Thesis (MScEng)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Natural fibre reinforced concrete (NFRC) is a type of concrete that has become of particular interest in recent years, due to its potential for being used as a sustainable and economically viable building material. Natural fibres are often cheap and widely available in developing nations. Sisal is one such fibre predominantly grown in Brazil and has been identified as having the potential to be commercially cultivated in Southern Africa. The durability of sisal fibres in a cementitious environment tends to be adversely affected due to the high alkalinity of pore water and the presence of calcium hydroxide. This research dealt with the use of sisal fibre reinforced concrete (SFRC) blocks. It focused on the mechanical and volumetric properties of blocks with varying fibre and condensed silica fume content (CSF). Two different SFRC blocks were produced (solid and hollow) using an average fibre length of 10 mm. Two matrix types were used: one using a 70:30 cement:fly-ash ratio and another using a 60:30:10 cement:fly-ash:CSF ratio by weight. Samples of each matrix type were prepared with 0, 0.5 and 1% fibre content by volume. Hollow blocks were tested for compressive strength and capillary water absorption, while solid blocks were tested for compressive strength, flexural strength, capillary water absorption, dimensional stability, drying shrinkage, density, total water absorption and void content. All tests were performed on samples with an age of 28 days. Solid block compressive tests were also performed on samples with an age of 7 days. The hollow blocks had significantly lower average compression strength than the solids, but an increase in fibre content caused a slight increase in strength. For solid blocks, it was found that the addition of natural fibres decreases the strength, although a partial substitution of cement with CSF, in conjunction with fibres, did increase the strength relative to blocks without CSF. The flexure strength was also lowered somewhat by the addition of fibres, but an increase in ductility was noted, although not quantified. The addition of CSF to fibre-containing blocks led to an increase in capillary water absorption, but a decrease in absorption through immersion. This shows that the addition of CSF does significantly alter the pore system of a cementitious matrix reinforced with natural fibres. Also, the dimensional stability increased with the addition of CSF and fibres. The same can be said for drying shrinkage. Even though an increase in fibre and CSF caused samples to shrink more under drying, they were more stable under cycles of wetting and drying. It was concluded that the addition of fibres to a matrix had a detrimental effect on strength, although ductility did increase. The volumetric properties of concrete were also adversely affected by the addition of fibres, although dimensional stability was improved. The partial substitution of cement with CSF did improve many of the mechanical and volumetric properties of samples containing sisal fibre. / AFRIKAANSE OPSOMMING: Natuurlike vesel bewapende beton (NVBB) is ’n tipe beton wat onlangs heelwat belangstelling ontlok het weens die potensiaal om gebruik te word as ‘n volhoubare en ekonomiese haalbare boumateriaal. Natuurlike vesels is dikwels baie goedkoop en wyd beskikbaar in ontwikkelende lande. Sisal is een so ‘n vesel wat verkry word vanaf die blare van ’n garingboom. Die plant word hoofsaaklik in Brasilië verbou en is al uitgewys weens sy potensiaal om op kommersiële skaal in Suidelike Afrika verbou te word. Die duursaamheid van sisal vesels is geneig om nadelig geaffekteer te word in die teenwoordigheid van kalsium hidroksied en ’n hoë-alkali omgewing, soos gevind in die porie-water van beton. Hierdie navorsing handel oor die gebruik van sisal vesel bewapende beton (SVBB) boublokke. Dit fokus op die meganiese- en duursaamheids eienskappe van blokke met verkillende inhoude van vesel en gekondenseerde silika dampe (GSD). Twee verskillende SVBB blokke is geproduseer (solied en hol) deur gebruik te maak van 10 mm vesels. Twee matriks tipes is gebruik: een met ’n 70:30 sement:vliegas verhouding en een met ’n 60:30:10 sement:vliegas:GSD verhouding, volgens gewig. Blokke van elke matriks tipe is geproduseer met 0, 0.5 en 1% vesel inhoud, volgens volume. Hol blokke is getoets vir druksterkte en kapillêre water absorpsie, terwyl soliede blokke getoets is vir druksterkte, buigsterkte, kapillêre water absorpsie, dimensionele stabiliteit, krimp onder uitdroging, digtheid, totale water absorpsie en luginhoud. Alle toetse is gedoen op blokke met ’n ouderdom van 28 dae. Druktoetse is ook gedoen op soliede blokke met ’n ouderdom van 7 dae. Die hol blokke het ’n aansienlike laer gemiddelde druksterkte as die soliede blokke gehad, maar ’n toename in veselinhoud het gelei tot ’n effense verhoging in druksterkte. ’n Toename in veselinhoud van soliede blokke het gelei tot ’n afname in druksterkte, alhoewel ’n gedeeltelike vervanging van sement met GSD gelei het tot ’n hoër druksterkte vir blokke met vesels. Die buigsterkte van soliede blokke het ook afgeneem met ’n verhoging in veselinhoud. ’n Verhoging in duktiliteit is waargeneem met ’n toename in veselinhoud, alhoewel dit nie gekwantifiseer is nie. Die toevoeging van GSD tot blokke bevattende vesels het gelei tot ’n verhoging in kapillêre water absorpsie, maar ’n verlaging in totale water absorpsie. Dit kan daarop wys dat die toevoeging van GSD die poriestelsel van NVBB noemenswaardig verander. Beide die dimensionele stabiliteit en krimp onder uitdroging het toegeneem met die toevoeging van GSD en vesels tot die blokke. Dus, die toevoeging het gelei tot ’n hoër krimpvervorming tydens uitdroging en ’n hoër stabiliteit tydens nat/droog siklusse. Daar is tot die gevolgtrekking gekom dat die toevoeging van sisal vesels tot ’n beton blok oor die algemeen ’n negatiewe effek het op sterkte, alhoewel duktiliteit toeneem. Die volumetriese eienskappe van beton word ook negatief geaffekteer met die toevoeging van sisal vesels, alhoewel dimensionele stabiliteit verbeter. Die gedeeltelike vervanging van sement met GSD lei tot die verbetering van beide meganiese en volumetriese eienskappe van beton blokke wat sisal vesels bevat.