Factors controlling the compressive strength of silica fume concrete in the range 100–150 MPa

Abstract

Effects of various factors on the compressive strength of silica fume high-strength concretes were investigated. Trial batches were prepared using commercially available materials and conventional experimental techniques. Tests showed that ASTM Type I and II cements gave strengths higher than Type III cement. The optimum cement content range was 504 to 623 kg/m3. The brand of a silica fume had a significant effect on compressive strength of concrete. The optimum amount of the optimum silica fume was 20% by weight of cement. ASTM Class C fly ash when added at a low dosage rate had a beneficial effect on the strength of concrete. The highest increase in the concrete strength was observed with the naphthalene-based superplasticizer and highly purified lignosulphonate based normal water reducer added at a dosage of 163 and 23cm3/100 kg of cement + silica fume, respectively. The optimum sand content, in terms of the strength and workability was within the range of about 653 to 890 kg/m3. Contrary to a general belief, the gravel was found capable of producing good quality high-strength concretes. An increase of the concrete mixing temperature from 16 to 27°C had a beneficial effect on the strength of hardened concrete. In general, the type and brand of materials were observed to exercise a significant effect on compressive strength of silica fume concretes. Therefore, while obtaining high-strength concrete it is important that all ingredients were selected based on results of laboratory trial mixtures. Tests showed that the compressive strength of silica fume concrete was noticeably affected by type of specimens and testing procedures. It is believed that this strength characteristic will be properly represented if determined on 102 × 203mm cast in steel moulds concrete cylinders, lapped and tested after 56 days of curing under moist conditions.