In this study, 12 specimens with three different lateral reinforcement ratios (ρ=0.022, 0.012 and 0.007) and four RG replacement ratios (0%, 30%, 50% and 100%) were prepared and tested under pure axial load in order to investigate the influence of recycled coarse aggregate (RG) and lateral tie reinforcement ratio (ρ) on the compressive behavior of a confined recycled aggregate concrete (RAC) column. The experimental data obtained from the tests are reported and compared with the predicted values obtained from the widely accepted Mander's confined concrete model developed for conventional confined concrete to assess applicability of the model to recycled aggregate concrete. The results showed that the effect of RG on the compressive behavior of the RAC was negligible at low stress level, and it began to appear as the load increased at load levels above about 35% of Peak, regardless of ρ. The slope of the normalized compressive strength (fcc' /fco' ) and normalized corresponding strain (εcc /εco ) against ρ showed that the effect on the stress and strain enhancement in the RG-30 series, and the smallest effect in the RG-50 series. The ratios of experimental values to those predicted from Mander's model, f'cc_exp/f'cc_model and εcc_exp/εcc_model, showed that the model tended to give unconservative strength (f'cc) and strain (εcc) values for the RAC columns.
…………………………………………………………………………………………………….... Introduction:-he need to recycle old construction materials has been well established over the last few decades by government agencies and the construction industry due to the increasing cost of waste storage and the depletion of natural resources [1]. Among the numerous construction waste materials, old concrete, in particular, is a promising source of recycled aggregate with sufficient quality for civil engineering applications with moderate performance requirements [2,3]. While most of the studies on the subject thus far have focused on the processing of old concrete and the properties of recycled aggregate concrete (RAC), only a limited number of studies have reported the performance of structural members made of RAC: beam [4][5][6], column [7], joint [8], and frame [9]. Although a direct comparison of the results from different studies is difficult due to a lack of coherent concrete constituents, the results generally indicate that the strength decreases with slight increase in the corresponding strain as recycled aggregate content in the concrete increases. his strength decrement was attributed to a weak interface between the new mortar and the recycled aggregate and between the adhered mortar and the recycled aggregate [10,11]. he reduction in strength due to RG can be of set by two approaches: adjusting proportions of concrete constituents or providing proper