Lightweight Alkali-Activated Material from Mining and Glass Waste by Chemical and Physical Foaming
Publication: Journal of Materials in Civil Engineering
Volume 31, Issue 3
Abstract
A foamed alkali-activated material (FAAM) based on tungsten mining waste (TMW) and municipal waste glass (WG) is fabricated by using aluminum powder and organic surfactant foaming agents. The compressive strength and density of the FAAM are investigated in terms of different parameters of production and formulation, including curing temperature as well as the dosage of , foaming agent, foam catalyzing agent, and stabilizing agent. FAAM made with aluminum powder consists of smaller open macropores and exhibits higher compressive strength compared with FAAMs with larger closed macropores obtained by organic surfactant counterparts. The final aluminum powder–based FAAM reaches a 7-day compressive strength in excess of 3 MPa and a density below . The implementation of an appropriate amount of foam stabilizer leads to a further 15% increase in compressive strength, 6% reduction in density, and a thermal conductivity below . The FAAM explored in this study represents an ideal material for building envelope insulation.
Introduction
The development and application of lightweight cementitious materials have in recent decades grown very rapidly, and such materials are among the leading technology in the special-purpose concrete category (Dhir et al. 2005). Autoclaved aerated concrete (AAC) is primarily used for making lightweight blocks to build partition walls. The lightweight nature of the blocks means that they impose a minimum loading on the building and provide good thermal and sound insulation (Mousa and Uddin 2009). Prefabricated panels can also be made from lightweight cementitious materials, with the latest innovation being hollow-core interlocking panels (Thanoon et al. 2004). Another useful application of lightweight cementitious materials is void filling for structural stabilization of disused structures (Amran et al. 2015).
Approximately 70% of heat energy is lost through the building envelope from typical residential housing without proper thermal insulation (O’Grady et al. 2017), making building insulation one of the fastest-growing applications of lightweight cementitious materials (Amran et al. 2015).
The industry has been working hard to develop ecofriendly and energy-efficient construction materials due to the increase in market demand. With the exception of organic insulation materials, which are based on a renewable and recyclable material, polymer-based insulation materials are associated with a host of environmental hazards in terms of toxicity. Polymer foam materials such as polystyrene and polyethylene remain very popular materials for insulation and make up almost half the market (Shen et al. 2009). Polystyrene is classified as a possible human carcinogen (Unwin et al. 2013), and the production of expanded polystyrene foam (EPS) has a global warming potential (GWP) 7 times greater than that of carbon dioxide (Pargana et al. 2014). Hence, the use of lightweight cementitious materials can constitute an effective method of energy conservation and environmental protection, particularly for the thermal-insulation engineering of buildings.
Currently, technologies for insulating performance are being explored, such as aerogels (Baetens et al. 2011) and vacuum insulating panels (VIPs) (Baetens et al. 2010). However, these cannot be produced in a cost-effective manner and are too fragile to meet the durability needs that are critical for mainstream building products (e.g., VIPs cannot be nailed, and lose thermal resistance rapidly if perforated), making them impractical solutions for today’s building environment.
There were several recent studies about lightweight foamed alkali-activated materials (AAM), which are referred to as geopolymers in some literature as well, based on fly ash (Najif and El-Hassan 2018) and bottom ash (Görhan and Kürklü 2014). AAMs have been demonstrated to possess many of the necessary qualities a lightweight cementitious material should display, namely high temperature resistance (Cheng-Yong et al. 2017), low shrinkage (Duxson et al. 2007), low coefficient of permeability (Tenn et al. 2015), low thermal conductivity (Wang et al. 2010) and good nailability (Duan et al. 2016). Furthermore, the appeal of being able to use high volumes of industrial waste materials for the production of AAMs and thus reduce the environmental pollution from portland cement is an added benefit.
So far, in building applications, research into foamed alkali-activated materials (FAAMs) is limited to structural-grade concrete with midrange densities of and compressive strengths of 13–15 MPa (Cheng-Yong et al. 2017), (Abdullah et al. 2012; Liu et al. 2014; Zhang et al. 2015). Of the few studies conducted to produce high-performance FAAMs, the resulting materials possessed either high insulating properties coupled with very low compressive strength (Feng et al. 2015) or high compressive strength coupled with poor thermal insulating properties (Wang et al. 2010). However, to the authors’ best knowledge, the use of FAAMs as a high-performance insulation material with high mechanical resistance and low thermal conductivity has not been proven.
This study investigated the potential of producing a high-performance FAAM made entirely from tungsten mining waste (TMW) and municipal waste glass (WG), which could satisfy not only thermal performance but also mechanical strength requirements of similar-grade products. The compatibility of a natural foam catalyzer and foam stabilizing agent were investigated in order to improve both the thermal insulation and compressive strength performance. In addition, the preparation of a FAAM using mechanically preformed foam composed of an anionic surfactant and the alkali activator, never reported in previous works, was studied.
Materials and Methods
Materials and Chemicals
The precursor materials used to produce the FAAM in this investigation consisted of tungsten mining waste and municipal waste glass. 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 micromorphology of the TMW and WG was presented by Kastiukas et al. (2016). The chemical composition of TWM and WG, determined by a sequential benchtop wavelength dispersive X-ray fluorescence (WD-XRF) spectrometer (Supermini200, Rigaku, Japan) mounted with LiF(200) and PET crystals, is given in Table 1. The raw materials used for the alkali activator were 98% pure sodium hydroxide (NaOH) (SH) (Fisher Scientific, Schwerte, Germany), and sodium silicate () (SS) (Solvay, Póvoa de Santa Iria, Portugal).
| Component | TMW | WG |
|---|---|---|
| 0.51 | 12.44 | |
| MgO | 2.16 | 1.76 |
| 14.89 | 2.12 | |
| 49.17 | 68.71 | |
| 8.98 | 0.33 | |
| 2.92 | 0.77 | |
| 13.69 | 1.48 | |
| CaO | 0.58 | 10.04 |
| 0.32 | 0.00 | |
| 0.50 | 0.00 | |
| ZnO | 1.25 | 0.00 |
| CuO | 0.32 | 0.00 |
| 4.26 | 0.00 |
Foaming was achieved by either a chemical foaming technique or a physical foaming technique. Aluminum powder with purity 99%, average particle size 75 μm, and molar mass (Sigma Aldrich, Dorset, United Kingdom) was used as the foaming agent for the chemical foaming technique. Sodium dodecyl benzenesulfonate (SDBS) (Sigma Aldrich), with molecular weight , was used for the physical foaming technique due to its ionic nature and thus enhanced foam stability compared with nonionic surfactants (Stubenrauch and von Klitzing 2003).
Manganese dioxide () with particle size less than 10 μm and molecular weight (Sigma Aldrich) was used to catalyze the reaction of the chemical foaming process. Starch (Sigma Aldrich) which is a natural, high-polymeric carbohydrate, was used to stabilize the chemical foaming process.
Methods
First, the essential parameters associated with the production of a FAAM were investigated, namely the curing temperature and dosage of (mass ratio of total in the activating solution to precursor). The optimum curing temperature and dosage of in terms of density were used as benchmarks and carried forward to produce the reference sample for evaluating the effects of manganese dioxide and starch.
The mix parameters analyzed through a laboratory experiment of 18 TMW-WG-FAAM samples were curing temperature (40°C, 60°C, 80°C, and 100°C), dosage of (3.1%, 3.3%, and 3.5%), aluminum powder content (3%, 6%, and 9% by weight), surfactant content (2%, 4%, and 6% by weight), content (0.2%, 0.4%, and 0.6% by weight) and starch content (2%, 4%, and 6% by weight).
All sample preparation was carried out in a laboratory maintained at 20°C. For the preparation of the nonfoamed base TMW-WG-AAM, the synthesis conditions for achieving the highest strength and satisfactory workability were adopted based on previously published results (Kastiukas et al. 2017). The precursor consisted of TMW and WG with a mass ratio of . The alkali activating solution consisted of 10M sodium hydroxide solution (plus the sodium silicate concentration) and 8% by weight water. The mass ratio of the alkali activating solution and precursor was fixed at 0.22.
To determine the relationship between the various parameters and indicators, the horizontal -axis presented the parameters, i.e., curing temperature, percent dosage of , foaming agent content, manganese dioxide content, and starch content, whereas the vertical -axis presented the average of the assessment indicators, i.e., compressive strength and density.
Chemical Foaming Method
The principle of chemical foaming with aluminum powder is based on the reaction between aluminum and SH to produce gas, which initiates the expansion of the system according to the following chemical reaction formula (Hajimohammadi et al. 2017):
(1)
The TMW and WG were dry-blended in a commercial mixer at 300 rpm for 5 min, forming the precursor materials. The alkali-activating solution was slowly added to the precursor materials and stirred for 2.5 min at 200 rpm, followed by 2.5 min at 500 rpm to form the AAM paste. The aluminum powder was subsequently added to the AAM by weight of sodium hydroxide and stirred for a further 1 min at 350 rpm. Plastic molds were filled with the paste in two stages. The TMW-WG-FAAM was then left to rest until the foaming process was complete. The rest period depended on the quantity of aluminum powder and the dosage of because different combinations produced different rates of expansion.
Mechanically Preformed Foaming Method
The anionic surfactant and the alkali activating solution were combined [Fig. 1(a)] and mixed at 1,200 rpm for 5 min to form the foamed alkali-activating solution [Fig. 1(b)]. TMW and WG were dry-blended in a commercial mixer at 300 rpm for 5 min, forming the precursor materials, and the foamed alkali-activating solution was mixed into the precursor at 300 rpm for 5 min [Fig 1(c)]. Fig. 1(d) shows the fresh surfactant TMW-WG-FAAM immediately after mixing. A beater attachment was used for the mixing to allow more air to be entrapped into the TMW-WG-FAAM.
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FAAM Heat-Curing Method
The specimens were placed in a temperature- and humidity-controlled environmental chamber at 95% relative humidity (RH). The curing temperature was initially evaluated between 40°C and 100°C, with the most appropriate temperature in terms of compressive strength used for the production of subsequent FAAM samples. After 24 h of curing, the prismatic FAAM samples were demolded, and each was then cut into three cubes.
Thermal Conductivity
The thermal conductivity was measured with a thermal conductivity meter (Fox 200, TA Instruments, New Castle, Delaware). The steady-state heat flux through the rectangular block samples was measured for a temperature gradient of 10°C between the upper and the lower face of the sample. Three identical samples for each TMW-WG-FAAM were measured for evaluation of the thermal conductivity. Before measurement, the samples were left for 12 h at 80°C and placed in a dry chamber for cooling for 30 min without moisture absorption.
Compressive Strength
The compressive strength of the TMW-WG-FAAM cubes was tested after 7 days in accordance with EN 196-1 (CEN 2016) using a 50-kN universal testing machine (Instron 5960, High Wycombe, United Kingdom) at a constant loading rate of . The compressive strength value was the average of values obtained from three specimens.
Imaging
TMW-WG-FAAM samples were vacuum impregnated with epoxy resin doped with a fluorescent dye (EpoDye, Solvent Yellow 43, Ballerup, Denmark) to highlight the pores. The samples were polished using a bench-top planar grinding machine (PlanarMet 300, Buehler, Lake Bluff, Illinois) and imaged using a fluorescence microscope (M205 FCA, Milton Keynes, Leica, United Kingdom). Images were analyzed using open source software ImageJ, version 1.8.0 using a sample surface area of .
Results and Discussion
TMW-WG FAAM by Chemical Foaming Technique
Effect of Heat Curing
Fig. 2 shows the effect of curing temperature on the 7-day compressive strength and density of the TMW-WG-FAAM samples using 6% by weight aluminum powder, , and an additional 8% by weight mixing water. The compressive strength of the sample increased with curing temperature, whereas the density remained in practical terms unchanged within the range . As expected, the lowest compressive strength was attained by the sample cured at the lowest temperature (i.e., 40°C), reaching 3.15 MPa. Likewise, the compressive strength increased with the increase in curing temperature due to the accelerated ion diffusion rate between the liquid and solid material, thus producing a denser colloidal structure (Sindhunata et al. 2006). TMW-WG-FAAM samples cured at the highest temperature, i.e., 100°C, obtained a compressive strength of 5.45 MPa. The ultimate compressive strength and density of the samples were not found to be interdependent, and thus the optimal curing temperature of TMW-WG-FAAM may be based on a compromise of the compressive strength. In this case, the 80°C-cured sample attained only a 4.6% lower compressive strength than the 100°C-cured sample but consumed approximately 40 kWh less energy during curing [based on the energy performance of a Weiss, C340-40 model (Loughborough, United Kingdom) environmental chamber operating for 24 h]. Considering the energy consumption during manufacturing, mechanical performance, and thermal resistance, curing at 80°C was chosen to be the optimum curing temperature, in line with results obtained by other studies (Rovnaník 2010), and thus was used for the preparation of all subsequent samples.
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Effect of Dosage of
Fig. 3 demonstrates the effect of the 3.1%, 3.3%, and 3.5% on the 7-day compressive strength and density of the TMW-WG-FAAM samples made using 6% by weight aluminum powder and 8% by weight mixing water. The density of TMW-WG-FAAM clearly decreased with the increase of the percentage of . The formation of gas led to a foaming effect which was enhanced with the increase of SH. Increasing the dosage of from 3.1% to 3.5% decreased the density by 49%, from 1.34 to . The increased foaming increased the porosity and reduced the density, but was naturally coupled with a reduction in the compressive strength of the TMW-WG-FAAM. In this case, the compressive strength decreased from 11.36 to 3.3 MPa. Under normal circumstances, aluminum does not react with water, because an impermeable protective layer composed of aluminum hydroxide forms within seconds (Hajimohammadi et al. 2017). With the addition of sodium hydroxide, the aluminum hydroxide goes into solution, and the layer of aluminum oxide previously formed by passive corrosion is dissolved. For this reason, the alkali-activating solution with a low content (less than 3.1%) involved a very slow reaction due to insufficient SH, leading to reduced volumetric expansion of the foam.
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Effect of Aluminum Powder Content
Fig. 4 shows the effect of 3%, 6%, and 9% by weight aluminum powder dosage on the 7-day compressive strength and density of the TMW-WG-FAAM sample made using 3.5% and 8% by weight mixing water. The sample density obtained with 3% by weight aluminum powder was , which decreased to 0.68 and for 6% and 9% by weight aluminum powder dosages, respectively. The compressive strength decreased by 67%, from 9.2 to 3 MPa. The reduction in compressive strength with the increase of aluminum powder dosage was expected and was due to the straightforward fact that more aluminum powder was available to react with the SH, producing more gas. Additionally, the high reaction rate between the aluminum powder and SH would have also led to the premature depletion of SH, reducing its availability for the required dissolution of aluminosilicate precursors, a factor known to interrupt the attainment of mechanical strength in AAMs (Ravikumar and Neithalath 2012). It can also be deduced that the extent to which the foaming action and thus reduction in density occurs is less dominant with the increase of aluminum powder than with the increase of the alkali content, i.e., percentage. The latter would make the alkali content and thus the appropriate optimization of the activating solution the controlling factor in aluminum powder FAAMs.
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Effect of Manganese Dioxide Content
Fig. 5 compares the effect of 0.2%, 0.4%, and 0.6% by weight manganese dioxide catalyzing agent dosage on the 7-day strength of TMW-WG-FAAM sample made using 6% by weight aluminum powder, , and 8% by weight mixing water. With the initial presence of 0.2% by weight manganese dioxide, the compressive strength of TMW-WG-FAAM significantly decreased by 61%, from 3.3 to 1.27 MPa. As the manganese dioxide content increased from 0.2% to 0.4% and 0.6% by weight, there appeared to be a much steadier reduction in the density and compressive strength. The large initial decrease and subsequent gradual reduction in density and thus compressive strength was due to the thermite reaction between the manganese dioxide and the aluminum powder foam. With the presence of manganese dioxide, the foaming action was observed to be more unstable, resulting in excessive size and subsequent rupture of bubbles. Therefore, it could be concluded that the incorporation of manganese dioxide should be avoided in aluminum powder FAAMs.
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Effect of Starch Content
Fig. 6 shows the effect of 2%, 4%, and 6% by weight starch on the density and compressive strength of TMW-WG-FAAM made with 6% by weight aluminum powder, , and 8% by weight mixing water. With the addition of 2% by weight starch, the density only marginally decreased, from 0.68 to , whereas the compressive strength had a more noteworthy increase, from 3.3 to 3.8 MPa. This indicates that starch did not necessarily participate in the chemical foaming process, but did, however, improve the compressive strength. Starch, being a polysaccharide, was likely able to achieve this improvement in compressive strength due to its aggregating action in aluminosilicate interparticle bonds (Novais et al. 2016). Nonetheless, when the starch concentration increased to 4% and 6% by weight, the compressive strength significantly decreased, coupled with an increase in the density. The addition of starch at greater than 2% by weight increased the relative concentration of particles in the system, thus increasing the reaction time and subsequent formation of reaction products. The loss of compressive strength could be explained by the reduced liquid:solid ratio due to the low molecular weight of starch, resulting in a prolonged coagulation time of the FAAM and reduced paste fluidity. The reduced fluidity due to the increased starch content created an open-textured material and allowed the bubbles to coalesce (circled in Fig. 7) and the gas generated during the aluminum powder and SH reaction to escape.
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TMW-WG FAAM by Physical Foaming Technique
Anionic surfactant contents of 2%, 4%, and 6% by weight were investigated in the preparation of the surfactant TMW-WG-FAAM. In all cases, the precursor:foam ratio was maintained at a constant ratio of 0.6.
Fig. 8 compares the effect of 2%, 4%, and 6% by weight anionic surfactant on the compressive strength and density of the TMW-WG-FAAM samples made with and 8% by weight mixing water. The compressive strength of the samples increased by 40% with an increase in the dosage of surfactant from 2% to 4% by weight, from 1.59 to 2.68 MPa. However, the density remained steady between 0.71 and . The increase in surfactant from 2% to 4% by weight did not lead to entrainment of more air in the sample, thus explaining the approximately constant density. Upon the addition of 6% by weight surfactant, the density of the sample increased, coupled with a reduction in the compressive strength. A likely explanation of the foaming inhibition with increased amounts of surfactant may be the presence of and ions from the precursor materials i.e., the TMW and WG, which would have a strong affinity for the negatively charged carboxylate end of the surfactant molecules. This would essentially deactivate the surfactant and thus interrupt the foaming. Furthermore, increased surfactant content may also have led to an unnecessary high foam content, increasing the drainage of water around the foam, thus increasing the likelihood of bubble collapse. However, further tests of increased surfactant content must be performed to confirm its impact on the compressive strength of TMW-WG-FAAM.
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FAAM Pore Imaging and Thermal Conductivity
Grey-level histogram analysis followed by a noise-cleaning process were performed on medium-magnification grey-scale surface images of TMW-WG-FAAM made with aluminum powder and surfactant. This procedure revealed clear outlines of all the pores and allowed for the calculation of their size by dividing the sum of their pixels by the total pixels in the image. Images of the deconvoluted TMW-WG-FAAM pore structures are presented in Fig. 9. In TMW-WG-FAAM made by chemical foaming technique [Fig. 9(a)], most of the pore walls, or surfaces of the pores, were broken and interconnected, indicating that an open-pore structure formed during foaming between the aluminum powder and SH. In comparison, most of the pores in TMW-WG-FAAM by the physical foaming technique [Fig. 9(b)] were spheroidal but possessed little connectivity, indicating that the use of a surfactant as a foaming agent leads to a closed foam structure. In addition, the average area of the pores in TMW-WG-FAAM formed by the physical foaming technique, (excluding the three large pores at the bottom right of Fig. 9(b), which were assumed to have formed during compaction), was 10% lower than the average pore size of the TMW-WG-FAAM formed by the chemical foaming technique, . The open-cell structure and larger average pore size of the chemical foaming technique allow for more air to be trapped within the material, thus leading to lower density and thus thermal conductivity.
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Using the images in Figs. 9(a and b), quantification of pore-area distribution using the variation of the pore-area fraction along the depth of the specimens was also performed. The images were divided into strips, and the pore-area fractions in each strip were determined. The variation of pore area [Fig. 9(c)] corresponded to the average pore area fraction measurements on 11 different horizontal sections for TMW-WG FAAM foamed with aluminum powder and surfactant. There was less variation with depth in the pore-area fraction of the TMW-WG FAAM made with surfactant. This indicates a more uniform distribution of pores across the TMW-WG FAAM made with surfactant, confirming observations from Fig. 9(b) which show it to possess more-spherical and uniformly distributed pores. For the TMW-WG FAAM made with aluminum powder, a higher degree of variation was observed through the image analysis, implying a less stable foam structure and the possibility of foam clogging, particularly at the top of the sample, where the porosity was determined to be approximately 18% less than at the bottom of the sample.
Table 2 summarizes the primary TMW-WG-FAAM properties, i.e., density, 7-day compressive strength, and thermal conductivity, for samples produced with the aluminum powder and surfactant foaming agents. Due to the open-pore structure of TMW-WG-FAAM formed by the chemical foaming technique, it achieved a lower density of and a thermal conductivity of . The TMW-WG-FAAM formed by the physical foaming technique achieved both a higher density and higher thermal conductivity of and , respectively, due to the closed-pore structure and smaller average pore area. In practice, closed-cell structures usually possess higher compressive strengths due to the higher core density. However, the open-cell TMW-WG-FAAM formed by the chemical foaming technique achieved a compressive strength of 3.8 MPa, while the closed foam structure of the TMW-WG-FAAM formed by the physical foaming technique only achieved 2.68 MPa. This is an interesting observation and leads to the postulation that the chemical foaming technique is not only linked to pore characteristics such as shape and connectivity as previously mentioned, but also to its strength. In this case, the TMW-WG-FAAM formed by the chemical foaming technique is thought to have contributed to reinforcing the pore wall structure; however, this requires further investigation.
| Sample | Density () | Compressive strength (MPa) | Thermal conductivity (W/mK) |
|---|---|---|---|
| Unfoamed TMW-WG-AAM | 2.10 | 61.0 | 0.280 |
| 6% by weight aluminum powder TMW-WG-FAAM with 2% by weight starch | 0.64 | 3.8 | 0.090 |
| 4% by weight surfactant TMW-WG-FAAM | 0.77 | 2.68 | 0.150 |
| Aerated concrete (AAC) (Hlaváček et al. 2015) | 0.60 | 4.5 | 0.160 |
| Foamed concrete (Wei et al. 2013) | 0.60 | 5.2 | 0.165 |
| Inorganic foams (Hlaváček et al. 2015) | 0.67 | 6.0 | 0.145 |
| Geopolymer foam concrete (Arellano Aguilar et al. 2010) | 0.60 | 1.3 | 0.470 |
| Geopolymer foam (Bai et al. 2017) | 0.58 | 4.4 | 0.158 |
| Porous fly ash geopolymer (Novais et al. 2016) | 0.56 | 1.23 | 0.107 |
Table 2 also lists thermophysical properties of traditional cement-based insulation materials and recently published foamed alkali-activated materials. Comparing the best-performing TMW-WG-FAAM reported in this study (prepared with 6% by weight aluminum powder and 2% by weight starch) and other materials, the TMW-WG-FAAM significantly outperforms traditional cement-based insulation materials such as AAC, foamed concrete, and cement expanded vermiculite in terms of thermal conductivity, and the combination of density and compressive strength is also unmatched.
Conclusions
This study revealed that alkali-activated foamed materials based on tungsten mining waste and waste glass can be successfully prepared by a chemical foaming method using aluminum powder and a physical foaming method using preformed foam with an anionic surfactant. The following conclusions can be drawn from the results of this work:
•
The curing temperature of TMW-WG-FAAM influenced the mechanical strength but did not affect the density. The final pore structure is formed during the initial foaming process, and thus curing temperature was chosen based on adequate compressive strength development, which in this case was 80°C.
•
The alkali content is strongly related to both the density and compressive strength of TMW-WG-FAAM, making it more of a dominant control factor than the content of aluminum powder. A dosage lower than 3.1% involves a very slow reaction due to insufficient NaOH, leading to a reduced volume of foaming.
•
The chemical foaming method with aluminum powder resulted in the creation of an open-cell pore structure, leading to significantly lower thermal conductivity and density, coupled with enhanced compressive strength.
•
Use of manganese dioxide foam catalyst agent, even at relatively low levels (0.2% by weight), resulted in unstable chemical foaming with aluminum powder and compromised compressive strength. On the other hand, the use of starch as a foam stabilizing agent led to improved compressive strength without affecting the density.
•
The combined technical and sustainability advantages of TMW-WG-FAAM make it a viable route to yield insulating materials comparable to both traditional cement-based insulation materials and other recently reported foamed alkali-activated materials.
Acknowledgments
Partial finance support from the European Commission Horizon 2020 Marie Skłodowska- Curie Research and Innovation Staff Exchange scheme through Grant No. 645696 [i.e., the Reuse of Mining Waste into Innovative Geopolymeric-based Structural Panels, Precast, Ready Mixes and Insitu Applications (REMINE) project] is greatly acknowledged.
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Journal of Materials in Civil Engineering
Volume 31 • Issue 3 • March 2019
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This work is made available under the terms of the Creative Commons Attribution 4.0 International license, http://creativecommons.org/licenses/by/4.0/.
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Received: Mar 23, 2018
Accepted: Aug 14, 2018
Published online: Dec 20, 2018
Published in print: Mar 1, 2019
Discussion open until: May 20, 2019
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