Recently, the use of recycled plastic waste in civil engineering applications has been increased. This paper aims to investigate the effect of water-cement ratio on the compressive strength of concrete that contents 2.5 % polypropylene (PP) as plastic waste. Two references concrete mixes were prepared. The first mix had a water-cement ratio of 0.45 with 2.5% plastic waste, the second mix with 0.45 water cement ratio but without plastic waste. Three concrete mixes with water cement ratios of (0.5, 0.4, and 0.3) were also used as parametric study cases. The results indicated that decreasing the water-cement ratio from 0.45 to 0.4 increases the compressive strength by 20.2%. In addition, the compressive strength increases by 36.2% with decreasing of water cement ratio from 0.45 to 0.3. While the compressive strength decreases by 12% with the increase of water-cement ratio from 0.45 to 0.5.

This investigation aims to use corn cover as natural fibers in concrete mixes to improve some mechanical properties like compressive strength, tensile strength, and flexural strength. using any type of fiber in concrete, in general, can improve the tensile and flexural strength of concrete. Concrete is weak in tension, so using fibers such as natural fibers like trunk fibers or industrial fibers such as steel fibers can improve tensile, the flexural strength of concrete and that may be decreasing the use of steel reinforcement in concrete, and also fibers can improve toughness and ductility of concrete because of its work inside the concrete that can reduce the propagation of cracks under loading. This study shows slight improvement on compressive strength by using fibers, but high increments in flexural strength, the optimum ratio of corn cover fibers was 2.5% by weight of cement which gives the highest values in compressive strength and flexural strength. compressive strength increased from (31.2 to 35.9) MPa (about 15% increment), increment for flexural strength was 70.6% for the optimum fibers content and the failure by using corn fibers was a ductile failure compared with plain concrete that gives sudden failure under flexure load, also tensile strength increased by using fibers, more fibers content beyond or more than 2.5% give lower values for the mechanical properties.