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.

This paper reports an investigation on the strength, durability and shrinkage of high strength rice husk ash concrete (HSRHAC) with w/b ratio of 0.27. Rice husk ash (RHA) was incorporated either as 10% ‘addition’ or 10% ‘replacement’ of cement. Specimens were subjected to water curing or air-drying and tested up to 180 days. For comparison purposes, concrete containing 10% condensed silica fume (CSF) and concrete containing superplasticizer alone (SpOPC) were also cast. Results show that with the aid of a polycarboxylic hyperplasticizer, high workability RHA concrete mixtures in the range of 200-250 mm slump and having 28 days strengths of 80 MPa can be routinely produced. In general, strengths of RHA concrete are higher than the control superplasticized concrete but marginally lower than CSF. Durability of concrete with regards to initial surface absorption (ISA) shows that RHA concrete exhibit similar ISA values compared to CSF concrete. After 3 cycles of wetting in magnesium sulphate solution for 30 days followed by 7 days air-drying, RHA concrete produced similar expansion compared to the CSF concrete but lower expansion than the SpOPC concrete. At 180 days, shrinkage of HSRHAC is similar to that of CSF. Based on the current study, it can be concluded that RHA is just as good as CSF in producing high strength concrete of Grade 80. Since RHA can be produced at a much lower cost than CSF, it is an attractive alternative material in the production of HSC.

The performance of two metakaolins as supplementary cementitious materials (SCMs) was evaluated at 8% by weight cement replacement. The metakaolins varied by their surface area (11.1 vs. 25.4 m2/g). Performance of metakaolin mixtures was compared to control mixtures at water-to-cement ratios of 0.40, 0.50, and 0.60 where no SCM had been used and to mixtures where silica fume had been used as partial replacement for cement. In both mixtures containing metakaolins, compressive, splitting tensile, and flexural strengths increased, as well as elastic modulus, as compared to control mixtures. Setting time was reduced in the pastes with both metakaolins. Additionally, considering durability, both metakaolins reduced rapid chloride ion permeability and expansion due to alkali-silica reaction when compared to control and silica fume mixtures. In general, the finer of the two metakaolins proved more effective in improving concrete properties, although both performed superior to silica fume.

The water/cementitious material ratio (w/cm) remains an essential, descriptive statistic for today’s increasingly complex HPC mixtures. The water/cement ratio (w/c) is also useful. A sample of 125 high performance concrete (HPC) mixtures of various materials and proportions was fitted with linear regression models relating compressive strength at ages of 1, 28 and 56 days to the w/cm and/or w/c. It was observed that strength generally increased as the w/cm or w/c was lowered. But linear regression models using a single independent variable, either the w/cm or w/c, failed to return a coefficient of determination, R2, more than 0.535. It was learned that the w/c provides a stronger indication of strength at 1 day. By 28 and 56 days, because of pozzolanic activity, the w/cm becomes a better indication of strength. Multiple linear regression models using both the w/cm and w/c capture more of the variability in the data.

The effect of air entrainment on the compressive strength of high performance concrete is presented in this paper. Generally, an increase in the total air content of one percent decreases the compressive strength of concrete two to five percent. This rule of thumb was developed from research on normal strength concrete, but there is little data on the strength reduction due to entrained air in high performance concrete. The paper presents compressive strength test results of several high performance concrete mixtures with total air contents ranging from two to six percent. The compressive strength of the mixtures varied from 42.4 MPa (6150 psi) to 95.9 MPa (13,900 psi). The results of the study support the use of this rule of thumb for high performance concrete. Data are also presented on the increased dosage rate of air entraining agents required in low water to cementitious material ratio concrete.