An overview of a twofold effect of crystalline admixtures in cement-based materials: from permeability-reducers to self-healing stimulators

This work presents an overview of the most relevant studies developed to understand the enhancement promoted by the double effect of the crystalline admixtures (CAs), both as permeability-reducers and as self-healing stimulators in cement-based materials. Thus, an in-depth investigation was carried out of the main mechanisms of CAs disclosed in the literature in order to associate the relationship between healing products and performance improvement in cementitious materials. Further, an examination of the impact of different factors in cementitious systems with CAs was reported, as well as the synergetic effects of CAs with other constituents. Finally, conclusions were drawn highlighting research needs and addressing future works in order to provide a substantial overview of the latest information in the literature for those who are working or intend to work with this type of admixture. • This paper presents a literature meta-analysis about the effect of Crystalline Admixtures (CAs). • The primary mechanisms along with the healing products provided by CAs are addressed. • The effects of CAs on the properties of cement-based materials as permeability-reducing admixtures are discussed. • The enhancement promoted by CAs as healing stimulators is analyzed focusing on the mechanical and durability recoveries. • The influence of different aspects, such as the environmental exposure, repeated preloading, crack width, and synergic effect are also analyzed.