The characterisation of compressed earth blocks stabilised with cement and agro-industrial residues

[摘要] ENGLISH ABSTRACT: The construction industry is renowned for its detrimental impact on the environment due tothe significant resource and energy consumption, as well as the large volumes of carbon dioxide emissions. The increased awareness raised for the conservation of the environment led to the introduction of the sustainable development concept.The South African government aims to address the national housing deficit of 2.3 million units through the development of sustainable human settlements and in addition, reduce the carbon emissions through the implementation of a carbon tax. A building material capable of sustaining thermal comfort within a structure will contribute towards a reduction in the total volume of energy consumed throughout a building's life cycle and the sustainable development of theconstruction industry. This creates the need for the development of an alternative building material with minimal environmental impact and an excellent thermal performance, compared to conventional masonry units.The compressed stabilised earth block was selected as a viable alternative, however its use is hindered by the paucity of knowledge and specifications pertaining to these masonry units. This study investigates specific properties ofcompressed stabilised earth blocks with the intention ofmaking an earnest contribution towards the development of this building material and contribute to the further development of technical specifications, which also forms the main objective of this investigation.The stabilising materials added to the soil mixtures used to produce these masonry units were varied in both quantity and type to investigate the influence thereof on the properties measured.These properties include the compressive strength, Young's modulus, fracture energy, tensile splitting strength, material density, porosity, thermal conductivity, water absorption and drying shrinkage.Some of the compressed stabilised earth blocks had a compressive strength in excess of the minimumrecommended by SANS 10249. The Young's modulus values, fracture energies and tensile splitting strengths measured for the various compressed stabilised earth blocks were relativelylow compared to conventional masonry units, while noteworthy thermal conductivity values were obtained. These masonry units exhibited undesirable water absorption and shrinkage, which should be accounted for when using compressed stabilised earth blocks for the constructionof sustainable human settlements in South Africa. The stabiliser content and type, along with the particle packing arrangement of each soil mixture within the block press chamber, had the most significant effect on the measured properties of compressed stabilised earth blocks.The secondary objective of this investigation is to assess the potential of South African sugar cane bagasse ash, a residue produced during the processing of sugar canes, as a supplementary cementitious material. This was done by determining the strength activity index of mortarcubes of which a portion of the cement was partially replaced by unprocessed sugar cane bagasse ash. Based on results obtained, unprocessed sugar cane bagasse ash, as obtained from South African sugar mills, may not be classified as a supplementary cementitious material. The effectof additional processing of the ash on its strength activity index was investigated by grinding the ash using a swing mill. This showed promising results and therefore additional processing methods by which the pozzolanic reactivity of sugar cane bagasse ash can be enhanced, shouldbe investigated and standardised.The properties of compressed stabilised earth blocks in which the cement was partially replaced by unprocessed sugar cane bagasse ash, was compared to an equivalent block in which the cement was partially replaced by fly ash. The fly ash blocks had enhanced properties compared to that of sugar cane bagasse ash blocks, which correlated to the reduced pozzolanic reactivity of sugar cane bagasse ash. The properties of both these types of compressed stabilised earth blocks were found to be comparable to that of compressed stabilised earth blocks manufactured from soil mixture stabilised solely with cement.The knowledge gained throughout this investigation justifies the classification of compressed stabilised earth blocks as a potential building material for the development of sustainable human settlements in South Africa. However, the application of these masonry units within the South African construction industry should be supported by extensive and focussed investigative studies.

[发布机构] Stellenbosch University