Florida DOT Concrete Batchman/Operator Practice Exam

How do you calculate a new design material weight when the Specific Gravity (SG) changes?

1. New SG * 62.4 = new unit weight, then use absolute volume

2. New SG / 62.4 = new unit weight, then use absolute volume

3. Absorption * new SG = new unit weight, then use total weight

4. Absorption * 62.4 = new unit weight, then adjust weight

The correct answer is: New SG * 62.4 = new unit weight, then use absolute volume

To understand how to calculate a new design material weight when the Specific Gravity (SG) changes, it is essential to grasp the relationship between SG and unit weight. Specific Gravity is a ratio that compares the density of a material to the density of water. The density of water is approximately 62.4 pounds per cubic foot. When you have a new Specific Gravity value, multiplying this value by the density of water (62.4 lb/ft³) gives you the new unit weight of that material. This calculation reflects the actual weight of a unit volume of the material based on how it compares to water. Once the new unit weight is determined, it can be applied to calculate the material’s volume requirements or to adjust the overall mix design. Using absolute volume is important in concrete mix design because it helps to ensure the correct proportions of materials are used to achieve the desired strength and durability of the concrete. By establishing the new unit weight through the provided method, batch sizes can be calculated effectively, leading to a well-balanced mix. Other options do not appropriately apply the relationship between Specific Gravity and unit weight in the context of concrete batch design, which is why they do not lead to the correct calculation for determining material weight when SG changes.