Role of cement content in specifications for concrete durability: cement type influences

摘要

In this paper, which describes part of a major investigation, the role of cement content in specifications for concrete durability is examined. The main cements considered were (a) Portland cement (PC; CEM Ⅰ), (b) PC/30% PFA (CEM Ⅱ/B-V) and (c) PC/50% GGBS (CEM Ⅲ/A), while other BS EN 197-1 cements were tested selectively. Concretes of fixed w/c ratio (w/(PC + addition) ratio), but with cement contents varying around the minimum values given in standards were evaluated. The workability of concrete with low cement and water contents was controlled with a superplasticiser and the fines content was maintained by the use of ground limestone as a filler. Tests were carried out to examine these effects on the fresh, engineering, permeation and durability properties of concrete. The results show that at fixed w/c ratio, reduction in cement content by up to 22% had no adverse effect on most concrete properties and, if anything, gave some improvement. The various cement types and combinations tested had little effect on the trends observed. Overall, it was concluded that, in addition to minimum strength class and maximum w/c ratio (and in some cases cover depth), specifying minimum cement content for concrete durability was not necessary.