Chemical Shrinkage and Cracking Resilience of Metakaolin Concrete

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Title: Chemical Shrinkage and Cracking Resilience of Metakaolin Concrete

Author(s): A. Markandeya, D. G. Mapa, M. Fincan, N. Shanahan, Y. P. Stetsko, K. A. Riding, and A. Zayed

Publication: Materials Journal

Volume: 116

Issue: 4

Appears on pages(s): 99-106

Keywords: cracking; metakaolin; pozzolans; shrinkage

Date: 7/1/2019

Abstract:
Metakaolin (MK) is a highly reactive pozzolan obtained from calcining clay with high kaolinite content at elevated temperatures (650 to 800°C). Its use at replacement levels between 5 and 20% enhances concrete properties such as high early- and later-age strength and lowers the diffusion coefficient due to pore size refinement. However, early-age cracking due to higher temperature rise and autogenous shrinkage is a concern. This study reports on the effect of the inclusion of prewetted lightweight aggregates (LWAs) on early-age cracking under semi-adiabatic conditions and uniaxial restraint using a rigid cracking frame. Lower cracking tendency is reported based on the tensile stress-strength ratio and cracking temperature. The chemical shrinkage coefficient for MK is determined using shrinkage measurements and thermodynamic modeling (GEMS). These findings can be used to determine appropriate LWA replacement levels in MK-blended concrete mixtures to minimize shrinkage and cracking potential.