EFFECT OF LOCAL METAKAOLIN ON PROPERTIES OF CONCRETE AND ITS SULPHURIC ACID RESISTANCE

Abstract

Recently, there is an energy crisis in Egypt. The Portland cement industry is a highly energy intensive process requiring about 112 k.w of energy-per ton of finished product. Therefore, the efforts should be made to find alternatives for Cement. Supplementary cementing materials (SCM) play an important role in the production of high strength and high performance concrete. In recent years worldwide, metakaolin (MK) has been studied because of its high pozzolanic properties. MK is obtained by the calcination of kaolinite. The raw material input in the manufacture of MK is kaolin. Although Egypt have a large reserve of kaolin however, MK is not widely produced and used due to the lack of adequate experiments. Therefore in these study local kaolins was thermally treated at specified conditions at 750˚C for three hours to produce what so-called MK material. This study investigates the influence of using two types of local metakaolin as supplementary cementing material on properties, strength and durability of concrete and compared with the performance of ordinary (control) and silica fume. The experimental study was carried out in two stages. The first stage consists of 14 concrete mixes from the two obtained types of metakaolin, MKA and MKB and in addition to silica fume (SF) with various percentage (8%, 12%, 15% and 20%) as partial replacement by cement weight to study fresh properties of concrete in terms of unit weight, compacting factor and slump (Superplasticizer Dosage), as well as the hardened properties in terms of compressive strength, water absorption and Porosity. The second stage in this research, investigated the effect of two metakaolins and comparing with silica fume as well as type of cement on concrete resistance to 3% sulphuric acid attack by measuring the percentage of mass loss and percentage reduction in compressive strength after 30, 60 and 90 days of acids immersion. Results show that similar to silica fume, Egyptian metakaolin can be considered as an effective pozzolanic mineral admixture where, metakaolin replacement of cement is effective in improving the fresh and mechanical properties of concrete. The optimum dosage of metakaolin, as a partial cement replacement is 15 to 20% for the used fineness in this study at W/Cm ratio 0.4. It achieves an increase in compressive strength by 25% as compared to control ones, as well as it has the lowest water absorption. A beneficial effect was found by incorporating combination of two admixtures 20% silica fume with 15% metakaolin on concrete sulphuric acid resistance.