Effectiveness of Partial Replacement of Wood Ash in Concrete Production Using Pebbles as Coarse Aggregates

Abstract

The construction sector is a major user of cement; with cement production requiring significant quantity of raw materials, energy and processes resulting in the release of large amounts of carbon dioxide (CO2) into the atmosphere. To address this concern, much research have been targeted at reducing the use of cement in concrete production. Wood ash (WA), a by-product of wood combustion locally available as waste from industrial and household sources has been identified as an alternative material to partially replacement cement in concrete production. This study investigates the utilization of wood ash as partial replacement for cement in concrete made with pebbles, using varying wood ash percentages of 5, 10, 15, and 20%. The primary objective is to assess the impact of this partial cement replacement on the strength properties of concrete. WA was obtained by controlled burning of African Birch tree logs in a Honey Trust bread bakery oven at a temperature of 2500C, and the pebbles from Bida town, Niger state, Nigeria. A water-cement ratio of 0.58 and a mix design ratio of 1:2.1:4.1. was used for the study. The mean strength of concrete with 0, 5, 10, 15, and 20% WA are 23.1N/mm2, 17.2N/mm2, 13.6N/mm2, 8.0N/mm2, and 7.6N/mm2 respectively. 20% replacement of cement has the lowest mean strength at 28 days. Partial replacement at 5, 10% are within specifications of 10N/mm2 for plain concrete while 15 and 20% are not suitable for structural concrete. The strength characteristics data obtained were used to develop empirical model equations relating the strength properties with the aid of regression analysis tool in Microsoft Excel. The empirical models developed relating the flexural (fbl = 0.3216√fcu) and splitting tensile (fst = 0.1056√fcu) strengths of concrete with the compressive strength recorded R2 values of 0.99 and 0.818, P-values of 3.53 × 10−4 and 3.50 × 10−2, and standard errors of 0.129 and 0.109 respectively. The study provides valuable insights into the feasibility of using WA as sustainable alternatives to cement in concrete production using pebbles. These findings are of great potential for the construction industry, offering a path towards greener construction practices while simultaneously reducing the environmental impact of WA disposal.