The results showed that high levels of RCA content have an effect on the concrete strength. The next phase of the study was, therefore, concerned with how to overcome this deficit and to establish means of producing RCA concrete of a specified strength that was equivalent to the corresponding NA concrete. For this,design strengths ranging from 50 to 70 N/mm 2 were considered. The mix proportions used for the NA concretes are given in Table 2. For P, CA concrete, relationships between 28-day strength and w/c ratio, Fig. 1 (a), were used to establish the adjustment necessary to w/c ratio to take account of the effect of RCA content, for a given design strength. A summary of mix proportions is given in Fig. 2.