Question

Q1: Define creep in concrete? Distinguish it from elastic deformation.

Q2: Discuss the rate of concrete drying shrinkage at different ages.

Q3: Explain the positive aspects of bleeding on concrete.

Q4: Explain the effects of size and grading of aggregates on workability of concrete?

Q5: Differentiate between additives and admixtures with examples.

Q6: Explain the working mechanism of retarders, plasticizers and air entrained
admixtures.

Q7: Define volume and weigh batching of concrete? Explain with examples.

Q8: Differentiate between continuous and batch type concrete mixers?

Q9: Explain, how to improve cohesiveness of concrete ingredients? Indicate its effects on
concrete segregation?

Q10: Discuss the primary reasons for the abnormal setting behaviors of concrete?
Describe how chemical and mineral admixtures may cause concrete abnormal setting with
the help of examples.

Answer 1

1. Creep : it is the dependant deformation of concrete due to sustained load

When structure is loaded, the concrete is subjected to elastic and inelastic deformations. The elastic deformations occur immediately after the load is applied according to the hooke's law. The inelastic deformations increase with time as the load is applied. This inelastic deformation is known as creep within increases at a decreasing rate during the loading period.

During the first month of loading, only one third to one fourth of the ultimate creep can be observed while after one year almost half to three fourth of ultimate creep can be observed.

While elastic deformagion is observed immediately after the loading.

2.drying shrinkage is contracting of a hardened concrete mixture due to the loss of capillary water. The shrinkage causes increase of tensile stress which leads to cracking, deformation.

Rate of drying shrinkage depends on several factors like properties and proportions of components, moisture available during mixing, type of mixing, member size etc.,

3. Bleeding of concrete is not objectionable always. Some times it is desirable.

If the co crete is to be revibfated, this allows the contractor to use highly pleacable mix, yet bleeding of the water reduces the water content from the mix during registration.

4. As the size of aggregate is reduced, the overall surface area will increase. So, more cement content is required to cover the increased surface area and will need more water to lubricate the aggregates. So smaller aggregates are less workable.

For well graded aggregates, the lesser volume of voids will require lesser compacting effort. So well graded aggregate are more workable.

5. Additives are added during the manufacture of cement to give special properties to it. For example puzzolona cement, sulphate resisting cement etc.,

Admixture are added to the fresh concrete while mixing to reduce the workability, increase strength, accelerate or decelerate the setting etc.,

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