Study of Lightweight Concrete Behaviour

Topics: Concrete, Strength of materials, Compressive strength Pages: 16 (4218 words) Published: September 22, 2010
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PROPERTIES OF LIGHTWEIGHT CONCRETE MANUFACTURED WITH FLY ASH, FURNACE BOTTOM ASH, AND LYTAG Yun Bai, Ratiyah Ibrahim, and P.A. Muhammed Basheer Queen’s University, Belfast, U.K.

Abstract
Fly ash (FA), furnace bottom ash (FBA) and Lytag (LG) were used in the current study to replace ordinary portland cement (OPC), natural sand (NS) and coarse aggregate (CA), respectively, and thereby to manufacture lightweight concrete (LWC). Two control mixes containing no replacement materials were designed with a 28-day compressive strength of 20 N/mm2 and 40 N/mm2. For each compressive strength, three different mixes, viz. (a) 100%OPC+100%NS + 100%CA, (b) 100%OPC + 100%FBA + 100%LG and (c) 70%OPC + 30%FA + 100%FBA + 100%LG, were manufactured with slump in the range of 30 ~ 60 mm. The density, compressive strength, pull-off surface tensile strength, air permeability, sorptivity and porosity of the concretes were investigated. The results indicated that it is possible to manufacture lightweight concrete with density in the range of 1560-1960 kg/m3 and 28-day compressive strength in the range of 20-40 N/mm2 with various waste materials from thermal power plants. However, the introduction of FBA into concrete would cause detrimental effect on the permeation properties of concrete. With part of OPC replaced with FA, the strength decreased, but the permeability of the resulting concrete improved. 1.

Introduction

Lightweight concrete (LWC) has been successfully used since the ancient Roman times and it has gained its popularity due to its lower density and superior thermal insulation properties [1]. Compared with normal weight concrete (NWC), LWC can significantly reduce the dead load of structural elements, which makes it especially attractive in multi-storey buildings. However, most studies on LWC concern “semilightweight” concretes, i.e. concrete made with lightweight coarse aggregate and natural sand. Although commercially available lightweight fine aggregate has been used in investigations in place of natural sand to manufacture the “total-lightweight”

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concrete [2, 3], more environmental and economical benefits can be achieved if waste materials can be used to replace the fine lightweight aggregate. Lytag is one of the most commonly used lightweight aggregates, which is manufactured by pyro-processing fly ash (FA), while FA and furnace bottom ash (FBA) are two waste materials from coal-fired thermal power plants. They are, respectively, lighter than traditional coarse aggregate, OPC and natural sand. The previous investigations carried out by the authors on using FBA from a thermal power plant in Northern Ireland as a sand replacement material indicated that FBA could be a potential fine aggregate in NWC for certain applications [4, 5]. However, the application of FBA in structural LWC is not well defined. Therefore, the current study investigates the possibility of manufacturing structural LWC with FA, FBA and Lytag

2. Experimental Program
2.1 Materials The cement used was the Class 42.5N portland cement supplied by Blue Circle, U.K., complying with BS 12: 1991 [6]. For the control mixes, the coarse aggregate used was 10 mm crushed basalt and the fine aggregate used was medium graded natural sand complying with BS 882: 1992 [7]. Both materials are from the local sources in Northern Ireland. They were oven dried at 40oC for 24 hours and cooled to 20oC before using in the manufacture of concrete. The FA and FBA used were supplied by Kilroot Power Station in Northern Ireland, U.K. The FBA was dried firstly in an oven at 105oC for 24 hours and then allowed to cool for 24 hours at 20oC. The FBA that passed 5 mm sieve (hereafter FBA sand) was used to replace natural sand. The Lytag used was with a size of 8 mm and was supplied by Finlay Concrete Products, Northern Ireland, U.K. It was also oven dried at 40oC for 24 hours and cooled to 20oC...

References: 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. Chandra, S. and Berntsson, L. Lightweight aggregate concrete: science, technology and applications. Noyes Publications. Berra, M. and Ferrara, G. “Normal weight and total-lightweight high-strength concretes: A comparative experimental study,” SP-121, 1990, pp.701-733. Kayali, O.A. and Haque, M.N. “A new generation of structural lightweight concrete,” ACI, SP-171, 1997, pp. 569-588. Bai, Y. and Basheer, P.A.M. “Influence of Furnace Bottom Ash on properties of concrete,” Proceedings of the Institution of Civil Engineers, Structure and Buildings 156, February 2003, Issue 1, pp. 85-92. Bai, Y. and Basheer, P.A.M. “Properties of concrete containing Furnace Bottom Ash as a sand replacement material,” Proceedings of structural faults and repair (CD-ROM), London, July 1-3, 2003. British Standards Institution. “Specification for Portland Cements,” BSI, London, 1991, BS 12. British Standards Institution. “Specification for Aggregates from Natural Sources for Concrete,” BSI, London, 1992, BS 882. British Standards Institution. “Method of Mixing and Sampling Fresh Concrete in the Laboratory,” BSI, London, 1986, BS1881: Part 125. “Lytag: an introduction to Lytag concrete,” September, 1996. British Standards Institution. “Method for Determination of Air Content of Fresh Concrete,” BSI, London, 1983, BS1881: Part 106. British Standards Institution. “Method for Determination of Slump,” BSI, London, 1983, BS 1881: Part 102. British Standards Institution. “Method for Determination of Compressive Strength of Concrete Cubes,” BSI, London, 1983, BS 1881: Part 116. British Standards Institution, “Methods for determination of density of hardened concrete,” BSI, London, 1983, BS 1881: Part 114. Basheer, P.A.M., Long, A.E. and Montgomery, F.R. “The Autoclam: A new test for permeability,” Concrete, July/August, 1994, pp. 27-29. Long, A.E. and Murray, A.M. “Pull-off test for in-situ concrete strength,” Concrete, Dec. 1981, pp. 23-24. British Standards Institution. “Method for determination of water absorption,” BSI, London, 1983, BS 1881: Part 122. Swamy, R.N. and Lambert, G.H. “Microstructure of Lytag aggregate,” The International Journal of Cement Composites and Lightweight Concrete (3), November 4, 1984.
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18. Long, A.E., Basheer, P.A.M. and Montgomery, F.R. “In-site permeability testing: A basis for service life prediction,” Proceeding of the Third CANMET/ACI International Symposium, Aukland, New Zealand, ACI SP-171, pp. 651-670. 19. Bamforth, P.B. “The properties of high strength lightweight concrete,” Concrete 21(4), April 1987, pp. 8-9.
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