Journal of Materials in Civil Engineering

This research was conducted to evaluate the concomitant effect of chloride and sulfate contamination and high temperature and humidity on carbonation in plain and blended cements. The cement mortar specimens were contaminated with chloride and sulfate ions and exposed to 55°C, 75% relative humidity (RH) and 3% CO ₂ atmosphere. The progress of carbonation was evaluated by measuring the depth of the carbonated layer and the weight gain. Morphological changes due to carbonation were examined using scanning electron microscopy. The results indicated greater carbonation in the contaminated specimens than in the uncontaminated specimens. This was observed in both plain and blended cements. The increased carbonation in the contaminated specimens is attributed to changes in the pore structure of cement due to the inclusion of contaminants.

An experimental investigation was carried out to generate the complete stress-strain curves of concrete in compression with a strength range of 50–120 MPa. The variation in concrete strength was achieved by varying the water-to-binder ratio of the mix, types of cement replacing admixture, replacement percentages, and the age at testing. The effects of these parameters on the shape of stress-strain curves are presented and discussed. The accuracy of predictions of a number of analytical models available in the literature are also discussed. Based on present test data, a simple model is proposed to generate the complete stress-strain relationships for high-strength concrete. The proposed model has been found to give a good representation of the actual stress-strain response.

In this study, certain mechanical and rheological properties of structural lumber subjected to shear stresses and the long-term lateral load-slip behavior of silicone elastomeric and polyvinyl-acetate adhesives (PVA) with an isocyanide hardener were evaluated as part of a larger project designed to predict the long-term behavior of stressed-skin panels under load. Sixteen pieces of solid wood and 16 glued joints were evaluated in several test series in order to determine the desired properties. Wood modulus of rigidity was determined from the initial deformation recorded in long-term tests. The relative creep was also determined under constant environmental conditions (20°C, 65% RH). Four combinations of long-term tests on glued joints were conducted on wood-chipboard and wood-steel connections with the two adhesives. Analyses showed that the creep rate, relative creep, and joint variability were greatest for the silicone adhesive. Two mathematical models (power functions with and without exponential terms) were evaluated as predictors of the deformation-time relationship for the PVA joints under constant loading. The power function with the exponential term was found to be the better predictor. However, both underestimated relative creep at longer load durations.

Layer coefficients of cement-stabilized soil were determined for use in the American Association of State Highway and Transportation Officials (AASHTO) pavement design method. The soils were an A-3 fine sand and an A-6 silty clay. The silty clay was blended with three different amounts of concrete sand. Cylindrical specimens of three differing cement contents were molded and tested for static compressive chord modulus and unconfined compressive strength. Layer coefficients were determined by using the modulus values with the AASHTO pavement design guide's layer coefficient nomograph; the coefficients ranged from 0.09 to 0.27, depending on soil type, sand content, and cement content. Regression equations based on strength, dry unit weight, and cement content were developed to allow estimation of layer coefficients. Layer coefficients were shown to increase with increasing cement content, dry unit weight, and, for the sand-clay mixtures, sand content.

Engineers are faced with choosing materials for bridges on a regular basis. Yet, little is known of the nonstructural factors that influence their decision and what they believe is important in bridge-material selection. As new materials enter the market for bridge applications, a thorough understanding of a highway official's current perceptions of materials will allow manufacturers to meet their needs better. Perceptions of major bridge materials by three distinct groups of decision makers were investigated within five geographic regions of the United States. The materials compared included prestressed concrete, steel, timber, and reinforced concrete. Bridge materials were compared not only on perceived performance, but also on eight preselected attributes. Important factors in the bridge decision process were identified. Comparisons were made by decision-making group and geographic region. Overall, prestressed concrete was rated highest in perceived performance, followed by reinforced concrete, steel, and timber. Perceptional maps provide insight for those manufacturers wanting to improve their perceived performance. Areas of future research for bridge materials were identified.

This paper describes part of an ongoing research project concerning high-density polyethylene (HDPE) liners used for pipeline rehabilitation. Tests were conducted in the laboratory, where a steel sleeve was welded on the outside surface of a steel pipe lined with a HDPE liner. Recommendations were made to establish welded joints using stitch welds of length equal to the minimum length specified by the applicable codes, with a center-to-center spacing of three times the weld length. A waiting period may be required between consecutive stitch welds, especially for small-diameter pipes. A second group of tests was conducted to evaluate the material performance of a liner strengthened by butt-fused HDPE rings. The overall stiffness of the liner increased with the addition of the butt-fused rings. Tension tests were conducted on dog-bone-shaped samples extruded from the stiffened liner. The butt-fusion process used to attach the stiffening rings increased the average tensile strength and average elasticity modulus of the material in the fusion area.

The aggregate gradation of the hot mix asphalts (HMA) used in southern Nevada before 1989 generally fell above the maximum density line (fine graded aggregate mix). Various asphaltic concrete pavements using an aggregate gradation curve that resides below the maximum density line for any nominal size aggregate have been placed in the southern Nevada area over the past few years. These pavements have shown improved resistance to rutting and permanent deformation. This paper presents mix design and performance (rutting) data of four (post-1990) projects in which the gradations range from continuous coarse graded to skip coarse graded aggregates (gradation curves that dropped sharply from the 3/4 in. sieve to the 1/2 in. sieve size then continued in a well-graded fashion). Maximum rut depths were measured for all traffic lanes at major intersections, and average rut depths were then calculated for each project. Rutting measurements were made after at least one annual cycle of operation. These measurements show a 50% rutting reduction when the continuous coarse graded aggregate HMA was used instead of the pre-1989 fine graded aggregate HMA. The rutting was further reduced by 50% when skip graded aggregate HMA was used instead of the continuous coarse graded HMA.