Acacia Karroo as Potential Admixture for Hot African Weather

Abstract

Africa needs a new approach for the use of admixtures that provide specific modification properties to concrete in addition to being compatible with African climatic conditions. For example, when concrete is mixed at elevated temperatures, there is quick loss of workability due to high evaporation of mixing water and the tendency is to add more water to the mix. Thus, there is need to develop admixtures that are natural (do not have to undergo derivation processes), readily available, cheap and environmentally-friendly. Gum Arabic (GA) is a sticky natural fluid which oozes from the Acacia tree when an insertion is made and contains natural resin which has arabin. GA comes from two species of Acacia tree, i.e. Acacia Senegal and Acacia Seyal. Gum Acacia Karroo (GAK) which is readily available in these hot areas was used as an admixture for mortar and concrete. GAK comes from Acacia Karroo Haynes which grows mainly in the Southern countries of Africa (Zimbabwe, Mozambique, Zambia and Angola) while Gum Arabic from Acacia Senegal or Seyal comes from countries in Northern Africa (Sudan, Chad, Nigeria). Preliminary results showed that mixes containing GAK have improved compressive strengths and chloride penetration resistance compared to the mixes without GAK, when temperature was increased from 23 °C to 40 °C at the age of 56 days. This suggests that GAK can be used at high temperatures as an admixture to improve these properties of concrete.