new approach for evaluating coarse-aggregate characteristics of asphalt-concrete mixtures and demonstrates use of an emerging technology for pavement engineering.

The vibration of buildings due to earthquake or wind can be reduced by hysteresis damping of structural members, and low yield point steel is one of the most efficient damping materials. One conventional mild steel, one modified mild steel, and two low yield point steels were low-cycle fatigue tested. The following findings were obtained: (1) the low-cycle fatigue strength (i.e., the relationship of strain to number of cycles to failure) of the low yield point steels can be expressed by the Manson-Coffin equation; (2) the strain rate exerts a small effect on the low-cycle fatigue properties of the low yield point steels; (3) the cumulative energy absorption capacity of the low yield point steels to failure varies from type to type (that of the mild steels is superior to that of the low yield point steels with strain amplitudes of larger than 0.8%); and (4) with strain amplitude of less than 0.7%, the cumulative energy absorption capacity of the low yield point steels is much higher than that of the mild steels.

This investigation was undertaken to evaluate the effectiveness of using hedmanite (rockwool natural fibers) as filler in improving the performance of asphalt concrete pavements, and to compare hedmanite with lime (as filler) modified mixes and the conventional asphalt mix containing crushed stone filler. In this study, optimum asphalt content was obtained by Marshall method and was used in all the modified mixes. The engineering properties, including resilient modulus, stability loss, split tensile strength, fatigue and permanent deformation, were determined. Results indicated that certain percentages of both hedmanite and lime are effective in improving the resilient modulus, while the Marshall stability loss and tensile strength loss were higher in hedmanite mixes than in lime mixes. Lime modified mixes showed better resistance to fatigue and rutting than hedmanite modified mixes. Results indicated that better quality asphalt concrete mixes can be prepared using lime rather than hedmanite as a filler.

Neat asphalt binders lack the proper viscoelastic balance that usually occurs when an effective elastic network is created by molecular association. It is hypothesized that proper viscoelastic balance can be formed by creating molecular entanglement in asphalt through the use of high molecular weight polymeric additives. In this research, a procedure for modifying asphalt binders was developed, together with criteria to evaluate the effectiveness of the polymer modification process. The procedure and criteria were used to modify Arab asphalt binders to satisfy the performance requirements of the Gulf countries, in terms of rutting, fatigue, and low-temperature cracking. The data collected clearly indicated that polymer modification is effective in improving the rheological properties of neat Arab asphalt binders to satisfy the performance requirements of the Gulf countries. Furthermore, life cycle cost analysis of various polymer modified mixtures indicated that polymer modification is feasible and economically justified.

The disposal of municipal solid waste ash has become a significant economic and environmental issue. Municipal solid waste ash can be considered to have a fly ash and a bottom ash component. Municipal solid waste bottom ash (MSWBA) from a refuse-derived fuel facility was evaluated as a potential portland cement concrete ingredient. Portland cement–related ASTM methods and other analytical techniques such as X-ray diffraction were used. The sample MSWBA was found to be a marginal concrete aggregate. The sample MSWBA met most ASTM C 331 standards such as size gradation, but the high angularity and brittle nature of the MSWBA would significantly affect concrete workability. The MSWBA sulfate and chloride concentrations also were high enough to create potential sulfate attack and reinforcing steel corrosion problems. Iron removal and aggregate processes such as size control offer cost-effective methods to improve MSWBA for use as an aggregate.

The Atlantic Richfield Products Company located in Blaine, Wash. generates about 6,356 Mg (7,000 tons) of coke dust every year. The coke dust is produced during the process of calcination in the hearths, storage silos, conveyor systems, and during the loading process into rail cars. The main objective of this research study is to investigate the potential use of calcined and green coke (uncalcined) dusts as modifiers in hot mix asphalt paving mixtures. Six different blends including control were subjected to binder testing and grading using Superpave testing equipment and procedures. Hveem mix designs also were conducted on the six mixtures. Coke dust was added by total weight of the asphalt cement binder. Research results indicate that both coke dusts will act as reinforcing agents for the asphalt cement binders. Both coke dusts seem to improve asphalt cement performance (high stiffness) at high temperatures (58 and 64°C) with minimal adverse effect (increased stiffness) at low temperatures (−12 and −18°C). At intermediate temperatures, penetration values at 25°C will decrease and dynamic shear values at 19 and 22°C generally will increase as a result of coke dust addition. Viscosity (stiffness), dynamic shear, Hveem stability, and voids in mineral aggregate tend to increase as a result of adding coke dust (whether it is calcined or green). Also, there is a slight improvement in retention of asphalt coating when coke dust is used. All mixtures exceeded the minimum Washington State Department of Transportation specification requirements for class B hot mix asphalt concrete. Thus, if proper aggregate is used, permanent deformation (rutting) and stripping will be reduced in coke dust–modified asphalt pavements.

This paper presents the results of an investigation into the influence of particle-size distribution (PSD) of ground granulated blast-furnace slag (GGBFS) on the compressive strength of slag mortar. The PSD of the GGBFS powder was defined by the parameters of the Rosin-Rammler distribution function, namely, position parameter, x₀ and slope n. These parameters describe the fineness and the size-range characteristics of the PSD, respectively. Samples of GGBFS with different PSDs were prepared using a method by which a commercially available GGBFS sample was first separated and then recombined into predetermined proportions. The results showed that varying the PSD of the GGBFS by keeping n constant and increasing x₀ decreased the compressive strengths of mortar mixes. Varying n at a constant x₀ was found to produce only a small change in compressive strength. However, at 70% GGBFS replacement, and for both water/cement ratios considered, the mortar mix containing the GGBFS sample with the widest range of distribution showed the highest strength at 28 days of age.

The use of pulsed radar for investigating the integrity of structural elements is gaining popularity and becoming firmly established as a nondestructive test method in civil engineering. Difficulties can often arise in the interpretation of results obtained, particularly where internal details are relatively complex. One approach that can be used to understand and evaluate radar results is through numerical modeling of signal propagation and reflection. By comparing the results of a numerical modeling with those from field measurements, engineers can gain valuable insight into the probable features embedded beneath the surface of a structural element. This paper discusses a series of numerical techniques for modeling subsurface radar and compares the precision of the results with those taken from real field data. It is found that more complex problems require more sophisticated analysis techniques to obtain realistic results, with a consequential increase in the computational resources to carry out the modeling.

The influence of intermittent wetting on the absorption characteristics of treated and untreated slag concretes is presented, with the surface of samples subjected to either water or chloride solution. Relatively simple methods were used to quantify the efficacy of the treated surface—in particular, the cumulative volumetric gain, weight loss, and surface resistivity measurements. Destructive testing was also used to investigate the depth of impregnation of the surface treatment and the penetration of chlorides into both the treated and untreated surfaces.