increased with cement content,but was kept within the limits
recommended by the manufacturer.
For RCA concretes, the
w/c ratios were kept constant as for the corresponding NA con- cretes, but the aggregate contents were slightly adjusted to maintain the yield. Standard strength (100mm cubes cured in water at 20~ testing was carried out at ages 7, 28, 60 and 90 days. Using the results, strength versus w/c ratio plots were produced, Fig. 1. The genera trendsobservedindicated
that up to 30% coarse RCA had no effect on the ceiling strength and thereafter a gradual reduction occurred with
increasing RCA content. At 28 days (Fig. 1 (a)), the maximum attainable strength for concrete with 100% RCA
was less than 75 N/ram 2, compared to over 80 N/ram 2 for concrete containing up to 30% coarse RCA. In addition,
for concrete made with 100% coarse RCA and natural sand, the start of strength ceiling effects were observed at a