Consider the following statements: Presence of Na2O and K2O in concrete leads to 1. expansive reaction in concrete 2. cracking of concrete 3. disruption of concrete 4. shrinkage of concrete Which of the above statements are correct?
Consider the following statements: Presence of Na2O and K2O in concrete leads to 1. expansive reaction in concrete 2. cracking of concrete 3. disruption of concrete 4. shrinkage of concrete Which of the above statements are correct? Correct Answer 1, 2 and 3
Concept:
Considerable trouble has been experienced through extensive pop-outs and cracking in a fairly close pattern, of concrete work probably a year or more after the concrete has been cast. Although this trouble may take a year to become plainly visible the effects can often be observed in petrographic thin sections of the concrete within a few months.
The phenomenon is accompanied by extensive expansion and may lead in bad cases to complete disruption and disintegration of the concrete and is known as alkali- aggregate reaction or sometimes concrete cancer.
The trouble is due to reaction between silica in aggregate and alkalis in the cement. In some cases alkalis, mainly from the cement supplemented by alkalis in the aggregate, react with carbonates in the aggregate to produce similar result.
The types of rocks which contain reactive constituents include traps, andesites, rhyolites, siliceous limestone and certain types of sandstones. The reactive components may be in the form of opals, cherts, chalcedony, volcanic glass (excepting basaltic glasses), zeolites, and tridmite.
So presence of Na2O and K2O in concrete leads to
1. Expansive reaction in concrete
2. Cracking of concrete
3. Disruption of concrete