1 Explain an advantage and a disadvantage of set acceleratin

1. Explain an advantage and a disadvantage of set accelerating agent additive in concrete.

2. Explain an advantage and a disadvantage of set retarding agent additive in concrete.

3. Explain an advantage and a disadvantage of air entraining agent additive in concrete.

4. Explain an advantage and a disadvantage of water reducing agent additive in concrete.

5. What are the two potential causes of impact recoil of the hose during concreting (shown in the movies and discussed in class)?

6. Name three types of concrete bored-piles discussed in class. Explain briefly.

7.During a concrete wall construction, concrete can be poured into the wall form either continuously or in layers (stages). What is the difference in lateral pressure induced by green (liquid) concrete between the two casting modes? In the latter mode of casting concrete wall, caution must be taken concerning the depth of concrete consolidation (using vibrator). Why?

Solution

(1) Answer:-

Advantages of set accelerating agent additive in concrete:-

(i) Reduces water requirement

(ii) Enables earlier release from precast moulds thus speeding production.

(iii) Reduces segregation and increase density and compressive strength.

Disadvantages:-

(i) Corrosion of reinforcement

(ii) Causes of discoloration which darkens the concrete

(iii) Shortens setting time

(2)Answer:-

Advantages of set retarding agent additive in concrete:-

(i) Reduces bleeding and segregation

(ii) Extended setting time

(iii) Improve workability

Disadvantages:-

(i) Rapid stiffening

(ii) Plastic shrinkage

(iii) Water evaporation is influenced by temperature.

(3) Answer:-

Advantages:-

(i) Increase durability

(ii) Workability increased

(iii) Reduced bleeding and segregation

Disadvantage:-

(i) It reduces compressive strength

(4) Answer:-

Advantages:-

(i) High strength can be obtained with the same cement content by reducing water cement ratio.

(ii) Increase workability of concrete.

Disadvantages:-

(i) Inclusion of additional cost for admixture.

(ii)Slump loss is usually greater than traditional concrete

(iii) In case of formed finishing or exposed finishing color blemishes and air voids are observed.