Abstract— The use of recycled demolished concrete in producing new concrete is an established method to improve sustainability through reducing the environmental impact of using virgin aggregates and through reducing construction waste. Six Sigma is a set of tools and strategies for process improvement. In this paper, the six-sigma DMAIC methodology is utilized to optimize the design parameters in order to improve and assure the quality of the resulting recycled aggregate concrete. The project aims to produce concrete with compressive strength of 25 MPa without using additives. Five parameters were used in the initial analysis that were reduced to three after refinement. The refined parameters are the ratio of recycled coarse aggregates, ratio of recycled fine aggregates and the water/cement ratio. It was concluded that the optimum values for the three parameters are 26%, 30 % and 0.5, in order. Keywords— Aggregates, concrete, recycled, six sigma. I. INTRODUCTION ESPITE the many advances in technology including material technology, concrete is still the premier construction material in all types of civil engineering works, including low and high-rise building, water retaining structures, bridges, and general infrastructure. Concrete is a manufactured product, essentially consisting of cement, aggregates, water and possibly admixture, additives or agents. Among these constituents, aggregates including sand, crushed stone or gravel form the major part by volume. Traditionally, aggregates have been readily available at economic prices and of qualities to suit all purposes. However, there has been a rising awareness to the environmental damage caused by quarries producing such primary aggregates. Therefore, countries with major cycles of demolition and construction works, such as the Arabian Gulf region, including Kuwait, are exploring ways to use recycled aggregates produced from such activities. Since its establishment in 2001, the Environment Preservation Industrial Company (EPIC) in Kuwait has been cooperating with major stakeholders in the private and Mohamad Terro, Professor, Kuwait University, Kuwait. Moetaz El-Hawary 2 , Associate Professor, Kuwait University, Kuwait, (corresponding author’s phone: 965-66016630; e-mail: hmoetaz@yahoo.com). Rana Al-Fares, Associate Professor, Kuwait University, Kuwait. Mark Goldstein, Goldmark Consultants, Louisville, KY. government construction sectors to encourage the utilization of recycled construction materials in projects around the country. The company receives the debris from demolished civil constructions and utilizes global production technologies with standard specifications to provide the construction market with quality recycled material mainly consisting of fine and coarse recycled aggregates. In addition to the many benefits to the environmental preservation envisaged by the use of recycled aggregates in civil works, financial savings are also incurred from reduction in transport and production energy costs. Reduction in waste landfills is a further important benefit to this trend. The subject of the use of recycled materials as aggregate replacement in concrete had received considerable research attention over the last decade. Richardson [1] investigated the possibility of achieving a concrete made with un-graded recycled aggregates with a comparable strength to that of concrete made with virgin aggregates (control sample). Yasuhiro Dosho,[2] developed a recycling system in which he replaced normal aggregates with recycled aggregates from construction wastes whilst ensuring safety, quality, and cost effectiveness. In his study, he stressed the tremendous impact on the environment from applying his proposed method to waste generated from the demolition of large scale buildings such as power-houses. Acknowledging that concrete from construction demolition sites apportions more than half of the total wastes in Hong Kong, W.Y.Tam, et al.[3] utilized a series of laboratory tests to set out some guidelines that would facilitate the use of RAC in the construction industry. He concluded his paper with highlights on potential reduction in the quality of RAC, a classification of RA for various construction applications, and alerts to users on possible extra slump loss due to the use of RAC. Moreover, a number of statistically-based approaches have emerged in many studies on the mixture design of concrete [4,5]. In such research studies, mostly a full or fractional factorial experimental setup approach is used to calibrate optimal values of concrete strength. Simon used a statistical approach to develop an internet-based software program to optimize concrete mixture proportions [6]. Soudki used a full factorial experimental study to optimize mix proportions that would produce concretes least sensitive to temperatures in hot climate [7]. He used the water/cement ratio, coarse/total Optimization and Quality Improvement of Recycled Aggregates Concrete Through the use of Six-Sigma Method Mohamad Terro, Moetaz El-Hawary, Rana Al-Fares, and Mark Goldstein D International Conference Data Mining, Civil and Mechanical Engineering (ICDMCME’2014), Feb 4-5, 2014 Bali (Indonesia) http://dx.doi.org/10.15242/IIE.E0214042 103