Alternative stabilised rammed earth materials incorporating recycled waste and industrial by-products: A study of mechanical properties, flexure and bond strength

Abstract

Developing low-embodied energy building materials can significantly contribute to reducing global greenhouse gas emissions. However, these new building materials must be properly understood before they can or will be adopted by the construction industry. Rammed earth materials with low greenhouse gas emissions have been developed based on the principles of alkali-activated stabilisation as replacements for conventional construction materials.In previous work by the authors, the strength development, durability and sustainability, via life cycle assessment, of these new materials have already been studied. However, how these materials interact with and affect embedded reinforcement is poorly understood, as are methods to test these properties. Their applicability in modern construction is therefore currently limited. This paper extends the understanding of these materials through flexural and push-out testing of specimens reinforced with steel and glass-fibre reinforced polymer bars. We determine mechanical properties of the alternatively-stabilised rammed earth materials and study the composite behaviour of the reinforced materials. The suitability of current testing standards for elastic modulus, Poisson’s ratio, and indirect tensile, bond, shear and flexural strengths, originally designed for concrete specimens, were evaluated for RE materials. These were compared with design rules and predictions made using concrete standard AS 3600 and rammed earth standards (NZS 4297-4299), handbook (HB 195) and rammed earth and concrete literature.Results showed that existing testing procedures specified for concrete specimens were appropriate for estimating Poisson’s ratio and shear modulus as well as for determining flexural and shear strengths for rammed earth. Existing rammed earth recommendations given in NZS 4297 for estimating elastic modulus should continue to be followed. An alternative compressive reinforcement bond test, similar to RILEM AAC 8.2 push-out standard for autoclaved aerated concrete, was proposed; however, more work is required to establish a better prediction model for bond strength. Results indicated that current expressions to relate indirect tensile to unconfined compressive strength are suitable for compressive strengths up to 20 MPa.