A new report by Austroads advises against a change in standards for producing cement.

Australian Standard AS3972:2010 specifies that general-purpose cement may contain up to 7.5 per cent limestone as a mineral addition. The cement industry proposed an increase of up to 12 per cent without changing the cement designation from general-purpose or providing alternative cements in the market with lower limestone content.

Austroads commissioned research to investigate whether the alteration could be justified, with respect to performance and durability. The project compared the properties of concrete made with a general-purpose cement containing 2.9 per cent limestone with concrete incorporating cement with 12 per cent limestone. Physical, mechanical, chemical and microstructural aspects of both plain cement concrete, and concrete incorporating cement blended with fly ash and slag, were tested.

Generally, there was no significant difference in compressive strength of corresponding pairs of concrete. However, the concrete containing cement mixed with 12 per cent limestone was inferior in drying shrinkage, modulus of elasticity and creep behaviour.

The results of the study indicate that it would be highly inadvisable to entirely replace the currently used Australian GP cement, which may contain up to 7.5 per cent limestone and complies with AS 3972:2010, with the cement proposed by the industry that would contain 12 per cent limestone, without the option of having cements of up to 7.5 per cent limestone addition readily available in the market to all cement and concrete users.

Read the report here: Properties of General-purpose Cement with Increased Percentages of Limestone