Characterisation and Evaluations of the Mechanical Properties of Alternative Masonry Units

[摘要] ENGLISH ABSTRACT: One of the greatest challenges facing the South African government is the provision of adequateand affordable housing to the 1.1 million families still living in informal settlements. Currently,the most widely used method of constructing low income housing (LIH) in South Africa isthrough the use of cement based masonry units. However, it is well known that concrete andcement have a significant negative impact on the environment due to carbon dioxide emissionsfrom the production of cement clinker, as well as the consumption of natural resources. In orderto reduce the environmental impacts, alternative masonry units (AMUs) are required that arestructurally viable, environmentally friendly and socially acceptable.To properly begin implementing AMUs in practice the evaluation and characterisation of theirmechanical properties are necessary. While standardised tests for conventional masonry unitsare widely available, it is unclear whether these tests are suitable for use on AMUs due to thelarge differences in the material properties between certain AMUs and conventional masonryunits. Few standards exist that have been designed with AMUs in mind.This study investigates whether the standards and guidelines available for conventional masonryunits can be applied to AMUs. Three different AMUs are compared with a conventional concretemasonry unit (CMU) in a variety of tests to determine if the applicable standards are successfulat classifying the mechanical properties of the AMUs. The AMUs that were chosen for thisinvestigation are: alkali-activated concrete blocks (AACBs), compressed stabilised earth blocks(CSEBs) and adobe blocks. These materials were chosen so that the mechanical properties ofeach material varied notably from each other and from the CMU.The AMUs and the benchmark CMU were tested for a large variety of mechanical properties.Not only can the results from these tests be used to determine if the standards and guidelinesare applicable to both conventional and alternative masonry units, but the data acquired fromthe investigation can be used in future numerical modelling.The standardised tests and mechanical properties investigated in this study include the following:• Compressive strength of the masonry units at 7, 14, 28, 56 and 91 days. Including bothbedface and headface tests at 28 days.• Modulus of elasticity and Poisson's ratio tests conducted on masonry cylinders.• Wedge splitting tests to determine the fracture energy of the materials.• Constant mass density tests.• Triplet tests to determine the shear behaviour at the interface of the masonry samples.Including both initial shear strength and internal angle of friction.• Compressive strength tests on small scale masonry wallets to determine both the compressivestrength and modulus of elasticity.The outcomes of the study showed that the AACBs and CSEBs satisfy the minimum strengthrequirements for LIH in South Africa, while the adobe blocks were too weak. The weak adobemasonry units caused the most complications during the test procedures, nevertheless, the investigationfound that with small adjustments to the standards, particularly the loading procedures,the tests could be successfully completed on the AMUs. Issues were however, encountered withthe tests for Poisson's ratio. The tests also provided a large variety of mechanical propertiesfor both conventional and alternative masonry units which can be used in future studies for thenumerical modelling of masonry for low income housing in South Africa. The knowledge gainedin this study can therefore be used to begin laying the framework for the minimum technicalspecifications for AMUs in South Africa.

[发布机构] Stellenbosch University