Behaviour of low density autoclaved aerated concrete masonry under concentrated loads
Autoclaved Aerated Concrete (Aircrete) (AAC) is the lightest form of concrete masonry. The material was introduced into the UK in the 1950's. It has been used extensively since that time to form block walls especially in the construction of dwellings. The current product is very different from that produced in earlier years having become progressively lighter. At the same time the ratio of the compressive strength to the density has been increased. Improvements in production techniques have made the present day material properties more consistent. Quality control criteria have become much more stringent and third party supervision has been introduced for manufacture and construction. Raw materials and process are carefully controlled to give consistent output. As Aircrete has become progressively lighter, new methods of assembly have recently been introduced which raise questions about the performance of the new material. The two principal drivers for lowering the density have been improved manufacturing economy by reduced raw material consumption and improvements in the thermal insulation properties of the material to meet today' s Energy requirements. Reducing density tends to have the effect of producing lower strengths and reducing robustness, durability and resistance to chemical attack. When undertaking the structural design of masonry walls, the stresses induced by concentrated loads can be more critical than those from the general run of uniformly distributed loads on walls. For masonry materials at the lower end of the strength range, their resistance to concentrated loads is central to their suitability for economic application in construction. The current rules and regulations regarding the ability of walls to support concentrated loads were developed on the basis of the strength and behavioural properties of masonry materials material which are stronger and denser than the lighter forms of Aircrete. In this research, the effects on the behaviour of low density Autoelaved Aerated Concrete blockwork of different forms of concentrated loading were examined using physical testing and mathematical modelling and the behaviour categorised mathematically. The research builds on an EPSRC research project at Kingston University and previous research undertaken by the author (MPhil). The results will enable structural design for concentrated loads on low density Aircrete to be undertaken with greater confidence. This will enable further economy in the use of the material and thereby further improve its economic viability. The conclusions and recommendations will influence national and European masonry structural design codes and standards used by structural engineers.