Question

8) WHAT IS ALKALI-SILICA REACTIVITY (ASR)? 9) HOW CAN "ASR" BE AVOIDED?

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Answer 1

8) ASR( alkali Silica reaction)

ASR is also know as concrete cancer because it decreases the life time of the concrete and when it effects a particular area of a structure it will spread to the whole structure.ASR means a reaction between two components in presence of water which leads to decrease of life time of concrete. Alkali silica reaction is occur in concrete due to the alkalinity of cement and unreacted silica that present in the aggregates.when the alkali compounds that present in the cement reacts with the Silica in presence of water a hydroscopic gel will be formed which causes expansion of the concrete by increasing the pressure inside. Due to ASR in the concrete it's durability ,compressive,tensile strengths will decrease. When it comes to tensile strength 80% of the tensile strength will decrease.

9)

1: ASR is caused due to unreacted silica in aggregates and alkaline compounds present in the cement.By reducing the Silica content and alkali nature of cement can avoid ASR

2:By decreasing water cement ratio we can reduce ASR because concrete gets more harder and becomes unpermeabule and does not allow any water through it.so by this we can reduce expansion of the structure

3:By addtion of admixture like lithium and barium salts we can avoid ASR. Addition these admixture is an expansive process.

4:ASR expansion can also reduced by air entrainment