Multi-sized fillers to improve strength and flowability of concrete

Abstract

Concrete with a low carbon dioxide footprint (LCDF) contains less cementitious materials (CM) than ordinary concrete and hence less cementitious paste. Besides the reduced carbon dioxide footprint, LCDF concrete offers other advantages such as reduced cost as well as improved dimensional stability due to reduced hydration heat, creep and shrinkage. Nevertheless, decreasing the quantity of CM has a negative impact on concrete workability. To restore workability, multi-sized fillers are advocated to replace aggregates and CM. Generally, fillers can improve the packing density of concrete due to the filling effect and thus more excess water or paste is available to facilitate spread and flow rate. Two types of fillers were examined in this study – limestone with particles smaller than 75 μm and foundry sand with particles of 75–400 μm. The particles of these two fillers are respectively similar and larger in size when compared with cement. Concrete mixes with no fillers and with mono- or multi-sized fillers were prepared and tested for flowability and strength. The results indicate that more superplasticiser is needed to achieve the same flowability when fillers are added. It was also found that, at the same water/CM ratio, fillers can improve concrete strength, and the use of multi-sized fillers can simultaneously improve the flowability and segregation resistance of concrete.