Ecologically, fly ash and limestone waste are posing a great threat to the environment and due to their disposable problems their use must be limited. However they can be used in the construction of cement concrete pavements on partial replacement basis .Extraction of sand from different sources causes lowering of water level in the rivers thus disturbing the natural geological features.
We have made an attempt to solve the economical and environmental problems by using a combination of fly ash and limestone waste as partial replacement of cement and sand respectively on percentage basis.
2. LITERATURE SURVEY .
In our research we found the percentage up to which the cement can be replaced by the waste material-fly ash and percentage up to which sand can be replaced by the waste material –limestone . The grade of concrete for experimentation used was M20 designed as per IS 10262-1982 with 28 days characteristic strength of 20MPa. The maximum size of aggregate used was 20mm and the workability was 0.8CF with moderate exposure conditions.
Without any use of limestone waste and fly ash , the average compressive strength at 7 days and 28 days was found out to be 18.54 MPa and 25.14 MPa respectively and water absorption was 0.39%. We replaced sand up to 40% by weight by limestone waste and found out that the 7 days strength increased by 37.84% and 28 days strength increased by 44.04% and water absorption increased by about 0.516%. and dry weight increased by 1.5%. We replaced cement with fly ash upto 40% and found out the 7 days compressive strength decreased by 64% and 28 days strength was reduced by 54.65%.
Based on the experimental study we concluded that by combined replacement of cement and sand by fly ash and limestone waste respectively upto 40% each., the 7 days strength was decreased by 16% and 28 days strength was reduced by 10.50% only which is desirable on economical and ecological grounds. Further , water absorption was increased only by about 1% and most importantly the average dry density was decreased by 5.8% .
3. PROPOSED METHODOLOGY AND DISCUSSION.
The main objective of the project is to effectively use a combination of fly ash and limestone waste as partial replacement of cement and sand respectively. The quantities of fly ash and limestone waste were varied from 0% to 40% and the various properties were determined at 5,10,20,30 and 40% respectively and for determining the properties, the cubes were casted as per IS 10262-1982 in a standard mould as specified. The standard consistency test was performed using vicats apparatus and slump test was performed to determine the workability. Water absorption was determined at different percentage replacements and the cubes were weighed to determine their dry density also.
CONCLUSIONS
After careful and elaborate study of effect of various waste materials on concrete properties, it can be concluded that:
1. Limestone waste can be used in concrete as a replacement of sand up to 40% and above from strength and durability point of view.
2. Fly ash can be used in concrete as a partial replacement of cement up to 30% from strength point of view.
3. A combined use of limestone waste and fly ash in concrete has shown positive result for 30% to 40%.
4. Use of limestone and fly ash in concrete can prove to be economical as it is non useful waste.
5. Use of limestone waste in concrete will eradicate the disposal problem of limestone waste and prove to be environment friendly thus paving way for greener concrete.
6. Use of limestone waste in concrete will preserve natural resources particularly river sand and thus make concrete construction industry sustainable.
7. Use of fly ash will eradicate its disposal problem and reduce carbon emissions (CO2), thus prove to be environment friendly thus paving way for greener concrete.
In order to be sustainable for future generations we must fully exploit by-product materials like limestone waste and fly ash. Both current production and stockpiled material should be fully utilized. This will reduce both the greenhouse gas emissions and the use of naturally occurring aggregates. It is our duty to take sensible engineering judgments based on facts about byproducts and not on the prejudice of assuming a ‘WASTE’ is somehow inferior or less suitable.