i am doing my final year project so i am looking on ways to improve the strength of recycled aggregated concrete and increased the percentage of recycled aggregate used without compromising the strength of concrete.
There are different you can do it. But be careful not to increase strength and lose on the durability. Also, some fibres are used to control crack, but do not increase flexural strength, and in fact may reduce it. For strength enhancement, steel fibres are the best>
Essentially concrete compressive strength is a factor of the water-cementetious ratio of the mix. So whatever you could do to lower this ratio would tend to increase the strength of the concrete. Adding a appropriate water reducing admixture or super-plasticizer would be the best way to accomplish this. This is also the basis for designing high strength concrete mixes.
To ground the recycled aggregate into a powder and then re-build it with some admixture like water reducation
I agree with Dr. Gordan, One of the best is admixture like sulphonated naphthalene formaldehyde as a superplasticizer and also you can use other chemical admixtures upto certain extent which will decrease the water requirements, porosity simultaneously increases the strength of the concrete.
In addition the comments above, higher compressive strength of recycled aggregate (of course related with virgin aggregate strength) improves concrete strength.
As recycled aggregates are more porous than the conventional concrete aggregates, they end up acting as defects in the structure, generating a drop of strength. Thus, all the ways used to increase the strength are in order to reduce this condition. Then you can try to increase paste strength as has been said, or decrease the effect of recycled aggregates. For this purpose, one of possible tools that could be used is the treatment of the aggregates themselves, as comminution to smaller dimensions. Thus, the smaller the size of the recycled aggregate, the lower the effect on the decrease in concrete strength. Another possible way is the density separation. There are studies that demonstrate that is possible to select recycled aggregates of higher density to minimize the loss of ultimate strength.
"Aggregate" has no strength! It is "loose" and can be disrupted by hand or foot. Aggregate is a filler which is used in concrete to save money, because the client would not be able to afford using concrete made only with cement and water, also known as grout.
Using appropriate concrete mix design criteria, adequate concrete strengths should be achieved, even for "poor" course aggregate. The only caveat would be if poor quality fine aggregate should be used, in which case relatively more cementetious materials would be required per unit weight of the concrete, and also concrete shrinkage would become a serious factor to be considered and controlled.
The simple answer is that the "strength" of recycled aggregate is what it is, and cannot be "increased", except by reducing the amount of the recycled aggregate used in the Mix and provided that the course aggregate is not actually a mudstone or similar which could disintegrate during production of the concrete.
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