APPLICATION POSSIBILITIES OF FIBER COMPOSITES WITH POLYMER-MATRIX IN BUILDING INDUSTRY

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1 Life Prediction and Aging Management of Concrete Structures 383 APPLICATION POSSIBILITIES OF FIBER COMPOSITES WITH POLYMER-MATRIX IN BUILDING INDUSTRY L. BODNAROVA and R. HELA Brno University of Technology, Faculty of Civil Engineering, Institute of Technology of Building Materials and Components, Czech Republic Abstract Drawn and cast composite profiles with polymer-matrix have in present time a non-replaceable position on the building products market, especially for special applications, where they successfully replace conventional materials and surpass them in properties. Involved are for instance applications of composite materials in surroundings with heavy corrosive load or structural members with high strength values and low mass which in shape variety and in possibility of being dyed through comply with particular esthetic points of view. The examined composite profiles and panels are prepared by pulltruding method. The binder is a polyester or vinylester resin and as reinforcement oriented glass or sometimes carbon fibres and flat reinforcements are used. In spite of very good experience with this material and with particular products some physical-mechanical properties of polymer-composites are not yet verified in present time. In the paper the test results of these polymer-composites under normal temperature and under thermal load are presented. 1. Introduction - Fibre Composites with Polymer-Matrix 1.1. Matrix The matrix of these composite materials is a thermosetting plastic. Thermosetting binders harden by chemical reaction after being mixed with a catalyst and an initiator. In comparison with thermoplastic resins they form three-dimensional polymer networks. The correctly hardened thermosetting plastic resists higher temperatures (up to about 110 o C), it doesn t go soft, resists creeping and has many other good properties. In comparison with thermoplastic materials it is more fragile and it can be not recycled in an easy way. The mostly spread for the manufacture of extruded building components are the polyester resins. 1.2.Reinforcement For the reinforcing polymer-composite materials mostly the following reinforcement types are used: a) Glass fibres, b) Carbon fibres c) Aramide fibres (trade name Kevlar) d) Basalt fibres.

2 384 2nd RILEM Workshop, Paris, 2003 In tested composite materials glass fibres were used as reinforcement. These fibres with the diameter of 4 till 20 m were fitted with a lubricating and finishing layer. The fibres were delivered in strands. The lubrication improves the handling with fibres, the finish the adhesion to the binder. glass fibres composite profile wimple glassfibre mat Figure 1 Composite profile PREFEN [ 2. Properties of composite profiles The tested composite profiles are formed by two main components - the matrix (polyester binder) and glass reinforcement. The resin has low specific density ( = kg.m -3 ), it has a relatively good resistance against chemical substances and aggressive medium. A disadvantage is a low elasticity modulus (E = 6 GPa), strength only up to 100 MPa and a small creep resistance. In comparison glass fibres, which are delivered as roving and as mats have high strength values, but they are fragile, susceptible to mechanical damage during handling and they have a smaller resistance to the effect of some chemical substances. By suitable composition and connection of fibres with the matrix to form the composite a material with very interesting properties is formed. The well hardened composite profile is lightweight ( = kg.m -3 ), firm ( t = 240 till 700 MPa), tough, creep resistant, resistant to chemical agents, ultra-violet radiation and atmospheric conditions, non-combustible (class C, B, A). From the utilization point of view very interesting is the possibility of final application of composite elements to the manufacture of quite complicated profiles, the possibility to control the composite properties by addition of different additives (It is possible to increase the resistance to UV-radiation, to combustion, to static electricity etc). 3. The field of realized tests The field of composite materials production undergoes in the Czech Republic a dynamic development. The manufacturers react to the offer of new admixtures, inhibitors and retardants. New possibilities provide even functional surfaces of hardening moulds. For this reason it is

3 Life Prediction and Aging Management of Concrete Structures 385 necessary to analyse in detail the properties of the resulting product. One, not quite clear problem is the question concerning the behaviour of this material in the medium of permanently higher temperature. The manufacturer very often is encountered with this question and he cannot give a sufficiently convincing answer. They is precisely known information concerning the degradation of applied actual resins, but it is necessary to consider the composite profile as a whole, which is formed by more factors (resin matrix, glass reinforcement, additives, process of production). For this reason a cooperation of the manufacturer with the Brno University of Technology, Faculty of Civil Engineering, Institute of Technology of Building Materials and Components, Czech Republic was established. The research works concerned had in view to keep an eye on physicalmechanical properties of glass-fibre composites PREFEN, under normal temperatures and even under thermal load (negative temperature and higher temperature). The composites were tested with different fillers: kaolin, talc, apyral (aluminium hydroxide as flame retardant filler), combustion retardant. 4. Sample preparation The samples were prepared by the pulltruding method with the hardening temperature of 160 o C. The matrix material was polyester resin, the reinforcement was glass fibres and as filler kaolin, talc, apyral and combustion retardant was used. The samples were placed in a medium with elevated temperature and after the defined time period the deflections with different loads were measured. 5. Test results 5.1. Effect of higher temperatures Samples with different fillers hardened at the temperature of 160 o C were placed into test boxes with conditioned medium and they were thermally loaded as follows: 20 o C 60 o C for the period of 50 hours 60 o C / 100 hours 100 o C / 50 hours 100 o C / 100 hours 110 o C / 336 hours. Surprising was the discovery, that in the case of some samples the value of limiting bending stress dropped, but small and in the case of highest temperature 110 o C for 336 hours it the stress even slightly increased Filler influence We can state that at the temperature of 20 o C, the type of common filler has no significant influence to the limiting strength of samples. Similarly at higher temperatures after a longtime thermal load for the period of 336 hours the composites with common fillers didn t show a significant material degradation. In the case of samples, where the function of filler is substituted by a retardant the results are diametrically different. In this case a significant decrease of strength values took place in the extent up to 99% at the temperature of 250 o C after 0,5 hour. This information is very important, because it proves the suitability of retarded profiles rather in applications, where the permanent temperature is not higher than 100 o C, but where exists fire hazard. The behaviour of the used combustion retardant is different from other fillers. This kind of retardant in direct contact with flame on the surface

4 386 2nd RILEM Workshop, Paris, 2003 creates foam (bubbles) and prevents the penetration of high temperature into the material. As the test results showed, the composite profile with the retardant behaves badly in a medium, where the material is for a longer time period influenced by heat flow and its positive effect manifests itself positively only under effect of high temperatures - fire. 600 Tensile bending strenght MPa /0 60/50 60/ /50 100/ /336 Thermal load o C/ time - hour apyral kaolin talc Figure 2 Effect of thermal load on composite samples with apyral, kaolin and talc 700 Tensile bending strenght MPa combustion retardant 20/0 110/5 250/0,5 Thermal load 0 C/ time - hour Figure 3 Effect of thermal load on composite samples with combustion retardant

5 Life Prediction and Aging Management of Concrete Structures Determination of frost resistance The composite samples were placed for 150 freeze/thaw cycles in the chamber for the period of 4 hours at the temperature of -18 o C and in a water bath with the temperature 18 o C for the period of 2 hours. In the Czech Republic there is no standard for the resistance of composite materials at low temperatures and therefore we have applied a method following the Czech Standard CSN for the frost resistance determination of concrete. 600 Tensile bending strenght MPa apyral kaolin talc Non Frozen Frozen cycles Figure 4 Tensile bending strength after 150 freeze/thaw cycles The results of bending strength tests you will find in the graph. In the case of all samples a slight decrease of strength values took place, the greatest drop had the material with apyral, where the resulting value was by 13 % lower. 6. Evaluation The subject of the paper is very stimulating for all manufacturers of composite materials and it is in a way unique. The present received results are inspiring for the next way of work. In the framework of further planed work and proposed researched projects, series of interconnected tests are intended with following recommendation: In the next phase it is not necessary to test the effect of different common fillers. However it is necessary to elongate the period of thermal load up to hours at temperatures between 80 o C till 150 o C. In the case of profiles retarded by a combustion retardant it will have a more practical importance to apply direct flame to the surface for different time periods and then investigate the mechanical properties (limit stress, E-modulus incl. Barcols surface hardness). All tests could obtain another dimension by using PES-resin, with guaranteed resistance against higher permanent temperature by the manufacturer (up to 160 o C ).

6 388 2nd RILEM Workshop, Paris, Acknowledgements This work was published with backing of GACR, within the research project No. 103/01/0814 Microstructural features and related properties of cement based highly liquefied composites and the GACR research project No. 103/01/1144 and research project CEZ - MSM , name of the project is: Research and Development of New Materials and Securing their Higher Durability in Building Structures. 8. References 1. Bodnarova, L. and Filip, M. Properties of fiber glass reinforced composites with polymer matrix, In The Concrete Days, Proceedings of an International conference, Pardubice, Czech Republic, November, 2002 (CBZ, Pardubice, 2002)