Hamidou Diawara

ABRASION RESISTANCE OF FINE AGGREGATE REPLACED SILICA FUME CONCRETE

This investigation evaluated the resistance to abrasion of concrete proportioned to have four levels of fine aggregate replacement (5%, 10%, 15%, and 20%) with silica fume. Control mixtures containing no silica fume were also used for comparison purposes. Three cement factors, namely, 500 lb/cu yd (900 kg/cu m), 650 lb/cu yd (1,157 kg/cu m), and 800 lb/cu yd (1,424 kg/cu m), and two water-to-cementitious materials ratios (w/cm)--0.325 and 0.40)--were employed. The fresh and bulk characteristics, such as slump, air content, time of setting, bleeding, unit weight, and compressive strength, were examined to characterize the selected matrixes. The standard testing method--American Society for Testing and Materials (ASTM) C 779, Procedure C, Ball Bearing--was used to ascertain the resistance to wear. The influence of silica fume addition, cement factor, w/cm, and curing were studied. The relationship between depth of wear and compressive strength was also presented. Finally, the fresh properties, compressive strength (and strength development), and abrasion resistance of the fine aggregate-replaced silica fume concretes were compared with those of the reference mixtures. Laboratory test results concluded that the resistance to wear of concrete containing silica fume as a fine aggregate replacement was consistently better with increasing amounts of silica fume up to 10%. The abrasion resistance and compressive strength decreased with increases in w/cm and improved with increases in cement factor and curing age. Both compressive strength and resistance to wear of fine aggregate-replaced silica fume concretes were better than those exhibited by the equivalent control matrixes. A significant correlation was found between the depth of wear and compressive strength.

Influence of Hauling Time on Fresh Properties of Self-Consolidating Concrete

This study was intended to evaluate the influence of hauling time on fresh self-consolidating concretes (SCCs) made with slump flows of 508, 635, and 711 mm (20, 25, and 28 in.). Nine different hauling times—10, 20, 30, 40, 50, 60, 70, 80, and 90 minutes—were used. Fresh performance of the selected SCCs was affected by hauling time in the form of loss in flowability and gain in flow rate and dynamic stability. A remediation technique consisting of admixture overdosing was able to revert the adverse influence of hauling time on the fresh characteristics of the selected matrices, as it produced SCCs with similar flow characteristics, dynamic stability, and passing ability to those obtained at the reference hauling time.

Sodium Sulfate Resistance of Fast-Track Portland Cement Concretes

The research study presented herein is intended to examine the sodium sulfate resistance of early opening-to-traffic portland-cement concrete. The trial matrixes of two categories of opening-to-traffic times, four cement factors, and three cement types are exposed to very severe external sodium sulfate attack based on ASTM C1012. The mixtures are examined for fresh properties (slump, bleeding, setting times, and adiabatic temperature), bulk characteristics (unit weight and compressive strength), and resistance to sodium sulfate (expansion and loss in mass and strength). The influence of parameters such as curing age, cement factor, and cement type on sodium sulfate resistance of the selected concretes is discussed. In addition, the expansion of the test specimens is compared with proposed acceptance limits found in the literature based on ASTM C452 or C1012. Laboratory test results conclude that, irrespective of cement type, the rate of expansion reduced with increases in cement factor throughout the immersion period. Neither mass of concrete residues nor notable strength loss was found in any opening time fast-track concretes used in the investigation. There was a statistically significant correlation between the sulfate expansion (the dependent variable) and immersion age, cement factor, cement type, and compressive strength (the independent variables).