Use of Recycled Concrete as Coarse Aggregate for High Strength Concrete

Abstract

This study is concerned with the production of high strength concrete using recycled concrete aggregates as alternative to natural aggregates. The study includes also the determination of the proportions, characteristics and components of concrete mixes required for production and use in multiple applications at suitable prices. The basic materials used in this research (ordinary Portland cement, natural aggregates, recycled concrete aggregates, natural valley sand, local tap water as well as super plasticizer additive). The proportions of these materials were carefully selected to improve the strength concrete, also conduct various laboratory tests of the materials to ensure their quality. Then the design of concrete mixes with different proportions of recycled concrete aggregate was carried out in order to achieve the high strength concrete. The selected materials, techniques and steps of mixing designs and mixing proportions were discussed for high strength concrete using four types of mixes, with mix proportions(1:1.57:2.73) for mix A, and, mix proportions(1:1.3:2.3) for mix B,C, and D. Mix (A) NAC; ordinary Portland cement 450 kg/m³ were used with natural uncrushed aggregates 1040 kg/ m³, and natural sand with fineness modulus 3.23. Mix (B); ordinary portland cement 450 kg/m³ was used with 30% recycled concrete aggregate 1040 kg/m³ by adding different levels of super plasticizer (0,3, 5, 8) litters per cubic meter, natural sand, with fineness modulus 3.23. Mix (C); ordinary portland cement 450 kg/m³ was used with 50% recycled concrete aggregate 1040 kg/m³ by adding different levels of super plasticizer (0,3, 5, 8) litters per cubic meter, natural sand, with fineness modulus 3.23. Mix (D); ordinary portland cement 450 kg/m³ was used with 100% recycled concrete aggregate 1040 kg/m³ by adding different levels of super plasticizer (0,3, 5, 8) litters per cubic meter, natural sand, with fineness modulus 3.23. These mixtures were tested to evaluate the mechanical properties to have high strength concrete .Then discussed the results obtained from the tests according to the results obtained, for mix B the highest strength concrete in 28 days obtained was 42.3N/mm². for the mix containing 3 liters per cubic meter of super plasticizer with a water ratio of 0.40. Then mix C found that the highest strength of concrete in 28 days was obtained 43 N / mm ² for the mix containing 5 liters per cubic meter of super plasticizer with a water ratio of 0.34. For mix D the highest strength concrete in 28 days obtained was 43 N/mm² for the mix containing 8 liters per cubic meter of super plasticizer with a water ratio of 0.35. The results of the mechanical tests of concrete in this study found that the recycled concrete can be a complete replacement for aggregates in the works that require a concrete strength of 40 N/ mm². Recycled aggregate cannot be applied in the high strength structure. But can be applied in the normal strength structure under the condition that does not involve a lot of handling works the ingredients must be selected and processed very carefully with the use of the additive.