- Email: [email protected]
Characterization of geopolymer fly-ash based foams obtained with the addition of Al powder or H2O2 as foaming agents
Characterization of geopolymer fly-ash based foams obtained with the addition of Al powder or H 2 O2 as foaming agents V. Ducman, L. Korat PII: DOI: Reference:
S1044-5803(16)30020-1 doi: 10.1016/j.matchar.2016.01.019 MTL 8164
To appear in:
Materials Characterization
Received date: Revised date: Accepted date:
26 September 2015 21 January 2016 24 January 2016
Please cite this article as: Ducman V, Korat L, Characterization of geopolymer flyash based foams obtained with the addition of Al powder or H2 O2 as foaming agents, Materials Characterization (2016), doi: 10.1016/j.matchar.2016.01.019
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT
Characterization of geopolymer fly-ash based foams obtained with the addition of Al powder or H2O2 as foaming agents
IP
ZAG, Dimičeva 12, 1000 Ljubljana, Slovenia, www.zag.si
AC
CE P
TE
D
MA
NU
SC R
1
T
V. Ducman1, L. Korat1
Corresponding author: Vilma Ducman, Ph.D. Slovenian National Building and Civil Engineering Institute - ZAG Dimičeva 12, 1000 Ljubljana SLOVENIA Tel. + 386 1 2804 438, Fax. + 386 1 2804 484 e-mail:[email protected]
ACCEPTED MANUSCRIPT Abstract Recent innovations in geopolymer technology have led to the development of various different
T
types of geopolymeric products, including highly porous geopolymer-based foams, which are
IP
formed by the addition of foaming agents to a geopolymer fly-ash based matrix. These agents
SC R
decompose, or react with the liquid matrix or oxygen in the matrix, resulting in the release of gases which form pores prior to the hardening of the gel. The hardened structure has good mechanical and thermal properties, and can therefore be used for applications in acoustic panels
NU
and in lightweight pre-fabricated components for thermal insulation purposes.
MA
This study presents the results of the pore-forming process in the case when two different foaming agents, i.e. aluminium powder amounting to 0.07, 0.13 and 0.20 mass. % and H2O2 amounting to 0.5, 1.0, 1.5 and 2.0 mass. %, were added to a fly-ash geopolymer matrix. The
TE
D
physical, mechanical, and microstructural properties of the thus obtained foams, and the effects of the type and amount of the added foaming agent, are presented and discussed. Highly porous
CE P
structures were obtained in the case of both of the investigated foaming agents, with overall porosities up to 59 % when aluminium powder was added, and of up 48 % when H2O2 was
AC
added. In the latter case, when 2 % of the H2O2 foaming agent was added, finer pores (with diameters up to 500 µm) occurred in the structure, whereas somewhat larger pores (some had diameters greater than 1 mm) occurred when the same amount of aluminium powder was added. The mechanical properties of the investigated foams depended on their porosity. In the case of highly porous structures a compressive strength of 3.3 MPa was nevertheless achieved for the samples containing 0.2 % of aluminium powder, and 3.7 MPa for those containing 2.0 % of H2O2.
Keywords: geopolymer foams, aluminium powder, H2O2, porosity, X-ray micro-tomography
ACCEPTED MANUSCRIPT 1. INTRODUCTION Geopolymers are inorganic systems which consist of, firstly, a reactive solid component which
T
contains sufficient amounts of SiO2 and Al2O3 in reactive form (e.g. different types of ash, and
IP
active clays) and, secondly, an alkaline activation solution which (apart from water) mainly
SC R
contains alkali hydroxides and silicates. These are important materials which could be used to replace concrete and some other industrial materials. They possess many favourable properties such as rapid setting and hardening, good long-term properties and durability [1], as well as a
NU
good ability to immobilize toxic metals [2], and improved resistance to acids and the action of fire
MA
[3]. Natural resources like clay (after thermal activation) and natural pozzolans such as volcanic ash can be used for their preparation, as well as a considerable range of secondary resources obtained from industrial waste, such as different types of ash (fly ash, sewage sludge ash, biomass
TE
D
ash), paper sludge, and slags which result from various production processes. Since their production is mainly based on waste materials, their accelerated use could contribute significantly
CE P
to the achievement of environmental goals, including the lowering of the CO2 footprint of the construction industry [4-5].
AC
Among many products that are based on geopolymer precursors, geopolymer foams appear to be a very promising material since they are formed at temperatures below 100 oC and possess properties similar to foamed glass or foamed ceramics, both of which are produced at highly elevated temperatures, above 900 oC. The main precursor for geopolymer is fly ash. In comparison with other thermally prepared natural raw materials (e.g. metakaolin) as a starting material fly ash is beneficial both from the point of view of costs, and from that of the environment, since it has a lower level of incorporated energy, and subsequently low CO 2 emissions. Fly ash appears to be one the most promising precursors for the large-scale industrial production of geopolymer products also due to its high workability and low water demand [6]. Geopolymer foams are formed by the addition of foaming agents to a slurry consisting of fly ash
ACCEPTED MANUSCRIPT and an alkali activator solution such as H2O2 or NaOCl, or a metal powder such as aluminium or zinc powder, or a silica fume which reacts with the liquid matrix or oxygen, which decomposes
T
resulting in the release of gases [7-11], according to the following reactions: (1) (2)
SC R
Al (s) + 3H2O (l) + OH- (aq.) → Al(OH)-4 (aq) + 3/2H2 (g)
IP
H2O2 (l) → 2H2O (l) + O2 (g)
Geopolymers can be also formed by by introducing a large volume fraction of air bubbles into the
saponin, and hydrolyzed proteins [12-13].
NU
mixture, mainly by using organic foaming agents such as detergents, resin soap, glue resins,
In the case when aluminium powder or H2O2 are added as foaming agents, densities as low as 0.4
MA
g/cm3 can be reached [14-16], a microstructure which is characterized by uniformly distributed pores being obtained. The mechanical, i.e. compressive strength of such material depends on their
TE
D
density, and has been found to amount to between 1 and 10 MPa for densities of between 0.36 and 1.4 g/cm3 [10]. It has also been found [14-18] that the type of ash used (i.e. its chemical
CE P
compositions, glassy phase, and particle size), as well as the proper design of the alkali activating admixture, has a strong influence on the mechanical properties of the geopolymer and thus also of
AC
the obtained geopolymer foams. Since the porosity of geopolymer-based foams is usually of the closed type, the use of mercury porosimetry (MIP) is very limited when trying to determine the pore size distribution. This is because this technique is unable to reach closed pores, and in the case of high pressures, it breaks the walls between the pores. X-ray micro-tomography is a nondestructive technique which can be successfully used to estimate porosity in such systems. With the support of suitable image analysis software, e.g. Avizo, pore size distribution, phase distribution, and voids and/or cracks can be quantified. Different types of inorganic porous materials, such as ceramic foams [19] and building materials [20], have been successfully analysed using this technique, which can also be used for the evaluation and quantification of porosity evolution in the foaming process in glasses or glassy based systems [21-23].
ACCEPTED MANUSCRIPT The aim of the present paper was to compare the efficiency of foaming using two different foaming agents, aluminium powder and H2O2, to assess their effect on the mechanical properties
T
of the hardened material, and to monitor the development of porosity in these systems by means
IP
of micro-tomography.
SC R
2. EXPERIMENTAL 2.1 Materials
The following starting materials were used in the preparation of the investigated geopolymer
NU
foams:
MA
- fly ash whose composition is given in Table 1,
- two different foaming agents, i.e. aluminium powder (produced by: New Materials Development Gmbh, particle size D50: <5 µm), and H2O2 (hydrogen peroxide solution 30 mass. %, produced
TE
D
by: Carlo Erba reagents),
- water-glass activating solutions (sodium silicate Crystal 0112, produced by: Tennants
CE P
distribution, Ltd., SiO2:Na2O = 1.97, 54.2 mass.% water solution), and - NaOH (produced by: Donau Chemie, 41.7 mass. % water solution).
AC
Fly ash is a very fine powder, with particle size below 400 µm, having 50 wt. % of particles below 40 µm, and with a BET specific surface of 1.7 cm2/g. Different mixtures were prepared, whose compositions are given in Table 2. In the case when Al powder was used as the foaming agent, the mixtures were prepared by first thoroughly mixing together the FA and Al powder and then adding to this dry mixture a solution of water glass and NaOH; these materials were then mixed for 5 minutes, and poured into moulds having dimensions of 2 x 2 x 8 cm. In the case when H2O2 was used as the foaming agent, it was added to the solution of water glass and NaOH. After this the procedure was the same as in the case of the mixtures made using the Al powder. In all cases commercial additives for foam
ACCEPTED MANUSCRIPT stabilisation were added. The samples were then put in an oven for 24 hours at a temperature of 70 o
C in order to accelerate the geopolymeric reaction, and thus achieve hardening of the structure.
T
2.2 Techniques
IP
Density was determined by weighing the individual test specimens, and dividing the thus
density).
SC R
determined weights by the corresponding dimensions of the specimens (i.e. so-called geometrical
Mechanical strength, i.e. bending and compressive strength were determined, at an age of 4 days o
NU
(curing for first 24 hours at a temperature of 70 C and for the following 3 days exposed to room
MA
temperature), by means of Toninorm equipment (Toni Technik, Germany), using a force application rate of 0.005 kN/sec.
The microstructure of individual cross-sections of the geopolymer foam specimens were
TE
D
examined by using the back-scattered electrons (BSE) image mode of low vacuum scanning electron microscopy (SEM), using JEOL 5500 LV equipment.
CE P
X-ray micro-computed tomography was used to study the structural characteristics of all the samples of the investigated geopolymer foams, using a "Xradia µCT-400" tomograph (XRadia,
AC
Concord, California, USA), set to 80 kV and 125 µA. The size of the foam specimen was: 2.0 x 2.0 x 2.0 cm, and they were imaged using a CCD camera equipped with a 0.39X magnification optical objective and a resolution of 32 µm. A high-precision rotating stage was used, so that 1000 projection images were taken from different view-points with exposure times of 2 s per projection. In order to reconstruct the pore structure of the geopolymer foams, as well as to determine their overall porosity and pore size distribution, Avizo Fire 3D-image analysis software was used, following the process for pore segmentation and quantification as described by [23]. The ROI (region of interest) box was determined from the centre of the sample, which had a size of 1.5 x 1.5 x 1.5 cm. 3. RESULTS
ACCEPTED MANUSCRIPT 3.1 Density and mechanical characterization The results of measurements of the density and mechanical properties of foams to which
T
aluminium powder and H2O2 had been added as foaming agents are presented in Table 3. As can
IP
be seen from this table, the measured density depends on the amount of the added foaming agent.
SC R
In the case when aluminium powder amounting from 0.07 to 0.2 % was added, the measured density was between 0.64 to 0.74 g/cm3, whereas when H2O2 was added it was between 0.61 to 1 g/cm3. In both cases there is a pessimum in the density values since with higher dosages, the
NU
density did not continue to decrease, but instead, contrary to expectations, it increased (Figs. 1a
MA
and b). This can be ascribed to coalescence and a slight collapsing effect [14]. From the results of the measured mechanical properties (Fig. 2) it can be seen that, as expected, these properties as the density decreases. It can also be seen that the measured strength depends on
TE
D
the density no matter which foaming agent is added. For example sample Al 0.2, which had a density of 0.73 g/cm3, had a compressive strength of 3.3 MPa, whereas sample H 1, which had a
CE P
density of 0.71 g/cm3, had a compressive strength amounting to 3.6 MPa that was very similar to that of the sample Al 0.2.
AC
3.2 X-ray micro-tomography
Quantitative analysis was performed using the Avizo Fire 3D image analysing software program. The results with respect to total porosity (pore shares), as well as to the total volume of the pores in different size areas, are given in Table 4 and in Figs. 3 and 4. From Figure 3, which provides a two-dimensional (XY orientation) cross-section of samples obtained by micro-tomography it can be seen that, in the case when Al powder was added as a foaming agent, the pores are much bigger than when H2O2 was added (Fig. 4), where a more finely porous structure can be observed. Whereas in the case of the Al powder foaming agent the total porosity is higher (Table 4), single pores can have diameters up to 2 mm, whereas in the
ACCEPTED MANUSCRIPT case of the H2O2 foaming agent there are fewer big pores, and their dimensions are also slightly smaller (up to 1 mm).
T
From Table 4 it can be seen that the measured porosity ranges between 37 up to almost 60 % of
IP
the total volume. Since the pores do not have a regular round shape, the volume of pores
SC R
corresponding to a certain pore size range is given as a representation of the pores (instead of pore size distribution, Table 5). In order to get a better insight the average value of the pore
NU
length, Feret diameters, which is defined as the distance between the two parallel planes restricting the object/pore perpendicular to that direction (also called “caliper diameter”) is given.
MA
In cases of both foaming agents, the main share of the pores lies in the range of pores which are smaller than 104 µm3, corresponding to a pore length of 120 µm. When H2O2 is the foaming
D
agent the amount of added agent does not significantly change the pore size distribution (i.e. the
TE
number of pores and the volume of the pores), the total pore volume increasing significantly only
CE P
when, instead of 0.5 %, 1.0 or more % of H2O2 is added (Tables 4 and 5, Fig. 6). In the case of the addition of aluminium powder the quantity of the added agent has a more pronounced
AC
influence, both on total pore volume and on the pore size distribution (Tables 4 and 5, Fig. 5).
3.3 SEM analysis
Selected samples were also investigated by means of SEM. Comparing images for samples with Al powder addition and H2O2 addition it can be noticed that in the case of H2O2 addition the pores are spherical in shape, and are also more uniformly distributed than in the case when Al powder is added (Figs. 7 and 8, respectively). The results of the SEM investigations support the findings of the performed micro-tomography, but additionally provide insight into the structure of the walls between the pores. In both cases the remains of the ash’s spherical particles can be clearly seen embedded in the matrix. Also the results of the SEM analysis clearly demonstrate the effect of pore percolation, which is especially seen when a higher amount of foaming agent is added, when
ACCEPTED MANUSCRIPT a higher pressure is created due to gas release [7]. For example, in the case of sample H 1 almost
T
every pore has been percolated (Fig. 8c).
IP
4. CONCLUSIONS
SC R
Both of the foaming additives, i.e. Al powder and H2O2, proved to be successful foaming agents for the investigated geopolymer matrix. The addition of Al powder amounting to between 0.07 and 0.2 mass. % resulted in a porous structure having a density of between 0.64 and 0.74 g/cm3,
NU
whereas the addition of H2O2 amounting to between 0.5 and 2 mass. % resulted in densities from
MA
0.61 to 1.00 g/cm3. The measured compressive strengths of the tested samples were within the range from 3.3 to 4.3 MPa for those in which Al powder was added, and within the range from 2.9 to 9.3 MPa when H2O2 was added. As expected, the measured compressive strengths were in
TE
D
correlation with the density: the higher the density, the higher the compressive strength. And, in the case of both additives, the measured values of the compressive strength at a certain density
CE P
are very similar. Porosity development was evaluated by means of micro-tomography. In the case of both additives, the pores were found to be uniformly distributed throughout the samples. The
AC
results of micro-tomography and SEM have shown the difference in pore size when different foaming agents are added: the samples with added aluminium powder had higher porosities and also bigger pores than the samples with added H2O2. In both cases the results of the analysis also confirmed that, when a higher amount of the foaming agent was added, the number of pores decreased, due to coalescence. However, the volume of these pores also increased; final overall porosities of 58 and 48 % being obtained for the optimal mixtures Al 0.2, and H 1, respectively.
Acknowledgements
ACCEPTED MANUSCRIPT This work has been financially supported by the Slovenian Research Agency (ARRS) through the project Z2-6748: "Mechanisms for the strengthening of different types of ash by means of a
IP
T
geopolymerization process".
SC R
5. REFERENCES
[1] Bakharev T. Durability of geopolymer materials in sodium and magnesium sulfate solutions.
NU
Cem Concr Res 2005;35:1233–1246.
[2] Alvarez Ayuso E, Querol X, Plana F, Alastuey A, Moreno N, Izquierdo M, Font O, Moreno T, Diez S, Vázquez E, Barra M. Environmental, physical and structural characterisation of
MA
geopolymermatrixes synthesised from coal (co) combustion fly ashes. J Hazard Mater 2008;154:175–183.
TE
Miner Eng 2003;16:205–210.
D
[3] Cheng TW, Chiu JP. Fire resistant geopolymer produced by granulated blast furnace slag.
CE P
[4] Deventer JSJ, Provis JL, Duxon P. Technical and commercial progress in the adoption of geopolymer cement. Miner Eng 2012;29:89–104.
AC
[5] Provis JL. Geopolymers and other alkali activated materials: why, how, and what?. Mater Struct 2014;47:11–25.
[6] Provis JL, Duxon P, Deventer JSJ. The role of particle technology in developing sustainable construction materials. Adv Powder Technol 2010;21:2–7.
[7] Bell JL, Kriven WM. Preparation of Ceramic Foams from Metakaolin-based Geopolymer Gels. In: Lin HT, Koumoto K, Kriven WM, Norton DP, Garcia E, Reimanis I, editors. Developments in Strategic Materials: Ceramic Engineering and Science Proceedings 2008;29:97– 112.
[8] Nyale SM, Babajide OO, Birch GD, Boeke N, Petrik, LF. Synthesis and characterization of coal fly-ash foamed geopolymer. Procedia Environmental Sciences 2013;18:722–730.
ACCEPTED MANUSCRIPT
[9] Henon H, Alzina A, Absi J, Smith DS, Rossignol S. Potassium geopolymer foams made with a
T
silica fume pore forming agent for thermal insulation. J Porous Mater 2013;20:37–46.
IP
[10] Zhang Z, Provis JL, Reid A., Wang H. Geopolymer foam concrete: An emerging material
SC R
for sustainable construction. Constr Build Mater 2014;56:113–127.
[11] Prud’homme E, Joussein E, Rossignol S. Alkali-activated concrete binders as inorganic thermal insulator materials. In: Pachego-Torgal F, Labrincha JA, Leonelli C, Palomo A,
MA
Woodhead Publishing; 2015, p. 687–728.
NU
Chindaprasit P, editors. Handbook of Alkali-activated Cements, Mortars and Concretes,
[12] Abdullah MMB, Hussin K, Bnhussain M, Ismail KN, Yahya Z, Razak RA. Fly Ash-based
D
Geopolymer Lightweight Concrete Using Foaming Agent. Int J Mol Sci 2012;13:7186–7198.
CE P
2014;40:5723–5730.
TE
[13] Cilla MS, Colombo P, Morelli MR. Geopolymer foams by gelcasting. Ceram Int
[14] Masi G, Rickard WDA, Bignozzi MC, Riessen A. The influence of short fibres and foaming agents on the physical and thermal behaviour of geopolymer composites. Advances in Science
AC
and Technology 2014;92:56–61. [15] Hlavaček P, Šmilauer V, Škvara F. Alkali-activated fly ash foams – synthesis, chemophysical properties and microstructure modelling. Advances in Science and Technology 2014;92:14–19.
[16] Sanyan JG, Nazari A, Chen L, Nguyen H. Physical and mechanical properties of lightweight aerated geopolymer. Constr Build Mater 2015;79:236–244.
[17] Nazari A, Pachego-Torgal F, Cevik A, Sanjayan JG. Prediction of the compressive strength of alkali-activated geopolymeric concrete binders by neuro-fuzzy modelling: a case study. In: Pachego-Torgal F, Labrincha JA, Leonelli C, Palomo A, Chindaprasit P, editors. Handbook of Alkali-activated Cements, Mortars and Concretes, Woodhead Publishing; 2015, p. 217–235.
ACCEPTED MANUSCRIPT [18] Lodeiro IG, Palomo A, Fernandez-Jimenez A. Crucial insights on the mix design of alkaliactivated cement-based binders. In: Pachego-Torgal F, Labrincha JA, Leonelli C, Palomo A, Chindaprasit P, editors. Handbook of Alkali-activated Cements, Mortars and Concretes,
IP
T
Woodhead Publishing; 2015, p. 49–75.
[19] Maire E, Colombo PP, Adrien J., Babout L, Biasetto L. Characterization of the morphology
SC R
of cellular ceramics by 3D image processing of X-ray tomography. J Eur Cer Soc 2007;27:1973– 1981.
NU
[20] Cnudde V, Cwirzen A, Masschaele B, Jacobs PJS. Porosity and microstructure
MA
characterization of building stones and concretes. Engineering Geology 2009;103:76–83.
[21] Atwood RC, Jones JR, Lee PD, Hench LL. Analysis of pore interconnectivity in bioactive
D
glass foams using X-ray microtomography. Scripta Mater 2004;51:1029–1033.
TE
[22] Maruyama B, Spowart JE, Hooper DJ, Mullens HM, Druma AM, Druma C, Alam MKA new technique for obtaining three-dimensional structures in pitch-based carbon foams. Scripta
CE P
Mater 2006;54:1709–1713.
[23] Korat L, Ducman V, Legat A, Mirtič B. Characterisation of the pore-forming process in lightweight aggregate based on silica sludge by means of X-ray micro-tomography (micro-CT)
AC
and mercury intrusion porosimetry (MIP). Ceram Int 2013;39:6997–7005.
ACCEPTED MANUSCRIPT Tables capture:
Table 2: Composition of the investigated mixtures (all in mass. %).
T
Table 1: Chemical composition of the used fly ash.
IP
Table 3: The measured densities, bending strengths and compressive strengths (together with the
SC R
corresponding standard deviations) of the samples of geopolymer foams made with Al powder (designated as Al) and with H2O2 (designated as H) as foaming agents.
NU
Table 4: Total porosity (pore shares) of the samples of the geopolymer foams (the ROI box) obtained by microtomography.
MA
Table 5: Pore size distribution determined by means of micro-tomography for the samples
AC
CE P
TE
D
presented as the number of pores or as the volume of pores with regard to the 3D volume.
ACCEPTED MANUSCRIPT
NU MA D TE CE P AC
IP
in mass. % 2.3 52.5 23.3 7.46 6.09 2.48 0,80 2.23
SC R
Components Loss on ignition (at 950 oC) SiO2 Al2O3 Fe2O3 CaO MgO Na2O K2O
T
Table 1: Chemical composition of the used fly ash.
ACCEPTED MANUSCRIPT
Table 2: Composition of the investigated mixtures (all in mass. %).
MA D TE CE P AC
Al powder
T
66.1 66.1 66.1 65.9 65.5 65.2 64.9
NaOH (41.7 mass. % water solution) 24.4 24.4 24.4 24.3 24.2 24.1 24.0
0.07 0.13 0.20 / / / /
IP
Al 0.07 Al 0.13 Al 0.2 H 0.5 H1 H 1.5 H2
Water glass (54.2 mass. % water solution) 9.4 9.4 9.3 9.3 9.3 9.2 9.2
SC R
FA
NU
Sample designation
H2O2 (30 mass. % water solution) / / / 0.5 1.0 1.5 2.0
ACCEPTED MANUSCRIPT Table 3: The measured densities, bending strengths and compressive strengths (together with the corresponding standard deviations) of the samples of geopolymer foams made with Al powder (designated as Al) and with H2O2 (designated as H) as foaming agents.
T
IP
0.74 (0.07) 0.64 (0.07) 0.73 (0.03) 1.00 (0.05) 0.71 (0.05) 0.61 (0.08) 0.66 (0.08)
Bending strength (MPa) 2.3 (0.35) 2.1 (0.31) 2.4 (0.30) 3.6 (0.31) 2.6 (0.40) 2.0 (0.30) 2.2 (0.25)
SC R
Density (g/cm3)
AC
CE P
TE
D
MA
NU
Sample designation (% addition of the foaming agent) Al 0.07 Al 0.13 Al 0.2 H 0.5 H1 H 1.5 H2
Compressive strength (MPa) 3.7 (1.36) 4.3 (1.20) 3.3 (0.92) 9.3 (1.52) 3.6 (1.11) 2.9 (0.30) 3.7 (0.54)
ACCEPTED MANUSCRIPT Table 4: Total porosity (pore shares) of the samples of the geopolymer foams (the ROI box) obtained by microtomography. Al 0.13
Al 0.2
H 0.5
Total porosity (%)
47.9
53.4
58.4
37.9
H1
T
Al 0.07
48.1
AC
CE P
TE
D
MA
NU
SC R
IP
Sample designation
H 1.5
H2
46.3
44.9
ACCEPTED MANUSCRIPT
Table 5: Pore size distribution determined by means of micro-tomography for the samples presented as the number of pores or as the volume of
Al 0.2
H 0.5
CR
Al 0.13
H1
H 1.5
H2
3D
Number Volume
Number Volume
Number
Volume
Number Volume
Number
Volume
Number
Volume
Number
Volume
Feret diam.
volume
of pores
of pores
of pores
of pores
of pores
of pores
of pores of pores
of pores
of pores
of pores
of pores
of pores
of pores
(µm)
(µm3)
(%)
(%)
(%)
(%)
(%)
(%)
6000
>1E9
2.69
74.26
4.92
68.20
1.11
57.91
US
Al 0.07
IP
T
pores with regard to the 3D volume.
4000
1E8-1E9
5.07
24.62
13.35
31.20
5.11
1300
1E6-1E8
16.72
0.91
9.32
0.52
300
5E4-1E5
11.68
0.10
7.65
250
1E4-5E4
31.61
0.09
120
<1E4
32.22
0.02
(%)
(%)
(%)
(%)
(%)
(%)
(%)
2.34
53.33
3.66
51.44
2.36
47.05
2.52
42.89
39.62
7.60
45.67
13.30
48.11
11.92
52.22
16.44
56.42
5.97
2.22
6.46
0.79
3.10
0.36
3.83
0.59
3.20
0.60
0.03
5.52
0.08
7.19
0.07
4.69
0.03
5.19
0.04
3.56
0.02
25.60
0.04
24.80
0.12
28.69
0.10
30.54
0.05
27.11
0.07
24.84
0.05
39.16
0.01
57.50
0.05
47.73
0.04
44.70
0.02
49.60
0.03
49.44
0.02
AC
CE P
TE D
MA N
(%)
ACCEPTED MANUSCRIPT Figures capture:
Figure 1: Measured densities of the investigated samples of geopolymer foams made with (a) Al
T
powder and (b) H2O2, as foaming agents.
IP
Figure 2: Measured bending strengths and compressive strengths of the investigated samples of
SC R
geopolymer foams made with Al powder and H2O2, as foaming agents.
Figure 3: Slice images (XY) and 3D images obtained by micro-tomography of the investigated
NU
geopolymer foams in the case when Al powder was used as the foaming agent. Figure 4: Slice images (XY) and 3D images obtained by micro-tomograph of the investigated
MA
geopolymer foams in the case when H2O2 was used as the foaming agent. Figure 5: Pore size distribution determined by means of micro-tomography for the samples with
D
Al powder as a foaming agent presented as (a) the number of pores with regard to the 3D
TE
volume, and (b) as the volume of pores with regard to the 3D volume.
CE P
Figure 6: Pore size distribution determined by means of micro-tomography for the samples with H2O2 as a foaming agent presented as (a) the number of pores with regard to the 3D volume, and (b) as the volume of pores with regard to the 3D volume.
AC
Figure 7: SEM analysis of the samples with the addition of Al powder as a foaming agent; (a) and (b) sample Al 0.07, and (c) and (d) sample Al 0.13, at two different magnifications. Figure 8: SEM analysis of the samples with the addition of H2O2 as a foaming agent; (a) and b) sample H 0.5, and (c) and (d) sample H 1, at two different magnifications.
ACCEPTED MANUSCRIPT
AC
CE P
TE
D
MA
NU
SC R
IP
T
Figure 1
ACCEPTED MANUSCRIPT
AC
CE P
TE
D
MA
NU
SC R
IP
T
Figure 2:
ACCEPTED MANUSCRIPT
AC
CE P
TE
D
MA
NU
SC R
IP
T
Figure 3:
ACCEPTED MANUSCRIPT
AC
CE P
TE
D
MA
NU
SC R
IP
T
Figure 4:
ACCEPTED MANUSCRIPT
AC
CE P
TE
D
MA
NU
SC R
IP
T
Figure 5:
ACCEPTED MANUSCRIPT
AC
CE P
TE
D
MA
NU
SC R
IP
T
Figure 6:
ACCEPTED MANUSCRIPT
AC
CE P
TE
D
MA
NU
SC R
IP
T
Figure 7:
ACCEPTED MANUSCRIPT
AC
CE P
TE
D
MA
NU
SC R
IP
T
Figure 8:
SC R
IP
T
ACCEPTED MANUSCRIPT
MA
D TE CE P
-
Preparation of geopolymer foams based on fly ash with the addition of Al powder or H2O2 as foaming agents, Determination of density, porosity and mechanical properties of such foams, Characterization of foaming process by means of X-ray micro-tomography (µcT).
AC
-
NU
HIGHLIGHTS:
S1044-5803(16)30020-1 doi: 10.1016/j.matchar.2016.01.019 MTL 8164
To appear in:
Materials Characterization
Received date: Revised date: Accepted date:
26 September 2015 21 January 2016 24 January 2016
Please cite this article as: Ducman V, Korat L, Characterization of geopolymer flyash based foams obtained with the addition of Al powder or H2 O2 as foaming agents, Materials Characterization (2016), doi: 10.1016/j.matchar.2016.01.019
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT
Characterization of geopolymer fly-ash based foams obtained with the addition of Al powder or H2O2 as foaming agents
IP
ZAG, Dimičeva 12, 1000 Ljubljana, Slovenia, www.zag.si
AC
CE P
TE
D
MA
NU
SC R
1
T
V. Ducman1, L. Korat1
Corresponding author: Vilma Ducman, Ph.D. Slovenian National Building and Civil Engineering Institute - ZAG Dimičeva 12, 1000 Ljubljana SLOVENIA Tel. + 386 1 2804 438, Fax. + 386 1 2804 484 e-mail:[email protected]
ACCEPTED MANUSCRIPT Abstract Recent innovations in geopolymer technology have led to the development of various different
T
types of geopolymeric products, including highly porous geopolymer-based foams, which are
IP
formed by the addition of foaming agents to a geopolymer fly-ash based matrix. These agents
SC R
decompose, or react with the liquid matrix or oxygen in the matrix, resulting in the release of gases which form pores prior to the hardening of the gel. The hardened structure has good mechanical and thermal properties, and can therefore be used for applications in acoustic panels
NU
and in lightweight pre-fabricated components for thermal insulation purposes.
MA
This study presents the results of the pore-forming process in the case when two different foaming agents, i.e. aluminium powder amounting to 0.07, 0.13 and 0.20 mass. % and H2O2 amounting to 0.5, 1.0, 1.5 and 2.0 mass. %, were added to a fly-ash geopolymer matrix. The
TE
D
physical, mechanical, and microstructural properties of the thus obtained foams, and the effects of the type and amount of the added foaming agent, are presented and discussed. Highly porous
CE P
structures were obtained in the case of both of the investigated foaming agents, with overall porosities up to 59 % when aluminium powder was added, and of up 48 % when H2O2 was
AC
added. In the latter case, when 2 % of the H2O2 foaming agent was added, finer pores (with diameters up to 500 µm) occurred in the structure, whereas somewhat larger pores (some had diameters greater than 1 mm) occurred when the same amount of aluminium powder was added. The mechanical properties of the investigated foams depended on their porosity. In the case of highly porous structures a compressive strength of 3.3 MPa was nevertheless achieved for the samples containing 0.2 % of aluminium powder, and 3.7 MPa for those containing 2.0 % of H2O2.
Keywords: geopolymer foams, aluminium powder, H2O2, porosity, X-ray micro-tomography
ACCEPTED MANUSCRIPT 1. INTRODUCTION Geopolymers are inorganic systems which consist of, firstly, a reactive solid component which
T
contains sufficient amounts of SiO2 and Al2O3 in reactive form (e.g. different types of ash, and
IP
active clays) and, secondly, an alkaline activation solution which (apart from water) mainly
SC R
contains alkali hydroxides and silicates. These are important materials which could be used to replace concrete and some other industrial materials. They possess many favourable properties such as rapid setting and hardening, good long-term properties and durability [1], as well as a
NU
good ability to immobilize toxic metals [2], and improved resistance to acids and the action of fire
MA
[3]. Natural resources like clay (after thermal activation) and natural pozzolans such as volcanic ash can be used for their preparation, as well as a considerable range of secondary resources obtained from industrial waste, such as different types of ash (fly ash, sewage sludge ash, biomass
TE
D
ash), paper sludge, and slags which result from various production processes. Since their production is mainly based on waste materials, their accelerated use could contribute significantly
CE P
to the achievement of environmental goals, including the lowering of the CO2 footprint of the construction industry [4-5].
AC
Among many products that are based on geopolymer precursors, geopolymer foams appear to be a very promising material since they are formed at temperatures below 100 oC and possess properties similar to foamed glass or foamed ceramics, both of which are produced at highly elevated temperatures, above 900 oC. The main precursor for geopolymer is fly ash. In comparison with other thermally prepared natural raw materials (e.g. metakaolin) as a starting material fly ash is beneficial both from the point of view of costs, and from that of the environment, since it has a lower level of incorporated energy, and subsequently low CO 2 emissions. Fly ash appears to be one the most promising precursors for the large-scale industrial production of geopolymer products also due to its high workability and low water demand [6]. Geopolymer foams are formed by the addition of foaming agents to a slurry consisting of fly ash
ACCEPTED MANUSCRIPT and an alkali activator solution such as H2O2 or NaOCl, or a metal powder such as aluminium or zinc powder, or a silica fume which reacts with the liquid matrix or oxygen, which decomposes
T
resulting in the release of gases [7-11], according to the following reactions: (1) (2)
SC R
Al (s) + 3H2O (l) + OH- (aq.) → Al(OH)-4 (aq) + 3/2H2 (g)
IP
H2O2 (l) → 2H2O (l) + O2 (g)
Geopolymers can be also formed by by introducing a large volume fraction of air bubbles into the
saponin, and hydrolyzed proteins [12-13].
NU
mixture, mainly by using organic foaming agents such as detergents, resin soap, glue resins,
In the case when aluminium powder or H2O2 are added as foaming agents, densities as low as 0.4
MA
g/cm3 can be reached [14-16], a microstructure which is characterized by uniformly distributed pores being obtained. The mechanical, i.e. compressive strength of such material depends on their
TE
D
density, and has been found to amount to between 1 and 10 MPa for densities of between 0.36 and 1.4 g/cm3 [10]. It has also been found [14-18] that the type of ash used (i.e. its chemical
CE P
compositions, glassy phase, and particle size), as well as the proper design of the alkali activating admixture, has a strong influence on the mechanical properties of the geopolymer and thus also of
AC
the obtained geopolymer foams. Since the porosity of geopolymer-based foams is usually of the closed type, the use of mercury porosimetry (MIP) is very limited when trying to determine the pore size distribution. This is because this technique is unable to reach closed pores, and in the case of high pressures, it breaks the walls between the pores. X-ray micro-tomography is a nondestructive technique which can be successfully used to estimate porosity in such systems. With the support of suitable image analysis software, e.g. Avizo, pore size distribution, phase distribution, and voids and/or cracks can be quantified. Different types of inorganic porous materials, such as ceramic foams [19] and building materials [20], have been successfully analysed using this technique, which can also be used for the evaluation and quantification of porosity evolution in the foaming process in glasses or glassy based systems [21-23].
ACCEPTED MANUSCRIPT The aim of the present paper was to compare the efficiency of foaming using two different foaming agents, aluminium powder and H2O2, to assess their effect on the mechanical properties
T
of the hardened material, and to monitor the development of porosity in these systems by means
IP
of micro-tomography.
SC R
2. EXPERIMENTAL 2.1 Materials
The following starting materials were used in the preparation of the investigated geopolymer
NU
foams:
MA
- fly ash whose composition is given in Table 1,
- two different foaming agents, i.e. aluminium powder (produced by: New Materials Development Gmbh, particle size D50: <5 µm), and H2O2 (hydrogen peroxide solution 30 mass. %, produced
TE
D
by: Carlo Erba reagents),
- water-glass activating solutions (sodium silicate Crystal 0112, produced by: Tennants
CE P
distribution, Ltd., SiO2:Na2O = 1.97, 54.2 mass.% water solution), and - NaOH (produced by: Donau Chemie, 41.7 mass. % water solution).
AC
Fly ash is a very fine powder, with particle size below 400 µm, having 50 wt. % of particles below 40 µm, and with a BET specific surface of 1.7 cm2/g. Different mixtures were prepared, whose compositions are given in Table 2. In the case when Al powder was used as the foaming agent, the mixtures were prepared by first thoroughly mixing together the FA and Al powder and then adding to this dry mixture a solution of water glass and NaOH; these materials were then mixed for 5 minutes, and poured into moulds having dimensions of 2 x 2 x 8 cm. In the case when H2O2 was used as the foaming agent, it was added to the solution of water glass and NaOH. After this the procedure was the same as in the case of the mixtures made using the Al powder. In all cases commercial additives for foam
ACCEPTED MANUSCRIPT stabilisation were added. The samples were then put in an oven for 24 hours at a temperature of 70 o
C in order to accelerate the geopolymeric reaction, and thus achieve hardening of the structure.
T
2.2 Techniques
IP
Density was determined by weighing the individual test specimens, and dividing the thus
density).
SC R
determined weights by the corresponding dimensions of the specimens (i.e. so-called geometrical
Mechanical strength, i.e. bending and compressive strength were determined, at an age of 4 days o
NU
(curing for first 24 hours at a temperature of 70 C and for the following 3 days exposed to room
MA
temperature), by means of Toninorm equipment (Toni Technik, Germany), using a force application rate of 0.005 kN/sec.
The microstructure of individual cross-sections of the geopolymer foam specimens were
TE
D
examined by using the back-scattered electrons (BSE) image mode of low vacuum scanning electron microscopy (SEM), using JEOL 5500 LV equipment.
CE P
X-ray micro-computed tomography was used to study the structural characteristics of all the samples of the investigated geopolymer foams, using a "Xradia µCT-400" tomograph (XRadia,
AC
Concord, California, USA), set to 80 kV and 125 µA. The size of the foam specimen was: 2.0 x 2.0 x 2.0 cm, and they were imaged using a CCD camera equipped with a 0.39X magnification optical objective and a resolution of 32 µm. A high-precision rotating stage was used, so that 1000 projection images were taken from different view-points with exposure times of 2 s per projection. In order to reconstruct the pore structure of the geopolymer foams, as well as to determine their overall porosity and pore size distribution, Avizo Fire 3D-image analysis software was used, following the process for pore segmentation and quantification as described by [23]. The ROI (region of interest) box was determined from the centre of the sample, which had a size of 1.5 x 1.5 x 1.5 cm. 3. RESULTS
ACCEPTED MANUSCRIPT 3.1 Density and mechanical characterization The results of measurements of the density and mechanical properties of foams to which
T
aluminium powder and H2O2 had been added as foaming agents are presented in Table 3. As can
IP
be seen from this table, the measured density depends on the amount of the added foaming agent.
SC R
In the case when aluminium powder amounting from 0.07 to 0.2 % was added, the measured density was between 0.64 to 0.74 g/cm3, whereas when H2O2 was added it was between 0.61 to 1 g/cm3. In both cases there is a pessimum in the density values since with higher dosages, the
NU
density did not continue to decrease, but instead, contrary to expectations, it increased (Figs. 1a
MA
and b). This can be ascribed to coalescence and a slight collapsing effect [14]. From the results of the measured mechanical properties (Fig. 2) it can be seen that, as expected, these properties as the density decreases. It can also be seen that the measured strength depends on
TE
D
the density no matter which foaming agent is added. For example sample Al 0.2, which had a density of 0.73 g/cm3, had a compressive strength of 3.3 MPa, whereas sample H 1, which had a
CE P
density of 0.71 g/cm3, had a compressive strength amounting to 3.6 MPa that was very similar to that of the sample Al 0.2.
AC
3.2 X-ray micro-tomography
Quantitative analysis was performed using the Avizo Fire 3D image analysing software program. The results with respect to total porosity (pore shares), as well as to the total volume of the pores in different size areas, are given in Table 4 and in Figs. 3 and 4. From Figure 3, which provides a two-dimensional (XY orientation) cross-section of samples obtained by micro-tomography it can be seen that, in the case when Al powder was added as a foaming agent, the pores are much bigger than when H2O2 was added (Fig. 4), where a more finely porous structure can be observed. Whereas in the case of the Al powder foaming agent the total porosity is higher (Table 4), single pores can have diameters up to 2 mm, whereas in the
ACCEPTED MANUSCRIPT case of the H2O2 foaming agent there are fewer big pores, and their dimensions are also slightly smaller (up to 1 mm).
T
From Table 4 it can be seen that the measured porosity ranges between 37 up to almost 60 % of
IP
the total volume. Since the pores do not have a regular round shape, the volume of pores
SC R
corresponding to a certain pore size range is given as a representation of the pores (instead of pore size distribution, Table 5). In order to get a better insight the average value of the pore
NU
length, Feret diameters, which is defined as the distance between the two parallel planes restricting the object/pore perpendicular to that direction (also called “caliper diameter”) is given.
MA
In cases of both foaming agents, the main share of the pores lies in the range of pores which are smaller than 104 µm3, corresponding to a pore length of 120 µm. When H2O2 is the foaming
D
agent the amount of added agent does not significantly change the pore size distribution (i.e. the
TE
number of pores and the volume of the pores), the total pore volume increasing significantly only
CE P
when, instead of 0.5 %, 1.0 or more % of H2O2 is added (Tables 4 and 5, Fig. 6). In the case of the addition of aluminium powder the quantity of the added agent has a more pronounced
AC
influence, both on total pore volume and on the pore size distribution (Tables 4 and 5, Fig. 5).
3.3 SEM analysis
Selected samples were also investigated by means of SEM. Comparing images for samples with Al powder addition and H2O2 addition it can be noticed that in the case of H2O2 addition the pores are spherical in shape, and are also more uniformly distributed than in the case when Al powder is added (Figs. 7 and 8, respectively). The results of the SEM investigations support the findings of the performed micro-tomography, but additionally provide insight into the structure of the walls between the pores. In both cases the remains of the ash’s spherical particles can be clearly seen embedded in the matrix. Also the results of the SEM analysis clearly demonstrate the effect of pore percolation, which is especially seen when a higher amount of foaming agent is added, when
ACCEPTED MANUSCRIPT a higher pressure is created due to gas release [7]. For example, in the case of sample H 1 almost
T
every pore has been percolated (Fig. 8c).
IP
4. CONCLUSIONS
SC R
Both of the foaming additives, i.e. Al powder and H2O2, proved to be successful foaming agents for the investigated geopolymer matrix. The addition of Al powder amounting to between 0.07 and 0.2 mass. % resulted in a porous structure having a density of between 0.64 and 0.74 g/cm3,
NU
whereas the addition of H2O2 amounting to between 0.5 and 2 mass. % resulted in densities from
MA
0.61 to 1.00 g/cm3. The measured compressive strengths of the tested samples were within the range from 3.3 to 4.3 MPa for those in which Al powder was added, and within the range from 2.9 to 9.3 MPa when H2O2 was added. As expected, the measured compressive strengths were in
TE
D
correlation with the density: the higher the density, the higher the compressive strength. And, in the case of both additives, the measured values of the compressive strength at a certain density
CE P
are very similar. Porosity development was evaluated by means of micro-tomography. In the case of both additives, the pores were found to be uniformly distributed throughout the samples. The
AC
results of micro-tomography and SEM have shown the difference in pore size when different foaming agents are added: the samples with added aluminium powder had higher porosities and also bigger pores than the samples with added H2O2. In both cases the results of the analysis also confirmed that, when a higher amount of the foaming agent was added, the number of pores decreased, due to coalescence. However, the volume of these pores also increased; final overall porosities of 58 and 48 % being obtained for the optimal mixtures Al 0.2, and H 1, respectively.
Acknowledgements
ACCEPTED MANUSCRIPT This work has been financially supported by the Slovenian Research Agency (ARRS) through the project Z2-6748: "Mechanisms for the strengthening of different types of ash by means of a
IP
T
geopolymerization process".
SC R
5. REFERENCES
[1] Bakharev T. Durability of geopolymer materials in sodium and magnesium sulfate solutions.
NU
Cem Concr Res 2005;35:1233–1246.
[2] Alvarez Ayuso E, Querol X, Plana F, Alastuey A, Moreno N, Izquierdo M, Font O, Moreno T, Diez S, Vázquez E, Barra M. Environmental, physical and structural characterisation of
MA
geopolymermatrixes synthesised from coal (co) combustion fly ashes. J Hazard Mater 2008;154:175–183.
TE
Miner Eng 2003;16:205–210.
D
[3] Cheng TW, Chiu JP. Fire resistant geopolymer produced by granulated blast furnace slag.
CE P
[4] Deventer JSJ, Provis JL, Duxon P. Technical and commercial progress in the adoption of geopolymer cement. Miner Eng 2012;29:89–104.
AC
[5] Provis JL. Geopolymers and other alkali activated materials: why, how, and what?. Mater Struct 2014;47:11–25.
[6] Provis JL, Duxon P, Deventer JSJ. The role of particle technology in developing sustainable construction materials. Adv Powder Technol 2010;21:2–7.
[7] Bell JL, Kriven WM. Preparation of Ceramic Foams from Metakaolin-based Geopolymer Gels. In: Lin HT, Koumoto K, Kriven WM, Norton DP, Garcia E, Reimanis I, editors. Developments in Strategic Materials: Ceramic Engineering and Science Proceedings 2008;29:97– 112.
[8] Nyale SM, Babajide OO, Birch GD, Boeke N, Petrik, LF. Synthesis and characterization of coal fly-ash foamed geopolymer. Procedia Environmental Sciences 2013;18:722–730.
ACCEPTED MANUSCRIPT
[9] Henon H, Alzina A, Absi J, Smith DS, Rossignol S. Potassium geopolymer foams made with a
T
silica fume pore forming agent for thermal insulation. J Porous Mater 2013;20:37–46.
IP
[10] Zhang Z, Provis JL, Reid A., Wang H. Geopolymer foam concrete: An emerging material
SC R
for sustainable construction. Constr Build Mater 2014;56:113–127.
[11] Prud’homme E, Joussein E, Rossignol S. Alkali-activated concrete binders as inorganic thermal insulator materials. In: Pachego-Torgal F, Labrincha JA, Leonelli C, Palomo A,
MA
Woodhead Publishing; 2015, p. 687–728.
NU
Chindaprasit P, editors. Handbook of Alkali-activated Cements, Mortars and Concretes,
[12] Abdullah MMB, Hussin K, Bnhussain M, Ismail KN, Yahya Z, Razak RA. Fly Ash-based
D
Geopolymer Lightweight Concrete Using Foaming Agent. Int J Mol Sci 2012;13:7186–7198.
CE P
2014;40:5723–5730.
TE
[13] Cilla MS, Colombo P, Morelli MR. Geopolymer foams by gelcasting. Ceram Int
[14] Masi G, Rickard WDA, Bignozzi MC, Riessen A. The influence of short fibres and foaming agents on the physical and thermal behaviour of geopolymer composites. Advances in Science
AC
and Technology 2014;92:56–61. [15] Hlavaček P, Šmilauer V, Škvara F. Alkali-activated fly ash foams – synthesis, chemophysical properties and microstructure modelling. Advances in Science and Technology 2014;92:14–19.
[16] Sanyan JG, Nazari A, Chen L, Nguyen H. Physical and mechanical properties of lightweight aerated geopolymer. Constr Build Mater 2015;79:236–244.
[17] Nazari A, Pachego-Torgal F, Cevik A, Sanjayan JG. Prediction of the compressive strength of alkali-activated geopolymeric concrete binders by neuro-fuzzy modelling: a case study. In: Pachego-Torgal F, Labrincha JA, Leonelli C, Palomo A, Chindaprasit P, editors. Handbook of Alkali-activated Cements, Mortars and Concretes, Woodhead Publishing; 2015, p. 217–235.
ACCEPTED MANUSCRIPT [18] Lodeiro IG, Palomo A, Fernandez-Jimenez A. Crucial insights on the mix design of alkaliactivated cement-based binders. In: Pachego-Torgal F, Labrincha JA, Leonelli C, Palomo A, Chindaprasit P, editors. Handbook of Alkali-activated Cements, Mortars and Concretes,
IP
T
Woodhead Publishing; 2015, p. 49–75.
[19] Maire E, Colombo PP, Adrien J., Babout L, Biasetto L. Characterization of the morphology
SC R
of cellular ceramics by 3D image processing of X-ray tomography. J Eur Cer Soc 2007;27:1973– 1981.
NU
[20] Cnudde V, Cwirzen A, Masschaele B, Jacobs PJS. Porosity and microstructure
MA
characterization of building stones and concretes. Engineering Geology 2009;103:76–83.
[21] Atwood RC, Jones JR, Lee PD, Hench LL. Analysis of pore interconnectivity in bioactive
D
glass foams using X-ray microtomography. Scripta Mater 2004;51:1029–1033.
TE
[22] Maruyama B, Spowart JE, Hooper DJ, Mullens HM, Druma AM, Druma C, Alam MKA new technique for obtaining three-dimensional structures in pitch-based carbon foams. Scripta
CE P
Mater 2006;54:1709–1713.
[23] Korat L, Ducman V, Legat A, Mirtič B. Characterisation of the pore-forming process in lightweight aggregate based on silica sludge by means of X-ray micro-tomography (micro-CT)
AC
and mercury intrusion porosimetry (MIP). Ceram Int 2013;39:6997–7005.
ACCEPTED MANUSCRIPT Tables capture:
Table 2: Composition of the investigated mixtures (all in mass. %).
T
Table 1: Chemical composition of the used fly ash.
IP
Table 3: The measured densities, bending strengths and compressive strengths (together with the
SC R
corresponding standard deviations) of the samples of geopolymer foams made with Al powder (designated as Al) and with H2O2 (designated as H) as foaming agents.
NU
Table 4: Total porosity (pore shares) of the samples of the geopolymer foams (the ROI box) obtained by microtomography.
MA
Table 5: Pore size distribution determined by means of micro-tomography for the samples
AC
CE P
TE
D
presented as the number of pores or as the volume of pores with regard to the 3D volume.
ACCEPTED MANUSCRIPT
NU MA D TE CE P AC
IP
in mass. % 2.3 52.5 23.3 7.46 6.09 2.48 0,80 2.23
SC R
Components Loss on ignition (at 950 oC) SiO2 Al2O3 Fe2O3 CaO MgO Na2O K2O
T
Table 1: Chemical composition of the used fly ash.
ACCEPTED MANUSCRIPT
Table 2: Composition of the investigated mixtures (all in mass. %).
MA D TE CE P AC
Al powder
T
66.1 66.1 66.1 65.9 65.5 65.2 64.9
NaOH (41.7 mass. % water solution) 24.4 24.4 24.4 24.3 24.2 24.1 24.0
0.07 0.13 0.20 / / / /
IP
Al 0.07 Al 0.13 Al 0.2 H 0.5 H1 H 1.5 H2
Water glass (54.2 mass. % water solution) 9.4 9.4 9.3 9.3 9.3 9.2 9.2
SC R
FA
NU
Sample designation
H2O2 (30 mass. % water solution) / / / 0.5 1.0 1.5 2.0
ACCEPTED MANUSCRIPT Table 3: The measured densities, bending strengths and compressive strengths (together with the corresponding standard deviations) of the samples of geopolymer foams made with Al powder (designated as Al) and with H2O2 (designated as H) as foaming agents.
T
IP
0.74 (0.07) 0.64 (0.07) 0.73 (0.03) 1.00 (0.05) 0.71 (0.05) 0.61 (0.08) 0.66 (0.08)
Bending strength (MPa) 2.3 (0.35) 2.1 (0.31) 2.4 (0.30) 3.6 (0.31) 2.6 (0.40) 2.0 (0.30) 2.2 (0.25)
SC R
Density (g/cm3)
AC
CE P
TE
D
MA
NU
Sample designation (% addition of the foaming agent) Al 0.07 Al 0.13 Al 0.2 H 0.5 H1 H 1.5 H2
Compressive strength (MPa) 3.7 (1.36) 4.3 (1.20) 3.3 (0.92) 9.3 (1.52) 3.6 (1.11) 2.9 (0.30) 3.7 (0.54)
ACCEPTED MANUSCRIPT Table 4: Total porosity (pore shares) of the samples of the geopolymer foams (the ROI box) obtained by microtomography. Al 0.13
Al 0.2
H 0.5
Total porosity (%)
47.9
53.4
58.4
37.9
H1
T
Al 0.07
48.1
AC
CE P
TE
D
MA
NU
SC R
IP
Sample designation
H 1.5
H2
46.3
44.9
ACCEPTED MANUSCRIPT
Table 5: Pore size distribution determined by means of micro-tomography for the samples presented as the number of pores or as the volume of
Al 0.2
H 0.5
CR
Al 0.13
H1
H 1.5
H2
3D
Number Volume
Number Volume
Number
Volume
Number Volume
Number
Volume
Number
Volume
Number
Volume
Feret diam.
volume
of pores
of pores
of pores
of pores
of pores
of pores
of pores of pores
of pores
of pores
of pores
of pores
of pores
of pores
(µm)
(µm3)
(%)
(%)
(%)
(%)
(%)
(%)
6000
>1E9
2.69
74.26
4.92
68.20
1.11
57.91
US
Al 0.07
IP
T
pores with regard to the 3D volume.
4000
1E8-1E9
5.07
24.62
13.35
31.20
5.11
1300
1E6-1E8
16.72
0.91
9.32
0.52
300
5E4-1E5
11.68
0.10
7.65
250
1E4-5E4
31.61
0.09
120
<1E4
32.22
0.02
(%)
(%)
(%)
(%)
(%)
(%)
(%)
2.34
53.33
3.66
51.44
2.36
47.05
2.52
42.89
39.62
7.60
45.67
13.30
48.11
11.92
52.22
16.44
56.42
5.97
2.22
6.46
0.79
3.10
0.36
3.83
0.59
3.20
0.60
0.03
5.52
0.08
7.19
0.07
4.69
0.03
5.19
0.04
3.56
0.02
25.60
0.04
24.80
0.12
28.69
0.10
30.54
0.05
27.11
0.07
24.84
0.05
39.16
0.01
57.50
0.05
47.73
0.04
44.70
0.02
49.60
0.03
49.44
0.02
AC
CE P
TE D
MA N
(%)
ACCEPTED MANUSCRIPT Figures capture:
Figure 1: Measured densities of the investigated samples of geopolymer foams made with (a) Al
T
powder and (b) H2O2, as foaming agents.
IP
Figure 2: Measured bending strengths and compressive strengths of the investigated samples of
SC R
geopolymer foams made with Al powder and H2O2, as foaming agents.
Figure 3: Slice images (XY) and 3D images obtained by micro-tomography of the investigated
NU
geopolymer foams in the case when Al powder was used as the foaming agent. Figure 4: Slice images (XY) and 3D images obtained by micro-tomograph of the investigated
MA
geopolymer foams in the case when H2O2 was used as the foaming agent. Figure 5: Pore size distribution determined by means of micro-tomography for the samples with
D
Al powder as a foaming agent presented as (a) the number of pores with regard to the 3D
TE
volume, and (b) as the volume of pores with regard to the 3D volume.
CE P
Figure 6: Pore size distribution determined by means of micro-tomography for the samples with H2O2 as a foaming agent presented as (a) the number of pores with regard to the 3D volume, and (b) as the volume of pores with regard to the 3D volume.
AC
Figure 7: SEM analysis of the samples with the addition of Al powder as a foaming agent; (a) and (b) sample Al 0.07, and (c) and (d) sample Al 0.13, at two different magnifications. Figure 8: SEM analysis of the samples with the addition of H2O2 as a foaming agent; (a) and b) sample H 0.5, and (c) and (d) sample H 1, at two different magnifications.
ACCEPTED MANUSCRIPT
AC
CE P
TE
D
MA
NU
SC R
IP
T
Figure 1
ACCEPTED MANUSCRIPT
AC
CE P
TE
D
MA
NU
SC R
IP
T
Figure 2:
ACCEPTED MANUSCRIPT
AC
CE P
TE
D
MA
NU
SC R
IP
T
Figure 3:
ACCEPTED MANUSCRIPT
AC
CE P
TE
D
MA
NU
SC R
IP
T
Figure 4:
ACCEPTED MANUSCRIPT
AC
CE P
TE
D
MA
NU
SC R
IP
T
Figure 5:
ACCEPTED MANUSCRIPT
AC
CE P
TE
D
MA
NU
SC R
IP
T
Figure 6:
ACCEPTED MANUSCRIPT
AC
CE P
TE
D
MA
NU
SC R
IP
T
Figure 7:
ACCEPTED MANUSCRIPT
AC
CE P
TE
D
MA
NU
SC R
IP
T
Figure 8:
SC R
IP
T
ACCEPTED MANUSCRIPT
MA
D TE CE P
-
Preparation of geopolymer foams based on fly ash with the addition of Al powder or H2O2 as foaming agents, Determination of density, porosity and mechanical properties of such foams, Characterization of foaming process by means of X-ray micro-tomography (µcT).
AC
-
NU
HIGHLIGHTS: