How does water that's absorbed by aggregates affect concrete's water-cement ratio?
Water-cement ratio is defined as the ratio of the amount of water, exclusive of that absorbed by the aggregates, to the amount of cement in concrete. In calculating the water-cement ratio, you don't include any water contained in the aggregate pores. However, if air-dry absorptive aggregates are being batched, the amount of water added at the plant must be increased to maintain the desired concrete slump and water-cement ratio. If the plant operator doesn't make this batching adjustment, the concrete can lose slump as aggregates absorb water. This is more likely when aggregate absorption exceeds 1%.