Investigating the Physical, Mechanical and Durability Properties of Concrete having Cement Partially Replaced with Rice Straw and Egg Shell Ashes

Abstract

Provision of adequate housing has become a challenge especially in developing countries. This has been occasioned by both high cost of building materials such as cement and low incomes of the populations. At the same time cement production has adverse effects to the environment. This has necessitated research into alternative supplementary materials that are abundant and renewable in nature that can be used to partially substitute cement in concrete thereby reducing the cost of construction making construction of housing affordable. Similarly by reducing cement consumption the adverse effect of cement production to the environment will be mitigated. Incorporating egg shells and rice straw ashes will mitigate their disposal problem. This research presents the properties of concrete made with cement partially replaced with rice straw ash and egg shell ash. Rice straw and egg shells were first incinerated, sieved and ground. The physical and chemical properties of the resultant ashes as well as other materials incorporated in the concrete mixes were also determined. A concrete mix with a compressive strength of 35 N/mm2 and a water cement/ ratio of 0.5 was designed to British Research Establishment method. The control was the concrete neat cement. Cement in concrete mix was partially replaced with rice straw ash at 5, 10, 15, 20, 25 & 30%. Compressive and splitting tensile strength of the concrete with cement partially replaced as indicated above was determined at 7, 14, 28, 56 and 90 days of curing age. Durability, resistance to acid attack as well as fresh properties of the concrete were also determined. An increase in compressive strength was observed for concrete with 5% & 10% partial replacement of cement with rice straw ash. The 7, 14, 28, 56 and 90 day strengths were found to be 32.7, 36.7, 38.8, 40.3, 41.3 N/mm2 and 33.7, 37.1, 40.2, 41.8, and 42.7 N/mm2, respectively. The control was found to have compressive strength of 27.9, 33.0, 35.9, 36.6 and 38.7 N/mm2 for 7,14,28,56 & 90 days of testing. When egg shell ash was added at 10% by weight of cement to concrete mixes made with cement partially replaced with rice straw ash at 15% and 20%, the 28, 56 & 90 days compressive strengths were found to increase by 25.3, 26.7 and 29.2% and 5.3, 3.26 and 3.9%, respectively. It was concluded that rice straw ash can be used to partially replace cement in concrete at an optimum of 10% by weight of cement while rice straw and egg shell ash can simultaneously be used to partially replace cement at 15% and 10% by weight of cement, respectively, in concrete and result in a concrete whose properties compare favourably with the control. These results can be applied in the construction industry to reduce the cement content hence cost of concrete material, cement being the most expensive ingredient in concrete. Authorities can also adapt this as an avenue of disposing agro-waste that is produced in bulk and poses disposal challenges. The blended concrete can be used for construct in regions where soils are acidic or to construct facilities exposed to acidic substances since they have better resistance to acid. The challenges include the scattered nature of the sources of the agro-waste, lack of a facility to incinerate, sieve and grind the agro-waste ashes and in sufficient quantities. The study findings are limited to Type 1 Ordinary Portland cement and not any other cement found in the market.