Effect of fire-retardant ceram powder on the properties of phenolic-based GFRP composites
Introduction
Composite sandwich panels have been the subject of active research in replacing conventional materials (such as concrete, aluminium and steel) for prefabricated building façades due to their high strength-to-weight ratio, excellent durability, corrosion free properties, good insulation, strong bonding and rapid offsite construction facilities [[1], [2], [3], [4], [5], [6]]. The sandwich systems are fabricated by attaching two thin laminated composite skins to a thick lightweight core that recently attracted attention in civil construction [7,8]. When applied as a building façade, the skins are exposed to the environment including fire and elevated temperature, which limit the use of organic materials in construction [9]. Recent incidents and consequences of fire in London Grenfell Tower, Dubai Torch Tower, Lacrosse Building at Melbourne and others are becoming a matter of great concern for design engineers. A report has been published that linked the rapid spread of fire to combustible construction materials [10]. Traditional fibre reinforced polymer (FRP) composites have relatively poor fire performance [11]. Therefore, the composite skins need to be modified to meet the fire requirements of building codes before their widespread application in modular construction.
One approach in improving fire performance of polymer composites is by incorporating fire retardant filler as a constituent to the matrix [12,13]. Several fire-retardant fillers are available in the market and the most common types are Alumina Trihydrate (Al(OH)3), also known as ATH, and Magnesium Hydroxide (Mg(OH)2), known as MDH [[13], [14], [15], [16]]. Instead of traditional fire retardant fillers, this study used Ceram Polymerik powder because of its greater design flexibility, lower smoke development, higher resistance against moisture, better thermal and electrical stabilities and cost effectiveness compared to existing systems [17,18]. Phenolic resin [19] was also chosen due to its superior flame resistance and low cost [9] over traditional resin systems such as polyesters [20], vinyl ester [21] and epoxy [22]. Recent studies by Manalo et al. [23] suggested that sandwich beams with glass FRP (GFRP) skins and phenolic core can retain more than 80% of their mechanical properties at 80 °C. While some studies showed that the mechanical properties of composites may degrade, the addition of fire retardant filler can greatly improve their fire resistance [12,24]. For example, the bending strength of an epoxy-based polymer matrix was reduced with the addition of ATH fillers but increased its glass transition temperature by 5 °C [25]. For composite laminates, the mechanical properties cannot be sacrificed significantly for meeting fire requirements. Therefore, the present study focused on investigating the properties of phenolic-based laminated GFRP composites with the addition of ceram powder and determining the optimal volume of ceram powder to achieve a balance in mechanical properties.
Different percentages of ceram powder were added to the matrix of the laminated composites during the fabrication. The mechanical properties of these composites were then evaluated including tensile, interlaminar shear, bond and bending properties. The effect of ceram powder on the glass transition temperature of laminates was also investigated. Finally, the optimal volume of ceram was determined using a structured technique based on the experimental results. The outcome of this study will contribute scientific knowledge for designing laminated composites for with optimal mechanical and fire resistance performance.
Section snippets
Materials
The materials employed in this investigation were fabrics, resin and filler.
Density and void content
The bulk density and void content of the laminated composites containing ceram powder was measured prior as they can have influence on the performance of composites. Fig. 2(a) shows the theoretical and measured density with the percentage of voids. The bulk density was measured by the weight per unit volume and calculated theoretically using Eq. (1). The volume of void content is measured by Eq. (2).
In Eq. (1) and Eq. (2): and are the
Design of optimal ceram volume
An optimal volume of ceram is the amount added to the matrix which produces composite laminates with physical and mechanical properties that can satisfy the performance requirements for a particular application. The results of the experimental investigations revealed that the addition of ceram powder from 30% to 50% can satisfy the minimum performance requirements of building façades of at least 100 MPa tensile strength (obtained 225–247 MPa), 10 GPa bending modulus (obtained 21.9–25.5 GPa),
Conclusions
This paper investigated the behaviour of GFRP laminated composites with a fire retardant ceram powder employed as a filler in the polymer matrix. The effect of ceram powder on the density, void content, tensile strength, interlaminar shear strength, bond strength, bending modulus and glass transition temperature were examined. A strategic decision-making method is applied to determine the optimal volume of ceram in the polymer matrix. The nature of the failure, load carrying capacity and
Acknowledgements
This project was funded through the ARC Training Centre for Advanced Manufacturing of Prefabricated Housing (ARC-CAMP.H) at the University of Melbourne. The technical assistance from Ms Jinghan Lu during specimen testing is highly acknowledged.
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