Use of metakaolin with stabilised extruded earth masonry units

• Small scale extruded bricks were manufactured under laboratory conditions.
• Bricks were tested in compression following dry and wet conditioning.
• Suitable compressive strengths with lime and metakaolin addition were achieved.
• Different stabilisation mechanisms with metakaolin, cement or lime and the soil exist.
• Interaction of the clay minerals varies but is key to strength development.

Modern earth masonry increasingly utilises conventional methods of extruded fired brick production for the manufacture of unfired earth bricks. However, these bricks are not generally recommended for structural applications due to their loss of strength under elevated moisture contents. Disproportionate collapse could occur following accidental or intentional wetting of a 100 mm thick load bearing unfired earth wall. Unfired clay bricks can be chemically stabilised, typically by the addition of cement or lime to improve wet strength. However, the use of such binders has been shown to be ineffective for silt and clay rich soils used for extruded bricks.The research presented in this paper demonstrates the change in compressive strength that can be achieved through the addition of metakaolin to cement and lime stabilised extruded earth masonry. Small-scale bricks were manufactured and tested in compression in both ambient environmental conditions and following a minimum of 16 h of full submersion in water. Though the addition of metakaolin did not universally improve performance. This research presents a feasible solution using 5% lime and 10% metakaolin, that would allow unfired extruded earth masonry units to be used for structural applications.