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Civil-Comp Proceedings
ISSN 1759-3433
CCP: 91
PROCEEDINGS OF THE TWELFTH INTERNATIONAL CONFERENCE ON CIVIL, STRUCTURAL AND ENVIRONMENTAL ENGINEERING COMPUTING
Edited by: B.H.V. Topping, L.F. Costa Neves and R.C. Barros
Paper 64

Optimization of Lightweight Aggregate Concrete Units using a Genetic Algorithm

L.C. Sousa1, C.F. Castro1, C.C. António1 and H. Sousa2

1IDMEC, 2GEQUALTEC/DEC,
Faculty of Engineering, University of Porto, Portugal

Full Bibliographic Reference for this paper
L.C. Sousa, C.F. Castro, C.C. António, H. Sousa, "Optimization of Lightweight Aggregate Concrete Units using a Genetic Algorithm", in B.H.V. Topping, L.F. Costa Neves, R.C. Barros, (Editors), "Proceedings of the Twelfth International Conference on Civil, Structural and Environmental Engineering Computing", Civil-Comp Press, Stirlingshire, UK, Paper 64, 2009. doi:10.4203/ccp.91.64
Keywords: optimization, genetic algorithms, lightweight concrete blocks, thermal analysis, thermal transmittance, finite element method.

Summary
Lightweight expanded clay aggregate is a granular ceramic material presenting low thermal conductivity making viable the production of concrete blocks as an alternative cost-effective solution for building economic single leaf walls with good thermal performance without compromising the wall structural properties [1,2,3].

The thermal behaviour of a wall can be characterized by the thermal transmittance of masonry enclosure according to normative requests [4,5,6]. The wall thermal performance is calculated using three-dimensional finite element simulations of units with exterior and joint mortars, considering the various basic processes of heat transfer namely, conduction, convection and radiation [7].

To search for an improvement of the thermal resistance of masonry units, the optimization algorithm will iterate as the topology of the unit evolves to an optimum. Since the optimisation problem has an associated discrete domain, a genetic algorithm is adopted to obtain the optimal solution [8]. The developed algorithm considers mixed code format for the data, the definition of the fitness function, the thermal transmittance of masonry enclosure, and a population evolution based on an elitist strategy.

Considering a block of 400 mm length including 5 mm vertical mortar joints on each side, 200 mm height including a 10 mm horizontal mortar joint on the top and bottom and a 350 mm thickness plus 20mm mortar at internal and external render finish surfaces then the total wall thickness becomes 390 mm.

The genetic optimization algorithm found an optimal unit solution exhibiting a thermal transmittance of the masonry wall equal to U = 0.54 W/(m2 K). This value is an indicative of good thermal insulation for single leaf walls built with lightweight concrete blocks.

References
1
A.M. Bastos, H. Sousa, A.F. Melo, "Methodology for the Design of Lightweight Concrete with Expanded Clay Aggregates", The Masonry Society Journal, 23(1), 2005.
2
K.S. Al-Jabri, A.W. Hago, A.S. Al-Nuaimi, A.H. Al-Saidy, "Concrete blocks for thermal insulation in hot climate", Cement and Concrete Research, 35(8), 1472- 1479, 2005. doi:10.1016/j.cemconres.2004.08.018
3
A. Tavil, "Thermal behavior of masonry walls in Istanbul", Construction and Building Materials, 18(2), 111- 118, 2004. doi:10.1016/j.conbuildmat.2003.08.014
4
EN 32573, "Thermal bridges in building construction-heat flows and surface temperatures-General calculation method", CEN TC89/WG1, Brussels, 1993.
5
EN 1996 "Eurocode 6: Design of Masonry Structures. Part 1-1: General rules for reinforced and unreinforced masonry structures", CEN, Brussels, 2005.
6
RCCTE-Leis, Decretos, Regulamento das Características de Comportamento Térmico de Edifícios, Portugal, D.L. no 80/2006 de 4 de Abril de 2006.
7
F.P. Incopera, D.P. Dewitt, "Fundamentals of Heat Transfer", John Wiley & Sons, New York, U.S.A., 1981.
8
C.F. Castro, C.A.C. António, L.C. Sousa, "Optimization of shape and process parameters in metal forging processes using genetic algorithms", Journal of Materials Processing Technology, 146, 356-364, 2004. doi:10.1016/j.jmatprotec.2003.11.027

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