NASCLA Accredited Commercial General ContractorConcreteHard
A concrete contractor is evaluating a concrete mix design for a high-performance concrete (HPC) structure. The design specifies a water-cementitious materials ratio (w/cm) of 0.35. During a test batch, the total weight of cementitious materials (cement + fly ash) is 600 lbs, and the total water content is 210 lbs. What is the calculated w/cm for this test batch, and how does it compare to the specified ratio?
- A0.30; it is lower than specified.
- B0.40; it is higher than specified.
- C0.45; it is significantly higher than specified.
- D0.35; it matches the specified ratio.
Show answer & explanationAnswer & explanation
Correct answer: D. 0.35; it matches the specified ratio.
The water-cementitious materials ratio (w/cm) is calculated by dividing the total weight of water by the total weight of cementitious materials. In this case, w/cm = 210 lbs (water) / 600 lbs (cementitious materials) = 0.35. This calculated ratio exactly matches the specified ratio of 0.35.
Why the other options are wrong
- A. Incorrect calculation.
- B. Incorrect calculation.
- C. Incorrect calculation.
Water-Cementitious Materials Ratio (w/cm)
The ratio of the mass of water to the mass of cementitious materials (cement + supplementary cementitious materials) in a concrete mix.
- Crucial factor in concrete strength and durability.
- Lower w/cm generally means higher strength and lower permeability.
- Must be carefully controlled during mixing.
Memory trick: Water on top, cement below, ratio's the key, watch it grow.