Effect of porous lightweight aggregate on strength of concrete

The microstructure of interfacial zone (IZ) of one kind of lightweight aggregate concrete was studied using Scanning Electron Microscope (SEM) equipped with an energy dispersive X-ray analysis system, as well as through back-scattered electron imaging (BSEI). This paper examined the topography of the IZ and the characteristic of the surface pores of the lightweight aggregate concrete. We demonstrate that the 'Wall Effect' does not exist on surface of the porous lightweight aggregate, resulting in a better bond than the normal concrete. A thin porous ettringite layer of 5 - 10 mum was found at the IZ of LWC. The formation of IZ of LWC was partly due to the lack of wall effect at the IZ and partly due to the interlocking of the cement paste onto the rough surface pores of the lightweight aggregate. However, it was likely that the large pore size of the ettringite network (0.3 to 1 mum) at the 1Z of the lightweight concrete (LWC) weakens the strength of concrete. (C) 2003 Elsevier B.V. All rights reserved.