Briefly discuss the comparison of measured slump with your o

Briefly discuss the comparison of measured slump with your observations made in the lab on workability. How did the addition of silica fume, fly ash, or fibers affect the workability? Discuss the effects of adding air entraining agent. When might slump not be a good indication of workability? (10pt)

Compare the assumed air content with that measured by the pressure and volumetric methods. Why are the values different or similar? In what cases would it not be acceptable to use the pressure method for air content and why. (10pt)

Compare the experimentally determined unit weight with that computed theoretically and give possible reasons for differences that may exist. (10pt)

Solution

Answer:- Slump Test:- Concrete slump test is done for determining workability of concrete. By the help of slump value we can calculate water cement ratio.

Types of concrete slump result:-

(i) True slump:- True slump is only slump that can be measured in test. Measurement can be taken between top of cone and top of concrete after cone has been removed.

(ii) Shear Slump:- Shear slump indicates that result is incomplete and concrete will be retested.

(iii) Collapsed Slump:- it indicates that water cement ratio is more high.

(iv) Zero Slump:- Zero slump is indication of very low water cement ratio.

Silica fumes increases workability when we add up to 20 % silica flumes in concrete .When we add more than 20 % silica flumes in concrete then workability of concrete decreases.

Flyash increases workability of concrete.

Fiber decreases workability of concrete.

Air entraining agent increases strength of concrete .They reduces air void of concrete.

When slump value come zero this result is not good for workability of concrete.

When came collapsed slump, then it means water is more .Concrete is not workable.

Comparison of assumed air content that measured by Pressure method and volumetric method :-

Pressure method requires the sample be placed in a pressure air meter and subjected to an applied pressure.Air content can be easily read.

Volumetric method measuring air content by agitating a known volume of concrete in an excess of water.This method is suitable for concrete containing all type of aggregate.

Value of air content measured from both method will be different.

Value from pressure method will be high.

When light weight aggregate are used in concrete then pressure method will be not used for measuring of water content.