USE OF THE RECYCLED POLYSTYRENE AS POLYMER ADMIXTURE TO PRODUCE POLYMER MODIFIED MORTAR

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1 USE OF THE RECYCLED POLYSTYRENE AS POLYMER ADMIXTURE TO PRODUCE POLYMER MODIFIED MORTAR Motta, L. A. C. (1), Alves Júnior, J. J. (1), Motta, T. S. (1), Meireles, C. S. (2), Ribeiro, S. (2), Assunção, R. M. N. (3) and Rodrigues Filho, G. (2) (1) Faculdade de Engenharia Civil da Universidade Federal de Uberlândia (FECIV-UFU), Brazil (2) Instituto de Química da Universidade Federal de Uberlândia (IQ-UFU), Brazil (3) Faculdade de Ciências Integradas do Pontal da Universidade Federal de Uberlândia (FACIP-UFU), Brazil ABSTRACT The work shows the use of the recycled materials as polymer admixture to produce polymer modified mortar. The products are obtained by the sulfonation of polystyrene from discarded cups. The properties investigated were mortar consistence, compressive strength and air incorporation. The mortar factor water/cement is equal the 0.7 and the polymer content in relation to the cement mass is of 6, 10 and 15%. The mortar with sulfonated PS presented major consistency index then reference mortar and the compressive strength increases with the polymer cement ratio lower than 15 wt.%. The use of the recycling polymer is advantageous by the protection to the environment and the reduction of the modified system cost. Keywords: recycling, polymeric admixture, polymer modified mortar, polystyrene. 1. INTRODUCTION The properties of cement mortar as workability, water retention, adhesion, waterproofness, strength and durability can be modified or improved by use of polymeric admixtures. Presently, latexes of a single or combinations of polymers like polyvinyl acetate, copolymers of vinyl acetate ethylene, styrene butadiene, styrene acrylic, acrylic and styrene butadiene rubber emulsions and epoxy emulsion are generally used [1,2,3]. The cement mortar and concrete which are made by mixing with the polymer-based admixtures are called polymermodified mortar (PMM) and concrete (PMC), respectively. The properties of the PMM make it a suitable material for making various structural and non-structural pre-cast products, repair of structural members, waterproofing, anticorrosive and decorative finishes, overlay of pavements, bridges and industrial floors [4]. A number of thermoplastic or thermosetting polymers are used in modifying mortars and concrete. These are used in various forms like: liquid resins, latexes, redispersible powders and water-soluble homopolymers or copolymers [2]. 103

2 In addition, PMM and PMC have considerable attraction because their process technology is very similar to that of ordinary cement mortar and concrete. However, the high cost of the resin is usually considered the main factor limiting the growth of polymer concrete and mortars. In modern life the use of polymers is increasing day by day and, consequently, the volume of the polymeric waste is growing. Moreover, as great interest has been shown recently in construction materials with ecological and safety characteristics, mortars and concrete are very attractive because of their capability for using recycled waste products as, for example, industrial wastes such as fly ash and slag. Therefore the use of a recycled polymer as admixture can reduce the PMM and PMC cost and decrease the damage to the natural environment by the increasing volume of the polymeric waste. The aim of the present work has been to prepare new polymer mortars formulated with recycled poly(styrenesulfonate) from the used polystyrene cups. 2. EXPERIMENTAL 2.1 Production of the polymeric admixture Wasted polystyrene plastic cups were used in order to prepare poly(styrenesulfonate), 3.0 g of polystyrene were dissolved in 30 ml of dichloromethane (CH2Cl2). 4.2 ml of acetic anhydride and 2.7 ml of H2SO4 97% were slowly added to this solution under constant stirring. Subsequently, the stirring was kept for 20 min, and then became occasional during the synthesis period. The reaction system was kept at 25ºC for 90 minutes. Next, the sulfonated polymer was precipitated with distilled water up to ph 5. The polymer was dried at room temperature and ground until a powder was obtained. The sulfonated polymers (PSSwastecups) were dissolved in THF to obtain 15% w/w solutions. 2.2 Mortars preparations Table 1. The physical and mechanical properties of cement and sand used. Cement properties Blaine surface area Initial setting time Unit weight Compressive strength at 7 days (m2/kg) (h) (g/cm3) (MPa) Sand properties Specific gravity Fineness modulus presence of silt (g/cm3) (%) Portland cement without mineral admixture (Brazilian Standard Type V- high early strength) and medium sand were used for mortar preparations. The physical and mechanical properties of cement and sand were determined second Brazilian standards (Table 1). Mortars 104

3 were prepared with water/cement ratio (w/c) of 0.7 and sand/cement ratio (s/c) of 3.9. The polymeric solution was previously prepared and added to the cement/sand/water and mixed in mechanic equipment. A reference mortar was prepared without polymer addition and the modified mortars were prepared with polymer/cement ratio (p/c) of 6, 10, and 12%. 2.3 Molding and cure of the specimens Cylindrical specimens of diameter 50mm and height 100mm were prepared for determination of mortar compressive strength. The specimens were laboratory-cured until test age (28 days). Were tested three specimens for each mortar. The dry cure was adoted because polymer modified concrete and mortar present improved water retention. The water evaporation is inhibited due to the filling and sealing effects of impermeable polymer films formed. Accordingly, a sufficient amount of water required for cement hydration is held in the mortar and concrete. This good water retention of the modified composites contributes to an increase in the long-term strength in dry curing. 2.4 Essay of the mortars The consistency index of the fresh mortar was evaluated using a slump table according to the Brazilian standard NBR 13276: The fresh mortar is placed on a slump table, which is spun thirty times, then three orthogonal diameters are collected and, by the arithmetic average, the consistency index value is given. Compressive strength test was carried out by axial compression of cylindrical specimens at 28 days of age, according to the Brazilian standard 13279: The air entrainment was determined according to the Brazilian standard NBR 9778: 2005, which specifies that the air content is the permeable voids volume/total volume ratio. 3. RESULTS AND DISCUSSION Several factors such as polymer type, polymer-cement ratio, water-cement ratio, air content and curing conditions affect the properties of the fresh and hardened mortars. The poly (styrenesulfonate) modified mortar presented excellent resistance to bleeding and segregation, with a cohesive and homogeneous aspect, in spite of it improved flowability. Even with the same water-cement ratio 0.7 for both modified and reference mortar without polymer, it was observed an improved workability over the ordinary mortar and increase on consistency index for the PSS mortar in relation to the reference (Figure 1). This modification was expected since the polymer improves the lubrication between the disperse cement particles, increase the entrained air, resulting in a fluid, homogeneous mortar. 105

4 220 Consistency index (mm) % 6% 10% 15% Polymer-cement ratio Figure 1. Variation of the mortars consistency index with polymer-cement ratio. Usually, in most modified mortars, a large quantity of air is entrained compared with in ordinary cement mortar because of the action of the surfactants contained as emulsifiers and stabilizers in the polymer. In the case of the sulfonated polystyrene, the solvent THF used to prepare the polymeric solutions is lost, increasing amount of voids. An excessive amount of entrained air causes a reduction in strength. The air content in the poly(styrenesulfonate) modified mortar was not too larger then reference mortar, as can be seen in the Figure 2, therefore the compressive strength was not strong affected (Figure 3), especially in the minor polymer content ,5 Air content (%) 20 19, , ,5 17 0% 6% 10% 15% Polymer-cement ratio Figure 2. Variation of the mortars air content with polymer-cement ratio. 106

5 27 Compressive strength (MPa) % 6% 10% 12% 15% Polymer-cement ratio Figure 3. Variation of the mortars compressive strength with polymer-cement ratio. Despite the increase of entrained air, the compressive strength of the poly (styrenesulfonate) modified mortar presented continue increase with the polymer content up to 10% polymer-cement ratio. In general, polymer modified mortar and concrete show a considerable increase in tensile or flexural strength but no improvement in compressive strength compared with ordinary cement mortar. This can be explained in terms of the contribution of high tensile strength by the polymers themselves and an overall improvement in cement paste-aggregate bond. However this increase of the compressive strength slows down for the highest polymer content. For PMMs with a P/C ratio higher than 15 wt.%, a decrease of the mechanical strength can be expected, because the overall damage threshold tends to increase for higher polymer contents. 3. CONCLUSION It was possible to produce poly (styrenesulfonate) from polystyrene cups waste, avoiding discard of this polymer of hard degradation in the environment. Based on the results of the essays of plastic consistency, air content and compressive strength, the produced polymer presented favourable properties for use in the mortar. Preliminary results indicated improving not only on the workability as improving fluidity without bleeding and segregation of the fresh mortar, but good properties also on the hardened mortar. Additional properties as water retention, permeability, absorption of water, bond strength, tensile strength, as well as other mixture are being studied now and the results will be published soon. 107

6 REFERENCES [1] Ohama, Y. Polymer-based admixtures. Cement and Concrete Composites, 20 (1998) [2] Ohama, Y. Recent progress in concrete polymer composites, Adv.Cement Based Materials. 5 (1) (1997) [3] Aggarwal, L.K.; Thapliyal, P.C.; Karade, S.R. Properties of polymer-modified mortars using epoxy and acrylic emulsions. Construction and Building Materials 21 (2007) [4] Mehta, P.K.; Monteiro, P.J.M. Concrete: structure, properties and materials. 2nd ed. Ibracon: São Paulo, (2008). p