Effect of Recycled Concrete Aggregates on Compressive Strength and Water Permeability of Concrete Tehmina Ayub 1 , Asad-ur-Rehman Khan 1 , Wajeeha Mahmood 1 1 Department of Civil Engineering, NED University of Engineering & Technology, Pakistan. Abstract. This paper discusses the effects of recycled concrete aggregates (RCA) on compressive strength and permeability of recycled aggregate concrete (RAC) by using recycled concrete aggregates as a replacement of natural coarse aggregates (NCA). Four replacement percentages were used to study the effect of replacement. Replacement percentages used were 30%, 50%, 70% and 100% with 0% replacement was used as control. Mix design of 1:1.24:2.6 was used in the study with water to cement ratio of 0.43. Influence of RCA on compressive strength was determined for all the mixes as per ASTM C39 standard. The permeability of all the mixes was determined by measuring absorption, sorptivity and Darcy’s coefficient. Results of compressive strength indicated that concrete with 30% replacement of NCA can be successfully used in structural concrete without compromising too much on strength. Whereas, the replacement of natural aggregates with RCA has a negative impact on the permeability of concrete at all replacement levels. Absorption, sorptivity and permeability of natural aggregate concrete is lower as compared to RAC with 30% replacement showing the better performance as compared to other replacement ratios. Keywords: Concrete Aggregates, sorptivity, Compressive Strength, Water Permeability of Concrete I. INTRODUCTION With the preferment of modern concrete technology, the progress of industrialization development based on the reduced cost of resource consumption and environmental destruction has been accelerating across the globe. Several significant test results are available in the literature related to the ordinary concrete made up of recycled concrete aggregates (RCA) with pozzolanic materials [1, 2] and without pozzolanic materials [3], as well as in the pervious concrete [4, 5]. Bhikshma and Divya [1] also studied the permeability of RAC using fly ash. For this purpose, the fly ash content was used up to 30%, and overall four (04) concrete grades M20, M25, M30, M35 were prepared while recycled aggregates completely replaced natural aggregates. Compressive strength of RAC for each concrete type was found increasing when the amount of fly ash used was less than or equal to 20 %. However, the trend was reversed with the increase in the amount of fly ash beyond 20% up to 30%. Results of permeability of RAC were expectedly higher than concrete made up of natural aggregates. Still, the addition of fly ash resulted in the overall enhancement of the permeability resistance of RAC. Saini and Goel [2] examined the strength and permeability of ordinary concrete with 50, and 100% recycled coarse aggregates by incorporating silica fume as 5 to 10% replacement of cement by weight. Utilization of 10% silica fume significantly improved the mechanical properties and durability performance of RAC. Adnan et al. [3] studied the permeability of RAC with NAC by using 0%, 25%, 50%, 75% and 100% content of RCA. Mix designs used in the study were cast with water to cement (w/c) ratio 0.4, 0.5 and 0.6. Water permeability of RAC was the main parameter investigated in the study which was found to be on the higher side for RAC as compared with NAC. Sriravindrarajah et al. [4] determined the 7 and 28 days compressive strength along with the water permeability under the falling head and void content of the pervious concrete. Reported results showed that the compressive strength and coarse aggregate size are inversely related, and the use of recycled aggregate lowered the 28-day compressive strength as compared to the natural aggregates. However, the water permeability is independent of aggregate type (i.e. natural or recycled) but mainly influenced by the concrete porosity. Ying et al. [5] investigated the INTERNATIONAL JOURNAL OF ENERGY and ENVIRONMENT DOI: 10.46300/91012.2020.14.6 Volume 14, 2020 ISSN: 2308-1007 25