what is alkali -silica reactivity ( asr ) ?

Alkali-silica reactivity is an expansive raction between reactive forms of silica in aggregates and potassium and sodium alkalis mostlu from cement , but also from aggregates m pozzolans , admixtures and mixing water , External sources of alkali from soil , decers and industrial processes can also contribute to reactiviry , THe raction forms an alkali-slica gel that sweelss as it draws water from the surrounding cement paste , therby inducing pressure , expansion and cracking of the aggregate and surrounding paste . This often results in map pattern crack , sometimes referred to as alligator pattern cracking , ASE can be avouded throught 1 ) proprt aggregates selection , 2) use of blended cement , 3 ) use of proper pozzolaic material and 4 ) contaminant -free mixing water