Investigation of Impact Resistance for Latex Modified Hardened Cement Pastes

Transcription

1 IJR International Journal of Railway Vol. 11, No. 1 / June 2018, pp The Korean Society for Railway Investigation of Impact Resistance for Latex Modified Hardened Cement Pastes Tri N.M. Nguyen*, Nam-Hyoung Lim**, Yun-Suk Kang***, and Jung J. Kim Abstract The objective of this study is to investigate the effect of latex polymer on the impact resistance of hardened cement pastes. The specimens for cement pastes having water to cement ratio of 0.5 were prepared. For the specimens of latex modified cement pastes, the mixture proportions of latex modified cement pastes were prepared to have the comparable compressive strength with the plain pastes having water to cement ratio of 0.5. Both specimens were cured in water for 28 days. The impact resistances were obtained by the digital equipped Charpy impact instrument. The observation shows that the impact resistance obtained from the hardened cement pastes including latex polymer is higher than those without polymer. The feasibility of using polymer as an admixture to enhance the impact strength of cement pastes as well as concrete is clarified. Keywords: track, cement, Impact resistance, latex polymer, Charpy impact test. 1. Introduction Material properties have been viewed as the basic foundation of construction. Evaluating and measuring the properties of brittle material under dynamic loading condition has been of interested of many researchers, and impact strength is one of importance property that needs to be considered. Among many methods, the Charpy V notch impact test is still the most reasonable and suitable experiment to peak this goal. This study proposes some mixture designs of cement pastes and compares their impact resistances obtained from Charpy V notch impact test. There are many factors affect to the impact strength of concrete such as: storage condition, mix of materials, the surface of aggregate, the bond between binder and coarse materials. First of all, the impact strength of water-stored concrete is lower than when it is dry [1]. In addition, the * ** *** Corresponding author: Department of Civil Engineering, Kyungnam University, Korea jungkim@kyungnam.ac.kr Kyungnam University, Korea Chungnam National University, Korea Korea Railroad Research Institute, Korea cthe Korean Society for Railway impact strength of concrete will be improved when using a mix of materials which have a limited variation in properties. Moreover, when the surface of aggregate is rough, the impact strength of concrete will be developed because of better mechanical interlocking [2]. More importantly, the impact strength will be decreased due to insufficient bond between aggregate and binder, the bond between coarse aggregate and cement pastes is known to be a source of weakness in concrete. Nowadays, there are many fillers can be used to enhance the strength of concrete as well as the bond between coarse aggregate and cement pastes, one of them is polymer. Polymer, particularly rubber latex polymer has the notable advantage that is improved the toughness property, when using an appropriate concentration, the brittle property of Portland cement paste will be transformed into one exhibiting ductile characteristic [3, 4]. Hence, this present study tries to determine the impact strength property of hardened cement pastes which are added some difference proportions of polymer. For determining the impact resistance, the Charpy V notch impact test is utilized, according to this method, the impact resistance of notched specimen is obtained by a hit of standardized pendulum-type hammer and compliance with some constant condition such as: testing temperature, relative humidity, the texture of the notches [5]. Vol. 11, No. 1 / June

2 Tri N.M. Nguyen, Nam-Hyoung Lim, Yun-Suk Kang, and Jung J. Kim / IJR, 11(1), 10-14, Materials and experiments 2.1 Materials In this study, specimens will be prepared at 3 difference mixtures: normal cement paste (plain paste) with a water to cement ratio (w/c) of 0.5, two proportions of Polymer cement pastes that the dosage of latex polymer is 5wt% and 10wt% respectively of cement content (equal to 50 grams and 100 grams of latex polymer respectively for 1000 grams of cement). The reason to choose two different proportions is to have similar consistency of the fresh cement pastes. This property was carried out by the setting time and flow table test which was done by others [6]. In this study, Portland cement and JAPT 1520 Polymer were utilized. First of all, polymer modified cement pastes are widely used in civil infrastructures, bridges, and concrete repaired fields due their excellent strength, environmental protection and workability. As regards to polymer latexes which are known to affect many properties of Portland cement pastes, mortar and concrete such as physical, mechanical and durability, the affection of polymer latexes is dependent on the type as well as the content using in the mixture [3]. Nowadays, there are many polymer latexes for modified cement pastes which have the excellent durability and water reduction, this study proposes a polymer latex which is named JAPT It is a commercial product of Jung Ang Polytech, and properties could be summarized by the following table: Table 1 Properties of JAPT Properties Unit Specification TSC % 47.0 ph 9-11 Sp.gr Kg/m 2 1,090 Viscosity Cps Below 500 Average Particle size Å 1,600 Tg o C 5 MFT o C 5 Table 2 depicts three mixture designs would be utilized to obtain the impact resistance in this study. In the mixture of cement and polymer, polymer took part in that reduced the used water, so, the content of water need to be reduced. In this study, the water:cement ratio were change to 0.4 and 0.3 respectively in the latex modified cement pastes instead of 0.5 in the plain pastes. Table 2 Material detailing No Cement Water Polymer Note Normal cement paste Polymer-cement paste (5%) Polymer-cement paste (10%) 2.2 Specimens preparation The apparatus and procedure of making the pastes are conducted to ASTM C First of all, the plain pastes (without admixture) were prepared using ordinary Portland cement with the w:c ratio of 0.5. For making polymer modified cement pastes, firstly, the polymer latex and water were added to a dry bowl, with proportion content was about 50 grams and 100 grams respectively depended on the expect mixture. Secondly, cement powder was added to the mixed liquid, then, mixing procedure was started. All materials proportion as well as their quantities should be conformed with the mixture designs in table 2, and all the process were matched with the guidance of ASTM C [7]. The procedure was carried out at 200C of room temperature and 50% of relative humidity. Then, the mixtures were poured into the same serial molds of 50 mm 20 mm 10 mm size which were covered by a thin oil film. Finally, the specimens were allowed to cured in the molds for 24 hours. After 24 hours, the specimens were demolded and cured in water at 20 ± 2 o C for 28 days. Fig. 1 The mixer according to ASTM C Geometry and dimensions of specimens: Figure 2 depicts the proposed geometry and dimension of specimen for the Charpy V notch test with the detail information: 2β = 450, a = 2 mm, ρ = 0.25 mm, w = 20 mm, B = 10 mm, Testing span = 50 mm. 11

3 Investigation of Impact Resistance for Latex Modified Hardened Cement Pastes Fig. 2 Geometry and dimension of Charpy V notch test specimens. a) Geometry and detail dimension of specimen for Charpy V notch test; b) Specimen after curing As is illustrated in figure 3, there is the digital equipped instrument for this study, the Charpy impact test machine, this is a complete and versatile pendulum impact test system which has a fully functional pendulum impact test system for both Charpy and Izod testing methods. The experimental setup consists of the specimen is showed in Figure 3, the notched specimen is freely supported in the anvil, the pendulum is held by a holding and releasing mechanism at the initiation state, having an initial energy about 2,986 J (30,438 kgf.cm); the angle between the pendulum and specimen approximate The hold-release-mechanism plays an important role that keeps the pendulum at static initiation state and starts the test without any vibration or imparting acceleration to the pendulum. The pendulum strike with a striking nose is designed to hit exactly at the center position of the specimen to peak the accuracy energy absorbed. The heavy anvil and basement is locked together to become a strongly support for the whole instrument. The notched specimen is supported as a horizontal simple beam and against two rigid anvils in such a position that its center of gravity and the center of the notch shall lie on tangent to the arc which is the orbit the pendulum at the position of impact, notice that the notch is placed opposite the impact interface. For starting the test, release the pendulum by pushing the handgrip of the release-mechanism, the pendulum swings and hits to specimen by the striking nose, the net breaking energy is indicated in the digital indicator. By using the digital instrument equipped with computer automatically compensate for windage and friction, this net breaking energy (or energy absorbed by the specimen) can be reliable. The impact resistance can be calculated by the net breaking energy per square meter and is indicated in Table 4. The average value of impact resistance shall not include the energy absorbed of specimen that did not break completely. The experiment was carried out at standard laboratory atmosphere of 23 ± 2 o C and 50 ± 5% relative humidity[5, 8, 9] For each mixture design, specimens were prepared at once source, and five specimens were tested at 28 days old. 3. Result and Discussion Figure 4 shows that all the specimens were broken completely, it means that the Charpy test can be used to evaluate the capacity of energy absorbed for cement pastes robustly; although they broke into two or three pieces but Fig. 3 The Charpy impact instrument 12

4 Tri N.M. Nguyen, Nam-Hyoung Lim, Yun-Suk Kang, and Jung J. Kim / IJR, 11(1), 10-14, 2018 Mix design Normal cement pastes Polymer -cement pastes (5%) Polymer - cement pastes (10%) Specimen number Table 4 Charpy test results for 28-day-old Net breaking Energy (J) Breaking area (mm 2 ) Impact resistance (J/m 2 ) The average impact resistance (J/m 2 ) The standard deviation Fig. 4 The breaking specimens they still had the same crack which was started at the hit point of striking nose to the notch cap. The line graph given by figure 5 depicts the Impact resistance of 28-day-old cement pastes with latex polymer admixture. From an overall perspective, there was a significant increase in the impact resistance when using polymer admixture for the cement paste. As illustrated, the impact resistance rose sharply when using the proportion by 5% of latex polymer with approximately J/m 2 compared to about 7600 J/m 2 for plain pastes. Similarly, there was also a slight increase in the impact resistance when changing the proportion of polymer from 5% to 10%. This result was compliance with many publication conclusions that indicated the advantages of latex polymer which enhanced many properties of concrete as well as cement pastes such as: workability, adhesive strength, durability, etc and the more latex concentration was used, the more amplitude was enhanced[10-12]. As we knew that the impact strength was due to the increase of compressive strength. Hence, at 28 days, the impact resistance of hardened latex modified cement pastes is increase by the increasing of dosage usage. 4. Conclusion Fig. 5 Effects of addition of latex polymer in plain pastes A comparison between the impact resistance results obtained from the mixture of polymer-cement pastes and plain pastes shows that both admixtures can be used to enhance the strength of cement pastes as well as concrete 13

5 Investigation of Impact Resistance for Latex Modified Hardened Cement Pastes under impact loading. The mixture designs proposed in present study is advantageous because they made from common commercial admixture. In addition, the present study also introduces the Charpy impact instrument which is a useful instrument for determining the impact resistance of cement pastes. Acknowledgements This research was supported by a grant (17RTRP- B ) from Railroad Technology Research Program funded by Ministry of Land, Infrastructure and Transport of Korean government. References 1. H.Green, (1964) Impact strength of concrete, Proceedings of the Institution of Civil Engineers, Vol. 28, pp A.M.Neville, (2005) Properties of Concrete. 3. Min Wang, R.W., Hao Yao, Shameel Farhan, Shuirong Zheng, Zhujun Wang, Congcong Du, Hao Jiang, (2016) Research on the mechanism of polymer latex modified cement, Construction and Building Materials, Vol. 111, pp Colak, A., (2005) Properties of plain and latex modified Portland cement pastes and concretes with and without superplasticizer, Cement and concrete research, Vol. 35, pp ASTM D ,Standard Test Method for Determining the Charpy Impact Resistance of Notched Specimens of Plastics, ASTM International, W.C., PA, 2010, 6. G.Barluenga, F.H.-O., (2004) SBR latex modified motar rheology and mechanical behaviour, Cement and concrete research, Vol. 34, pp ASTM C305-14,Standard Practice for Mechanical Mixing of Hydraulic Cement Pastes and Mortars of Plastic Consistency, ASTM International, W.C., PA, 2014, 8. Toshiro Kobayashi, H.T.a.T.M., (2002) Analysis of Test data obtained from Charpy V and Impact Tensile Test, From Charpy to Present Impact Testing, pp V.S.Gopalaratnam, S.P.S.a.R.H., (1984), A Modified Instrumented Charpy Test for Cement-based Composites, Experimental Mechanics, pp I.Ray, A.P.G., M.Biswas, (1995) Effect of Latex and Superplasticiser on Portland Cement Mortar in the Hardened State., Cement and concrete composites, Vol. 17, pp Etsuo Sakai, J.S., (1995) Composite Mechanism of Polymer Modified Cement, Cement and concrete research, Vol. 25, pp Ohama, Y., (1998) Polymer-based Admixtures, Cement and concrete composites, Vol. 20, pp