Journal of Materials in Civil Engineering

The heat stability of antistripping (AS) additives held in hot asphalt cement is investigated by observing the changes in additive concentration and additive performance with holding time at 162.8°C. The effect of mix curing by hot storage 149°C on stripping resistance is also investigated. The diffusitivity of an additive in hot‐asphalt cement is measured to determine the rate of additive migration to the aggregate surface during curing. The concentrations of all commercial AS additives tested are observed to decrease significantly when heated in asphalt at 162.8°C, with a corresponding loss in effectiveness. It is also found that mixture curing by hot storage remarkably improved stripping resistance. This is believed to be due to improved adhesion of asphalt to the aggregate surface. Additive migration rate to the aggregate surface is shown to be higher than apparent curing rate. This implies that the enhanced stripping resistance observed with curing is not due to additive migration. Asphalt hardening occurring during mixture curing is shown to have only a second‐order effect on stripping resistance.

Sludge is an inevitable by‐product of municipal sewage treatment. Its abundance results from rapid industrial growth, and increased treatment requirements create problems of disposal. The disposal problem could be drastically reduced if sludge were to be recycled for economical uses. This paper describes the experimental study on the use of sewage sludge together with limestone and clay as raw materials for making cementitious building material. A ground mixture of the raw materials was incinerated to produce cement. The effects of mixture compositions, incineration temperatures, and incineration durations on the properties of cement were investigated. From the results, an optimum condition of mixture composition of the raw materials, incineration temperature and duration, and curing condition upon the highest possible strength development of the cement was determined. The study shows that sewage sludge could be used to produce cement satisfying the strength requirements in the ASTM standard for masonry cement.

Fiberglass reinforced plastic (FRP) rebars can be used advantageously in concrete exposed to marine or corrosive environments. FRP rebars are resistant to corrosion and have a high strength‐to‐weight ratio. However, to fully utilize FRP rebars as reinforcement for concrete, some aspects of their behavior have to be determined including: bond and anchorage in concrete, long‐term strength, and durability in alkaline environments. In this paper the bond strength of FRP rebars in concrete is discussed. Results of pullout tests on FRP and steel rebars in concrete are presented. From the experimental results, it is concluded that the anchorage design for steel rebars is not directly applicable on FRP rebars. For the same test conditions, the average nominal bond stress at failure was greater for the steel rebars than for the FRP rebars. The slip of the rebars relative to the concrete surface was greater for the FRP rebars than for the steel rebars. The results presented herein indicate the need for special consideration for bond and anchorage design of FRP rebars.

Selected physical properties of asphalt cement are significantly changed by artificial aging under thin film oven test conditions. The changes in physical properties are also reflected in the molecular size distribution as determined by high‐pressure gel permeation chromatography (GPC). Statistical analyses show that absolute and kinematic viscosity are related to large‐sized and some small‐sized molecules, while penetration is related only to medium‐sized molecules. Dividing GPC chromatograms into 10 slices shows better resolution than using three or six slices in regression analysis. The regression analysis shows significant correlations between the three physical properties and GPC chromatograms. These models establish relationships between various physical properties and the molecular size distribution of asphalt cements. Since these models are developed for three different asphalt cement sources, three different grades for each source, and three different aging conditions, they demonstrate the general applicability of using GPC analysis to characterize asphalt cements, predict their physical properties, and identify the aging of asphalt cements.

The corrosion of steel and copper and two of its parameters (time of wetness and dry ${\mathrm{SO}}_2$ deposition) were measured at 44 locations on a building in Montréal over a period of seven months during autumn and winter. Depending on the location, the corrosion rates change around the building by a factor of three for copper and a factor of five for steel. The dry‐deposition rate of sulfur dioxides changes by a factor of three, and the time of wetness by at least two orders of magnitude. The two metals respond very differently to the same corrosion conditions at the same location. The results show the importance of and the complexity of the interaction of a building and its materials with the microclimates generated locally by the size, orientation, and design features of the building. Standard racks for measuring the atmospheric corrosion/degradation can be used to obtain the highest corrosion/degradation rates and the highest values of the two measured parameters on the exterior of the building.

The compressive and tensile properties of polyester polymer and polymer concrete were studied under various curing conditions, temperature, and strain rate. The curing temperature was varied from room temperature to 80°C. The strain rate was varied between 0.01% to 60% strain per minute and the temperature between 22°C and 120°C. The optimum curing condition for polymer and polymer concrete are different. The strength, failure strain, modulus, and stress‐strain relationship of polyester polymer and polymer concrete are influenced by the curing method, testing temperature, and strain rate to varying degrees. The influence of test variables on the mechanical properties of polymer and polymer concrete are quantified. Pretreating the aggregates with a silane coupling agent further enhances the compressive and tensile strength of the polymer concrete. The compressive strength of polymer and polymer concrete are related to their compressive modulus and splitting tensile strength. A constitutive model is used to predict the compressive stress‐strain behavior of polymer and polymer concrete.

The effects of accelerated heat aging on three polyvinyl chloride (PVC) roofing membranes was determined using thermogravimetry (TG), dynamic mechanical thermal analysis (DMA), and tensile testing. The heat aging was done at 100°C and 130°C. In general, it was found that the degradation of the reinforced PVC roofing membranes was proportional to the aging temperature and exposure time. Furthermore, it was found that these thermoanalytical techniques can be used to not only record the changes incurred by the samples due to heat aging, but also to provide a ranking of the heat stability of the various materials. The order of stability, using these techniques, was determined to be $V1<V3<V2$, which corresponded with the observed order of stability from actual records obtained on roofs. The results obtained demonstrate that TG and DMA, in conjunction with tensile testing, provide a viable, routine method of evaluating the quality of single‐ply PVC‐based roofing membranes.

A fatigue study was performed on two commercial high‐strength concretes of 70 MPa and 95 MPa with water/cementitious material ratios of 0.28 and 0.23, respectively. Specimens were cast at the construction site and cured in the laboratory. Tests were performed under constant amplitude, and strains were measured continuously using strain gauges. The McCall model for fatigue life prediction was found to be satisfactory, and safer than the usual Wöhler curves. Strain evolution and stiffness degradation with the number of cycles in high‐strength concrete were found to be similar to those of normal concrete. Strain at failure under cyclic loading was found to be of the same order as the strain at peak load under static loading. Interesting correlations between strain rate and number of cycles to failure and between stiffness decrease rate and number of cycles to failure were found. Evolution of the hysteresis loop was studied. Energy dissipated was found to decrease after the first cycles, and increased steadily thereafter up to failure. Finally, the differences in deformation characteristics between the two high‐strength concretes studied in this investigation were analyzed.

Permanent deformation in asphalt concrete pavements manifests itself as depressions along the wheel paths, ruts. The prediction of rut depth requires a knowledge of materials characteristics that relate the asphalt concrete permanent strains to stress and temperature. This paper analyzes the character of permanent strains as inferred from a creep/recovery test. It is shown that the separation of the strains into the time‐independent elastic and plastic strains and the time‐dependent viscoelastic strains requires tests with various times to unloading. The analysis is illustrated with the results of a series of uniaxial compression creep/recovery tests on one asphalt concrete mixture. The tested material exhibits temperature‐dependent elastic and plastic strains that are proportional to the level of stress. The time‐ and temperature‐dependent viscoelastic strains are nonlinearly related to the stress level and stress history. An approximate constitutive equation that disregards this nonlinearity is presented.

Long-term durability of highway structures is, and will for the forseeable future, be a major problem facing engineers. Movement of deleterious ionic species in solution through the cover region and the resulting corrosion and spalling is a worldwide problem, particularly with the heavy use of deicing salt for winter maintenance. In connection with the durability of the concrete cover, it is not the strength that is of interest but other properties, such as the continuity and tortuosity of pores and the absorption and diffusion characteristics of air- and water-filled pores. Since the surface of concrete is subjected to drying action, it has a nonuniform water content that is generally less than saturation. As a consequence, the problem of water movement through the cover is one of unsaturated flow, and involves capillary suction forces. Many factors influence the surface-absorption characteristics of concrete. In this paper, attention is directed toward investigating the influence of surface finish and casting procedures. Samples were cured under normal laboratory conditions, and absorption characteristics are quantified in terms of cumulative volume gain and depth of penetration. It is shown that the top and bottom surfaces of concrete samples display different sorptivity characteristics. Typical results are given.

The paper reports on the effects of consolidation method and specimen size on optimum water content, density, and compressive strength of laboratory-prepared roller-compacted concrete (RCC) specimens for pavement construction. The three selected consolidation methods include the vibrating table/surcharge method presently under consideration by ASTM for casting cylinders, and two impact methods using Marshall and Proctor hammers. The selected mold sizes are 15.2 cm by 30.5 cm (the standard 6 in. x 12 in.) and smaller, 10.2 cm by 20.3 cm (4 in. x 8 in.), cylinders. The experimental results indicated that fabrication method (i.e., vibration/surcharge versus impact) significantly affects optimum moisture content, density, and 28-day compressive strength. Specimen size seems to be less of a factor. The choice of the laboratory consolidation method—for density measurement and specification in particular—may have important consequences in the construction, quality control, and overall performance of RCC pavements.