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What is Difference between Soundness and Chemical Expansion in Concrete? (Part-1)

The title of this post should be unsoundness of aggregate instead of concrete. However let’s consider soundness and chemical expansion of concrete; both produce expansion related problem to concrete. Here we like to differentiate between two terms.


Soundness of aggregate defines the capacity of aggregate against excessive volume changes which is related to variation in physical states of aggregates. Here important keyword is physical state; whereas there may have some volume changes due to chemical reaction between aggregate and alkali content of cement.
Chemical expansion in concrete due to alkali-aggregate reaction
Now we will try to list physical factors that can changes volume of aggregate. The volume changes we are listing may be permanent or large:

  1. Freezing and thawing
  2. Wetting and drying cycles
  3. Thermal changes when temperatures rise above freezing.


Now we know the physical causes of volume changes; unsound aggregate is that result deterioration in concrete due to volume changes under above physical causes.


Now we like to include some chemical reactions that can cause volume changes. These are:


  1. Alkali-aggregate reactions
  2. Alkali-carbonate reactions
  3. Other types of alkali-silica reactions etc.


These are most common types of chemical causes that can produce expansion, deteriorating the concrete properties and most concerned property is durability.


Dear reader the chemical reactions will be discussed in our next part of this topic. We hope we will enjoy these posts.

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