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Journal of Ceramic Science and Technology 3/2017
Vol. 8, No. 3 · September 2017
A Review of Particle- and Fiber-Reinforced Metakaolin-Based Geopolymer Composites
R.A. Sá Ribeiro, R.A. Sá Ribeiro, M.G. Sá Ribeiro, W.M. Kriven
Pages 307-322 · DOI: 10.4416/JCST2017-00048
Research on reinforced metakaolin-based geopolymers for structural applications is reviewed. Geopolymers have been synthesized using metakaolin produced from kaolinite extracted from several regional soils. Kaolin is converted into metakaolin by calcination from 650 °C up to 800 °C. To obtain higher strength and stiffness, the geopolymer matrix is reinforced with particles and fibers. In addition, synthetic and natural particles and fibers have been used to enhance durability, thermal properties and shrinkage ratio of lighter geopolymer composites. Owing to the unavailability of a standard for …
Why Alkaline Activation – 60 Years of the Theory and Practice of Alkali-Activated Materials
P. Krivenko
Pages 323-334 · DOI: 10.4416/JCST2017-00042
Sixty years ago, just the idea of the presence of free alkalis in a cement matrix was considered by ordinary Portland cement people to be absurd, and this was a basic postulate accepted in cement chemistry. In 1957, a scientist from Kyiv, Ukraine (then, USSR), Victor Glukhovsky, put forward an assumption that was taken as a basis for development and realization of a principally new class of cementitious materials, which first appeared under the name of \"alkaline cements\" (nowadays also known under the general name of \"alkali-activated cements\"). The validity of these ideas is confirmed by …
Geopolymers are ceramic-like inorganic polymers produced at low temperature, generally below 100 °C. They consist of chains or networks of mineral molecules linked with covalent bonds. The raw materials are mainly minerals of geological origin, hence the name \"geopolymer\". They comprise several molecular units for example: silico-oxide (Na,K)-(-Si-O-Si-O-) for (Na,K)-poly(silicate) or (Na,K)-poly(siloxonate), silico-aluminate (Na,K)-(-Si-O-Al-O) for (Na,K)-poly(sialate), ferro-silico-aluminate (Na,K)- (-Fe-O-Si-O-Al-O-) or (Na,K)-poly(ferro-sialate), alumino-phosphate (-Al-O-P-O-) for poly(a …
Intumescent Geopolymer-Bound Coatings for Fire Protection of Steel
M.-B. Watolla, G.J.G. Gluth, P. Sturm, W.D.A. Rickard, S. Krüger, B. Schartel
Pages 351-364 · DOI: 10.4416/JCST2017-00035
The passive fire protection of steel structures and other load-bearing components will continue to gain importance in future years. In the present contribution, novel intumescent aluminosilicate (geopolymer-bound) composites are proposed as fire-protective coatings on steel. Steel plates coated with these materials were exposed to the standard temperature-time curve as defined in ISO 834 – 1:1999. The coatings partially foamed during curing and expanded further during thermal exposure, demonstrating their intumescent characteristic. Thermogravimetry and oscillatory rheometry determined that th …
Control of Polycondensation Reaction Generated from Different Metakaolins and Alkaline Solutions
A. Gharzouni, A. Gharzouni, I. Sobrados, E. Joussein, S. Baklouti, S. Rossignol
Pages 365-376 · DOI: 10.4416/JCST2017-00040
The purpose of the present study is to control the polycondensation reaction of various geopolymer samples based on six metakaolins and two potassium alkaline solutions with different reactivities. First, metakaolin characterization revealed three levels of reactivity, which increase essentially with the increase in the degree of purity, amorphous phase and water demand value. The formation of geopolymer samples was then investigated. In situ thermal analysis showed that depending on the metakaolin surface reactivity, the availability of dissolved species decreases the energy required for olig …
High-Temperature Behaviour of Alkali-Activated Composites based on Fly Ash and Recycled Refractory Particles
L. Carabba, S. Manzi, E. Rambaldi, G. Ridolfi, M.C. Bignozzi, M.C. Bignozzi
Pages 377-388 · DOI: 10.4416/JCST2017-00047
This study aims to develop innovative and sustainable alkali-activated composites with enhanced performance at high temperatures. To reduce production costs and promote a circular economy model, coal fly ashes are selected as a precursor for the alkali activation and recycled refractory particles are used to develop products with high thermal dimensional stability. Matrices and composites are investigated as a function of two curing conditions (heat curing vs room temperature curing) and amounts of dispersed phase (recycled refractory particles) added to the matrix. Thermal stability is assess …
Influence of Elevated Temperatures on the Mechanical Behavior of Jute-Textile-Reinforced Geopolymers
A.C. Constâncio Trindade, H.A. Alcamand, P.H. Ribeiro Borges, F. de Andrade Silva
Pages 389-398 · DOI: 10.4416/JCST2017-00045
Geopolymers may present important structural and environmental advantages compared to Portland-cement-based materials. They can achieve high mechanical strength at early ages and exhibit much better thermal durability than Portland-cement-based materials. Geopolymers are brittle materials and an increasing number of studies have been conducted on the incorporation of fibrous reinforcement into these matrices in recent years. Natural fibers appear as a reinforcing group that imply environmental superiority, resulting in improved mechanical behavior. This study evaluates the mechanical behavior …
Sodium tetrahydroborate (NaBH4 = SB) and ammonia-borane (NH3BH3 = AB) were dissolved in sodium aluminate and silicate solutions. Bringing them together caused immediate gel formation and recrystallization of SB and AB during drying. The gel forms geopolymer (G) type units, which enclose and protect the SB and AB crystals inside. SB-G composites are stable over a long time without any loss in SB. An optimized SB-G releases about 1820 L hydrogen per kg, i.e. containing an equivalent of about 80 % of pure SB (2270 L/kg) obtained by means of acidic titration. SB and SB-G remain stable up to 400 °C …
Fly-Ash-Based Geopolymers: How the Addition of Recycled Glass or Red Mud Waste Influences the Structural and Mechanical Properties
N. Toniolo, G. Taveri, K. Hurle, J.A. Roether, P. Ercole, I. Dlouhý, A.R. Boccaccini
Pages 411-420 · DOI: 10.4416/JCST2017-00053
One of the main advantages of geopolymer technology is its capability to accommodate several types of waste that would otherwise be disposed of in landfills in the production of geopolymer materials. This study investigates the possibility of substituting proportions of fly ash, normally used for the synthesis of geopolymers, with recycled glass and red mud waste. Compressive and flexural strength testing, fracture toughness determination, SEM and FTIR analyses were performed. The results show that the compressive strength decreases as the amount of glass in the geopolymer increases; on the ot …
Methods for Geopolymer Formulation Development and Microstructural Analysis
A. van Riessen, W.D.A. Rickard, R.P. Williams, G.A. van Riessen
Pages 421-432 · DOI: 10.4416/JCST2017-00065
Alkali-activated materials (AAMs) and geopolymers have been extensively studied, although widespread commercialisation has been hampered, in part, by the use of precursors that are rarely homogeneous and are generally poorly characterised. Even when precursors are well characterised, their extent of reaction during geopolymer synthesis is not well known, leading to a disparity between targeted and actual compositional ratios. Small variations in compositional ratios, particularly Si:Al, can lead to dramatic changes in physical properties. A process for characterising precursors, focussing on t …
