Partial Replacement of Cement by Fly Ash & Rha and Natural Sand by Quarry Sand in Concrete

Abstract

The use of rice husk ash as a by-product in the production of concrete can be considered as important for India since India is one of the leading rice cultivating country in the world. It also provides social aids related to problems associated with ash dumping in the environment. This husk consists of 75% organic volatile matter plus remaining 25% of the weight is converted into ash called as rice husk ash (RHA). This RHA contains majority of amorphous silica around 90%. In the present study,10% RHA is used as a cement replacement material. Proportion of sand is around 35% of total volume of concrete. Natural sand is mostly quarried from river beds that consist of higher percentage of inorganic materials, sulphates, clay, chlorides and silt which affect the durability, strength of concrete & steel thereby decreasing the life of structure. At least 30 % to 50% of Fine particles below 600 microns must be present for the production of good concrete. These particles are not present in river sand in necessary quantities. Also increase in digging may result in fall of ground level there by affecting the environment. So to fulfill the need of fine aggregate the simplest way is to use crushed natural stone i.e manufacturing sand. It produces the concrete of similar properties compared with concrete made with natural sand, such as compressive strength, tensile strength, modulus of rupture and degree of shrinkage. In the present study, various proportions have been considered such as 1. 30% Fine aggregate and 0% rice husk ash mix together in concrete by replacement of cement with the increase of RHA by 2.5% (gradually) and parallely decreasing FA by 2.5% (gradually) ,last proportion taken 22.5% FA and 7.5% RHA. 2. 70% cement, 22.5 % Fly ash & 7.5% RHA, partially replace natural sand by quarry sand i.e. 0% - 45% with an increase of 15% (gradually).The main purpose of the investigation is to obtain the optimum mix design and to examine the physical properties– density, strength (bending and compression), water absorption and moisture content.