International Concrete Abstracts Portal

SP-228CD This CD-ROM of Special Publication 228 contains the papers presented at the Seventh International Symposium on the Utilization of High-Strength/High- Performance Concrete that was held in Washington, D.C., USA, June 20-24, 2005. The symposium continued the success of previous symposia held in Stavanger, Norway, (1987); Berkeley, California (1990); Lillehammer, Norway, (1993); Paris, France, (1996); Sandefjord, Norway, (1999); and Leipzig, Germany, (2002). The symposium brought together engineers and material scientists from around the world to discuss topics ranging from the latest applications to the most recent research on high-strength and high-performance concrete. In the years since the first symposium was held in Stavanger, there has been worldwide growth in the use of both high-strength and high-performance concrete. In addition to more research and applications of traditional types of high-performance concrete, the use of self-consolidating concrete and ultra-high-performance concrete has moved from the laboratory to practical applications. This publication offers the opportunity to learn the latest about these developments.

It is widely recognized that addition of fly ash improves strength and durability of concrete, besides improving economy and ecology. In recent times the emphasis globally is on mixing high volume fly ash in high performance concrete. India produces 100 million tones annually out of which only 20 % is utilized. In an ongoing program, an experimental investigation is carried out to assess the performance of three types of concrete: one with ordinary Portland cement, another with blended cement and a third with site mixed high volume fly ash (with cement replacement level of 50 %). All three are exposed to acidic environment. A total of 180 cubes of 100 mm size are cast for the study. Batches consisting of 54 cubes in each are immersed in water, and 1 % solutions of H2SO4 and (NH4)2SO4 respectively. The changes in weight and compressive strength are monitored fortnightly for 90 days. Coefficient of water permeability is determined for these mixtures. Concrete with high volume fly ash showed better resistance when exposed to acidic environment, though strength decreased marginally. Concrete with blended cement is found more impermeable than concrete with fly ash mixed at site. It was concluded that high volume fly ash concrete is more durable than ordinary concrete.

High Reactivity Metakaolin (HRM) is an engineered pozzolanic mineral admixture, reacting aggressively with calcium hydroxide which results in significant performance of concrete. HRM has been introduced to be a beneficial alternative for silica fume, required in the formulation of high strength/performance concrete. In this study, different aspects of concrete mechanical behaviors have been studied including compressive, flexural and splitting tensile strengths. Also some characteristics of concrete durability were investigated including water absorption, water penetration and gas permeability. In mixture proportioning, 5%, 10% and 15% of cement content is replaced by HRM or silica fume for comparative study. It was observed that both concrete with HRM and silica fume would perform almost the same in improving the mechanical properties of the materials. However in the case of workability and durability, a better performance was obtained in concrete with HRM. It was concluded from the investigation that HRM could be an appropriate substitute for silica fume in producing high performance concrete.

Two series of high strength concrete representing a total of fifteen mixes were investigated with respect to strength, modulus of elasticity, shrinkage and freeze-thaw resistance. A 30 % replacement of cement by fly ash was accomplished in both series. Main variables in the mix design were the binder composition and the water/binder-ratio which covered a range of 0.28 to 0.40. Workability was better than the workability of similar concretes containing silica fume. The compressive strength achieved at 90 days was classified as grade C45/55 to C80/95 depending on the mix design. The values of Young’s modulus exceeded the values predicted by current standards. The excellent durability was verified in freeze-thaw tests. The investigation proved that replacing up to 30 percent of the cement by fly ash is possible without jeopardizing strength or durability.

The early age strength development of concretes containing ground granulated blast furnace slag (ggbs) at cement replacement levels of 20, 35, 50 and 70% have been investigated to give guidance for their use in fast track construction. 28-day target mean strengths for all concretes was 100 MPa. Although supplementary cementitious materials like ggbs are economical, their use has not gained popularity in fast track construction because of their slower strength development at early ages and at standard cube curing temperatures. There are however indications that supplementary cementitious materials are heavily penalised by the standard cube curing regimes. Measurements of temperature rise under adiabatic conditions have shown that high levels of cement replacement by ggbs, e.g. 70% are required to obtain a significant reduction in the peak temperature rise. However, despite that these temperature rises are lower than those of portland cement mixtures they are still sufficient to provide the activation energy needed for the reaction of ggbs to “kick-in” earlier. The early-age strength under adiabatic conditions of ggbs mixtures can be as high as 250% of the strength of companion cubes cured at 200C. The high early age temperatures are shown to be especially beneficial to ggbs concretes. Maturity measurements will be needed in order to take advantage of the enhanced in-situ early age strength development of ggbs concretes. The contractor needs to be able to confirm that the actual strength of the concrete in the structure at the time of formwork removal exceeds a certain compressive strength. Maturity functions like the Nurse-Saul and the Arrhenius equation have been examined for their applicability to ggbs concretes. Activation energies, required as input for the Arrhenius equation, have been determined according to ASTM C1074-98.