Preparation Conditions for the Synthesis of Alkali-Activated Binders Using Tungsten Mining Waste

This study evaluated the results of preparation conditions for the production of an alkali-activated binder (AAB) based on a binary mixture of tailings from tungsten mine waste (TMW), and waste glass (WG) activated with a mixture of sodium silicate (SS) and sodium hydroxide (SH). A 40% by weight WG increased the amorphous nature of the binary blend by 21% without initiating the alkali-silica reaction. The SS-SH activator solution was subjected to a variation of mixing times, and its sensitivity was measured using temperature monitoring and Fourier transform infrared spectroscopy (FTIR). After 20 min of mixing, the SS-SH activator solution showed a 3.13°C reduction in temperature and a 21.4% increase in unbound water content, and as a result imparted a 26% drop in the mechanical strength of TMW-WGAAB at 28 days. The TMW-WGAAB was also determined to develop the highest compressive strength when cured at 80°C for 24 h in sealed conditions. The following conditions, supported by X-ray diffraction (XRD) and FTIR, are responsible for the most significant dissolution of the aluminosilicate oxides. DOI: 10.1061/(ASCE)MT.1943-5533.0002029. This work is made available under the terms of the Creative Commons Attribution 4.0 International license, http://creativecommons.org/licenses/by/4.0/. Author keywords: Alkali-activated binder; Binary blend; Curing temperature; Geopolymer; Material preparation; Mixing time; Precursor reactivity; Synthesis conditions; Tungsten mining waste; Waste glass.


Introduction
Although the development of portland cement (PC) research and its application has considerably matured in the last few decades, it is still facing challenges due to its impact on the environment.The production of cement is one of the industry's most energy-intensive processes, next only to steel and aluminum (Napp et al. 2014).In 2011, the European states accounted for 7.6% of total global cement production (European Cement Association 2014).The manufacture of PC can consume approximately 3.2-6.3GJ of energy (thermal and electrical) per ton of clinker product (Rahman et al. 2016), with almost half of this being used for the fine grinding of clinker to make the cement.The main raw material used in cement production has traditionally been the abundantly available limestone, which, by its inevitable transformation into lime, is responsible for more than 60% of the cement industry's CO 2 emissions (Mikulčić et al. 2012).For every kilogram of PC clinker produced, approximately 0.87 kg of CO 2 is released (Telesca et al. 2017).Therefore, the main challenge of the cement industry is focused on the CO 2 emission reduction to 1.55 Gt=year (approximately 45% of the current value) by 2050 (Telesca et al. 2017).
To reduce the carbon footprint and conveniently dispose of the variety of waste material available from multiple industries, alkaliactivated binders (AABs) have attracted increasingly more attention from the scientific community as environmentally favorable alternatives to PC (Barbosa et al. 2000;Ariffin et al. 2014).Aluminosilicate-rich materials can be alkali-activated to produce a three-dimensional polymer like a network containing both crystalline and amorphous phases (Panagiotopoulou 2007).These particular binders yield high strength with rapid setting, good durability, and high resistance to chemical attack (Zhao et al. 2007;Sangiorgi et al. 2017;Thomas and Peethamparan 2015).Despite the existence of strong economic and environmental drivers, alkali-activated binders are still not widely implemented throughout the world.They represent an attractive alternative for the partial or complete substitution of PC, offering comparable performance (Neupane 2016) and cost (Duxson et al. 2007a) while reducing greenhouse gas emissions (Duxson et al. 2007b).
The raw materials used for synthesizing AABs are typically calcined clays or low-calcium fly ashes (Duxson et al. 2007a).However, the supply of fly ash in Europe is in decline due to the industry becoming increasingly less reliant on coal-fired power stations (Carroll 2015), while the disposal of the 85% of host rock generated from kaolin clay mining is an increasingly critical issue (Murray 2002).On the other hand, mining and quarrying waste still represent 15% of the total waste in Western Europe and 31% in Eastern Europe (Pacheco-Torgal et al. 2009b), while the United States alone is estimated to produce between 1,000 and 2,000 Mt of mining waste annually (Szczepańska and Twardowska 2004).The favorable mineralogical composition of mining waste for alkali activation (Jiao et al. 2013;Ye et al. 2014;Ahmari et al. 2014) combined with its continuously large production make it an attractive and environmentally friendly feedstock for AABs.
Some mining and quarrying wastes can be reused in earthworks and construction, in particular, the coarser fractions.Typical applications include use in asphalt pavements (Albuquerque et al. 2006;Akbulut and Gürer 2007) and concrete (Yellishetty et al. 2008;Hebhoub et al. 2011).However, recent studies on the reuse of fine tailings as raw material for AABs are considered to be most promising from environmental, technical, and economic points of view.For this study, the wastes of particular interest are fine tailings derived from tungsten mining.Preliminary research has been conducted on the transformation of this type of waste into AABs and has shown promising results.Pacheco-Torgal et al. (2007) first highlighted the potential of using calcined tungsten mining waste (TMW) mud blended with calcium hydroxide for the development of a high early strength geopolymeric binder.Tungsten mining waste was also identified to be very effective for stabilizing and solidifying heavy metals, particularly when used in conjunction with blast-furnace slag (Choi et al. 2009), and overall it suggested that mortar with acceptable properties can be developed using up to 10% by mass tungsten mining waste.Later, alkali-activated artificial aggregates were produced from such mining waste mud, and their properties were studied as a potential substrate for fixedfilm wastewater-treatment processes (biofilm reactors).The results showed that the aggregates obtained have suitable resistance to acid attack and may be used as a substrate for fixed-film biological reactors for the treatment of acid wastewaters (Silva et al. 2012a).Also, mine tailings blended with other industrial by-products such as fly ash have resulted in the production of an AAB with high compressive strength, mainly due to the Si:Al ratio of the raw material blend falling within the optimum Si:Al ratio for alkali activation (Zhang et al. 2011;Ahmari and Zhang 2012).
Despite the research conducted so far, it remains that tungsten mining waste possesses a low degree of reactivity due to it crystalline phases.Thermal treatments have previously been studied to improve the amorphicity of tungsten mining waste, and satisfactory strengths have been achieved (Pacheco-Torgal et al. 2009b), nonetheless at the expense of the high amount of energy.A more sustainable method would be to blend the tungsten mining waste with a material that would increase not only its level of amorphicity but also maintain its environmental appeal.In this case, waste glass (WG) would be the ideal candidate because it is a very common construction and household waste material with a highly amorphous structure.It is estimated that out of 18 million tons of glass wastes accumulated in 2012 in the European Union, only 35% of this was recycled (Glass for Europe 2013).The feasibility of using ground waste glass to improve mechanical performance has already been achieved with PC concrete (Shao et al. 2000) and initiated with metakaolin-based AABs (Christiansen and Sutter 2013).
Also when assessing novel binder materials, it is of as much importance to study the preparation and manufacturing techniques as it is the final material properties.This is a domain that currently remains understudied for AABs in general, let alone those based on tungsten mining waste.
Thus, the primary objective of this study is to determine the fundamental aspects of AAB synthesis using tungsten mining waste as the principle raw material with the added feasibility of its partial replacement by waste glass.Particular focus will be on (1) the influence of waste glass on tungsten mining waste reactivity; (2) alkali activator solution preparation and kinetics; and (3) AAB curing temperature and curing duration.

Materials
The raw materials used in this investigation consisted of TMW, WG, sodium hydroxide (NaOH) (SH), and sodium silicate (Na 2 SiO 3 ) (SS).The TMW was derived in powder form from the Panasqueira mine in Castelo Branco, Portugal, and the WG was received from the local municipality of Covilhã, Portugal.The chemical composition of the TMW and WG was obtained by scanning electron microscopy and energy-dispersive X-ray (SEM-EDX) analysis (Supra 35VP/EDAX, Oberkochen, Germany).Due to the waste nature and microscopic inhomogeneity of the TMW, chemical analyses were made from different batches collected from the mine.Therefore, the results of TMW reported in Table 1 are the average values accompanied by the standard deviation (SD).According to Table 1, for TMW, the oxides SiO 2 , Al 2 O 3 , Fe 2 O 3 , and SO 3 are the most abundant, while the oxides SiO 2 , MgO, SO 3 , and Fe 2 O 3 showed the greatest variability.Grain size distribution analysis was performed for the precursor materials after mechanical sieving by laser diffraction analysis according to BS ISO 13320 :2009(ISO 2009).The TMW has a mean particle size of 26 μm, while the waste glass has a mean particle size of 39.68 μm.The WG was intentionally used with a slightly larger mean particle size to reduce the energy consumption during the milling process.The bulk powder densities of TMW and WG were determined using a gas displacement pycnometer (AccuPyc II 1340, Micromeritics, Norcross, Georgia) and were determined as 3.08 and 2.53 g=cm 3 , respectively.Sodium hydroxide solution was prepared by dissolving sodium hydroxide pellets (98% purity obtained from Fisher Scientific, Schwerte, Germany) in deionized water and allowed to cool before use.Sodium silicate (obtained from Solvay SA, Póvoa de Santa Iria, Portugal) had a SiO 2 =Na 2 O ¼ 3.23 (8.60% by weight Na 2 O, 27.79% by weight SiO 2 , 63.19% by weight H 2 O, and 0.4% by weight Al 2 O 3 ).

Synthesis of Samples
All sample preparation was carried out at 20°C.The TMW alkaliactivated binders with up to 40% by mass replacement with WG were blended with an IKA (Staufen, Germany) Ultra-Turrax T50 mixer at 360 revolutions per minute (rpm) for 60 s.Based on the research on alkali activation available in the literature concerning mechanical strength and efflorescence formation potential in AABs combined with the experience gained from previous studies (Pacheco-Torgal et al. 2008;Silva et al. 2012b;Kastiukas et al. 2016), the following ranges were selected for the constituents of the AABs: The following ratios produced an AAB with a flowability of 130 AE 5 mm determined using the method proposed by EN 1015-3:1999(CEN 2006) and initial and final setting times of 90 and 110 min determined by EN 196-3 (CEN 2005).In the precursor:activator ratio, the precursor is the TMW and WG, and the activator is the solution containing the alkali, the silicate, and the water.
To produce the TMW-WG AAB, the TMW and WG were mixed in the dry state for 5 min, forming the precursor materials.The sodium hydroxide and sodium silicate solutions were mixed for a period ranging from 2.5 to 60 min at 700 rpm, depending on the type of condition being tested, forming the alkali activator.The alkali-activator solution was slowly added to the precursor materials, and the resulting paste was stirred for 2.5 min at 200 rpm, followed by 2.5 min at 400 rpm.The resulting AAB was then placed in 40 × 40 × 160 mm prismatic polystyrene foam molds.
The mold was filled with the AAB in three stages and manually vibrated after each successive filling stage to release trapped air bubbles, and sealed with a film to avoid the loss of water and ingress of CO 2 .Samples that were made to test curing exposed to the atmosphere were cured unsealed.The specimens were placed in a temperature-and humidity-controlled environmental chamber at 50% relative humidity (RH) for curing between 20 and 80°C for 4-36 h, depending on the type of condition being tested.After curing, prisms were demolded and left in a laboratory condition of 20°C for curing until the test age.The specimens cured at 20°C were demolded after 48 h due to a slow setting.Table 2 summarizes synthesis conditions tested in this study, i.e., activator solution mixing time, curing temperature, and curing time.
To observe for chemical changes in the activator solution during mixing, first it was decided to isolate the activating solution and monitor its temperature during the mixing process.The temperature evolution of the activator solution was measured using the setup shown in Fig. 1.The activator solution was prepared at the same SS:SH solution ratio as that used to make the TMW-WG ABB, i.e., 4.0.A polystyrene enclosure was used to contain the activator solution and provided a thermodynamically stable environment.Two K-type thermocouples with the tips wrapped in temperaturesensitive copper tape were connected to a multichannel data logger and used to measure the temperature of the activator solution and enclosure's interior, respectively.Once the activator temperature was deemed constant, mixing was started and continued for 20 min at 700 rpm.

Compressive Strength
The demolded samples were left to rest at 20°C and a relative humidity of 75% until the specific age of testing.The compressive strength of the prismatic sample fractured counterparts was tested after 1, 3, 7, and 28 days in accordance with EN 196-1 using a universal testing machine (Instron 5960, Buckinghamshire, United Kingdom) at a constant loading rate of 144 kN=min.The compressive strength value was the average of values obtained from three specimens.

Scanning Electron Microscopy
Microstructural studies utilized SEM (Zeiss Supra 35VP, Oberkochen, Germany) equipped with energy-dispersive X-ray (EDX) analyzer (EDAX, Mahwah, New Jersey).Backscattered and secondary electron images were collected from polished specimens to overcome the main limitation of fracture surfaces.To prepare the polished specimens, 5-mm-thick slices were cut using a low-speed saw.The samples were first impregnated with ultralow-viscosity resin and then polished.

Stopping the Activation Process
Both the XRD and FTIR samples were tested in a state where the alkali activation process was stopped using the combined water and solvent extraction protocol developed by Chen et al. (2014).In summary, it involved stirring the AAB specimen in deionized water and then removing the liquid by centrifuging.Upon addition of methanol, soluble silicate species could be observed in the liquid layer.Thus, water extraction by centrifuging was used to remove the precipitates.Specimens were then ground to micrometer-sized particles using a mortar and pestle, and a solvent of methanol and acetone mixture was added, followed by further grinding.The solvent was removed using vacuum filtration; this latter procedure was repeated five times.

Influence of Waste Glass on Tungsten Mining Waste Reactivity
The recorded FTIR spectra of raw TMW and WG and blended as TMW-WG are shown in Fig. 2. For the WG spectra, the highest absorption coefficient is associated with the Si-O bending vibration near 453 cm −1 .A weaker band due to the bending mode near 1,000 cm −1 is accompanied by the still weaker feature near 775 cm −1 .For the TMW, the highest absorption coefficient is associated with the bending vibration of the Si-O between 465 and 424 cm −1 .Weaker features are associated with the bending vibration of Si-O at 984 cm −1 and its symmetric stretching vibration between 797 and 694 cm −1 .The weakest bands at 827 and 1,163 cm −1 can be associated with the bending of the Si-O bond of the original TMW.The absorbance spectrum of the TMW-WG blend displays the same spectral bands as the raw TMW, only at lower intensities, due to the combination of different intensities.
Results of the XRD analyses shown in Fig. 3 reveal that the TMW precursor material predominantly consists of muscovite and quartz with traces of albite and pyrite and is similar to the TMW chemical composition identified by Pacheco-Torgal et al. (2009a).The WG is revealed to consist of quartz, lime, and sodium oxide with traces of potassium and iron oxide.Using a general nonlinear least squares system software (DIFFRAC.SUITE), the TMW and WG were determined to be 97 and 15% crystalline, respectively.Compared with other materials commonly used as AAB precursors such as fly ash (van Jaarsveld and van Deventer 1999) and metakaolin (Provis et al. 2005), the TMW is of a far less amorphous nature.In this study, a sustainable approach was chosen to increase the amorphicity of the TMW through the addition of WG.The addition of 40% by weight WG led to an increase in the amorphicity, qualitatively indicated by the more intense amorphous background from 15 to 45°in the TMW-WG blend XRD spectrum and also by a 21% calculated reduction in crystallinity.The compressive strength of TMW-WG AAB was used to evaluate the strength contribution potential as a function of the degree of amorphicity.Thus Fig. 4 shows the evolution of compressive strength in TMW-WG AAB with 20, 30, and 40% by weight WG replacement over 28 days.The results obtained for pure TMW AAB are also included.Each reported result corresponds to the average measurement in three specimens per each WG replacement value and age; the deviation of results fluctuated between 0.22 and 1.4%.In Fig. 4 it can be observed that the compressive strength increased with an increase in the WG content at all ages.The highest 28-day strength was obtained by the 60TMW40WG sample at 41 MPa, which is 127% higher than the control sample 100TMW.The compressive strength would be influenced primarily by the additional release of reactive silica.However, it also expected that the CaO content in the WG would contribute to the strengthening of the reaction products, most likely in the form of a (C, N)-A-S-H gel.
The compressive strength results with the highest replacement level of WG, i.e., 40% by weight, is consistent with the compressive strength results previously obtained by Pacheco-Torgal et al. (2009b), specifically 39.6 MPa at 28 days, for mortar prepared with TMW.However, this was achieved only after an energy-intensive calcination treatment of the TMW at 950°C for 2 h.
Finally, the reactive silica-containing WG combined with the highly alkaline activator solution may create the potential for the deleterious process of alkali-silica reaction (ASR) and required validation.The TMW-WG AAB with the highest replacement of WG, i.e., 40% by weight, was stored at a RH of 80% at 38°C to accelerate the ASR reaction; a thin section of this sample is shown in Fig. 5. Observation of the section, which is representative of the WG as a whole, revealed that there were no signs of ASR gel formation around the WG particles or in the open voids.Data reported in the literature established that if the waste glass is ground to be less than 75 μm, the ASR effect does not occur, and binder durability is guaranteed (Shao et al. 2000).Water is also a necessary condition for ASR; considering the TMW-WG AAB only required a water or precursor demand of 0.179, this may also be the reason for the absence of ASR.

Alkali Activator Preparation Conditions
To prepare the TMW-WG AAB, it is necessary that the alkali activator is in a homogeneous state upon mixing with the powder precursors.Fig. 6 shows the effect of activator mixing time on the 80TMW20WG AAB compressive strength.It can be seen that the 28-day strength increases when using the activator that has been mixed between 2 and 5 min only (i.e., M2.5 and M5), reaching the maximum 28-day strength of 17 MPa at an activator mixing time of 5 min (i.e., M5).As the activator mixing time is extended, an immediate drop in compressive strength is observed.The activator solution mixing time has a strong effect on the 28-day strength; a 26% drop in compressive strength is recorded for the TMW-WG AAB when prepared using an activator solution stirred for 20 min, i.e., M20.Fig. 7 presents the results of the activator solution temperature during mixing.The dashed and solid curves represent the activator and enclosure air temperature, respectively.Over the course of 20 min of mixing, an average reduction of 3.13°C in activator temperature was recorded from three identical tests, while the enclosure temperature was recorded to remain stable at 23 AE 0.1°C.This drop activator solution temperature is an endothermic process resulting from the reorientation of the water molecules, leading to a disruption of the hydration shells surrounding the ions.The positive metal ions, in this case, Na þ , are particularly at risk because they inherently possess weaker attractions to the negative oxygen end of the water molecule.The prolonged mixing can be thought to cause a net stripping effect of the water molecules from the ions.The latter would effect the dissolution and subsequent mobility of the siliceous material present in TMW and WG, leading to a less intense attack on the silicon-oxygen bonds and thus a reduction in mechanical performance, as verified by the results in Fig. 6.Further interpretation of this is shown by the ATR-FTIR spectra of the activator mixed for 5 and 20 min in Fig. 8.The 3,270 cm −1 band (which is a sensitive and well-defined band corresponding to the O-H vibrations in water) is revealed to increase in intensity by 21.4%, which based on literature concerning FTIR spectra of water at different temperature (Praprotnik et al. 2004) may be considered as a significant amount.It is an indication that the activator solution mixed for 20 min possesses a higher unbound water content with fewer solvated ions and more available as free molecules.Also, visually observed after 20 min of mixing was the partial gelation of the soluble silicate anions detected by the loss of uniform fluid flow and the adherence of solid gel to the glass wall.Polymerization of silicates commonly occurs at pH close to neutral, but can also be triggered by an increased water content (Hu et al. 1993).Gelation would also contribute to reducing the effectiveness of the activator to balance the charge of the aluminate groups in the phyllosilicate, resulting in a negative effect on the kinetics of the reaction and therefore the development of mechanical strength.From a practical outlook, it must be emphasized that the preparation of the alkali activator is independent of the mixing of the final binder.Therefore, the alkali activators dependence on mixing time should not be considered to interfere with the upscaling potential of AABs.
Tungsten Mining Waste-Waste Glass AAB Curing Temperature and Curing Time Samples T20-T80 in Table 2 were made so that the effect of different curing temperatures on compressive strength of TMW-WG AAB could be studied.The prisms cast were cured under sealed conditions at 20, 40, 60, and 80°C for 24 h, then tested for compressive strength after 1, 3, 7, and 28 days.The compression strength results in Fig. 9 present details on the role of temperature on the properties of TMW-WG AAB.The compressive strength of all the samples at all ages increased with increasing curing temperature.Samples cured at 20°C (i.e., T20) did not develop appreciable compressive strength for the first 7 days of curing and were only able to attain 2.6 MPa after 28 days.The highest compressive strengths were obtained by curing at 80°C (i.e., T80), allowing the TMW-WG AAB to attain 22 MPa at 28 days.From this, it can be concluded that the reaction that took place was a temperature-driven process.van Jaarsveld et al. (2002) and Bakharev (2005) reported comparable compressive strength results for fly ash-based AABs.Curing the samples above 80°C was not attempted due to the sufficient strength gained from curing at 80°C.Higher temperatures would also require a greater energy input, a factor this study wanted to avoid by keeping the production of the binder as little energy intensive as practically possible.Fig. 10 shows the FTIR spectra of the TMW-WG blend of raw materials and the TMW-WG AAB cured at different temperatures (i.e., T20-T80).The TMW-WG AAB cured at 20°C (i.e., T20), as expected, displays the highest absorbance, which can be inferred as reduced hardening activity and thus slow strength development.The spectra of samples cured at 40 and 60°C (i.e., T40 and T60) match each other closely, indicating that similar molecular structures are present in both samples when curing at the respective temperatures.However, the change in absorbance for the sample cured at 80°C (i.e., T80) is more evident.The latter spectrum shows a great reduction in absorbance and broadening between 850 and 1,100 cm −1 associated with the Si-O-Si symmetric stretching vibrations for the gel product and is an indication of increased activation.A similar feature can be observed at 775 and 694 cm −1 , the region of the spectrum also representing symmetric stretching vibration of the raw material Si-O bonds.The development of a more amorphous gel phase with the increase in curing temperature can be inferred from the spectrum of the TMW-WG AAB sample at 80°C matching that of the raw WG, which is confirmed to be inherently amorphous from the XRD results (Fig. 3).Nonetheless, the presence of asymmetric stretching vibration (Si-O-Si) related to nonsolubilized particles at ∼1,000 and ∼450 cm −1 in the TMW-WG AAB indicates that unreacted precursor materials are still present, supporting the same result found in the XRD analysis.Milling the precursor materials to a fine particle size has been shown to improve reactivity and dissolution in an alkali activator solution.In the case of fly ash, Temuujin et al. (2009) showed that vibration milling could reduce the median particle size by more than 50% and improve the compressive strength by 80%.This method of mechanical activation could potentially be used to improve the dissolution properties of TMW further, as long as the additional energy input did not compromise the low-energy potential of the TMW-WG AAB.
Just as important as curing temperature is the AAB heat curing duration.Samples D4-D36 in Table 2 were prepared to study the effect of curing time on the compressive strength of TMW-WG AAB.Samples were cured in sealed conditions for 4, 12, 24, and 36 h at 80°C and tested for compressive strength after 1, 3, 7, and 28 days.Fig. 11 shows that the compressive strength improves with an increase in curing time from 4 to 24 h.The improvement in compressive strength continues at an even higher rate when the curing time increases from 12 to 24 h.However, after 36 h of curing a depreciation of the compressive strength at 36 h (identified by the square on the 1-day curve in Fig. 11), 3 and 7 days is observed, leaving the 28-day strength unchanged.Thus, it can be concluded that the activation reaction that took place was timedependent.Fig. 12 shows the SEM images of TMW-WG AAB samples cured at 80°C for 24 and 36 h.The microstructure of the sample cured for 24 h consists of close-packed quasi-unreacted WG particles embedded in a continuous matrix of gel products, while the sample cured for 36 h exhibits visible contraction, particularly  Mo et al. (2014) suggested that the contraction of AAB samples cured under sealed conditions at 80°C occurs after 7 days.However, the results of this study suggest that contraction can initiate as early as 36 h.It is possible that prolonged exposure to the elevated temperature may have led to the water evaporation rate being greater than that of resaturation, thus triggering the accumulation of internal stresses and subsequent contraction of the AAB matrix.
The absorbance spectra for the raw TMW-WG blend and TMW-WG AAB cured for varying periods of time (i.e., D4-D36) are shown in Fig. 13.A reduction in the absorption intensity of the main bands at ∼1,000, ∼775, and ∼446 cm −1 indicates that longer curing times led to the further dissolution of Si-O from the raw materials.Also, the position of Si-O bending vibration peaks shifted from 999 and 463 cm −1 in the raw TMW-WG to 989 and 446 cm −1 , respectively, for the TMW-WG AAB specimen cured for 24 h, a type of shift associated with a greater extent of polymerization in aluminosilicates (Sarkar et al. 2015).Also, the absorbance spectrum for the TMW-WG AAB sample cured for 24 h (i.e., D24) displays lower absorbance intensities than the TMW-WG AAB sample cured for 36 h.It can be inferred from this latter result that curing times above 24 h can lead a reduction in Si-O dissolution and complements the mechanical strength results in Fig. 11, which clearly show reductions in compressive strength for samples cured for 36 h.Previous research regarding the curing time of AABs made from fly ash (Li et al. 2013) and metakaolin (Heah et al. 2011) have uncovered similar results.Also, the broadening of the characteristic bands between 1,100-850 cm −1 and 800-750 cm −1 implies the overlap of more bands with a higher intensity, which in this case is attributed to the asymmetric stretching vibrations of T-O-Si (where T = Si or Al) (Khater 2013).

Conclusions
The effect of waste glass addition to tungsten mining waste alkaliactivated binders was assessed by strength testing, XRD, SEM, and FTIR analyses.Additionally, preparation conditions such as activator mixing time, curing temperature, and curing time on hardening kinetics was assessed, leading to the following discoveries: • The addition of WG is a very sustainable and practical method of improving TMW's degree of amorphicity, compared with traditional calcination treatments.Up to 40% by weight of WG with a mean particle size of 39.6 μm can be successfully blended with TMW to increase the amorphous nature of the binary blend by 21% without the initiation of the alkali-silica reaction.• Prolonged activator mixing can reduce the dissolution of the aluminosilicate precursor due to fewer available alkali metal ions in solution.The initiation of silicate gelation due to prolonged stirring would also contribute to reducing the activator effectiveness.The correct preparation of the activator solution is imperative and would be expected to extend to other classes of alkali-activated cementitious systems.Fig. 13.ATR-FTIR absorbance spectra of as received raw TMW-WG and TMW-WG AAB at 28 days cured at 80°C for 4, 12, 24, and 36 h

Table 1 .
Chemical Composition of Raw TMW and WG Determined by SEM-EDX

Table 2 .
Summary of Preparation and Curing Regimes for the Variables Studied Fig. 1.SS-SH activator solution temperature measurement setup © ASCE 04017181-3 J. Mater.Civ.Eng.
• The optimum conditions for obtaining the most significant dissolution of the aluminosilicate oxides were curing for 80°C for 24 h.When curing time is greater than 24 h, i.e., 36 h as investigated in this study, it can lead to a reduction in compressive strength and contraction of the AAB matrix, even under sealed conditions.Partial financial support from the European Commission Horizon 2020's MARIE Skłodowska-CURIE Research and InnovationStaff Exchange Scheme through the Grant 645696 (i.e., REMINE project) is greatly acknowledged.The first author thanks Thomas Gerald Gray Charitable Trust and Brunel University London for providing fees and a bursary to support his Ph.D. study.