Self-healing performance of aged cementitious composites

Accepted Manuscript Self-healing performance of aged cementitious composites Gürkan Yıldırım, Arash Hamidzadeh Khiavi, Seda Yeşilmen, Mustafa Şahmaran PII:

S0958-9465(17)30997-6

DOI:

10.1016/j.cemconcomp.2018.01.004

Reference:

CECO 2973

To appear in:

Cement and Concrete Composites

Received Date: 5 November 2017 Revised Date:

19 December 2017

Accepted Date: 2 January 2018

Please cite this article as: Gü. Yıldırım, A.H. Khiavi, S. Yeşilmen, M. Şahmaran, Self-healing performance of aged cementitious composites, Cement and Concrete Composites (2018), doi: 10.1016/ j.cemconcomp.2018.01.004. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. 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.

ACCEPTED MANUSCRIPT 1

Self-healing Performance of Aged Cementitious Composites

2

Gürkan Yıldırıma, Arash Hamidzadeh Khiavia, Seda Yeşilmenb, Mustafa Şahmaranc* a

3

Department of Civil Engineering, Adana Science and Technology University, Adana, Turkey b

4

c

5

Department of Civil Engineering, Çankaya University, Ankara, Turkey

Department of Civil Engineering, Hacettepe University, Ankara, Turkey

7

Abstract

RI PT

6

This study investigates the autogenous self-healing capability of one-year-old engineered

9

cementitious composites (ECC) with different mineral admixtures to understand whether self-

10

healing performance in late ages is similar to that of early ages. Sound and severely pre-cracked

11

specimens were subjected to different environmental conditions including water, air, “CO2-

12

water,” and “CO2-air” for one year plus 90 days of initial curing. Self-healing performance of

13

ECC mixtures was assessed in terms of crack characteristics, electrical impedance testing, rapid

14

chloride permeability testing and microstructural analysis. Laboratory findings showed that the

15

presence of water is crucial for enhanced autogenous self-healing effectiveness, regardless of

16

mixture composition. “CO2-water” curing resulted in the best self-healing performance of all

17

curing conditions, which was confirmed with results from different performance tests throughout

18

the experimental study. By further curing specimens under “CO2-water” (depending on the ECC

19

mixture composition), cracks as wide as half a millimeter (458 µm) were easily closed by

20

autogenous self-healing within only 30 days of further curing, and all cracks closed completely

21

after 90 days. Because high levels of CO2 emission are a global problem, the effectiveness of

22

“CO2-water” curing in closing microcracks of aged cementitious composites specimens through

23

autogenous self-healing can help reduce the increasing pace of CO2 release. The results of this

24

study clearly suggest that late-age autogenous self-healing rates of ECC specimens can be

25

significantly enhanced with proper further environmental conditioning and mixture design.

AC C

EP

TE D

M AN U

SC

8

26 27

Keywords: Engineered Cementitious Composites (ECC); Self-healing; Curing Conditions;

28

Electrical Impedance; Rapid Chloride Permeability.

29 30 31 32 *:

Corresponding author, Phone: +90-312-297-6991 e-mail: [email protected]

1

ACCEPTED MANUSCRIPT 33

1. Introduction Engineered Cementitious Composites (ECC) are feasible new-generation concrete materials

35

for suppressing crack initiation and further growth of crack width [1-3]. ECCs are one of a

36

special branch of High Performance Fiber-Reinforced Cementitious Composites (HPFRCCs) and

37

are characterized by superior tensile ductility due to the formation of multiple microcracking.

38

The ability of ECC to exhibit multiple microcracks with typical widths of less than 100 µm is a

39

direct consequence of pseudo strain-hardening behavior [4]. Tight microcracking is one of the

40

key parameters in increasing the time to initiation of deterioration, slowing down the rate of

41

deterioration, prolonging the serviceability of structures and, last but not least, favoring self-

42

healing capability with no external interference (autogenous self-healing) [4-9].

SC

RI PT

34

To date, ECCs incorporated with different polymeric fibers such as polyethylene (PE) [10],

44

polyvinyl alcohol (PVA) [11], and high tenacity polypropylene (HTPP) [12] have been

45

successfully manufactured without sacrificing multiple microcracking behavior. Moreover, the

46

latest efforts have shown that polymeric fibers (e.g., PVA) in ECCs can alternatively be

47

substituted with eco-friendly natural fibers (e.g., hemp and flax) after chemical surface treatment

48

[13,14]. Despite the effectiveness of different fibers on composite materials’ multiple

49

microcracking behavior, due to the cost of polymeric fibers, most studies have been centered on

50

less expensive PVA fiber-based ECC mixtures.

TE D

M AN U

43

Due to concerns about uniform distribution of fibers and ultimate tensile ductility, no coarse

52

aggregates are used in ECC production, therefore overall Portland cement amount as the binding

53

phase for the mixtures is significantly high. However, considering the high energy consumption,

54

negative environmental impact of Portland cement production, along with its dimensional

55

stability problems, Portland cement content in ECC is generally reduced by replacing it with

56

high volumes of pozzolanic materials such as fly ash, slag, limestone powder and metakaolin.

57

Use of pozzolans in high volumes contributes to the superior tensile ductility and durability

58

characteristics of ECC [15]. It has also been reported that the degree of autogenous self-healing

59

is dependent on the composition of cementitious composites, and it increases along with the ratio

60

of pozzolan/cement [16,17]. This effect is due to the kinetic nature of pozzolanic reactions and

61

the higher long-term availability of unreacted pozzolanic materials compared to Portland cement.

62

However, even when high amounts of pozzolans are used in ECC production, autogenous self-

63

healing of very mature specimens may not be as effective as the younger ones due to inadequate

64

availability of portlandite and moisture in the long term.

AC C

EP

51

2

ACCEPTED MANUSCRIPT It is notable that most self-healing studies, use ECC specimens subjected to initial pre-

66

cracking at 28 days of age or earlier [5-7,15-17]. Therefore, understanding of the self-healing

67

performance of aged ECC is very limited. To account for this, recent studies focusing on the

68

self-healing performance of 180-day-old (medium-term) ECC specimens [4,18-20] were

69

performed. In a different study, HPFRCC specimens subjected to the longest initial curing period

70

(11 months) before the application of pre-cracking for self-healing assessment were utilized [21].

71

However, considering the significantly high cracking occurrence at late ages and its

72

detrimental effects on the structural service life, more information is needed about the lifespan of

73

self-healing in aged ECC. Therefore, contrary to the majority of self-healing studies of early-age

74

ECC specimens and those focusing on medium-term self-healing, this research investigated

75

autogenous self-healing capability of very mature (one-year-old) ECC specimens produced with

76

different pozzolans (Class-F fly ash, Class-F fly ash with hydrated lime, ground granulated blast

77

furnace slag) and cured under different environmental conditions (water, air, CO2-water and

78

CO2-air). In addition to commonly preferred environments for further curing (e.g. water and air),

79

CO2-rich environmental conditioning options (e.g. CO2-water and CO2-air) were also tested; up

80

to certain limit, they may be advantageous for capturing increased CO2 concentrations in the

81

atmosphere. These research findings are expected to provide useful data for understanding the

82

effectiveness of autogenous self-healing capability of ECC, regardless of the time of damage

83

occurrence (i.e. cracking) and under a wide spectrum of environmental exposures.

84

TE D

M AN U

SC

RI PT

65

2. Experimental program

86

2.1. Ingredients, proportioning, manufacturing and initial curing of mixtures

EP

85

ECC mixtures produced in this study were composed of CEM I 42.5R type ordinary

88

Portland cement (PC), fine silica sand with a maximum aggregate size of 0.4 mm, specific

89

gravity of 2.60 and water absorption capacity of 0.3%, potable mixing water, liquid

90

polycarboxylic ether-based high-range water reducing admixture (HRWRA) with solid content

91

of 40% and polymeric PVA fibers at 2% of mixture volume, with a diameter of 39 µm, length of

92

8 mm, nominal tensile strength of 1610 MPa, elastic modulus of 42.8 GPa, maximum elongation

93

of 6%, and specific gravity of 1.3. Mixtures also incorporated pozzolanic materials including

94

Class F fly ash (FA, ECC-FA) and ground granulated blast furnace slag (GGBFS, ECC-S). An

95

additional mixture (ECC-FA/CH) was manufactured by incorporating 5% commercially

96

available hydrated lime (CH) by total weight of cementitious materials (i.e. PC + FA) into the

AC C

87

3

ACCEPTED MANUSCRIPT 97

ECC-FA mixture. Chemical and physical properties of PC, FA, GGBFS and silica sand are

98

illustrated in Table 1. All mixtures were produced with a constant water to cementitious materials ratio (W/CM)

100

of 0.27 and pozzolanic materials to PC ratio of 1.2, by weight. Mixture proportions are presented

101

in Table 2. During mixing, all dry components of the matrix (PC, FA, GGBFS, CH and sand

102

[changed depending on the mixture type]) were mixed together, then pre-weighed water and high

103

range water reducing admixture were added. Finally, fibers were slowly added and dispersed.

104

HRWRA amount was not kept constant in different mixtures due to varying fineness values of

105

specific ingredients, and was therefore adjusted in accordance with the desirable fresh mortar

106

properties to favor fiber distribution.

SC

RI PT

99

All tests performed in this study used Ø100×50 mm cylindrical specimens. For extraction of

108

smaller scale cylinders to be used in tests, Ø100×200 mm cylindrical specimens were cast using

109

different ECC mixtures. After initial casting of fresh mixtures, Ø100×200 mm cylindrical

110

specimens were kept in their molds for 24 hours at 50±5% RH and 23±2 oC, with their surfaces

111

covered with plastic sheets. After 24 hours, specimens were taken out of their molds. Initial

112

curing in isolated plastic bags at 95±5% RH and 23±2 oC was initiated on the second day to the

113

end of one year. After a year of initial curing, Ø100×50 mm specimens were extracted from

114

whole Ø100×200 mm specimens with a diamond blade saw.

115 116

2.2. Initial damage introduction

TE D

M AN U

107

To monitor self-healing behavior, the one-year-old Ø100×50 mm cylinders were pre-loaded

118

under splitting tensile loading to generate cracks of varying numbers and widths. Given the

119

different compositions of ECC mixtures, achieving similar microcracking damage with a

120

constant pre-loading level was not possible. Therefore, to determine their ultimate splitting

121

tensile deformation capacities, four Ø100×50 mm cylinder specimens from each mixture were

122

loaded until failure at a loading rate of 0.005 mm/s using a closed-loop controlled material

123

testing system. After testing, splitting tensile stress vs. deformation plots for each specimen were

124

drawn and deformation levels corresponding to maximum splitting tensile stress levels were

125

defined as the ultimate splitting tensile deformation capacity, with results averaged for each

126

mixture. One-year ultimate splitting tensile deformation capacities of different mixtures were

127

very similar, with levels of around 2 mm. All specimens from different mixtures with a common

128

initial pre-loading level were therefore pre-cracked to impart microcracks. A common initial pre-

129

loading level was set at 70% of ultimate splitting tensile deformation capacity of different

130

specimens, meaning that application of initial pre-loading almost caused severe failure for all

AC C

EP

117

4

ACCEPTED MANUSCRIPT 131

specimens. In addition to the pre-loaded specimens, the same number of sound specimens was

132

also used in tests for comparison purposes.

133 134

2.3. Further environmental conditioning After initial pre-loading on the 365th day, reference measurements from sound and pre-

136

loaded specimens were recorded using different test methods. Beyond 365 days, further

137

environmental curing was applied to specimens in two separate curing cabinets. Both cabinets

138

had a 120-liter capacity, and the ability to achieve relative humidity between 20-95% and

139

temperatures between -10 – 60 °C. The only difference between the two cabinets was that

140

Cabinet II was able to achieve a CO2 concentration of up to 20% in the controlled environment.

141

As seen in Fig. 1, Cabinet I was set to achieve a controlled environment with 50±5 oC and

142

50±5% RH, while Cabinet II was set to 50±5 oC, 50±5% RH and 3% CO2 concentration. Each

143

cabinet also contained a separate container for submerging specimens in water. Specimens (both

144

sound and pre-loaded) cured in air in Cabinet I at 50±5 oC, 50±5% RH are shown as “air,” while

145

specimens cured in water in Cabinet I at 50±5 oC, 50±5% RH are shown as “water.” The same

146

procedure was followed for Cabinet II (Fig. 1).

M AN U

SC

RI PT

135

To account for possible variations in each of the proposed environmental conditioning, four

148

sound and pre-loaded specimens from each mixture were used for each rapid chloride

149

permeability [RCP] and electrical impedance [EI] test. The further environmental conditioning

150

lasted for 90 days, with RCP and EI tests repeated after each 15-day interval. A temperature

151

range of 50±5 oC was selected based on the conclusions of Reinhardt and Jooss [22], who stated

152

that high temperatures are favorable for faster self-healing kinetics. An RH level of 50±5% was

153

selected and a separate water container was used in each cabinet, since self-healing is reported to

154

be more pronounced in fully and/or partially wet conditions [23]. The RH level was also selected

155

because it favors calcium carbonate precipitation through carbonation reactions, which is

156

reported to be one of the main mechanisms significantly contributing to autogenous self-healing

157

[24]. There is a consensus between the results of carbonation tests conducted at natural and/or

158

below 4% CO2 concentrations, indicating that this type of accelerated test can be used to interpret

159

probable long-term carbonation effect [25], which can influence long-term self-healing of

160

microcracks. Hence, in Cabinet II, CO2 level was set at 3%. By comparing self-healing

161

performances of specimens placed in different cabinets, the influence of promoted carbonation

162

reactions on autogenous self-healing of ECCs was more clearly assessed.

163 164

2.4. Proposed testing methods for self-healing

AC C

EP

TE D

147

5

ACCEPTED MANUSCRIPT 165

Electrical impedance (EI) measurements were recorded from different Ø100×50 mm

166

cylindrical specimens to assess self-healing, using a concrete electrical resistivity meter with

167

uniaxial configuration. Details of the electrical resistivity meter and proposed EI testing to assess

168

autogenous self-healing of cementitious composites have been thoroughly discussed in the recent

169

works of the authors [26,27], thus no further explanations were provided here. One of the most important considerations for EI testing is the individual moisture states of

171

specimens during testing. Since electrical measurements can be affected by extra moisture and

172

high temperature levels after curing under different conditions, various drying/cooling

173

procedures were followed for specimens cured in air and water in each cabinet before EI testing.

174

After being removed from the cabinets on specified days, air-cured specimens were left out in a

175

controlled room at 50±5% RH, 23±2 oC for 24 hours. When water-cured specimens reached

176

testing age, they were dried out in an oven at 60 oC for around 24 hours, then allowed to cool in a

177

controlled room at 50±5% RH, 23±2

178

environmental conditions were determined based on specimens reaching a constant weight at

179

room temperature. The difference between any two successive weight measurements was less

180

than 0.5% of the lowest value obtained. All specimens were tested at similar moisture states.

o

SC

RI PT

170

M AN U

C for another 24 hours. Drying duration and

Rapid chloride permeability (RCP) testing, conducted according to the ASTM C1202 [28]

182

standard, was also used to evaluate self-healing of ECC specimens. RCP tests were performed on

183

water-saturated specimens and results were recorded in terms of electrical charge passed in

184

Coulomb (C).

TE D

181

In addition to EI and RCP tests, visual observations of microcracks were also made before

186

and after self-healing occurrence using a video microscope with 125× magnification capability.

187

For each given mixture and curing condition, specified ages and results recorded from specimens

188

used for RCP and EI tests were averaged and microcrack characteristics were measured from a

189

specific surface based on those averages.

AC C

EP

185

190

Finally, after 90 days of further curing in different environmental conditions, ultimate self-

191

healing products from different ECC mixtures were further analyzed using thermogravimetry

192

(TGA/DTG), X-ray diffraction (XRD) and scanning electron microscopy (SEM). For

193

thermogravimetric analysis, powder samples weighing approximately 50 mg were subjected to

194

temperatures escalating from room temperature to 1050°C at a rate of 10°C/min. Temperature

195

exposure occurred in a carbon dioxide-free environment with 100 ml/min nitrogen flow. Before

196

grinding, specimens were kept in acetone up to testing to stop the hydration process. For the

197

chemical evaluation of final self-healing products, XRD analyses were performed on powder

198

samples gently scratched with a razor from the surfaces of healed microcracks of ECCs 6

ACCEPTED MANUSCRIPT subjected to different further environmental conditions. These samples had an approximate

200

weight of 20 mg and particle size of less than 150 µm. Chemical compositions of self-healed

201

microcracks were further detailed with SEM micrographs.

202 203

3. Experimental results

204

3.1. Crack characteristics

RI PT

199

Before being exposed to further environmental conditioning, crack widths of ECC

206

specimens were measured after initial pre-loading. In Fig. 2, densities of crack width

207

measurements are presented. While constructing this figure, 3-parameter Weibull distribution

208

which had the best fit was selected among various distributions. Fig. 2 shows a higher number of

209

microcracks with smaller widths in ECC-FA specimens. For example, after initial pre-loading,

210

ECC-S specimens exhibited a smaller number of microcracks with widths of less than 100 µm

211

and a larger number of microcracks with widths higher than 150 µm. Microcracks formed over

212

ECC specimens with slag after initial pre-loading had a tendency to have larger openings than

213

those containing fly ash. Replacing Portland cement with slag led to a stronger matrix in

214

comparison to fly ash, resulting in cracks with larger widths and spacing.

M AN U

SC

205

Previous comparisons between ECC systems in which Portland cement was replaced with

216

slag and fly ash showed similar behavior [23,26,29]. ECC-FA/CH specimens also exhibited

217

wider cracks than ECC-FA. This behavior can be explained using the same argument made for

218

ECC-S specimens: adding hydrated lime (CH) to ECC-FA systems favors pozzolanic reactions

219

in the long term, resulting in a stronger matrix and a higher probability for fiber rupture rather

220

than fiber pull out upon loading, and therefore a smaller number of cracks with larger widths

221

[30]. Clear [31] reported that in order for a crack to be healed completely, crack width should be

222

less than 300 µm. Based on this finding and the data in Fig. 2, it is possible that almost all

223

purposely-introduced microcracks with different widths upon initial pre-loading can be healed

224

autogenously, regardless of mixture type.

AC C

EP

TE D

215

225

Despite the suggestion made by Clear [31], studies conducted by Jacobsen et al. [16],

226

Şahmaran and Yaman [32], Reinhardt and Jooss [22], Edvardsen [33] and Aldea et al. [34]

227

proposed that for pronounced self-healing, crack widths should not be more than 5-10 µm, 50

228

µm, 100 µm, 200 µm and 205 µm, respectively. Based on these suggestions, the long-term self-

229

healing performances of ECC mixtures further cured under different conditions were analyzed

230

with respect to initial crack width. Fig. 3 shows 90-day self-healing performances of ECC

231

mixtures under different curing conditions for specimens with microcrack widths of less than 7

ACCEPTED MANUSCRIPT 232

100 µm, between 100 and 200 µm, and more than 200 µm. Percental improvements given in Fig.

233

3 were formulated as [1 ˗ (crack width after 365+90 days/crack width after 365 days) × 100].

234

Calculations of improvements were made for each microcrack and average of results for a

235

specific range of crack width was shown in Fig. 3. Fig. 3 shows that all specimens demonstrated a certain extent of self-healing in all curing

237

conditions. Irrespective of initial crack widths, self-healing rates of specimens cured under water

238

were always higher than those cured in air. Depending on the mechanism (i.e. further hydration

239

and calcium carbonate precipitation), necessary elements such as moisture and CO2 needed to

240

find their own way through the microcracks to heal them. Although the selected humidity level

241

of 50±5% RH is high enough for considerable self-healing to take place, there is a clear

242

difference between being submerged in water and letting specimen surfaces be exposed to

243

external moisture without high osmotic pressure. The pronounced self-healing capability of

244

submerged specimens can therefore be related to the continuous availability of moisture near

245

crack surfaces. When water curing applied in Cabinets I and II is compared, the effect of high

246

CO2 exposure on the self-healing capability of ECC specimens can be more easily visualized.

247

Fig. 3 shows that self-healing rates of specimens submerged in water in Cabinet II (with CO2

248

level of 3% [CO2-water curing]) were higher for all initial crack widths and all mixtures. The

249

effectiveness of water curing under a CO2-rich environment compared to water curing in

250

atmospheric CO2 conditions became much more pronounced for microcracks with initial widths

251

larger than 200 µm. It is widely accepted that carbonation reactions are terminated when

252

concrete material is too dry (RH<40%), since CO2 cannot dissolve to produce carbonic acid

253

(H2CO3) with insufficient water. When concrete is saturated (RH>90%), carbonic acid is unable

254

to penetrate into the saturated pores and diffuse throughout the concrete, again preventing

255

carbonation.

EP

TE D

M AN U

SC

RI PT

236

In Cabinet II, environmental conditioning was set at 50±5 oC, 50±5% RH, 3% CO2. In this

257

environment, the goal was to dissolve the high concentration of CO2 at an ideal range of relative

258

humidity (50±5% RH), to obtain carbonic acid and then saturate the curing water with it. When

259

carbonic acid diffuses into concrete material, it can react with calcium hydroxide (CH) to

260

produce calcium carbonate through direct carbonation. Moreover, after being diffused into

261

concrete, it can be reduced into bicarbonate (HCO3–) and carbonate (CO32–) ions, depending on

262

the pH value of pore solution. These carbonates may react with Ca2+ ions leached away from

263

both CH and calcium silicate hydrate (C-S-H) gels to form calcium carbonate [23,26]. The more

264

pronounced self-healing performance in CO2-water curing was therefore largely attributed to

AC C

256

8

ACCEPTED MANUSCRIPT 265

direct carbonation reactions and calcium carbonate precipitation, and slightly to further hydration

266

reactions in a completely wet environment. These results are further detailed later in this paper. To achieve complete healing of microcracks, width is important; considering the total

268

amount of product that needs to be produced via different self-healing mechanisms. The

269

importance of initial microcrack widths can be visualized more easily by looking at Fig. 3. When

270

the self-healing performances of microcracks of different widths are compared for different ECC

271

specimens further exposed to CO2-water curing, at least 77% of all microcracks with widths of

272

less than 100 µm were completely healed. When initial crack widths of specimens under the

273

same curing condition were greater than 200 µm, more than half (52%) were completely healed.

RI PT

267

Table 3 displays crack characteristics of different ECC mixtures. It also shows that

275

depending on mixture type, cracks of up to 458 µm in one-year-old specimens can be healed

276

completely after 90 days of CO2-water curing. Moreover, 90 days was more than enough for

277

complete closure of large cracks, even after 15 days of further curing significant amounts of self-

278

healing products were observed on the surface of cracks (Fig 4). Most self-healing studies have

279

concluded that self-healing rate is much more pronounced in early-age specimens, given the

280

abundance of unhydrated cementitious components to be further hydrated and fill microcracks.

281

Nevertheless, the current study suggests that along with the high early-age self-healing rate of

282

ECC specimens reported in literature, late-age self-healing rates of aged ECC specimens can be

283

similar to early-age with proper further environmental conditioning and mixture design. These

284

results could answer the long-standing question of whether autogenous self-healing in the

285

microcracks of aged ECCs is as effective as it is in younger specimens.

TE D

M AN U

SC

274

Based on their compositions, different ECC mixtures resulted in different self-healing

287

performances. Fig. 3 shows that for almost all curing conditions and initial crack widths, self-

288

healing performance of ECC-FA was more pronounced. Superior self-healing performance of

289

ECC-FA was much more evident under CO2-water curing for all crack widths; the 90-day

290

healing rate of ECC-FA specimens with widths of less than 100 µm was 100% under CO2-water

291

curing beyond 365 days of initial curing. For ECC-FA specimens with initial crack widths

292

between 100 µm and 200 µm and larger than 200 µm under the same curing conditions, healing

293

rates were 99.4% and 98.8%, respectively. It is interesting to note that under CO2-water curing,

294

cracks up to 458 µm wide were healed even after an additional 30 days (Table 3 and Fig. 4).

295

Under certain environmental conditioning, completely self-healed maximum microcrack widths

296

(458 µm) recorded from aged ECC-FA specimens were considerably higher than those reported

297

in literature [16,22,31-34]. ECC-FA specimens exhibited higher self-healing rates under CO2-

AC C

EP

286

9

ACCEPTED MANUSCRIPT 298

water curing due to the precipitation of calcium carbonate, as will be further detailed in

299

forthcoming sections. In terms of crack plugging, performance rankings of other mixtures changed depending on

301

crack width and further curing conditions. In general, ECC-FA was followed by ECC-FA/CH

302

and ECC-S. However, despite their lower crack healing performances compared to ECC-FA

303

(Fig. 3), maximum crack widths of completely self-healed microcracks in ECC-FA/CH (356 µm)

304

and ECC-S (397 µm) mixtures were still well above the threshold of 300 µm mentioned by Clear

305

[31].

306 307

3.2. Electrical impedance (EI)

308

3.2.1. One-year-old specimens

SC

RI PT

300

Direct electrical measurements (electrical impedance – EI) recorded from sound and pre-

310

loaded ECC specimens for different further curing conditions are shown in Fig. 5. At the time of

311

each EI testing, special care was taken to bring all ECC specimens subjected to different

312

environmental conditions to a similar moisture state (by reaching constant weight conditions) in

313

order not to risk the sensitivity of EI measurements.

M AN U

309

There were minor differences in the EI values of one-year-old sound ECC specimens.

315

Electrical resistivity testing is a commonly used method to evaluate microstructural properties of

316

cement-based composites, which is largely influenced by the changes in porosity, pore solution

317

chemistry, pore network tortuosity and moisture state at the time of testing [35]. After 365 days,

318

sound specimens of different mixtures resulted in similar microstructural properties with similar

319

maturity, making EI results very close. On the other hand, upon initial pre-loading for crack

320

introduction, average EI results of one-year-old sound ECC specimens increased dramatically

321

(Fig. 5), although increment rates were very different depending on mixture type. For example,

322

average one-year EI results of ECC-FA specimens to be subjected to 90 days of further curing

323

were 58 kΩ, while the same value increased by 117% – reaching 126 kΩ – for pre-loaded

324

specimens of the same age. For ECC-FA/CH and ECC-S specimens, similar increment rates with

325

initial pre-loading were 170% (46 kΩ to 124 kΩ) and 479% (38 kΩ to 220 kΩ), respectively.

326

More pronounced increments noted in the EI results of sound ECC-S specimens upon initial pre-

327

loading were attributed to decisiveness of crack width values on individual EI results rather than

328

crack numbers (see Section 3.1) [26,27]. Another reason for the higher increments in EI results

329

of ECC-S upon initial pre-loading may be the influence of PVA fibers bridging opposite crack

330

faces. Although PVA fibers are non-conductive, they are covered with fragments of conductive

AC C

EP

TE D

314

10

ACCEPTED MANUSCRIPT cementitious matrix. Given the higher fracture toughness and fiber-to-matrix chemical bonding

332

of ECC-S specimens, more fibers are likely to break than be pulled out under loading, which

333

reduces the chance for crack bridging and contributes to higher increment rates in EI results of

334

pre-loaded ECC-S.

335 336

3.2.2. Effects of further environmental conditioning beyond initial 365 days of curing

RI PT

331

The changes in average EI results of sound and pre-loaded specimens with 90 days of

338

different environmental conditioning are shown in Fig. 5. This figure showed that although

339

water-cured specimens were dried to reach a similar moisture state throughout EI testing, the

340

inner pores of ECC specimens remained saturated. As a result, EI results of water- and air-cured

341

specimens showed a large difference for both sound and pre-loaded specimens. Therefore, it was

342

decided to compare the results of water- and air-cured specimens among themselves.

SC

337

Almost all EI results of sound specimens of ECC mixtures subjected to air curing

344

(regardless of CO2 exposure) increased continuously until the end of 365+90 days. Although

345

ECC specimens were older than one year at the time of testing, continuous increments in the EI

346

results of sound ECC specimens were attributed to the densification of cementitious paste, which

347

further reduced both the amount of pore solution transporting conductive ions and the number of

348

least-resistive paths. For further air-cured sound ECC specimens, EI values and rates of

349

increment in EI values of ECC-FA mixtures were the highest among different ECCs, especially

350

when compared to ECC-S mixture. For example, while EI results of sound specimens further

351

cured for 90 days under CO2-air conditioning increased by 1210% (60 kΩ to 792 kΩ), the same

352

increment rates were 1103% (46 kΩ to 559 kΩ) for ECC-FA/CH and 810% (45 kΩ to 409 kΩ)

353

for ECC-S mixtures. Similar behavior was also monitored in air conditioning without high CO2

354

concentration, albeit to a lesser extent. This behavior of further air-cured sound specimens was

355

associated with the ionic states of specimens at the time of testing. The pore solution chemistry

356

of cementitious composites plays a key role in EI results, especially at late ages. When mixed

357

with water, cementitious components add considerable concentrations of Na+, K+, OH-, Ca2+ and

358

SO42- ions into the mixing water. As a result of setting and early hydration, however, Ca2+ and

359

SO42- ions diminish appreciably, leaving a pore solution that is composed mainly of dissolved

360

alkali hydroxides. In an aqueous medium at 25 oC, ionic conductivities of Na+, K+ and OH- are

361

50.1, 73.5 and 198 cm2 equiv-1 Ω-1, respectively [36]. Given the significantly higher electrical

362

conductivity of OH- ions compared to other alkalis in pore fluid, and the faster consumption of

363

calcium hydroxide through pozzolanic reactions in the presence of Class-F fly ash particles, the

364

substantially higher EI results recorded at later ages are more understandable. On the other hand,

AC C

EP

TE D

M AN U

343

11

ACCEPTED MANUSCRIPT 365

the addition of external CH in ECC-FA/CH and the more pronounced cementing capability of

366

slag particles compared to pozzolanic behavior in ECC-S are likely to increase the amount of CH

367

and associated OH- ion concentrations, leading to lower increments in EI results with time. Another important point to note was that average EI results of sound specimens subjected to

369

air curing with high CO2 were higher than those that were not, especially at late ages. This

370

behavior, observed with high CO2 concentration, was attributed to accelerated carbonation and

371

its effects on pore solution chemistry. Because carbonation is known to reduce pore solution

372

alkalinity, the higher-than-expected rates of carbonation with CO2-rich air curing which

373

ultimately reduced the associated OH- ions in the pore solution, could be the reason for the

374

abovementioned behavior of sound specimens. Carbonation is also known to reduce porosity,

375

since the volume of carbonation products is larger than the consumed CH. Reduced porosity in

376

carbonated regions may have also played a role in further increasing the EI values of sound

377

specimens cured in CO2-rich air.

M AN U

SC

RI PT

368

Fig. 5 also shows consistent differences in the EI results of pre-loaded ECC specimens cured

379

in air with and without high CO2 concentration. Furthermore, differences in air-cured EI results

380

of pre-loaded ECC-FA specimens with and without high CO2 concentration were much smaller

381

than in ECC-FA/CH – and especially in ECC-S specimens – due to crack characteristics. ECC-

382

FA exhibited the smallest crack widths of all mixtures due to carbonation.

TE D

378

Carbonation is a process that starts from the surface of the specimens, and is then governed

384

by CO2 diffusion through the surface. The largest crack widths observed in ECC-S specimens

385

had a higher surface area and increased diffusion depths, and carbonation reactions were

386

therefore expected to be more prevalent in these specimens. Thus, the differences between EI

387

values for pre-loaded specimens cured in air with and without high CO2 concentration were

388

larger when crack widths were larger. Fig. 5 shows that EI results of ECC-S specimens air-cured

389

under high CO2 concentration were higher than other mixtures, while EI results of ECC-S

390

specimens air-cured under atmospheric CO2 were lower.

AC C

EP

383

391

Average EI results of sound specimens further cured under water were different than those

392

of air-cured specimens, as they did not show marked changes regardless of high CO2 exposure

393

and mixture type. Although continuous increments in EI results of water-cured sound specimens

394

were anticipated with improved matrix properties over time, and specimens were dried at 60 oC

395

for 24 hours to reach a constant weight before EI testing, no distinctive changes in values were

396

noted with further curing due to the water remaining in the isolated pores of ECC specimens.

397

Fig. 6 shows the ratio of EI values of pre-loaded specimens to sound specimens (EIPL/EIS)

398

along with the rate of crack healing against additional curing days for different ECC mixtures 12

ACCEPTED MANUSCRIPT under different environmental conditions. The figure shows a correlation between the crack

400

healing rates and EIPL/EIS ratios of ECC specimens, suggesting that pre-loaded specimens can

401

reach original EI results of sound specimens by plugging cracks through self-healing. EIPL/EIS

402

ratios of specimens cured under water with and without high CO2 exposure converge close to

403

one, and crack healing rates of these specimens are significantly higher than those cured in air,

404

suggesting superior self-healing performance. As previously detailed and shown in Fig. 4, the

405

most prominent self-healing of microcracks for all ECC mixtures was achieved with CO2-water

406

curing. Correlatively, the smallest EIPL/EIS ratios were recorded from CO2-water cured

407

specimens for almost all ECC mixtures.

RI PT

399

For almost all ECC specimens cured in water with and without high concentrations of CO2,

409

most self-healing was achieved within the first additional 15 days (as also reported in Section

410

3.1), so that EIPL/EIS ratios started to stabilize around one during this period. In some instances,

411

however, convergence of EIPL/EIS ratios around one continued beyond the first 15 days. In

412

addition to under water curing, air curing was also effective in converging EIPL/EIS ratios around

413

one, depending on mixture type, curing condition and additional curing period. For example,

414

ECC-FA exhibited EIPL/EIS ratio of 1.235 after 90 days of additional CO2-air curing beyond the

415

first 365 days. This suggests a certain amount of self-healing occurrence in terms of electrical

416

measurements, even when cured in air.

TE D

M AN U

SC

408

When the self-healing performances of different mixtures are compared in terms of EI

418

results, EIPL/EIS ratios closest to one were obtained mostly from ECC-FA specimens regardless

419

of further curing condition. This behavior was attributed not only to smaller crack widths due to

420

initial pre-loading, but also to the ionic states of specimens at time of testing (Fig. 6).

421 422

3.3. Rapid chloride permeability (RCP)

423

3.3.1. One-year-old specimens

AC C

EP

417

424

Fig. 7 shows average RCP test results of sound and pre-loaded ECC specimens subjected to

425

different environmental conditions. Fig. 7 clearly shows that RCP test results of all ECC

426

specimens after the initial 365 days of curing were very low. One-year RCP test results of sound

427

specimens allocated to be further cured under different environmental conditions were 150 C, 98

428

C and 186 C for ECC-FA, ECC-FA/CH and ECC-S mixtures, respectively. Although variations

429

in RCP results were small, the lowest values were recorded from sound ECC-FA/CH specimens

430

at the end of one year of initial curing.

13

ACCEPTED MANUSCRIPT When the amount of fly ash (specifically Class-F fly ash) used in mixtures exceeds 30-40%,

432

hydration is delayed because the amount of CH formed as a result of cement hydration is not

433

sufficient to completely diminish the excessive amounts of fly ash [29]. It therefore appears that

434

adding hydrated lime to ECC specimens with high volumes of fly ash (ECC-FA) triggered the

435

pozzolanic capacity of the cementitious systems. This led to higher improvements in chloride ion

436

penetrability of ECC-FA/CH specimens by forming additional C-S-H gels and filling the empty

437

spaces between the fine grains. Given that RCP test is an electrochemical test method, pore

438

solution chemistry is decisive on the overall results. However, compared to EI testing, RCP test

439

is less dependent on the ionic composition of pore solution and more on its porosity and pore

440

tortuosity [27]. It can therefore be concluded that ECC-FA/CH has better permeability properties

441

than ECC-FA due to pore refinement in the presence of extra calcium hydroxide addition.

SC

RI PT

431

Initial pre-loading of one-year-old sound ECC specimens caused RCP test results to

443

increase, since new microcracks provided new pathways for chloride ions. Average RCP test

444

results of sound specimens allocated for further curing under different environmental conditions

445

increased from 127 C to 514 C for ECC-FA, from 86 C to 655 C for ECC-FA/CH, and from 177

446

C to 594 C for ECC-S. Although certain increments in RCP test results were noted with initial

447

pre-loading, and increment rates varied for different ECC mixtures, chloride ion penetrability

448

values were still in the very low range (less than 1000 C) according to ASTM C1202 standard. It

449

is important to keep in mind that initial pre-loading was at 70% of ultimate splitting tensile

450

deformation capacity, which is a very high level of damage.

451 452

3.3.2. Effects of further environmental conditioning beyond initial 365 days of curing

EP

TE D

M AN U

442

Fig. 7 shows that RCP test results continuously decreased regardless of further curing

454

condition, for all sound ECC specimens from different mixtures, due to the development of

455

matrix properties with time. Depending on the further curing condition, values as low as 16 C

456

(from ECC-FA/CH specimens further cured under CO2-water curing) were obtained from sound

457

specimens after 365+90 days. However, no detailed discussions were made regarding the

458

changes in RCP test results of further cured sound specimens, since the values were already

459

relatively low, even at the end of 365 days of initial curing.

AC C

453

460

Similar to the behavior of sound specimens, average RCP test results of pre-loaded

461

specimens decreased continuously with time regardless of the type of further conditioning (Fig.

462

7). Although results decreased continuously until the end of 90 days beyond the initial 365, the

463

rate of decrements in RCP test results of pre-loaded specimens were significantly higher than

464

sound specimens for the first 15 days. This suggests pronounced self-healing achievement during 14

ACCEPTED MANUSCRIPT 465

this period (Fig. 7). For example, average RCP test results of pre-loaded specimens of ECC-FA,

466

ECC-FA/CH and ECC-S subjected to 15 days of further CO2-water curing improved by 79%

467

(from 527 C to 111 C), 76% (from 631 C to 152 C) and 63% (from 530 C to 196 C) respectively.

468

Results of RCP tests were in line with EI tests and analysis of crack characteristics. CO2-water curing was the most effective further curing condition for lowering average RCP

470

test results of pre-loaded ECC specimens, regardless of mixture type. Water curing without high

471

CO2 concentration was the second most effective curing condition, followed by CO2-air and air

472

curing. The effectiveness of water curing on self-healing (regardless of the CO2 concentration) in

473

terms of chloride ion penetrability in the first 15 days of further curing is clearly illustrated in

474

Fig. 7, with steeper slopes of RCP curves for water-cured specimens than those cured in air. For

475

effective self-healing performance, therefore, the presence of water is critically important.

SC

RI PT

469

As mentioned, RCP test is less dependent on moisture state than EI test, since RCP tests are

477

conducted under fully-saturated conditions. Results of specimens exposed to different curing

478

conditions can more easily be compared among themselves. Looking at the first 15 days of

479

curing, where self-healing was much more prevalent, the highest drops in permeability were in

480

ECC-FA/CH, which exhibited larger cracks compared to ECC-FA. This explains the higher

481

permeability results recorded just after initial pre-loading. The smallest crack widths in ECC-FA

482

led to slower healing rates in terms of RCP test results, since self-healing is more diffusion-

483

dependent when crack widths are small. In addition, self-healing rate was even slower for air-

484

cured specimens because it relies mostly on CO2 diffusion and subsequent carbonation. The

485

permeability drop was relatively fast and high for ECC-S specimens subjected to water and CO2-

486

air curing, as the water and CO2 penetrated through the relatively large cracks formed during

487

pre-loading. However, for specimens air cured in atmospheric CO2 levels, low levels of

488

carbonation and continuing pozzolanic reactions were less effective against such large cracks.

EP

TE D

M AN U

476

Self-healing performances of different ECC mixtures in terms of lowering RCP test results

490

were very close to each other, although decrement rates were slightly more pronounced for ECC-

491

FA and ECC-FA/CH, especially with water-based further curing. According to Andrade [37],

492

OH- ions in pore fluid act as supporting electrolytes and are responsible for the movement of

493

substantial amounts of charge during RCP testing, given their higher conductivity (198 cm2

494

equiv-1 Ω-1) compared to other ions present in the pore fluid (Na+, K+, Ca2+, and Cl–). The higher

495

decrement rates in RCP test results of ECC-FA specimens could therefore be related to OH- ion

496

depletion caused by diminished portlandite with further pozzolanic capability. The superior

497

performance of ECC-FA/CH in reducing RCP test results, on the other hand, was attributed to

AC C

489

15

ACCEPTED MANUSCRIPT 498

pore refinement in the presence of added calcium hydroxide. These results indicate that RCP test

499

results are more influenced by matrix properties than the ionic state of pore solution.

500 501

3.4. Self-healing products Although reaction products of autogenous self-healing appear in literature, results are

503

inconsistent due to heterogeneous dispersion and time-dependent compositions of reaction

504

products [38]. Therefore, to detail ultimate reaction products from different ECC mixtures,

505

specimens were investigated using thermo-gravimetry (TGA/DTG), X-ray diffraction (XRD)

506

and scanning electron microscopy (SEM).

RI PT

502

As mentioned earlier, the main self-healing product of ECC mixtures was calcium carbonate

508

(CaCO3). TGA/DTG analysis was therefore used to further evaluate the precipitated CaCO3 on

509

microcrack surfaces. The presence of vaterite, aragonite, calcite and amorphous CaCO3 has been

510

reported for cementitious composites with different levels of carbonation [39]. CaCO3

511

decomposition occurs mainly in the 500-900 °C [40] range. Amorphous forms of CaCO3 start to

512

decompose in the same temperature range as CH [41], which complicates quantification of CH

513

or amorphous CaCO3 using TGA/DTG analysis. Thus, quantification of self-healing products

514

was limited to the polymorphs of CaCO3 in this study. The onset temperatures in TGA/DTG

515

analysis were visually determined, and DTG peaks in the ranges of 500-600 °C, 600-750 °C,

516

750-800 °C were quantified as vaterite, aragonite and calcite, respectively, which was similar to

517

previous studies [41,42]. Fig. 8 shows total percentages of CaCO3 calculated via TGA/DTG

518

analysis for each ECC in accordance with the selected further curing condition.

TE D

M AN U

SC

507

Fig. 8 shows a distinct difference between vaterite amounts in specimens subjected to air

520

and water curing for all ECC mixtures, regardless of CO2 exposure. The percentage of vaterite

521

was consistently lower in specimens subjected to water-based curing, probably due to the

522

dilution of ions in saturated medium and increased pozzolanic reactions in the presence of water.

523

Both mechanisms decrease the pH value of pore solution, and low pH value favors the formation

524

of aragonite over vaterite [39,43]. Additionally, the C/S ratio of C-S-H gels increases with high

525

calcium content, promoting vaterite formation, which is consistent with higher vaterite contents

526

observed in ECC-S specimens [39]. Amorphous CaCO3 forms when the pH value of the pore

527

solution is low, especially in the case of carbonation. But CO2 release from amorphous CaCO3

528

coincides with H2O release from CH, which makes it harder to calculate their masses accurately,

529

especially without a well-defined peak in the TGA/DTG chart [44]. It is important to note that

530

the highest total amounts of CaCO3 were obtained from specimens cured in CO2-water,

531

excluding ECC-FA/CH. Moreover, the highest total amounts of CaCO3 were not always

AC C

EP

519

16

ACCEPTED MANUSCRIPT recorded from specimens subjected to water-based curing (with and without high CO2

533

concentration), which was reported to be the most beneficial type of further environmental

534

conditioning for effective self-healing. In addition, for almost all further curing conditions, the

535

highest CaCO3 contents were found in ECC-S specimens (Fig. 8), although self-healing of cracks

536

(as explained in Section 3.1) was better in other mixtures (ECC-FA, ECC-FA/CH). Therefore,

537

although higher amounts of CaCO3 were obtained mostly from ECC-S, this may not be enough

538

for complete self-healing, which suggests the importance of tight microcracking.

RI PT

532

XRD patterns of ECC mixtures in different curing conditions are shown in Fig. 9. Quartz

540

peaks were significantly more pronounced than peaks for other crystals, regardless of applied

541

curing condition. This was attributed, to a large extent, to the presence of silica sand obtained

542

during scratching for sample preparation and, to a lesser extent, to the formation of C-S-H and

543

C-A-S-H gels within microcracks. Along with quartz (Q), well-defined peaks of calcite (C),

544

vaterite (V) and aragonite (A) were also observed in XRD analysis. The presence of different

545

CaCO3 species under CO2-water curing was more pronounced for all mixtures, supporting

546

previous TGA/DTG findings.

M AN U

SC

539

Self-healing products formed inside microcracks were also characterized with SEM

548

micrographs and further analyzed with EDX detector. Fig. 10 shows representative SEM

549

micrographs of different ECC mixtures further cured for 90 days under CO2-water curing beyond

550

initial 365 days. The figure clearly shows that this type of curing was significantly effective in

551

completely closing microcracks for all mixtures. In all EDX data recorded from different

552

specimens, Ca peaks reached the highest points, which suggests that the main self-healing

553

products under CO2-water curing in which the highest self-healing performance was achieved

554

were different calcium carbonate species. However, traces of Si and Al peaks were also observed

555

in ECC-FA and ECC-FA/CH, confirming the formation of C-S-H and slight formation of C-A-S-

556

H gels in the microcracks of these specimens.

557 558

4. Conclusions

AC C

EP

TE D

547

559

This study investigated autogenous self-healing performance of one-year-old (aged) ECC

560

mixtures with different compositions. ECC mixtures were produced with Class-F fly ash (FA,

561

ECC-FA), Class-F FA with hydrated lime (ECC-FA/CH) and ground granulated blast furnace

562

slag (S, ECC-S). One-year-old specimens were further aged for 90 days under water, air, CO2-

563

water and CO2-air curing, and self-healing assessments were made via crack characterization,

564

electrical impedance (EI) test, rapid chloride permeability (RCP) test and microstructural

565

analysis (TGA-DTG, XRD and SEM). Conclusions drawn from the study are listed below: 17

ACCEPTED MANUSCRIPT • In terms of crack plugging performance and other testing methods, CO2-water curing was

567

the best among all curing conditions, followed by water curing. These findings indicate that

568

water is a must-have component for enhanced autogenous self-healing efficiency. By

569

properly adjusting mixture proportions and selecting further environmental conditioning,

570

widths as large as 458 µm can easily be healed within only 30 days of further curing, despite

571

the very high maturity. Also, a crack healing rate of 100% (from ECC-FA mixture further

572

cured under CO2-water conditioning) can be achieved within 90 days of further curing,

573

irrespective of different crack characteristics.

RI PT

566

• As a new method, EI testing is fast and effective in capturing microcrack occurrence in

575

sound specimens and self-healing in pre-loaded specimens. EI results of sound specimens

576

from different mixtures increased significantly when microcracks were formed, indicating

577

that crack widths, rather than crack numbers, play an important role in increasing EI results

578

upon pre-loading. Depending on mixture type, further conditioning and subsequent drying of

579

specimens for EI testing, EI results similar to those of sound specimens can be obtained

580

from severely damaged specimens, especially ECC-FA. However, EI testing is quite

581

sensitive to changes in pore solution chemistry and moisture state of specimens at the time

582

of testing.

M AN U

SC

574

• Compared to EI, RCP testing is less dependent on the ionic states of specimens. One-year

584

RCP test results of most of ECC specimens (sound and pre-loaded) are either very low (less

585

than 1000 C) or negligible (less than 100 C), in accordance with ASTM C1202.

586

Microcracking caused marked escalations in RCP test results due to the creation of new

587

paths for free movement of chloride ions. However, even after microcracking – which

588

caused severe damage – average chloride ion penetrability results of specimens from

589

different mixtures stayed at very low levels. 15 days of further water-based curing

590

(especially CO2-water) was enough for most pre-loaded specimens to achieve nearly the

591

same RCP test results as sound specimens, suggesting self-healing occurrence.

AC C

EP

TE D

583

592

• Self-healing products formed inside microcracks with CO2-water curing originated mainly

593

from the precipitation of different CaCO3 species, although minor quantities of C-S-H and

594

C-A-S-H gels were also found in the microcracks of some specimens (ECC-FA and ECC-

595

FA/CH). This finding was confirmed with TGA/DTG, XRD analysis and SEM micrographs.

596

Considering the effects of different curing conditions, there appeared to be a difference in

597

the amounts of vaterite in specimens subjected to further water- and air-based curing.

18

ACCEPTED MANUSCRIPT CO2 emissions caused by industrial development, transportation and other industries are at

599

alarming levels nowadays. Although this is widely accepted to be a negative thing, it can also

600

be a very advantageous parameter in terms of autogenous self-healing of microcracks in ECCs.

601

Therefore, using ECC materials in places where CO2 concentrations in the air are particularly

602

high can help reduce those concentrations and significantly contribute to the sustainability of

603

infrastructures through enhanced self-healing capability. The current study also suggests that

604

along with the high early-age self-healing rate of ECC specimens reported in literature, self-

605

healing rates of aged ECC specimens can be similar to early-age with proper further

606

environmental conditioning and mixture design. Acknowledgement

SC

607 608

RI PT

598

The authors gratefully acknowledge the financial assistance of the Scientific and Technical

610

Research Council (TUBITAK) of Turkey provided under Project: MAG-112M876 and the

611

Turkish Academy of Sciences.

612 613

References

614

1.

V.C. Li, Advances in ECC research, ACI Spec. Publ. 206 (2002) 373–400.

615

2.

V.C. Li, On engineered cementitious composites (ECC) – a review of the material and its

617

applications, J. Adv. Concr. Technol. 1 (2003) 215–230. 3.

TE D

616

M AN U

609

V.C. Li, Engineered cementitious composites (ECC) – material, structural, and durability performance, in: E. Nawy (Ed.), Concrete Construction Engineering Handbook, CRC Press,

619

Boca Raton, 2008, pp. 1-46.

620

4.

EP

618

G. Yıldırım, A. Alyousif, M. Şahmaran, M. Lachemi, Assessing the self-healing capability of cementitious composites under increasing sustained loading, Adv. Cem. Res. 27 (2015)

622

581-592.

623

5.

AC C

621

G. Yıldırım, M. Şahmaran, M. Balçıkanlı, E. Özbay, M. Lachemi, Influence of cracking and

624

healing on the gas permeability of cementitious composites, Constr. Build. Mater. 85 (2015)

625

217-226.

626

6.

M. Şahmaran, G. Yıldırım, R. Noori, E. Özbay, M. Lachemi, Repeatability and

627

pervasiveness of self-healing in engineered cementitious composites, ACI Mater. J. 112

628

(2015) 513-522.

629 630

7.

A. Alyousif, M. Lachemi, G. Yıldırım, M. Şahmaran, Effect of self-healing on the different transport properties of cementitious composites, J. Adv. Concr. Technol. 13 (2015) 112-123.

19

ACCEPTED MANUSCRIPT 631

8.

D. Snoeck, K. Van Tittelboom, S. Steuperaert, P. Dubruel, N. De Belie, Self-healing

632

cementitious materials by the combination of microfibres and superabsorbent polymers, J.

633

Intel. Mat. Syst. Str. 25 (2014) 13-24.

634

9.

D. Snoeck, N. De Belie, Repeated autogenous healing in strain-hardening cementitious composites by using superabsorbent polymers, J. Mater. Civil Eng. 28 (2015) 04015086.

636

10. V.C. Li, Engineered cementitious composites (ECC) - tailored composites through

637

micromechanical modeling, in: N. Banthia, A. Bentur, A. Mufti (Eds.), Fiber Reinforced

638

Concrete: Present and the Future, Canadian Society of Civil Engineers, (1998), pp. 1–38.

639

11. M. Şahmaran, M. Al-Emam, G. Yıldırım, Y.E. Şimşek, T.K. Erdem, M. Lachemi, High-

640

early-strength ductile cementitious composites with characteristics of low early-age

641

shrinkage for repair of infrastructures, Mater. Struct. 48 (2015) 1389-1403.

SC

RI PT

635

12. B. Felekoğlu, K. Tosun-Felekoğlu, M. Keskinateş, E. Gödek, A comparative study on the

643

compatibility of PVA and HTPP fibers with various cementitious matrices under flexural

644

loads, Constr. Build. Mater. 121 (2016) 423-428.

M AN U

642

645

13. D. Snoeck, N. De Belie, Mechanical and self-healing properties of cementitious composites

646

reinforced with flax and cottonised flax, and compared with polyvinyl alcohol fibres,

647

Biosyst. Eng. 111 (2012) 325-335.

14. D. Snoeck, P.A. Smetryns, N. De Belie, Improved multiple cracking and autogenous healing

649

in cementitious materials by means of chemically-treated natural fibres, Biosyst. Eng. 139

650

(2015) 87-99.

653 654 655 656

volumes fly ash, Cem. Concr. Res. 39 (2009) 1033-1043.

EP

652

15. M. Şahmaran, V.C. Li, Durability properties of micro-cracked ECC containing high

16. S. Jacobsen, J. Marchand, H. Hornain, SEM observations of the microstructure of frost deteriorated and self-healed concretes, Cem. Concr. Res. 25 (1995) 1781-1790. 17. S. Liu, M. Zuo, Influence of slag and fly ash on the self-healing ability of concrete, Adv.

AC C

651

TE D

648

Mater. Res. 306 (2011) 1020–1023.

657

18. C.C. Hung, Y.F. Su, Medium-term self-healing evaluation of Engineered Cementitious

658

Composites with varying amounts of fly ash and exposure durations, Constr. Build. Mater.

659

118 (2016) 194-203.

660

19. C.C. Hung, Y.F. Su, H.H. Hung, Impact of natural weathering on medium-term self-healing

661

performance of fiber reinforced cementitious composites with intrinsic crack-width control

662

capability, Cem. Concr. Compos. 80 (2017) 200-209.

20

ACCEPTED MANUSCRIPT 663

20. C.C. Hung, Y.F. Su, Y.M. Su, Mechanical properties and self-healing evaluation of strain-

664

hardening cementitious composites with high volumes of hybrid pozzolan materials,

665

Compos. Part B-Eng. 133 (2018) 15-25. 21. L. Ferrara, V. Krelani, F. Moretti, M.R. Flores, P.S. Ros, Effects of autogenous healing on

667

the recovery of mechanical performance of high performance fibre reinforced cementitious

668

composites (HPFRCCs): part 1, Cem. Concr. Compos. 83 (2017), 76-100.

669 670

RI PT

666

22. H.W. Reinhardt, M. Jooss, Permeability and self-healing of cracked concrete as a function of temperature and crack width, Cem. Concr. Res. 33 (2003) 981-985.

23. M. Şahmaran, G. Yıldırım, T.K. Erdem, Self-healing capability of cementitious composites

672

incorporating different supplementary cementitious materials, Cem. Concr. Compos. 35

673

(2013) 89-101.

SC

671

24. G. Yıldırım, Ö.K. Keskin, S.B. Keskin, M. Şahmaran, M. Lachemi, A review of intrinsic

675

self-healing capability of engineered cementitious composites: recovery of transport and

676

mechanical properties, Constr. Build. Mater. 101 (2015) 10-21.

677 678

M AN U

674

25. R.K. Dhir, M.C. Limbachiya, M.J. McCarthy, A. Chaipanich, Evaluation of portland limestone cements for use in concrete construction, Mater. Struct. 40 (2007) 459-473. 26. M. Şahmaran, G. Yıldırım, G.H. Aras, S.B. Keskin, Ö.K. Keskin, M. Lachemi, Self-healing

680

of cementitious composites to reduce high CO2 emissions, ACI Mater. J. 114 (2017), 93-

681

104.

TE D

679

27. G. Yıldırım, G.H. Aras, Q.S. Banyhussan, M. Şahmaran, M. Lachemi, Estimating the self-

683

healing capability of cementitious composites through non-destructive electrical-based

684

monitoring, Ndt&E Int. 76 (2015) 26-37.

685 686

EP

682

28. ASTM C1202, Standard test method for electrical indication of concrete’s ability to resist chloride ion penetration, ASTM International, West Conshohocken, Pennsylvania, (2012). 29. G. Song, G.P.A.G van Zijl, Tailoring ECC for commercial application, 6th RILEM

688

Symposium on Fiber-Reinforced Concretes (FRC) - BEFIB, Varenna, Italy, (2004) 1391-

689

1400.

AC C

687

690

30. G. Yıldırım, M. Şahmaran, H.U. Ahmed, Influence of hydrated lime addition on the self-

691

healing capability of high-volume fly ash incorporated cementitious composites, J. Mater.

692

Civil Eng. 27 (2014) 04014187.

693 694 695 696

31. C.A. Clear, The effects of autogenous healing upon the leakage of water through cracks in concrete, Wexham Springs: Cement and Concrete Association, (1985) p. 28. 32. M. Şahmaran, İ.Ö. Yaman, Influence of transverse crack width on reinforcement corrosion initiation and propagation in mortar beams, Can. J. Civil Eng. 35 (2008) 236–245. 21

ACCEPTED MANUSCRIPT 697 698 699 700

33. C. Edvardsen, Water permeability and autogenous healing of cracks in concrete, ACI Mater. J. 96 (1999) 448–455. 34. C. Aldea, W. Song, J.S. Popovics, S.P. Shah, Extent of healing of cracked normal strength concrete, J. Mater. Civil Eng. 12 (2000) 92–96. 35. C. Shi, Effect of mixing proportions of concrete on its electrical conductivity and the rapid

702

chloride permeability test (ASTM C1202 or ASSHTO T277) results, Cem. Concr. Res. 34

703

(2004) 537-545.

RI PT

701

704

36. A.W. Adamson, Physical chemistry, 2nd ed. Orlando, Academic Press, (1973).

705

37. C. Andrade, Calculation of chloride diffusion coefficients in concrete from ionic migration

707 708

measurements, Cem. Concr. Res. 23(1993) 724-742.

SC

706

38. H. Huang, G. Ye, C. Qian, E. Schlangen, Self-healing in cementitious materials: materials, methods and service conditions, Mater. Design 92 (2016) 499-511.

39. L. Black, C. Breen, J. Yarwood, K. Garbev, P. Stemmermann, B. Gasharova, Structural

710

features of C–S–H (I) and its carbonation in air—a Raman spectroscopic study. Part II:

711

carbonated phases, J. Am. Ceram. Soc. 90 (2007) 908-917.

713 714 715 716 717

40. P.E. Grattan-Bellew, Microstructural investigation of deteriorated Portland cement concretes, Constr. Build. Mater. 10 (1996) 3-16.

41. W.F. Cole, B. Kroone, Carbon dioxide in hydrated Portland cement, ACI J. Proc. 56 (1960) 1275-1296.

TE D

712

M AN U

709

42. Z. Sauman, Carbonation of porous concrete and its main binding components, Cem. Concr. Res. 1 (1971) 645–662.

43. G.W. Groves, A. Brough, I.G. Richardson, C.M. Dobson, Progressive changes in the

719

structure of hardened C3S cement pastes due to carbonation, J. Am. Ceram. Soc. 74 (1991)

720

2891-2896.

722 723 724

44. L. Brecevic, Solubility of amorphous calcium carbonate, J. Cryst. Growth 98 (1989) 504– 510.

AC C

721

EP

718

725 726 727 728 22

ACCEPTED MANUSCRIPT 729

List of Tables and Figures

730

Table 1 Chemical and physical properties of FA, GGBFS, PC and silica sand.

731

Table 2 Ingredients of different ECC mixtures.

732

Table 3 Characterization of microcracks depending on mixture type and further 90-day

733

environmental conditioning.

RI PT

734

Fig. 1. Conditioning of sound and pre-loaded specimens in different curing cabinets.

736

Fig. 2. Distributions of microcrack widths created after initial pre-loading of different ECC

737

mixtures.

738

Fig. 3. Percental self-healing performances of ECC mixtures with respect to different initial

739

crack widths after 90 days of further curing.

740

Fig. 4. Typical photos of self-healing of cracks with large widths in a limited period of further

741

CO2-water curing.

742

Fig. 5. Average EI test results of ECC specimens under different curing conditions.

743

Fig. 6. Evaluation of EIPL/EIS ratio versus rate of crack healing with respect to further curing age

744

(solid lines represent logarithmic trendlines for ratio of EI results, dotted lines represent rate of

745

crack healing).

746

Fig. 7. Average RCP test results of ECC specimens under different curing conditions.

747

Fig. 8. Total amount of calcium carbonate calculated using TGA/DTG analysis for ECC

748

mixtures in accordance with different further curing conditions.

749

Fig. 9. XRD patterns of ECC mixtures in accordance with different further curing conditions.

750

Fig. 10. SEM micrographs with EDX patterns of products in self-healed cracks (taken from CO2-

751

water cured specimens cured for 90 additional days after 365 days).

753 754 755

M AN U

TE D

EP

AC C

752

SC

735

756 757 758 759 23

ACCEPTED MANUSCRIPT Table 1 Chemical and physical properties of FA, GGBFS, PC and silica sand. Chemical Composition FA GGBFS PC Silica sand CaO 3.48 35.09 61.43 0.02 SiO2 60.78 37.55 20.77 99.79 Al2O3 21.68 10.55 5.55 0.06 Fe2O3 5.48 0.28 3.35 0.02 MgO 1.71 7.92 2.49 0.01 SO3 0.34 2.95 2.49 K2O 1.95 1.07 0.77 0.01 Na2O 0.74 0.24 0.19 0.02 Loss on Ignition 1.57 2.79 2.20 0.07 Physical Properties Specific Gravity 2.10 2.79 3.06 2.60 2 Blaine Fineness (m /kg) 269 425 325 -

SC

RI PT

760

761

763 Mixture ID. ECC-FA ECC-FA/CH ECC-S

765

Further curing condition

Total # of cracks from all tested specimens 40 35 26 34 38 37 28 38 37 28 37 29

AC C

Mix ID.

768

Sand 453 453 474

HRWRA 5.1 5.7 6.0

Table 3 Characterization of microcracks depending on mixture type and further 90-day environmental conditioning.

EP

766 767

Table 2 Ingredients of different ECC mixtures. Ingredients, kg/m3 PC FA GGBFS CH Water PVA 566 680 331 26 539 648 62 331 26 593 712 347 26

TE D

764

M AN U

762

CO2-air CO2-water ECC-FA Air Water CO2-air ECCCO2-water FA/CH Air Water CO2-air CO2-water ECC-S Air Water *CW: Crack width

Average of initial CW* (µm) 112 138 109 102 110 134 112 121 152 166 136 174

Max. CW Average CW Max. CW closed after after 90d. (µm) 90d. (µm) curing, (µm) 348 458 302 463 456 356 247 426 332 453 396 471

119 458 121 99 69 356 64 80 386 39 397

74 0 78 47 91 17 83 85 131 62 111 79

Average rate of self-healing after 90d. curing (%) 42 100 37 73 31 91 34 51 20 68 30 63

24

ACCEPTED MANUSCRIPT Sound

4 -RCP 4 - EI

Pre-loaded

4 -RCP 4 - EI

Sound

4 -RCP 4 - EI

Pre-loaded

4 -RCP 4 - EI

Sound

4 -RCP 4 - EI

Air oC

50±5 50±5% RH

Cabinet I

769

50±5 oC 50±5% RH 3% CO2

4 -RCP 4 - EI

Sound

4 -RCP 4 - EI

M AN U

Cabinet I

Pre-loaded

SC

Air

RI PT

Water

Water

Pre-loaded

770 771 772

Fig. 1. Conditioning of sound and pre-loaded specimens in different curing cabinets.

AC C

EP

TE D

773 774

4 -RCP 4 - EI

775 776 777 778

Fig. 2. Distributions of microcrack widths created after initial pre-loading of different ECC mixtures.

25

Fig. 3. Percental self-healing performances of ECC mixtures with respect to different initial crack widths after 90 days of further curing.

AC C

779 780 781 782 783 784 785 786 787 788 789 790 791 792 793 794

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

26

ACCEPTED MANUSCRIPT 365+15 d.

365+30 d.

M AN U

795 796 797

SC

ECC-S

RI PT

ECC-FA

365 d.

Fig. 4. Typical photos of self-healing of cracks with large widths in a limited period of further CO2-water curing.

798

802 803 804 805 806

EP

801

AC C

800

TE D

799

27

808 809 810

Fig. 5. Average EI test results of ECC specimens under different curing conditions.

AC C

807

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

811

28

817 818 819 820 821

TE D

816

EP

815

Fig. 6. Evaluation of EIPL/EIS ratio versus rate of crack healing with respect to further curing age (solid lines represent logarithmic trendlines for ratio of EI results, dotted lines represent rate of crack healing).

AC C

812 813 814

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

29

823 824

Fig. 7. Average RCP test results of ECC specimens under different curing conditions.

AC C

822

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

30

SC

RI PT

ACCEPTED MANUSCRIPT

825

Fig. 8. Total amount of calcium carbonate calculated using TGA/DTG analysis for ECC mixtures in accordance with different further curing conditions.

M AN U

826 827 828

AC C

EP

TE D

829

830 831

Fig. 9. XRD patterns of ECC mixtures in accordance with different further curing conditions.

31

ACCEPTED MANUSCRIPT

(a) ECC-FA

M AN U

SC

Crack Path

RI PT

Crack Path

TE D

(b) ECC-FA/CH

832 833

AC C

EP

Crack Path

(c) ECC-S Fig. 10. SEM micrographs with EDX patterns of products in self-healed cracks (taken from CO2water cured specimens cured for 90 additional days after 365 days).

834 835 836

32