Using Viscosity Modifiers to Reduce Effective Diffusivity in Mortars

Three viscosity modifiers (a commercial shrinkage-reducing admixture, a polypropylene glycol, and a cellulose ether) are used to reduce the effective diffusivity of chloride ions through mortars during a 1-year exposure. Two delivery mechanisms were studied: (1) adding a viscosity modifier to the mix water and (2) diluting the viscosity modifier in water, prewetting fine lightweight aggregate (LWA) with the solution, and replacing a portion of the sand with the prewetted 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-$\mathrm{mol}/\mathrm{L}$ chloride solution. After 24 and 52 weeks 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 using LWA saturated with a viscosity modifier 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 on diffusion, such as corrosion of the steel reinforcement and sulfate attack.