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

Malherbe, Danielle (2016-03)

Thesis (MEng)--Stellenbosch University, 2016.

Thesis

ENGLISH ABSTRACT: The construction industry is renowned for its detrimental impact on the environment due to the 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 the construction 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 of compressed stabilised earth blocks with the intention of making 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 minimum recommended by SANS 10249. The Young’s modulus values, fracture energies and tensile splitting strengths measured for the various compressed stabilised earth blocks were relatively low 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 construction of 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 mortar cubes 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 effect of 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, should be 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.

AFRIKAANSE OPSOMMING: Die konstruksiebedryf is welbekend vir die nadelige invloed wat dit op die omgewing het, weëns die beduidende hulpbron en energie volumes wat jaarliks verbruik word asook die koolstofdioksied uitlaatgasse wat in die atmosfeer vrygelaat word. Die toenemende bewustheid, rakende die bewaring van die omgewing, het gelei tot die implementering van die volhoubare ontwikkellingskonsep. Die Suid-Afrikaanse regering beoog om die nasionale behuisingstekort, van 2.3 miljoen eenhede, met die ontwikkelling van volhoubare nedersettings aan te spreek en ook die land se koolstofdioksied uitlaatgasse, deur die heffing van ’n ‘koolstof’ belasting, te verminder. ’n Boumateriaal, wat die vermoë beskik om termiese gemak binne ’n gegewe ruimte te handhaaf, kan bydra tot die vermindering van die totale volume energie wat gedurende die gebou se lewensduur verbruik word. Dit skep die behoefte vir die ontwikkelling van ’n alternatiewe boumateriaal wat ’n minder nadelige invloed op die omgewing het en ook verbeterde termiese gedrag openbaar, teenoor dié van konvensionele boustene wat tans gebruik word. Die saamgeperste gestabiliseerde grondblok is as ’n moontlike alternatief geidentifiseer, maar die gebruik daarvan word tans deur die algehele gebrek aan kennis en spesifikasies verhoed. Spesifieke eienskappe van saamgeperste gestabiliseerde grond blokke word tydens hierdie studie ondersoek, met die oog op ’n daadwerklike bydrae tot die verdere ontwikkelling van hierdie boumateriaal en die betrokke spesifikasies. Gesamentlik vorm dit die hoof doel van hierdie studie. Beide die hoeveelheid en tipe stabiliseringsmateriale wat tot die verskeie grondmengsels bygevoeg is, is gewissel om sodoende die uitkomste daarvan op die gekose eienskappe te bepaal. Die eienskappe wat ondersoek was is die druksterkte, Young’s modulus, wig-splyting kraakenergie, treksterkte, materiaal digtheid, porositeit, termiese geleiding, water absorpsie en droë krimping. Sommige van die saamgeperste gestabiliseerde grond blokke het hoër druksterktes as die minimum, wat in SANS 10249 aanbeveel word. Die Young’s modulus, wig-splyting kraakenergie en treksterkte was laag relatief tot die van konvensionele boustene, terwyl beduidende termiese gedrag deur die grondblokke getoon is. Die grondblokke het ongewenste water absorpsie en krimp gedrag getoon en moet in ag geneem word wanneer hierdie stene vir die ontwikkelling van volhoubare nedersettings in Suid-Afrika gebruik word. Die hoeveelheid en tipe stabiliseringsmateriaal tesame met die orientasie van die grondpartikels van die verskeie grondmengsels, het die mees beduidende invloed op die eienskappe van die saamgeperste gestabiliseerde grondblokke gehad. Die potensiaal van Suid-Afrikaanse suikerriet bagasse-as, ’n afvalproduk wat tydens die verwerking van suikerriete verkry word, is ook in hierdie studie ondersoek. Die potensiaal is geassesseer deur die bepaling van die aktiwiteitsindeks van mortier kubusse, waarvan ’n gedeelte van die sement met ongeprosesseerde suikerriet bagasse as vervang is. Gebasseer op die toetsresultate, kan ongeprosesseerde suikerriet bagasse as, soos verkry van Suid-Afrikaanse suikermeule, nie as ’n geskikte sement vervangingsmateriaal beskou word nie. Die invloed van addisionele prosessering op die aktiwiteitsindeks van die suikerriet bagasse as, is ondersoek deur die as fyn te maal. Belowende resultate is verkry; gevolglik moet addisionele prosessering metodes ondersoek en gestandardiseer word. Dit sal lei tot die verbetering van die aktiwiteitsindeks van suikerriet bagasse as. Die eienskappe van saamgeperste gestabiliseerde grondblokke, waarin ’n gedeelte van die sement met ongeprosesseerde suikerriet bagasse as vervang is, is met dié van ’n gelyke blok waarin ’n gedeelte van die sement met vliegas vervang is, vergelyk. Die vliegas blokke het verbeterde eienskappe getoon wat ooreengestem het met die verswakte pozzolaan reaktiwiteit van suikerriet bagasse as. Die eienskappe van beide die vliegas en suikerriet bagasse as blokke was vergelykbaar met dié van saamgeperste gestabiliseerde grond blokke vervaardig uit grondmengsels wat slegs met sement gestabiliseer is. Die kennis wat deur die loop van hierdie studie opgedoen is, regverdig die klassifisering van saamgeperste gestabiliseerde grond blokke as ’n potensiële boumateriaal wat vir die ontwikkeling van volhoubare Suid-Afrikaanse nedersettings gebruik kan word. Die gebruik van hierdie boustene in die Suid-Afrikaanse bou industrie moet egter deur ekstensiewe en gefokusde navorsing gestaaf word.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/98356
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