Alkali-Activated Binary Binders with Carbonate-Rich Illitic Clay (original) (raw)
Related papers
Effect of Alkali Concentration on the Activation of Carbonate-High Illite Clay
Applied Sciences, 2020
The present study explores the effect of activating solution concentration (4, 6 and 8 M NaOH) on mechanically and thermally pre-treated carbonate-high illite clay (LCR). Pastes were prepared with an alkaline solution/clay (S/B) ratio of 0.55, which were cured at room temperature and relative humidity > 90% in a climatic chamber. At two and 28 days, compressive mechanical strength was determined, and the reaction products were characterised by X-ray Powder Diffraction analysis (XRPD), Fourier-transform infrared spectroscopy (FTIR) and Scanning Electron Microscopy - Energy Dispersive X-ray spectroscopy (SEM/EDX). Results obtained showed that the presence of reactive calcium in the starting clay induces co-precipitation of a mix of gels: An aluminium-enriched C-S-H gel (C-A-S-H) and a N-A-S-H gel, in which sodium is partially replaced by calcium (N,C)-A-S-H. Pastes prepared with higher (6 or 8 M) activator concentrations exhibit a more compact matrix than the ones prepared with 4 M...
Low-Grade Clay as an Alkali-Activated Material
MDPI, 2021
The potential application of alkali-activated material (AAM) as an alternative binder in concrete to reduce the environmental impact of cement production has now been established. However, as the production and availability of the primarily utilized waste materials, such as fly Ash and blast furnace slag, decrease, it is necessary to identify alternative materials. One such material is clay, which contains aluminosilicates and is abundantly available across the world. However, the reactivity of untreated low-grade clay can be low. Calcination can be used to activate clay, but this can consume significant energy. To address this issue, this paper reports the investigation of two calcination methodologies, utilizing low-temperature and high-temperature regimes of different durations, namely 24 h heating at 120 C and 5 h at 750 C and, and the results are compared with those of the mechanical performance of the AAM produced with untreated low-grade clay. The investigation used two alkali dosages, 10% and 15%, with an alkali modulus varying from 1.0 to 1.75. An increase in strength was observed with calcination of the clay at both 120 and 750 C compared to untreated clay. Specimens with a dosage of 10% showed enhanced performance compared to those with 15%, with Alkali Modulus (AM) of 1.0 giving the optimal strength at 28 days for both dosages. The strengths achieved were in the range 10 to 20 MPa, suitable for use as concrete masonry brick. The conversion of Al (IV) is identified as the primary factor for the observed increase in strength.
materials, 2023
Concrete is the most used construction material, needing large quantities of Portland cement. Unfortunately, Ordinary Portland Cement production is one of the main generators of CO2, which pollutes the atmosphere. Today, geopolymers are an emerging building material generated by the chemical activity of inorganic molecules without the Portland Cement addition. The most common alternative cementitious agents used in the cement industry are blast-furnace slag and fly ash. In the present work, the effect of 5 wt.% -limestone in mixtures of granulated blast-furnace slag and fly ash activated with sodium hydroxide (NaOH) at different concentrations was studied to evaluate the physical properties in the fresh and hardened states. The effect of -limestone was explored through XRD, SEM-EDS, atomic absorption, etc. The addition of -limestone increased the compressive strength reported values from 20 to 45 MPa at 28 days. It was found by atomic absorption that the CaCO3 of the -limestone dissolved in NaOH, precipitating Ca(OH)2 as the reaction product. SEM-EDS analysis showed a chemical interaction between C-A-S-H- and N-A-S-H-type gels with Ca(OH)2, forming (N, C)A-S-H- and C-(N)-A-S-H-type gels, improving mechanical performance and microstructural properties. The addition of -limestone appeared like a promising and cheap alternative for enhancing the properties of low-molarity alkaline cement since it helped exceed the 20 MPa strength recommended by current regulations for conventional cement.
Construction and Building Materials, 2021
The feasibility of transforming the residues of cultivation of two rocks into secondary raw materials through the alkali activation process has been assessed. Mixtures of a sulfate-bearing kaolinitic clay (L02-K) and a sludge derived by the sewing of Pietra Serena stone (sPS) have been investigated. These materials were preliminarily treated at high temperature to improve their reactivity (heat-treated samples are hereafter labelled as L02-MK and sPS-800). Pastes were prepared with mixtures of L02-MK and sPS-800 in different weight proportions by using 8 M NaOH solutions as alkaline activator and cured at 85 • C for 24 h. Mechanical strength was determined after 1, 7 and 28 days and the reaction products were characterized by XPRD, SEM/EDX and MAS-NMR. Sulfate solubility was quantified by leaching tests. The alkali activation of the sole sulfate-bearing clay gives a material with developed mechanical strength of 4 (1) MPa. Some N-AS -H gel forms together with gibbsite and thenardite, which can be easily leached. Better results are obtained by the activation of mixtures of the two precursors, and mixed alkali cements or hybrid cements are obtained. The presence of CaO from heat-treated Pietra Serena sludge improves the mechanical strength of the resulting pastes up to 11.8(9) MPa. In this case, a mixture of gels forms, specifically, a calciumrich gel (C-AS -H-type) co-exists with (N,C)-AS -H-type gel. U-phase and CAN-type zeolites also form. They trap sulfate from the clay and considerably reduce sulfate solubility. In conclusion, L02-MK and sPS-800 are promising raw materials for alkaline cements, whose properties may suggest application in soil stabilization or in waste confinement.
Elsevier, 2021
This paper reports the strength development in alkali-activated clay (AAC) synthesised from untreated and calcined low grade clays. The effects of clay calcination and the temperature adopted in different curing regimes on the mechanical properties of AAC were studied from a microstructural viewpoint. Solid-state MAS NMR, FTIR, EDS, and TEM imaging were used for the microstructural studies. Calcination of the clay resulted in an increase in the 7-day compressive strength of AAC from 31.7 MPa to 47.8 MPa. 29 Si MAS NMR results indicated that ratio of Q 4 (2Al) percentage to Q 4 (4Al) percentage correlates positively with the compressive strength. Curing the AAC at higher temperatures resulted in higher strength, but there was a conflict between strength development due to ongoing polymerisation and strength deterioration due to post-curing crack propagation. FTIR results indicated the formation of a more polymerized structure and stronger bonds in the AAC as a result of calcination. In addition, FTIR showed a higher Si-O bond strength in AAC cured at a higher temperature, which positively correlated with the compressive strength of the specimens. EDS and TEM results revealed the presence of a silicon-rich phase in AAC syn-thesised from the untreated clay. This sodium silicate gel exhibited poor hydrolytic stability which could result in long term durability issues.
[Clay Minerals] Alkali activation of natural clay using a Ca(OH)2Na2CO3 alkaline mixture
A B S T R AC T : An experimental investigation was conducted on the alkali activation of a kaolinitic clay using an alkaline mixture composed of hydrated lime (Ca(OH) 2 ) and sodium carbonate (Na 2 CO 3 ) solution. The Ca(OH) 2 /Na 2 CO 3 alkaline mixture was developed to overcome the high cost and chemical aggression associated with classical alkaline solutions. The mineralogical composition and microstructure of the alkaline mixture and alkali-activation products were studied using X-ray diffraction, attenuated total reflectance-Fourier transform infrared spectroscopy, thermogravimetric analysis and energy-dispersive X-ray-scanning electron microscopy techniques. Pirssonite (Na 2 Ca(CO 3 ) 2 ·2H 2 O), calcite (CaCO 3 ), and sodium hydroxide (NaOH) formed as a result of mixing of Ca(OH) 2 with Na 2 CO 3 . The alkali activation of natural clay with the Ca(OH) 2 /Na 2 CO 3 alkaline mixture produced a binding agent identified as hydroxysodalite phase (Na 8 Al 6 Si 6 O 24 (OH) 2 ·4H 2 O) when pure kaolinite was used, and cancrinite carbonate (Na 6 Ca 1.5 [Al 6 Si 6 O 24 ](CO 3 ) 1.5 ·1.8H 2 O) when kaolinitic clay with high a calcite content was used. The mechanical strength of the binder developed was evaluated on cylindrical specimens containing granite waste as a filler material under dry and soaked conditions. The classical NaOH activator was used for comparison. For specimens produced using a Ca (OH) 2 /Na 2 CO 3 mixture as the alkaline activator, the recorded strength value was 21 MPa which was 35% less than that achieved by the classical NaOH solution. Durability tests on samples soaked in water for 24 h showed a reduction in strength from 34 to 22 MPa for specimens prepared with NaOH solution, and from 21 to 11 MPa for the specimens prepared with a Ca(OH) 2 /Na 2 CO 3 alkaline mixture.
Alkali-Activated Material Based on Red Clay and Silica Gel Waste
Waste and Biomass Valorization, 2019
Industrial by-products such as silica gel waste and red clay based on natural illite, have been used as precursors for the preparation of alkali activated materials (AAM). Raw materials, precursors and the alkali-activated materials were examined using X-ray diffraction, XRFA and SEM analysis. The reactive concentrations of Si and Al were determined using the colorimetric method. The compressive strength of alkali-activated samples was also evaluated. The precursors were made from Lithuanian red clay (Ukmergė deposit) and silica gel waste. The clay and silica gel waste were first mixed together and then calcined at 900 °C or 600 °C to obtain the precursors. The results show that during the calcination process, new phase CaF 2 formed in the precursors. It is possible that fluoride compound which forms during the calcination process, acts as a flux (at a temperature of 900 °C), and for this reason, the reactive amorphous phase is transformed into mullite and cristobalite (crystalline phases), which are not reactive. According to the XRD diffractogram, calcination at a temperature of 600 °C was sufficient to convert the crystalline structure of kaolinite into an amorphous phase. In this case, at a calcination temperature of 600 °C, it was recommended to use up to 25% of silica gel waste. The maximal compressive strength (7 MPa) was achieved by using 5% of silicagel waste. It was concluded that red clay-silica gel waste AAM can be considered for the production of green composite materials.
Alkali activation of natural clay using a Ca(OH)2/Na2CO3 alkaline mixture
Clay Minerals, 2017
An experimental investigation was conducted on the alkali activation of a kaolinitic clay using an alkaline mixture composed of hydrated lime (Ca(OH)2) and sodium carbonate (Na2CO3) solution. The Ca(OH)2/Na2CO3 alkaline mixture was developed to overcome the high cost and chemical aggression associated with classical alkaline solutions. The mineralogical composition and microstructure of the alkaline mixture and alkali-activation products were studied using X-ray diffraction, attenuated total reflectance-Fourier transform infrared spectroscopy, thermogravimetric analysis and energy-dispersive X-ray-scanning electron microscopy techniques. Pirssonite (Na2Ca(CO3)2·2H2O), calcite (CaCO3), and sodium hydroxide (NaOH) formed as a result of mixing of Ca(OH)2 with Na2CO3. The alkali activation of natural clay with the Ca(OH)2/Na2CO3 alkaline mixture produced a binding agent identified as hydroxysodalite phase (Na8Al6Si6O24(OH)2·4H2O) when pure kaolinite was used, and cancrinite carbonate (N...
Applied Clay Science, 2018
The present study focuses on the assessment of the effects of different activation methods on carbonate-rich clays, to understand the mineralogical differences originated and to exploit such information to industry for traditional and innovative applications, especially as a precursor for alkali activated binders. Illite carbonate-rich clay samples were subjected to thermal activation in ox/red atmosphere between 400 and 900 °C, mechanical activation (grinding for 5, 10 and 15 min) and to a combination of such treatments. Mineralogical and textural changes in the activated samples were evaluated through X-ray powder diffraction, Fourier transform infrared spectroscopy and thermal techniques. The activated samples with the highest content of amorphous phase underwent leaching tests in a 3 M NaOH solution by means of inductively coupled plasma-mass spectrometry. The application of the three processing routines , yielded three types of activated clays with different leaching modes of Si, Al, K and Ca: (1) high energy grinding preferentially delaminates clay minerals and reduces the grain size of calcite. K leaching reaches the highest values; (2) thermal heating at 800 °C increases relatively the Si/Al solubility ratio, but the absolute concentrations of these elements are equal or lower than those obtained from ground clays. The relatively higher leaching of Ca is influenced by the formation of non-stoichiometric and poorly crystalline Ca-silicates and-alu-minosilicates; (3) high energy grinding combined with heating treatment yields an extended amorphisation, mainly at the expense of clay minerals, with the highest leaching of Si and Al, and the lowest of Ca. New formed K-feldspars inhibit the concentration of K in alkaline solution
Mine Clay Washing Residues as a Source for Alkali-Activated Binders
Materials, 2021
The aim of this paper is to promote the use of mine clay washing residues for the preparation of alkali activated materials (AAMs). In particular, the influence of the calcination temperature of the clayey by-product on the geopolymerization process was investigated in terms of chemical stability and durability in water. The halloysitic clay, a mining by-product, has been used after calcination and mixed with an alkaline solution to form alkali activated binders. Attention was focused on the influence of the clay’s calcination treatment (450–500–600 °C) on the geopolymers’ microstructure of samples, remaining in the lower limit indicated by the literature for kaolinite or illite calcination. The mixtures of clay and alkali activators (NaOH 8M and Na-silicate) were cured at room temperature for 28 days. The influence of solid to liquid ratio in the mix formulation was also tested in terms of chemical stability measuring the pH and the ionic conductivity of the eluate after 24-h immer...