An investigation of the microstructure and durability of a fluidized bed fly ash–metakaolin geopolymer after heat and acid exposure

Duan, Ping; Yan, Chunjie; Zhou, Wei; Luo, Wei; Shen, Chunhua

doi:10.1016/j.matdes.2015.03.009

Cited by 212 publications

(44 citation statements)

References 85 publications

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“…1 to 4). The values of E are 30.3, 34.7 and 29.8 GPa for MuCo (20,25 and 30 wt.% of geopolymer cement respectively) treated at 1250°C; values two times higher with respect to Co series (13.3, 14.2 and 16.4 GPa respectively) as it can be observed in the Figs. 3 and 4.…”

Section: Correlation Of the Sintering Behavior And Phases Evolution Wmentioning

confidence: 51%

“…5 to 8 are contributive for the thermal shock resistance and thermal stability of the geopolymer refractory concretes. The changes of the position of the pores bands from 0.01 to 0.054 and 10 μm are correlated to the transformation, during sintering, of the geopolymer gels that are generally characterized by an important band of pores with peak centered at 0.01 μm [25][26][27][28]. As already indicated above, before sintering, the geopolymer refractory concretes present homogeneous macrostructure with kyanite aggregates bound together through the good contact adhesion with the geopolymer cement ( Fig.…”

Section: Porosity and Pore Size Distribution And Microstructurementioning

confidence: 84%

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Transformation of the geopolymer gels to crystalline bonds in cold-setting refractory concretes: Pore evolution, mechanical strength and microstructure

et al. 2015

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Two K2O-MgO-Al2O3-SiO2 based geopolymer gels with bulk chemical composition corresponding to cordierite (Co) and 1:1 mullite-cordierite (MuCo) were successfully transformed to crystalline bonds in high temperature service of cold-setting made refractory concretes. Kyanite aggregates changed the flexural strength of the gels from11 to 28 MPa due to the development of good adhesive bonds. Under thermal cycles, up to 1250 °C, the cumulative pore volume remained at 0.09 mL/g, as fromthe absence of important densification/shrinkage. However, the behavior of the cumulative pore volume curves changed from that of a matrix with a wide range of distribution of pore sizes to that, of matrix, consisting of relatively coarse grains. The latter exhibits a rise at 10 μm as void spaces created around the contact points among the coarse kyanite grains and that at 0.054 μm as poreswithin the crystalline phases (cordierite, kalsilite, leucite,mullite, enstatite) formed. Themicrostructural observations confirmed the transformation of gel pores (size around 0.01 μm) to interparticle and intergranular pores due to the crystallization. The flexural strength of refractory concretes increased from28MPa to 40MPa in agreement with the increase in the elastic modulus from 9 to 30 GPa. The crystallization was enhanced by the MgO content (being important in Co compared to MuCo) and the kyanite concentration as particles of kyanite effectively acted as phase separation and nucleation site

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Section: Correlation Of the Sintering Behavior And Phases Evolution Wmentioning

confidence: 51%

Section: Porosity and Pore Size Distribution And Microstructurementioning

confidence: 84%

Transformation of the geopolymer gels to crystalline bonds in cold-setting refractory concretes: Pore evolution, mechanical strength and microstructure

et al. 2015

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“…Adding materials such as QZ and SF into the FA geopolymers can enhance the mechanical properties of the composite geopolymers at high temperature. Fine filler Researchers Tchakoute et al [76] Lahoti et al [77] Aygörmez et al [78] Duan et al [43] Duan et al [79] Rovnaník anď Safránková [53] Duan et al [60] Zhang et al [80] Roviello et al…”

Section: Chemical Compositionsmentioning

confidence: 99%

Thermal and Mechanical Properties of Geopolymers Exposed to High Temperature: A Literature Review

Dai

Wang

2020

Advances in Civil Engineering

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Geopolymers are prepared by alkali solution-activated natural minerals or industrial waste materials, which have been widely used as new sustainable building and construction materials for their excellent thermal and mechanical properties. The thermal and mechanical properties of geopolymers at high temperature have attracted great attention from many researchers. However, there are few systematic works concerning these two issues. Therefore, this work reviewed the thermal and mechanical behaviors of geopolymers at high temperature. Firstly, the thermal properties of geopolymers in terms of mass loss, thermal expansion, and thermal conductivity after high temperature were explained. Secondly, the mechanical properties of residual compressive strength and stress-strain relationship of fly ash geopolymers and metakaolin geopolymers after high temperature were analyzed. Finally, the microstructure and mineralogical characteristics of geopolymers upon heating were interpreted according to the changes of microstructures and compositions. The results show that the thermal properties of geopolymers are superior to cement concrete. The geopolymers possess few mass loss and a low expansion ratio and thermal conductivity at high temperature. The thermal and mechanical properties of the geopolymers are usually closely related to the raw materials and the constituents of the geopolymers. Preparation and testing conditions can affect the mechanical properties of the geopolymers. The stress-strain curves of geopolymer are changed by the composition of geopolymers and the high temperature. The silicon-type fillers not only improve the thermal expansion of the geopolymers but also enhance mechanical properties of the geopolymers. But, they do not contribute to reducing the thermal conductivity. the different raw materials, aluminosilicate precursor and reinforcement materials, result in different geopolymer damage during the heating. However, phase transitions can occur during the process of heating regardless of the raw materials. The additional performance enhancements can be achieved by optimizing the paste formulation, adjusting the inner structure, changing the alkali type, and incorporating reinforcements.

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“…Under hydrochloric acid solution, geopolymer mortar exhibited better resistance if compared with control mortars, where the mass loss of geopolymer mortar after 180 days of immersion was 36%, which is relatively insignificant as compared with PC and HAC mortars which recorded mass losses of 48% and 60%, respectively. Significant mass losses measured in control mortars are connected to higher calcium contents in these systems which react with the acid solutions, resulting in the decomposition of hydration products …”

Section: Resultsmentioning

confidence: 99%

Strength development and acid resistance of geopolymer based on waste clay brick powder and phosphorous slag

Vafaei

Allahverdi

2019

Structural Concrete

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This study aims to investigate the strength development and durability of geopolymer mortars based on waste clay brick powder (WCBP) and phosphorus slag exposed to acid attack. WCBP was partially replaced with slag (8, 16, and 24 wt%) and resulting blends were activated by an aqueous solution of NaOH and sodium silicate with different SiO 2 /Na 2 O ratios (M S ) and Na 2 O concentrations. The optimized geopolymer mortar specimens were also immersed in sulfuric and hydrochloric acid solutions of pH = 1 for 6 months to assess changes in their physical and structural properties. The results were compared with those of Portland cement and high alumina cement mortars as control specimens. The key durability parameters measured were the evaluation of mass change, compressive strength loss, and deteriorated depth. Complementary studies were also carried out using Xray diffractometry, Fourier transform infrared spectroscopy, and scanning electron microscopy in line with energy dispersive X-ray techniques to quantify the compositional and microstructural changes. The results demonstrate a potential of valueadded reuse application for WCBP by adding a suitable amount of slag. The findings also showed that geopolymer mortars were less susceptible to acid attack than the control mortars; however, superior enhancement in durability properties was not achieved. K E Y W O R D Sacid resistance, compressive strength, demolition materials, geopolymer, waste brick

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An investigation of the microstructure and durability of a fluidized bed fly ash–metakaolin geopolymer after heat and acid exposure

Cited by 212 publications

References 85 publications

Transformation of the geopolymer gels to crystalline bonds in cold-setting refractory concretes: Pore evolution, mechanical strength and microstructure

Transformation of the geopolymer gels to crystalline bonds in cold-setting refractory concretes: Pore evolution, mechanical strength and microstructure

Thermal and Mechanical Properties of Geopolymers Exposed to High Temperature: A Literature Review

Strength development and acid resistance of geopolymer based on waste clay brick powder and phosphorous slag

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