Utilisation of waste material in geopolymeric concrete

Fly ash (FA), silica fume (SF) and rice husks are hazardous waste materials that have no use and in the past have been
landfilled. However, landfilling is becoming expensive and causes contamination to soil and ground water. Utilisation of
waste material in concrete is also very effective in overcoming the problems caused by the production of cement; namely
the emission of carbon dioxide and degradation of the environment due to the quarrying of raw materials (limestone and
clay) for the production of cement. This research studywas based on the complete elimination of ordinary Portland cement
(OPC) from concrete that can achieve 28 days target cube strength in the range of 40--50 MPa with the emphasis on the
curing techniques applicable for in situ construction; namely ambient and external exposure curing. Fly ash was utilised as
a base sourcematerial and silica fume and microwave-incinerated rice husk ash (MIRHA)were used as replacements for the
fly ash by 3, 5 and 7%. Alkaline activators, namely sodium hydroxide and sodium silicate solution were used as activators
of silica and aluminium in the source material and sugar was incorporated in the mix to increase the hardening time of the
concrete. Compressive strength, flexural strength and scanning electron microscopy (SEM) tests were conducted on the
specimens and the results showed that at 3, 7, 28, 56 and 90 days the fly ash along with silica fume, MIRHA and alkaline
activators could be a good replacement of cement. The compressive strength of external exposure curing for the
geopolymeric concrete reached up to 48.7 MPa at 28 days and this concrete had awell developedmicrostructure shown by
= SEM analysis. The flexural strength showed values which were comparable with OPC concrete.