Aggregate Gradation & Moisture Corrections

• Moisture states, driest to wettest: oven-dry (OD), air-dry, saturated surface-dry (SSD), and wet. Mix designs are written for SSD aggregate.
• Absorption is the water an aggregate holds at SSD, as a percentage of its OD weight. Water beyond absorption is free water and joins the mix.

Worked: wet sand on a cold morning

The design calls for 1,800 lb of SSD sand. Absorption is 1.0%; the stockpile tests at 4.0% moisture. OD weight = 1,800/1.01 = 1,782 lb. Batch 1,782 × 1.04 = 1,853 lb of wet sand, and cut the mix water by 1,782 × 0.03 = 53 lb.

Its cumulative percentages retained on the No. 4, 8, 16, 30, 50 and 100 sieves are 2, 15, 35, 58, 80 and 96: FM = 286/100 = 2.86, within the usual 2.3–3.1 band for concrete sand.