North Carolina General Contractors Practice Exam

By how much can a superplasticizer typically increase the slump?

1. 1-3 inches

2. 2-4 inches

3. 5-7 inches

4. 7-9 inches

The correct answer is: 7-9 inches

Superplasticizers are high-range water reducers used in concrete to significantly increase its workability without the need for additional water. These chemical admixtures can greatly enhance the slump of concrete, which is a measure of its consistency and fluidity. The typical increase in slump when using superplasticizers tends to fall within the range of about 2 to 4 inches. This capability allows for a more fluid mix that facilitates easier placement and helps in achieving complex shapes or densely reinforced sections while maintaining strength by not adding extra water that could weaken the concrete. The option indicating a 7-9 inch increase in slump is an overestimation of what superplasticizers can usually achieve. Such substantial increases are not common practice and can even compromise the integrity of the concrete if too much fluidity leads to segregation or lower strength due to an improper water-cement ratio. Understanding the practical limits of superplasticizers is valuable knowledge for contractors in ensuring that concrete remains workable while maintaining its structural properties. Therefore, recognizing that superplasticizers can typically increase slump by 2-4 inches is essential for effective concrete mix design and construction practices.