American Journal of Engineering Research (AJER) 2013 Recent Advances in Structural Engineering, RASE2013 Page 14 American Journal of Engineering Research (AJER) e-ISSN : 2320-0847 p-ISSN : 2320-0936 Volume-3 pp-14-19 www.ajer.org Research Paper Open Access Mechanical Properties of Rice Husk Ash (RHA) - High strength Concrete Deepa G Nair , K. Sivaraman, and Job Thomas Division of Civil Engineering, Cochin University of Science and Technology, Kochi, Kerala, India, PIN 682022 Abstract: - High strength and high performance concrete are being widely used all over the world. Most of the applications of high strength concrete have been found in high rise buildings, long span bridges etc. The potential of rice husk ash as a cement replacement material is well established .Earlier researches showed an improvement in mechanical properties of high strength concrete with finely ground RHA as a partial cement replacement material. A review of literature urges the need for optimizing the replacement level of cement with RHA for improved mechanical properties at optimum water binder ratio. This paper discusses the mechanical properties of RHA- High strength concrete at optimized conditions. Keywords: - Rice husk ash, high strength concrete, pozzolanic activity I. INTRODUCTION centof the rice paddy is husk, giving an annual total production of 120 million ton. It is estimated that 1,000kg of rice grain produce 200kg of rice husk; after rice husk is burnt, about 20 percent of the rice husk or 40 Kg would become RHA Rice husk ash (RHA) is a general term describing all types of ash produced from burning rice husks. In practice, the type of ash obtained varies considerably according to the burning technique. At 550°C – 800°C amorphous ash is formed and at temperatures greater than this, crystalline ash is formed. This study is conducted to investigate the optimum replacement level of rice husk ash (RHA) to cement in high strength concrete. The research involved partial replacement of cement by RHA and thereby making concrete more affordable to the common man and also to find a solution to the disposal problems created by rice husk. II. MATERIALS AND METHODS The ingredients used for the study were the same as those used for conventional concrete except the usage of mineral and chemical admixture. For this study Ordinary Portland cement of 53 grade with specific gravity 2.93 was used. River sand passing through 4.75mm sieve with fineness modulus of 2.89 and specific gravity 2.49 which falls under grading zone II was used as fine aggregate. The coarse aggregate used was crushed granite with a maximum nominal size of less than 20mm, bulk density of 1400 kg/m3 and specific gravity 2.85. Mineral admixture The addition of RHA to cement has been found to enhance cement properties: The addition of RHA speeds up setting time, although the water requirement is greater than for OPC. RHA cement has improved compressive strength due to its higher percentage of silica. RHA cement has improved resistance to acid attack compared to OPC, thought to be due to the silica present in the RHA which combines with the calcium hydroxide and reduces the amount susceptible to acid attack. More recent studies have shown RHA has uses in the manufacture of concrete for the marine environment. Replacing 10percent Portland cement with RHA can improve resistance to chloride penetration. RHA can also replace silica fume in high strength concrete. Silica fume or micro silica is the most commonly used mineral admixture in high strength concrete. The major characteristics of RHA are its high water demand and coarseness compared with condensed silica fume. To solve these problems RHA needs to be ground finely into particles of 8-10 μm and a super plasticizer added to