Effects of Total Internal Water Content on Freeze-Thaw Durability and Scaling Resistance of Internally-Cured Concrete

Abstract

The effects of total internal (TI) water, provided by normalweight coarse and fine aggregates and pre-wetted fine lightweight aggregate (LWA), in the range of 6.8 to 17.3%, corresponding to internal curing (IC) water in the LWA ranging from 0 to 15.1%, by weight of cementitious materials, on the freeze-thaw durability and scaling resistance of 12 concrete mixtures are evaluated. Cementitious materials consist of portland cement only or portland cement with a 30% weight replacement by slag cement. The coarse aggregate consists of limestone (with an oven-dry absorption of 1.8%) or granite (with an oven-dry absorption of 0.6%), which provide 5.5 to 5.6% or 1.9% internal curing water by the weight of cementitious materials, respectively.

All of the mixtures with the limestone coarse aggregate failed the test, with the average dynamic modulus of elasticity (EDYN) dropping below 95% of the initial value well before the 660 freeze-thaw cycles specified by the Kansas Department of Transportation, demonstrating that the limestone itself is susceptible to freeze-thaw damage. The mixtures containing granite coarse aggregate had an average relative EDYN above 95% of the initial value at 660 freezethaw cycles in the test of freeze-thaw durability at TI water contents up to 15.7% (corresponding to an IC water content of 13.4% from the LWA) by the weight of cementitious materials. The only mixture with granite coarse aggregate that failed the test had a 30% weight replacement of portland cement with slag cement and a TI water content of 17.3% by weight of the cementitious materials (corresponding to 15.1% IC water from LWA). This result indicates that it is possible to have too much internal curing water. In the scaling test, the mixtures with granite coarse aggregate, all of which contained LWA, had lower mass losses than mixtures with limestone coarse aggregate, although all but one of the 12 mixtures passed the test with a cumulative 56-day mass loss below 0.1 lb/ft2. For concrete with granite coarse aggregate, the mass loss increased slightly with increased TI water content when portland iv cement was used as the only cementitious material. When a 30% weight replacement of portland cement with slag cement was used, the mass loss increased for a TI water content above 12.5% (corresponding to 9.9% IC water from LWA), but remained below the failure limit, suggesting no benefits for a TI water content above 12.5% by the weight of cementitious materials. The mixtures with portland cement as the only cementitious material had lower mass losses than the mixtures with a 30% weight replacement of portland cement with slag cement for the same coarse aggregate. Pre-wetted fine lightweight aggregate (LWA) for internal curing (IC) should equal 7 to 8% by weight of cementitious materials. The results provide no evidence that it would be advantageous to stray much above these values and demonstrate that high TI/ IC water contents can be deleterious.