Performance of high-volume fly ash concrete in marine environment

This paper presents the durability performance of concrete incorporating high-volumes of fly ash exposed to a harsh marine environment for 19 to 24 years. Concrete specimens (305 x 305 x 915 mm [1 x 1 x 3 ft.]) were cast using W/CM in the range of 0.31 to 0.46, various types of fly ash with replacement levels of 56 or 58%, and various types of normal density and lightweight aggregates. Surface erosion/scaling was seen on all specimens; the extent of erosion was slightly worse for fly ash concrete with normal density aggregate compared to the controls (without fly ash), but fly ash concrete with two of the three lightweight aggregates exhibited severe surface erosion. Laboratory testing included taking cores from each block and determining the existing chloride profile, compressive strength and "chloride permeability" (ASTM C1202). The depth of chloride penetration was found to be in excess of 100-mm (4 in.) for the concrete specimens without fly ash, whereas the presence of fly ash significantly decreased the depth of penetration to approximately 30 and 40 mm in specimens containing either normal density or lightweight aggregate, respectively. The increased penetration in the concrete with lightweight aggregates is attributed to the surface erosion observed with these concretes. The results from the chloride permeability testing also indicate significant increases in the resistance to chloride-ion penetration for fly ash concrete.