Properties of epoxy polymer concrete matrix: Effect of resin-to-filler ratio and determination of optimal mix for composite railway sleepers
Introduction
The weakness of an Ordinary Portland Cement (OPC) mortar in terms of its tensile strength, modulus and strain, rapid strength development, drying shrinkage and resistance to chemical attacks has led to the utilisation of polymer matrices for bridge decks, concrete crack repairs, the coating and binding of composite panels, pavement overlays, hazardous waste containers, waste-water pipes, decorative construction panels and other structures in aggressive environmental conditions [1], [2], [3], [4]. Unlike an OPC mortar, a polymer matrix consists of a thermoset resin with filler materials. The chemistry behind the development of polymer matrix is governed by the chemical reaction between resin and hardener. Generally, this reaction is exothermic (i.e., generated heat) and forms long polymer chains during the curing process which create the matrix’s flexibility and strength. The properties of a polymer matrix depends largely on the type and amount of resin, type of filler and curing conditions used [5], [6].
Different types of thermoset resins are available in the market. The choice of a particular one depends mainly on its tensile and compressive properties, glass transition temperature, durability, material availability, ease of processing, cost and specific user demand. In the past, researchers have investigated different resin systems in polymer concrete with the most commonly used resins epoxy [7], polyester [8] and vinyl-ester [2]. Despite the cost benefits of vinyl-ester and polyester compared with epoxy, they are not suitable if excellent mechanical and thermal properties, superior resistance to humidity, low shrinkage and high elongation are required in order to produce a durable and flexible polymer matrix [9]. Moreover, epoxy can provide a unique balance of chemical and mechanical properties combined with extreme processing versatility. Because of its superior mechanical, durability and thermal properties compared with those of other types of resins, this study examined whether epoxy is a suitable material in a polymer matrix for a coating of civil infrastructure. However, its high cost is identified as the primary obstacle.
To minimise the cost of an epoxy polymer matrix, light weight filler materials can be added to the resin. Research on the effects of different filler materials such as fly ash [6], [10], [11] and silica fume [6], on the polymer concrete have been investigated by several researchers, with the use of the former shown to improve the mechanical, chemical and durability properties of polymer concrete [11]. A comparative study of the performances of fly ash and silica fume with epoxy resin reported that a combination of fly ash and epoxy can provide higher mechanical strength than one of epoxy and silica fume [6]. The addition of a filler can also improve a matrix’s compressive and tensile properties although its flexural strength may decrease [6]. However, Lokuge and Aravinthan [2] found that the addition of fly ash showed trends of increasing compressive strength but decreasing tensile and flexural strengths. In contrast to the traditional concept of using fly ash as a filler, this study incorporated two other filler materials, a fire retardant filler and hollow microsphere to improve fire and shrinkage performances respectively which are two important properties required for coating materials.
The fibre composites are the load carrying components of the existing and emerging composite sleeper technologies. Research and development projects on composite railway sleepers are now looking for an effective coating material to protect the load-carrying components of a sleeper against unfavourable weather conditions, particularly from ultraviolet (UV) radiation. The outdoor application of railway sleepers are routinely exposed to the UV radiation that can degrade the performance and needs a suitable coating to protect the fibre reinforcement [12]. Although the superior properties of an epoxy polymer matrix support its use as a coating material, a procedure for its mix design is not well established. In a previous study, the mix proportions of polymer concrete were arbitrarily selected and significant research carried out to investigate their behaviours [2]. For an economical design of a polymer concrete matrix, it has been recommended that minimum amount of resin is used to minimise the cost [2], and therefore, it is important to optimise the mix proportions. However, the effect on the properties of a polymer matrix due to an introduction of filler is still unknown. This study investigated the effects of different resin-to-filler ratios on the thermal, physical, mechanical and durability properties of a polymer matrix and determined an optimal one for coating of composite railway sleepers.
Section snippets
Materials
The materials employed in this investigation were an epoxy resin and light-weight filler.
Heat generation
The temperature generated while mixing together the epoxy resin (Part-A) and hardener (Part-B) was measured by a temperature gun at 10-min intervals. The maximum temperature recorded was 75 °C for the mix containing 100% resin, that is, 0% filler (F0). However, the peak temperature decreased in succeeding mixes with gradual increases in the amount of filler up to 60%, as shown in Fig. 3.
Fig. 3(a) demonstrates that, for the mix with 0% filler, the peak temperature was obtained at 150 min after
Evaluation of polymer mix for railway sleepers
Research and development of fibre composite railway sleepers are now looking for a suitable coating material to protect their load carrying components against adverse environments [12], [27]. The superior mechanical, thermal and durability properties of a polymer matrix composed of epoxy resin and light-weight filler materials demonstrated a suitable and effective coating material. The main focus of this part of the study is to evaluate a suitable polymer matrix for the coating of composite
Determination of optimal mix for railway sleepers
An optimal mix is one which can satisfy the requirements of a particular application in the best possible way. The Analytic Hierarchy Process (AHP) is a multi-criteria decision-making method that derives ratio scales from paired comparisons based on mathematics and psychology. The relative importance of each attribute can be expressed by the fundamental scale of AHP proposed by Saaty and Vargas [37]. The main advantage of this method is its capability to check and reduce inconsistencies in
Conclusion
This study experimentally investigated the thermal, physical, mechanical and durability properties of epoxy-based polymer matrices containing different resin-to-filler ratios from which the optimal mix was selected and the following conclusions drawn.
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The exothermic reaction between the resin (Part-A) and hardener (Part-B) could generate temperatures up to 75 °C which were uncomfortable to handle and difficult to work with. The addition of a filler to the resin resulted in a temperature within a
Acknowledgement
The first author gratefully acknowledged the financial support by Australian Postgraduate Award (APA) scholarship from the University of Southern Queensland, and authors are also acknowledged the materials support by the Department of Industry Innovation, Science, Research and Tertiary Teaching Enterprise Connect Researcher-In-Business Funded by the Australian Government.
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