Keywords: Beijing-Shanghai High Speed Railway, polyurea, surface preparation system, adhesion, coverage effect

Transcription

1 Advanced Materials Research Online: 0-0- ISSN: , Vols. -6, pp doi:0.08/ 0 Trans Tech Publications, Switzerland Studies on Surface Preparation Systems for Polyurea Protective Coating of Beijing-Shanghai High Speed Railway Bridge Concrete Beams Weibo Huang a, Xudong Liu b, Zhang Jing c and Ping LU d Research Institute of Functional Materials, Qingdao Technological University, Qingdao, CHINA *Corresponding author: Post Office Box No., Fushun Road, Qingdao, CHINA spua@6.com a, liu.xu.dong-@6.com b,charity.zj@gmail.com c, lvping-qd@6.com d Keywords: Beijing-Shanghai High Speed Railway, polyurea, surface preparation system, adhesion, coverage effect Abstract. The comprehensive performance of three kinds of surface preparation systems of polyurea coatings for Beijing-Shanghai High-Speed Railway bridge concrete beams protection both in situ and in lab were studied in this paper. The pull-off test and visual inspection were used to determine the adhesion and coverage effect of the bug hole of shot blasted concrete surface. Adhesion tests were conducted both in situ and in lab over a period of year. Five failure models were identified based on the failure mechanisms observed during the tests. It showed that, the adhesion strength of Qtech- system increased initially (from.7 to.8 MPa) and then tended to be stable (about.mpa) both in lab and in situ, E and E system increased initially (from. to.9 MPa) then decreased to. MPa under low temperature. The tack free time of Qtech- was about hours less than E and E system. Accordingly, the adhesion and tack-free time of epoxy based system (E, E) was very sensitive to application temperature and humidity in jobsite. Polyurethane based system (Qtech-) have a good adhesion and surface coverage effect to concrete surfaces than epoxy based system under the same ambient condition, it showed an excellent comprehensive performance than epoxy one (E, E) both in adhesion and in elimination of pinhole for upcoming polyurea application. Introduction Concrete structures have been widely fabricated in the construction of civil infrastructure facilities such as high-speed railway, stadium, tunnels, and over sea bridges. All of the concrete structures are subjected to environment-induced deterioration and the concrete is degrading rapidly [~]. New kind of coating protection technique was considered as the most effective method for improving the durability of concrete. The preparation of new protective coating materials and the investigation of high performance coating techniques are significant since coating protection becomes the primarily and available method for the protection of concrete []. Polyurea is a class of excellent performance protective coating, aromatic and normal aliphatic polyureas are there into generally applied in the preparation of the high weathering durability and anti-corrosion protective coatings [~0]. The,8km Beijing-Shanghai main railway line is one of the most important infrastructure in China, connecting two of the country's most prominent economic areas and forming the busiest railway route. The new high-speed line will be designed for 0km/h operation and reduce the journey time between Beijing and Shanghai from hours to just. As the success of polyurea technology applied to Beijing-Tianjin intercity rail way, Beijing-Shanghai High Speed Railway is unquestionably another giant polyurea protective engineering. According to Temporary Technological Guideline for Spraying Polyurea As the Waterproofing Layer on the Bridge Beams of Beijing-Shanghai High Speed Railway (Temporary Technological Guideline) [], The aromatic polyurea is selected to apply Beijing-Shanghai high speed railway as bridge concrete waterproof membrane to improve the durability of bridge concrete. Bridge concrete systems often require vapor barriers or other means of water- proofing and anti-corrosion to prevent water and corrosion medium intrusion, which can ultimately lead to delamination and failure of the coating system []. All grease compounds and other foreign matter All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications, (ID: , Pennsylvania State University, University Park, USA-/0/6,0:7:)

2 766 Future Material Research and Industry Application on the surface should be removed by sand blasting, shot blasting, mechanical grinding or suitable chemical means. The concrete surface should also be prepared with a grip enhancing profile to aid in proper adhesion of the substrate and polyurea system. The shot blasting technology was considered as the best preparation method of the substrate surface that presented the highest values of bond strength in shear and in tension from all other considered techniques []. Compared with grinding technology in Beijing-Tianjin inner-city rail, which generated a large number of dusts and cannot form completely rough surface, the shot blasting technology was applied in Beijing-Shanghai High Speed Railway. All defects in the concrete should be routed and filled with an appropriate compatible material and surface preparation system. Any bug holes should be filled the same and any sharp or rough surfaces should be ground to avoid protrusions [~]. The first one is a picture of grinding technology at construction jobsite of Beijing-Tianjin inner-city rail, as shown in Fig.a. The second one is a picture of blasting treatment technology at construction jobsite of Beijing-Shanghai High Speed Railway, as shown in Fig.b. The third one is a picture of Beijing-Shanghai High Speed Railway Bridge, as shown in Fig.c. The fourth one is a picture of Beijing-Shanghai High Speed Railway concrete beam surface, as shown in Fig.d.The fifth one is a picture of concrete surface defects after shot blasting, as shown in Fig.e. a b c d e Fig. Concrete surface defects after shot blasting Fig.. (a) Grinding technology at construction jobsite of Beijing-Tianjin inner-city rail way (b) shot blasting technology at construction jobsite of Beijing-Shanghai High Speed Railway (c) Beijing-Shanghai High Speed Railway Bridge (d) Beijing-Shanghai High Speed Railway concrete beam surface and (e) concrete surface defects after shot blasting. The tack-free time is a measure of the surface cure process and may generally be correlated to the upcoming polyurea application. It is an important indicator of surface preparation system. It should be influenced by a variety of factors such as ambient temperature and humidity, especially during the cold season of autumn-winter and the rainy season of winter- spring. Adhesion is another significant factor affecting performance of polyurea coating. Protective coatings must tightly bond to the concrete substrate to provide long-term protection against corrosive environments. Everaldo Bonaldo and Joaquim A.O. Barros [6] studied the bond characterization between concrete substrate and repairing SFRC using pull-off testing; Vipulanandan and Liu [7~8] studied the tensile bonding strength of epoxy coatings to concrete substrate. However, the interface adhesion is highly affected by a myriad of complicated conditions including material properties, construction conditions, the application method, the quality of concrete substrate, and the way in which the concrete substrate was prepared for surface preparation system. The direct consequence resulted from adhesion failure was polyurea coating delamination

3 Advanced Materials Research Vols especially in cold winter. This severe phenomenon widely existed in Beijing-Shanghai high speed railway polyurea application at the beginning of cold winter( < ) and confused polyurea industry ranging from raw materials suppliers and distributors, formulator/system suppliers, contractors/applicators, end-users and consultants. Therefore, it is essential to study the influences of these critical factors, in order to design more reliable coating system and improve the protective performance. A new kind of all weather base surface preparation system according to the patent methods [9] was studied in this paper. It provided comprehensive solution for Beijing-Shanghai high speed railway waterproof membrane application in myriad climatic factors of changes. In the present study, epoxy-based and polyurethane-based surface preparation system of polyurea protective coating for concrete have been selected to investigate their tack-free time, coverage effect and adhesion characteristics both in situ and lab. Effect of ambient temperature and humidity on curing, failure types and correlations between lab and situ test have been also studied. Experimental Materials )Coating system Polyurethane-based, epoxy-based surface preparation systems were selected to coat the concrete substrates. The main composition of the studied coating systems codified by E, E and Qtech- were presented in the TABLE I.Code Qtech- surface preparation system was prepared according to the patent methods [9]. )Concrete substrates The concrete cubes (00mm 00 mm 00mm) specimens were demoulded from a stainless steel mould, where concrete mix was made according to GB/T90-00 [0].Mix proportions for the concretes are given in TABLE II.The 8-day average compressive strength of QF- and QF- was 7.MPa and.mpa respectively. TABLE IMain composition of paint systems Code Primer Putty Intermediate Topcoat Total thickness(µm) E Epoxy Epoxy based Aromatic polyurea Aliphatic Acrylic polyurethane 0 E Epoxy Epoxy based Aromatic polyurea Aliphatic Acrylic polyurethane 0 Qtech- PU PU based Aromatic polyurea Aliphatic Acrylic polyurethane 0 TABLE II Mix proportioning of concrete in kg/m Mix proportioning(kg/m ) Code Coarse aggregate Fine aggregate W/C Cement Water No. No. Sand Crushed sand Superplasticizer QF QF Testing program. The pull-off tests [] (according to ASTM D-0) were used to determine the bonding strength of coatings to concrete under different ambient temperature (T) and humidity (H). The lab tests simulated conditions were as follows: the cold dry ambient condition was 0,(0±)%, hot wet ambient condition was 0,(90±) %.The tack-free time tests [] performed according to ASTM C679-0(009) under the lab test conditions. Dry concrete specimens were cured at room condition (temperature ± and humidity 0±%) and wet concrete specimens were immersed in water at least for 7 days before coating. The situ test conditions changed with the seasons including low temperature drying and hot humid environment. The adhesion tests both in lab and situ were conducted over a period of year.

4 768 Future Material Research and Industry Application In this test a 0-mm-diameter circular area was used for testing. The selected representative test areas and the clean surfaces in a manner will not affect integrity of the coating or leave a residue. The concrete cubes were cut through the coating around the edges of the dolly with the included cutting tool, removing any excess adhesive. A metal pull-off plate was then glued to the isolated coating section by using a rapid setting epoxy. Bonding strength was determined by pulling the metal fixture of the substrate. A picture of the PosiTest pull-off adhesion tester was shown in Fig. (a) and a schematic diagram of the test used for adhesion was shown in Fig. (b). a Fig..Adhesion test: (a) Picture of the PosiTest pull-off adhesion tester.(b) Schematic diagram of the test Concrete surface preparation )Laboratory specimens Prior to apply surface preparation system in laboratory, the surface of cured concrete cubes should be polished cleanly and smoothly. The coating system application contented prime brushing, putty scratching, polyurea spraying and topcoat spraying. The pictures of concrete cubes were shown in Fig.. b Fig.. Picture of the concrete cubes in lab ) Construction jobsite specimens The concrete surface preparation at the construction jobsite of Beijing-Shanghai High Speed Railway was as follows: examine the concrete surface, clean the concrete, roughen or profile the surface, repair surface defects and getting concrete ready for resurfacing. The surface should be checked for existing sealers, curing materials, grease, oil, efflorescence, and dirt that need to be removed. The most important characteristic for bonding strength is the texture or "profile" of the concrete. The detailed construction procedures were referred to Temporary Technological Guideline []. The pictures of concrete in jobsite were shown in Fig..The first one is a picture of polyurea protective coating system in jobsite, as shown in Fig.a. The second one is a picture of field pull off test, as shown in Fig.b. a Fig.. Picture of concrete in jobsite (a) Beijing-Shanghai High Speed Railway jobsite pull off test, (b) polyurea protective coating system in jobsite. b

5 Advanced Materials Research Vols Results and Discussions Adhesion results. The test results of adhesion both in situ and in lab under different ambient condition were presented in Fig. and Fig. 6. It showed that the bonding strength development tendency, failure models, the maximum value and environment adaptability was different with the test time. Fig. showed the adhesion test result from the laboratory, Qtech- had very good bond strength under 0 / (0±) % and 0 / (90±) % condition. The bond strength of Qtech- increased from.mpa to.66mpa under 0 / (90±) % condition, the same phenomenon was also observed under 0 / (0±) % condition. All failure models were concrete failures; the bonding strength development tendency of Qtech- surface preparation system was increased first and then tended to be stable during the test period. E and E were performed lower bonding strength than Qtech- system under the same condition. Although both E and E surface preparation system were epoxy based, the adhesion, the bonding strength development tendency and failure models were different. Under 0 / (90±) % lab condition, the adhesion of E system reached to. MPa after months, the maximum value of E was. MPa and the trend of adhesion development was increased gradually then went stable level. However, under the same laboratory condition, the adhesion of E system was higher than E during the first 9 months, then, the adhesion of E decreased, most of failure models were surface preparation system and bond interface failure. At the same time, under another lab condition (0 / (0±) %), the max adhesion of E and E did not reach. MPa according to Temporary Technological Guideline, the adhesion increased initially (the adhesion of E and E increased about 0% from month to month) and it reached the peak value.7,. MPa respectively, then decreased, the failure models were surface preparation failure, bonding interface failure and cohesive failure. Fig. 6 showed that: the adhesion test result of three kinds of system in situ were about 0.8 MPa lower than in lab, the bonding strength development tendency in situ was similar as in lab. The comparison and analysis of Fig. and Fig.6 indicated that the Qtech- system showed a better performance than E and E system in cold or extreme condition. This phenomenon can be explained as follows: the Qtech- system was a kind of polyurethane based system, when applied in wet ambient it acted as moisture cured polyurethane system and under cold dry condition it acted as plural-component polyurethane system. The epoxy based showed an unsatisfactory effect performance, as viscosity and liquidity of epoxy based system (E, E) was very sensitive to application temperature, humidity and viscosity in site especially in cold winter, it led to high changes of internal properties in coating system inducing to the first signs of delamination. By another testing result, we find Qtech- based PU resin has a flexible deformation at very low temperature, but E and E based epoxy resin is a rigid and stress focused primers to cause the delamination between primers and polyurea. Adhesion(MPa) 6 E E Qtech- 0,(90±)% E E Qtech- 0,(0±)% Test Time(Months) Fig..Adhesion test results from lab

6 770 Future Material Research and Industry Application Adhesion(MPa) 7 6 E(cold dry) E(hot wet) E(cold dry) E(hot wet) Qtech-(hot Qtech-(cold dry) wet) Test Time(Months) Fig.6. Adhesion test results from jobsite *. Number next to the date point indicates the failure model Table III Failure models in pull off tests Failure Model Pull off test Model Concrete failure Model Polyurea failure Model Surface preparation system failure Model Bonding interface failure Model Hybrid failure *.The blue straight dash line stands for.mpa which according (Temporary Technological Guideline) Failure models analysis. Based on results of., several failure models were observed in adhesion tests to analyze the failure mechanism; the failure models in pull off tests were defined and summarized in TABLE III.

7 Advanced Materials Research Vols As shown in Table, Failure Model was concrete failure, it occurred in concrete because of the tension in the pull-off tests. This mode of failure was the most desired failure as the adhesion between polyurea and concrete was higher than flexure strength of concrete. Failure Model was polyurea coating failure, which was cohesive failure of polyurea coating. This type of failure showed that the tensile strength of polyurea coating was lower than the bonding strength and the tensile strength of concrete. Failure Model was surface preparation system failure in which the failure occurred inner surface preparation system. This type of failure indicates that the surface preparation system strength was lower than both flexure strength of concrete and polyurea coating. It would be due to environmental adaptability or curing problem of surface preparation system. Failure model was bonding interface failure in which the failure occurred between surface preparation system and polyurea coating. This type of failure shows that the surface preparation system has poor material compatibility to polyurea. The direct consequence resulted from this failure model was polyurea coating delamination. This severe phenomenon widely existed in Beijing-Shanghai high speed railway polyurea application, especially in cold winter at -0 to -. Some of the four failure models above were the most common observed failure models in the bonding tests. In addition to the four failure models, some other failure models were also observed in the tests. Failure model failures were a combined concrete and surface preparation system, there was also failure between bonding and polyurea coating, and it showed that the bonding strength of this was close to the tensile /flexure strength of coating. Tack free time tests. Tack free time was an important indicator of surface preparation system; it played a significant role in upcoming polyurea application. The tack free time tests of three kinds systems both in lab and in situ were given in Fig.7. (a) and(b). Fig.7. (a) and (b) showed that the tack free time of Qtech- surface preparation system was lower than E and E surface preparation system both in lab and in site. The best tack free time was less than hour according Temporary Technological Guideline. It can be obviously obtained that the tack free time of E and E system was far beyond the limit ( hour) Fig.7, especially in low temperature, the tack free time prolong to about 7., hour or more, it mainly due to the low temperature react activity of epoxy based system. The upcoming polyurea application would be delayed for long tack free time of E and E system. Qtech- E E 0 (90±)% -- (0±)% -- 0 (0±)% Qtech- a E E Tack Free Time,Hours Qtech- E E 0 Cold dry condition -- Hot wet condition E Qtech- B 6 0 Fig.7. Tack free time tests. (a) In lab tests results, (b). In site tests results E 8 Tack Free Time,Hours

8 77 Future Material Research and Industry Application Coverage effect. All defects must be repaired by surface preparation system prior to turning the polyurea application over for use. At Beijing-Shanghai high speed rail way construction jobsite Kunshan, Jiangsu Province, the coverage effect tests of three kinds of surface preparation system were conducted under the same environmental condition (T:,H: 8%). The results were given in Fig.8. As evident from the Figs, the coverage effect of EP and EP surface preparation system were not satisfactory. There were still a lot of bug holes, pinholes and defects (Fig.8a, b) on concrete surface. While Qtech- surface preparation system showed a good coverage effect, there were nearly no defects on the prepared concrete surface. a b c Fig. 8. Coverage effect results (a) concrete beam surface surface after shot blast (b) EP base treatment system (c) EP base treatment system (d) Qtech- base treatment system d Conclusions The comprehensive performance of three kinds of surface preparation system of polyurea coatings for Beijing-Shanghai High-Speed Railway bridge concrete beams protection both during hot wet and cold dry jobsite condition were investigated in this paper. The results cannot be generalized to all surface preparation system in the market. Based on the experimental results, the following observations are advanced: () The adhesion test showed that Qtech- (according patent methods) system had good bonding strength (more than. MPa ) both in cold dry and hot wet jobsite environment condition than E and E system, It showed that the adhesion of epoxy based system (E, E) was very sensitive to application temperature humidity and viscosity in site. All of the failure models of Qtech- system were concrete failure. () The tack free time of Qtech- system was lower than E and E system. It was an effective approach to shorten the polyurea application time. The tack-free time of epoxy based system (E, E) was very sensitive to application temperature. () The visual inspection can be used to effectively evaluate the coverage effect of surface preparation system on shot blasted concrete. Both of E and E system coverage effect tested in situ were unsatisfactory, Qtech- system showed a desired coverage effect when applied on to the shot blasted Beijing-Shanghai high speed railway bridge concrete beam surface. () Although both E and E surface preparation system were epoxy based, their properties and performance were different. () From the all tests researched in this paper, Qtech- surface preparation plays a significant role in the polyurea application of Beijing-Shanghai high speed railway; it has completely solved the polyurea application problem all the year round. Acknowledgment This study was supported by the Polyurea Development Associate China, Research Institute of Functional Materials of Qingdao Technological University and various contractors related the Beijing-Shanghai high speed railway polyurea project.

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11 Future Material Research and Industry Application 0.08/ Studies on Surface Preparation Systems for Polyurea Protective Coating of Beijing-Shanghai High Speed Railway Bridge Concrete Beams 0.08/ DOI References [] Howarth G.A. Polyurethanes, polyurethane dispersions and polyureas: Past, present and future. Surface coatings international part B: coatings transactions. 00, 86(): /BF06996