7 Describe what is meant by ASR and the conditions in which

7. Describe what is meant by ASR and the conditions in which this could occur. Briefly outline how the occurrence of ASR could be avoided or its adverse effects minimized. 8. Define the term saturated surface-dry condition of aggregate and discuss how the moisture content of coarse aggregate in saturated surface-dry condition is determined.

Solution

(7) Answer:-

ASR:- Alkali silica reaction also known as concrete cancer . It is reaction between cement and silica , found in aggregate.

Reaction causes expansion of aggregate by formation of a soluble and viscous gel of sodium silicate .This gel swells and increases in volume when absorbing water.

We can control ASR by controlling alkali metal content in cement. By using dry aggregate , we can control ASR .

We can control ASR by limiting reactive silica content of the aggregate.

(8) Answer:-

Saturated surface dry condition :- It is a condition in which surface of aggregate are dry but inner particle voids of aggregate contains water.

Moisture content = ( M_ssd – M_{oven dry} )/M_{oven dry}

Where

M_ssd = Mass of saturated surface dry aggregate

M_{oven dry} = Mass of oven dry aggregate