Superplasticizers
- ACause around 4-7% reduction in water
- BAre useful for producing flowing concreteCorrect
- CCannot provide higher strength at lower w/c values
- DDecrease the workability at same w/c ratio
Solution
Concept
Superplasticizers enable high water reduction (15-30%) and are primarily used to produce flowing concrete or high-strength low-w/c ratio concrete.
Step-by-step solution
1. Understand the definition and purpose of superplasticizers (High Range Water Reducers). 2. Evaluate Option A: Regular plasticizers cause 5-15% reduction, while superplasticizers cause 15-30% reduction (not 4-7%). 3. Evaluate Option B: Superplasticizers are widely used to produce flowing concrete with high slump without segregation. 4. Evaluate Option C: They *can* provide higher strength at lower w/c ratios by maintaining workability while reducing water. 5. Evaluate Option D: They *increase* the workability at the same w/c ratio.
Explanation
Superplasticizers (high-range water reducers) are chemical admixtures used to produce flowing concrete with high workability or to reduce water content significantly (by 15-30%) to achieve high strength. Therefore, they are extremely useful for producing flowing concrete.
Why the other options are wrong
A: Conventional plasticizers cause 5-15% water reduction, whereas superplasticizers cause 15-30%. C: They enable very low w/c ratios while maintaining workability, thereby yielding higher strength. D: They substantially increase workability at the same w/c ratio.
Shortcut
Superplasticizers = High Range Water Reducers -> High water reduction (15-30%) and High workability (flowing concrete).
Common mistake
Confusing regular plasticizers (water reduction 5-15%) with superplasticizers (water reduction 15-30%).
Correct answer: B) Are useful for producing flowing concrete