Compressive strength of extruded unfired clay masonry units

Interest in traditional unfired clay building materials has grown in the UK in recent years. Although the use of traditional vernacular techniques, such as cob, adobe and rammed earth, have raised the profile of earthen architecture, wider impact on modern construction is likely to come from modern innovations such as extruded unfired masonry units. A large driver behind the move to unfired clay masonry is the significant reduction in embodied energy when compared with fired bricks and concrete blockwork, and the passive environmental control provided by clay. This paper summarises the results of extensive testing on commercial mass-produced extruded unfired clay bricks. The focus of this study was to investigate the properties affecting the compressive strength of these building products. Both theoretical models and test results demonstrate that the clay content plays a large role in defining the compressive strength of these materials. The reduction in strength with increases in moisture content are similar for different material sources and these strength reductions are unlikely to cause problems under normal operating conditions, even at relative humidity levels up to 95%.