Green plants’ extracts’ potential as concrete admixtures

Abstract

In Kenya, the rate of construction of building structures for homes falls short of what is required to meet the demand. High cost of buildings is a major contributing factor to this unfortunate condition. Cost of building materials significantly influences the overall cost of the structure. Today, concrete is the most widely used construction material and most modern buildings would have some structural elements made of concrete. This research investigated the feasibility of developing a concrete admixture from green plants biomass of a locally growing plant that could be cheaper than the available alternative. In the years 2010/2011, Kenya had over 90,000 hectares of industrial forest plantations composed of mainly Cypress, Pines and Eucalyptus (Kenya Forest Service 2012). These plants were selected for study on account of their guaranteed availability. Waste products are the bark and saw dust during conversion process, at saw mills and shavings in the wood products workshops. These wastes can be the raw materials for concrete admixtures. For each plant, both the bark and wood were subjected to extraction process. The extraction was effected by the use of tap water, heat (121oC), and pressure (0.1 N/mm2). The liquor so obtained, without further processing, was used as a concrete admixture at varying dosage levels. These dosages were expressed as mass percentages of the cement content. The dosages were incrementally varied from 0.0% (control) to 47.5% for the bark extract. For the wood extracts, the dosages were 10%, 20% and 40%. For each concrete mix, the mass of the mixing water was reduced by a mass equal to the mass of the dosage of the plant extract. At the upper dosage limit of 47.5%, the mixing water had been completely substituted with the plant extract, taking into account the water absorption of the aggregates. The strength tests were carried out at 3, 7, 28, and 61 days. The casting of concrete for strength tests was done at a constant workability of 45 mm slump; with a tolerance of 5 mm. Use of the admixtures resulted in compressive strength improvement of 10%, 17%, and 10% for cypress, pine and eucalyptus, respectively. Hence, from strength consideration, pine extract was found to be the most effective. Estimated saving in cement content, when pine extract was used, was 9.84%. Cement accounts for 70% of the concrete materials cost. Therefore, concrete materials cost saving was about 7%. Mixes for workability testing were done at a constant water/cement ratio of 0.61. Slump test was used for the assessment of the workability. Workability improved from 45mm (control) to 155mm, 160 mm, and 165 mm slump for cypress, pine and eucalyptus, respectively. Therefore, from workability assessment, eucalyptus extract, was the most effective.