Effect of clay as deleterious material on properties of normal-strength concrete

Abstract

Sustainability concerns prompted use of crushed aggregates in concrete, wherein deleterious materials might get inadvertently included. Some deleterious materials are allowed up to limiting values by most standards, which, however, are silent about the quantification of their effects on properties of concrete – which would be site specific. For an important Indian infrastructure, this study quantifies effects of clay fines as deleterious material in concrete, on workability (slump) and strength (cube compression; split tensile; flexural tensile tests) around the limit (1% of fine aggregates by weight) stipulated by the Indian standard. The novelty of the study is that, contrary to the literature in this domain, the effects are studied without alteration of the mix proportions – a different practical scenario. The limit of clay fines in concrete allowed by Indian standard was found to be adequate considering strength parameters, but for maintaining target workability, the limit would be revised to 0.5% of the fine aggregates. Generally, the variations of concrete properties with the increasing clay fines were: (1) the workability and split tensile strength reduced monotonically, in non-linear fashion; (2) compressive strength (beyond 7 days) and the flexural tensile strength (modulus of rupture) reduced monotonically in linear manner.