We were discussing about chemical expansion and soundness of aggregate in concrete. We have already learnt about the differences in the processes under which expansion occurs; they are physical process (unsound aggregate) and chemical process (expansion due to chemical reaction).
Aggregate in concrete generally take (70-80) % volume in concrete and therefore draw a significant attention from engineers. While we are designing a mix, we are very much conscious about strength and regarding aggregate properties some physical tests are done often ignoring its chemical compositions.
The strength of concrete might not affected by chemical compositions, but chemical composition may have severe impact on concrete durability. In this part our concern is chemical reactions. Let’s discuss this point.
Some aggregate have silica which can react with alkalis of cement paste, resulting expansion. The impact is formation of overall cracks in structures, we will learn about this reaction elaborately in upcoming posts.
The aggregate containing carbonates react with alkali of cement and results expansion.
Other types of alkali-silica reactions
In some sand-gravels, found in river, have very high reactivity against alkali in cement matrix which also produces expansion resulting cracking in concrete.
Dear reader we will discuss about the chemical volume expansion elaborately in our next posts. Please stay with us.