Concrete, Asphalt & Their Tests

• Concrete strength is governed by the water-cement ratio: more water raises slump and lowers strength.
• Slump measures workability; compressive strength f′c is the 28-day cylinder test.
• Absolute volume of an ingredient = weight / (specific gravity × 62.4 pcf). The volumes of cement, water, aggregates and air sum to the batch volume.
• Aggregate moisture: batch weights are corrected from the saturated-surface-dry (SSD) condition using absorption and moisture content.

Worked: air voids

A compacted specimen has bulk specific gravity G_mb = 2.400 and the loose mix has maximum specific gravity G_mm = 2.500. Vₐ = 100 × 0.100/2.500 = 4.0%, the usual design target.