STUDY OF HIGH STRENGTH CONCRETES USING FLY ASH AND SILICA FUME

Abstract

During the last 15 years, high strength concretes with 28-day cube strength of 60-120 N/mm2 have entered the field of construction of high rise buildings and bridges. The present study aims at producing concrete with the highest strength which can be achieved using locally available materials. The strength which can be achieved depends on the quality of materials. The materials used in the study have been carefully selected. The relevant properties of the materials have been determined. There are two sets of concrete mixes with water/binder ratios of 0.40 and 0.30. Each set includes five concrete mixes with various fly ash and silica fume contents. The mix design is based on ACI Committee 211 guide lines for selecting mix proportions for High Strength Concretes. The fresh concrete has been tested for slump, compacting factor, and density. The entrapped air contents of compacted concretes have also been determined. To study the strength gain characteristics of the ten concrete mixes, compressive strengths are determined at the age of 3, 7, 28 and 56 days. The flexural strengths are determined at the age of 7, 28, and 56, days. The temperature rise during hydration has also been measured for all the mixes. The 28-day cube strengths achieved are 71.5-77.2 N/mm2 for concretes with w/c+p = 0.40, and 92.2-99.6 N/mm2 for concretes with w/c+p = 0.30. The optimum percentage of cement which can be replaced by fly ash has been found to be 15% for the fly ash used in the study.