The maximum water-cement ratios for plain cement concrete and reinforced cement concrete under severe exposure conditions are _____ and _____ respectively. Consider the aggregates are normal weight with 20 mm nominal maximum size.
- A0.50; 0.45Correct
- B0.45; 0.45
- C0.40; 0.40
- D0.60; 0.50
Solution
Concept
IS 456:2000 sets a maximum free water-cement ratio for each exposure condition, and the limit is stricter for RCC than for PCC.
Step-by-step solution
1. Use IS 456:2000, Table 5 (minimum cement content and maximum w/c ratio for 20 mm aggregate). 2. Severe exposure, PCC: maximum free w/c ratio = 0.50 (minimum cement 250 kg/m³, minimum grade M20). 3. Severe exposure, RCC: maximum free w/c ratio = 0.45 (minimum cement 320 kg/m³, minimum grade M30).
Explanation
In severe exposure, concrete must be dense and less permeable, so the w/c ratio is limited. RCC has steel that can rust, so its limit (0.45) is stricter than the PCC limit (0.50).
Correct answer: A) 0.50; 0.45