Chloride Diffusion in High-Performance Lightweight Aggregate Concrete


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Title: Chloride Diffusion in High-Performance Lightweight Aggregate Concrete

Author(s): M.D.A. Thomas

Publication: Special Publication

Volume: 234


Appears on pages(s): 797-812

Keywords: chlorides; diffusion; expanded slate; lightweight aggregate; permeability; service life prediction

Date: 3/22/2006

This paper reports the results of a study on the resistance of lightweight aggregate concrete to the penetration of chloride ions. Concrete specimens were fabricated with a blended silica fume cement at a water-cementitious materials ratio of W/CM = 0.40 or 0.30 and with combinations of aggregate as follows: (i) limestone coarse aggregate and river sand, (ii) expanded slate coarse aggregate and river sand, or (iii) expanded slate coarse and fine aggregate. A further series of mixes was made using the latter combination of aggregates with the blended cement being partially replaced with 25, 40 or 56% fly ash. Concrete specimens were subjected to a series of tests including “rapid chloride permeability” (ASTM C 1202), and non-steady-state diffusion (bulk diffusion test). Tests were conducted at 28 and 56 days, and 1 and 3 years. The results up to one year clearly show the benefits of incorporating expanded slate in the concrete, with permeability and diffusion coefficients being reduced significantly. The improvements attributed to the presence of the lightweight aggregate appeared to increase with the maturity of the concrete and, after 3 years continuous curing, the reduction in the apparent chloride diffusion coefficient was observed to be as much as 70%. As expected, the addition of fly ash produced further reductions in permeability and diffusion. The data developed in this study were used as input parameters for service life predictions. Although, there are insufficient data to allow firm conclusions to be drawn from these analyses, it is clear that the incorporation of lightweight aggregate will lead to a significant extension of the service of life.