The service life distribution of concrete structures typically follows a bathtub-shaped function, with a finite probability of early-age failures being followed by a life with a relative low probability of failure that ultimately increases dramatically as the end of service is reached. Ideally, new concrete technologies should reduce the failures occurring at both ends of this service life spectrum. VERDiCT (Viscosity Enhancers Reducing Diffusion in Concrete Technology) is one such technology, having the potential to reduce the propensity for early-age cracking, while also reducing long term transport coefficients of deleterious ions such as chlorides. In this paper, the performance of a typical VERDiCT admixture, a viscosity modifier/shrinkage-reducing admixture, is investigated in both mortars and concretes. A reduction in early-age cracking is achieved by eliminating the autogenous shrinkage stresses that typically develop in lower water-to-cementitious materials ratio concretes. By substantially increasing the viscosity of the pore solution in the concrete, the resistance to ionic diffusion is proportionally increased. Here, chloride ion diffusion coefficients are evaluated for two types of concretes containing typical substitution levels of supplementary cementitious materials, namely either 25 % fly ash or 40 % slag by mass. For the mixtures investigated in this study, the effective diffusion coefficient was reduced by approximately 33 %, which, in practice, may imply a 50 % increase in their service life, while the autogenous shrinkage was virtually eliminated. However, these benefits in early-age cracking resistance and long term durability are tempered by up to a 20 % reduction in compressive strength that may need to be accounted for at the design stage.
Citation: Aci Materials Journal Journal
Pub Type: Journals
Autogenous deformation, diffusion, durability, service life, sorption, strength, viscosity.