Effect of acid attack on microstructure and composition of metakaolin-based geopolymers: The role of alkaline activator (original) (raw)
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Science of Sintering, 2020
This paper outlines the production of an inorganic polymer/geopolymer using a metakaolin by an environmental friendly, energy saving, clean technology to conserve natural environment and resources. The influence of alkali activation, i.e. different concentration of NaOH as a component of alkali activator mixture on the process of geopolymerization of metakaolin is investigated. Also, process of aging time of geopolymer is followed by several analytical methods. The structure of metakaolin and metakaolin based geopolymers and their physicochemical properties were studied using X-ray diffraction (XRD), Fourier transformation infrared spectroscopy (FTIR) and after 28days scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) was applied for the surface characterization of the samples. A shift of the Si-O or Si-O-X (X=Al, Si, Na...) bands as the molarity of activator increasing during geopolymerization process was observed by FTIR. Mass spectra of geopolymers were ...
Ceramics International, 2014
The present work aims to investigate the influence of the alkaline activator concentration of kaolin-based geopolymers on the compressive strength at the curing early age regarding the structural characteristics. We used alkaline activators (Na, K) at molar concentrations from 4 M to 12 M, while the volume ratio sodium silicate/MOH was kept equal to 0.20 for all compositions. Samples were consolidated by curing at 70 1C for 24 h, and the mechanical and structural characterizations were obtained after 3 days of aging. Results show that the type and the concentration of the alkali-MOH solutions changed both the amount of reacted-kaolinite, the structural characteristics of gel phases, the formation of new crystalline phases, and the compressive strengths at the early age. For all compositions, the increase of MOH concentration led to an improvement of the compressive strength at the early age, attaining 88-165% of the standard value of 4 M MOH geopolymers. Optimized compressive strengths were 25 MPa and 32 MPa for [NaOH] ¼ 10 M and [KOH] ¼12 M respectively. We propose that an optimized alkali concentration is found with an adequate charge-balance of the Si-Al tetrahedral substitution, which prevents the formation of carbonated species from the alkaline excess.
Effect of the rate of calcination of kaolin on the properties of metakaolin-based geopolymers
Journal of Asian Ceramic Societies, 2015
Kaolin samples of the same mass were treated at 700 • C for the same duration of 30 min by varying the rate of calcination (1, 2.5, 5, 10, 15 and 20 • C/min) in order to obtain metakaolins which were used to produce geopolymers. Depending on the nature of each type of material, kaolin, metakaolins and geopolymers were characterized using thermal analysis, chemical analysis, XRD, FTIR, particle size distribution, specific surface area, bulk density, setting time and compressive strength. FTIR and XRD analyses showed that metakaolins except at 1 • C/min contained residual kaolinite whose quantity increased with the rate of calcination of kaolin and which influenced the characteristics of geopolymers. Thus as the rate of calcination of kaolin increased, the setting time increased (226 min (rate of 1 • C/min)-773 min (rate of 20 • C/min)) while the compressive strength reduced (49.4 MPa (rate of 1 • C/min)-20.8 MPa (rate of 20 • C/min)). From the obtained results the production of geopolymers having high compressive strength along with low setting time requires that the calcination of kaolin be carried out at a low rate.
Study on solids-to-liquid and alkaline activator ratios on kaolin-based geopolymers
Kaolin and alkali activator were mixed with the solids-to-liquid ratios in range of 0.60–1.20 (Al2O3/Na2O molar ratio of 0.63–1.27). Sodium silicate and sodium hydroxide ranged between 0.16 and 0.36 (SiO2/Na2O molar ratio of 3.19–3.67) were mixed together to prepare alkali activator. The results concluded that compressive strength was affected by both S/L and Na2SiO3/NaOH ratios and strength increased with ageing day. Both these ratio also influenced the workability of the mixes. Besides, the kaolin geopolymers showed good volume stability in water. Compressive strength was highest at S/L and Na2SiO3/NaOH ratios of 1.00 and 0.32, respectively. In term of molar ratios, optimum was achieved at Al2O3/Na2Oof 1.09 and SiO2/Na2O molar ratios of 3.58. Microstructures showed that kaolin particles were slightly activated with large part of unreacted raw materials remained in the system. Geopolymer sample reduced in peak intensities over time as presented by XRD analysis and the presence of crystalline peaks in the kaolin geopolymers was Zeolite X. FTIR analysis showed the presence of geopolymer bonding increased over age. In overall, kaolin geopolymers does not undergo complete geopolymerization and showed slow strength development. Vast research works have to be carried out to further improve the properties of kaolin geopolymers.
The present work aims to investigate the influence of the alkaline activator concentration of kaolin-based geopolymers on the compressive strength at the curing early age regarding the structural characteristics. We used alkaline activators (Na, K) at molar concentrations from 4 M to 12 M, while the volume ratio sodium silicate/MOH was kept equal to 0.20 for all compositions. Samples were consolidated by curing at 70 1C for 24 h, and the mechanical and structural characterizations were obtained after 3 days of aging. Results show that the type and the concentration of the alkali-MOH solutions changed both the amount of reacted-kaolinite, the structural characteristics of gel phases, the formation of new crystalline phases, and the compressive strengths at the early age. For all compositions, the increase of MOH concentration led to an improvement of the compressive strength at the early age, attaining 88–165% of the standard value of 4 M MOH geopolymers. Optimized compressive strengths were 25 MPa and 32 MPa for [NaOH] ¼ 10 M and [KOH] ¼12 M respectively. We propose that an optimized alkali concentration is found with an adequate charge-balance of the Si–Al tetrahedral substitution, which prevents the formation of carbonated species from the alkaline excess.
Metakaolinite-based geopolymer has been synthesized at about 25 °C from metakaolin which has been calcined in different temperatures (600-900 °C) and different Na 2 O/SiO 2 ratio activator (0.3-1.1). Compressive strength and microstructure of cement pastes after 7-28 days curing at ambient temperature were measured. Compressive strength tests on the samples showed that the sample made with calcined kaolin at 700 °C and molar ratio of 0.6 has highest average compressive strength of 32 MPa after 28 days of curing. Evaluation of infrared spectroscopy (FTIR) and microstructure showed that geopolymer cement developed and new molecular structure established.
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2007
Statistical analysis of a systematic series of geopolymers with varying alkali type (sodium and potassium) and Si/Al ratio after 7 and 28 days ageing has been used as a basis for observing the development of mechanical properties with time. Minimal change in the compressive strength of specimens was generally observed in specimens of different alkali or between 7 and 28 days of ageing. However, mixed-alkali specimens with high Si/Al ratio exhibited significant increases in strength, while pure alkali specimens displayed decreased strength. The development of Young's modulus of geopolymers between 7 and 28 days was observed to be dependent on alkali, with the Young's moduli of Na-specimens decreasing at low Si/Al ratio, but increasing at high Si/Al ratio, while K-specimens exhibited the opposite effect. Mixed-alkali specimens all exhibited nominal change in Young's moduli, without any significant effect of Si/Al ratio being observed.
Kaolin-based geopolymers with various NaOH concentrations
International Journal of Minerals, Metallurgy, and Materials, 2013
Kaolin geopolymers were produced by the alkali-activation of kaolin with an activator solution (a mixture of NaOH and sodium silicate solutions). The NaOH solution was prepared at a concentration of 6-14 mol/L and was mixed with the sodium silicate solution at a Na2SiO3/NaOH mass ratio of 0.24 to prepare an activator solution. The kaolin-to-activator solution mass ratio used was 0.80. This paper aimed to analyze the effect of NaOH concentration on the compressive strength of kaolin geopolymers at 80 • C for 1, 2, and 3 d. Kaolin geopolymers were stable in water, and strength results showed that the kaolin binder had adequate compressive strength with 12 mol/L of NaOH concentration. When the NaOH concentration increased, the SiO2/Na2O decreased. The increased Na2O content enhanced the dissolution of kaolin as shown in X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) analyses. However, excess in this content was not beneficial for the strength development of kaolin geopolymers. In addition, there was the formation of more geopolymeric gel in 12 mol/L samples. The XRD pattern of the samples showed a higher amorphous content and a more geopolymer bonding existed as proved by FTIR analysis.
2017
In the present work we sought to determine the most convenient calcination temperature of Tunisian kaolinitic clay in order to produce a more reactive metakaolin and to determine the most suitable potassium hydroxide (KOH) and sodium hydroxide (NaOH) concentration to produce geopolymer cements with good physical and mechanical performance, less energy consumption and low carbon dioxide emission. This product would play the role of a construction material able to replace Portland cement. The kaolinitic clay fractions collected from Tabarka (Tunisia) were first calcined at different temperatures ranging from 550 °C to 1 100 °C. Calcined fractions were then activated by potassium hydroxide and sodium hydroxide solutions with concentrations of between 5 M to 18 M. The mineral and chemical composition of raw and geopolymer samples was characterized by X-ray diffraction, infrared spectroscopy and thermal analysis, whereas the mechanical and physical properties of hardened samples were cha...