Microstructure of pre-wetted aggregate on lightweight concrete

A study was made on microstructure and water absorption rate of ‘Litcon’—a porous lightweight aggregate made from expanded clay. EDAX analysis on the aggregate particle showed different chemical compositions between the shell and the inner core of the lightweight aggregate. S.E.M. examination on the resulting concrete showed a good mechanical bonding between the cement and the aggregate interface, though traces of inter-granular cracks were observed. When the pre-wetting time of the aggregate increased, the strength and the workability of the concrete increased too. The high workability of fresh concrete was attributed to the localised high water content at the surface of the pre-wetted aggregate. The surface pores of the aggregate shell absorbed the water built-up at the cement/aggregate transition phase thus resulting with lower water content at the transition zone. EDAX analysis confirmed migration of cement phase into the aggregate shell. This loss of fluidity at the transition zone may have a significant effect on the permeability of lightweight concrete.