Alkali – aggregate reaction
Some aggregates contain particular variety of silica which react with the alkali (Na2O and K2O ) of cement , producing expansive reaction which cause cracking and disruption of concrete. Such disruption occur when
a) a high moisture level is present with in the concrete,
b) a cement with alkali content or another source of alkali,
c) aggregates containing an alkali reactive mineral
When past data is available on the cement aggregate combination and which does not indicate any cracking due to alkali aggregate reaction, no further precaution is required. If the data is not known take the one of the following precautions
1) Use of non-reactive aggregate from alternate source
2) Use of Low alkali ordinary Portland cement having total alkali content not more than 0.6 percent (as Na2O equivalent) or using 20 % fly ash or 50 % GGBFS as replacement to OPC.
3) Limiting the total cement content in the concrete mix , there by limiting total alkali content in concrete mix.
Some aggregates contain particular variety of silica which react with the alkali (Na2O and K2O ) of cement , producing expansive reaction which cause cracking and disruption of concrete. Such disruption occur when
a) a high moisture level is present with in the concrete,
b) a cement with alkali content or another source of alkali,
c) aggregates containing an alkali reactive mineral
When past data is available on the cement aggregate combination and which does not indicate any cracking due to alkali aggregate reaction, no further precaution is required. If the data is not known take the one of the following precautions
1) Use of non-reactive aggregate from alternate source
2) Use of Low alkali ordinary Portland cement having total alkali content not more than 0.6 percent (as Na2O equivalent) or using 20 % fly ash or 50 % GGBFS as replacement to OPC.
3) Limiting the total cement content in the concrete mix , there by limiting total alkali content in concrete mix.
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