Civil Engineering and Architecture 11(5A): 3154-3161, 2023 http://www.hrpub.org DOI: 10.13189/cea.2023.110825 Effect of Mixing Time on Some Hardened Concrete Properties Mohammed Salman Al-lami 1 , Diala Atiyat 2,* , Mutaz Qutob 1 1 Department of Civil Engineering, Faculty of Engineering, Isra University, Pakistan 2 Department of Architecture Engineering, Faculty of Engineering, Isra University, Pakistan Received March 17, 2023; Revised June 14, 2023; Accepted July 19, 2023 Cite This Paper in the Following Citation Styles (a): [1] Mohammed Salman Al-lami, Diala Atiyat, Mutaz Qutob , "Effect of Mixing Time on Some Hardened Concrete Properties," Civil Engineering and Architecture, Vol. 11, No. 5A, pp. 3154 - 3161, 2023. DOI: 10.13189/cea.2023.110825. (b): Mohammed Salman Al-lami, Diala Atiyat, Mutaz Qutob (2023). Effect of Mixing Time on Some Hardened Concrete Properties. Civil Engineering and Architecture, 11(5A), 3154 - 3161. DOI: 10.13189/cea.2023.110825. Copyright©2023 by authors, all rights reserved. Authors agree that this article remains permanently open access under the terms of the Creative Commons Attribution License 4.0 International License Abstract The mixing time of ready-mixed concrete may be prolonged for many reasons, which may affect the resulting properties in its fresh and hardened states. The effects of prolonged mixing time on the slump, compressive strength, porosity, and permeability of concrete were investigated in this paper. All mixtures were prepared with the proportion 1:1.5:2 by weight for cement, fine aggregate, and coarse aggregate, respectively. The investigated variable was the effect of water-to-cement ratios, which were 0.40, 0.45, 0.55, and 0.65. The materials were continuously mixed up for 15, 60, 120, and 240 minutes without any additional mixing water. To reduce the evaporation of the mixing water, the drum opening was tightly covered with a polyethylene perforated film. The results showed an increasing trend in the coefficient of permeability values with mixing time for all mixtures except for the mixture with a water-to-cement ratio of 0.65 which showed a reduction in value. A different trend of results for the coefficient of permeability in comparison with that for porosity was observed. The prolonged mixing time (longer than 90 minutes discharged limit specified by ASTM) does not cause a negative effect on compressive strength as long as it has workability that facilitates the casting process, as the mixtures with higher water-to- cement ratios showed an increasing trend in compressive strength. Keywords Concrete Properties. Mixing Time, Compressive Strength, Permeability, Porosity 1. Introduction The concrete industry has developed in all its aspects such as design methods, machinery, and equipment. The different types of concrete have varied according to the diversity of their components and requirements. Urban development has accompanied the widespread use of ready-mix concrete all over the world. The time of mixing concrete may be prolonged for many reasons, which may affect its properties. The prolonged mixing time causes the degradation of aggregate particles, which increases the amount of very fine material in the mix and produces friction, which raises the concrete temperature. Both of these factors reduce plasticity during transport and lead to the rejection of a substantial number of truckloads of concrete. Obla et al. [1] estimated the amount of concrete waste to be about 3% of total production. Rahman et al. [2] found the properties of self- compacting concrete (SCC) such as compressive strength, split tensile strength, and permeability were affected when the mixing time was extended from 5 minutes to 90 and 180 minutes. The compressive and cleavage tensile strength decreased while permeability values increased. According to ACI 318-19 Code, Section 26.5.1.1, and the requirements of ASTM C94, the discharge of the concrete shall be completed within 90 minutes from the introduction of the mixing water to the cement and aggregates or the introduction of the cement to the aggregates.