Credibility of Soundness Tests of Concrete Aggregates

We have already learnt about many aspects of soundness and different test methods for determining soundness of aggregates for concrete construction. The tests we have and will discuss are:

a. Sulfate soundness (BS 812 and ASTM C88) test

b. Freezing and thawing test

c. Methylene blue test

The last two tests will be discussed later. ASTM C33 recommended to perform freezing and thawing test when aggregate fail to pass sulfate soundness test. Methylene blue test is conducted to identify expansive clay minerals remains in some aggregates.

 

There have also other tests to determine soundness. But no one produce reliable results that can actually measure soundness. ASTM C88 test measures reduction in aggregate size under formation of salt crystal into pores of aggregates. BS 812 also produces similar types of measure. They just produce a qualitative measures of soundness depending on which we cannot reject a stock of aggregates.

ASTM C33 provides limits of loss 10% and 15% for sodium sulfate and magnesium sulfate test respectively. Freezing and thawing test also produce a qualitative measure of soundness. Now why we are emphasizing on the word ‘qualitative’? This is due to:

We are ignoring presence of hydrated paste of cement surrounding aggregate on the behavior or performance of them under laboratory disruptive action. Therefore we require a satisfactory service record of concrete produced with identical aggregate from identical source under identical expected durability exposure.