Sonali Arora - Questions

CONCRETE CANCER – The phenomena in which extensive expansion of concrete occurs and may lead to the total disruption and disintegration of concrete is called concrete cancer. This process is popularly known as Alkali – Aggregate Reaction.

CAUSE – This phenomenon occurs due to the reaction between Alkalis in cement and silica in aggregate. This reaction results in extensive pop-outs and cracking in a fairly closed pattern of concrete, a year or more after the concrete has been cast, and further leads to concrete cancer.

PREVENTION –

• BY SELECTING NON REACTIVE AGGREGATE – Non – reactive aggregates can be identified by chemical test, mortar bar test and petrographic examination.

• BY USING LOW ALKALI CEMENT – CEMENT WITH ALKALI LESS THAN 0.6% SHOULD BE USED.

• BY AIR ENTRAINING AGENTS – The alkali – silica gel imparts osmotic pressure over the set concrete and further this osmotic pressure is main cause of cracks. but when air entraining agents are added, they absorb osmotic pressure and, resultantly, control the expansion.

• BY CONTROLLING MOISTURE – the old concrete should not be allowed top come in water contact. Apply mortar amalgamated with water proofing agents to control the moisture in concrete.

• BY ADDING PUZZOLANAS – the cause of reaction is particular proportion and fineness of silica but when fly ash or surkhi is added, the particular proportion and fineness of silica is disturbed and aggregates do not react.