Three viscosity modifiers (a commercial shrinkage-reducing admixture, a polypropylene glycol, and cellulose ether) are used to reduce the effective diffusivity of chloride ions through mortars during a one-year exposure. Two delivery mechanisms were studied: adding a viscosity modifier to the mix water; and diluting the viscosity modifier in water, pre-wetting fine lightweight aggregate (LWA) with the solution, and replacing a portion of the sand with the pre- wetted LWA, which is equivalent to the practice of using LWA for internal curing. After a 28- day curing period, the cylinders were submerged in a 1 mol/L chloride solution. After 6 months and 12 months of exposure, micro X-ray fluorescence analysis was used to profile the radial chloride concentration under ambient air pressure. The effective diffusivity was estimated by regression, assuming ideal Fickian radial diffusion. Compared with the control mortar (no admixture, no LWA), the addition of the viscosity modifier to the mix water reduced the effective diffusivity by nearly a factor of two, and the combined effect of pre-wetted LWA reduced the effective diffusivity by a factor greater than two. Therefore, the use of these viscosity modifiers has the potential to double the service life of any concrete that may be subjected to degradation that depends upon diffusion, such as corrosion of the steel reinforcement and sulfate attack.
Citation: Cement and Concrete Composites
Pub Type: Journals
Diffusion, lightweight aggregate, micro X-ray fluorescence, mortar, service life, viscosifier, viscosity