A trade-off concept for lightweight concrete in chloride environments

The aim of this study was to investigate the influence of supplementary cementing materials (SCM’s) on the initial surface absorption (ISA), sorptivity and chloride penetrability to ASTM C1202 and NT Build 492 of lightweight aggregate based concretes (LWAC), and to compare these properties to those of normal-weight aggregate based concretes (NWAC). The lightweight aggregate (LWA) was Lytag, a fly ash based aggregate, which was pelletised during manufacture. Three normal-weight aggregates (NWA) were investigated, including, natural river gravel, jurassic oolitic limestone and crushed dolomitic limestone. The SCM’s used were fly ash (FA), ground granulated blastfurnace slag (GGBS), limestone (LS), silica fume (SF), and metakaolin (MK). CEM I replacement was undertaken on a percentage mass basis. Experimental work focused on concrete mixes with a fixed water/binder ratio of 0.50 and a constant total binder content of 330kg/m3. 28-day results indicate that with respect to aggregate influence, for CEM I only concrete, reduced concrete performance is obtained when replacing normal-weight aggregate with lightweight on a like-for-like basis. These negative effects can be reduced however, by good cement addition specification, as was found in the majority of the concretes in this study. These benefits include, to varying degrees, enhanced compressive strength, and increased resistance to water permeation and chloride ion penetration. A trade-off between aggregate type and binder combination is therefore desirable, to enable enhanced concrete chloride ion resistance.