The analysis of cracking risk by shrinkage restraint of an alkali-activated slag mortar

¹ Université Paris-Saclay, CEA, DEN-Service d’Etude du Comportement des Radionucléides (SECR), F-91191, Gif-sur-Yvette, France
² Université Paris-Saclay, CNRS, ENS Paris-Saclay LMT, 94235 Cachan, France
³ INSA Rennes, 20 Avenue des Buttes de Coesmes, 35000, Rennes, France
⁴ Orano, NWM, Technical Department, 125 Rue de Paris, 92320 Chatillon, France

^* Corresponding author: farid.benboudjema@ens-paris-saclay.fr

Abstract

Alkali-activated slag (AAS) binders show in general larger autogeneous shrinkage strains than ordinary Portland cement (OPC) based binders. However, AAS can be a relevant alternative to OPC, if, for example low hydration heat release and fine pores, are required. This study proposes an evaluation of the advantage of using AAS materials in small-sized or massive structures with regard to cracking risk by autogeneous shrinkage and thermal strains. A cracking risk index is calculated; this risk is defined as the ratio between stress generated by full restraint and tensile strength. All required experimental data were investigated in an OPC and AAS mortar, these are: heat release, autogeneous shrinkage, Young’s modulus, tensile strength and basic creep evolutions. The material parameters of a rate-dependent model developed in 1D were then identified. Numerical simulations were then performed for different thicknesses in full-restraint conditions. These show that, as expected, basic creep is a very important material parameter to assess. Indeed, basic creep enables the significant reduction of the generated stresses. Besides, it is found that the more the structure is large (and sensitive to cracking by risk by thermal strain), the more the AAS material is becoming appropriate compared to the OPC material.