Materials: Aggregates, Cement, Admixtures, and Reinforcement
What this domain tests
This domain tests incoming material control and the properties that affect precast/prestressed concrete: aggregate grading and moisture, cementitious composition, admixture compatibility, reinforcement grade, and prestressing strand. Questions often link a material certificate or test result to acceptance and batching action.
Core rules
- Aggregates are commonly qualified under ASTM C33; check gradation, deleterious substances, absorption, and moisture. Reactive aggregates require ASR mitigation per the specification.
- Cement may be ASTM C150, C595, or C1157; SCMs such as fly ash, slag, or silica fume must match the approved mixture and project limits.
- Admixtures are qualified under ASTM C494 or C1017 and must be stored per manufacturer instructions. Compatibility and dosage should be verified in trial batches.
- Reinforcement commonly follows ASTM A615 or A706; prestressing strand follows ASTM A416. Check grade, size, surface condition, and certification.
- Store cement and SCMs dry, protect admixtures from freezing, and keep reinforcement and strand free of oil, mud, and harmful corrosion.
Worked example
A stockpile has 5.2% total moisture and 1.0% absorption. For 1,800 lb of aggregate at saturated-surface-dry mass, free water is 1,800 x (0.052 - 0.010) = 75.6 lb. The wet batch mass is 1,800 x 1.052 = 1,893.6 lb, and the batcher reduces added water by 75.6 lb. If the operator uses total moisture without subtracting absorption, the mixture becomes 18 lb too wet.
Traps
Using total moisture instead of free water; accepting a cement certificate without checking the specified type; mixing admixture brands without trial verification; and allowing strand or reinforcement to sit in mud or standing water.