For a 32 MPa concrete, what is the specified water-to-cement ratio and air entrainment?

• A. .45 water/cement ratio and 5-8% air entrainment
• B. .50 water/cement ratio and 2-4% air entrainment
• C. .60 water/cement ratio and 0% air entrainment
• D. .40 water/cement ratio and 10-12% air entrainment

Answer: (A)

In concrete design, strength and durability come from balancing the amount of water relative to cement and the amount of entrained air. For a target strength around 32 MPa, using a water-to-cement ratio near 0.45 provides enough cement hydration to achieve the desired strength while keeping the paste relatively dense and less permeable. At the same time, adding an air-entraining admixture creates a controlled network of tiny air voids, typically about 5–8% of the volume, which improves workability and, more importantly, enhances resistance to freeze-thaw cycles by giving water somewhere to expand without cracking the concrete. So the combination of a 0.45 water-to-cement ratio with 5–8% air entrainment aligns with standard practice for 32 MPa concrete. Higher water content would weaken the mix, and too little air or too much air would either reduce durability in freeze-thaw conditions or diminish strength.