During concrete batching, what adjustment is required to the batch weights to compensate for the moisture content of aggregates, ensuring accurate mix proportions?

During concrete batching, an adjustment to the batch weights of aggregates is necessary to account for their moisture content to ensure accurate mix proportions. Aggregates can exist in various moisture states: oven-dry (OD), air-dry (AD), saturated surface-dry (SSD), and wet. In mix design calculations, aggregates are usually assumed to be in the saturated surface-dry (SSD) condition, meaning the pores are filled with water, but the surface is dry. However, in practice, aggregates are often in an air-dry or wet condition. If the aggregates are air-dry, they will absorb water from the mix water, reducing the effective water-cement ratio and potentially affecting workability and strength. To compensate, the batch weight of the air-dry aggregate must be increased by an amount equal to its absorption, and the amount of added mixing water must be reduced by the same amount. If the aggregates are wet, they contain more moisture than the SSD condition; this excess moisture is called surface moisture. In this case, the batch weight of the wet aggregate must be decreased by an amount equal to its surface moisture, and the amount of added mixing water must also be reduced accordingly. This ensures that the total water content in the mix, including the water from the aggregates and the added water, matches the design water content, maintaining the desired water-cement ratio and achieving the specified concrete properties. For example, if a mix design calls for 1000 kg of aggregate in the SSD condition, but the aggregate on hand has a surface moisture content of 2%, the batch weight of the aggregate should be reduced to 980 kg, and the added water should be reduced by 20 kg.