Question

Q.1 Concrete is a composite material. From microscopic point of view, it can be considered
as a three-phase composite with aggregate, cement paste and interface zone between
these two components.

1. For concrete with 28-day compressive strength of 35 Mpa (5076psi) made with
ordinary Portland cement and crushed granite aggregate, which phase of the
concrete is generally the weakest?
2. If the granite aggregate for the concrete mentioned in (i) is replaced by lightweight
aggregate. How would this affect the strength of concrete?
3. If we would like to increase the strength further, what approach shall we take?

Note: Explain in detail answer quetion.

Answer 1

1) Here Interfacial transition zone is the weakest because it is the weakest phase in concrete, microcracks starts developing from this zone which results in weekening the concrete strength

Transition zone is important zone in the concrete because the properties of concrete depends on this phase

Since the concrete strength also depends upon the binding between the concrete components,if the size of crushed granite of well graded it will bind perfectly

2) If we use light weight aggregate instead of normal aggregate it will reduce the strength of concrete,it can be proved by labouratory tests

If higher strength aggregate is used it will increase the strength of concrete,and vise versa

Light weight concrete can be used in area were strength is not a parameters,such as partition walls, ceiling etc

Light weight concrete have advantage over normal as it is economic,reduce dead load,etc

3) Using high grade cement

Less water cement ratio

Mineral admixture

Proper compaction

Well graded aggregate

Proper curing ,etc