FUNDAMENTAL PROPERTIES OF MMA-MODIFIED SOFT UP POLYMER MORTAR MIXED WITH WASTE RUBBER POWDER

Transcription

1 FUNDAMENTAL PROPERTIES OF MMA-MODIFIED SOFT UP POLYMER MORTAR MIXED WITH WASTE RUBBER POWDER Kyu-seok Yeon, Jung-ho Jeong, Taek-jeong Kweon, Jong-man Beck, Xing Qi Jin. Kangwon National University, Korea Abstract In this study, the Mehtyl Methaacrylate (MMA)-modified mortar mixed with waste rubber powder that has a low elastic modulus and a relatively larger strain than that of silica was produced by using the soft unsaturated polyester (UP) resin as a binder. Compressive and flexural strengths decreased with increasing the content of waste rubber powder. The adhesion strengths for the various cases of MMA content and substrate were surveyed. The setting shrinkage and the strain according to MMA content and waste rubber powder content were also examined. 1. Introduction Recently, in constructional industry field, polymer concrete is gathering an interest as the new material that has excellent dynamical properties and chemical resistances. Since the polymer concrete using UP resin has excellent compressive, flexural and shear strengths, it can be practically applied for repairing and strengthening. Especially, the workability, the flexural strength, the compressive strength and the setting shrinkage of MMA-modified polymer mortar and concrete are generally improved as the MMA content increases. However, the polymer concrete has a weak point such as brittle fracture because it is weak for an impact. In this study, the MMA-modified mortar was produced by using the soft UP resin mixed with waste rubber powder that has a small elastic modulus to develop a ductile material. Then the basic properties and the adhesion strength were surveyed. 2. Materials 2.1 Binder and shrinkage reducing agent In this study, UP resin was used as a binder. In order to reduce the shrinkage, the shrinkage reducing agent (SRA) was made by dissolving the thermal plastic in styrene monomer. 2.2 MMA (Methyl Methaacrylate) and initiator MMA monomer was used for the binder. Mineral turpentine solution with cobalt octanoic (CoOc) acid 8 % is generally used as an accelerator, and methyl ethyl ketone peroxide (MEKPO) 55 % is used as an initiator.

2 2.3 Filler and rubber powder Ground calcium carbonate of which particle size is 1-3 μm, fineness is 2,5~3, cm 2 /g, and water content is below.1 % was used. Waste rubber powder of which particle size is mm, rubber contents is 98 %, iron content is below.1 % and water content is below.1 %, was used for the filler. 3. Test Method 3.1 Strength properties Cylindrical specimen was prepared by the method regulated in KS F 2419 (Method of making polyester resin concrete specimens). Compressive strength was examined by the method prescribed in KS F 2481 (Method of test for compressive strength of polyester resin concrete) and KS F 2482 (Method of test for flexural strength of polyester resin concrete). The dimension of specimen for the compressive strength and the flexural strength tests was cm. Table 1 shows the mixing proportion of polymer mortar for strength tests. 3.2 Adhesion strength The adhesion strength was tested by KS L 126 (Testing method for bond strength of ceramic tile to portland cement). The dimension of specimen was mm. Epoxy was used to bond the specimens. Table 2 shows the mixing proportions for adhesion strength and setting shrinkage tests. Table 1: Mix proportions for strength test Binder formulation by mass Mix proportions by mass (%) Fine aggregate % Phr Rubber powder Binder Filler UP MMA SRA CoOc MEKPO contents (%) No. 1 No Table 2: Mix proportions for adhesion strength and setting shrinkage test Binder formulations by mass Mix proportions by mass (%) % phr * MMA UP SRA Initiator contents : 1 Binder Filler Rubber

3 3.3 Setting shrinkage Setting shrinkage was measured by fixing LVDTs of.5 mm precision to both sides of the specimen of cm in accordance with the Ohama-Demura test method. Test values of the setting shrinkage were continuously recorded for 24 hours by the data logger; every 1 minutes for the initial 3 hours and every 3 minutes thereafter. Photo 1 shows an experimental setup for the setting shrinkage test. 3.4 Elastic modulus The stress-strain relationship was studied by the method prescribed in KS F 2438 (Testing method for static modulus of elasticity and Poission's ratio in compression of cylindrical concrete specimens): It was surveyed by measuring the vertical strain 3 times during applying the load until 4% of maximum load. Photo 1:Setting shrinkage test Photo 2:Test of elastic modulus 4. Results and discussions 4.1 Strength properties Fig. 1 and Fig. 2 show the behaviors of compressive and flexural strengths of MMA-modified mortar mixed with waste rubber powder versus the content of powder in percent. When the content increased from 3 % to 8 %, the compressive strength decreased about 66 % in the range of 44.1MPa to 14.7MPa, and the flexural strength also decreased about 6 % in the range of 19.6MPa to 7.84MPa when rubber powder content increased from 3 % to 8 %. By noting that the compressive and the flexural strengths of MMA-modified polymer mortar not mixed with rubber powder are about 63.7MPa and 24.5MPa, these results show that these strengths decrease about 2%~7%. This decrement is believed by the fact that the rubber powder has small elastic modulus and thus lowers the adhesiveness. 4.2 Setting shrinkage Regardless of MMA contents, the setting shrinkage showed a reducing tendency as SRA content increased. When MMA content increased, the setting shrinkage reduced regardless of SRA content. Decreasing effect, occurred by adding SRA, of the setting shrinkage is larger than that by adding MMA. Fig. 3 and Fig. 4 show the variation of the setting shrinkage according to MMA and SRA contents.

4 Compressive strength (MPa) Contents of rubber powder (%) Fig. 1: Compressive strength by contents of rubber powder Flexural strength (MPa) Contents of rubber powder (%) Fig. 2: Flexural strength by contents of rubber powder Length change (1-4 ) SRA content:1 (wt. %) MMA content (wt. %) 2 3 Length change (1-4 ) MMA content:2 (wt.%) SRA content (wt. %) Elasped time (s) Fig.3: Setting shrinkage by MMA contents Elasped time (s) Fig.4: Setting shrinkage by SRA contents 4.3 Adhesion strength The adhesion strength of soft UP resin mortar adhered to the substrates of cement concrete (polymer mortar) and cured 7 days according to various MMA contents is shown in Fig. 5 and Fig. 6. The strength increased until the content of 2 % and rather tends to decreased therafter. It is believed that the result was caused by that the bleeding effect due to the difference of specific gravities of MMA and filler makes a bonding between substrate and specimen weaken. Characteristic of adhesion strength under water is similar to that in air-dried condition, and, regardless of MMA content, the strength under water is 2~3 % less than that in air-dried condition. In the case of under water curing, no bonding occasionally happened: Water molecules remained on the adhesion surface were believed to interfere with the adhesiveness between substrate and mortar, and consequently lower the adhesion strength.

5 Adhesion Strength (MPa ) Air Concrete Adhe sion Strength(MPa ) Water Concrete MMA % MMA 1% MMA 2% MMA 3% MMA 4% MMA % MMA 1% MMA 2% MMA 3% MMA 4% Fig. 5: Adhesion strength according to MMA contents for cement concrete of substrate Adhes ion Strength (MPa) Air PM Ad hesion Stre ngth (MPa ) Water PM MMA % MMA 1% MMA 2% MMA 3% MMA 4% MMA % MMA 1% MMA 2% MMA 3% MMA 4% Fig. 6: Adhesion strength according to MMA contents for polymer mortar of substrate Stress (kgf/cm 2 ) Fig. 7: Stress-strain curve 4.4 Stress-strain curve It is generally known that the ultimate strain of cement concrete and polymer concrete using UP resin as a binder are about.3 and.8. Fig. 7 shows the behaviors of stress-strain curve for various content rubber powders. The polymer mortar made by using soft UP resin as a binder has a very ductility comparing with the polymer mortar using UP resin and fine aggregate. It is evaluated that this property has a high resistance to stress concentration in an interface by the absorption ability of impact and temperature change. Strain 3% 5% 7% 9%

6 5. Conclusions Results obtained in this study are summarized as follows ; 1. Strength properties of MMA-modified soft UP resin polymer mortar mixed with waste rubber powder showed a tendency that the compressive and the flexural strengths decreased 2 %~7 % as rubber powder content increased. 2. Regardless of MMA content, as SRA contents increases, the setting shrinkage reduced. The setting shrinkage showed a decreasing tendency with increasing MMA content regardless of SRA content. 3. Adhesion strength showed the highest value in 2 % of MMA content regardless of curing conditions, and, after 2 %, it gradually reduced. It is believed to be caused by that the bleeding effect due to the difference of specific gravities of MMA and filler makes a bonding between substrate and specimen weaken. 4. On the maximum stress, the strain is constant about.18 and, on the other hand, the maximum ultimate strain tended to increase from.6 to.11 by increasing the rubber powder content. References [1] Kyu-seok Yeon, myung-ki Joo, Keun-woo Ryu, Jong-yun Choi, Nan-ji Jin, Workability and Strength Properties of MMA Modified Polyester Polymer Concrete, Proceedings of the Korean Concrete Institute, Vol. 14, No.2 (22), [2] M. Aamer Rafique Bhutta, Process Technology of Polymethyl Methacrylate Mortars and Concretes for Underwater Construction Work, Nihon University, (1995). [3] Y. Ohama, K. Demura, M. A. R. Bhutta, T. Kobayashi, T. Kawano, Adhesion between Fresh Polymethyl Methacrylate Mortar and Fresh Cement Mortar or Concrete, Proceedings of the 2 nd International RILEM Symposium ISAP 99, RILEM Publications. [4] Y. Ohama, M. Komiyama, Early Strength and Length Change of Polyester Resin Concrete with Shrinkae-Reducing Agent, The 22 nd Japan Congress on Materials Research, (1979)