Accepted Manuscript: Composites Part B
Accepted Manuscript: Composites Part B
Accepted Manuscript: Composites Part B
PII: S1359-8368(18)32267-4
DOI: 10.1016/j.compositesb.2018.08.065
Reference: JCOMB 5895
Please cite this article as: Ali AH, Mohamed HM, Benmokrane B, ElSafty A, Chaallal O, Durability
performance and long-term prediction models of sand-coated basalt FRP bars, Composites Part B
(2018), doi: 10.1016/j.compositesb.2018.08.065.
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to
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2 Bars
3 Ahmed H. Ali,1,3 Hamdy M. Mohamed,2,3 Brahim Benmokrane,2 Adel ElSafty,4 and Omar
4 Chaallal1
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6 Department of Construction Engineering, École de Technologie Supérieure, Montreal, Canada.
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7 Department of Civil Engineering, University of Sherbrooke, Sherbrooke, Quebec, Canada.
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8 Department of Civil Engineering, Helwn University, Cairo, Egypt.
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9 Civil Engineering, School of Engineering, University of North Florida, Jacksonville, Florida,
10 USA.
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11 Adel.el-safty@unf.edu
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24 ABSTRACT
25 Basalt-fiber-reinforced polymer (BFRP) bars are expected to provide benefits that are
26 comparable or superior to other types of FRP while being significantly cost-effective. However,
27 extensive investigations are needed to evaluate the long-term characteristics and durability
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28 performance of these bars. This article presents an experimental study that investigated the
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29 physical, mechanical, microstructural, and durability characteristics of newly developed basalt-
30 fiber-reinforced polymer (BFRP) bars. The physical, mechanical properties and microstructural
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31 characteristics were evaluated first on the unconditioned BFRP bars. The durability performance
32 of the BFRP bars was then assessed by conducting the mechanical tests, such as transverse-shear
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test, flexural test, and interlaminar-shear test, on the specimens after different exposure periods
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34 (1,000; 3,000; and 5,000 h) at 60oC. Thereafter, the BFRP bar properties were assessed and
compared with the values obtained on the unconditioned specimens. The test parameter was
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36 conditioning time (1,000; 3,000; and 5,000 h). The test results revealed that the unconditioned
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37 BFRP bars had the best physical properties. On the other hand, the long-term durability
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Keywords: Basalt-FRP; tensile strength; alkaline solution, flexural strength, transverse shear-
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47 INTRODUCTION
48 The durability and life performance of reinforced concrete structures have become a major
49 concern for the infrastructure systems (Wang et al. 2016a; Ali et al. 2018a). One of the main
50 factors reducing durability and service life of reinforced concrete structures is the corrosion of
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51 embedded steel reinforcement bars, particularly where deicing salts are routinely used, such as in
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52 concrete deck slabs and parking garages (Wang et al. 2015; Ali et al. 2018b). Recently, fiber-
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54 both new constructions and rehabilitation and strengthening of existing structures, because of
55 their noncorrodible nature, higher tensile strength, and lower weight relative to conventional
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steel reinforcing bars (ACI 440.1R-15; Arias et al. 2012; Benmokrane et al. 2018, 2016a; Wang
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57 et al. 2015; Ali et al.2017a). FRPs are available with a wide range of mechanical properties
(tensile strength, bond strength, and modulus of elasticity) and are made with high-tensile-
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59 strength fibers such as glass, carbon, and aramid embedded in polymer matrices as polyesters,
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60 vinyl esters, or epoxies. Moreover, FRPs can be produced as bars, ropes, tendons, and grids in a
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61 wide variety of shapes and surface configurations as well as with varied characteristics (ACI
63 Recent developments in FRP technology and innovate, new types of fibers—such as basalt fibers
64 which is made from basalt rock —are being introduced to manufacture basalt fiber-reinforced
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65 polymers (BFRPs). BFRP is the most recently FRP composite, appearing within the last decade
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66 (Wang et al. 2016b, 2014; Shen et al. 2016; Benmokrane et al. 2015). BFRPs are non-corrosive,
67 non-magnetic, posses high resistance against low and high temperatures, good chemical
69 resistance and durability, as well as the lower potential cost with respect to many other FRP
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70 materials. Consequently, the basalt fibers are ideally appropriate for applications involving high
71 temperature, chemical resistance, durability, mechanical strength, and low water absorption
72 (INFOMINE 2007). In comparison to others FRP types, BFRP fibers lie between glass and
73 carbon for both stiffness and strength. BFRP has higher strength and modulus, similar cost, and
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74 greater chemical stability compared with E-glass FRP. Furthermore, it offers over five times the
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75 strength and one-third the density of commonly used low-carbon steel bars (Arias et al. 2012;
76 Zhishen et al. 2012). In the past decade, numerous studies on the durability of glass and carbon
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77 FRP bars have been conducted which mainly comprises their performances under alkali, acid and
78 salt environments [Ng and Lee 2002; Tȁljsten et al. 2003; Davalos et al. 2011; Won and Park
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(2006); Chen et al. 2006 and 2007; Karbhari et al. 2007; Robert et al. 2010; Davalos et al. 2012,
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80 Benmokrane et al. 2016 (a, b), 2012, and 2014]. The majority of these studies has highlighted on
the short-term performance of FRP bars. Moreover, most of these studies have investigated the
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82 durability characteristics of glass FRP bars for reinforced concrete structures. Few studies,
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83 however, have assessed the physical, mechanical and durability characteristics of basalt-FRP, in
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84 order to understand their behavior and generate higher confidence in these newly developed FRP
85 materials, under alkali and salt environments (Wang et al. 2016, 2014; Shen et al. 2016;;
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86 Benmokrane et al. 2015, Elgabbas et al. 2015, Zhishen et al. 2012). Sim et al. (2005)
87 investigated the applicability of the basalt, glass, and carbon fibers as a strengthening material
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88 for structural concrete members through various experimental works for durability, mechanical
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89 properties, and flexural strengthening at elevated temperatures. They reported that immersing
90 basalt and glass fibers in an alkaline solution led to volume and strength loss through a surface
91 reaction, whereas carbon fibers did not show any significant strength reduction. The basalt fibers,
92 however, retained about 90% of their strength at ambient temperature after exposure at 600°C for
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93 2 h. Aging results indicate that the interfacial region in basalt composites might be more
95 however, might also be more durable than the glass-epoxy interface in tension-tension fatigue,
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97 An experimental study was conducted, by Parnas et al. 2007, to determine if BFRP composites
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98 were feasible, practical, and a beneficial alternative for transportation applications. The
99 researchers of the mentioned study concluded that the chemical composition of basalt fibers is
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100 close to glass fibers, except that the basalt contains a high ratio of iron oxide, conferring its
101 brown color. Aging results indicate that the interfacial region in basalt composites might be more
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vulnerable to environmental damage than in glass composites. The basalt-epoxy interface,
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103 however, might also be more durable than the glass-epoxy interface in tension-tension fatigue,
because basalt composites have a longer fatigue life. In 2008, Wang et al. investigated the
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105 chemical durability and mechanical properties of a kind of alkali-proof basalt fiber and its
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106 reinforced epoxy resin matrix composites in alkaline solution for 3 months. The basalt fiber was
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107 boiled in distilled water, sodium hydroxide and hydrochloric acid, respectively. Then the mass
108 loss and strength change of the fibers were studied showing that the alkali resistance of the basalt
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109 fiber is better than acid resistance. The experimental results also showed that, after exposure, the
110 modulus of the BFRP was unaffected, but its strength decreased by 40%.
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111 In the last two years, an extensive research project has been conducted at the Department of Civil
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112 Engineering at the University of Sherbrooke to assess the short-term and long-term
113 characteristics of newly developed BFRP bars as a preliminary step in introducing these new
114 materials into pilot projects and FRP design codes and material specification (Benmokrane et al.
115 2015; Elgabbas et al. 2015). Benmokrane et al. 2015 presented an experimental study that
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116 investigated the physical, mechanical, and durability characteristics of three different types of
117 fiber-reinforced polymer (FRP) bars made of basalt and glass fibers with vinylester and epoxy
118 resins. They found that the glass/vinylester composite had the best physical and mechanical
119 properties and lowest degradation rate after conditioning in alkaline solution. The basalt/epoxy
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120 composite ranked second, while the basalt/vinylester composite evidenced the lowest physical
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121 and mechanical properties and exhibited significant degradation of its physical and mechanical
122 properties after conditioning. Elgabbas et al. 2015 investigated the durability and long-term
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123 performance of BFRP bars in an alkaline solution (up to 3000 h, at 60oC) to determine their
124 suitability as internal reinforcement for concrete elements. It was noticed that the BFRP bars had
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good mechanical behavior and could be placed in the same category as grade II and grade III
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126 GFRP bars (according to tensile modulus of elasticity).
This paper represents an experimental investigation to determine the physical, mechanical, and
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128 durability characteristics of newly developed BFRP bars, manufactured by a Canadian company
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129 (Pultrall Inc.), as corrosion-resistant reinforcing material for bridge deck, girder, and pile
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130 applications in marine and aggressive environment. Since BFRPs have not been included in
131 design standards and specifications yet, the results of this experimental study will contribute to
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135 Sand coated basalt FRP bars manufactured by a Canadian company (Pultrall Inc. 2015) were
136 used in this study as shown in Fig. 1. The BFRP bars manufactured from continuous basalt fibers
137 impregnated in vinylester resins using the pultrusion process. The nominal cross-sectional area
138 of the bar is 284 mm2, as reported by the manufacturer, while the actual (immersion) cross-
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139 sectional area is 362 mm2, as specified in CSA-S806-12 (2012). The mechanical properties
140 reported herein were calculated using the nominal cross-sectional area.
142 For this study, tensile [ASTM D7205 (ASTM 2011)], transverse shear [ASTM D7617 (ASTM
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143 2011)], flexural (ASTM D4476 (ASTM 2009)], and short-beam shear testing [ASTM D4475
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144 (ASTM 2008)] were conducted as the appropriate mechanical tests. The BFRP bars were
145 provided into 2,400; 350; and 300 mm lengths for tensile strength, transverse shear strength, and
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146 flexural properties, respectively. In addition, some specimens were cut into 120 mm lengths so
147 that the short-beam shear test could be performed according to ASTM D4475 (ASTM 2008). For
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tensile testing, Fig. 2b shows the dimensions of the typical tensile test specimens as specified in
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149 ASTM D7205.
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151 The basalt-FRP specimens were completely immersed in alkaline solution inside stainless steel
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152 containers specially manufactured for the study (Fig. 3). The alkaline solution was prepared
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153 using calcium hydroxide, potassium hydroxide, and sodium hydroxide (118.5 g of Ca(OH)2 +
154 0.9 g of NaOH + 4.2 g of KOH in 1 L of deionized water) according to CSA S806 and ACI
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155 440.3R. The pH of alkali solution was 12.8. It is worth noting that the alkaline environment in
156 concrete has a pH above 12 (ACI 440.4R-04). The BFRP specimens and stainless steel
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157 containers were kept at 22°C and 60°C for 1,000; 3,000; and 5,000 h of conditioning. The
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158 stainless steel containers were covered with polyethylene sheeting to avoid water evaporation
159 during conditioning. Furthermore, the water level was kept constant throughout the study to
160 avoid a pH increase that could result from decreased water level and a significant increase of
161 alkaline ions in the solution. The immersion temperatures were chosen to accelerate the
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162 degradation effect of aging, but they were not high enough to produce any thermal-degradation
163 mechanisms. The BFRP specimens were removed from the alkaline solution after 1,000, 3,000,
164 and 5,000 h and tested under transverse shear, flexural, and short-beam shear to compare their
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166 PHYSICAL CHARACTERIZATION OF BFRP BARS
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167 The Physical and microstructural analyses were conducted on BFRP specimens. Physical
168 properties included: (1) cross section area (2) basalt-fiber content, (3) moisture absorption, (4)
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169 cure ratio, (5) glass-transition temperature, (6) transverse coefficient of thermal expansion, and
170 (7) wicking. These properties were determined according to CSA S807. Moreover, optical
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microscopy (OM), and scanning electronic microscopy (SEM) analyses were performed to
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172 investigate the material’s microstructure.
Cross-Sectional Area
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174 Three 280 mm long specimens were prepared and tested to determine the actual cross-sectional
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175 area of the BFRP bars as specified in CSA-S806-12 (2012), Annex A. All BFRP specimens
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176 were kept in the test environment for 24 hours prior to weighing and measuring. The actual
179 where, L is specimen length; V0 is the volume of water added without BFRP specimen; V1 is the
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182 Basalt fiber content was determined by thermogravimetry according to ASTM E1131. A very
183 small piece of material (a few tenths milligrams) was cut from the center of the bar, placed in
184 platinum crucible and then heated up to 550°C under inert atmosphere. The weight loss (WL) has
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185 been recorded at a temperature equal to 550°C. Since the material only contains basalt fibers and
186 resin, fiber content by weight was then calculated according to the following equation:
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189 Water-Immersion Test
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190 The moisture uptake at saturation of BFRP bars was determined according to ASTM D570,
191 except that the immersions were performed in tap water instead of distilled water. Three 50-mm-
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192 long specimens were cut, dried, and weighed prior to immersion in water at 50°C for three
193 weeks. The samples were removed from the water after three weeks, surface dried, and weighed.
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The water content at saturation in weight percent (Ws) was calculated using Equation 3.
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195 Ws = 100 · (Ps – Pd)/Pd (3)
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196 where Ps and Pd are the sample weights in saturated and dry states, respectively.
198 Cure ratio was determined according to ASTM D5028. The enthalpy of polymerization of the
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199 sample is measured by DSC and compared to the enthalpy of polymerization of pure resin,
200 taking into account the weight percentage of resin in the matrix. Thirty to fifty milligrams of
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201 sample were accurately weighed and placed in aluminum crucible. The samples were then heated
202 from room temperature to 200°C at a heating rate of 20°C/min and the area of the peak of
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203 polymerization was calculated. The measurement was carried out on 3 specimens.
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205 Glass transition temperature, Tg, was determined for 12.5 mm BFRP specimens by Differential
206 Scanning Calorimetry (DSC) using ASTM E 1131 test method. Thirty to forty milligrams of
207 composite sample were weighed and placed in an aluminum pan. The sample was then heated up
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208 to 200°C under nitrogen at a heating rate of 20°C/min. The value of Tg was taken at the mid-
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212 All BFRP bars were tested under tension according to the ASTM D7205. Each specimen was
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213 instrumented with a linear variable differential transformer (LVDT) to capture the elongation
214 during testing. The test was carried out using a Baldwin testing machine and the load was
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215 increased until failure. Before test, steel pipes were attached to the BFRP test specimens
216 according to CSA S806-12, Annex B “Anchor for testing FRP specimens under monotonic,
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sustained, and cyclic tension”. Fig. 2 shows the test setup, dimensions of test specimen, and
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218 overview of the BFRP specimens attached with steel tubes. The test specimens were
instrumented with one linear variable differential transformer (LVDT, 200 mm length) to capture
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220 specimen elongation during testing. For each tensile test, the specimen was mounted in the
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221 tensile machine with the steel pipe anchors gripped by the wedges of the upper and the lower
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222 jaws of the machine. The average loading rate ranged between 250 to 560 MPa/min. The applied
223 load and bar elongation were recorded during the test using a data acquisition system monitored
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224 by a computer. Due to the brittle nature of FRP, no yielding occurs and the stress-strain behavior
227 Transverse shear tests were performed according to ASTM D7617 (ASTM 2011) to characterize
228 the BFRP bars. The transverse shear strengths of BFRP bar specimens were measured on
229 samples subjected to elevated temperature (60oC) for 1,000; 3,000; and 5,000 h of immersion in
230 alkaline solution. This property was investigated to provide some indications on the retention of
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231 the matrix related mechanical properties of BFRP bars subjected to high temperatures and
232 alkaline environment. As shown in Fig. 4, the test setup consisted of a 230 × 100 × 110 mm steel
233 base equipped with lower blades spaced at 50 mm face to face, allowing for the double
234 transverse-shear failure of the specimen caused by an upper blade. All specimens were cut at a
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235 length of 350 mm and tested in shear according to ASTM D7617. Six unconditioned and
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236 conditioned specimens 350 mm in length were tested under laboratory conditions with an MTS
237 810 testing machine equipped with a 500-kN load cell. A displacement-controlled rate of 1.3
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238 mm/min was used during the test, which yielded between 30 and 60 MPa/min until specimen
239 failure. The loading was done without subjecting the test specimens to any shock. The
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transverse-shear strength of BFRP bars, τ u , was calculated as τ u = Ps / 2 A , where Ps is the failure
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241 load (N); A is the cross-sectional area (mm2).
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243 Flexural tests were conducted on unconditioned and conditioned BFRP specimens for 1,000;
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244 3,000; and 5,000 h, at 60oC (ASTM 4476). All BFRP specimens were cut at a length of 300 mm
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245 and an overhang of 10% of the supported span was allowed at each support as shown in Fig. 5.
246 Six unconditioned and conditioned specimens were tested under laboratory conditions using
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247 MTS 810 testing machine equipped with 500 kN load cell. The specimens were loaded at the
248 midspan with a circular nose; the specimen ends rested on two circular supports that allowed the
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specimens to bend. A displacement-controlled rate of 3.0 mm/min was used during the test. The
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250 rate of loading was done without subjecting the test specimen to any shock. The applied load and
251 deflection were recorded during the test using a data acquisition system monitored by a
252 computer. The flexural strength of the BFRP bars, fu, was determined as fu = PLC/(4I), where P is
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253 the failure load, L is the clear span, C is the distance to the centroid of the extreme-most fibers,
256 In pultruded FRP bars, fibers are arranged unidirectionally and bonded with the polymer matrix,
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257 the horizontal stresses would be more conducive to inducing interface degradation than
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258 transverse-shear stresses (Park et al. 2008). The shear test was conducted on six specimens of
259 BFRP bar according to ASTM D4475 (ASTM 2008) in order to calculate the interlaminar shear
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260 strength, which is governed by the fiber/matrix interface. The tests were carried out with a 500-
261 kN MTS 810 testing machine. The distance between the shear planes was set to 6 times the
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nominal diameter of the FRP bars. Fig. 6 shows the test setup and typical modes of failure of the
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263 tested specimens. A displacement-controlled rate of 1.3 mm/min was employed during the test.
The applied load was recorded with a computer-monitored data acquisition system. The
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265 interlaminar shear strength, Su, of the BFRP bars was determined as S u = 0.849 P / t 2 , where Su
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266 interlaminar-shear strength (MPa); P = shear failure load (N); and t = thickness of BFRP
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270 Table 1 presents the physical properties of the unconditioned basalt-FRP bars, where the glass
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transition temperature (Tg) was determined with differential scanning calorimetry (DSC) [ASTM
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272 D3418 (ASTM 2012b)] (see Fig.7). From Table 1, the test results indicated that the basalt-fiber
273 content in weight of basalt-FRP bars was 81.0%. The mass percentages of water uptake after 24
274 h, 7 days and at saturation were found to be 0.04%, 0.18, and 0.25% on average. The water-
275 absorption values obtained not exceed the limits specified in CSA S807 and ACI 440.6M-08
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276 (1%). The material’s cure ratio is high (100%). Table 1 presents, also, the Tg values for the first
277 and second heating of unconditioned samples (reference samples). Note that, for the
278 unconditioned specimen, the Tg corresponding to the second heating run was close to the Tg
279 corresponding to the first scan. These results confirm the high cure ratio of more than 99%
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280 measured by DSC and shown in Table 1.
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281 Scanning electron microscopy (SEM) observations and image analysis were performed to
282 observe the microstructure of BFRP specimens. All specimens observed in the SEM were first
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283 cut, polished, and coated with a thin layer of gold-palladium by a vapor-deposit process. After
284 coating the surfaces, microstructural observations were performed on a JEOL JSM-840A SEM.
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These observations were conducted to see any defect in polymer matrix, basalt fibers, or
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286 interfaces, if any. A general view of basalt-FRP bar was obtained as shown in Fig.8. No pore or
void was found in a SEM micrograph at the interfaces between the fibers and matrix. It has to be
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288 noted that the material contains fibers with various diameters as shown in Fig. 9. SEM
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289 micrograph of interface between basalt and resin matrix in Fig. 10 clearly shows that no defect in
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290 polymer matrix, basalt fibers, or interfaces was observed. The bonding between the basalt fibers
291 and the thermosetting resin is good since there were no free gaps at the interface.
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294 The tensile test of unconditioned BFRP specimens showed an approximately linear behavior up
295 to failure. Specimens failed through rupture of fibers. The failure was accompanied by
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296 delamination of fibers and resin, as shown in Fig. 11. Table 2 presents the experimental results
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297 obtained during the tensile tests concerning the ultimate tensile strength, modulus of elasticity,
298 and ultimate strain of unconditioned BFRP bars. As shown in Table 2, the tensile strength,
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299 modulus of elasticity, and ultimate strain of unconditioned BFRP bars were equal to 1,646±12
300 MPa; 69.7 GPa; and 2.4%, while these values, as reported by the manufacturer, are 1,636 MPa;
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64 GPa; and 2.5%, respectively. Fig. 11 shows the mode of failure during the tensile tests for
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302 unconditioned (reference) BFRP bars.
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304 Table 2 shows that the transverse-shear strength of the unconditioned basalt-FRP bars was
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305 241±2.1 MPa, while Table 3 shows the transverse-shear strength and strength-retention ratio of
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306 the tested BFRP bars after 1,000, 3,000, and 5,000 h of immersion in the alkaline solution at
307 60°C. Table 3 indicates that the BFRP bars were affected by accelerated aging with a transverse-
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308 shear strength reduction of 12% after 5,000 h of immersion. Fig. 12 shows the effect of the
309 alkaline solution on the transverse shear strength after different exposure times. The BFRP bars
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310 exhibited no significant reductions in the early stages (less than 3,000 h).
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312 The three-point flexural strength, flexural modulus of elasticity, and ultimate outer-fiber strain of
313 the tested unconditioned BFRP bars, are presented in Table 2. The flexural strength and flexural
314 modulus of elasticity were 653±15 MPa and 41.0 GPa, respectively. Table 3 and Fig. 13a show
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315 the experimental results obtained during the flexural tests of aged BFRP bars tested after
316 immersion in alkaline solution. Fig. 13a shows flexural strength loss observed with BFRP
317 reinforcing bars conditioned in alkaline solution during 5000 h (208 days). The BFRP bars had
318 flexural-strength reductions of 2% and 10 % after 1,000 h, and 3,000 h, while the bars showed a
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319 lower reduction of 19 % after 5,000 h. These observations confirm that the bond between the
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320 BFRP fibers and resin after conditioning was lower than that before conditioning. Consequently,
321 debonding occurring at the fiber–matrix interface caused the fibers to separate from the resin.
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322 Fig. 13a shows the effect of the alkaline solution on flexural strength. Fig. 5b shows the mode of
323 failure of failure during the flexural tests for reference and specimen aged at 60oC during 5,000
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h. It can be seen in Fig. 5a that the tested specimen was loaded until rupture occurs in the
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325 extreme tensile fibers and that aged and reference BFRP bars have similar mode of failure. Note
that the extreme compressive fibers did not show any premature compression failure. Progressive
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327 damage propagation occurred through matrix cracking, fiber breaking, and interfacial debonding
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329 Table 3 gives, also, the flexural modulus of elasticity and the retention ratio of the tested BFRP
330 bars after 1,000, 3,000, and 5,000 h of immersion. The bars had no significant differences in
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331 flexural modulus of elasticity after 5,000 h. The reduction ranged from 3% to 11% in comparison
332 to the references. Fig. 13b illustrates the effect of the alkaline solution at 60oC on the flexural
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333 modulus of elasticity, with all bar specimens exhibiting a steady reduction rate.
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335 The short-beam shear test revealed that the unconditioned BFRP bars had the interlaminar-shear
336 strength of 30.2±2.7 MPa, (Table 2). It is worth mentioning that the high values of the
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337 interlaminar-shear strength reveal a strong interface between the resins and reinforcing fibers,
338 which was clarified in the SEM analysis of the unconditioned BFRP specimen.
339 Table 3 also shows the apparent horizontal shear (interlaminar shear) strength and strength-
340 retention ratios of the tested FRP bars after 1,000, 3,000, and 5,000 h of immersion in alkaline
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341 solution. The reduction ratio for the BFRP bars after 5,000 h was 21%. Fig. 14 shows the effect
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342 of the alkaline solution on the interlaminar-shear strength, with the BFRP bars, for different time
343 of immersions.
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344 PREDICTION OF LONG-TERM BEHAVIOR AND SERVICE LIFE FOR
performance of FRP (Bank et al. 2003; Robert et al. 2013, 2009; Benmokrane et al. 2016, Chen
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349 et al. 2006, 2007). Eq. (4) expresses the Arrhenius relation-ship, in terms of the degradation rate
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351 k= Ae RT (4)
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352 where k = degradation rate; A = constant relative to the material and degradation process; Ea =
353 reaction’s energy of activation; R = universal gas constant; and T = temperature in °C. The
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354 primary assumption with this model is that only one dominant degradation mechanism of the
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355 material operates during the reaction and that this mechanism will not change with time and
356 temperature during the exposure (Chen et al. 2007). Only the rate of degradation will be
358 Dejke (2001) used another approach to generate a relative TSF. He proposed using the TSF to
359 transform the time in the accelerated test to actual service lives for GFRP reinforcement.
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360 Because the time for a certain reaction to take place must be proportional to the inverse of the
361 rate of reaction, Dejke (2001) proposed determining the TSF in accordance with Eq. (5).
1 1
B( − )
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TSF = 1 = e T1 + 273.15 T2 + 273.15 (5)
t2
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363 where T1 and T2 = exposure temperatures (°C); and t1 and t2 = times required to obtain a certain
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364 level of decrease in mechanical property at temperatures T1 and T2, respectively. The TSF is
sensitive to activation energy, and a good estimate of Ea is needed to generate a reasonable TSF.
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366 According to the procedure proposed by Bank et al. (2003), the natural logarithm of time to
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367 reach a set of levels of normalized performances versus 1/T, expressed as the inverse of absolute
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368 temperature (1,000/K), was used to predict the service life of the BFRP bars at mean annual
369 temperatures (MAT) of 10°C. The temperature of 10°C corresponds well to the mean average
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370 temperature of northern regions, where deicing salts are often used. A coefficient of
371 determination (R2) value close to 1 was desired. ASTM procedures, however, recommend a
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372 minimum value of 0.80 for acceptability; the obtained R2 values were between 0.96 and 0.99.
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373 The service-life time necessary to reach the established tensile-strength retention levels (PR) can
374 be extrapolated for any temperature from the Arrhenius plot. Consequently, predictions were
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375 made for transverse shear-strength retention as a function of time for immersion at 10°C, and the
general relation between the PR and the predicted service life at the average temperature of 10oC
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376
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377 can be drawn (Fig. 16). The predicted time to reach the determined tensile-strength retention
378 level (PR) for the BFRP bars aged in an alkaline solution simulating the concrete environments
379 at an isotherm temperature of 10oC is approximately 150 years for a PR of more than 80%.
380 Moreover, the predicted service life of the BFRP bars aged in the alkaline solution at an isotherm
381 temperature of 10oC with a PR of less than 80% can be estimated as being infinity. These
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382 predictions show that the BFRP bars tested in this study are a high durability in a concrete
383 environment. On the other hand, the prediction curves for the BFRP bars predicted transverse
384 shear-strength retention of 82% after a service life of 75 years. Table 4 presents the transverse
385 shear-strength retention after 10, 25, 50, 75, and 100 years of service at MATs of 10°C and
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386 30°C. Table 4 indicates that, even after a service life of 100 years, which corresponds to the
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387 maximum expected service life, the shear-strength retention was still 81.3 %, for BFRP bars. At
388 30°C, the shear-strength retention of BFRP bars was 76.1, 77.0, 78.1, and 79.0% after a service
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389 life of 200, 150, 100, 75 years, respectively, (Table 4).
391
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In 2007, FIB Bulletin (40) Task Group 9.3 proposed durability design approach for FRP bars by
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392 incorporating factors of relative humidity (RH), exposed mean average temperature (MAT), and
services life (FIB 2007). The long-term design transverse shear-strength is given by Eq. (6)
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393
f fko
f fd =
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395 where ffd is a long-term design value of transverse shear-strength for BFRP bars; ffko is the
396 characteristic value of transverse shear-strength (short term), which the composite bars can resist
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397 after exposure to a practical test environment for 1,000 h and this value can be expressed as a
398
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1
η env ,t = (7)
400
[(100 − R10 ) / 100]n
401 where R10 is the standard reduction in transverse shear-strength in percent per decade
402 (logarithmic decade) due to environmental effects, which can be extrapolated from each
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403 individual degradation line (Fig. 15). The exponent n is the sum of four influence terms as shown
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406 where nmo, nT, nSL, nd are the influence terms for moisture condition, temperature, desired service
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408 It can be seen that an exponential approach is used in the design strength equation, for which the
409 reason is because the deterioration is described best by the kinetics of the chemical and physical
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410 processes (Weber 2006). This assumption itself is reasonable; however, as can be seen, the base
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411 of the exponential in expressions (6) and (7) is the strength retention (1−R10), other than the
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412 strength reduction R10. As known, the kinetics of the chemical and physical processes is linked to
413 the outer layer of BFRP bar that degrades by the environmental attacks. Hence, the power terms
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414 n, including the effects of moisture, temperature, time, and diameter, should be a link to the outer
415 degraded part of BFRP bar reflected as R10. Thus, the design strength equation in the FIB (2007)
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417 The values of the environmental influence parameter R10 of the BFRP specimens conditioned at
418 22°C, 40°C, and 60°C were 7.3%, 7.7%, and 9.5%. From the curve fitting, the shear-strength
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419 retentions after 100 years were 78%, 76%, and 68% at 22°C, 40°C, and 60°C, respectively.
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420 According to fib Bulletin 40 (2007), for instance, nmo= 1 and nSL = 3.0 at a service life of 100
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421 years, assuming a moisture-saturated condition. As adopted by Serbescu et al. (2014), nT is equal
422 to 0.5, 1.5, and 2.5 at 22°C, 40°C, and 60°C, respectively. The value R10 for all the environments
423 tested can be determined by using the average slope of the individual degradation lines,
424 assuming that the degradation rate is similar regardless of environment (Serbescu et al. 2014).
425 Thus, R10 is equal to 8.17%. The estimated shear-strength retention (1/ ηenv,b) is equal 68.1%,
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426 62.6%, and 57.5% at 22°C, 40°C, and 60°C, respectively. Noticeable differences between the
427 two methods were observed for each environmental conditioning. The differences might be
428 attributed to increased concrete strength resulting from immersion. This is not considered in the
429 equation, nor are the effects of moisture diffusion on the degradation mechanism. Table 5 reports
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430 the (1/ηenv,b) predications at different moisture-saturated conditions and mean annual
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431 temperatures (MATs) after 100 years of service life. The shear-strength retentions after 100 years
432 of service life in dry, moist, and moisture saturated environments and MATs varied from 65% to
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433 88%, as reported on Table 5. In order to validate the FIB Bulletin (40) model’s reliability, further
434 work is needed with different accelerated moist environments, different service life influence,
In this research study, new basalt-FRP bars were exposed to an alkaline solution simulating a
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437
438 concrete environment to determine the bras’ suitability as internal reinforcement for concrete
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439 elements. Physical, mechanical, microstructural analyses and durability characterization were
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440 conducted. The BFRP specimens were immersed in alkaline solution (1,000; 3,000; and 5,000 h)
441 and subjected to elevated exposure temperature (60°C) to simulate the alkaline effect of concrete.
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442 In addition, differential-scanning calorimetry (DSC) and scanning electron microscopy (SEM)
443 were used to characterize the physical properties of BFRP bar specimens. Based on the results of
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444 this study, the following conclusions may be drawn on the tested products:
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445 1- The test observation indicated that the basalt fiber content is 81% by weight and the
446 water uptake at saturation is equal to 0.25%. The cure ratio of the material is very high
447 (close to 100%) but its glass transition temperature is116oC (H) by DSC.
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448 2- Optical microscopy and electronic scanning microscopy (SEM) analysis of the
449 unconditioned BFRP bars showed that no defect in polymer matrix, basalt fibers, or
450 interfaces was observed. The bonding between the basalt fibers and the thermosetting
451 resin was good since there was no free gap at the interface.
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452 3- The results indicate that the transverse-shear strength of the BFRP specimens was slightly
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453 affected by increasing the immersion duration at higher temperature levels. After 5,000 h
454 of immersion in the alkaline solution at 60oC, test result indicated that 12 % degradation
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455 in the transverse-shear occurred.
456 4- The flexural strength of the BFRP bars was significantly affected by accelerated aging
aging (21% reduction after 5,000 h, at 60oC). The fiber–resin interface plays a significant
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461 6- According to the long-term predictions, the transverse shear-strength retention of the
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462 BFRP bars immersed in the alkaline solution will decrease by 19.8% and 23.0% after
463 150 years at an isotherm temperature of 10°C and 30°C, respectively. It was shown that
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464 the BFRP bars service life with a transverse shear-strength retention of less than 79.6 and
466 ACKNOWLEDGMENTS
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467 This study was conducted with funding from the Fonds de recherche du Quebec en nature et
468 technologie (FRQNT), the Natural Sciences and Engineering Research Council of Canada
469 (NSERC) Research Chair in Innovative FRP Reinforcement for Concrete Infrastructure, and the
470 service des matériaux d'infrastructures of the Ministry of Transportation of Quebec. The authors
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471 wish to express their gratitude and appreciation to Pultrall Inc., Thetford Mines, Quebec, for
472 material support. The technical assistance from the staff of the Structural Laboratory in the
473 Department of Civil Engineering, Faculty of Engineering at the University of Sherbrooke is also
474 acknowledged.
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475 REFERENCES
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476 ACI (American Concrete Institute). (2004). “Guide test methods for fiberreinforced polymers
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478 MI.
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485 Ali, A. H., Benmokrane, B., Mohamed, H.M., Manalo, A., and El-Safty, A. (2018b). “Statistical
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490 Load and Severe Environments on Durability Performance of Carbon-Fiber Composite Cables
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496 Type on Physical, Mechanical and Durability Performance of Glass-FRP Bars in Concrete
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506 Arias, J.P.M., Vazquez, A., and Escobar, M. E. (2012). “Use of sand coating to improve bonding
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549 Chen, Y., Davalos, J. F., Ray, I., and Kim, H. Y. (2007). “Accelerated aging tests for evaluation
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556 Davalos, J .F., Chen, Y., and Ray, I. (2012) “Long-term durability prediction models for GFRP
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558 Davalos, J.F, Chen, Y., and Ray, I. (2011). “Long-term durability prediction models for GFRP
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570 Katsuki, F., and Uomoto, T. (1995). "Prediction of Deterioration of FRP Rods due to Alkali
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571 Attack." Proceedings of the Second International RILEM Symposium (FRPRCS-2), Non-
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572 Metallic (FRP) Reinforcement for Concrete Structures, L. Taerwe, ed., E&FN Spon, London, pp.
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574 Ng, SC., and Lee, S. (2002). “A study of flexural behavior of reinforced concrete beam
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577 Parnas, R., Shaw, M., and Liu, Q. (2007). “Basalt fiber reinforced polymer composites.”
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581 Robert, M., Wang, P., Cousin, P., and Benmokrane, B. (2010). “Temperature as an accelerating
582 factor for long term durability testing of FRPs should there be any limitations.” J. Compos.
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585 Materials.” Journal of Composite Materials, Vol. 10, pp. 2-20.
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586 Shen, D., Ojha, B., Shi, X., Zhang, H., and Shen, J. (2016). “Bond stress–slip relationship
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588 Reinforced Plastics Composites, 35(9), 747-763.
589 Sim, J., Park, C., and Moon, D. Y. (2005). “Characteristics of basalt fiber as a strengthening
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material for concrete structures.” Compos. Part B, 36(6–7), 504–512.
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591 Taljsten B., Carolin, A. and Nordin, H. (2003). “Concrete structures strengthened with near
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593 Tannous, F. E., and Saadatmanesh, H. (1998). "Environmental Effects on the Mechanical
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594 Properties of E-glass FRP Rebars." ACI Materials Journal, 95(2), pp. 87-100.
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595 Wang, J., GangaRao, H., Liang, R., and Liu, W. (2016a) “Durability and prediction models of
596 fiber-reinforced polymer composites under various environmental conditions: A critical review.”
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598 Wang, J., GangaRao, H., Liang, R., Zhou, D., Liu, W., and Fang, Y. (2015). “Durability of glass
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599 fiber-reinforced polymer composites under the combined effects of moisture and sustained
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601 Wang, X., Wu, G., Wu, Z. (2014). “Evaluation of prestressed basalt fiber and hybrid fiber
602 reinforced polymer tendons under marine environment.” Material Design, 64, 721–728. 9.
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603 Wang, X., Zhao, X., Wu, Z., Zhu, Z., and Wang, Z. (2016b). “Interlaminar shear behavior of
604 basalt FRP and hybrid FRP laminates.” Journal of composite materials, 50(8), 1073-1084.
605 Won, J.P., and Park, C.G. (2006). “Effect of Environmental Exposure on the Mechanical and
606 Bonding Properties of Hybrid FRP Reinforcing Bars for Concrete Structures.” Journal of
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607 composite materials, 40(12), 1063-1076.
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608 Zhishen, W., Xin, W., Gang, W. (2012) “Advancement of structural safety and sustainability
609 with basalt fiber reinforced polymers.” Proc. of 6th International Conference on FRP
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610 Composites in Civil Engineering (CICE), Rome, Italy, IIFC, 2012, p. 29.
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629 Table 3. Retention of mechanical properties of the conditioned BFRP bars.
630 Table 4. Transverse shear-strength retention at different service-life periods at MATs of 10 and
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631 30°C based on Arrhenius model.
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632 Table 5. Transverse shear-strength retention predications after service life of 100 years based on
633 the method in fib Bulletin 40.
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Run 2 117
Moisture uptake (%) 0.25 <1.0 1.0 (D2); 0.75 (D1)
Diameter (mm) 20.0 N/A N/A
Cross-sectional area (mm2) 362 N/A N/A
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Wicking dots 0.0 N/A N/A
649 *Note: CTE = coefficient of thermal expansion. D1 and D2 classifications can be found in CSA S807-10.
650 *The mechanical properties were calculated using the nominal cross-sectional area.
651
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Short-beam shear strength (MPa) 30±0.5 -- --
Four-point flexural strength (MPa) 653±15 N/A N/A
Flexural modulus (stiffness) (GPa) 77.2±0.3 N/A N/A
698 *The mechanical properties were calculated using the nominal cross-sectional area.
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719
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60 233 96.7 642 98.3 75.8 98.2 28.0 93.3
22 239 99.1 594 90.9 76.6 99.2 27.9 93.0
Basalt-FRP
3,000 40 233 96.7 592 90.6 76.7 99.3 27.3 91.0
bars
60 230 95.4 590 90.3 73.9 95.7 27.0 90.0
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22 227 94.2 540 83.0 76.2 98.7 25.8 86.0
5,000 40 222 92.1 533 81.6 76.1 98.5 25.3 84.3
60 214 88.8 528 80.0 70.8 91.7 24.1 80.0
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721 Note: τu= Transverse shear strength (MPa); fu= Four-point flexural strength (MPa); Su = Short-beam shear strength (MPa); Ret. =
722 Retention of strength (%).
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741 Table 4. Transverse shear-strength retention at different service-life periods at MATs of 10 and
742 30°C based on Arrhenius model
Transverse shear-strength retention
Service life (%)
(Years)
10oC 30oC
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10 86.9 84.9
25 84.7 82.1
50 83.0 80.2
75 82.0 79.0
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100 81.3 78.1
150 80.2 77.0
200 79.6 76.1
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760 Table 5. Transverse shear-strength retention predications after service life of 100 years based on
761 the method in fib Bulletin 40
Moisture
Material
condition
nmo MAT (oC) nT nSL n ηenv,b 1/ ηenv,b
<5 -0.5 3.0 1.5 1.136 87.9%
Dry 5~15 0.0 3.0 2.0 1.185 84.3%
-1
(RH = 50%) 15~25 0.5 3.0 2.5 1.237 80.8%
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25~35 1.0 3.0 3.0 1.291 77.4%
<5 -0.5 3.0 2.5 1.237 80.8%
Basalt-FRP
Moist 5~15 0.0 3.0 3.0 1.291 77.4%
bars (12 mm 0
(RH = 80%) 15~25 0.5 3.0 3.5 1.347 74.2%
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in diameter)
25~35 1.0 3.0 4.0 1.406 71.1%
<5 -0.5 3.0 3.5 1.347 74.2%
Moisture
5~15 0.0 3.0 4.0 1.406 71.1%
saturated +1
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15~25 0.5 3.0 4.5 1.407 68.1%
(RH = 100%)
25~35 1.0 3.0 5.0 1.531 65.3%
762 * Note that: R10=8.17% and nSL = 3.0
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779
782 Fig. 2. Tensile test: (a) test setup; (b) specimen dimensions (mm); (b) overview of the basalt-
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783 FRP specimens attached with steel pips
784 Fig. 3. Stainless-steel container built for aging the BFRP bar specimens in alkaline solution at
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785 60ºC
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786 Fig. 4. Transverse shear test setup and specimens at failure
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788 Fig. 6. Interlaminar-shear test setup (short-beam test) and specimens at failure
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789 Fig. 7. DSC scans for glass transition temperature (Tg)
791 Fig. 9. Micrographs of the basalt-FRP bar cross section at medium magnification
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792 Fig. 10. Micrographs of the bars for basalt fiber/matrix interface
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793 Fig. 12. Effect of conditioning in the alkaline solution at 60°C on transverse-shear strength
794 Fig. 13. Effect of conditioning in the alkaline solution at 60°C on mechanical properties:
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796 Fig. 14. Effect of conditioning in the alkaline solution at 60°C on interlaminar-shear strength
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797 Fig. 15. Plot of the transverse shear strength retention of BFRP bars as a function of time
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798 Fig. 16. General relation between the PR and the predicted service life at mean annual
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807 Fig. 1. BFRP bar 20 mm in diameter used in this investigation
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700 1000 mm 700
20
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Di=38 mm
(LVDT, 200 mm)
(b) Do=48 mm
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Plastic Cover
for BFRP Bar
824
(a) (c)
825 Fig. 2. Tensile test: (a) test setup; (b) specimen dimensions (mm); (b) overview of the basalt-
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860 (a) Test setup (b) Specimens at failure
Fig. 4. Transverse shear test setup and specimens at failure.
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877 (a) Test setup (b) Specimens at failure
878 Fig. 5. Typical flexural test setup and specimens at failure
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0.0
Reference BFRP specimen
-0.1
40 60 80 100 120 140 160 180
U
919 Temperature (oC)
AN
920 Fig. 7. DSC scans for glass transition temperature (Tg)
921
M
922
923
D
924
TE
925
926
EP
927
928
C
929
AC
930
931
932
933
934
42
ACCEPTED MANUSCRIPT
935
PT
RI
SC
936
U
938
AN
939
940
M
941
942
D
943
TE
944
945
EP
946
947
C
948
AC
949
950
951
43
ACCEPTED MANUSCRIPT
PT
RI
952
SC
953 Fig. 9. Micrographs of the basalt FRP bar cross section at medium magnification
954
U
955
AN
956
957
M
958
959
D
960
TE
961
962
EP
963
964
C
965
AC
966
44
ACCEPTED MANUSCRIPT
PT
RI
967
U SC
AN
M
968
D
969 Fig. 10. Micrographs of the bars for basalt fiber/matrix interface
TE
970
971
EP
972
973
C
974
AC
975
976
977
978
979
45
ACCEPTED MANUSCRIPT
PT
RI
980
SC
981 Fig. 11. Typical failure mode of tested BFRP specimens subjected to tensile test
982
U
983
AN
984
985
M
986
987
D
988
TE
989
990
EP
991
C
AC
46
ACCEPTED MANUSCRIPT
120
Transvers Shear Strength
PT
(%) 60
45
30
RI
15
SC
0
0 1000 3000 5000
992 Exposure time (hours)
993 Fig. 12. Effect of conditioning in the alkaline solution at 60°C on transverse-shear strength
994
U
AN
995
M
996
997
D
998
TE
999
1000
EP
1001
1002
C
1003
AC
1004
1005
1006
1007
1008
47
ACCEPTED MANUSCRIPT
1009
1010
120 120
(a) Flexural strength (b) Flexural modulus of elasticity
105 100 105 100
Flexural strength retention (%)
98.3
PT
90.4 90.6 88.1
90 90
81.0
75 75
RI
60 60
45 45
SC
30 30
15
15
0
U
0
0 1000 3000 5000
0 1000 3000 5000
Exposure time (hours) Exposure time (hours)
AN
1011
1012 Fig. 13. Effect of conditioning in the alkaline solution at 60°C on mechanical properties:
M
1014
D
1015
TE
1016
1017
EP
1018
1019
C
1020
AC
1021
1022
48
ACCEPTED MANUSCRIPT
120
PT
60
45
30
RI
15
0
SC
0 1000 3000 5000
1023 Exposure time (hours)
Fig. 14. Effect of conditioning in the alkaline solution at 60°C on interlaminar-shear strength
U
1024 AN
1025
1026
M
1027
1028
D
1029
TE
1030
1031
EP
1032
1033
C
1034
AC
1035
1036
1037
1038
49
ACCEPTED MANUSCRIPT
1039
1040
1041
PT
105
y = -6.6739x + 111.08
Transverse Shear strength retention
100 years
200 years
90 R² = 0.9049
RI
85
(%)
(%)
80 80
R10
SC
75
70
70 Log decade
65 (a) (b)
22C 40C 60C
60
60 1000 10000 100000 1000000
U
1.5 1.7 1.9 2.1 2.3 2.5
Log[Time (days)] Time (hours)
1042
AN
1043 Fig. 15. Plot of the transverse shear strength retention of BFRP bars as a function of time
1044
M
1045
1046
D
1047
TE
1048
1049
EP
1050
1051
C
1052
AC
1053
1054
1055
1056
1057
50
ACCEPTED MANUSCRIPT
1058
1059
105
Shear-Strength Retention (%)
100
PT
95
90
85
T = 10oC
RI
80
75
T = 22oC
70
SC
65
60
0 50 100 150 200
U
1060 Service Life (Years)
AN
1061 Fig. 16. General relation between the PR and the predicted service life at mean annual
1062 temperatures of 10 and 22°C
1063
M
1064
D
TE
C EP
AC
51
ACCEPTED MANUSCRIPT
Highlights
Basalt FRP
PT
Shear strength of BFRP
RI
Tensile strength of BFRP
U SC
AN
M
D
TE
C EP
AC