Composites Part B: Engineering

Volume 91, 15 April 2016, Pages 205-218

Experimental testing of basalt-fiber-reinforced polymer bars in concrete beams

Introduction

The service life of reinforced-concrete (RC) structures may be shortened due to the corrosion of steel reinforcement and related types of deterioration. Although routine maintenance is needed to counter durability-related deterioration, the cost of repairing, rehabilitating, or strengthening of steel RC structures can be high [1], [2]. New materials, such as fiber-reinforced polymer (FRP), which is non-corrodible by nature, can be used, especially in harsh environmental conditions, to eliminate corrosion problems.

The use of glass-, carbon-, and aramid-FRP (GFRP, CFRP, and AFRP) reinforcement has been extensively investigated and used as reinforcement in concrete structures. The current design codes and guidelines such as ACI 440.1R [3], CSA S806 [4], and CSA S6 [5] allow the use of GFRP, CFRP, and AFRP as the main reinforcement in concrete structures and provide design recommendations for using these bars. Advances in FRP technology, however, have resulted in increasing demand to introduce new types of fibers such as basalt fibers. Wu et al. [6] reported that basalt-FRP (BFRP) bars are the most recent FRP composite materials developed to enhance the safety and reliability of structural systems compared to GFRP, CFRP, and AFRP composites. Nevertheless, fundamental studies on and relevant applications of BFRP are still limited because the technology is relatively recent compared to other FRP composites. Besides, the current FRP material specifications and design codes do not include BFRP as an FRP alternative.

Background

Basalt is a natural inorganic material that is found in volcanic rocks originating from frozen lava, with a melting temperature between 1500 °C and 1700 °C [7], [8]. The molten rocks are then extruded through small nozzles to produce continuous filaments of basalt fiber with diameters ranging from 13 to 20 μm [9]. BFRP fibers lie between glass and carbon for both stiffness and strength [10], [11]. The good properties of basalt fiber [12], combined with cost-effective manufacturing, have led to

Research project

With the main objective of integrating BFRP reinforcement into current FRP design codes and standards, an extensive research project is being conducted at the University of Sherbrooke, Quebec, through the activities of the NSERC Research Chair in FRP Reinforcement for Concrete Infrastructure. The project includes (i) Part I: short- and long-term characterization of newly developed BFRP bars; (ii) Part II: structural testing of full-scale concrete bridge deck slabs reinforced with BFRP bars, and

Reinforcing bars

Basalt-fiber-reinforced polymer (BFRP) bars (Magmatech, London, UK) 10, 12, and 16 mm in diameter were used as tension reinforcement in the tested beams. The bars had a sand-coated surface over helical wire wrapping, as shown in Fig. 1, to enhance the bond between the bars and the surrounding concrete. The fiber content of the BFRP bars was 87.2%, 90.6%, and 89.9% (by weight) for the 10, 12, and 16 mm diameters, respectively. The physical characterization of the tested BFRP bars can be found

First cracking moment

All beams behaved similarly until first cracking. Their cracking loads and precracked stiffness were essentially the same regardless of reinforcement ratio. Table 3 provides the cracking moments of all tested beams. The reported cracking moment, excluding the self-weight of the beams, ranged from 7.24 to 9.87 kN m with an average of 8.84 kN m. This value is approximately 13.5% of the average ultimate moment capacity. The cracking moments, Mcr, were predicted using Eq. (4):${M}_{\text{cr}}=\frac{{f}_{\text{r}}×{I}_{\text{g}}}{{y}_{\text{t}}}$where the

Crack width

The average kb value calculated based on the beam test results was used in predicting the crack width of each beam. The crack width was calculated using Eq. (6). Table 5 provides a comparison between the average measured crack widths of the first three flexural cracks and the predicted crack widths at 0.3Mn and 0.67Mn using CSA [4] (Eq. (6)). Since the crack width equation of ACI [29] is the same as that of CSA [5], it was also used in predicting the crack width of the tested beams. The

Summary and conclusion

This experimental study aimed at determining the bond-dependent coefficient (kb) and investigating the structural performance of newly developed sand-coated BFRPs bars in normal-strength concrete beams. A total of six concrete beams reinforced with BFRP bars were constructed and tested up to failure. The tested beams measured 200 mm wide, 300 mm high, and 3100 mm long. BFRP bars sizes of 10, 12, and 16 mm with sand-coated surfaces over helical wrapping were used. The beam specimens were tested

Acknowledgments

The authors would like to express their special thanks and gratitude to the Natural Science and Engineering Research Council of Canada (NSERC)-Canada Research Chair in Advanced Composite Materials for Civil Structures and the Fonds de la recherche du Quebec–Nature et Technologie–(FRQ-NT) for their financial support, MagmaTech Ltd (United Kingdom) for the donation of the Basalt FRP bars, and for the technical help provided by the staff of the structural lab of the Department of Civil Engineering

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