waterglass grouting material

waterglass grouting material

Construction and Building Materials 138 (2017) 240–246 Contents lists available at ScienceDirect Construction and Building Materials journal homepag...

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Construction and Building Materials 138 (2017) 240–246

Contents lists available at ScienceDirect

Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat

Flexible and stretchable polyurethane/waterglass grouting material Zhengpeng Yang, Xuefeng Zhang, Xuan Liu, Xuemao Guan, Chunjing Zhang ⇑, Yutao Niu Institute of Materials Science and Engineering, Henan Polytechnic University, Jiaozuo 454000, China

h i g h l i g h t s  Flexible and stretchable polyurethane/waterglass grouting material was prepared via a facile and effective strategy.  The grouting material showed a large elongation of up to 137%.  A probable formation mechanism of grouting material was proposed.  The grouting material exhibited favorable thermostability and repairment performance.

a r t i c l e

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Article history: Received 15 October 2016 Received in revised form 28 December 2016 Accepted 26 January 2017

Keywords: Grouting material Polyurethane Waterglass Flexibility Stretchability

a b s t r a c t Flexibility and stretchability are of ever increasing importance in constructing high-performance grouting materials. Herein, a facile, effective and cost-efficient strategy to make organic-inorganic hybrid chemical grouting material in a ‘‘flexible and stretchable” way was based on polymerization of carbon double bond and excellent synergistic interactions among N-Methylol acrylamide, butenediol, waterglass and prepolymer. Upon the optimal percentages of waterglass (44%), N-Methylol acrylamide (3.5%), butenediol (1.5%), Alkylphenol polyoxyethylene (OP-9, 0.5%), 2,20 -azobis[2-(2-imidazolin-2-yl)propane] (0.35%), 2,2-dimorpholinodiethylether (DMDEE, 0.15%) and prepolymer (50%), the obtained polyurethane/waterglass grouting material with three-dimensional interpenetrating network structure displayed an excellent flexibility, satisfactory compressive strength of 13.4 MPa at 50% compression state, and relatively large elongation of up to 60% with a stable stretching for 200 times. The grouting material was mainly composed of amorphous polyurethane and crystalline polysilicic acid/NaHCO3/Na2CO3 composite, and its probable formation mechanism was proposed. Additionally, the grouting material possessed favorable thermal stability and repairment performance for roadway cracks. This work may open a simple and convenient avenue for the preparation of organic-inorganic hybrid chemical grouting material with flexibility and stretchability. Ó 2017 Elsevier Ltd. All rights reserved.

1. Introduction Grouting, known as a technology for repairing and strengthening, has been widely adopted in recent years to reinforce the loose or broken matrixes [1–3]. Currently, Flexibility and stretchability are of practical importance in constructing high-strength, strongpermeability grouting materials owing to the requirement of construction (etc. mine, roadbed, bridge). The chemical grouting materials have been widely explored for a variety of applications to include roadway, bridge, defense and underground engineering due to their strong adhesion, easy manipulation and high permeability into the micro fracture of broken matrix [4,5]. To realize the high-performance grouting

⇑ Corresponding author. E-mail address: [email protected] (C. Zhang). http://dx.doi.org/10.1016/j.conbuildmat.2017.01.113 0950-0618/Ó 2017 Elsevier Ltd. All rights reserved.

reinforcement, various chemical grouting materials such as polyurethane [6,7], waterglass [8,9], epoxy resin [10], acrylamide [11], methacrylate [12], acrylate [13] and lignin [14] have been developed. Among the aforementioned chemical grouting materials, polyurethane and waterglass have been attracting tremendous attentions for years in terms of their extraordinary properties. More specifically, polyurethane possesses light weight, low viscosity, good permeability, low thermal conductivity and high mechanical performance [15–17], while the waterglass shows high thermal stability, low cost and nontoxic nature [18,19]. The highly efficient consolidation of polyurethane and waterglass grouting materials has been achieved, nevertheless, they show some drawbacks, such as high cost, flammability, poor barrier property and thermal stability of polyurethane [20,21], and poor curing controllability and low mechanical properties of waterglass [22], which limit their practical applications. Therefore, finding a facile, effective and cost-efficient

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way to achieve polyurethane or waterglass grouting materials with improved performance is highly desirable. The composite strategy is an important consideration in the performance improvement of materials. In view of respective properties of polyurethane and waterglass, it is expected that the combination of polyurethane with waterglass into the organicinorganic hybrid grouting material may integrate the advantages of two materials but avoid their drawbacks, producing a more effective and economic grouting material for reinforcement. Recently, the waterglass-modified polyurethane grouting materials with flame resistance, low cost, high thermal stability and mechanical properties have been developed, and presented a satisfactory performance towards grouting reinforcement [23,24]. Our group also reported the protocol of the synthesis of silicate/polyurethaneurea composites based on dipropylene glycol dibenzoate, the obtained composites exhibited high thermal stability and fascinating mechanical performance [25]. However, most of these polyurethane/waterglass composite grouting materials are fragile and stiff, which cannot meet all of the requirements in many practical applications, particularly in these strengthening engineering fields with large load disturbance and temperature fluctuation. Up to date, few attempts have been successfully made to achieve flexible and stretchable polyurethane/waterglass composite grouting material although we are aware of its lower cost and practical importance for reinforcement. Thus, Searching for some new materials and methods is urgently demanded to meet the rapid growing demand of flexibility and stretchability in practical applications. In this work, a flexible and stretchable polyurethane/waterglass grouting material was prepared successfully via a simple and effective strategy. The microstructure, composition and property of the resultant grouting material were explored in detail, and its possible formation mechanism was proposed. 2. Experimental 2.1. Materials The prepolymer (16.7 wt% NCO, 420 mPas) was purchased from Shanghai Hecheng Polymer Science and Technology Co., Ltd. Waterglass (Na2OnSiO2mH2O, modulus 2.3) was supplied by Zhengzhou Jiankete Engineering Materials Co., Ltd. N-Methylol acrylamide was purchased from Tianjin Tianfu Chemical Industry Co., Ltd. Butenediol was supplied by Zhejiang Jinjinle Chemical Industry Co., Ltd. Initiator (2,20 -azobis[2-(2-imidazolin-2-yl)pro pane]) was purchased from Shanghai Hengyuan Biological Technology Co., Ltd. Emulgator (OP-9, 93 mg KOH/g) was obtained from Shanghai Sinopharm Chemical Reagent Co., Ltd. Catalyst (DMDEE) was supplied by Shanghai Rongrong Chemical Co., Ltd. All other chemicals were of analytical grade and purchased from Shanghai Sinopharm Chemical Reagent Co., Ltd. The main parameters of the above materials were tabulated in Table 1.

Table 1 The main parameters of materials. Ingredient

Index

Prepolymer

NCO content (%): 16.7, Viscosity (25 °C, mPas): 420 Modulus: 2.3 Purity (%) P98 Viscosity (20 °C, mPas): 21.8, Purity (%) P99 Molecular weight: 323, Purity (%) P98

Waterglass N-Methylol acrylamide Butenediol 0

2,2 -azobis[2-(2-imidazolin-2-yl) propane] OP-9 DMDEE

Hydroxyl number (mg KOH/g): 93 Amine value (mmol/g): 7.9–8.1, Purity (%) P99

2.2. Preparation of grouting material The preparation of grouting material was performed according to our method with some modification [25]. Specifically, waterglass, N-Methylol acrylamide, butenediol, emulgator, initiator and catalyst with weight ratio of 88:7:3:1:0.7:0.3 were added into a plastic cup and homogenized at 300 rpm for 5–10 min, denoted as component A. The prepolymer was introduced into another plastic container, denoted as component B. Subsequently, the equal solutions in above two plastic containers were mixed for 30 s by vigorous stirring (500 rpm), and then a fully cured specimen for tests was achieved under the room temperature. The detailed preparation information of grouting material was illustrated in Table 2. 2.3. Characterization Scanning electron micrograph (SEM) was performed on a Hitachi S-4800 field emission scanning electron microscope (Hitachi Ltd., Tokyo, Japan) working at 15 kV. IR spectra were recorded using Fourier transform infrared spectroscopy (FTIR: Thermo Nicolet, WI. USA). Raman spectra were conducted on a Renishaw RM3000 Raman spectrometer (InVia, Renishaw Co., UK). X-ray diffraction (XRD) was carried out on a Bruker-AXS D8 X-ray diffractometer using Cu Ka radiation. The thermo gravimetric data were obtained between 28 and 800 °C with the DSC-TGA Q600 thermal analyzer system at a heating rate of 5 °C/min, under air atmosphere. 2.4. Mechanical measurements All the tensile and compressive strength measurements were carried out on a universal testing machine (Model WDW-20, Jinan Hengruijin Instrument Equipment Co., Ltd, China) at room temperature. The tensile tests were done according to the standard of GB/ T1040.2-2006 with sample dimensions of 25  5  2 mm3, and the compressive tests were performed according to the standard of GB/ T1041-92 with sample dimensions of 40  40  40 mm3. 3. Results and discussion The route of design and fabrication of the flexible and stretchable polyurethane/waterglass grouting material was schematically shown in Fig. 1. N-Methylol acrylamide, butenediol, initiator, emulgator and catalyst were added to waterglass under continuous stirring to form a homogenous solution, denoted as component A. The colorless prepolymer was used as component B. After facile mixing of components A and B, a stable milky solution was formed. The as-prepared uniform mixture was directed transformed into rectangular or square specimens via a room-temperature-curing process. Thus, the cured polyurethane/waterglass grouting material with flexibility and stretchability was finally fabricated. The obtained polyurethane/waterglass grouting material exhibited the intriguing flexibility and good resistance to deformation as shown Fig. 2a. Bending had no damage to the grouting material Table 2 The detailed preparation information of grouting material.

Component A

Component B

Ingredient

Percentage (%)

Waterglass N-Methylol acrylamide Butenediol OP-9 2,20 -azobis[2-(2-imidazolin-2-yl)propane] DMDEE Prepolymer

44 3.5 1.5 0.5 0.35 0.15 50

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Fig. 1. Schematic illustration for the fabrication process of the flexible and stretchable polyurethane/waterglass grouting material.

Fig. 2. Flexible and mechanical properties of cured polyurethane/waterglass grouting material. (a) A photograph of bending polyurethane/waterglass grouting material specimen. (b) The compressive strength as a function of curing time. Average of three measurements (mean ± S.D.) The inset photographs display the original and 50% compression status of polyurethane/waterglass grouting material. (c) Typical stress-strain curve of polyurethane/waterglass grouting material during the stretching process. (d) Stress-strain curves of 200 stretching cycles.

specimen. Fig. 2b presents the compressive strength of grouting material specimen at 50% compression state as a function of curing time. The compressive strength almost linearly increased with the curing time up to twelve hours, and then increased slowly to achieve a stable value (13.4 MPa). Significantly, even after compression for 50%, the grouting material specimen had no obvious cracks and kept a favorable compressive strength, and could fully

recover to its initial state, further demonstrating the excellent mechanical flexibility and strength of the grouting material. The grouting material specimen could be stretched by the application of a relatively small force. As seen in Fig. 2c, two stages were clearly observed during the stretching process, a nearly linear relationship between force and strain was displayed at each stage, and the fracture elongation and strength were measured to approxi-

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Fig. 3. Cross-sectional SEM images of cured polyurethane/waterglass grouting material.

mately 137% and 2.1 MPa, respectively. Furthermore, note that within the strain region of 60%, the grouting material specimen could be completely recover to its original length due to its outstanding elasticity. Fig. 2d shows the cyclic test of grouting material specimen for two hundred times with a strain of 60%, the almost unchanged stress-strain curves confirmed the excellent mechanical ductility and long-term stability of grouting material, which was beneficial to its practical applications. The favorable mechanical performance of polyurethane/ waterglass grouting material can be closely related to the microscopic structure of the grouting material. Form the cross-sectional SEM images of grouting material specimen (Fig. 3a and b), we found that the fracture surface was compact and free from appreciable cracks. The organic phases in grouting

material were interconnected with each other, forming a network to unite the grouting material into an integrated whole, which was responsible for the flexibility and stretchability of grouting material. Some spherical or ellipsoidal insertions with an average diameter of about 10 lm were uniformly distributed into organic polymer, causing a relatively high mechanical strength of grouting material. Remarkably, a small number of small and irregular pores still existed in grouting material specimen due to the CO2 production in the curing process of grouting material [24]. SEM observation reveals an integrated and flexible structure of grouting material, indicating the homogenous and synergistic reaction of grouting material, which is favorable for its mechanical performance. The chemical structure and composition of grouting material were identified by FTIR, Raman and XRD, and for a comparison,

Fig. 4. FTIR (a) and Raman spectra (b) of waterglass, polyurethane and polyurethane/waterglass grouting material. (c) XRD pattern of polyurethane/waterglass grouting material.

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the Raman and FTIR spectra of polyurethane and waterglass were also analyzed. As shown in Fig. 4a, all characteristic bands of waterglass and polyurethane appeared in the FTIR spectrum of grouting material, as expected. For instance, OAH stretching at 3100–3600 cm1, NAH stretching at 3378 cm1, asymmetric CAH stretching at 2840–2972 cm1, carboxylic [email protected] stretching at 1717 cm1, CAO stretching at 1091 cm1, asymmetric SiAO stretching at 888–1137 cm1, bending vibration of aromatic and alkene moieties at 580–869 cm1, and SiAOASi bond rocking vibration at 473 cm1. Furthermore, note that a new weak band corresponding to urea linkage appeared at 1662 cm1 due to the reaction between NCO groups in prepolymer and H2O molecules. Fig. 4b shows the Raman spectra of waterglass, polyurethane and grouting material, the representative bands of grouting material matched well with the characteristic bands of polyurethane and waterglass, such as [email protected], CAC, and CAOAC vibrations of polyurethane at 1718, 1612 and 1182 cm1, respectively, and the vibration of SiAOASi corresponding to waterglass at 957–1072 cm1. Remarkably, the band intensity at 1612 cm1 was significantly enhanced, suggesting the formation of carbon chain caused by polymerization of carbon double bond in the curing process of grouting material. XRD was performed to further understand the crystalline structure of grouting material. As seen in Fig. 4c, a comparatively broad diffraction peak at about 2h = 20° is a characteristic peak of polyurethane [25], the relatively strong and narrow diffraction peaks at 2h = 29.1°, 33.8° and 36.9° can be perfectly indexed to the typical crystal planes of polysilicic acid [26], the diffraction peaks at 2h = 27.9°, 31.7°, 40.0°, 45.5° and 51.3° can be generally considered as the characteristic peak of Na2CO3 [27], and the peaks at 2h = 30.4°, 44.6° and 52.5° can be assigned to those XRD patterns of NaHCO3 [28]. Notably, the diffraction peaks corresponding to polysilicic acid, Na2CO3 and NaHCO3 were very sharp, indicating an excellent crystalline structure. FTIR, Raman and XRD analyses indicate that the cured grouting material is composed of amorphous organic phase (polyurethane) and crystalline inorganic phase (polysilicic acid, Na2CO3 and NaHCO3), further demonstrating the feasibility of the fabrication of grouting material. According to the raw materials and cured products, the possible formation mechanism of grouting material can be described by the following. Prepolymer reacts with H2O, N-Methylol acrylamide and butenediol to produce CO2, urea and urethane linkages in the presence of catalyst, and carbon double bonds in N-Methylol acrylamide and butenediol are polymerized with the action of the initiator. These reactions result in the existence of organic phase in grouting material. Meanwhile, the carbonation reaction

will produce silicic acid gel, Na2CO3 and NaHCO3 due to the presence of CO2 and waterglass. Dehydration reaction of silicic acid gel brings inorganic polysilicic acid/NaHCO3/Na2CO3 composite. During the consolidation process of grouting material, SiAO bonds between organic and inorganic phases will generate due to the reaction between prepolymer and polysilicic acid, which can be proved by the aforementioned FTIR analysis and other report [24], and small pores in grouting material can be attributed to the CO2 production. Thus, a three-dimensional interpenetrating network structure is formed eventually, as schematically illustrated in Fig. 5. Thermal stability of grouting material was investigated by thermo gravimetric analysis. As seen in Fig. 6, three stages existed in the process of pyrolytic reaction. In the first stage, the mass of grouting material showed a slight decrease between 50 °C and 117 °C due to the loss of free water wrapped in the material, the weight loss reached 8.2% and the maximum weight loss rate was at 67 °C. In the second stage, the mass of the grouting material decreased sharply when the temperature was varied from 237 °C to 359 °C, the weight loss reached 58% and the maximum weight loss rate was observed at 336 °C. The weight loss can be related to the splitting and partial oxidation of organic compounds in the grouting material. In the last stage, the mass of grouting material decreased gradually between 367 °C and 563 °C, the weight loss reached 78.3% and the maximum weight loss rate was observed at 493 °C. The weight loss can be related to the complete oxidation of organic compounds. A negligible weight loss was

Fig. 6. Thermal stability of polyurethane/waterglass grouting material.

Fig. 5. Schematic representation for the structure of polyurethane/waterglass grouting material.

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Fig. 7. The application of polyurethane/waterglass grouting materials for crack repair of roadway.

exhibited when the temperature was above 563 °C. From the characteristic temperatures in TGA curves, it can be seen that the grouting material appears to be thermally stable below 256 °C. The resultant flexible and stretchable grouting material was used for the repairment of roadway cracks, and positive feedbacks have been received from field observations. As seen in Fig. 7a and c, the grouting material could permeate into tiny cracks of cement and asphalt roads through pump injection, and the fractured zone was integrated into a whole, causing the reinforcement of geologic defects or weakness in the roadway pavement. From the enlarged photographs (Fig. 7b and d), no gap appeared between grouting material and roadway after three months, indicating a favorable repairment performance of grouting material. To better understand the durability of grouting material, the water penetration tests were performed under pressure on cube specimens according to EN 12390-8 [29]. Our study indicated that no obvious water penetration depth was detected when the curing time was varied from 1 to 90 days, further indicating the excellent stability of grouting material.

4. Conclusions In summary, a polyurethane/waterglass grouting material with excellent flexibility and stretchability has been successfully prepared via a facile room-temperature-cured process. When the percentages of waterglass, N-Methylol acrylamide, butenediol, OP-9, 2,20 -azobis[2-(2-imidazolin-2-yl)propane], DMDEE and prepolymer were 44%, 3.5%, 1.5%, 0.5%, 0.35%, 0.15% and 50%, respectively, the resultant grouting material possessed a three-dimensional interpenetrating network structure and excellent mechanical performance, the compressive strength at 50% compression state and the elongation with a stable stretching could reach 13.4 MPa and 60%, respectively. FTIR, Raman and XRD analyses indicated that the main compositions of grouting material were amorphous organic phase (polyurethane) and crystalline inorganic phase

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