The influence of aggregate type on the strength and elastic modulus of high strength concrete

• The coarse aggregate type has an apparently contradicting influence on strength and elastic modulus of HSC.
• Aggregate with higher strength and stiffness results in lower strength but higher elastic modulus of HSC.
• In contrast to compressive strength, tensile strength of concrete is not significantly affected by coarse aggregate type.

This paper examines the influence of 2 common South African aggregate types on the compressive strength, split and flexural tensile strength and elastic modulus properties of high strength concrete. Two different aggregate types (Andesite and Granite) were used to produce concrete with target strengths ranging from 30 MPa to 120 MPa. Granite concrete was found to have a higher compressive strength, while the stiffer Andesite aggregate produced concrete with a significantly higher elastic modulus. An attempt is made to explain this phenomenon with fracture mechanic theories. No trend was identified for the influence of aggregate type on splitting and flexural tensile strength. The effectiveness of the SANS and EN elastic modulus prediction models was analysed against the test results and it was found that both prediction models accurately predicted elastic modulus values for the Andesite concrete, but produced far less accurate predictions for the Granite concrete.