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.

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.

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.