In construction industry, demolished construction waste is recently used as reprocessed aggregate to produce environmentally friendly concrete which is a good substitute to normal crush due to increased demand of ecological growth and conservation benefits. Though, the properties of recycled aggregate concrete are smallest as compared to concrete produced from natural aggregate and these properties can be enhanced by adding some materials having cementitious properties. Rice husk ash (RHA) is used as partial replacement of cement in recycled aggregate concrete to improve the properties as well as to conserve the natural resources. The elementary purpose of this investigation is to determine the compressive strength of concrete by the replacement of cement with different percentages of rice husk ash such as 0%, 7.5%, 10%, 12.5%, 15%, and 17.5% respectively with different curing conditions. For the experimental program approximate 198 cylinders (18 for rapid curing, 90 for normal water curing and 90 for acid curing) are casted with the mix proportion of 1:2:4 and water to cement ratio of 0.50 whereas curing is done at the ages of 3,7,14,21 and 28 days. Various experiments are performed on fresh and hardened concrete to determine the effects of rice husk ash on recycled aggregate concrete with different curing conditions. Linear regression analysis is carried out to determine the compressive strength of concrete. It is pragmatic from the slump test results that the workability of recycled aggregate concrete is decreased by increasing the quantity of rice husk ash. This reduction in slump is due to high water absorption of recycled aggregates and rice husk ash. Further, the compressive strength of recycled aggregate concrete with normal and acid curing is decreased by increasing the percentages of rice husk ash. It is also observed that at 28- days of normal water curing for mix M1,M2,M3,M4,M5 and M6 the compressive strength is increased by 0.96%, 2.74% 1.45%,4.50%,4.23% and 4.22% respectively as compared to the compressive strength values at 28 days of acid water curing. Therefore, it is concluded that recycled aggregate concrete with 10 to 12% of rice husk ash is suitable for properties of concrete. The acid water curing has negative impacts on hardened properties of concrete as it reduced the compressive strength of concrete as compared to normal water curing.

The most important property of concrete is its compressive strength, which is carried out after 28-days proper curing of concrete. This test is affected by other factors like the condition of curing, water to cement ratio, method of transportation, handling of the concrete, extent of vibrations and quality of the ingredients of mix proportion. This research study is an attempt to develop a simple Mathematical equation also known as mathematical model, by using linear regression analysis to estimate the 28-day fc’ (Compressive Strength) of concrete from the test results carried out atearly age. This simple linear equation develops a relationship of 28.5 hours accelerated cured compressive strength with normal cured compressive strength after 28-days. These results show that most of the predicted values of compressive strength, calculated via equations, lies within permissible range difference for compressive strength achieved by experimental method, which is clear indication of credibility of the equations obtained for compressive strength at different age of concrete. The results showed that compressive strength of concrete increases with the increase in content of FA (Fly Ash) upto 30% replacement, and the compressive strength of the concrete starts decreasing beyond 30% FA substitution. This argument is totally in line with all the literature carried out for this research.

Recycled aggregate concrete is required owing to environmental conservation and actual consumption of resources. In the construction industry, for the manufacturing of concrete the demand for replacement of ordinary aggregates by recycled aggregates has increased worldwide due to the large quantity of structure and destruction waste. The objectives of this research is to evaluate the effects of strength of concrete by replacing the normal crush with different percentages such as 25%, 50%, 75% and 100% of recycled aggregates. To conduct this study, a total of 120 cylinders (60 for compression and 60 for splitting cylinder test) are casted with mixing ratio of 1:1.9:3.8 and water to cement ratio of 0.59 while curing is carried out for 7, 14, 21 and 28 days. Numerous laboratory tests are performed like workability test, compression tests and splitting tensile strength tests, to check and compare effects of the recycled aggregate concrete with reference mix M1 (0%RA). The results illustrate that the workability of concrete decreases when the quantity of recycled aggregates are increased due to more water absorbing capacity. Further, it is also perceived that the compressive strength of concrete is decreased by 3.8%, 5.7%, 12.9%, and 15.8% respectively at 28 days of curing by substituting coarse aggregates with various percentages such as 25%, 50%, 75% and 100% of recycled aggregates as compared to reference concrete mix M1 (0% RA). Similarly, splitting tensile strength is also decreased when the quantity of recycled aggregates in ordinary concrete is increased. Moreover, this reduction in workability and strength of concrete is due to more water absorbing capacity of recycled aggregates. Hence it is concluded from the research that up to 25% replacement of natural aggregate with recycled aggregates, the recycled aggregate concrete is usually preferable to reduce the cost of construction as well as improve the environmental pollution issues. It is also observed that the splitting tensile strength of a concrete batch should vary between 9 – 11% of its respective compressive strength test results.

The most important property of concrete is its compressive strength, which is carried out after 28-days of proper curing of concrete. This test is affected by other factors like the condition of curing, water to cement ratio, method of transportation, handling of the concrete, extent of vibrations and quality of the ingredients of mix proportion. This research study is an attempt to develop a simple mathematical model, by using linear regression analysis to estimate the 28-day fc’ (Compressive Strength) of concrete from the test results carried out at early age. This simple linear equation develops a relationship of 28.5 hours. These results show that most of the predicted values of compressive strength, calculated via equations, lie within permissible range difference for compressive strength achieved by experimental method, which is clear indication of credibility of the equations obtained for compressive strength at different age of concrete. The results show that compressive strength of concrete increases with the increase in content of FA (Fly Ash) upto 30% replacement, and the compressive strength of the concrete starts decreasing beyond 30% FA substitution. This argument is totally in line with all the literature carried out for this research.

The most important property of concrete is its compressive strength, which is carried out after 28-days of proper curing of concrete. This test is affected by other factors like the condition of curing, water to cement ratio, method of transportation, handling of the concrete, extent of vibrations and quality of the ingredients of mix proportion. This research study is an attempt to develop a simple mathematical model, by using linear regression analysis to estimate the 28-day fc’ (Compressive Strength) of concrete from the test results carried out at early age. This simple linear equation develops a relationship of 28.5 hours. These results show that most of the predicted values of compressive strength, calculated via equations, lie within permissible range difference for compressive strength achieved by experimental method, which is clear indication of credibility of the equations obtained for compressive strength at different age of concrete. The results show that compressive strength of concrete increases with the increase in content of FA (Fly Ash) upto 30% replacement, and the compressive strength of the concrete starts decreasing beyond 30% FA substitution. This argument is totally in line with all the literature carried out for this research.