BASIC PROPERTIES OF UNDERWATER POLYMER MORTARS USING WASTE EXPANDED POLYSTYRENE-METHYL METHACRYLATE-BASED BINDERS

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1 BASIC PROPERTIES OF UNDERWATER POLYMER MORTARS USING WASTE EXPANDED POLYSTYRENE-METHYL METHACRYLATE-BASED BINDERS Atsushi Moroka 1) and Yoshihiko Ohama 2) 1) Graduate School of Engineering, Nihon University, Japan 2) College of Engineering, Nihon University, Japan Abstract The purpose of this investigation is to develop underwater polymer mortars using a methyl methacrylate (MMA) solution of expanded polystyrene (EPS) as an effective recycling method for waste expanded polystyrene. An EPS solution is prepared by dissolving a preformed cellular polystyrene thermal insulating material as a model of waste expanded polystyrene in MMA. and air-placed polymer mortars using EPS-MMA-based binders with N, N-dimethyl aniline or N, N-dimethyl-p-toluidine as a promoter, ground calcium carbonate as a filler and silica sands as fine aggregates are prepared with various initiator contents and promoter contents, and tested for working life and strength properties. As a result, the working lives of the underwater and air-placed binders and polymer mortars are shortened with increasing initiator content and promoter content. The working lives of the underwater binders and polymer mortars are longer than those of the air-placed binders and polymer mortars. Their flexural and compressive strengths are increased with increasing initiator content and promoter content. The flexural and compressive strengths of the underwater polymer mortars are about 48 to 93% of those of the air-placed polymer mortars. 1. Introduction In Japan, polymethyl methacrylate (PMMA) mortars and concretes having good workability, low-temperature curability 1), underwater curability 2) and high-early-strength development are popularly employed for field applications and precast products. On the other hand, the authors have prepared the styrene solutions of waste expanded polystyrene for polymer mortars by dissolving waste expanded polystyrene in styrene, and developed a new polymer mortar system by using the styrene solutions of waste expanded polystyrene as binders for the system 3). Methyl methacrylate is one of vinyl monomers, and can be used not only as a solvent to dissolve waste expanded polystyrene but also as an ingredient of binders for polymer mortars like styrene. In this paper, a methyl methacrylate solution of waste expanded polystyrene (EPS solution) is prepared at a waste expanded polystyrene concentration of 40% by dissolving waste expanded polystyrene in methyl methacrylate, polymer mortars using the EPS solution-based binders with various initiator contents and promoter contents are mixed, placed in underwater and air, and tested for working life and strength properties.

2 2. Materials 2.1 Chemicals for binder systems Expanded polystyrene (EPS) (density, 17kg/m 3 ), specified in JIS A 9511 (Preformed cellular plastics thermal insulation materials), was used as a model of waste expanded polystyrene. The physical properties of EPS are given in Table 1. Methyl methacrylate for industrial use (MMA) was employed not only as a solvent to dissolve EPS but also as an ingredient of binders for polymer mortars. γ -methacryloxypropyltrimethoxy silane (silane) was used as a coupling agent. Fifty% dicyclohexyl phthalate powder of benzoyl peroxide (BPO) was used as an initiator, and N, N-dimethyl aniline (DMA) and N, N-dimethyl-p-toluidine (DMT) were used as promoters. The water content of the EPS was controlled to be less than 0.1% by heat drying at 60ºC for 48h. The properties of MMA for binders are shown in Table Filler and fine aggregates Commercially available ground calcium carbonate (size; 2.5µm or finer) was used as a filler. Silica sands No.26 and No.100, specified in JIS G 5901 (Molding silica sand), were employed as fine aggregates. The water contents of the filler and fine aggregates were controlled to be less than 0.1% by heat drying at 105ºC for 48h. The properties of the filler and fine aggregates are shown in Table 3. Table 1: Physical properties of EPS. Density Thermal conductivity Flexural strength Compressive strength Molecular weight (kg/m 3 ) [20ºC, W/(m K)] (N/cm 2 ) (N/cm 2 ) ca Table 2: Properties of MMA for binders. Solubility Density Viscosity Purity Molecular weight (20ºC, %) (20ºC, g/cm 3 ) (20ºC, mpa s) (%) Water in In water Table 3: Properties of filler and fine aggregates. Size Density Type of filler or fine aggregate (µm) (g/cm 3 ) Filler Ground calcium carbonate < Silica sand No Fine aggregate Silica sand No Water content (%) < Testing procedures 3.1 Preparation of EPS solution and EPS-MMA-based binders An EPS solution with an EPS concentration of 40% is prepared by dissolving EPS in MMA at about 60ºC in a stainless steel vessel. Binders for the polymer mortars were prepared by mixing silane, BPO and DMA or DMT with the EPS solution according to the formulations of binders given in Table 4. The working life of the binders was determined underwater and in air at 20ºC according to JIS K 6833 (General testing methods for adhesives).

3 Table 4: Formulations of EPS-MMA-based binders for polymer mortars. Formulations (%) Formulation EPS solution Initiator Promoter No. Silane BPO DMA DMT EPS MMA (phr*) (phr) (phr) (phr) Note, * : parts per hundred parts of resin (by mass). 3.2 Preparation of fresh polymer mortars Fresh polymer mortars with the mix proportions given in Table 5 were prepared by mixing ground calcium carbonate, silica sands No.26 and No.100 with binders in accordance with JIS A 1181 (Method of making polyester resin concrete specimens). Table 5: Mix proportions of polymer mortars using EPS-MMA-based binders. Mix proportions (%) Filler Fine aggregate Filler-binder ratio Binder Silica sand (by mass) Ground calcium carbonate No.26 No Working life test The working life of fresh polymer mortars was determined underwater and in air at 20ºC by the finger-touching method prescribed in JIS A 1186 (Measuring method for working life of polyester resin concrete). 3.4 Strength tests According to JIS A 1181, fresh polymer mortars were placed in molds mm by tamping underwater at 20ºC and in air at 20ºC and 60% (RH), and then cured for 24h in the molds kept underwater and in air. Cured specimens were tested for flexural and compressive strengths according to JIS A 1184 (Method of test for flexural strength of polyester resin

4 concrete) and JIS A 1183 (Method of test for compressive strength of polyester resin concrete using portions of beams broken in flexure), respectively. 4. Test results and discussion Fig.1 illustrates the effects of BPO (as an initiator) content and DMA or DMT (as a promoter) content on the working lives of underwater and air-placed EPS-MMA-based binders and polymer mortars. Regardless of placing conditions, the working lives of the EPS-MMA-based binders and polymer mortars are shortened with increasing BPO content and DMA or DMT content. In general, the working lives of the underwater binders and polymer mortars are longer than those of the air-placed binders and polymer mortars because the heat of polymerization reaction of the binders is absorbed by water. The differences in the working lives between the underwater- and air-placings are hardly recognized at high BPO content and DMA or DMT content. The effect of DMA or DMT content on the working lives is stronger than the effect of BPO content. The effect of DMT content is marked rather than the effect of DMA content DMA Polymer mortar DMT Polymer mortar Working life (min) DMA content (phr) Working life (min) Binder Binder Fig.1: Effects of BPO content and DMA or DMT content on working lives of underwater and air-placed EPS-MMA-based binders and polymer mortars. DMT content (phr) Fig.2 shows the working life of underwater and air-placed EPS-MMA-based binders using DMA or DMT as a promoter vs. working life of underwater and air-placed polymer mortars using the binders. Despite of placing conditions, the working life of the underwater and air-placed polymer mortars using DMA or DMT tends to be about 2.3 to 2.5 or 3.4 to 3.6 times longer than that of the binders. It is considered that the filler and fine aggregates in the polymer mortars act as heat sinks to absorb the exotherm induced by the polymerization of the binders 4). There is a close correlation between the working lives of the underwater and air-placed binders and polymer mortars, and the correlation can be expressed by the following empirical equations (1) to (4).

5 In the case of using DMA as a promoter, ; W m = 2.53W b (γ = 0.95) (1) Air-Placed; W m = 2.27W b (γ = 0.98) (2) In the case of using DMT as a promoter, ; W m = 3.37W b (γ = 0.95) (3) Air-Placed; W m = 3.65W b (γ = 0.98) (4) where W m and W b are the working lives (min) of the underwater and air-placed polymer mortars and EPS-MMA-based binders, respectively, and γ is a correlation coefficient. Working life (min) of polymer mortar, Wm DMA Wm=2.53Wb+14.6 (γ*=0.95) Wm=2.27Wb+16.6 (γ*=0.98) Working life (min) of polymer mortar, Wm DMT Wm=3.65Wb-15.4 (γ*=0.98) Wm=3.37Wb-13.9 (γ*=0.95) Working life (min) of binder, Wb Working life (min) of binder, Wb Fig.2: Working life of underwater and air-placed EPS-MMA-based binders using DMA or DMT as promoter vs. working life of underwater and air-placed polymer mortars. Note, *: correlation coefficient. Fig.3 exhibits the effects of BPO (as an initiator) content and DMA or DMT (as a promoter) content on the flexural strength of underwater and air-placed polymer mortars using EPS-MMA-based binders. The flexural strength of the polymer mortars using EPS-MMA- based binders with DMA tends to increase with increasing BPO content and DMA content regardless of placing conditions. The flexural strength of underwater polymer mortars using EPS-MMA-based binders with a DMT content of 0.10phr increases with increasing BPO content. The flexural strength of underwater and air-placed polymer mortars using binders with DMT contents of 0.25 and phr increases with increasing BPO content, and reaches a maximum or become nearly constant at a BPO content of 2.00phr. The flexural strength of the underwater and air-placed polymer mortars using DMT increases with an increase in the DMT content irrespective of BPO content. Despite of placing conditions, the flexural strength is greatly affected by DMT content rather than BPO content. The flexural strength of the underwater polymer mortars is smaller than that of the air-placed polymer mortars irrespective of BPO content and DMA or DMT content. The flexural strength of the underwater polymer mortars using DMA is decreased to about 48 to 72% of that of the air-placed ones using DMA. The flexural strength of the underwater polymer mortars using DMT is reduced to about 76 to 90% of that of the air-placed ones using DMT. The flexural strength decrease rate due to the underwater placing is small at high DMA or DMT content. The flexural strength decrease is marked in the use of DMA rather than the use of DMT.

6 DMA Flexural strength (MPa) Fig.3: Effects of BPO content and DMA or DMT content on flexural strength of underwater and air-placed polymer mortars using EPS-MMA-based binders. DMA content (phr) Flexural strength (MPa) DMT DMT content (phr) Fig.4 represents the effects of BPO (as an initiator) content and DMA or DMT (as a promoter) content on the compressive strength of underwater and air-placed polymer mortars using EPS-MMA-based binders. In spite of placing conditions, the compressive strength of the polymer mortars using EPS-MMA-based binders increases with increasing BPO content and DMA or DMT content. The compressive strength of the underwater polymer mortars using DMA is lower than that of the air-placed polymer mortars irrespective of BPO content and DMA content. The compressive strength of the underwater polymer mortars using DMA is reduced to about 59 to 87% of that of the air-placed ones using DMA. The trend in the compressive strength development in the use of DMA is similar to that in the flexural strength development in the use of DMA. By contrast, the compressive strength reduction due to the underwater placing in the polymer mortars using DMT is small compared to that in the polymer mortars using DMA. The compressive strength of the underwater polymer mortars using DMT is reduced to about 81 to 93% of that of the air-placed ones using DMT. The underwater polymer mortars using DMT develop almost the same flexural and compressive strengths as the test results by Bhutta et al. 2) The poor setting of the only air-contacted surface layers of air-placed polymer mortars using binders with low BPO content and DMT content, i.e., BPO contents of to 3.00phr and a DMT content of 0.10phr was observed because of the polymerization inhibition effect of oxygen in the air 5) on MMA, and their strength tests were not conducted. However, the poor setting of air-placed polymer mortars using binders with low BPO content and DMA content was not recognized. By contrast, the setting of underwater polymer mortars was not affected by oxygen in the air regardless of BPO content and DMA or DMT content.

7 Compressive strength (MPa) DMA Fig.4: Effects of BPO content and DMA or DMT content on compressive strength of underwater and air-placed polymer mortars using EPS-MMA-based binders. 5. Conclusions DMA content (phr) Compressive strength (MPa) DMT The conclusions obtained from the above test results are summarized as follows: DMT content (phr) (1) The working lives of underwater and air-placed polymer mortars using EPS-MMA-based binders are shortened with increasing BPO content and DMA or DMT content. The working lives of the underwater binders and polymer mortars are longer than those of the air-placed binders and polymer mortars. Their working lives can be controlled by adjusting BPO content and DMA or DMT content. The working life of the polymer mortars using DMA or DMT tends to be about 2.3 to 3.6 times longer than that of the binders regardless of placing conditions. There is a reliable correlation between the working lives of the underwater binders and polymer mortars as expressed by the equations (1) and (3). The working life of the underwater polymer mortars is predicted by using the working life of the binders using DMA or DMT according to the equations (1) and (3). (2) The flexural and compressive strengths of polymer mortars using EPS-MMA-based binders increase with an increase in BPO content and DMA or DMT content irrespective of placing conditions. The flexural and compressive strengths of the underwater polymer mortars are about 48 to 93% of those of the air-placed polymer mortars in spite of BPO content and DMA or DMT content. (3) In general, the flexural and compressive strengths of air-placed polymer mortars using DMA are larger than those of air-placed polymer mortars using DMT. However, the decreases in the flexural and compressive strengths due to underwater placing are marked in the use of DMA rather than the use of DMT. (4) The setting of underwater polymer mortars was not affected by oxygen in the air irrespective of BPO content and DMA or DMT content.

8 (5) From the above results, underwater polymer mortars using EPS-MMA-based binders have almost the same qualities as underwater PMMA mortars, and can be used in similar applications to them. References [1] Kobayashi, T. and Ohama, Y., Low-temperature curing characteristics of polymethyl methacrylate resin concrete, Transactions of the Japan Concrete Institute, 5 (1983) [2] Bhutta, M.A.R., Ohama, Y. and Demura, K., Basic properties of polymethyl methacrylate mortars for underwater placement, Proceedings of the Thirty-Seventh Japan Congress on Materials Research, Kyoto, March 1994, (The Society of Materials Science, Japan, Kyoto, 1994), [3] Choi, N.W. and Ohama, Y., Effects of initiator and promoter on working life and strength properties of polymer mortars using waste expanded polystyrene solution (in Japanese), Cement Science and Concrete Technology, (56) (2003) [4] McNerey, M.T., Research in progress: rapid all-weather pavement repair with polymer concrete, Applications of Polymer Concrete, (American Concrete Institute, Detroit, 1981) [5] Asami, K., Acrylic resin (in Japanese), (The Nikkan Kogyo Shimbun, Tokyo, 1960),