Efficient Strengthening Technique to Increase the Flexural Resistance of Existing RC Slabs
Publication: Journal of Composites for Construction
Volume 12, Issue 2
Abstract
Composite materials are being used with notable effectiveness to increase and upgrade the flexural load carrying capacity of reinforced concrete (RC) members. Near-surface mounted (NSM) is one of the most promising strengthening techniques, based on the use of carbon fiber-reinforced polymer (CFRP) laminates. According to NSM, the laminates are fixed with epoxy based adhesive into slits opened into the concrete cover on the tension face of the elements to strength. Laboratory tests have shown that the NSM technique is an adequate strengthening strategy to increase the flexural resistance of RC slabs. However, in RC slabs of low concrete strength, the increase of the flexural resistance that NSM can provide is limited by the maximum allowable compressive strain in the compressed part of the slab, in order to avoid concrete crushing. This restriction reduces the effectiveness of the strengthening, thus limiting the use of the NSM technique. A new thin layer of concrete bonded to the existing concrete at the compressed region is suitable to overcome this limitation. Volumetric contraction due to shrinkage and thermal effects can induce uncontrolled cracking in the concrete of this thin layer. Adding steel fibers to concrete [steel fiber-reinforced concrete (SFRC)], the postcracking residual stress can be increased in order to prevent the formation of uncontrolled crack patterns. In the present work, the combined strengthening strategy, a SFRC overlay and NSM CFRP laminates, was applied to significantly increase the flexural resistance of existing RC slabs. Experimental results of four-point bending tests, carried out in unstrengthened and strengthened concrete slab strips, are presented and analyzed.
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Acknowledgments
The writers acknowledge the financial support of the Portuguese Science and Technology Foundation (FCT), Ph.D. Grant No. UNSPECIFIEDSFRH/BD/11232/2002. Thanks also go to the companies “Companhia Geral de Cal e Cimento S.A. (SECIL),” Sika S.A., “Central do Pego,” “Pedreiras Bezerras,” Bekaert NV, “DegussaConstruction Chemicals Portugal S.A.,” S&P Reinforcement, which generously have supplied cement; overlay bond product; fly ash; aggregates; steel fibers; superplasticizer and CFRP adhesive; and CFRP laminate, respectively.
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Information & Authors
Information
Published In
Journal of Composites for Construction
Volume 12 • Issue 2 • April 2008
Pages: 149 - 159
Copyright
© 2008 ASCE.
History
Received: Aug 24, 2006
Accepted: Mar 26, 2007
Published online: Apr 1, 2008
Published in print: Apr 2008
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