Properties of unfired, illitic-clay bricks for sustainable construction

Illitic clays are used for brickmaking worldwide. This paper explores the feasibility of using these clays unfired, to lower the environmental impact of construction. The results suggest that illitic clay can be used unfired. The geotechnical parameters of the clay are within the limits considered suitable for earth construction, and the compressive and flexural strengths fall within recommended limits in earth standards. Masonry constructed with the unfired illitic brick, bound with a standard hydraulic-lime mortar would reach a 28-day strength of 2.45 N/mm2 which meets structural requirements in some European masonry standards.

Stabilization improved durability but lowered strength and vapour permeability, and did not significantly change thermal properties. The results suggest that both the quantity and composition of the clay fraction in an earth material determine the success of stabilization. The strength reduction caused by lime stabilization is mainly attributed to the adsorption of the Ca2+ by the illite, which prevents free Ca2+ from taking part in the pozzolanic reaction that builds up strength. The extremely high specific surface area of the illitic clay particles (24 m2/g) enhanced lime adsorption consequently damaging pozzolanic reaction and strength development.

If half of an annual production of 15 million brick was unfired, producers would economise over 4 million euros in kiln fuel and carbon tax in 10 years, and would approximately half their carbon emissions, lowering massively the global environmental impact of brick production.