Construction industry relies heavily on conventional ma­terials such as cement, granite and sand for the production of concrete. The River sand which is most commonly used fine aggregate in the production of concrete, poses the problem of acute shortage in many areas, whose contin­ued use has started posing serious problems with respect to its availability, cost and environmental impact. Attempt is being made in this project to use the locally available materials to replace the river sand to produce low cost concrete. Saw dusts are the loose particles or wood chip­pings obtained as by products from sawing of timber into standard useable sizes produced by sawmills. Sawdust has been used in concrete, but not widely. Although se­riously limited by its low compressive strength, the ad­vantages that sawdust concrete offers are considerable reduction in weight of the structure, thereby reducing the dead loads transmitted to the foundation, high economy when compared to normal weight concrete. The crusher dust produced from granite crushers and waste by product from quarry is one of the alternative materials for river sand. The utilization of crusher dust which can be called as ROBO sand has been accepted as a building material in the western countries also in some states of India. Lots of research has been done regarding the crusher dust as alter­native materials for river sand and reported that crushed stone dust can be used to partially replace the natural sand in concrete. Saw dust and robo sand in proportion used as fine aggregates in concrete and the compressive and split tensile strength were tested. There were totally five mixes prepared for the investigation, gradually increasing the replacement percentages from 0-100% with sawdust and robo sand in proportion. The compressive and split tensile strength gradually decreases for the increasing replace­ment percentages. The optimum mix found to produce M20 grade of concrete is 10% of saw dust and 40% of robo sand, totally 50% replacement of river sand. The weight reduction achieved is 7% and cost reduction is 2% per cubic meter of concrete.