Bond behavior between ASR-damaged concrete and CFRP sheets: Empirical modeling

Journal Pre-proof Bond behavior between ASR-damaged concrete and CFRP sheets: Empirical modeling Rami H. Haddad, Ahmad Al-Sayed PII:

S2352-7102(19)31125-8

DOI:

https://doi.org/10.1016/j.jobe.2019.101166

Reference:

JOBE 101166

To appear in:

Journal of Building Engineering

Received Date: 3 July 2019 Revised Date:

30 December 2019

Accepted Date: 31 December 2019

Please cite this article as: R.H. Haddad, A. Al-Sayed, Bond behavior between ASR-damaged concrete and CFRP sheets: Empirical modeling, Journal of Building Engineering (2020), doi: https:// doi.org/10.1016/j.jobe.2019.101166. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier Ltd.

Sample CRediT author statement Haddad: Funding acquisition, Methodology, Writing- Original draft preparation, Supervision, Writing- Reviewing and Editing; Al-Sayed: Data curation; Investigation; Software.

2

Bond behavior between ASR-damaged Concrete and CFRP sheets: empirical modeling

3 4

Rami H. Haddad, Ahmad Al-Sayed

1

5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54

Department of Civil Engineering, Jordan University of Science and Technology, P.O. Box 3030, 22110 Irbid, Jordan Abstract Bond behavior between concrete, which has been cracked by alkali-silica reaction (ASR), and fiber-reinforced concrete polymer (CFRP) sheets is investigated with double-lap shear specimens, assembled using concrete blocks (150x200x150 mm3) and CFRP sheets at various bond lengths and widths. The blocks were cast with reactive silica particles before being treated in a sodium hydride solution to accelerate ASR; others were prepared using non-reactive particles and kept in lime water as controls. Empirical models were developed to predict bond force based on the present data. Results show significant reductions in the ultimate bond force (reaching about 69%) as ASR progresses.

Keywords: Alkali-silica Reactions; Bond force; Double-lap shear testing; Empirical Modeling.

1

55

1. Introduction

56 57

After many years in service, concrete structures may deteriorate upon exposure

58

to chemical and/or physical attacks such as an alkali-silica reaction (ASR). It is a

59

chemical reaction that takes place within the concrete, made of reactive aggregates and

60

high-alkalis cement, in the presence of ample humidity contents [1]. The product is a

61

complex alkali-silicate gel, which swells upon absorption of water from the surrounding

62

environment. The resulting expansion of such concrete may: (a) create a multi-

63

directional pressure that causes intensive map cracking; (b) impose compression on

64

concrete in the vicinity of steel reinforcement, and (c) introduce additional tensile

65

stresses in steel reinforcement [2–4]. Consequently, the load capacity of flexural

66

members, undergoing an aggressive ASR, is reduced while their long-term durability is

67

jeopardized especially in aggressive environments where the ASR-induced cracking may

68

allow the easy intrusion of chloride and/or sulfate contaminated water [3–4]. In most

69

cases, upgrading the load capacity and improving the water tightness of such elements

70

are required, yet the presence of the ASR cracking, even in absence of other

71

deterioration forms, may weaken the extent of benefit from any proposed repair

72

methodology.

73

In the past, many repair techniques were proposed to improve the mechanical

74

performance and durability of reinforced concrete elements upon their damage by

75

aggressive fires, sulfate attack, or ASR. These include the use of traditional reinforced

76

concrete jackets, laminates of fiber reinforced, and fabric-reinforced cementitious

77

matrix (FRCM) systems [5–8]. For example, Haddad et al. show that ASR-cracked

78

concrete beams with light compression steel reinforcement are able to fully recover

79

their flexural performance and durability upon repair using U-shaped jackets, made of

2

80

synthetic and steel fiber reinforced cementitious grout [8]. Steel plates and profiles are

81

used effectively in strengthening/repairing various types of structural elements [9].

82

Although the majority of these repair techniques impart tangible improvements to

83

mechanical properties of repaired elements and resistance against external durability

84

attacks, their use in the field is still limited. Their application to various structural

85

elements requires a relatively long time; also they increase the structure’s dead load and

86

inflict undesirable aesthetic and dimensional changes. As well, they require periodical

87

maintenance especially when steel reinforcement or elements are used [5–9].

88

Fiber reinforced polymer (FRP) composites have been widely employed in

89

retrofitting reinforced concrete elements [10–12]. The repair efficiency of

these

90

techniques requires the full transfer of tensile stresses from concrete to the repair

91

composites, which is usually ensured by attaching a satisfactory area of the composite to

92

well-prepared concrete substrates using the correct adhesive. In most cases, original or

93

newly-replaced concrete covers become cracked or delaminated after a short-in-service

94

life. This is attributed to the detrimental effect of concrete drying shrinkage, external

95

attacks, or inefficient repair techniques applied previously [13–14].

96

nature of the external attacks on concrete and its severity shapes the pattern and extent

97

of concrete cracking [15–20]. Concrete cracking results in premature debonding of

98

externally bonded (EB) FRP composites, thereby, undermining the benefits of the entire

99

repair process [15–21].

Certainly, the

100

Several empirical models were proposed to predict the ultimate bond force

101

(strength) and slippage between EB-FRP composites and concrete in terms of the

102

geometric and/or mechanical characteristics of the FRP-concrete joint, however, none

103

accounts for any deterioration effect [22–34]. Only recently the impact of degradation in

3

104

concrete due to heating, sulfate attack, or reinforcing steel corrosion was incorporated

105

in bond modeling of the FRP-concrete joints [15–17, 19].

106 107 108 109

2. Problem’s Statement, objective, and methodology

110 111

Carbon FRP (CFRP) composites are used on a large scale in repairing various

112

structural steel, reinforced concrete and wood elements [15–23]. The significance of

113

using this technique to repair flexural elements with ASR-deteriorating concrete was

114

not substantiated due to the lack of data regarding the bond behavior between the

115

ASR-damaged concrete and EB-CFRP composites. Thus, we present this work to

116

tackle in-depth the impact of concrete damage by ASR on its bond to EB-CFRP sheets;

117

factoring in the ASR damage level and the geometric characteristics of EB-CFRP

118

sheets. We expect our findings regarding the impact of ASR cracking on the bond

119

between concrete and CFRP sheets to gain great value for field applications.

120

Forty-five double-lap shear bond concrete specimens were assembled by

121

attaching two smooth and parallel faces of test and dummy blocks to EB-CFRP single

122

sheets at varying bond lengths and widths. Bond specimens were aligned vertically in

123

a universal testing machine using a special setup (shown in Fig. 1) before being tested

124

for bond force versus slippage relationship. Three groups of the concrete blocks were

125

cast with reactive silica particles and cured for 28 days before subjected to special

126

treatment in a sodium hydroxide solution until three levels of damage by ASR were

127

achieved, whereas those of the fourth group were cast with none-reactive silica

128

particles and kept in lime water as controls. The bond test results were compared to

129

determine the effect of ASR cracking level and the geometric characteristics of EB-

130

CFRP sheets before the obtained data was utilized in the development of empirical

131

models for the prediction of the bond force and the slippage in terms of the key 4

132

parameters of this study. The designation and number of bond specimens and their

133

task designation are summarized in Table 1.

134 135 136 137 138 139

3. Experimental program 3. 1 Concrete materials Ordinary Portland cement (Type I) along with coarse limestone aggregate at

140

19 mm maximum aggregate size, a blend of silica sand, and fine limestone with Pyrex

141

was used to cast specimens designated for ASR treatment. The Pyrex was used at

142

15% replacement percentage of the blend of fine particles (by wt). Another identical

143

concrete mixture was prepared using none-reactive glass particles instead of the

144

Pyrex to cast reference specimens, kept in lime water. Absorption and bulk specific

145

gravity for the coarse aggregates were determined according to ASTM-C127, whereas

146

the unit weight was determined according to ASTM-C29 [34]. The fineness modulus

147

of the fine aggregates was determined according to ASTM-C136 [34]. The absorption

148

and bulk specific gravity for the fine aggregates were determined according to ASTM-

149

C128 [34]. The Pyrex glass and the none-reactive glass particles were crushed from

150

broken leftover pieces before sieved into separate sieve sizes then graded according

151

to ASTM C1260 [34]. The physical properties of the aggregate particles used are listed

152

in Table 2. A third concrete mixture was prepared using coarse and fine limestone

153

and silica sand for casting 45 dummy concrete blocks, used for assembling the

154

present double-lap shear specimens of Fig. 1.

155 156 157 158 159

3. 2 CFRP sheet and bonding adhesive Unidirectional carbon FRP (CFRP) sheets were attached to the present concrete blocks using Sika designated adhesive. The physical, geometric, and

5

160

mechanical properties for CFRP sheets are shown in Table 3, whereas the physical

161

and mechanical properties of the recommended adhesive are listed in Table 4.

162 163

3.3 Concrete mix design, casting, and curing

164 165

All concrete mixtures were designed at an effective 0.5 w/c ratio

166

ordinary Portland cement according to ACI-211 mix design procedure to attain a

167

slump of 40 mm and 28-day compressive strength of 30MPa [35]. Mix proportions for

168

the present three mixtures are listed in Table 5. These were uniformly mixed in a

169

titling type mixer for two minutes according to ASTM test method C 192M [34].

using

170 171

The concrete blocks (150x150x200 mm3) were cast in specially-designed, 20-

172

mm-thick wooden molds. Concrete was poured in the wooden mold in two layers of

173

100 mm thickness each before being consolidated by a vibrating table according to

174

ASTM-C143 [34]. Steel molds (100x 200 mm2) were also used to cast a total of 12

175

standard cylinders from Pyrex concrete and 9 cylinders from glass concrete for the

176

determination of the splitting and compressive strengths. Concrete was cast in three

177

layers; each was consolidated by a vibrating table according to ASTM-C143 [34].

178

Three prismatic specimens (50x50x300 mm3) were cast from each Pyrex or glass

179

concrete mixtures. Threaded stainless-steel knobs were mounted at both ends of each

180

steel mold, before concrete was filled in a single layer, and then vibrated with

181

concrete at both ends while being pressed by fingertips to ensure excellent concrete

182

consolidation around the steel knobs. All specimens were unmolded after 24 hours of

183

casting before being placed in water to cure for 28 days.

184 185 186

3.4 Alkali-silica reaction (ASR) accelerating method

187 188

Thirty Pyrex concrete blocks, fifteen standard cylinders, and three prisms

189

designated for ASR treatment were immersed in a sodium hydroxide solution of 1 M 6

190

using a special conditioning chamber of Fig. 2. It is equipped with an electronic

191

regulator to maintain the temperature at 60 °C during immersion. The present regime

192

adopts the temperature level, recommended by RILEM Test Method TC 191, to heat

193

the sodium hydroxide immersion solution, recommended by ASTM testing method C

194

1260 [34, 36]. This protocol accelerated alkali-silica reaction (ASR) and caused

195

concrete damage within a relatively short time period.

196

Periodic crack width and expansion measurements were carried out to

197

determine the treatment periods corresponding to different ASR damage levels. At

198

time periods of 45, 80 and 120 days, one-third of the specimens were moved out to

199

the laboratory shelves awaiting further tests and surface preparation procedures.

200

Similar tests were simultaneously carried out on glass concrete specimens (controls),

201

immersed in lime water under a temperature of 60oC.

202 203

3. 5 Bonding of CFRP to Concrete Blocks

204 205

Thirty prismatic ASR cracked concrete specimens and fifteen control

206

specimens were bonded to CFRP sheets according to the manufacturer’s instructions.

207

First, loose and friable materials were completely scrapped from the surfaces where

208

CFRP to be attached using a mechanical brush before using a vacuum cleaner to

209

remove defects from the concrete’s surface and expose any holes or voids. Then, the

210

borders of the bond areas between the CFRP sheets and the two parallel surfaces

211

(150x200 mm2) of the prisms were marked in black. Prior to the application of

212

primer resin by a brush, the concrete substrate was dried using a volatile liquid. A

213

resin, prepared by mixing its two ingredients (A and B) together for a uniform light

214

gray color, was used to bond the CFRP sheets to the concrete blocks. The fabric sheets

215

(already cut into required dimensions) were placed on the resin (spread uniformly 7

216

over the marked area at 1 kg/m2) and rolled until the adhesive coating appeared on

217

the surface of the sheets. Finally, a second adhesive layer was painted over the

218

surface of the fabric sheets at 0.5 kg/m2, as shown in Fig. 3(a)

219 220

After 48 hours as of the above-prescribed procedure, the two CFRP sheets,

221

extending from the two parallel faces of test blocks, were adhered to the dummy

222

concrete blocks, positioned at the same alignment with the former blocks.

223

Furthermore, two additional CFRP sheets (150x200 mm2) were adhered on the top of

224

the CFRP sheets, extending onto the two parallel surfaces of dummy blocks, to reduce

225

the probability of bond failure at this part of the double-lap shear specimens, as

226

shown in Fig. 3(b). Finally, all specimens were left to cure at laboratory temperature

227

for at least 7 days.

228 229 230 231 232 233

3.6 Testing program

234

concretes prepared using glass (group I) and Pyrex concrete (Group II), was

235

evaluated according to ASTM C496 (100x200 mm2) after 45, 80, and 120 days of

236

immersion in lime water and sodium hydroxide solution at 60oC, respectively [34].

237

Additionally, three glass concrete cylinders were tested for final compressive strength

238

at 120 days as of treatment in lime water at 60oC according to ASTM C 39 [34]. The

239

average of readings from three specimens was found to be 37 MPa with a coefficient

240

of variation less than 5%.

3. 6.1 Evaluation of concrete strength The splitting strength of the standard cylinders (100x200 mm2), representing

241 242 243 244

8

245 246

3. 6.2 Double-lap shear test

247 248

Bond force-slip behavior was determined using the double-lap shear test setup

249

shown in Fig. 1. The setup comprises two thick steel plates (200x50x20 mm3) used to

250

encompass and maintain both test and dummy concrete blocks fixed in position by

251

long-threaded bolts. Two 30mm-diameter bars, welded to the exterior plates, were

252

used to tightly grip the entire assembly to the lower and upper heads of the testing

253

machine and maintain similar alignment for both blocks. A pull force was transferred

254

from the universal testing (UT) machine to the upper assembly at a stroke

255

displacement rate of 250 µm/minute until the CFRP sheets separated from the lower

256

test blocks.

257

Two LVDTs were employed to measure the relative displacements (slippage)

258

between the two faces of the test concrete blocks and CFRP sheets. As shown in the

259

schematics of Fig. 1, each LVDT was mounted on a fiberglass clamper adhering to the

260

end of the CFRP sheet while its knob was touching a fiberglass prismatic piece, glued

261

to the concrete surface. The load from the load cell and the slippage from the LVDT

262

were acquired using a data acquisition system.

263 264 265 266

3. 6.3 Expansion and cracking measurements

267

triplicate Pyrex and glass concrete prisms (50x50x300 mm3), immersed in sodium

268

hydroxide or lime water, respectively. Accordingly, expansion history was recorded

269

based on the average of three readings from three prisms with a coefficient of

270

variation less than 6%. Moreover, crack mapping and width measurements were

271

performed on the ASR-damaged concrete blocks. For clarity, all cracks were marked

272

in black using a fine-headed marker. The widths of the cracks were measured using a

Length measurements were performed by a comparator apparatus on

9

273

crack detection microscope having a magnification potential of 35X and a measuring

274

accuracy of 0.02 mm.

275 276 277 278

4. Results and discussion

279

cracking mapping and its extent, ASR expansion history, and splitting strength

280

measurements. The impact of the ASR damage on bond failure modes is presented in

281

sections 4.2. Finally, the behavior between concrete and CFRP sheets is tackled in

282

section 4.3 with emphasis placed on key parameters.

283 284 285 286 287

4.1 Evaluation of deterioration of concrete due to ASR

288

patterns and intensity, 3) expansion history, and 4) splitting strength. Fig. 4 shows

289

the cracking patterns for the ASR-damaged concrete blocks. The pictures reveal that

290

cracks spread further and their sizes increase as ASR progresses especially after

291

stages II and III. The pictures with marked cracks were scanned and analyzed by an

292

image processing AutoCAD program to determine the cracking intensity after the

293

three different ASR stages, considered in the present study. The results of Table 6

294

show clearly significant increases in the crack intensity as ASR progresses beyond

295

stage II. Furthermore, multiple cracking width measurements were acquired from

296

three concrete blocks after each ASR stage. The results reveal that the average

297

cracking width remains below 40 µm after stage I, yet enlarges to 70 µm and 100 µm

298

after ASR stages II, and III, respectively. The cracking trends observed are consistent

299

with those seen in the ASR-damaged field structures indicating that the use of Pyrex

The extent of the ASR damage in concrete is evaluated in section 4.1 based on

The extent of the ASR damage is characterized by its: 1) cracks width, 2)

10

300

as a partial replacement of fine particles has not altered the mechanism of concrete

301

expansion; hence, cracking by ASR.

302 303

Linear expansion history for Pyrex and glass concretes is depicted in Fig. 5. As

304

shown, Pyrex concrete undergoes progressive significant expansion with immersion

305

in sodium solution until about 12 weeks when the rate of expansion tangibly reduces

306

reaching an ultimate expansion of 2263 µstrain after 15 weeks of treatment at 60oC.

307

In contrast, the curve pertaining to glass concrete shows slow expansion rate with an

308

ultimate expansion of 250 µstrain achieved at an age of 15 weeks. The splitting

309

strength of the standard concrete cylinders (100x200 mm2) cast from glass and Pyrex

310

concretes was determined after treatment in lime water and sodium hydroxide

311

solutions at 60oC, respectively. Averages from three readings are listed in Table 6

312

along with the relative cracking intensity, crack width ranges, and linear expansion.

313

As can be deduced, ASR had caused significant degradation in the splitting strength of

314

concrete with residuals of 61.9, 55.8, and 50.4% after ASR stages I, II, and III,

315

respectively. Splitting rather compressive strength was adopted in this work due to

316

its much higher sensitivity to ASR cracking.

317

In summary, ASR stages I, II, and III correspond to an average crack width

318

ranges of less than 40, (40-70), and (70-100) µm, a cracking intensity of about 9%, 24,

319

and 33% of the concrete surface area, and a residual expansion of ultimate value at

320

47, 80, and 100% with reductions in splitting strength of concrete at about 62, 56,

321

and 50%, respectively. These cracking status indicators reflect significant differences

322

between damage levels in concretes corresponding to these stages.

323 324

11

325 326 327

4.2 Failure mode

328

seconds of double-lap shear testing. Small cracking and popping sounds were heard at

329

relatively moderate loads prior to sudden failure. The duration of testing until the bond

330

failure between the CFRP sheets and concrete is mainly affected by the bond width,

331

bond length, and the ASR-treatment level. As shown by the typical pictures of Fig. 6, two

332

types of failures between the CFRP sheets and concrete can be identified: a) concrete

333

skin peeling-off (CSP) failure in which very thin layer of concrete surface peels-off; its

334

depth is affected by the ASR damage level and CFRP sheets geometric configuration; and

335

b) concrete shearing-off failure (CS), which occurs in specimens W15-L12-S3 prior to

336

concrete skin peeling-off due to the relatively high contact area between the attached

337

CFRP sheets and concrete.

338 339 340 341 342 343

Double-lap shear specimens show no signs of detachment during the first few

4.3 CFRP-concrete bond 4.3.1 Effect of ASR damage level The effect of ASR damage on the bond behavior between the CFRP sheets and

344

concrete can be understood by referring to Figs. 7 through 11. The shown curves are

345

obtained by nonlinear fitting of load force-slip data pertaining to two identical specimens

346

whose results differences are less than 10%. The curves representing different ASR-

347

damage levels follow almost similar trend behavior, represented in a linear segment until

348

about 50% of the ultimate bond force after which a nonlinear behavior is identified. The

349

different curves indicate clearly that the ultimate bond force, bond force at slippage, bond

350

stiffness, slippage at the ultimate bond force, and bond stiffness are significantly reduced

351

by the ASR damage.

12

352

The bond characteristics relevant to varying damage levels and attachment

353

configurations of the CFRP sheets are summarized in Table 7. As can be deduced, the

354

ranges for residual ultimate bond strength are 73%-93%, 58%- 69%, and 35% -54% after

355

the stages I, II and III of ASR, respectively. Similarly, bond force at slippage reduces as ASR

356

progresses with residual ranges of 66-91%, 43%-75%- and 23%-70%, respectively. Bond

357

stiffness demonstrates a similar trend behavior to that of the residual bond forces, but at a

358

lower sensitivity to the ASR damage. The relevant values of Table 7 can be easily

359

recognized from observing the trend behavior of the linear portions of Figs. 6–10, which

360

demonstrates slight variation in their slopes as ASR treatment progresses. On the other

361

hand, slippage at ultimate bond force shows relatively high sensitivity to the ASR damage

362

at ranges of 59-91%, 36-61% and 29-54%, respectively. Finally, bond toughness, computed

363

as the area underneath the bond load versus slip diagram, is the most affected by the ASR

364

damage with residuals reduce to as low as 16%. It should be indicated that the residuals of

365

bond characteristics are also affected by the attachment configuration of the CFRP sheets,

366

as discussed later on. The use of ultimate bond force in this work as an indicator of bond

367

integrity between the CFRP sheets and concrete aim to avert approximations associated

368

with the use of the bond strength. The embedment lengths considered in the present work

369

(60-180 mm) were chosen to exceed the effective length at 50 mm, estimated according to

370

the equations of next section. Hence, no modifications to the experimentally obtained

371

ultimate bond force were needed. In addition, most of the literature data used in the

372

validation of the present empirical model are reported as the ultimate bond force rather

373

strength [37].

374 375 376

13

377 378 379

4.3.2 Effect of CFRP Geometry

380

have a significant impact on bond behavior, as demonstrated by the plots of Figs. 7 -11. As

381

can be deduced, using CFRP sheets at a longer length and wider width result in higher bond

382

force with glass concrete (control). However, the slippage at the ultimate bond force is

383

increased when the CFRP sheets are extended further in length yet reduced in width. Table

384

7 shows that the ultimate bond force (kN), bond force at slippage (kN), slippage at the

385

ultimate bond force (µm), bond stiffness (MPa/m), and bond toughness (J) are (19.5, 1.8,

386

210.6, 177.7, and 3.0), (31.5, 4.3, 244.9, 279.8, and 6.0), and (41.4, 3.5, 264.6, 279.0, and

387

7.9) for control double-lap shear specimens, assembled at bond lengths of 60, 120, 180

388

mm, respectively. The corresponding characteristics for control double-lap shear

389

specimens at bond widths of 50, 100, and 150 mm are (18.4, 1.7, 281.4, 140.1, and 3.8),

390

(31.5, 4.2, 244.9, 279.8, and 6.0), and (37.1, 3.5, 224.4, 402.1, and 5.9), respectively. The

391

results demonstrate logical increases in the ultimate bond force, bond force at slippage, and

392

bond stiffness and toughness with bond length and width.

393

ultimate force is increased with longer bond lengths or narrower bond width of the CFRP

394

sheets.

The present findings reveal that the geometric characteristics of the CFRP sheets

As expected, slippage at the

395

The bond lengths for the CFRP sheets, attached to present intact concrete blocks, are

396

selected to reflect realistic field practice at values from 60 to 180 mm. Those were higher

397

than the development bond length, estimated at about 50 mm. This was computed based

398

on the effective bond length formula, recommended by the relevant American and

399

European specifications, given as [38–39]:

400 401

=

(1)

14

=

402

Where,

403 404 405

,

(2) represents the development bond length of the CFRP composites, whereas

, and n represent modulus of elasticity, thickness, and laminates number of the CFRP

sheets, respectively.

406

The computed effective bond length explains the lower sensitivity of the ultimate

407

bond force (bond strength) for control test specimens as the bond length is increased, as

408

shown by Table 7. Upon cracking of concrete blocks by ASR, the bond lengths for the CFRP

409

sheets fell short of the minimum bond development length requirements for the ASR-

410

damaged concrete. Accordingly, the results of bond behavior between the CFRP sheets and

411

concrete start showing tangible sensitivity to ASR damage level as well as the geometric

412

characteristics of the sheets, as deduced from the results of Table 7 and Figs. 7–11.

413

The double-lap shear specimens with Pyrex concrete blocks, undergoing

414

progressive alkali-silica reaction, experience clear reductions in their residual bond

415

characteristics at varying magnitudes; depending upon the geometrical properties of

416

CFRP sheets. Table 7 indicates that the specimens, assembled using the ASR-damaged

417

blocks and the CFRP sheets at the lowest bond length of 60 mm, are the most susceptible

418

to ASR damage since they show the lowest residual properties, followed in sequence by

419

those at bond lengths 120 and 180 mm, respectively. The residual characteristics

420

(ultimate bond force, bond force at slippage initiation, slippage at ultimate bond force,

421

bond stiffness, and bond toughness) for the double-lap shear specimens at bond lengths

422

of 60, 120, and 180 mm after stage I of ASR treatment are (73, 91, 70, 92, and 48%), (80,

423

71, 73, 92, and 55%), and (81, 94, 59, 99, and 61%) as compared to (39, 30, 53, 80, and

424

20%), (45, 51, 54, 66, and 23%), and (53, 42, 51, 94, and 26%) after ASR stage III,

425

respectively. As ASR progresses, cracks

increase in severity before extending and 15

426

widening underneath the CFRP sheets during the double-lap shear testing. This creates

427

weaker concrete substrates which result in lowering the loads required for slippage

428

initiation and causing the entire separation of the externally attached CFRP sheets;

429

especially when the CFRP sheets are adhered to the ASR-damaged concrete at lower

430

bond length.

431

The bond characteristics, summarized in Table 7, indicate that the double-lap

432

shear specimens, assembled using the ASR-damaged concrete blocks and CFRP sheets at

433

the lowest bond width of 50 mm, are the most susceptible to the ASR damage since their

434

relevant bond characteristics tend to degrade at a much higher rate than that of the

435

specimens at higher bond widths of 100 and 150 mm. The residuals for (ultimate bond

436

force, bond force at slippage initiation, slippage at ultimate bond force, bond stiffness,

437

and bond toughness) after stage I are (76, 89, 63, 82, and 46%), (80, 71, 73, 92, and

438

55%), and (93, 66, 91, 94, and 62%) for the specimens at bond widths of 50, 100, and

439

150 mm, as compared to (31, 70, 29, 61, and 16%), (45, 51, 54, 66 and 23%), and (54,

440

23, 45, 76, and 21%) after stage III, respectively. The higher degradation in bond

441

characteristics, upon the formation of ASR cracks in the specimens assembled at a lower

442

bond width, is related to the less ability of the thinner CFRP sheet to arrest and control

443

the opening of the pre-existing ASR cracks under the double-lap shear loading. This

444

suggests that using CFRP sheets at higher widths of 100 and 150 mm imparts more

445

control on the crack extension towards the central portion of the sheet as the bond load

446

is increased.

447 448 449 450 451

5. Empirical Modeling 5.1 Empirical modeling of bond force and slippage

16

452

The previous discussion reveals that the ultimate bond force and the

453

corresponding slippage are affected by the ASR damage level as well as the geometric

454

configuration of EB-CFRP sheets. In this part, empirical models for the prediction of

455

these two characteristics are presented, their fit of regression data is established, and

456

their predictability of literature data is examined. The equations for the ultimate bond

457

force (

458

respectively, are proposed according to:

) and slippage at the ultimate bond force ( ), measured in kN and µm

459 460 461 462 463 464 465 466 467 468

469

470

471

=

=

$ %&' β() β*) +, ′

! β"

- - β"- β.- β/-

Where,

and

-

(3)

+, ′

(4)

are taken 1 for ordinary strength concrete,

!

,

and

-

are

regression coefficients, and β" and β"- are degradation parameters for the ultimate

bond force and slippage at the ultimate bond force, respectively, whereas , 0 represents

the compressive strength of the intact standard cylinders (100x200 mm2). The geometric parameters, 12 and 1 , are expressed in terms of bond length and width .

4

relative to concrete dimensions, . and 4 , respectively, according: 3

β2 = 5 β. = 5

6 7

8

6 . ;<

6!.=;7

β2- = >

6 <

9

83 8

*

*

*3

9

6 . ;7

(5)

9

83

*3

3

9

8

83

A 8

? .=;< @

(6)

9

83

(7)

B

17

β.- =

472

@6 <

*

*3

? .=;7@

9

*

*3

(8) B

473

The above equations are similar to or modified versions of those of Haddad and

474

Al Dalou' [40]. The standardization of the geometric dimensions of the EB-CFRP sheets

475

with respect to that of concrete in these equations makes the implementation of the

476

models of equations 3 and 4 for field computations easy and visible.

477

The statistical parameters of equations 3 and 4 are determined by linear fitting of

478

the results from control specimens, as depicted in Fig. 12, with degradation parameters

479

β" and β"- set to 1. As can be noticed, the model's fit of the present data can be rated as

480

excellent since the coefficient of determination (R2) exceeds 0.96. Accordingly, the

481

degradation parameters β" and β"- are computed for different ASR-damaged double-

482

lap shear specimens by dividing measured

483

corresponding controls using equations 3 and 4. The degradation parameters computed

484

for the ultimate bond force and slippage at the ultimate bond force shows high

485

sensitivity not only to the damage level by ASR but also to EB-CFRP attachment

486

configurations as previously outlined with the corresponding values ranging from 0.20

487

to 0.80.

and

by values predicted for the

The next step aims to establish a statistical correlation between the computed

488 489

C

"

,

"-

and the damage extent in concrete. This was accomplished by introducing

490

damage indices in terms of residual splitting strength, DEF G , DEF- G , and concrete

491

residual expansion relative to the ultimate value, DEF G H , DEF- G H , which account for the HI

HI

492

ASR-damage level as well as the geometric characteristics of the EB-CFRP sheets.

493

Accordingly, equations 9–11 are calibrated such that the damage indices range from

18

494

zero for control specimens to less than 1.0 for ASR-damaged ones. Finally, statistical

495

correlations are established between the latter damage indices and degradation

496

parameters based on Figs. 13–14. As can be deduced, the data can be best presented

497

using linear relationships according to equations (12) to (15) with R2 ranging from 0.89

498

to 0.92. As noticed, the combination of the degradation parameters and the square root

499

of the compressive strength for intact concrete in Equations (3–4) can be considered as

500

a valid quantification of the physical status of the ASR-damaged concrete based upon its

501

bond with EB-CFRP sheets.

502

503

504

N L

DEF G

= O M L K N L

DEF- G

= O M L K

*

!.=;<* *

3

*3

*

!.=;<* *

*3

3

+

. <8 8

3

83

+

8

8

83

HI

Q

3

Q

*3

T

SZ

*

!.=;<* *

A ' 9 RS

' 9 RS

6

. <8

DEF G H = DEF- G H = 3 \O HI

8

6

3

+

W L V L U

W L V L U

−1

(9)

−1

(10)

8

. <8 8

83

3

Q

]

H ^ SZHI

− 1_

(11)

505

1"` = −1.073DEF G

+ 1.016 ≤ 1

(12)

506

1"` = −0.757DEF G H + 1.015 ≤ 1

(13)

507

1"- = −0.7965DEF- G

+ 1.008 ≤ 1

(14)

508

1"- = −0.8987DEF- G H + 1.000 ≤ 1

(15)

HI

HI

509

The fit of the models, developed in equations 3 and 4, was examined against the

510

measured bond characteristics, as detailed in Table 8. Predictions are made using

511

degradation parameters, computed according to equations (12) to (15). The results of

512

Table 8 indicate that the average errors of predicting the bond force and its 19

513

corresponding slippage are 10 and 13% when the residual splitting strength was used to

514

evaluate damage level, respectively. Lower corresponding average errors at 9 and 6%

515

are noticed when the residual expansion by ASR was used for the quantification of

516

damage in concrete, respectively. Errors in prediction, however, show some scattering in

517

their distribution with limited numbers of outliers. This may be attributed to some

518

limitations in the ability of the damage indices proposed in equations 9–11 in providing

519

precise quantification of the actual damage extent in concrete as a result of exposure to

520

ASR.

521 522

5.2 Model's predictability

523

Due to the rarity of published data on bond characteristics between the ASR-

524

damaged concrete and CFRP composites, the precision of the predictions by the present

525

model of the ultimate bond load was examined using data from tests on intact double-

526

lap shear concrete specimens before comparing to those of the well-known published

527

models such as that of Lu et al. [30], Wu et al. [31], and Chen and Teng [41]. The test data

528

were based on the ultimate bond force data from single or double-lap shear specimens,

529

comprised from ordinary and high strength concrete blocks that are firmly attached to a

530

single layers of CFRP sheets by adhesives of close mechanical properties, [15-16, 42-46]:

531

Table 9 provides further details of the test data used in the present model's validation.

532

Predictions by the present model, as illustrated in Fig. 15 (a), can be rated as very

533

good in light of the heterogeneity of the test data. As can be noticed, most predictions

534

were concentrated around the perfect prediction line with a limited number of outliers.

535

It should be indicated that the present model demonstrates similar levels of

536

predictability for normal and high strength concrete. Furthermore, the data of Fig. 15 (a-

537

d) show that the present model demonstrates the highest precision of predictions and 20

538

the lowest percentage of outliers among all tested models of this study. This is

539

supported by the fact that predictions by the models of Lu et al. [30] and Cheng, and

540

Tang [41] tend to deviate noticeably from the ideal prediction line, whereas those by the

541

model of Wu et al. [31] show a high-scattering tendency.

542

To validate further the predictability precision of present model as compared to

543

that of various literature models, averages of predicted/measured, the ultimate bond

544

force ratios are computed along with relevant standard deviations and coefficients of

545

variation based on the results graphically depicted in Figs. 15. These are at (1.22, 0.32,

546

26%), (0.70, 0.12, 18%), (1.30, 1.0, 77%), and (2.57, 1.45, 56%) for the proposed model

547

and those by Chen and Teng [41], Wu et al. [31], and Lu et al. [30], respectively. The

548

ratios of (predicted to measured) for the ultimate bond force confirm the previous

549

conclusions regarding the highest precision of prediction by the present model as

550

compared to that by other tested models [30-31, 41]. The standard deviation and

551

coefficient of variation results, however, indicate some scattering tendency in the

552

predictions by the present model, although remain below that associated with the

553

predictions by the models of Lu et al. [30] and Wu et al. [31]. It is evident that the

554

prediction precision of the present model can be further refined and its scattering

555

tendency minimized when additional data from future research works on the bond

556

between the CFRP sheets and ASR-damaged concrete is made available for

557

incorporation in the modeling process.

558 559

6. Conclusions

560 561

An experimental program was designed and implemented to investigate the

562

impact of ASR-induced damage in concrete on its bond to CFRP sheets, used for repair

563

purposes. Concrete blocks (200x200x150 mm3) were cast using ordinary strength 21

564

concrete and cured for 28 days before being subjected to three levels of damage using an

565

accelerated method in a sodium hydroxide solution. Control and ASR-damaged blocks

566

were then attached to CFRP sheets at different bond lengths (60–180 mm) and widths

567

(50–150 mm) before being subjected to double-lap shear test using a special setup for

568

bond force versus slippage measurements. Furthermore, an empirical model was

569

developed upon the present findings to predict the bond strength between concrete and

570

CFRP sheets in terms of the geometric and materials characteristics of concrete and

571

CFRP sheets as well as the ASR-damage extent. Followings are the major conclusions:

572 573

1. The pattern of cracking in the blocks treated in alkali-silica reaction (ASR)

574

confirms the typical map cracking, stipulated for concrete and damaged by ASR.

575

The intensity and size of the cracks increases as ASR progresses with noticeable

576

reductions in splitting strength. The ASR cracking width reaches as high as 100

577

µm whereas splitting strength is reduced by 50% after 15 weeks of treatment in

578

a sodium hydroxide solution at 60oC.

579

2. The expansion history for concrete with reactive silica particles follows a known

580

trend behavior for the ASR-treated concrete with an ultimate value at 2266 µm

581

achieved after 15 weeks of treatment in a sodium hydroxide solution at 60oC. In

582

contrast, concrete with the none-reactive particles achieves an ultimate

583

expansion of less than 250 µm and shows no signs of cracking or degradation in

584

the splitting strength.

585

3. The bond force-slip relationships of different double-lap shear specimens

586

maintain similar trend behavior, regardless of the geometric characteristics of

587

the CFRP sheets or degree of concrete deterioration by ASR. This is represented

22

588

in a linear segment until approximately 50% of the ultimate bond strength

589

followed by a non-linear portion until failure.

590

4. ASR causes significant reductions in bond characteristics, namely, the ultimate

591

bond force, bond force at slippage, slippage at the ultimate bond force, bond

592

stiffness, and bond toughness by as much as 69%, 77%, 71%, 39%, and 84%,

593

respectively. Hence, the potential of repairing of concrete elements using CFRP

594

sheets is undermined when the level ASR damage in concrete exceed that

595

reported for stage II of this work.

596

5. The present findings reveal that the degradation in the concrete-CFRP bond

597

behavior is shaped by the ASR severity as well as the geometric characteristics of

598

CFRP sheets.

599

6. All double-lap shear specimens show concrete skin peeling-off (CSP) bond

600

failure, except those, prepared at the highest bond length and width, which show

601

concrete shearing (CS) failure mode.

602

7. The empirical models developed to predict the ultimate bond force shows high

603

prediction precision and superiority of present as compared to that of well-

604

known literature models.

605

8. The conclusions provided in this work are based on the accelerated ASR

606

treatment described.

Further experimental research is recommended to

607

introduce adjustments (if any) on the present model based on experiments that

608

involve exposing large-scale loaded concrete specimens to slower ASR treatment

609

protocols before being repaired using CFRP composites and tested for bond

610

performance.

611 612 613

7. Acknowledgement 23

614

The authors acknowledge the financial support by Dean of Research at Jordan

615

University of Science and Technology, Irbid, Jordan, under project number

616

111/2018.

617 618 619 620 621 622 623 624 625 626

8. Conflict of Interest There is no conflict of interest in publishing this submission.

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[2]

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[3]

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775

28

Table 1. Specimen type and task designation. Designation

L (mm) W (mm) PSN

W10-L6-S0

60

100

3

W10-L12-S0 W10-L18-S0 W5-L12-S0 W15-L12-S0 W10-L6-S1,2,3 W10-L12-S1,2,3 W10-L18-S1,2,3 W5-L12-S1,2,3 W15-L12-S1,2,3

120 180 120 120 60 120 180 120 120

100 100 50 150 100 100 100 50 150

3 3 3 3 2x3 2x3 2x3 2x3 2x3 45

SCN 12

9

W, Bond width; L, Bond length; S, ASR stage; numeral subscript 0 designated control specimens whereas subscripts 1- 3 designate ASR stages 1-3, respectively; PSN, double lap shear specimens number; SCN, standard cylinder number.

Table 2. Physical properties of aggregate and particles used in preparing different concrete mixtures.

Property BSGDRY BSGSSD FM Absorption (%) UW (kg/m3)

CL 2.54 2.58 NA 2.3 1442.6

FL 2.58 2.68 3.01 2.43 1630.6

SS 2.57 2.59 1.34 0.67 NA

Pyrex or Glass 2.23 2.25 2.9 0 NA

BSG, bulk specific gravity; SSD, saturated surface dry; FM, fineness modulus; UW, unit weight; CL, coarse limestone; FL, fine limestone; SS, silica sand; NA, not available.

28

Physical and mechanical properties of MBrace fiber sheet as provided by the manufacturer. Fiber orientation 0° (unidirectional) Warp: Black carbon fibers (99% of total area weight) Fiber Construction Weft: White thermoplastic heat-set fibers (1% of total area weight) Design Cross Section 0.166 mm Thickness Fiber Weight 300 g/m² Width 500 mm Material Type Carbon Elasticity Modulus 230,000 N/mm² Tensile Strength 4900 N/mm² Elongation at Break 2.1% Table 3.

Typical properties of Master Brace Saturant used for bonding CFRP sheets as provided by the manufacturer. Two parts A&B, thyrotrophic Product Description epoxy based impregnating resin/ adhesive. Part A: resin, Part B: hardener Appearance / Colors Color: part A: White Part B: grey Mixed: light grey Yield First coat = 0.7 – 1.5 kg/m2 Final coat = 0.7 kg/m2 Mix Ratio A; B = 4; 1 by weight Density Mixed resin (A+B): 1.30 kg/Lt Bond Strength >4 N/mm2 Tensile Ultimate Strength 30 N/mm2 (7 days at 23°C) Tensile Elastic Modulus 4500 N/mm2 (7 days at 23°C) Tensile Rupture Strain 0.9%

Table 4.

29

Table 5. Concrete mix proportions for different mixtures. Weight (kg/m3) Material

Pyrex Glass Typical Concrete Concrete Concrete* Water 250 250 250 Cement 430 430 430 Corse aggregate 792 792 792 Fine aggregate 503 503 631 Silica 210 210 210 Pyrex (in ASR specimen) 128 NA NA Glass NA 128 NA KOH powder 4.3 NA NA *, Concrete mixture used for casting dummy concrete blocks; NA, not available. Table 6. Crack width, splitting strength and expansion for concrete with Pyrex and subjected to ASR accelerated treatment in sodium hydroxide solution of 1 M. σsp ASRStage Stage I Stage II Stage III

CW (µm)

CI (%)

< 40 40-70 70-100

9.2 24.1 32.9

GC (MPa) 4.15 4.19 4.27

PC (MPa) 2.57 2.34 2.15

RSS (%) 61.9 55.8 50.4

Expansion (µm)

RE (%)

1056 1816 2263

47 80 100

CW, crack width; CI, cracking intensity; σsp, splitting strength; GC, glass concrete; PC, Pyrex concrete; RSS, residual splitting strength; RE, residual expansion.

30

Table 7. Bond characteristics and failure modes for different double lap shear specimens, assembled using ASR damaged concrete blocks and CFRP sheets. Specimen UPL BFS So BST BT FM Designation kN kPa kN µm MN/m J 18.5 3090 1.8 210.6 177.7 3.0 CSP W10-L6-S0 100* 100 100 100 100 100 13.5 2250 1.6 140.8 163.4 1.5 CSP W10-L6-S1 73 73 91 70 92 48 10.7 1780 1.1 123.0 151.9 1.0 CSP W10-L6-S2 58 58 59 61 85 31 8.1 1343 107.1 0.5 141.6 0.6 CSP W10-L6-S3 39 39 30 53 80 20 31.5 2626 4.24 244.9 279.8 6.0 CSP W10-L12-S0 100 100 100 100 100 100 25.2 2098 2.5 179.2 256.2 3.3 CSP W10-L12-S1 21.46 11 80 80 71 73 92 55 1789 138.5 21.5 2.7 226.2 2.1 CSP W10-L12-S2 68 68 64 57 81 34 1120 132.0 13.4 2.2 183.8 1.4 CSP W10-L12-S3 45 45 51 54 66 23 41.4 2300 3.5 264.6 279.0 7.9 CSP W10-L18-S0 100 100 100 100 100 100 33.7 1870 157.1 3.3 275.4 4.9 CSP W10-L18-S1 61 81 81 94 59 99 1589 139.2 28.6 2.4 270.0 2.4 CSP W10-L18-S2 69 69 68 53 97 30 21.8 1211 1.7 135.0 262.8 2.1 CSP W10-L18-S3 53 53 42 51 94 26 18.4 3069 1.7 281.4 140.2 3.8 CSP W5-L12-S0 100 100 100 100 100 100 14.1 2341 176.5 1.1 114.3 1.8 CSP W5-L12-S1 46 76 76 63 82 89 9.88 1647 1.3 100.2 111.0 1.1 CSP W5-L12-S2 54 54 75 36 79 29 5.7 948 81.1 1.2 85.8 0.6 CSP W5-L12-S3 31 31 70 29 61 16 37.1 2058 3.5 224.4 402.1 5.9 CSP W15-L12-S0 100 100 100 100 100 100 34.3 1905 2.3 203.3 379.8 3.7 CSP W15-L12-S1 93 93 66 91 94 62 24.3 1348 135.3 1.5 308.7 2.4 CSP W15-L12-S2 66 66 43 60 77 41 100.8 18.00 999 0.8 306.9 1.2 CS W15-L12-S3 54 23 45 21 54 76 *, Residual characteristics with respect to control double lap shear specimens; UPL, Ultimate double lap shear load; τave, bond strength; S0, Ultimate Slippage; BFS, Bond force at slippage initiation; BST, Bond stiffness; BT, Bond toughness; FM, Failure mode; CSP, Concrete skin peeling-off; CS, concrete shearing-off.

31

Table 8. Measured bond force and slippage versus those predicted using equations 1 and 2 considering present parameters. Pm PPRS EPRS PPE EPE So,m So,PR EPRS So,PE EPE W L ASR (kN) (kN) (%) (kN) (%) (µm) S (µm) (%) (µm) (%) 100 60 No 18.5 18.9 2 18.9 2 211 218 4 218 4 100 120 31.5 28.0 11 28.0 11 245 245 0 245 0 100 180 41.4 40.7 2 40.7 2 265 271 2 271 2 50 120 18.4 19.1 4 19.1 4 281 277 2 277 2 150 120 37.0 40.1 8 40.1 8 224 214 5 214 5 I 100 60 13.5 13.0 4 14.1 5 141 136 4 149 10 100 120 25.2 20.8 18 21.9 13 179 167 7 178 6 100 180 28.6 31.1 9 32.5 14 157 192 22 202 7 50 120 14.0 13.1 7 14.3 2 177 172 3 189 10 150 120 34.3 30.7 10 32.1 6 203 151 26 160 4 II 10.7 13.0 100 60 21 10.1 5 123 103 16 95 7 100 120 21.5 17.9 16 16.9 21 139 137 1 126 8 100 180 28.6 27.4 4 25.7 10 139 161 16 149 9 50 120 9.9 10.6 8 10.2 4 100 130 30 119 11 150 120 24.3 27.1 12 25.4 5 135 128 6 118 8 100 60 III 8.1 6.9 15 7.6 5 107 72 33 80 7 100 120 13.4 13.7 2 13.8 2 132 129 2 130 0 100 180 21.8 22.0 1 21.5 1 135 175 30 172 2 50 120 5.7 6.9 21 7.7 35 81 98 21 109 14 150 120 18.0 21.8 21 21.3 18 101 124 23 121 2 P, ultimate bond force; So, Bond slippage at ultimate bond force; subscripts m, PRS, and PE refers to measured, predictions based upon residual strength; and predictions based upon expansion, respectively; E, error of prediction.

32

Table 9. Literature data from bond tests on pull-out specimens used for validation of present empirical model. ′ Reference NVP range range MPa 50 − 150 60 − 100 Al-Rousan et al. [15] 36-44 6 150 150 100 50 − 150 Haddad et al. [16] 29-40 9 150 150 60 − 100 50 − 150 26-42 29 Al-Rousan et al. [42] 150 150 40 − 120 50 − 150 Haddad et al. [42] 30 6 150 150 100 50 − 400 21-26 18 Bilotta et al. [44] 150 400 25 − 100 75 − 190 Yao et al. [45] 19-27 54 150 350 200 50 Pellegrino et al. [46] 58-63 14 300 100 , CFRP sheet's bond length of CFRP to that of concrete; of concrete;

′

, CFRP sheet's bond width to that

, compressive strength of concrete; NVP, number of validation points.

33

Fig. 1 Schematics of present Pull-off test setup.

Solution Container

Control Panel Fig. 2 Treatment champer used to accelerate ASR

34

(a) Squeezing out the resin through the (b) Anchoring CFRP sheet on the fiber using a roller. dummy block. Fig. 3 Steps of attaching CFRP sheets to the concrete blocks.

Stage I

Stage II

Stage III

Fig. 4 Crack patterns of concrete blocks after three levels of ASR treatment

35

2500

Pyrex Concrete Glass Concrete

Expansion µm

2000 1500 1000 500 0 0

3

6

9 12 Time (Week)

15

18

Fig. 5 Expansion history for concrete prepared with Pyrex and none-reactive glass particles and subjected to a special treatment in NaOH solution of 1 M.

(a) Control; CSP

(b) Stage I; CSP

(c) Stage II; CSP

(d) Stage III; CS

Fig. 6 Cropped bond failure surfaces for pull-off specimens, assembeled using control and ASR-damaged concrete blocks and CFRP sheets at bond length and width of 150 and 120 mm, respectively.

36

Bond Force (kN)

25.0 20.0 15.0 10.0 5.0 0.0 0.00

0.05

0.10

W10-L6-S0 W10-L6-S2

W10-L6-S1 W10-L6-S3

0.15 0.20 Slip (mm)

0.25

0.30

Bond Force (kN)

Fig. 7 Bond force-Slip curve for pull-off specimens (W10-L6) experienced different ASR stages.

45.0 40.0 35.0 30.0 25.0 20.0 15.0 10.0 5.0 0.0 0.00

W10-L12-S0 W10-L12-S2 0.05

0.10

0.15 0.20 Slip (mm)

W10-L12-S1 W10-L12-S3 0.25

0.30

Fig. 8 Bond-Slip curve for pull-off specimens (W10-L12) experienced different ASR stages.

37

Bond Force (kN)

45.0 40.0 35.0 30.0 25.0 20.0 15.0 10.0 5.0 0.0 0.00

0.05

W10-L18-S0

W10-L18-S1

W10-L18-S2

W10-L18-S3

0.10

0.15 0.20 Slip (mm)

0.25

0.30

Fig. 9 Bond force-Slip curve for pull-off specimens (W10-L18) experienced different ASR Sages.

Bond Force (kN)

25.0 20.0 15.0 10.0 5.0 0.0 0.00

W5-L12-S0 W5-L12-S2 0.05

0.10

0.15 0.20 Slip (mm)

W5-L12-S1 W5-L12-S3 0.25

0.30

Fig. 10 Bond force-Slip curve for pull-off specimens (W5-L12) experienced different ASR sages.

38

Bond Force (kN)

45.0 40.0 35.0 30.0 25.0 20.0 15.0 10.0 5.0 0.0 0.00

W15-L12-S0 W15-L12-S2 0.05

0.10

0.15 0.20 Slip (mm)

W15-L12-S1 W15-L12-S3 0.25

0.30

Fig. 11 Bond force-Slip curve for pull-off specimens (W15-L12) experienced different ASR Sages.

39

Pu (kN)

45 40 35 30 25 20 15 10 5 0 0.30

0.35

0.40

0.45 0.50 (β βLβw)^0.5

0.55

0.60

300 250 So(µm)

200 150 100 50 0 0.00

0.20

0.40 0.60 (β βLSβwS)^0.5

0.80

1.00

Fig. 12 Curve fitting of ultimate bond force (top) and slippage at ultimate bond force (bottom) pertaining to control pull-off specimens.

40

1.2

y = -1.0727x + 1.0163 R² = 0.8992

1 βDP

0.8 0.6 0.4 0.2 0 0

0.2

0.4

0.6

0.8

1

1.2 y = -0.785x + 1.0102 R² = 0.898

1

βDS

0.8 0.6 0.4 0.2 0 0

0.2

0.4

0.6

0.8

1

Fig. 13 Degradation parameters for ultimate bond force (top) and slippage at ultimate bond force (bottom) versus damage indices defined in Equations 7 and 8, respectively.

41

1.2 y = -0.7571x + 1.0148 R² = 0.9161

1

βDP

0.8 0.6 0.4 0.2 0 0

0.2

0.4

0.6

0.8

1

1.2 y = -0.8987x + 1.0001 R² = 0.9033

1

βDS

0.8 0.6 0.4 0.2 0 0

0.2

0.4

0.6

0.8

Fig. 14 Degradation parameters for ultimate bond force (top) and slippage at ultimate force (bottom) versus damage index defined in Equation 9.

42

1

Pmodel (kN)

Pmodel (kN)

40 35 30 25 20 15 10 5 0

Present

40 35 30 25 20 15 10 5 0

Lu et al. [30]

0 5 10 15 20 25 30 35 40 Pexp (kN)

40 35 30 25 20 15 10 5 0

Wu et al. [31]

Pmodel (kN)

Pmodel (kN)

0 5 10 15 20 25 30 35 40 Pexp (kN)

40 35 30 25 20 15 10 5 0

Chen and Teng [41]

0 5 10 15 20 25 30 35 40 Pexp (kN)

0 5 10 15 20 25 30 35 40 Pexp (kN)

Fig. 15 Precision of predictions of ultimate bond force using present as compared to well-known literature's models.

43

Pmodel (kN)

Pmodel (kN)

40 35 30 25 20 15 10 5 0

40 35 30 25 20 15 10 5 0 0 5 10 15 20 25 30 35 40 Pexp (kN)

0 5 10 15 20 25 30 35 40 Pexp (kN)

40 35 30 25 20 15 10 5 0

(b) Lu et al. [30]

40 35 30 25 20 15 10 5 0

Pmodel (kN)

Pmodel (kN)

(a) Present

0 5 10 15 20 25 30 35 40 Pexp (kN) (c) Wu at al. [31]

0 5 10 15 20 25 30 35 40 Pexp (kN) (d) Chen & Teng [41]

Fig. 15 Precision of predictions of ultimate bond force using present as compared to well-known literature's models.

• • •

Bond characteristics between CFRP and concrete were determinately affected by ASR. Dimensions of CFRP sheets affected the percentage reduction in bond due to ASR. Bond models developed showed higher precision as compared to those in literature.

Dear Editor, Please be informed that there is no conflict of interest by submitting this paper. Best Wishes

Prof. Rami Haddad