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A Study on a New Method for Simultaneous Internal Curing and hydrophobic in Concrete
Liyun Tang, Danna Wu, Wei Song, Jianguo Zheng, Peiyong Qiu, Yongtang Yu, Li Han, Haitao Shao, Lei Zhang, Hailiang Jia
PII: S2352-7102(24)02841-9
DOI: https://doi.org/10.1016/j.jobe.2024.111273 Reference: JOBE 111273
To appear in: Journal of Building Engineering Received Date: 28 August 2024
Revised Date: 16 October 2024 Accepted Date: 5 November 2024
Please cite this article as: L. Tang, D. Wu, W. Song, J. Zheng, P. Qiu, Y. Yu, L. Han, H. Shao, L. Zhang, H. Jia, A Study on a New Method for Simultaneous Internal Curing and hydrophobic in Concrete, Journal of Building Engineering, https://doi.org/10.1016/j.jobe.2024.111273.
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© 2024 Published by Elsevier Ltd.
A Study on a New Method for Simultaneous Internal Curing
1
and hydrophobic in Concrete
2
Liyun Tang
a,*, Danna Wu
a, Wei Song
a, Jianguo Zheng
b, Peiyong Qiu
a, Yongtang Yu
c,
3
Li Han
a, Haitao Shao
a, Lei Zhang
a, Hailiang Jia
a4
aSchool of Architecture and Civil Engineering, Xi’an University of Science and Technology, Xi’an 5
710054, China 6
bChina Jikan Research Institute of Engineering Investigations and Design Co., Ltd, Xi’an 710043, 7
China 8
cChina United Northwest Institute for Engineering Design & Research Co, Ltd, Xi’an, 710077, 9
China 10
*Corresponding Authors:
11
Liyun Tang 12
School of Architecture and Civil Engineering, Xi’an University of Science and Technology, Xi’an 14
710054, China 15
Abstract
16
The high hydrophilicity and permeability of concrete caused by many pores and hydroxyl groups 17
produced by cement hydration are the main factors leading to dry shrinkage, cracking, and poor 18
corrosion resistance of concrete. Giving concrete internal curing and hydrophobicity is an 19
effective measure to solve the above problems. In this paper, a new idea and preparation method 20
for an organic combination of hydrophilic and hydrophobic materials are proposed to improve the 21
service life of concrete structures. Furthermore, the combined effects of hydrophilic and 22
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hydrophobic amphoteric materials (HAM) on the mechanical properties, internal curing properties, 23
and hydrophobic properties of concrete were comprehensively investigated. In addition, the 24
physical and chemical action mechanisms were analyzed in conjunction with microscopic tests.
25
The results indicated that HAM rapidly released water within 3-7 days before concrete curing, and 26
then slowly released water accompanied by the release of hydrophobic materials, gradually from 27
hydrophilic to hydrophobic properties; The addition of HAM did not reduce the mechanical 28
properties of concrete, which solved the problem of low compressive strength of integral 29
hydrophobic concrete; The addition of HAM reduced the drying shrinkage of concrete by 30
154.12%, increased the contact angle to 96°, and decreased the water absorption rate by 36%, 31
allowing the concrete to achieve better internal curing and a hydrophobic effect. The preparation 32
of this material can open up a new way to solve the hydrophilic and hydrophobic properties 33
required by concrete at the same time, and fill the gap that concrete can not balance hydrophilic 34
and hydrophobic properties.
35
Keywords Hydrophilic and hydrophobic amphoteric materials; Internal curing; Hydrophobicity;
36
Mechanical robustness 37
1. Introduction
38
Concrete is the foundation of modern construction and plays an important role in the 39
construction field, such as marine structures, bridge projects, salt lakes, infrastructure in salty soil 40
areas, etc. Its performance is also affected by many factors, of which the role of water is 41
particularly important [1-5]. Inadequate curing of concrete in the early stages of hydration is very 42
likely to lead to its drying shrinkage or incomplete hydration [6-11]. After the completion of 43
curing, external water as a carrier to carry harmful media such as Cl-, SO42- and CO2 infiltration 44
into the interior of the concrete is the main cause of deterioration of the concrete, including 45
cracking, spalling, and delamination [12-16] Improper application of the role of water in the 46
concrete will severely affect the service life of the concrete. However, the existing concrete 47
materials are only capable of addressing the conservation characteristics or hydrophobic properties 48
of concrete. They are unable to simultaneously address the concrete drying shrinkage, cracking, 49
and poor impermeability problems, which are particularly challenging to resolve. Furthermore, the 50
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material itself exhibits certain inherent limitations in its performance. To illustrate, while the 51
integral hydrophobic material enhances the permeability of concrete, it also significantly reduces 52
the compressive strength of concrete by altering the pore structure and hindering the hydration 53
process of concrete [17,18]. While hydrophilic materials can facilitate the internal curing of 54
concrete by absorbing water, they are unable to address the issue of poor durability of concrete 55
due to water absorption [19,20]. In light of the aforementioned considerations, it is of paramount 56
importance to prepare a material that can simultaneously satisfy the hydrophilic and hydrophobic 57
properties required for concrete. This material can regulate the effect of water in different stages of 58
concrete, solve the problem of drying shrinkage, and cracking of concrete, and prevent water from 59
penetrating the concrete to extend the service life of concrete.
60
Cracks produced by drying shrinkage of concrete are a preferred entry path to the outdoor 61
environment, and their presence accelerates the corrosion and degradation of concrete, with 62
environmental, economic, and social consequences[21]. Concrete hydrophilic material is an 63
internal curing material capable of absorbing and storing water, which can absorb a large amount 64
of water in a short period, time and release it at the right time, to keep the inside of the concrete 65
moist and promote the hydration of cement [22,23]. In the present era, the hydrophilic materials 66
most commonly utilized in both domestic and international contexts are predominantly porous 67
lightweight aggregates and high water absorption resins (SAP). Studies have shown that SAP can 68
not only store nearly one hundred times its weight in water, but it also possesses water retention 69
properties superior to those of lightweight aggregates at room temperature [24-26]. Yang et al. and 70
Craeye et al. [27,28] found that the incorporation of SAP can play a good role in internal curing 71
and can reduce the risk of concrete cracking. However, within 72h of concrete curing, SAP will 72
hinder the early hydration process of concrete and the formation of a refined pore structure, while 73
after 72h the release of water from SAP promotes the hydration of cement and continues to 74
compensate for the water required by concrete, thus enhancing the strength of concrete [29,30].
75
Zhang et al. and Esteves et al. [31,32] found by XRD analysis that the incorporation of SAP 76
promotes the formation of cement hydration products and early calcite, which reduces the drying 77
shrinkage of concrete, however, the property of SAP to lose water and form collapsed macropores 78
was not eliminated [33]. Although SAP can provide a beneficial internal curing effect and 79
effectively alleviate the drying shrinkage of concrete, it is unable to resolve the durability issue of 80
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concrete caused by water erosion.
81
Hydrophobic admixtures achieve an overall hydrophobic effect on concrete by altering the 82
surface tension within pores and cracks, thereby maintaining the concrete's impermeability even as 83
the surface wears and cracks appear [34-36]. Hydrophobic admixtures used in concrete mainly 84
include hydrophobic liquids and hydrophobic powders [37-39]. Mora et al. [40] incorporated 85
hydrophobic nano-SiO2 into concrete, which showed a significant reduction in water absorption 86
but a decrease in strength. Shah et al. [41] found that the hydrophobicity of hydrophobic 87
nano-SiO2 led to the creation of more macropores in the concrete and doubled the porosity, which 88
was the main factor in the decrease of its strength. With the increase in admixture, the strength and 89
specific strength were lower, which decreased by 76% and 57%, respectively. Xiang et al. and Qu 90
et al. [42,43] added silane-based water repellents to concrete, which showed superhydrophobicity 91
as well as good impermeability and low water absorption, but the compressive strength of 92
concrete was significantly reduced and the degree of concrete hydration was affected. In addition 93
to hydrophobic nano-SiO2 and silane-based water repellents as hydrophobic admixtures, many 94
scholars have investigated fluorine-containing water-repellent agents; however, this type of 95
fluorine-containing materials is not only complicated to prepare, but also burdensome to the 96
environment [44-46]. In summary, hydrophobic concrete has advantages in terms of durability 97
such as erosion resistance, but the reduction of mechanical strength due to the incorporation of 98
hydrophobic materials and the unfriendly environment limit its application. How to balance the 99
above problems is the key to expanding its application areas and scope.
100
The use of materials with both hydrophilic and hydrophobic properties has been explored in 101
various fields, including functional nanofunctional interfacial materials, energy storage materials, 102
and biomedical materials [47-49]. However, the synthesis and conversion process of these 103
hydrophobic-hydrophilic reversible switching materials is complex, often involving external 104
stimuli such as temperature, pH, and light [50-51]. Nevertheless, applications of 105
hydrophobic-hydrophilic reversible switching materials in other fields have been able to 106
demonstrate that the idea of combining the hydrophilic and hydrophobic properties of concrete 107
can be realized.
108
Considering the findings of previous studies and the confirmed limitations, this paper prepared 109
hydrophilic and hydrophobic amphoteric materials ( HAM ) that can store, and release water first 110
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and then release hydrophobic materials, aiming to make concrete have both internal curing and 111
hydrophobic properties. The effects of HAM incorporation on the mechanical properties, internal 112
curing performance, and hydrophobic effect of concrete were discussed. Finally, the action time of 113
hydrophilic and hydrophobic of HAM in concrete was explored by SEM, and the mechanism of 114
HAM was explored. The research of this material is helpful in solving the problem that concrete 115
curing cannot take into account both hydrophobic and hydrophilic properties. It also provides 116
technical and theoretical support for the popularization and application of hydrophilic and 117
hydrophobic amphoteric materials in practical engineering.
118
2. Materials and methods
119
2.1. Selection of materials 120
The cement used in this study is PO42.5 ordinary silicate cement. The main chemical 121
composition and physical properties are presented in Table 1 and Table 2. The fine aggregate 122
chosen is medium sand with a fineness modulus of 2.7, while the coarse aggregate is gravel with a 123
particle size of 5~25 mm. The main raw materials for HAM are selected from highly absorbent 124
resin (SAP), sodium methyl silicate (SM), and hydrophobic silica aerogel powder (SDAM). SAP 125
was selected from Yixing Chemical Co., Ltd. with a particle size of 200~400 mesh, characterized 126
by high water absorption, good water storage, and easy water release. It is used as a hydrophilic 127
material, and the morphology of SAP before and after water absorption is shown in Fig. 1. SM is 128
produced by Beijing Mengtaiweiye Co., Ltd. and has a relative density of 1.23~1.26. It has 129
excellent water repellency and is used as a hydrophobic liquid. SDAM is produced by Shenzhen 130
Zhongning Technology Co., Ltd. and its particle size is less than 50 μm, insoluble in water, easily 131
soluble in anhydrous ethanol, and is used as a hydrophobic solid material.
132
Table 1 133
Main chemical composition of cement (wt%).
134
Compound CaO SiO2 Al2O3 MgO SO3 K2O Fe2O3
Cement 60.23 24.98 8.16 1.05 1.75 0.7 3.13
135
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Table 2 136
Physical properties of cement.
137
Specific surface area/(m2·kg-1)
Setting time/min Flexural strength/MPa Compressive strength/MPa
Initial set Final set 3d 28d 3d 28d
345.7 180 240 5.7 8.7 31.5 53.6
138
139
Fig. 1. Before and after SAP water absorption effect. (a) SAP before water absorption; (b) SAP 140
after water absorption.
141
2.2 Preparation of HAM 142
The specific preparation process of HAM is illustrated (Fig. 2). SM was mixed with water, and 143
the mixture was slowly stirred with a mixer at 200 r/min for 5 min at room temperature to achieve 144
a homogeneously dispersed hydrophobic mixture (Fig. 2a). Then, SAP was added to the 145
hydrophobic mixture and stirred continuously for 10 min to ensure that the mixed solution was 146
absorbed by SAP to obtain HAM. SDAP was mixed with an ethanol solution, and the magnetic 147
stirring speed of 500 r /min was used to accelerate the dissolution of SDAP. After the dissolution, 148
the subsequent preparation process was the same as that of SM. (Fig. 2b).
149
(a) (b)
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150
Fig. 2. Preparation process of HAM. (a) Preparation of HAM with SM as hydrophobic material; (b) 151
Preparation of HAM with SDAP as hydrophobic material.
152
HAM was prepared by controlling the mass of SAP and adjusting the ratios of SDAM, SM, 153
anhydrous ethanol, and water. The absorptive capacity of SAP for hydrophobic materials was 154
measured and is shown in Table 3.
155
The results of the absorption capacity of SAP on hydrophobic materials in Table 3 show that 156
SAP has the most significant effect on the water absorption of SM diluted 1:10 with water and the 157
solution diluted with water after dissolving SDAP in anhydrous ethanol, which essentially reaches 158
10 times the mass of SAP. However, the absorption of anhydrous ethanol and SDAP dissolved in 159
anhydrous ethanol was poor and essentially non-absorbable. In addition, the use of anhydrous 160
ethanol in the preparation of HAM should be minimized due to its effect of blocking concrete 161
hydration [52].
162
The absorption effect of SAP on hydrophobic materials is essentially affected by water, and an 163
increase in the water content percentage enhances the absorption effect of SAP. Relevant studies 164
[53,54] have shown that when SAP absorbs 20 times its weight in water, it has the best curing 165
effect on concrete. When SAP absorbs 40 times as much water, it skips the absorption and storage 166
processes, releasing water directly. Therefore, it is important to investigate the hydrophobic effect 167
of SAP absorbing 20 and 40 times its weight of hydrophobic substances on concrete's hydrophobic 168
effect and the impact of internal curing in this study.
169
Table 3 170
(a)
(b)
Water SM
Mixing Stirring
SAP
Adding
Cement HAM
Water
SAP
Cement HAM Adding
Stirring Mixing
Ethanol SDAP
Dissolving
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SAP absorption capacity for hydrophobic materials.
171
Material type Treatment Absorption effect of SAP
Ethanol Withheld Non-absorption
SM
Withheld 2~5 times
Diluted 1:10 with water 10~15 times
SDAP
Ethanol dissolved 1~2.5 times
Ethanol dissolved andwater diluted 7~13 times
2.3. Experimental design 172
According to the preparation of HAM and the varying absorption capacity of SAP to 173
hydrophobic materials, different sets of working conditions were established to investigate the 174
impact of HAM on the mechanical properties, drying shrinkage properties, and hydrophobic 175
properties of concrete. The specific division of working conditions for concrete specimens is 176
outlined in Table 4. The water-cement ratio of the concrete was kept at 0.45 during the 177
experiments, and the SAP content was 0.2% of the cementitious material. The concrete mixes are 178
shown in Table 5.
179
Table 4 180
Concrete test block working condition division table.
181
Sample Group Treatment process of samples
1 DZ-0 Blank control
2
S-J-10
1:10 SM and water mixture 3S-J-5
1:5 SM and water mixture4
Q-S-0.2
SAP5 L-SJ-1 Pre-absorb 20 times the 1:10 SM and water mixture
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6 L-SJ-2 Pre-absorb 20 times the 1:5 SM and water mixture 7 L-SS-1 Pre-ascorb 20 times SDAP ethanol solution 8 L-SS-2 Pre-ascorb 40 times SDAP ethanol solution 182
Table 5 183
Mix proportions of concrete.
184
Cement (kg/m3) Sand (kg/m3) Rock (kg/m3) Water (kg/m3)
380 653 1265 171
2.4. Preparation and curing of concrete specimens 185
The preparation and curing of concrete specimens were carried out following the Chinese 186
standard GB/T 50081-2019 [55]. To ensure the uniformity of HAM dispersion in concrete, HAM 187
was added to the well-mixed cement and aggregate in three batches. It was dry-mixed in a mixer, 188
fully dispersed, and homogenized, and then added to water in batches for concrete preparation 189
[56,58]. The prepared concrete was loaded into various molds for specimen preparation and then 190
placed on the vibrating table to ensure complete and uniform vibration. The concrete specimens 191
were kept in the molds for 24 hours and then de-molded, followed by curing in water at 20 ± 2°C 192
for 3 days, 7 days, and 28 days. The age was measured from the start of mixing and adding water.
193
2.5. Drying Shrinkage Test 194
The concrete shrinkage device comprises a micrometer and an iron bracket to prepare 195
specimens measuring 100 mm × 100 mm × 400 mm. The concrete sample was cured with mold 196
for one day, and it needed to be cured in a constant temperature and humidity box for two days 197
after demoulding, and then transferred to a creep chamber with a temperature of 20 ± 2°C and a 198
humidity of 60%. Subsequently, the concrete shrinkage device was employed for monitoring and 199
data collection. Before measuring the initial values, the specimens were placed in the creep 200
chamber for 4 hours, and then the micrometer readings from 1 to 28 days were recorded. The first 201
day recorded by micrometer was the first day after three days of the specimen curing.
202
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2.6. Water absorption test 203
The water absorption test method was performed according to the Chinese standard GB/T 204
50081-2019 [55]. The cured 100 mm × 100 mm × 100 mm concrete specimens were dried and 205
treated in a drying oven at 110°C and then weighed for initial mass for M0. Soon after, the 206
concrete was placed in a water bath, and when the specimen was saturated, it was removed and the 207
water was wiped off the surface of the concrete with a damp cloth. The weight of the 208
water-saturated concrete was then weighed and recorded as Mg. 209
Calculation of water absorption of specimens:
210
% 100
0 0
= − M
M
WR Mg (1)
211
In Eq. (1), WR is the water absorption, Mg is the quality of concrete specimens after water 212
absorption, and M0 is the quality of concrete specimens after drying.
213
2.7. Mechanical strength measurement 214
According to the Chinese standard GB/T 50081-2019 [55], the concrete compressive test was 215
conducted using a hydraulic universal pressure testing machine. Specimens of concrete with 216
dimensions of 100 mm × 100 mm × 100 mm were prepared, and compressive strength tests were 217
conducted on specimens that had been cured for 3, 7, and 28 days. The loading rate was set at 218
0.5-0.8 MPa per second, and the standard pressure conversion factor was 0.95.
219
A concrete flexural test was conducted using a hydraulic universal pressure testing machine.
220
Test blocks of concrete with dimensions of 100 mm × 100 mm × 400 mm were prepared. The test 221
blocks were cured for 3, 7, and 28 days, and the loading rate was set at 0.05-0.08 MPa per second.
222
The standard pressure conversion factor was 0.85.
223
2.8. microstructural properties of concrete 224
The pore structure of concrete was tested and analyzed using NMR (NMR, 225
MacroMR12-150H-I) tests. The sample blocks were soaked sufficiently to fill the pores of the 226
concrete with water and then placed in the pore microstructure analyzer to analyze the pore 227
structure characteristics of HAM.
228
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X-ray diffraction analysis (XRD, DX-2700 BH). Concrete specimens were obtained from 229
various locations following the crushing of concrete that had been cured for 3 and 28 days. The 230
process of hydration was terminated by the use of anhydrous ethanol, after which the material was 231
dried to a constant weight and ground to a powder (passing through a 200 mesh sieve).
232
To study the hydrophobicity of HAM, the contact angle of the water droplets on the surface 233
(JC2000D4G) was measured. The contact angle test was carried out by using PTEF abrasive to 234
pour concrete samples. After curing the sample for 28 days, the surface of the sample was polished 235
with sandpaper to clean the stains and ensure the clean surface of the concrete [59,60]. A syringe 236
needle was used to drop 10 μL of water droplets on the surface of the mortar, the mean value of 237
the three different positions of the same sample was taken as the final result.
238
Surface morphologies were obtained through a scanning electron microscope (SEM, FEI 239
Quanta 650FEG SEM-EDS system) of the concrete samples. The specimens utilized in the 240
electron microscope test were derived from the fractured components following compression 241
damage in the compressive test. Random sampling was employed to ensure the reliability and 242
validity of the test results.
243
3. Results and discussion
244
3.1. Mechanical strength analysis 245
The effect of hydrophilic materials, hydrophobic materials, and HAM on the compressive and 246
flexural strength of concrete was shown (Fig. 3). Fig. 3a showed that although the 3d and 7d 247
compressive strengths for all conditions were lower than the control P-D-0, the 28d compressive 248
strength of the 0.2% internally doped SAP was higher than the control. The strength of 249
cementitious materials incorporated with SAP recovered with age, which was consistent with the 250
pattern studied by previous researchers [61-63]. This may have been because, since the addition of 251
SAP caused a slight delay in the formation of calcite during the early stages of cement hydration 252
and delayed the transformation of calcite to the monosulfide type, which was associated with 253
many of the properties of the cement paste, especially the early mechanical properties [31]. The 254
increase in its strength might have been because, since the addition of SAP introduced additional 255
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water into the concrete, which promotes the hydration process of the concrete, the formation of 256
more hydration products from silica-calcite, and a greater increase in strength.
257
Compared with the hydrophobic group S-J-5, the 3d compressive strengths of all four HAM 258
groups were lower, with a maximum reduction of 20.4%, but with the increase of curing time, the 259
3d compressive strengths of the four HAM groups became similar to that of the hydrophobic 260
group. When the maintenance age reached 28d, the long-term strength of all four HAM groups 261
was higher than that of the hydrophobic group, with a maximum increase of 24.8%. It can be 262
shown that the rapid release of water from HAM before 3d-7d of concrete curing led to a decrease 263
in concrete strength, which resembles the mechanism of SAP. As the age of maintenance increased, 264
HAM slowly released water, which may be accompanied by the release of some hydrophobic 265
materials. The slow release of water by HAM supplemented the water required for concrete curing 266
and promoted concrete hydration, while the timing of the release of hydrophobic materials 267
indirectly contributed to the different strengths of concrete in the four groups of HAM. The 268
differences between 7d compressive strength and 3d compressive strength in L-SJ-1, L-SJ-2, 269
L-SS-1, and L-SS-2 were 4.1 MPa, 2.8 MPa, 3.3 MPa, and 2.3 MPa. Respectively, The differences 270
between 28d compressive strength and 7d compressive strength were 8.4 MPa, 7.5 MPa, 5.8 MPa, 271
and 7.6 MPa. From the strength difference at different ages, it can be inferred that L-SS in HAM 272
may have started to release some of the hydrophobic materials at the age of 3d-7d, while L-SJ 273
began to release hydrophobic materials after the age of 7d.
274
It was observed that the effect of HAM on the flexural strength of concrete was essentially the 275
same as that on the compressive strength (Fig. 3b). Compared to the control group, the 3d 276
concrete flexural strength of Q-S-0.2 and L-SS-1 increased by 2.7% and 5.4%, respectively, and 277
the 28d flexural strength of L-SS-1 in the HAM improved by 1.9%. In HAM concrete, L-SJ-1 and 278
L-SJ-2 had a greater impact on the early flexural strength of the concrete, which was reduced by 279
27.0% and 18.9%, respectively, compared to the control.
280
Comparing the strengths of hydrophilic and hydrophobic amphoteric concretes for four 281
different service conditions, we observed that the fewer hydrophobic components in the material, 282
the higher the long-term strength. As an example, in the ethanol solution of 0.2% SAP 283
pre-absorbed hydrophobic silica aerogel powder, the 28d compressive strength of L-SS-1 284
exceeded that of L-SS-2 by 2.6 MPa, resulting in a strength increase of 6.9%. Additionally, 285
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between the two different HAMs, the compressive strength of silica aerogel powder as the 286
hydrophobic raw material was significantly higher than the other group. Possible reasons for this 287
phenomenon were:
288
(1) SM was adsorbed on the surface of cement particles or calcium hydroxide, preventing water 289
molecules from approaching the cement surface. It could also disturb the ionic balance in the 290
pores and inhibit the crystallization of calcium silicate, thus hindering the hydration process of 291
cement [64,65].
292
(2) When HAM released SDAM, as the concrete’s exothermic ethanol evaporated, SDAM 293
gradually hardened and filled the concrete pores, making the concrete denser. This explains why it 294
had less effect on the strength of concrete [66].
295
(3) Before the HAM was released or only partially released SDAM, the SDAM hardened with 296
the evaporation of ethanol, resulting in less impact on the strength of the concrete.
297
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298
Fig. 3. Concrete strength of different types of materials. (a) Compressive strength of concrete; (b) 299
Flexural strength of concrete.
300
3.2. Pore structure analysis 301
3.2.1. Pore distribution pattern analysis 302
Porosity was an important factor affecting the durability of concrete structures; the more 303
harmful holes there were, the easier it was for harmful ions to penetrate the concrete matrix with 304
water, causing corrosion of the concrete. Fig. 4 shows the NMR relaxation time T2 spectra of 305
concrete at different ages. As illustrated in the figure, three distinct wave peaks were observed 306
across all working conditions, from left to right, designated as peak 1, peak 2, and peak 3. These 307
3.7 3.5
3.0 3.8
2.7 3.0
3.9 3.5 4.4
3.9 3.4
4.3 3.7
4.1 4.3 4.4
5.2
4.2 4.7
5.2
4.9 4.9
5.3 4.9
P-D-0 S-J-10 S-J-5 Q-S-0.2
L-SJ-1 L-SJ-2
L-SS-1 L-SS-2 0
1 2 3 4 5 6
Design code
Flexural strength (MPa)
3d 7d 28d
(b)
36.4
31.8 28.9 29.5
23.0 24.6 30.9
27.7 39.7
27.5 27.5
35.6
27.1 27.4 34.4
30.0 41.1
36.8 32.2
44.1
35.5 34.9
40.2 37.6
P-D-0 S-J-10 S-J-5 Q-S-0.2
L-SJ-1 L-SJ-2 L-SS-1
L-SS-2 0
10 20 30 40 50
Design code
Compressive strength (MPa)
3d 7d 28d
(a)
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peaks were classified into three categories, namely gel pores (d < 10 nm), capillary pores (10 nm <
308
d < 1000 nm), and harmful pores (d > 100 nm), in that order [67-69]. The extent of change in the 309
corresponding signal amplitude on the T2 spectral curve of concrete did not remain consistent as 310
the age of the concrete increased. The number of harmful pores in the concrete under the 311
admixture of hydrophilic and hydrophobic materials in Fig. 4d and Fig. 4h) was less, indicating a 312
denser structure and a greater quantity of hydration products to fill the internal pores of the 313
concrete. The incorporation of hydrophobic materials in Fig. 4b and Fig. 4c had the effect of 314
increasing the peak signal intensity in all three parts of the concrete’s gel pores, capillary pores, 315
and harmful pores. This indicates that the incorporation of hydrophobic materials inhibited the 316
hydration of concrete, which in turn led to an increase in concrete pores.
317
As illustrated in Fig. 4, a comparison of the pore alterations in P-D-0 revealed that, despite a 318
decline in the peak signal intensity of S-J-10 and S-J-5 gel pores, there was a notable increase in 319
the peak signal intensity of transition pores and harmful pores. It was demonstrated that the 320
drainage of hydrophobic materials resulted in a deficiency of adequate humidity within the 321
concrete, which impeded the hydration reaction within the concrete. This not only facilitated the 322
formation of additional initial defects, such as macro-pores and micro-cracks, within the concrete 323
but also altered the distribution and connectivity of the voids and micro-cracks within the concrete, 324
leading to an increase in the number of harmful pores.
325
Q-S-0.2 T2 spectrum signal intensity peak rule of change was similar to P-D-0, three kinds of 326
pores are with the increased of maintenance time and decreased. The pore type was mainly gel 327
pores. Although the proportion of harmful pores was relatively large in the early stage, it 328
significantly reduced when the age of maintenance reaches 28d, and the peak signal intensity of 329
harmful pores dropped to less than 5. The reason for this phenomenon was opposite to that of the 330
two groups of S-J-10 and S-J-5. This resulted from the additional introduction of moisture by 331
mixing SAP, which promoted the hydration process of concrete.
332
Furthermore, the higher internal humidity in the hydration stage of cement could re-split the 333
hydration and improve the compactness of concrete. Relative to the effect of Q-S-0.2 on concrete 334
pore space, the change rule of the peak T2 spectral signal intensity of HAM prepared in this paper 335
(L-SJ-1, L-SJ-2, L-SS-1, L-SS-2) was similar to that of the change of the concrete pore space 336
under the admixture of hydrophilic internal curing materials. The T2 spectral curves of concrete 337
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showed a decrease in the peak signal intensity of the gel pores, capillary pores, and harmful pores 338
components with increasing curing time. And the peak harmful pores signal strength at 28d was 339
lower, indicating that HAM prepared in this paper effectively fulfilled its role in improving the 340
internal curing humidity, reducing the harmful pores, and improving the compactness of concrete.
341
342
Fig. 4. NMR relaxation time T2 spectra at different ages. (a) P-D-0; (b) S-J-10; (c) S-J-5; (d) 343
Q-S-0.2; (e) L-SJ-1; (f) L-SJ-2; (g) L-SS-1; (h) L-SS-2.
344
3.2.2. Pore size distribution change analysis 345
The percentage of gel pores remained the highest in all working conditions, with an average of 346
more than 60% (Fig. 5). The gel pores percentage of the control group (P-D-0) was consistently 347
higher than 60% or more, and increased by 40.98% from 61% to 86% as the age of maintenance 348
increased. Its harmful pores and capillary pores percentages have been decreasing with the 349
increase of age, and at 28d of maintenance, the harmful pores and capillary pores percentages 350
decreased to 4% and 11%, respectively, which decreased by 80.0% and 42.1%. The percentage of 351
gel pores in the hydrophilic group (Q-S-0.2) at 3d, 7d, and 28d exceeded 84%. The percentage of 352
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harmful pores and capillary pores were below 10%. This ratio remained consistent with age, 353
indicating that the additional water diversion facilitated the development of the early pore space.
354
The hydrophobic groups (S-J-5 and S-J-10) have poorer pore development under doping 355
compared to P-D-0 and Q-S-0.2. The porosity of the gel pores remained unchanged with the 356
increase of age, and the gel pores porosity percentage of S-J-10 grew from 59% to 60%, an 357
increase of only 1%. The gel pores porosity of S-J-5 exhibited a minimal increase, rising from 62%
358
to 66%. In contrast, the pore changes of harmful pores and capillary pores at both doping levels 359
were more pronounced. The percentage of capillary pores of S-J-5 increased from 7% at 3d to 27%
360
at 28d, representing a 20% increase.
361
362
Fig. 5. Variation of pore size distribution of concrete at different ages. (a) P-D-0; (b) S-J-10; (c) 363
S-J-5; (d) Q-S-0.2; (e) L-SJ-1; (f) L-SJ-2; (g) L-SS-1; (h) L-SS-2.
364
The HAMs prepared in this paper differed in the variation of the pore percentage of each size 365
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due to the difference in the preparation means and materials. In general, concrete with L-SJ-1, 366
L-SJ-2, and L-SS-1 had better pore occupancy. The 28d gel pores occupancy was 80%, 88%, and 367
87%, respectively, while the 28d harmful pores occupancy decreased with time, over time. The 368
final 28d harmful pores occupancy was 7%, 6%, and 5%, representing a decrease of 41.17%, 369
68.42%, and 75.00%, respectively. It can be shown that HAM regulated the release time of water 370
as well as hydrophobic materials resulting in a denser concrete structure, which also greatly 371
reduced the effect of hydrophobic materials on the mechanical properties of concrete.
372
3.3. Internal Conservation Performance Test 373
3.3.1. Chemical composition analysis 374
The XRD plots of different types and working conditions of HAM under 28d standard curing 375
conditions appeared significantly different from the control XRD plots (Fig. 6). Significant 376
diffraction peaks appeared near 26°, 27° and 32° in Fig. 6(a) for SiO2, CaCO3 and Ca(OH)2, 377
respectively. Additionally, the specimen had a higher diffraction peak (SiO2) at 26° than the peak 378
near 27° (CaCO3). The difference in the diffraction peaks at 3d and 28d showed that the cement 379
was not sufficiently hydrated under 3d curing conditions, while the degree of hydration increased 380
with age.
381
It was found that SiO2 was present in the 3d and 28d profiles of the concrete in the hydrophobic 382
group (Fig. 6a-c). Additionally, the height of the diffraction peaks was higher than that of the 383
diffraction peaks in the control group, indicating that the incorporation of hydrophobic materials 384
led to insufficient hydration of the cement. The above results were in agreement with those of 385
Feng and Falchi [70,71], which could be attributed to the fact that the incorporation of 386
hydrophobic materials inhibited the further reaction of cement hydration products and the 387
hydration degree eventually became saturated with increasing age. Fig. 6d-h showed that the 388
height of the diffraction peaks of SiO2 was lower under both SAP and HAM admixture. Especially, 389
the diffraction peaks of SiO2 were not found in the diffraction pattern of 28d (Fig. 6g), which 390
indicated that the admixture of HAM and SAP had a similar hydration degree to the cement 391
specimen. Additionally, the degree of hydration was higher, and hydrophobic components in HAM 392
had less effect on concrete. It could be seen that the hydration crystallization products of 393
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SAP-added cement were mainly Ca(OH)2, CaCO3, and C-S-H. This indicated that the 394
incorporation of SAP and HAM did not affect the composition of the hydration products but 395
changed the diffraction peak intensity of the hydration products. When the age of curing was 3d, 396
the cement pastes of Q-S-0.2, L-SJ-2, L-SS-1, and L-SS-2 all produced more Ca(OH)2, indicating 397
that the additional water diversion accelerated the hydration process of cement. Compared with 398
S-J-10, S-J-5, and P-D-0, the Ca(OH)2 peak intensity of the cement paste with added SAP was 399
gradually enhanced, indicating that the incorporation of SAP and HAM could promote the 400
hydration process of cement. The cement hydration reaction was accelerated the water dissipation 401
was faster, and the release of water from the materials could timely replenish the water required 402
for cement hydration, which further improved the hydration degree. Therefore, it could be 403
summarized from the XRD patterns of different hydration stages of the cement that the 404
synthesized HAM exerted its hydrophilic performance, and this hydrophilic action was similar to 405
the mechanism of action of the curing materials in SAP, which promoted the hydration process of 406
the cement by providing the concrete with sufficient water for the early hydration of the cement.
407
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408
Fig. 6. XRD spectra of the concrete. (a) P-D-0; (b) S-J-10; (c) S-J-5; (d) Q-S-0.2; (e) L-SJ-1； (f) 409
L-SJ-2； (g) L-SS-1； (h) L-SS-2.
410
3.3.2. Shrinkage performance results analysis 411
It was observed that the shrinkage deformation of the concrete exhibited an increasing trend 412
with the increase of the test time (Fig. 7). The early shrinkage deformation of concrete was 413
relatively large, and the trend of concrete deformation became more moderate after about 16 d.
414
10 20 30 40 50 60 70 80
▲
2q / o
28d
3d SiO2 ■ CaCO3
¨ Al2SiO5 ▲ Ca(OH)2
■
■
¨ ■
¨ ¨■
■
■
■■ ■ ■
▲ ▲
(e)
10 20 30 40 50 60 70 80
SiO2 ▲ Ca(OH)2
■ CaCO3 ¨ Al2SiO5
2q / o
28d
▲ 3d
■
¨■
▲ ■¨ ▲
¨
▲ ■
▲
▲
■■ ■ ■▲
▲
(f)
10 20 30 40 50 60 70 80
28d
3d SiO2 ▲ Ca(OH)2 ■ CaCO3
▲
■
▲ ■ ▲
2q/o
■
■
■
■ ▲
▲
(g)
10 20 30 40 50 60 70 80
2θ/°
3d 28d SiO2 ▲ Ca(OH)2 ■ CaCO3
▲
■
▲ ■ ■ ▲ ▲
▲ ■
▲
■
▲
■ ■ ■
(h)
10 20 30 40 50 60 70 80
■
SiO2 ■ CaCO3
28d
3d
■
2q / o
■
■
■ ■ ■
(c)
10 20 30 40 50 60 70 80
28d
3d
SiO2 ▲ Ca(OH)2
■ CaCO3 ¨ Al2SiO5
2q / o
■
■
▲ ▲ ■ ■
■ ■
(a)
10 20 30 40 50 60 70 80
28d
3d
2q / o
SiO2 ▲ Ca(OH)2
■ CaCO3
▲
■
▲ ■ ■ ■ ■
■
■ ■ ■
(b)
(d)
10 20 30 40 50 60 70 80
▲■ ©
SiO2 ▲ Ca(OH)2
■ CaCO3 © C-S-H
©▲■ ■ ■ ▲■
28d
■ 3d
■
▲ © ■
■
2q / o
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The main reasons for the above phenomenon were as follows:
415
(1) the hydration reaction of cement led to the reduction of water in concrete, while the 416
capillary pore water surface was prone to tensile stress due to the reduction of water, resulting in 417
large volume shrinkage of concrete in the early stage [30].
418
(2) Considering the kinetic theory of hydration of cementitious materials [72], there was a 419
growth in hydration rate and a hydration peak at 3d for concrete.
420
(3) In the late stage of concrete hydration, the hydration products formed by silica-calcite 421
compensated for the volume of concrete [73,74]. Additionally, the strength of the concrete itself 422
improved and stabilized, enhancing its ability to resist deformation during this stage and resulting 423
in better shrinkage inhibition.
424
Compared to control P-D-0, Q-S-0.2 showed a 227.27% reduction in drying shrinkage, while 425
L-SJ-1, L-SJ-2, L-SS-1, and L-SS-2 in HAM of concrete were reduced by 72.8%, 154.12%, 100%, 426
and 71.43%, respectively. L-SJ-2 was the optimal inhibition of concrete drying shrinkage among 427
HAMs. This might be attributed to the fact that the effect of water storage and release of 428
hydrophilic SAP in HAMs had a significant impact on mitigating drying shrinkage. However, 429
when less hydrophobic solution was stored in HAMs, the released hydrophobic material had less 430
effect on concrete drainage, and the released water could better replenish the consumed free water 431
to alleviate the capillary pressure.
432
In general, the internal mixing of SAP and HAM had a good modification effect on the 433
shrinkage and deformation of concrete. After the internal mixing of SAP and HAM, on the one 434
hand, the mixing of SAP and HAM improved the water retention of concrete, hindering the loss of 435
free water. The hydrophilic part of the early hydration of concrete provided enough water, and the 436
internal water change of concrete was small, weakening the stress effect of the internal capillary 437
water of the concrete, which reduced the shrinkage deformation of the concrete. On the other hand, 438
due to the early hydration of the concrete being sufficient, the overall compactness of the concrete 439
was significantly improved, thus reducing the shrinkage deformation of the concrete.
440
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441
Fig. 7. Effect of different admixtures on drying shrinkage of concrete.
442
3.4. Hydrophobicity test 443
3.4.1. Wettability 444
The static contact angles of water droplets on the surface of eight groups of concrete specimens 445
and the morphological characteristics of water droplets on the surface of different specimens were 446
shown (Fig. 8). The water droplets of P-D-0 and Q-S-0.2 penetrated the interior of concrete after 447
staying on the surface for only a few seconds during the test, and the contact angles measured at 448
the time of staying were 4.43° and 5.06°. The concrete with only incorporeted hydrophobic 449
materials had the largest contact angle, and the surface contact angle increased with more concrete, 450
reaching 99.49° and 104.57°, respectively. Different concrete with HAM exhibited varying 451
wettability, with L-SS-1 having the best hydrophobicity, characterized by a contact angle of 96.00°.
452
L-SJ-1 and L-SS-2 followed closely, with contact angles of 82.53° and 80.44°, respectively.
453
Although the contact angle of these two groups did not reach 90°, their water droplets appeared 454
micro-bead-like on the surface of the substrate and coalesced without diffusion. Therefore, it can 455
be assumed that the hydrophobic effect could be realized if the doping amount of this group of 456
materials was increased.
457
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 0
40 80 120 160 200 240 280
Drying shrinkage value（1.0×10-6 ）
Time (d)
P-D-0 S-J-10 S-J-5 Q-S-0.2 L-SJ-1 L-SJ-2 L-SS-1 L-SS-2
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458
Fig. 8. Water contact angle and water absorption rate variation.
459
3.4.2. Water absorption analysis 460
The water absorption of concrete was closely related to its hydrophilicity and hydrophobicity.
461
Concrete contained a large number of hydroxyl groups, which could form hydrogen bonds with 462
water molecules, making it highly hydrophilic [75]. The higher the hydrophilicity, the higher the 463
water absorption rate, and the more vulnerable to water erosion. The incorporation of hydrophobic 464
materials could form a hydrophobic barrier inside the concrete, thereby reducing the water 465
absorption of the concrete [76]. To comprehensively analyze the effect of HAM admixture on the 466
overall hydrophobic effect of concrete, a 48-hour concrete immersion water absorption test was 467
conducted, and the test results were shown (Fig. 8). The water absorption rate of the control P-D-0 468
was 5.0%, and the water absorption rates of S-J-10 and S-J-5 doped with hydrophobic materials 469
were 3.9% and 3.6%, respectively, which were reduced by 22% and 28% compared to P-D-0. The 470
water absorption of concrete Q-S-0.2 with SAP was 4.5%, which was 10% lower compared to 471
P-D-0. The water absorption of all four groups of HAM concretes was reduced, and the absorption 472
rates of L-SJ-1, L-SJ-2, L-SS-1, and L-SS-2 were 3.7%, 4.1%, 3.2%, and 3.9%, respectively.
473
These rates were reduced by 26%, 18%, 36%, and 22%, respectively, compared with P-D-0. This 474
suggests that the HAM could inhibit the migration of water in the water absorption process.
475
Both water absorption and contact angle responded to the interaction between the material and 476
water, with the contact angle representing surface hydrophobicity and water absorption indicating 477
long-term water absorption. The contact angle and water absorption results indicated that the 478
4.43
99.49 104.57
5.06
82.53
46.32 96
80.44 5
3.9 3.6
4.5
3.7 4.1
3.2 3.9
P-D-0 S-J-10 S-J-5 Q-S-0.2 L-SJ-1 L-SJ-2 L-SS-1 L-SS-2 0
20 40 60 80 100 120
Design code
water contact angle water absorption
Water contact angle（°）
3.0 3.2 3.4 3.6 3.8 4.0 4.2 4.4 4.6 4.8 5.0 5.2
Water absorption（%）
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addition of HAM improved the hydrophobicity of the concrete. In other words, the hydrophobic 479
components in the HAM formed a hydrophobic barrier that prevented water penetration. It was 480
surmised that concrete with L-SJ-2 and L-SS-2 had more harmful pores. The more harmful pores 481
in concrete, the higher the water absorption rate. However, compared with normal concrete, 482
although the pore structure of L-SJ-2 and L-SS-2 was not as good as that of normal concrete, they 483
still exhibited better hydrophobicity. This was because, since when the hydrophobic component 484
and the pores were affected simultaneously, the establishment of hydrophobicity could 485
compensate for the increase in water absorption caused by the increase in pores [77,78].
486
3.5. SEM test 487
In this paper, the internal microstructural morphology of concrete at 3d and 28d under different 488
HAM admixtures was observed by SEM, and the degree of hydration, distribution of HAM, 489
concrete compactness, and hydration products were effectively determined by morphology. Inside 490
the HAM-added concrete, it could be observed that the hydration products were mainly C-S-H gel, 491
Ca(OH)2, calcite, etc., and the C-S-H gel grew locally aggregated (Fig. 9). It could be seen that in 492
the 3d of the L-SJ concrete with HAM, water was being released (Fig. 9a). However, at this time, 493
the release of hydrophobic materials was not observed. The water release process around the 494
HAM appeared to involve a large number of hydration products, including C-S-H and Ca(OH)2. 495
The 28d electron microscope images of the L-SJ group revealed hydrophobic substances adsorbed 496
on the surface of hydration products (Fig. 9b). Additionally, the presence of calcium aluminate 497
(AFt) was also observed. However, AFt was not a stable substance, which delayed the setting of 498
the cement and led to the expansion of the concrete. If AFt failed to be converted into low-sulfur 499
type hydrated calcium thiosaluminate (AFm), the mechanical properties of the concrete were 500
negatively impacted. This might be the reason for the relatively low mechanical properties of this 501
group of HAM concrete. The time of appearance of hydrophobic material in L-SJ could indicate 502
that when the age of curing was 3d, the HAM with SM as hydrophobic material only released 503
water and did not release hydrophobic material. At the age of 28d the appearance of hydrophobic 504
material could indicate that the group of HAM better regulated the release time of hydrophobic 505
material and reduced the impact of premature release of hydrophobic material on the hydration of 506
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concrete.
507
508
Fig. 9. Micro-morphology of HAM specimens. (a) 3d morphological features of L-SJ specimen;
509
(b) 28d morphological features of L-SJ specimen; (c) 3d morphological features of L-SS specimen;
510
(d) 28d morphological features of L-SS specimen.
511
The HAM sphere that was releasing water could be observed, and hydrophobic materials 512
appeared on the surface of the sphere (Fig. 9c). This indicated that the L-SS at 3d also released 513
some hydrophobic materials during the process of water release. In the electron micrograph of 28d 514
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of L-SS group, the observed hydration products were mainly C-S-H and Ca(OH)2 (Fig. 9d), and 515
AFt in Fig. 9b was not observed, which could indicate that the hydration degree of L-SS was 516
better than that of L-SJ, and its mechanical properties should be better than that of L-SJ group.
517
Meanwhile, Hydrophobic substances were adsorbed on the surface of the hydration products.
518
However, the shape was altered, and it was speculated that a chemical reaction might have taken 519
place with the substances in the concrete, thus altering their shape. The release time of 520
hydrophobic materials in L-SJ and L-SS observed in SEM corresponded to the possible release 521
time of hydrophobic materials inferred from the difference in compressive strength at different 522
ages. This demonstrated that L-SJ in HAM was in the hydrophilic stage before the age of 7d and 523
gradually released hydrophobic materials from the hydrophilic stage to the hydrophobic stage after 524
7d. On the other hand, L-SS in HAM began to release hydrophobic materials after the age of 3d 525
and gradually and slowly transitioned from the hydrophilic stage to the hydrophobic stage.
526
3.6. Analysis of HAM action mechanism 527
The mechanism of action of the HAM prepared in this paper was shown (Fig. 10), and the 528
process of action was manifested as the physical process of storage, water release, and the role of 529
hydrophobic materials, as well as the chemical process of hydration reaction, complex reaction, 530
dehydration reaction, and hydrophobic interaction. HAM used SAP as a carrier for water, SM, and 531
SDAM storage. When the capillary pressure in concrete was affected by the osmotic pressure and 532
humidity difference inside the concrete, HAM released the stored water (Fig. 10a) [79].The water 533
release process of HAM promoted the hydration of cement, and its chemical reaction involved the 534
reaction of tricalcium silicate (3CaO·SiO2 or C3S) and dicalcium silicate (2CaO·SiO2 or C2S) with 535
water to produce calcium silicate hydrated gel (C-S-H) and calcium hydroxide (CH) as shown in 536
Eqs. 2 and Eqs.3 below [80,81].
537
(
3 · 2)
6 2 3 ·2 2·3 2 3( )
22 CaOSiO + HO→ CaO SiO HO+ CaOH （2）
538
(
2 · 2)
4 2 3 ·2 2·3 2( )
22 CaOSiO + HO→ CaO SiO HO+CaOH （3）
539
As cement hydration gradually consumed water to achieve the effect of curing within the 540
concrete, the slow water release phase of HAM was accompanied by the release of some SM and 541
SDAM and began to exert its hydrophobic effect, this was confirmed in Fig. 9. Related studies 542
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have shown that hydrophobic materials inhibited the hydration of concrete [82,83]. Their effect 543
was mainly related to the large adsorption of hydrophobic emulsion particles onto the surface of 544
the cement particles. This resulted in the formation of an emulsion particles encapsulation layer 545
that inhibited the transport and exchange of water at the interface of the cement particles, as well 546
as the nucleation and deposition of hydration products [65]. Since the HAM prepared in this paper 547
utilized SAP to adsorb the hydrophobic materials, the hydrophobic emulsion particles could not be 548
directly adsorbed on the surface of cement particles during the pre-hydration stage of the concrete.
549
This reduced the impact on the hydration of the concrete. Instead, SAP preferentially released the 550
less dense water, and the introduction of water promoted the hydration process of the cement [84].
551
552
Fig. 10. Mechanism of HAM action (R: hydrophobic groups for SM and SDAM). (a) hydration 553
reaction; (b) complex reaction; (c) dehydration reaction; (d) hydrophobic interaction [85].
554
HAM exerted its hydrophobic effect in the later stages of concrete hydration, and Fig. 11 555
demonstrated the predicted chemical reaction mechanism between L-SJ and L-SS cement 556
hydration products in HAM. The main difference between the reaction of L-SJ and L-SS was that 557
SM in L-SJ reacted with carbon dioxide and water in the air to decompose into silanols (Fig. 11a) 558
[86]. In contrast, SDAM in L-SS modified the surface of silica aerogel powder with 559
methyltriethoxysilane as a silica-source precursor to achieve hydrophobicity, so the chemical 560
reaction principle of its hydrophobic effect in concrete was that firstly, methyltriethoxysilane 561
reacted and hydrolyzed with water to silanol in an alkaline environment (Fig. 11b) [88,89]. After 562
Cement (c)
H-O-R OH
Dehydration reaction
HAM Cement
(d)
Cement
R R
Hydrophobic interaction H2O
H2O C3S
C2S +
H2O
H2O
H2O H2O H2O H2O H2O
H2O H2O
H2O H2O
Cement
Hydration reaction
HAM (a)
SM or SDAM
Cement
H2O C3S
C2S +
Hydration reaction (b)
H-O-R OH
Dehydration reaction
HAM
H2O H2O H2O
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that, the reaction of L-SJ and L-SS was almost the same, and some of the silanols underwent 563
polycondensation reactions to produce siloxane polymers during hydrolysis of silanols (Fig. 11c).
564
Secondly, the silanol and siloxane polymers reacted with the hydroxyl groups in the concrete 565
hydration products and bonded to the surface of the concrete hydration products in the form of 566
silicone-oxygen bonds, while the silanol continued to undergo the condensation reaction under the 567
alkaline environment (Fig. 11d) [89,90]. The crosslinked SM and SDAM network structure 568
mainly covered the surface of the hydration products, causing the concrete to change from 569
hydrophilic to hydrophobic, and the freshly exposed concrete could exhibit hydrophobicity even if 570
the surface was worn (Fig. 11e) [90,91].
571
572
Fig. 11. Schematic of HAM chemical reaction.
573
4. Conclusion
574
In this paper, a HAM that could store material, released water first and released hydrophobic 575
material later was prepared, and the effect of HAM and its action mechanism was 576
(b)
CH3SiO(OC2H5)3 +H2O Ca(OH)2 CH3Si(OH)3
O[SiCH3O2H]n
O[Si CH
3O2 H]
n
Si O[SiCH3O2H]n O[SiCH3O2H]n
(e)
Si CH3
OH O
concrete OH O[SiCHO
