Effect of freeze - Thaw cycles on the physicomechanical properties of a pozzolanic mortar

- Pozzolanic materials may improve the mortar's frost resistance.
- The treated clay has not improved the mortar's behavior when exposed to 300 F-T cycles.
- Despite its pozzolanic potential, damage increased with the clay content.
- The clay fineness (only 3870 cm2/g) was the main factor of its low efficiency.
- The F-T cycles have favored the progress of cement hydration reactions.

This paper presents an assessment of the frost resistance, after 300 freeze - thaw cycles, of mortars made from cements having different amounts of pozzolan addition. Calcined Algerian clay was used, as clinker replacement, at 0, 10, 15 and 20% by weight. In order to limit its physical pozzolanicity, the fineness of the treated clay, at 700 °C for 5 h, was chosen very close to that of clinker. The aim of this work is to study the influence of the pozzolanic addition on the physical, mechanical and thermal properties of mortars undergoing this kind of cyclical loading. Experimental results show that compressive strength and thermal conductivity decreased, while porosity, water absorption and hydration progress increased. The deteriorations were in an absolute increase with the increase of treated clay level. Although the variant with 10% of addition was the least affected, it was found that whatever the substitution level, the clay fineness has not led to an improvement in pozzolan mortars behavior against the frost attack compared with the control CEM I.