Control of Conversion Reaction in High Alumina Cement by Adding Different Additives

This paper makes an attempt in experimental investigation for assessing the material characteristics and long-term performance of high alumina cement concrete construction at elevated temperature. High Alumina Cement (HAC), sometimes known as calcium aluminate cement (CAC) or aluminous cement) is composed of calcium aluminates, unlike Portland cement which is composed of calcium silicates. It is manufactured from limestone or chalk and bauxite. In unshaped refractories, High- alumina cements (HACs) are the main binder and are currently most used in industries. In the first generation of unshaped refractory, the HACs were the one and only binding agent used. High Alumina Cement (HAC) concrete is a high strength, sulphur resistance, fire resistant concrete used as a good refractory material. High strength in High Alumina Cement concrete is achievable under temperature control i. e, at low temperature (at 18?20 C) as per IS- 6452 and IS-4031. The use of HAC has its advantages in situations under low temperature for gain of early strength. However, HAC as a construction material has its inherent draw back due to its chemical conversion characteristics. HAC concrete when cured above 250 C results in loss of strength due to conversion reaction. The present investigation aims at studying the effect of mixing ?conversion-preventing additive materials used in High alumina cement to control the exothermic reaction like Fly Ash, OPC, Crusher Dust, Rice Husk, Coconut Shell, Urea, Silica Zel, Tri-calcium Orthophosphate and Sodium Hexa-meta Phosphate etc. at 380 C of casting temperature to find the compressive strength of HAC for M40 grade concrete. The conversion reaction in high alumina cement/concrete samples is examined by X-Ray Diffraction. The setting time of high alumina cement (HAC) may be considerably influenced by addition of small quantities with gradually variation of 1%, 2%, 3% and 4% each of Fly Ash, OPC, Crusher Dust, Rice Husk, and Coconut Shell by weight of HAC in combined manner. The addition of above ingredients causes to decrease conversion reaction with water which has been studied. The use of temperatures more than 25?C during the hydration of high alumina cement in concrete leads to the formation of the cubic hydrate C3AH6. Hence, to avoid the conversion reaction in High Alumina Cement that results in formation of chemical compounds like CAH10 and C3AH6, different additives have been used to control the exothermic reaction inside the concrete mass. Concretes made with neat HAC have shown much reduced strength at 38?C after only three to four days, due to well known 'conversion' reactions. The hydration chemistry of blends of cement found and several mineral and chemical admixtures have been studied by using x-ray diffraction. The conclusion is that although the process is thermodynamically favoured by increasing temperatures of hydration, kinetically it is governed by the availability of free (liquid) water within the cement microstructure. High strength can be achieved in high alumina cement (HAC) through the incorporation of Fly Ash, OPC, Crusher Dust, Rice Husk and Coconut Shell additions.