Construction and demolition wastes are produced every day around the world. Thus the idea of using recycled concrete aggregate in new concrete production appears to be an effective utilization of concrete waste. This paper presents the results of an experimental study to evaluate the effects of recycled concrete aggregate (RCA) percentages under different curing conditions. The percentages of recycled coarse aggregate to dolomite were (0:100%, 25:75%, 50:50%, 100:0%) respectively. The concrete properties which were studied were the mechanical properties (compressive and splitting strength) and mass transport properties (ISAT and sorptivity). The concrete specimens were exposed to three different curing conditions, moist (standard), open-air, and painted specimens using the substance (Curassol 1). The coarse recycled concrete aggregates were obtained by crushing a laboratory produced primary concrete at age of 28 days. The results showed that curing using paint material was the most efficient method of curing at all ages and percentages of recycling except at 100% recycling, where the maximum value of both compressive and tensile strengths was obtained using water curing. Also, in moist curing, full replacement of coarse aggregates gave the highest compressive strength at age of 28 days. In all cases of recycled aggregate ratios, curing using water caused a decrease in the concrete permeability.

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In some buildings, when quality control is poor, the upper parts of columns have a weak compressive strength, especially in floor zone. Low compressive strength for upper part of the column will lead to a reduction in bearing capacity of column. Strengthening of this part using traditional methods such as R.C jackets and steel jackets will not satisfy the architectural conditions. Also the Egyptian code for design and construction of fiber reinforced polymers prevents partial strengthening of rectangular columns with fiber laminates. This study is carried out to investigate the overall behavior of R.C square columns with poor concrete at upper part, strengthened with CFRP. The wrapped part of column was the upper part only. An experimental program was undertaken testing ten square columns 200 • 200 • 2000 mm. One of them was a control specimen and the other nine specimens were strengthened with CFRP. The main parameters studied in this research were the compressive strength of the upper part, the height of the upper poor concrete part, and the height of CFRP wrapped part of column. The experimental results including mode of failure, ultimate load, concrete strain, and fiber strains were analyzed. The main conclusion of this research was, partial strengthening of square column using CFRP can be permitted and gives good results of the column carrying capacity.