ABSTRA CT
With voyage reinforced concrete has become most widely used construction material in construction industry. Construction of new buildings in place of old structures in present era is unavoidable particularly in city centers to compensate the growing population and migration from other areas. But this leads to extensive demolishing waste which needs proper management. If this waste can be utilized in new construction, then will not only reduce the waste management but also saves natural sources of aggregates. Any of the structure during its service life has to face lot of hazards, fire is one among them. The behavior of reinforced concrete structures during and after fire has remained active research area. This research work combines both aspects to study the effect of fire on concrete cubes made by replacing 50% natura l coarse aggregates with coarse aggregates from demolished concrete. Demolished concrete in the shape of large blocks is collected.
from Nawabshah city. These large blocks are then processed to maximum of I “size by hammering and sieving.

Using I :2:4 m ix total of 180 cubes in two batches are prepared. In one batch I 00% natural coarse aggregates are used and in second batch 50% natural coarse aggregates are replaced with coarse aggregates from demolished concrete. All cubes are cured for 7, 14 and 28 days. After elapsed time cubes are tested for compressive strength. The
Obtained results are presented in both tabular and graphical format to compare with reference concrete.
7 day cured cubes observed strength reduction of 23.05% at zero hour fire in comparison to reference concrete. Whereas these values for 3, 6, 9 and 12 hours are 25.28%.
30.57%, 37.26% and 47. 14% respectively. These results show that concrete cubes with recycled aggregates survived 75% strength for 3 hour fire and about 53% strength for 12 hour fire. In comparison to 7 days cured cubes the results of 14 days cured with respect to reduction in strength or survived compressive strength arc hcttcr.28 days curing is the standard curing to be done in every project. Compressive strength result of this curing age, in comparison to result of 7 days and 14 days curing are better wit about 6% result for 3 hour fire and about 25% reduction for 12 hour fire. 12 hour is normally good
Enough time to control fire hence can be said that even if fire prolongs for 12 hours recycled concrete can survive up to 75% of its strength. also it is observed from graphical presentation of results that associative from of decrease in strength is same and associative behavior of cubes remained same.


graphical presentation of results that associative form of decrease in strength is same and
associative behavior of cubes remained same.