ABSTRACT
The characteristic strength of concrete is defined as that level of compressive strength below which 5% of all valid test results is expected to fall. Strength classes are specified in terms of both cylinder strength and equivalent cube strength. Recommended strength classes with indicative values for the secant modulus of elasticity at 28 days are given in Table 4.2. The values given for normal-weight concrete are appropriate for concretes made with quartzite aggregates. For limestone and sandstone aggregates, these values should be reduced by 10% and 30% respectively. For basalt aggregates the values should be increased by 20%.
