Investigation of the development of ultrahigh-strength Portland cement concrete (UHSC) consolidated by statically applied high confining stress systems

Abstract

Large size (12-in. cubes) specimens of ultrahigh-strength portland-cement concrete and mortar were successfully produced by using a high-pressure confining mold (12-million-pound total load capacity) designed, developed, and patented at Texas A&M University. The high consolidation pressures were applied by the 2.4-million-pound capacity universal testing machine (UTM) at the Waterways Experiment Station, Vicksburg, Mississippi. Twelve concrete and mortar mixtures were produced by varying the parameters of: (1) cement type (Types I and III); (2) fly ash content (0 and 30 percent by weight); (3) coarse aggregate (0 and 67 percent, by weight of total aggregate); (4) fine aggregate (33 and 100 percent, by weight of total aggregate content); (5) W/C ratio (one for mortar and one for concrete); and (6) curing mode (regular and accelerated). The cube production procedure consisted of mixing mortar or concrete, hand-placing and vibrating in the mold. After placing the drive ram and assembly onto the base of the UTM, the consolidating load was applied at a rate of 120,000 lb (54,400 kg) per minute up to a total load of 2.4 million lb (1,088,600 kg). Each cube of mortar or concrete was then cured either in the regular or accelerated mode. Two mixtures were consolidated in layers by placing one-half the amount of concrete in the mold, and consolidating to the total stress level of the UTM. The remaining mixture was placed in the mold, the ram reset, and the concrete reconsolidated to the peak stress level. Specific gravity, pulse velocity, compressive strength, porosity, and petrographic examination tests were performed on cores. In conclusion, strength tests verify that (1) large specimens of ultrahigh-strength concrete (UHSC) were produced, (2) the porosity of the high-pressure-consolidated concrete and mortar was lower than that of conventionally consolidated concrete and mortar, (3) unit weights and pulse velocities of UHSC were considerably higher than those of conventional concrete and mortar, (4) the classical chemistry and phase morphology of cement hydration products prevail (i.e., high consolidation pressures caused no change in the chemistry nor phase morphology), and (5) the success of sample preparation by layers was inconclusive.