Doubling the service life of concrete structures. II: Performance of nanoscale viscosity modifiers in mortars

A new approach for increasing the service life of concrete structures is evaluated in a series of mortar specimens. The new approach consists of employing nanoscale viscosity modifiers to increase the viscosity of the concrete pore solution and concurrently and proportionally decrease the diffusion rates of deleterious ions such as chlorides and sulfates. In part I of this series, viscosities of bulk solutions of the admixtures in water and electrical conductivities of admixture solutions also containing potassium chloride were examined to verify the viability of this new technology. In the current paper, these studies are extended to quantifying the performance of one of these admixtures in mortars by measuring the penetration depth of chloride ions in cylindrical specimens exposed to a 1 mol/L chloride ion solution for up to 1 year. While significant reductions in the 1 year penetration depth are produced when the viscosity modifier is utilized via conventional addition to the mixing water, the best performance is achieved when a solution of the viscosity modifier is utilized to pre-wet fine lightweight aggregates that are then added to the mortar mixture. A scaling function appropriate for radial diffusion was used to estimate the relative effective diffusion coefficients. Compared to a reference mortar, the best mixture reduced the effective diffusion coefficient by a factor of 2.7, consistent with the overall objective of doubling concrete service life.