Periodicals of Engineering and Natural Sciences ISSN 2303-4521 Vol. 7, No. 4, December 2019, pp.1563-1566 Available online at: http://pen.ius.edu.ba 1563 Optimization of water-cement ratio in concrete contains recycled polypropylene (PP) plastic waste Alaa Jaleel Naji 1 , Hayder Abbas Al-Yousefi 2 , Mohammed Abbas Mousa 3 , Murtadha Jasim Hussein 4 1 Road and Transportations Engineering Department, University of Al-Qadisiyah, Ad Diwaniyah, Iraq 2 Chemical Engineering Department, University of Al-Kufa 3 Road and Transportations Engineering Department, University of Al-Qadisiyah, Ad Diwaniyah, Iraq 4 Civil Engineering Department, University of Al-Qadisiyah, Ad Diwaniyah, Iraq ABSTRACT 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. Keywords: Polypropylene; water-cement ratio; plastic waste; compressive strength Corresponding Author: Alaa Jaleel Naji Assistant Lecturer, Road and Transportations Engineering Department University of Al-Qadisiyah, Ad Diwaniyah, Iraq. Email: alaa.alnsray@qu.edu.iq 1. Introduction and Literature Review The expansion of global plastic consumption produces an increase in plastic waste which leads in turn to severe consequences on the environment. The process of plastic waste disintegration is taking a long time, and most components are toxic. So, reuse or recycling of plastic waste is preferred. plastic waste utilization in the concrete instead of fine aggregate has been studied by many researchers during the last years [1–7]. In 2012, Rai et al. carried out an experimental study focused on a plastic waste addition with ratios of (0%, 5%, 10%, and 15%) to normal concrete as a partial replacement of the sand with and without superplasticizer. Forty-eight cube specimens have been cast, six cubes were cast for each percentage of plastic waste without superplasticizer, and six cubes for each different percentages of plastic waste have been cast with superplasticizer. Compressive strength, dry density, fresh density, workability have been tested; the results indicated that the workability and compression strength were decreasing due to partial replacement of plastic waste. On the other hand, the superplasticizer enhanced the workability and compression strength, generally dry density and fresh density decreasing with the increase of plastic ratio in each concrete mixture [2]. In 2016, Ahmed researched the behavior of high performance concrete with using plastic waste ratios (0%, 2.5%, 5%, and 7.5%) as replacement from fine aggregate with partial replacement of silica fume as 10 % of