- Original article
- Open Access
Behaviour of Carbon and Basalt Fibres Reinforced Fly Ash Geopolymer at Elevated Temperatures
© The Author(s) 2018
- Received: 28 July 2017
- Accepted: 15 March 2018
- Published: 25 May 2018
This paper presents the behaviour of potassium activators synthesized fly ash geopolymer containing carbon and basalt fibre at ambient and elevated temperature. Six series of fly ash based geopolymer were cast where carbon and basalt fibre were added as 0.5, 1 and 1.5% by weight of fly ash. One extra control series without any fibre was also cast. Each series of samples were tested at ambient temperature and also heated at 200, 400, 600 and 800 °C and thus a total of 35 series of samples were tested in this study. The result shows that the geopolymer containing 1 wt% basalt and 1 wt% carbon fibre exhibited better compressive strength, lower volumetric shrinkage and mass loss than other fibre contents. Among two fibres composites, the carbon fibre geopolymer exhibited better performance than its basalt fibre counterpart regardless of temperature. The microstructure of carbon fibre reinforced geopolymer composite is more compact containing fewer pores/voids than its basalt based counterpart at elevated temperatures. The results also support the fact that carbon fibre is better than basalt fibre at elevated temperature and showed better bonding with geopolymer at elevated temperature.
- fly ash
- basalt fibre
- carbon fibre
- potassium hydroxide
- potassium silicate
Geopolymer is an environmentally friendly inorganic—amorphous binder which exhibit ceramic like property in fire or at elevated temperatures. At ambient temperature geopolymers are amorphous and transform to crystalline above 500 °C (Zoulgami et al. 2002). Extensive researches have been conducted to study various mechanical and durability properties of geopolymer (Davidovits 1991; Duxson et al. 2007; Rangan 2008; Duan et al. 2016). Significant efforts have also been made by many researchers to study the effect of elevated temperatures on mechanical properties of geopolymer. However, most of the studies were on different geopolymers which consisted of various types of source materials and alkali activators, e.g., fly ash activated by sodium based alkali activators, fly ash activated by combined sodium and potassium based activators, combined fly ash and slag activated by sodium based activator, metakaolin activated by combined sodium and potassium based activators, etc. (Bakharev 2006; Kong et al. 2007; Kong and Sanjayan 2008, 2010; Guerrieri and Sanjayan 2010; Rickard et al. 2012; Abdulkareem et al. 2014; Ranjbar et al. 2014; Shaikh and Vimonsatit 2015).
Fillers and aggregates can be added to geopolymers to reduce the thermal expansion/shrinkage of the composite and extend the usable temperature range. Various additives are used in geopolymer matrix to improve its fire resistance e.g., α-quartz and granite aggregates (van Riessen 2007; Kamseu et al. 2010), α-alumina particles (Bell et al. 2005; Lin et al. 2009), wollastonite (Silva et al. 1999), etc. Various organic and inorganic fibres are also added to reinforce geopolymers to improve its fire resistance. Masi et al. (2015) reported a study where poly vinyl alcohol (PVA) and basalt short fibres are added to fly ash based geopolymer activated by sodium hydroxide and sodium aluminate solutions. Results show better mechanical properties of basalt fibre reinforced geopolymer at elevated temperatures than its PVA fibre reinforced counterpart. In another study the effect of elevated temperatures on fibre-matrix interaction of continuous basalt fibre reinforced dehydroxylated halloysite geopolymer is evaluated (Welter et al. 2015). Zhang et al. (2014) reported effects of various short carbon fibre contents on the compressive and bending strength of metakaolin-fly ash geopolymers at evaluated temperatures. Results show that 2% carbon fibre reinforced geopolymer containing 50% fly ash and 50% metakaolin exhibited excellent behaviour at 500 °C. In a comprehensive review of properties of basalt fibre composites in Fiore et al. (2015) it is shown that basalt fibre can be a sustainable alterative to steel and other fibres due to their environmental friendliness and suitability with various matrix. Although both basalt and carbon fibres show excellent thermal stability at elevated temperatures and class F fly ash is commonly used as source material for geopolymer not enough research studied the behaviour of carbon and basalt fibre reinforced fly ash based geopolymer at elevated temperatures. In a recent study the authors (Hosan et al. 2016) show better fire resistance of class F fly ash geopolymer synthetized by potassium based alkali activators than that of sodium based activators. In this paper the above potassium hydroxide and potassium silicate synthesized class F fly ash geopolymer is reinforced with various wt % of carbon and basalt fibres to study their compressive and physical behaviour as well as the microstructures of the geopolymer composites at various elevated temperatures of 200, 400, 600 and 800 °C.
The class F fly ash geopolymer is synthesized using potassium silicate and potassium hydroxide and the resulting matrix is reinforced with different wt% of basalt and carbon fibres at 0.5, 1 and 1.5%. Potassium silicate to potassium hydroxide ratios of 3 was selected in this study as this ratio was found as the optimum content for fire resistant based on authors previous research (Hosan et al. 2016). Control geopolymer paste synthesized by sodium and potassium based activators without any fibers was also cast as control. A constant activator/fly ash ratio of 0.35 was considered in all the series in both parts. For each series fibre reinforced geopolymers, six 50 mm cube specimens were casted and heated at 200, 400, 600 and 800 °C temperatures.
Chemical composition of fly ash (mass%).
All the samples were prepared in a Hobart mixer. The ingredients were mixed for about 4 min. The fresh geopolymer pastes were cast into standard 50 mm plastic cube moulds and compacted using a vibrating table. The specimens were subjected to heat curing. In this regard, all moulds were sealed to minimize moisture loss and placed in an oven at 70 °C for 24 h. At the end of heat curing period, the specimens were removed from the oven and kept undisturbed until being cool and then removed from the moulds and left in the laboratory at ambient temperature until the day of testing. Compressive strength of all specimens was measured according to AS 1012.9 (2014) using a loading rate of 0.33 MPa/s. For each mix, at least three specimens were tested in order to check the variability of performance under compression. The volumetric shrinkage of pastes was determined by measuring the length of three sides of the cubes before and after heating at respective elevated temperatures. The difference in volume changes indicates the volumetric shrinkage and six specimens were used to measure the volumetric shrinkage for each series. Similar method was also used to determine the mass loss of geopolymer pastes after exposed to respective elevated temperatures.
This measurement was performed with a PoreMaster series—Quantachrome instruments, with a pressure ranged between 0.0083 and 207 MPa, and the pore diameter and intrusion mercury volume were recorded at each pressure point. Small broken pieces of approximately 10 mm in sides are collected from the crushed geopolymer cubes containing 1 wt% carbon and basalt fibres at ambient, 400 and 800 °C temperatures. The pressures were converted to equivalent pore diameter using the Washburn equation (Washburn 1921), as expressed in Eq. (1):
5.1 Physical Behaviour
5.2 Compressive Strength
It can be seen in both cases the 1.5% shows very similar volumetric shrinkage to the pure geopolymer. Whereas the other contents shows slight deviation at 400 and 600 °C, however they show slightly lower volumetric shrinkage at 800 °C. If we compare these phenomenon with measured residual compressive strength in Fig. 6 we can also see that in carbon fibre geopolymer the 0.5 and 1.0% show slightly higher compressive strength at all temperatures. And in the case of basalt fibre geopolymer it was 1.0%. It seems to the authors that at lower fibre content e.g., at 0.5 and 1.0% both fibres might have dispersed more uniformly in the geopolymer than at higher fibre content. These well dispersed fibres at lower fibre content might have bridged the micro cracks more effectively which prevented the further propagation and/or formation of cracks, as a result higher residual compressive strength and lower volumetric shrinkage in geopolymer containing those lower fibre contents are observed.
5.3 Porosity and Microstructure of Geopolymer with Fibre
It can be seen in the experiment that the measured compressive strength of basalt fibre composite at ambient temperature is lower than its carbon fibre counterpart. There is also established correlation between reduction in compressive strength and presence of higher air voids in cementitious composites (Lian et al. 2011; Santos et al. 2017). Therefore, the lower ambient temperature compressive strength of basalt fibre geopolymer composite than carbon fibre geopolymer composite indicate higher amount of pores/voids in the former than the latter and upon heating at various elevated temperatures the moisture evaporated from these pores increased the porosity. This has also been observed in the MIP and SEM tests. It is also found that the fibre content of 1 wt% in both basalt and carbon geopolymer composites exhibited higher ambient as well as elevated temperatures compressive strengths, lower mass loss and lower volumetric shrinkage than other fibre contents e.g., 0.5 and 1.5% in this study. Based on above discussion it is clear that the likelihood of higher pores/voids in geopolymer composites containing 1.5 wt% carbon and basalt fibres is higher than that containing 1 wt% of carbon and basalt fibres, which caused lower compressive strength at ambient as well as at elevated temperatures. Similar results are also observed in the case of mass loss. However, the composites containing 1.5 wt% carbon and basalt fibres shrinks slightly more than other fibre contents which is not clear and deserve more research in future.
Geopolymer containing 1 wt% basalt and 1 wt% carbon fibre exhibited better compressive strength, lower volumetric shrinkage and mass loss than other fibre contents at all elevated temperatures. Among two fibres composites, the carbon fibre geopolymer exhibited better performance than its basalt fibre counterpart at all elevated temperatures and ambient temperature. 1 wt% of carbon and basalt fibres are the optimum fibre content in fly ash geopolymer at elevated temperatures. 1 wt% carbon fibre reinforced geopolymer exhibited negligible cracking than its basalt fibre counterpart and pure geopolymer up to 600 °C. At 800 °C the cracking in 1 wt% carbon fibre reinforced geopolymer is less than its basalt fibre counterpart and pure geopolymer.
The microstructure of carbon fibre reinforced geopolymer composite is also better in terms of lower pores/voids and more compact microstructure than its basalt based counterpart at elevated temperatures. Pore volume of larger diameter pores is increased at elevated temperatures in basalt fibre geopolymer than that of carbon fibre geopolymer. The maximum concentration of pores of basalt fibre composites are shifted towards medium to large capillary pores after exposure to elevated temperatures.
No significant damage and change in diameter of both fibres at elevated temperatures are observed in SEM analysis. The results also support the fact that carbon fibre is better than basalt fibre at elevated temperature and showed better bonding with geopolymer at elevated temperature, which is indicated by more compact microstructure of carbon fibre geopolymer.
The higher compressive strength and lower mass loss and volumetric shrinkage of carbon fibre reinforced fly ash geopolymer at various elevated temperatures up to 800 °C indicate its superior role as filler in geopolymer at fire than that of basalt fibre.
Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.
- Abdulkareem, O. A., Al-bakri, A. M. M., Kamarudin, H., Nizar, I. K., & Saif, A. A. (2014). Effects of elevated temperatures on the thermal behaviour and mechanical performance of fly ash geopolymer paste, mortar and light weight concrete. Construction and Building Materials, 50, 337–387.View ArticleGoogle Scholar
- Ali, M. A., Majumdar, A. J., & Singh, B. (1975). Properties of glass fibre cement—the effect of fibre length and content. Journal of Materials Science, 10, 1732–1740.View ArticleGoogle Scholar
- AS 1012.9. (2014). Methods of testing concrete—Compressive strength tests—Concrete, mortar and grout specimens. Syndey: Standards Australia.Google Scholar
- Bakharev, T. (2006). Thermal behaviour of geopolymers prepared using class F fly ash and elevated temperatures curing. Cement and Concrete Research, 36, 1134–1147.View ArticleGoogle Scholar
- Bell, J., Gordon, M., Kriven, W. M., Comrie, D. (2005). Graphite fiber reinforced geopolymer molds for near net shape casting of molten diferrous silicide, conference paper. In Workshop on Geopolymers and Geopolymer Concrete (p. 12). Perth, WA.Google Scholar
- Chen, X., Wu, S., & Zhou, J. (2013). Influence of porosity on compressive strength and tensile strength of cement mortar. Construction and Building Materials, 40, 869–874.View ArticleGoogle Scholar
- Davidovits, J. (1991). Geopolymers-inorganic polymeric new materials. Journal of Thermal Analysis, 37(8), 1633–1656.View ArticleGoogle Scholar
- Duan, P., Yan, C. J., Luo, W. J., & Zhou, W. (2016). A novel surface waterproof geopolymer derived from metakaolin by hydrophobic modification. Materials Letters, 164, 172–175.View ArticleGoogle Scholar
- Duxson, P., Fernández-Jiménez, A., Provis, J. L., Lukey, G. C., Palomo, A., & van Deventer, J. S. (2007). Geopolymer technology: the current state of the art. Journal of Materials Science, 42(9), 2917–2933.View ArticleGoogle Scholar
- Fiore, V., Scalici, T., Bella, G. D., & Valenza, A. (2015). A review on basalt fibre and its composites. Composites B, 74, 47–94.View ArticleGoogle Scholar
- Guerrieri, M., & Sanjayan, J. G. (2010). Behaviour of combined fly ash/slag based geopolymers when exposed to high temperatures. Fire and Materials, 34, 163–175.Google Scholar
- Hosan, A., Haque, S., & Shaikh, F. U. A. (2016). Compressive behaviour of sodium and potassium activators synthetised fly ash geopolymer at elevated temperatures: A comparative study. Journal of Building Engineering., 8, 123–130.View ArticleGoogle Scholar
- Kamseu, E., Rizzuti, A., Leonelli, C., & Perera, D. (2010). Enhanced thermal stability in K2O metakaolin-based geopolymer concretes by Al2O3 and SiO2 fillers addition. Journal of Materials Science, 45, 1715–1724.View ArticleGoogle Scholar
- Kong, D. L. Y., & Sanjayan, J. G. (2008). Damage behaviour of geopolymer composites exposed to elevated temperatures. Cement & Concrete Composites, 30, 986–991.View ArticleGoogle Scholar
- Kong, D. L. Y., & Sanjayan, J. G. (2010). Effect of elevated temperatures on geopolymer paste, mortar and concrete. Cement and Concrete Research, 40, 334–339.View ArticleGoogle Scholar
- Kong, D. L. Y., Sanjayan, J. G., & Sagoe-Crentsile, K. (2007). Comparative performance of geopolymers made with metakaolin and fly ash after exposure to elevated temperatures. Cement and Concrete Research, 37, 1583–1589.View ArticleGoogle Scholar
- Lian, C., Zhuge, Y., & Beecham, S. (2011). The relationship between strength and porosity of porous concrete. Construction and Building Materials, 25, 4294–4298.View ArticleGoogle Scholar
- Lin, T. S., Jia, D. C., He, P. G., & Wang, M. R. (2009). Thermomechanical and microstructural characterisation of geopolymers with alpha alumina particulate filler. International Journal of Thermophysics, 30, 1568–1577.View ArticleGoogle Scholar
- Masi, G., Rickard, W. D. A., Bignozzi, M. C., & van Riessen, A. (2015). The effect of organic and inorganic fibers on the mechanical and thermal properties of aluminate activated geopolymers. Composites B, 76, 218–228.View ArticleGoogle Scholar
- Rangan, B. V. (2008). Low-calcium fly ash-based geopolymer concrete, chapter 26. In E. G. Nawy (Ed.), Concrete construction engineering handbook (2nd ed.). New York: CRC Press.Google Scholar
- Ranjbar, N., Mehrali, M., Alengaram, U. J., Metselaar, H. S. C., & Jumaat, M. Z. (2014). Compressive strength and microstructural analysis of fly ash/palm oil fuel ash based geopolymer mortar under elevated temperatures. Construction and Building Materials, 65, 114–121.View ArticleGoogle Scholar
- Ribero, D., & Kriven, W. M. (2016). Properties of geopolymer composites reinforced with basalt chopped strand mat or woven fabric. Journal of the American Ceramic Society, 99(4), 1192–1199.View ArticleGoogle Scholar
- Rickard, W. D. A., Temuujin, J., & van Riessen, A. (2012). Thermal analysis of geopolymer pastes synthesized from five fly ashes of variable compositions. Journal of Non-Crystalline Solids, 358, 1830–1839.View ArticleGoogle Scholar
- RILEM TC 129-MHT. (1995). Test methods for mechanical properties of concrete at high temperatures-compressive strength for service and accident conditions. Materials and Structures, 28, 410–414.View ArticleGoogle Scholar
- Santos, F. M. D., Barista, F. B., Panzera, T. H., Christiforo, A. L., & Rubio, J. C. C. (2017). Hybrid composites reinforced with short sistal fibres and micro ceramic particles. Revistamateria, 22(2), e11838.Google Scholar
- Shaikh, F. U. A., & Vimonsatit, V. (2015). Compressive strength of fly ash based geopolymer concrete at elevated temperatures. Fire and Materials, 39, 174–188.View ArticleGoogle Scholar
- Silva, F. J., Mathias, A. F., & Thaumaturgo, C. (1999). Evaluation of the fracture toughness in poly(sialate-siloxo) composite matrix, conference paper. Geopolymer, 99, 97–106.Google Scholar
- van Riessen, A. S. (2007). Thermo-mechanical and microstructural characterisation of sodium-poly(sialate-siloxo) (Na-PSS) geopolymers. Journal of Materials Science, 42, 3117–3123.View ArticleGoogle Scholar
- Washburn, E. W. (1921). Note on a method of determining the distribution of pore sizes in a porous material. Proceedings of the National academy of Sciences of the United States of America, 7(4), 115–116.View ArticleGoogle Scholar
- Welter, M., Schmücker, M., & MacKenzie, K. J. D. (2015). Evolution of the fibre–matrix interactions in basalt-fibre-reinforced geopolymer-matrix composites after heating. Journal of Ceramic Science and Technology, 06(01), 17–24.Google Scholar
- Zhang, M. H., & Islam, J. (2012). Use of nano-silica to reduce setting time and increase early strength of concretes with high volume fly ash or slag. Construction and Building Materials, 29, 573–580.View ArticleGoogle Scholar
- Zhang, H., Kodur, V., Cao, L., & Qi, S. (2014). Fibre reinforced geopolymers for fire resistance applications. Procedia Engineering, 71, 153–158.View ArticleGoogle Scholar
- Zoulgami, M., Lucas-Girot, A., Michaud, V., Briard, P., Gaudé, J., & Oudadesse, H. (2002). Synthesis and physico-chemical characterization of a polysialate-hydroxyapatite composite for potential biomedical application. The European Physical Journal-Applied Physics, 19, 173–179.View ArticleGoogle Scholar