Exploring Rice Husk Ash As A Supplementary Cementitious Material And Its Impact On Building Energy Performance

Global cement production is responsible for 5-7% of anthropogenic greenhouse gases produced annually and is one of the biggest contributors to the reduction of finite natural resources. This excessive production and utilisation of cement is currently considered unsustainable due to its negative impacts on the environment, especially with regard to climate change and its resulting effects. Alternative measures have been recommended to reduce the negative impact of cement production. One of these alternatives is the use of supplementary cementitious materials (SCMs) for the partial replacement of cement in construction. Rice husks, an agricultural waste, are one of these SCMs and have been selected for this study due to the large quantities being produced in the study context and their ability to combine with hydrated cement to form compounds possessing cementing properties. In addition to rising global cement consumption and waste production, energy consumption is also rising. Building operations account for 55% of global energy consumption. As the building envelope is a major contributor to building energy performance, especially the external walls, its optimisation is therefore imperative to reduce energy consumption and carbon dioxide emissions. This research aimed to critically investigate the use of Nigerian rice husk ash as a supplementary cementitious material, its influence on the thermal properties of sandcrete blocks, and the resulting impact on building energy performance. A mix of methods, including observations, surveys (questionnaires and interviews), experimental investigation, and simulation study, were employed for this study to properly address each of the objectives set out. The results of the interviews and questionnaires served to provide evidence on the perceptions of householders and building professionals on the use of rice husk ash (RHA) and RHA blended blocks and also gather reasons for its low utilisation from building experts and researchers who have done similar studies. The environmental investigation included the production of RHA using rice husks from a major rice mill in Nigeria to justify rice husk ash as a suitable supplementary cementitious material for partial cement replacement. The production of the RHA masonry blocks followed, and tests were conducted in line with the research questions set out for this study to determine the effects of Nigerian rice husk ash on the physical and thermal properties of sandcrete blocks. Amorphous RHA was produced, which complied with the ASTM C618-19 standard for testing and utilisation of SCMs. Three variations of RHA block samples were then created for this investigation: RHA 5%, RHA 10%, and RHA 15%. For the three variations used, RHA15% recorded the best thermal performance when compared to the control sample. It recorded a U-value of 3.04 W/m2K. This was followed by the RHA10%, which recorded a U-value of 3.34 W/m2K. The average values for RHA5% did not record any significant difference in thermal properties when compared to the control sample, which had a U-value of 3.67 W/m2K. The building simulation results helped quantify the improvements to building energy performance from reuse of the rice waste using prototype buildings from the study context (a bungalow and a duplex/storey building). The largest improvement to the building fabric was recorded with the RHA15% blocks, which resulted in a 9.9% and 11.3% reduction in solar heat gains through the external walls for the bungalow and duplex/storey building, respectively. This led to a 6.55% and 4.2% reduction in cooling loads and a 4.1% and 2.8% reduction in CO2 emissions, respectively, for the bungalow and duplex/storey building. Furthermore, questionnaires and interviews revealed that participants would readily use the RHA blended blocks if they were inexpensive, strong enough for use, and blended well with other materials. The outcomes of this research will prove useful to householders, researchers, architects, and policymakers in their decision-making processes, and will be valuable in bridging the knowledge gap as well as introducing new methods that can be adopted for similar studies.