The effect of natural pozzolan on delayed ettringite formation of the heat-cured mortars

•The use of finer pozzolan in partial replacement of cement controlled or even eliminated the DEF expansion.•The substitution of cement with coarse pozzolan is not only ineffective but even accelerated the DEF expansion.•The DEF was correlated with the evolution of the mass, compressive strength, elastic modulus and porosity of the specimens. Delayed Ettringite Formation (DEF) is an internal sulfate attack caused by early age heating to a temperature of over 70°C. In this paper, the effect of natural Algerian pozzolan on the expansion of cement mortars caused by DEF was investigated. For this purpose, a portion of cement was replaced by natural pozzolan, with three different dosages (10%, 20% and 30%) and finenesses (fine, medium, and coarse). The results obtained highlighted the significant effects of natural pozzolan on DEF and the correlation existing between the expansion of the heat-cured mortars and the evolution of their mechanical properties.