Mechanical behaviour of high metakaolin lightweight aggregate concrete

The work described in this paper forms part of a much larger investigation of the behaviour of a new developed type of lightweight aggregate concrete which would be suitable for use as load bearing concrete masonry units. The experimental work investigated the effect of high metakaolin (MK) content on the mechanical behaviour of newly modified lightweight aggregate concrete. 15% metakaolin and waste glass were used as a partial replacement for both ordinary Portland cement and natural sand. A medium grade expanded clay type Techni Clay was used as a coarse aggregate in the concrete mixes. Equal amounts of waste glass with particles sizes of 0.5-1 and 1-2 mm were used throughout this study. Unit weight, compressive and splitting tensile strengths were measured at various ages in accordance with the relevant British/EN standards. Fresh concrete properties were observed to justify the workability aspect. An assessment was carried out to indentify the pozzolanic activity of metakaolin material. The tests results were compared with the obtained results of controlled and lower metakaolin contents concretes which were previously studied. The tests results showed that metakaolin material had an explicit role in improving the strength and unit weight of modified lightweight concrete mixes. Compressive and splitting tensile strengths increase with an increase in the metakaolin content, while a counteractive behaviour was recorded for the unit weight aspect. The metakaolin material showed higher pozzolanic activity which was overcame there duction of compressive strength due to the negative effect of glass aggregate. However, the workability of concrete mixes degraded at higher metakaolin inclusion. © 2011 WIT Press.