Impact of the partial substitution of cement and sand by ash from several types of wood species in cementitious materials manufacture: valorization in the industrial field

Abstract

The main objective of this article is to evaluate the potential use of wood ash as a substitute for cement and sand in mortars. Three types of wood were selected: Ayous, Sapelli and Fraké, all of which were sourced from carpentry in Cameroon. The sawdust was dried and combusted to obtain ash, then ground and sieved. Six types of mortar were produced, with cement substitution at 0%, 5%, 10%, 15%, 20% and 25%. The physico-mechanical properties of these substitutions were determined after 7, 28 and 56 days. The results of the cement paste consistency show that it increases with the addition of ash, due to the fact that sawdust ash requires a large quantity of water. The addition of ash caused an increase in setting time due to the fact that sawdust ash is less reactive than Ordinary Portland cement, resulting in a delay in the rate of cement hydration. Apparent density values decreased with the addition of sawdust ash, probably due to the hygroscopic behavior of type of ash in mortar specimens. The highest pozzolanic index is that of 5% replacement by ash and almost identical absorption for all mortars at this substitution percentage. Acid attack results revealed a higher durability of mortar specimens with the higher percentage of ash substitution. Optimum compressive strengths for the different substitution percentages were observed at 5%, 15% and 10% respectively for Ayous, Sapelli and Fraké. The best wood ash is Sapelli because of its chemical composition and resistance to compression in mortars. At 56 days, compressive strength values exceed those of the reference composition. This may be due to pozzolanic reactions in the mortars of ash.