Influence of water/powder ratio on strength properties of self-compacting concrete containing coal fly ash and bottom ash

The paper deals influence of water/powder ratio on strength properties of self-compacting concrete (SCC) containing coal bottom ash. SCC was made with coal bottom ash as replacement of fine aggregates in varying percentages of 0%, 10%, 20% and 30% and fly ash as replacement of cement in varying percentages of 15-35%. Strength properties tests were carried out at the ages of 28, 90 and 365 days for the various mixes. Results indicate the behaviour similar to normal SCC of increase in strength on decrease of water-powder ratio. A comparison between SCC with various fly ash contents and with various replacements of fine aggregates with bottom ash showed that SCC obtained strength increase on decrease of w/p from 0.439 to 0.414 for 0% bottom ash, 0.50-0.47 for 10% bottom ash, 0.58-0.51 for 20% bottom ash and 0.620-0.546 for 30% bottom ash. All mixes showed strength gain beyond 28 days and the mixes with 15% and 35% fly ash mixes gained strength of the order of 60 MPa and 40 MPa, respectively at 90 days. However, it was possible to produce SCC with a compressive strength of 40-50 MPa with 15-35% fly ash replacement. The bottom ash could be used up to 20% keeping in view the decrease of strength of about 15-20% (if fly ash percentages with 15% and 20% are not taken into consideration), as they show higher decrease of strength. Thus, the optimum fly ash percentage was 25-35% and bottom ash percentage was up to 20% in the present study. (C) 2011 Elsevier Ltd. All rights reserved.