Design development of aggregates cooling systems for hot weather concreting
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Design development of aggregates cooling systems for hot weather concreting Khaled I. E. Ahmed • A. M. S. Hamouda M. S. Gadala
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Received: 6 January 2015 / Accepted: 2 February 2015 Ó Springer Science+Business Media Dordrecht 2015
Abstract Using hot aggregates, in concrete production, results in a drop in compressive strength of the produced concrete. Various methods have been proposed for cooling concrete aggregates. This paper proposes new two designs for aggregates cooling systems for various production rate demands. Conveyor system for small to moderate production rates and rotating drum for high production rates. Simulation of the heat flow during the cooling process over the conveyor and through the drum are analyzed with the objective of understanding the effect of the various design parameters and achieving minimum cooling time with the least possible power. Finite element models for the new designs are proposed and discussed. The results of the finite element analysis of the new designs are presented for various initial conditions and cooling rates.
K. I. E. Ahmed A. M. S. Hamouda (&) Mechanical and Industrial Engineering Department, College of Engineering, Qatar University, Doha 2713, Qatar e-mail: [email protected] K. I. E. Ahmed e-mail: [email protected] M. S. Gadala Mechanical Engineering Department, University of British Columbia, Vancouver, BC, Canada e-mail: [email protected]
Keywords Hot weather concreting Aggregates cooling Cooling drum Aggregate beds conductivity Heat transfer Finite element Thermal contact resistance
1 Introduction Ready-mixed concrete manufacturers, in hot weather regions are faced with drops in compressive strengths of concrete produced in summer, Fig. 1. High ambient temperatures increase the rate of evaporation from fresh concrete resulting in lower effective water content and hence lower effective water-cement ratio per weight (AC1 Committee 305 1999; Khan and Khuzdar 2007; Bader 2003; Haque and Kayali 2007; Mouret et al. 1997; El-Hacha et al. 2010). Reduction of compressive strength has also been observed on specimens produced under a controlled environment and tested in a laboratory (Bhutta et al. 2013; Haque et al. 2007). High temperature speeds cement hydration and the bonding between the cement grains becomes weaker. Therefore, the early-age strength increases with higher curing temperatures because the reaction rate is faster, but 28-day strength decreases because of the poor bonding between cement grains at these elevated temperatures. It is noted that higher temperature aggregates results in greater concentration of calcium hydroxide at the interface. This observation leads to the assumption that the transition
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Fig. 1 Effect of aggregate temperature on the 28-day concrete compressive strength based on the data given by AC1 Committee (1999)
zone might be weakened by chemical phenomenon due to the rise of the constituent temperatures (Haque et al. 2007). The weather conditions of many regions of the world are associ
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