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Towards a clean environment: The potential application of eco-friendly magnesia-silicate cement in CO2 sequestration
Journal Pre-proof Towards a clean environment: The potential application of eco-friendly magnesiasilicate cement in CO2 sequestration Hamdy A. Abdel-Gawwad, Hassan Soltan Hassan, S.R. Vásquez-García, Isabel Israde-Alcántara, Yung-Chin Ding, Marco Antonio Martinez-Cinco, S. Abdel-Aleem, Hesham M. Khater, Taher A. Tawfik, Ibrahim M. El-Kattan PII:
S0959-6526(19)34745-6
DOI:
https://doi.org/10.1016/j.jclepro.2019.119875
Reference:
JCLP 119875
To appear in:
Journal of Cleaner Production
Received Date: 6 August 2019 Revised Date:
23 December 2019
Accepted Date: 24 December 2019
Please cite this article as: Abdel-Gawwad HA, Hassan HS, Vásquez-García SR, Israde-Alcántara I, Ding Y-C, Martinez-Cinco MA, Abdel-Aleem S, Khater HM, Tawfik TA, El-Kattan IM, Towards a clean environment: The potential application of eco-friendly magnesia-silicate cement in CO2 sequestration, Journal of Cleaner Production (2020), doi: https://doi.org/10.1016/j.jclepro.2019.119875. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. 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. © 2019 Published by Elsevier Ltd.
Authors Contributions Section
Hamdy A. Abdel-Gawwad Preparation of chemicals and materials, Methodology, Statistical analysis, Interpretation of data, Spectroscopic analysis, Revision of manuscript, language editing
Hassan Soltan Hassan Preparation of chemicals and materials, Methodology, Statistical analysis, Interpretation of data, Spectroscopic analysis, Revision of manuscript, language editing
S.R. Vásquez-García Preparation of chemicals and materials, Methodology, Statistical analysis, Interpretation of data, Spectroscopic analysis, Revision of manuscript, language editing
Isabel Israde-Alcántara Preparation of chemicals and materials, Methodology, Statistical analysis, Interpretation of data, Spectroscopic analysis, Revision of manuscript, language editing
Yung-Chin Ding Preparation of chemicals and materials, Methodology, Statistical analysis, Interpretation of data, Spectroscopic analysis, Revision of manuscript, language editing
Marco Antonio Martinez-Cinco Preparation of chemicals and materials, Methodology, Statistical analysis, Interpretation of data, Spectroscopic analysis, Revision of manuscript, language editing
S. Abdel-Aleem Preparation of chemicals and materials, Methodology, Statistical analysis, Interpretation of data, Spectroscopic analysis, Revision of manuscript, language editing
Hesham M. Khater Preparation of chemicals and materials, Methodology, Statistical analysis, Interpretation of data, Spectroscopic analysis, Revision of manuscript, language editing
Ibrahim M. El-Kattan Preparation of chemicals and materials, Methodology, Statistical analysis, Interpretation of data, Spectroscopic analysis, Revision of manuscript, language editing
Taher A. Tawfik Preparation of chemicals and materials, Methodology, Statistical analysis, Interpretation of data, Spectroscopic analysis, Revision of manuscript, language editing
CO2 Sequestration Process
CO2
Eco-Friendly Method
CO2
CO2
MgO Different Types Of Volcanic Ashes + MgO
Super CO2 sequestration cement
1
Towards a clean environment: The potential application of eco-friendly
2
magnesia-silicate cement in CO2 sequestration
3
Hamdy A. Abdel-Gawwad*1, Hassan Soltan Hassan*2,3, S.R. Vásquez-García2, Isabel Israde-Alcántara4,
4
Yung-Chin Ding5, Marco Antonio Martinez-Cinco2, S. Abdel-Aleem6, Hesham M. Khater1,
5
Taher A. Tawfik7, Ibrahim M. El-Kattan8
6
1
Raw Building Materials Research and Processing Technology Institute, Housing and Building National
7 8
Research Center (HBRC), Cairo, Egypt 2
Posgrado de Ingeniería Química, Universidad Michoacana de San Nicolas de Hidalgo, 58000, Morelia,
9
Michoacan, Mexico 3
10 4
11
Geology Department, Faculty of Science, New Valley University 72511, El- Kharga, Egypt
Instituto de Investigaciones en ciencias de latierra Edif. U-4, Cd. Universitaria, Morelia, Michoacán,
12 13
Mexico 5
Institute of Mineral Resources Engineering, National Taipei University of Technology, Taipei, Taiwan 6
14 15
7
16
8
Construction and Building Department, Higher Institute of Engineering on 6thOctober, Giza, Egypt.
Environmental Science and Industrial Development Department, Faculty of Postgraduate Studies for
17 18
Chemistry Department, Faculty of Science, Fayoum University, Fayoum, Egypt
Advanced Sciences, Beni-Suef University, Beni-Suef, Egypt * Corresponding authors: Hassan Soltan Hassan (email: [email protected])
19
Hamdy A. Abdel-Gawwad (email: [email protected])
20 21
Abstract
22
The key point of this study is the fabrication of magnesia-based cement with promising
23
mechanical properties and high efficiency of CO2-capture. The naturally occurring
24
volcanic ashes (white & red ashes) and reactive magnesium oxide are the main materials
25
used in the synthesis of eco-friendly CO2-capture materials. Volcanic ashes were
26
individually mixed with reactive magnesium oxide at ash to magnesium oxide ratio of
27
25:75 Wt. %. The dry blends can react with water to yield hardened materials (at ambient
1
28
temperature) with compressive strength depends on the type of volcanic ash. A
29
considerable change in the features of the hardened samples was recorded when the
30
fabricated materials exposed to 100% CO2 gas for 28-days. This change is mainly due to
31
CO2-capture by magnesium hydroxide Mg(OH)2 within the fabricated materials, resulting
32
in the formation of Nesquehonite minerals MgCO3.3H2O as proved by X-ray diffraction,
33
thermo-gravimetric, and infra-red instrumental techniques. The thermo-gravimetric
34
analysis demonstrates that, the fabricated sample containing low amorphous red ashes has
35
higher CO2-capture capacity (~260 kg/ton) compared to that having high amorphous
36
white volcanic ashes (~220 kg/ton) at 28-days of CO2-exposure. Accordingly, the
37
fabricated magnesia-based cement is not only used as cementitious material with
38
outstanding mechanical properties, but also used as a super CO2-absorbent precursor.
39
This can strongly contribute in the mitigation of global warming potential caused by
40
different industrial activities.
41 42
Keywords: Volcanic ashes; CO2-capture; Global warming phenomenon; Magnesia-based
43
cement
44
1. Introduction
45
Although the development of science and technology is the urgent issue in the 21th-
46
centurey, it led to serious climatic change that could threaten the mankind survival and
47
other life forms. Indeed, the increase of CO2 emission (which is mainly resulted from
48
industrial activities) is the essential reason behind global warming phenomenon that
49
strongly affects the climatic change (Lee et al., 2010; Miller and Croft). As stated by
50
the UN Intergovernmental Panel on Climatic Change (IPCC), the concentration of CO2 in
51
atmosphere will reach 550 ppm as earlier as 2050, causing an increase in the average 2
52
temperature of the earth by 1.4-5.8ºC, a rise in sea level, extreme drought, wildfires,
53
floods, and food shortages for hundreds of millions of people (The UN
54
Intergovernmental Panel on Climatic Change (IPCC) 2005). Cement (Abdel-
55
Gawwad et al., 2019a; Abdel-Gawwad et al., 2019b; Hassan et al., 2019), petro-
56
chemical (Tao and Patel, 2009) and iron & steel manufacturing (Peng et al., 2016) are
57
the most industries, which mainly contribute to the increment of CO2- emission. Thus, the
58
modification in the processing of these industries to mitigate CO2-emission and the
59
invention of a new technology with high efficacy in the CO2-separation are urgently
60
required.
61
CO2-sequestration as an innovative method of gas absorption has been previously
62
studied by different researchers via the exposure of cementitious materials to CO2 gas
63
(Pan et al., 2016; Sharma and Goyal, 2018). CO2-sequestration method was performed
64
by the transformation of hydration products, within the cementitious materials, into
65
carbonate-containing phases. The rate of CO2-capture mainly depends on different
66
parameters, including CO2-concentration, air humidity, air temperature, and cement type
67
(Behfarnia and Rostami, 2017; Czarnecki and Woyciechowski, 2015).
68
The carbonation was found to have a detrimental effect on the structural Portland
69
cement concrete (Breccolotti et al., 2013; Kim et al., 2009). The negative effect of
70
carbonation on the properties of structural concrete is originated from the significant drop
71
in pH value as the carbonation has high efficiency on the transformation of calcium
72
hydroxide within hardened concrete (pH ~12) into calcium carbonate (pH ~9), resulting
73
in an enhancement of the probability of steel corrosion (Kulakowski et al., 2009).
74
Moreover, at later ages of CO2- exposure, CO2 can destruct the binding capacity of the 3
75
hardened materials by its interaction with calcium silicate hydrate (the dominant binding
76
phase of hydrated cement) to yield calcium carbonate (with lower binding capacity) and
77
silicon dioxide (Wang et al., 2019). Nevertheless, Portland cement demonstrated the
78
higher carbonation resistivity compared to that of alkali activated cement (Bakharev et
79
al., 2001; Li and Li, 2018). The main reason behind this finding is the presence of
80
Ca(OH)2 in structural Portland cement concrete as it acts as a carrier for CO2,
81
accompanied by the formation protective layers of calcium carbonate on calcium silicate
82
hydrate phase (Bakharev et al., 2001; He et al., 2018).
83
The replacement of Portland cement by magnesium oxide has resulted in the
84
formation of what is known as MgO-cement (Gonçalves et al., 2019);. This cement
85
represented several advantages over Portland cement, including highest capability for
86
CO2-sequestration, accompanied by the highest resistivity of the hydration and
87
carbonation product to aggressive media, enhancing the probability of utilization of
88
different industrial byproducts as it has lower sensitivity to impurities, potential to be re-
89
use as MgO can be used alone as cementitious material by its carbonation (Unluer and
90
Al-Tabbaa, 2013). The MgO utilization alone has several advantages in terms of
91
capability of CO2-capture, mechanical properties and durability over Portland cement-
92
MgO (Liska and Al-Tabbaa, 2008, 2009). The MgO-MgCO3 porous block showed
93
higher CO2 uptake and compressive strength compared to Portland cement block at the
94
same accelerated carbonation conditions (Unluer and Al-Tabbaa, 2013). In the other
95
work, MgO was used alone in the CO2-capture. This method was beneficially used in the
96
production of light weight blocks with density of 700-900 kg/m3 and compressive
97
strength reaches 2MPa (Morrison et al., 2016).
4
98
Magnesium silicate-based cement is categorized as eco-friendly cement as it
99
generates CO2-emission too lower than that of Portland cement (Shen et al., 2016). This
100
cement can be prepared by mixing reactive MgO with amorphous silicate precursors (Jin
101
and Al-Tabbaa, 2013; Zhang et al., 2011). Different silicate-rich wastes have been used
102
in the fabrication of this cement comprising silica fume (Zhang et al., 2018), glass and
103
ceramic wastes (Abdel-Gawwad et al., 2018a), fly ash (Choi et al., 2014) , and rich
104
husk ash, (Sonat and Unluer, 2019). The main hydration products of the prepared
105
cement are magnesium silicate hydrate and magnesium hydroxide (Abdel-Gawwad et
106
al., 2018a; Sonat and Unluer, 2019). Although few researchers have conducted the
107
normal and accelerated carbonation on naturally-occurring magnesium silicate rock
108
(Eikeland et al., 2015), up till now there is no published work have evaluate the
109
efficiency of the synthesized magnesium silicate cement in CO2-sequestration and its
110
reflection on its performance.
111
Accordingly, the motivation behind this work is the evaluation of the impact of
112
accelerated carbonation on the fabricated magnesium silicate cement in which reactive
113
magnesium oxide and naturally occurring volcanic ashes are the main precursor. The
114
impact of carbonation age and volcanic ash nature (including chemical composition and
115
amorphous content) on the mechanical properties and the rate of CO2-capture have been
116
evaluated. The reasonable reason behind this study is the formulation of cementitious
117
materials, with high mechanical properties and low production energy, which could be
118
beneficially used in the production of non-structural concrete with high efficacy in the
119
sequestration of CO2.
120 5
121
2. Experimental
122
2.1. Materials
123
Two types of naturally occurring volcanic ashes (namely, white and red volcanic ashes)
124
and reactive magnesium oxide (MgO) are the main raw materials used in the fabrication
125
of CO2-capture materials. White and red volcanic ashes (WVA and RVA) were obtained
126
from, a field area close to Morelia city, Michoacán state, Mexico; meanwhile, MgO was
127
purchased from Fisher Scientific Chemical Company (UK). The chemical compositions,
128
which were conducted by X-ray fluorescence (XRF: Xios PW1400), and physical
129
properties of volcanic ashes and MgO are reported in Table 1. The chemical analyses of
130
the starting materials prove that the WVA and RVA are mainly aluminosilicate materials.
131
X-ray diffraction (XRD) (Fig. 1) proves that, the pattern of WVA represents a hump at 2θ
132
range of 15-30º with the appearance of well-resolved sharp peaks affiliated to crystalline
133
phases such as albite, and margarita minerals. This hump is an indication of the
134
amorphous nature of WVA. The RVA demonstrates crystalline thenardite, margarita, and
135
wavelite peaks with no appearance of an amorphous hump, indicating the low
136
amorphicity content in RVA. The quantitative Rietveld XRD-analysis shows that, the
137
WVA demonstrates amorphicity content of 72% higher than that identified in the case of
138
RVA (39%).
139
2.2. Fabrication of CO2-capture materials
140
Flow chart of the preparation steps including hydration and carbonation curing is
141
represented in Fig. 2. Firstly, WVA and RVA are ground to pass through 100 µm sieve
142
followed by dry mixing with MgO for 5 min, using ball mill machine. Volcanic ashes-
143
MgO blends were designed at weight ratio of 1:3. The MgO was used with high content 6
144
in cement blend to offer favorable conditions for accelerated carbonation. After
145
formulation step, mixing water (at water to solid ratio of 0.40) was added to homogenous
146
dry WVA-MgO and RVA-MgO mixes, yielding workable pastes. The details of mixing
147
proportions are reported in Table 2. The fresh pastes were transferred to stainless steel
148
molds of 50 x 5 x 50 mm, followed by curing in humidity chamber with 99±1% relative
149
humidity (RH) at 23±2ºC. After 24h of curing, the hardened cubes were demolded and
150
cured at the same conditions for 28-days to achieve considerable compressive strength.
151
The 28-days cured samples (zero time of carbonation) were transferred to
152
stainless steel CO2-champer with RH of 75%. To ensure the medium with 100% CO2
153
environment before conducting accelerated carbonation test, the open chamber was
154
flashed with CO2 for 2 min. After CO2-flushing, the top outlet of the chamber was closed
155
to proceed the accelerated carbonation of the hardened materials. The CO2-pressure
156
adjusted at 20 atm. using dial gauge contented to CO2 cylinder. At different time intervals
157
such as 1, 14, and 28-days, the carbonated samples were taken out and kept for 24h at
158
50±5 % RH and 23±2ºC before conducting strength measurements and solid phase
159
identification using XRD, thermo-gravemetric (TG/DTG) analysis, and Fourier transform
160
infrared (FTIR) spectroscopy.
161
2.3. Experimental methods
162
Compressive strength testing was carried out on the hardened cubes following the
163
procedure described by (C109M, 2016). The compressive strength value was taken as an
164
average of 5-specimens readings. In order to remove irregularities, the surface of the
165
specimen was carefully polished by filter paper. Compressive strength measurements
166
were carried out using five tones German Brüf Pressing Machine with a maximum load 7
167
capacity of 175kN. Mercury intrusion data from an Auto Pore IV 9500 porosimeter was
168
applied to determine the change in the total porosity of the hardened materials before and
169
after carbonation reaction.
170 171
2.4. Phase identifications
172
XRD-analysis was used to determine the crystalline phases in the cured and carbonated
173
samples using Philips PW3050/60 diffractometer with 5 to 60 (2θº) scanning range,
174
1s/step scanning speed, and 0.05°/step resolution. All the obtained peaks were identified
175
according to powder diffraction file (PDF). A DT-50-Thermal Analyzer (Schimadzu Co-
176
Kyoto, Japan), which provided by cryostat for cooling process, was used to perform the
177
TGA of carbonated and cured samples. The weight percentage of CO2-sequestrated (CO2
178
wt. %) by the hardened samples during CO2-exposure was calculated by dividing the
179
weight loss of MgCO3-phase (WL) by the total weight loss (TWL) of sample as follow: 2,
.% =
∗ 100
180
FTIR-analysis was carried out on some selected samples in order to identify the
181
functional groups of hydration products via KBr discussing Genesis-IIFT-IR
182
spectrometer at the wavenumber range of 400-4000 cm-1.
183 184
3. Results and discussion
185
Interestingly, reactive magnesium oxide-volcanic ash blends can react with water to yield
186
hardened materials with acceptable mechanical properties. The exposure of the hardened
187
materials to accelerated carbonation causes a significant changes their performances.
188
3.1. XRD-analysis 8
189
The X-ray diffractograms (Fig. 3) proved that brucite {Mg(OH)2}, and periclase (MgO),
190
quartz, and albite are the main phases of the hardened M-WVA mixture at zero time. The
191
exposure of hardened material to CO2 has resulted in the formation of nesquehonite
192
(MgCO3. 3H2O: PDF # 20-669). Same observation was reported by the previous work
193
(Liska et al., 2008; Vandeperre and Al-Tabbaa, 2007; Dung and Unluer, 2017) as the
194
nesquehonite phases has been formed in MgO-fly ash-Portland cement (PC) system. In
195
contrast, Abdel-Gawwad et al., (2018c) have reported that magnesium carbonate was
196
formed during accelerated carbonation of hardened PC-MgO blends. The increase of
197
exposure time leads to the enhancement of nesquehonite formation accompanied by the
198
increase of Mg(OH)2 consumption. Mg(OH)2 acts as an active site for CO2 capture as it
199
can interact with hydrated CO2 to yield nesquehonite mineral. It’s worth mentioning that
200
magnesium silicate hydrate (MSH: as the main binder of this system) is characterized by
201
low crystallinity; so, it cannot be detected by XRD. This is in consistence with previous
202
works (Abdel-Gawwad et al., 2018b). As represented in Fig. 4, there is no difference
203
between the mineralogical compositions of the hydration and carbonation products of M-
204
WVA and M-RVA samples. Nevertheless, the pattern affiliated to M-RVA sample
205
exhibits brucite mineral with lower peak intensity compared to that identified in the case
206
of M-WVA one. This gives strong evidence on the high efficacy of M-RVA in the
207
sequestration of CO2.
208
3.2. FTIR-spectroscopy
209
The FTIR spectra also confirmed that the transmittance bands affiliated to stretching
210
vibration of CO32- (at 1479 cm-1) in the case of carbonated M-WVA was appeared with
211
higher intensity compared to that identified in the case of zero time-hardened samples 9
212
(Fig. 5). The intensity of band characteristics for stretching vibration of OH within
213
Mg(OH)2 (at 3694cm-1) decreases with CO2 exposure time up to 28-days accompanied by
214
an enhancement in CO32- band intensity. This perfectly proves that the consumption of
215
Mg(OH)2 and the formation of carbonate containing phase are ongoing with time. It is
216
important to note that, the intensity of transmittance bands related to bending vibration of
217
HOH within MSH decreases with exposure time in the case of spectrum affiliated to
218
hardened samples exposed to CO2 gas for 28-days. This highlights the fact that the
219
probability of MSH carbonation enhances with the increase of exposure time. The
220
intensity of a symmetric stretching vibration band of Si-O-Si(Al) (at 1043cm-1) in the
221
case of M-WVA seems to be with higher intensity comparing with that appeared in the
222
spectrum of M-RVA (Fig. 6). This proves the higher reactivity of WVA in the interaction
223
with Mg(OH)2, resulting in an enhancement in MSH formation. Complementary, the M-
224
RVA spectrum exhibits OH band with Mg(OH)2 with lower intensity compared with that
225
identified in the case of M-WVA one. This is an indication of the high efficiency of M-
226
RVA sample in the capture of CO2.
227
3.3. DTG-analysis
228
Fig. 7 represents the DTG-thermograms of M-WVA and M-RVA hydrated for 28-days
229
(zero time). Different weight losses can be observed at different temperatures. The weight
230
loss affiliated to the dehydration of combined water within MSH are detected at
231
temperature range of 50-200 ºC (Abdel-Gawwad et al., 2018a, b). The weight loss
232
related to the dehydroxylation of Mg(OH)2 was identified at 300-400 ºC (Abdel-
233
Gawwad et al., 2018c). A small peak which appeared at 600-700 ºC is mainly referred to
234
the decomposition of carbonate group within MgCO3 (Abdel-Gawwad et al., 2018a,b,c). 10
235
The M-WVA demonstrates combined water weight loss within MSH greater than that of
236
determined in the case of M-RVA at the same curing time. The sample with the higher
237
MSH-weight loss (M-WVA) possesses the lower Mg(OH)2 content and vice versa,
238
confirming the strong relation between MSH formation and Mg(OH)2 consumption
239
during hydration process (before carbonation). This synergistic effect mainly depends on
240
the amorphous content in volcanic ash. The reactivity of volcanic ash in the consumption
241
of Mg(OH)2 enhances with the increase of amorphous content in its microstructure. This
242
is in line with previous work (Abdel-Gawwad et al., 2018a), which reported that the
243
silicate-rich-waste with high amorphous content has high efficacy on the consumption of
244
Mg(OH)2 and the formation of MSH.
245
The exposure of M-WVA to accelerated carbonation (Fig. 8) has resulted in the
246
formation of new peak related to the dehydration of combined water (at 200-300ºC)
247
within nesquehonite mineral (MgCO3.3H2O) accompanied by the increase of weight loss
248
related to decarbonation of MgCO3. With increasing exposure time, the weight loss of
249
these phases increases associating with a noticeable decrease in Mg(OH)2 weight loss.
250
This should be explained by the capture of CO2 by Mg(OH)2 in the formation of
251
carbonate-containing-phases. The M-WVA mixtures exposed for 28-days was found to
252
exhibit the lowest MSH weight losses and the formation of the highest nesquehonite
253
content. This is an indication of the potential impact of CO2 on the carbonation of MSH
254
resulting in the formation of carbonate-containing-phases. Comparing of the carbonated
255
M-WVA, the exposure of M-RVA to CO2 leads to the formation of higher nesquehonite
256
weight loss (Fig. 9). This could be related to the high availability of Mg(OH)2, in the
11
257
hydrated M-RVA at zero time (See Fig. 7) which acts as an active site for the capture of
258
CO2.
259
Generally the increase of weight loss (estimated by TGA) of hydrated and
260
carbonated phases is an indication of the increment of their content. As reported in Table
261
2, the M-WVA mixture demonstrate MSH weight loss at zero time 35% higher than that
262
recorded in the case of M-RVA one, indicating the significant role of amorphous content
263
within volcanic ash in the uptake of hydrated magnesia and the formation of MSH-binder
264
(Abdel-Gawwad et al., 2018a). Both hydrated mixtures at zero time exhibit low
265
carbonate loss, confirming the fact that the hydration is the dominant reaction which
266
occurs during the curing of the hardened sample in 99±1 % RH, complying with previous
267
work (Abdel-Gawwad et al., 2018c). A considerable increase in MgCO3 weight loss in
268
parallel with a remarkable decrease in Mg(OH)2 weight loss was detected with the
269
increase of exposure time of the hydrated samples to CO2. This demonstrates the
270
carbonation process of the hydrated magnesia is ongoing with time. The weight loss of
271
MSH slightly changes during the first 14-days of carbonation process, followed by a
272
significant decrease in its value after 28-days of CO2-exposure time. This means that after
273
the first 14-days of accelerated carbonation, the MSH (responsible for the strength of
274
hydrated samples) is carbonated by CO2, yielding MgCO3 (with lower binding capacity
275
compared to MSH) and SiO2 (Eikeland et al., 2015; Wang et al., 2019). This explains
276
why the compressive strength of the carbonated samples shift toward lower value at 28-
277
days of curing (See later Fig. 10). At all carbonation ages, The M-RVA demonstrates
278
CO3 weight losses higher than those recorded in the case of M-WVA. This should be
279
explained by the high availability of Mg(OH)2 within the hydrated M-RVA (caused by
12
280
the low pozzolanic activity of RVA) which represents active sites for carbonation
281
reaction. The mathematical calculations prove that the intrusion of CO2 sequestration by
282
the hardened materials enhances with time. At 28-days of exposure time, the M-WVA
283
and M-RVA samples absorb ~ 22 and 26% CO2, respectively. This means that each ton
284
of the prepared materials absorb ~220 and 260 kg/ton, respectively. This strongly
285
contributes to the mitigation of the global warming potential (GWP) resulted from
286
different industrial activities.
287
3.4. Physical and mechanical properties
288
The relationship between compressive strength development and porosity of the
289
carbonated samples at different ages is displayed in Fig. 10. Firstly, the hardened M-
290
WVA and M-RVA at zero time demonstrate compressive strength values of 62 and
291
49MPa, respectively. This variation in strength is mainly due to the change in amorphous
292
content in each volcanic ash, meaning that the physical nature of volcanic ash plays a
293
circular role in the performance of the hardened material (Abdel-Gawwad et al., 2018a).
294
As proved by Rietveld XRD-quantitative analysis, WVA represents amorphous content
295
(72 %) higher than that recorded by RVA (39 %). The ash with high amorphous content
296
exhibits high capability to interact with Mg(OH)2, yielding excessive content of MSH
297
binding phase, complying with TG/DTG and FTIR-analyses. At the first 14-days of
298
carbonation, a significant increase in compressive strength associating with porosity
299
reduction has been recorded. The positive role of accelerated carbonation on strength
300
development and porosity reduction has been observed in the case of different
301
cementitious systems having MgO (Morrison et al., 2016). The reason behind this effect
302
is the increase of CO2-capture (See Fig. 11), yielding carbonate-containing-phases. 13
303
The accumulation of carbonate phases mainly contributes to the reduction of pore
304
volume of the hardened material. Moreover, the CO2-capture has no effect on MSH-
305
binder formed in the hardened matrix at this period (Fig. 11). Interestingly, the hardened
306
M-WVA mixture exposed to CO2 for 14-days represents compressive strength value
307
higher than that of the hydrated sample (at zero time) by ~47 % accompanied by the
308
lower porosity. Although the hardened M-RVA mixture shows compressive strength
309
values lower than those of M-WVA one, it records compressive strength development
310
higher than that of M-WVA mixture, especially at 14-days of CO2-exposure (55 %). This
311
should be explained by the higher zero-time porosity (32 %) of the hardened M-RVA
312
compared to that of M-WVA one (24%). The higher porosity has potential impact on the
313
acceleration of carbonation rate including the fast intrusion of CO2-gas into the hardened
314
materials (Morrison et al., 2016). The high porosity of the hardened M-RVA mixture at
315
zero time is due to the low amorphous content in RVA as it has low efficacy in the
316
interaction with hydrated magnesium oxide, resulting in the formation of low MSH-
317
content. Moreover, the high crystallinity of RVA causes the formation of excessive
318
Mg(OH)2 content which in turn easily transforms to nesquehonite after exposure of
319
hardened material to CO2.
320 321
It is postulated that the rate of CO2 diffusion into the hardened material enhances
322
with the increase of its pore volume, confirming the higher CO2-capture in the case of M-
323
RVA sample as compared with M-WVA one. The 28-days carbonated samples
324
demonstrate the highest CO2-capture (Fig. 11). Nevertheless, they represent compressive
325
strength lower than those of 14-days carbonated ones (Fig. 10). This is likely derived
14
326
from the fact that the continuous exposure of hardened samples to CO2 has resulted in a
327
significant reduction in MSH-content within hardened matrix, complying with TG/DTG
328
results. It can be said that regardless the role of amorphous content in volcanic ashes in
329
prepared materials, it potentially affects the rate of CO2 capture within hardened
330
materials.
331
3.5. Mechanism of accelerated carbonation
332
The reaction mechanism of CO2-sequestration by the fabricated materials is shown in
333
Fig. 12 (Fernández Bertos et al., 2004). The capture process initiates by the diffusion
334
and penetration of CO2-gas through the hardened materials, followed by transformation
335
of CO2 from gas state to liquid one (H2CO3: as intermediate step). This transformation is
336
caused by the high moisture content within hardened materials. Carbonic acid (H2CO3) is
337
unstable compound which immediately ionized to H+, HCO3-, and CO32-. Carbonate ions
338
interact with Mg(OH)2 (as a byproduct of the hydration of MgO-volcanic ashes
339
mixtures), yielding nesquehonite (MgCO3.3H2O). At later ages, MSH (as the main binder
340
of the hardened materials) can be carbonated to form silicate hydrate and MgCO3.3H2O,
341
resulting in a significant loss in mechanical properties. As shown in Fig. 13, a noticeable
342
change in the color of hardened materials was recorded when they exposed to accelerated
343
carbonation, confirming the formation of carbonate phase caused by CO2-caprture by
344
these materials.
345
3.6. Beneficial use of the prepared materials
346
The above mentioned outcomes proved that the designed hardened materials from
347
naturally occurring volcanic ashes and MgO were found to have high efficacy in the CO2-
348
capture accompanied a remarkable change in their physical and mechanical properties. 15
349
Moreover, the proposed method in the present study can be beneficially applied in the
350
sustainable disposal aluminosilicate and magnesia-rich-wastes in the cleaner production
351
of cementitious materials with high performance and efficacy in the sequestration of
352
CO2-gas. This not only strongly contributes to the conservation of naturally-occurring
353
resources used in construction, but also reflects on the mitigation of global warming
354
potential caused by industrial and human activities.
355 356
4. Conclusions
357
The work focused on the impact of accelerated carbonation on the performance of the
358
hardened magnesium silicate cement under humidity and accelerated carbonation
359
conditions. These materials were fabricated by mixing magnesium oxide-volcanic ashes
360
blends with water, followed by humidity curing. As proved by different analyses,
361
magnesium silicate hydrate and magnesium hydroxide are the main hydration products
362
within fabricated materials. Magnesium hydroxide was found to be the active site for
363
CO2-capture, resulting in the formation of nesquehonite phase in the open pores of the
364
hardened mixtures. The amorphous content in volcanic ashes plays a circular role in the
365
performance of the fabricated materials and their ability to CO2-capture. The fabricated
366
material containing volcanic ash with low amorphous content represented the higher
367
effectiveness in the CO2-sequestration compared to that having high amorphous content.
368
The main reasons behind this criterion are the formation of porous hardened material and
369
the enhancement of magnesium hydroxide availability. The beneficial use of these
370
materials in different engineering projects is not only based on their high efficacy in the
16
371
CO2-capture, but also due to the enhancement of their physical and mechanical properties
372
with CO2-exposure.
373 374
Acknowledgment
375
I would like to give my deepest appreciation to my wife Dr. Fatma A. M. Abdel-aal,
376
Lecturer in pharmaceutical analytical chemistry department, Faculty of Pharmacy,
377
Assiut University, Egypt for her faithful and honest efforts with me. She supported and
378
stands by my side in every moment in this research. A special gratitude to the Consejo
379
Nacional De Ciencia Y Tecnologia (CONACYT) for their support and faithful efforts
380
to accomplish this work. A faithful important thankful to Prof. Dr. Ricardo Morales
381
Estrella, and Senorita Griselda Ledesma Lopez Michoacan State University,
382
Mexico, for their faithful support and efforts to perform this research.
383
A special gratitude to the president of New Valley University Prof. Dr. Abdel Aziz
384
Tantawy, Prof. Dr. Mohamoud Mohamed Ahmed and Dr. Mohamed Osman for
385
their faithful support during this project. As well as, I would like to thank Profs.
386
Abdalla M. El Ayyat and Nageh A. Obaidalla, Assiut University, Egypt, for their
387
support during my scientific career. Finally, a special gratitude to Prof. J.L. Rico & Mr.
388
Manuel Robles Laboratorio de Catalisis, Faultad de Ingenieria Quimica, Edificio
389
VI, for their support in the lab works.
390 391 392 17
393
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492 493 494 495
Table 1: Chemical compositions and physical properties of starting materials
496
Table 2: Mixing proportions of magnesium silicate-based cement
497
Table 3: TG-weight losses and calculated CO2 content sequestrated by the prepared materials at different CO2-exposure times
498 499 500 501
Fig. 1. XRD-patterns of white and red volcanic ashes (WVA and RVA)
502
Fig. 2. Basic diagram of the preperation, hydration, and carbonation processes
503
Fig. 3. XRD-patterns of the hardened carbonated M-WVA mixtures at different times of
504 505 506
CO2-exposure Fig. 4. XRD-patterns of the carbonated M-WVA and M-RVA mixtures at 28-days of CO2-exposure
507
Fig. 5. FTIR-spectra of the carbonated M-WVA mixtures at different times of CO2-
508
exposure
509
Fig. 6. FTIR-spectra of the carbonated M-WVA and M-RVA mixtures at 28-days of
510 511 512
CO2-exposure Fig. 7. DTG-thermograms of the hardened M-WVA and M-RVA mixtures at 28-days of curing in humidity
21
513 514 515 516 517 518 519 520 521 522 523
Fig. 8. DTG-thermograms the carbonated M-WVA mixture at different times of CO2exposure Fig. 9. DTG-thermograms of the hardened M-WVA and M-RVA mixtures at 28-days of CO2-exposure Fig. 10. Relationship between strength and porosity of the carbonated samples exposed to CO2-gas at different times Fig. 11. Relationship between CO2-capture and MSH content of the carbonated samples exposed to CO2-gas at different times Fig. 12. Proposed reaction mechanism of the accelerated carbonation adapted from (Fernández Bertos et al., 2004) Fig. 13. Digital photos of hardened samples before and after accelerated carbonation
524
22
Table 1: Chemical compositions and physical properties of starting materials
Mixtures notations
Chemical compositions, wt. %
Physical properties
SiO2
CaO
MgO
WVA
71.30
2.39
0.45
4.60
13.10
1.17
5.01
0.91
0.83
2.65
72
White
RVA
47.32 10.81
2.32
15.61
15.30
2.30
1.84
1.29
2.52
2.83
39
Red
99.57
-
-
-
-
-
-
1.92
-
White
MgO
-
-
Fe2O3 Al2O3 Na2O K2O P2O5 TiO2 Specific gravity
Amorphous Color content
Table 2: Mixing proportions of magnesium silicate-based cement WVA
RVA
MgO
Mixture notation
W/P ratio wt. %
WVA-MgO
25
-
75
0.40
RVA-MgO
-
25
75
0.40
Table 3: TG-weight losses and calculated CO2 content sequestrated by the prepared materials at different CO2-exposure times Mixtures notations
M-WVA
M-RVA
Exposure time (day)
Weight loss wt. % CO2 wt. % ratio in the sample
MSH
Mg(OH)2
MgCO3
Total loss
0
3.20
4.12
0.38
10.49
3.62
1
3.31
3.54
1.65
13.38
12.33
14
3.39
2.16
2.89
14.75
18.09
28
2.54
1.75
3.54
15.97
22.16
0
2.36
5.16
0.45
11.25
4.01
1
2.41
3.28
2.19
13.51
16.21
14
2.45
2.14
3.26
14.99
21.74
28
2.01
1.86
4.19
16.04
26.12
Fig. 1. XRD-patterns of white and red volcanic ashes (WVA and RVA)
1
Fig. 2. Basic diagram of the preperation, hydration, and carbonation processes
2
Fig. 3. XRD-patterns of the hardened carbonated M-WVA mixtures at different times of CO2exposure
3
Fig. 4. XRD-patterns of the carbonated M-WVA and M-RVA mixtures at 28-days of CO2exposure
4
1-d
14-d
28-d
Transmittance, %
Zero time
4000
3400
2800
2200
1600
1000
400
Wavenumber, cm-1 Fig. 5. FTIR-spectra of the carbonated M-WVA mixtures at different times of CO2-exposure
5
M-WA
Transmittance, %
M-RA
4000
3400
2800
2200
1600
1000
400
Wavenumber, cm-1 Fig. 6. FTIR-spectra of the carbonated M-WVA and M-RVA mixtures at 28-days of CO2exposure
6
2
DTG, mg/min
1.6 CO32- within carbonate phase
1.2
0.8 H2O within MSH
0.4
M-WA M-RA
OH within Mg(OH)2
0 0
100
200
300
400
500
600
700
800
Temperature, ºC Fig. 7. DTG-thermograms of the hardened M-WVA and M-RVA mixtures at 28-days of curing in humidity
7
2
DTG mg/min
1.6
1.2
H2O within nesquehonite
0.8 CO32- within nesquehonite
H2O within MSH
0.4 OH within Mg(OH)2
Zero time
0 0
100
200
300
400
500
600
700
800
Temperature, ºC Fig. 8. DTG-thermograms the carbonated M-WVA mixture at different times of CO2-exposure
8
2
DTG mg/min
1.6
1.2
H2O within nesquehonite H2O within MSH
0.8 OH within Mg(OH)2
0.4
CO32- within nesquehonite
M-WA M-RA 0 0
100
200
300
400
500
600
700
800
Temperature, ºC Fig. 9. DTG-thermograms of the hardened M-WVA and M-RVA mixtures at 28-days of CO2exposure
9
Fig. 10. Relationship between strength and porosity of the carbonated samples exposed to CO2gas at different times
10
Fig. 11. Relationship between CO2-capture and MSH content of the carbonated samples exposed to CO2-gas at different times
11
Fig. 12. Proposed reaction mechanism of the accelerated carbonation adapted from (Fernández Bertos et al., 2004)
12
M-RVA
M-WVA
Before
Before
After After
Fig. 13. Digital photos of hardened samples before and after accelerated carbonation
13
Highlights ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ Eco-friendly Cementitious material with high CO2 capture Capacity.
Two naturally volcanic ashes and reactive magnesium oxide are the main raw materials
The amorphous content plays an important role in the performance of CO2 absorption
The absorption capacity of CO2 was ranging from (~260- 220 kg/ton) in 28 days
1
Declaration of Interest Statement
The authors confirms that there is no conflict of interest
Best Regards, Hassan Soltan Hassan Corresponding author Cleaner Production Author & Reviewer
S0959-6526(19)34745-6
DOI:
https://doi.org/10.1016/j.jclepro.2019.119875
Reference:
JCLP 119875
To appear in:
Journal of Cleaner Production
Received Date: 6 August 2019 Revised Date:
23 December 2019
Accepted Date: 24 December 2019
Please cite this article as: Abdel-Gawwad HA, Hassan HS, Vásquez-García SR, Israde-Alcántara I, Ding Y-C, Martinez-Cinco MA, Abdel-Aleem S, Khater HM, Tawfik TA, El-Kattan IM, Towards a clean environment: The potential application of eco-friendly magnesia-silicate cement in CO2 sequestration, Journal of Cleaner Production (2020), doi: https://doi.org/10.1016/j.jclepro.2019.119875. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. 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. © 2019 Published by Elsevier Ltd.
Authors Contributions Section
Hamdy A. Abdel-Gawwad Preparation of chemicals and materials, Methodology, Statistical analysis, Interpretation of data, Spectroscopic analysis, Revision of manuscript, language editing
Hassan Soltan Hassan Preparation of chemicals and materials, Methodology, Statistical analysis, Interpretation of data, Spectroscopic analysis, Revision of manuscript, language editing
S.R. Vásquez-García Preparation of chemicals and materials, Methodology, Statistical analysis, Interpretation of data, Spectroscopic analysis, Revision of manuscript, language editing
Isabel Israde-Alcántara Preparation of chemicals and materials, Methodology, Statistical analysis, Interpretation of data, Spectroscopic analysis, Revision of manuscript, language editing
Yung-Chin Ding Preparation of chemicals and materials, Methodology, Statistical analysis, Interpretation of data, Spectroscopic analysis, Revision of manuscript, language editing
Marco Antonio Martinez-Cinco Preparation of chemicals and materials, Methodology, Statistical analysis, Interpretation of data, Spectroscopic analysis, Revision of manuscript, language editing
S. Abdel-Aleem Preparation of chemicals and materials, Methodology, Statistical analysis, Interpretation of data, Spectroscopic analysis, Revision of manuscript, language editing
Hesham M. Khater Preparation of chemicals and materials, Methodology, Statistical analysis, Interpretation of data, Spectroscopic analysis, Revision of manuscript, language editing
Ibrahim M. El-Kattan Preparation of chemicals and materials, Methodology, Statistical analysis, Interpretation of data, Spectroscopic analysis, Revision of manuscript, language editing
Taher A. Tawfik Preparation of chemicals and materials, Methodology, Statistical analysis, Interpretation of data, Spectroscopic analysis, Revision of manuscript, language editing
CO2 Sequestration Process
CO2
Eco-Friendly Method
CO2
CO2
MgO Different Types Of Volcanic Ashes + MgO
Super CO2 sequestration cement
1
Towards a clean environment: The potential application of eco-friendly
2
magnesia-silicate cement in CO2 sequestration
3
Hamdy A. Abdel-Gawwad*1, Hassan Soltan Hassan*2,3, S.R. Vásquez-García2, Isabel Israde-Alcántara4,
4
Yung-Chin Ding5, Marco Antonio Martinez-Cinco2, S. Abdel-Aleem6, Hesham M. Khater1,
5
Taher A. Tawfik7, Ibrahim M. El-Kattan8
6
1
Raw Building Materials Research and Processing Technology Institute, Housing and Building National
7 8
Research Center (HBRC), Cairo, Egypt 2
Posgrado de Ingeniería Química, Universidad Michoacana de San Nicolas de Hidalgo, 58000, Morelia,
9
Michoacan, Mexico 3
10 4
11
Geology Department, Faculty of Science, New Valley University 72511, El- Kharga, Egypt
Instituto de Investigaciones en ciencias de latierra Edif. U-4, Cd. Universitaria, Morelia, Michoacán,
12 13
Mexico 5
Institute of Mineral Resources Engineering, National Taipei University of Technology, Taipei, Taiwan 6
14 15
7
16
8
Construction and Building Department, Higher Institute of Engineering on 6thOctober, Giza, Egypt.
Environmental Science and Industrial Development Department, Faculty of Postgraduate Studies for
17 18
Chemistry Department, Faculty of Science, Fayoum University, Fayoum, Egypt
Advanced Sciences, Beni-Suef University, Beni-Suef, Egypt * Corresponding authors: Hassan Soltan Hassan (email: [email protected])
19
Hamdy A. Abdel-Gawwad (email: [email protected])
20 21
Abstract
22
The key point of this study is the fabrication of magnesia-based cement with promising
23
mechanical properties and high efficiency of CO2-capture. The naturally occurring
24
volcanic ashes (white & red ashes) and reactive magnesium oxide are the main materials
25
used in the synthesis of eco-friendly CO2-capture materials. Volcanic ashes were
26
individually mixed with reactive magnesium oxide at ash to magnesium oxide ratio of
27
25:75 Wt. %. The dry blends can react with water to yield hardened materials (at ambient
1
28
temperature) with compressive strength depends on the type of volcanic ash. A
29
considerable change in the features of the hardened samples was recorded when the
30
fabricated materials exposed to 100% CO2 gas for 28-days. This change is mainly due to
31
CO2-capture by magnesium hydroxide Mg(OH)2 within the fabricated materials, resulting
32
in the formation of Nesquehonite minerals MgCO3.3H2O as proved by X-ray diffraction,
33
thermo-gravimetric, and infra-red instrumental techniques. The thermo-gravimetric
34
analysis demonstrates that, the fabricated sample containing low amorphous red ashes has
35
higher CO2-capture capacity (~260 kg/ton) compared to that having high amorphous
36
white volcanic ashes (~220 kg/ton) at 28-days of CO2-exposure. Accordingly, the
37
fabricated magnesia-based cement is not only used as cementitious material with
38
outstanding mechanical properties, but also used as a super CO2-absorbent precursor.
39
This can strongly contribute in the mitigation of global warming potential caused by
40
different industrial activities.
41 42
Keywords: Volcanic ashes; CO2-capture; Global warming phenomenon; Magnesia-based
43
cement
44
1. Introduction
45
Although the development of science and technology is the urgent issue in the 21th-
46
centurey, it led to serious climatic change that could threaten the mankind survival and
47
other life forms. Indeed, the increase of CO2 emission (which is mainly resulted from
48
industrial activities) is the essential reason behind global warming phenomenon that
49
strongly affects the climatic change (Lee et al., 2010; Miller and Croft). As stated by
50
the UN Intergovernmental Panel on Climatic Change (IPCC), the concentration of CO2 in
51
atmosphere will reach 550 ppm as earlier as 2050, causing an increase in the average 2
52
temperature of the earth by 1.4-5.8ºC, a rise in sea level, extreme drought, wildfires,
53
floods, and food shortages for hundreds of millions of people (The UN
54
Intergovernmental Panel on Climatic Change (IPCC) 2005). Cement (Abdel-
55
Gawwad et al., 2019a; Abdel-Gawwad et al., 2019b; Hassan et al., 2019), petro-
56
chemical (Tao and Patel, 2009) and iron & steel manufacturing (Peng et al., 2016) are
57
the most industries, which mainly contribute to the increment of CO2- emission. Thus, the
58
modification in the processing of these industries to mitigate CO2-emission and the
59
invention of a new technology with high efficacy in the CO2-separation are urgently
60
required.
61
CO2-sequestration as an innovative method of gas absorption has been previously
62
studied by different researchers via the exposure of cementitious materials to CO2 gas
63
(Pan et al., 2016; Sharma and Goyal, 2018). CO2-sequestration method was performed
64
by the transformation of hydration products, within the cementitious materials, into
65
carbonate-containing phases. The rate of CO2-capture mainly depends on different
66
parameters, including CO2-concentration, air humidity, air temperature, and cement type
67
(Behfarnia and Rostami, 2017; Czarnecki and Woyciechowski, 2015).
68
The carbonation was found to have a detrimental effect on the structural Portland
69
cement concrete (Breccolotti et al., 2013; Kim et al., 2009). The negative effect of
70
carbonation on the properties of structural concrete is originated from the significant drop
71
in pH value as the carbonation has high efficiency on the transformation of calcium
72
hydroxide within hardened concrete (pH ~12) into calcium carbonate (pH ~9), resulting
73
in an enhancement of the probability of steel corrosion (Kulakowski et al., 2009).
74
Moreover, at later ages of CO2- exposure, CO2 can destruct the binding capacity of the 3
75
hardened materials by its interaction with calcium silicate hydrate (the dominant binding
76
phase of hydrated cement) to yield calcium carbonate (with lower binding capacity) and
77
silicon dioxide (Wang et al., 2019). Nevertheless, Portland cement demonstrated the
78
higher carbonation resistivity compared to that of alkali activated cement (Bakharev et
79
al., 2001; Li and Li, 2018). The main reason behind this finding is the presence of
80
Ca(OH)2 in structural Portland cement concrete as it acts as a carrier for CO2,
81
accompanied by the formation protective layers of calcium carbonate on calcium silicate
82
hydrate phase (Bakharev et al., 2001; He et al., 2018).
83
The replacement of Portland cement by magnesium oxide has resulted in the
84
formation of what is known as MgO-cement (Gonçalves et al., 2019);. This cement
85
represented several advantages over Portland cement, including highest capability for
86
CO2-sequestration, accompanied by the highest resistivity of the hydration and
87
carbonation product to aggressive media, enhancing the probability of utilization of
88
different industrial byproducts as it has lower sensitivity to impurities, potential to be re-
89
use as MgO can be used alone as cementitious material by its carbonation (Unluer and
90
Al-Tabbaa, 2013). The MgO utilization alone has several advantages in terms of
91
capability of CO2-capture, mechanical properties and durability over Portland cement-
92
MgO (Liska and Al-Tabbaa, 2008, 2009). The MgO-MgCO3 porous block showed
93
higher CO2 uptake and compressive strength compared to Portland cement block at the
94
same accelerated carbonation conditions (Unluer and Al-Tabbaa, 2013). In the other
95
work, MgO was used alone in the CO2-capture. This method was beneficially used in the
96
production of light weight blocks with density of 700-900 kg/m3 and compressive
97
strength reaches 2MPa (Morrison et al., 2016).
4
98
Magnesium silicate-based cement is categorized as eco-friendly cement as it
99
generates CO2-emission too lower than that of Portland cement (Shen et al., 2016). This
100
cement can be prepared by mixing reactive MgO with amorphous silicate precursors (Jin
101
and Al-Tabbaa, 2013; Zhang et al., 2011). Different silicate-rich wastes have been used
102
in the fabrication of this cement comprising silica fume (Zhang et al., 2018), glass and
103
ceramic wastes (Abdel-Gawwad et al., 2018a), fly ash (Choi et al., 2014) , and rich
104
husk ash, (Sonat and Unluer, 2019). The main hydration products of the prepared
105
cement are magnesium silicate hydrate and magnesium hydroxide (Abdel-Gawwad et
106
al., 2018a; Sonat and Unluer, 2019). Although few researchers have conducted the
107
normal and accelerated carbonation on naturally-occurring magnesium silicate rock
108
(Eikeland et al., 2015), up till now there is no published work have evaluate the
109
efficiency of the synthesized magnesium silicate cement in CO2-sequestration and its
110
reflection on its performance.
111
Accordingly, the motivation behind this work is the evaluation of the impact of
112
accelerated carbonation on the fabricated magnesium silicate cement in which reactive
113
magnesium oxide and naturally occurring volcanic ashes are the main precursor. The
114
impact of carbonation age and volcanic ash nature (including chemical composition and
115
amorphous content) on the mechanical properties and the rate of CO2-capture have been
116
evaluated. The reasonable reason behind this study is the formulation of cementitious
117
materials, with high mechanical properties and low production energy, which could be
118
beneficially used in the production of non-structural concrete with high efficacy in the
119
sequestration of CO2.
120 5
121
2. Experimental
122
2.1. Materials
123
Two types of naturally occurring volcanic ashes (namely, white and red volcanic ashes)
124
and reactive magnesium oxide (MgO) are the main raw materials used in the fabrication
125
of CO2-capture materials. White and red volcanic ashes (WVA and RVA) were obtained
126
from, a field area close to Morelia city, Michoacán state, Mexico; meanwhile, MgO was
127
purchased from Fisher Scientific Chemical Company (UK). The chemical compositions,
128
which were conducted by X-ray fluorescence (XRF: Xios PW1400), and physical
129
properties of volcanic ashes and MgO are reported in Table 1. The chemical analyses of
130
the starting materials prove that the WVA and RVA are mainly aluminosilicate materials.
131
X-ray diffraction (XRD) (Fig. 1) proves that, the pattern of WVA represents a hump at 2θ
132
range of 15-30º with the appearance of well-resolved sharp peaks affiliated to crystalline
133
phases such as albite, and margarita minerals. This hump is an indication of the
134
amorphous nature of WVA. The RVA demonstrates crystalline thenardite, margarita, and
135
wavelite peaks with no appearance of an amorphous hump, indicating the low
136
amorphicity content in RVA. The quantitative Rietveld XRD-analysis shows that, the
137
WVA demonstrates amorphicity content of 72% higher than that identified in the case of
138
RVA (39%).
139
2.2. Fabrication of CO2-capture materials
140
Flow chart of the preparation steps including hydration and carbonation curing is
141
represented in Fig. 2. Firstly, WVA and RVA are ground to pass through 100 µm sieve
142
followed by dry mixing with MgO for 5 min, using ball mill machine. Volcanic ashes-
143
MgO blends were designed at weight ratio of 1:3. The MgO was used with high content 6
144
in cement blend to offer favorable conditions for accelerated carbonation. After
145
formulation step, mixing water (at water to solid ratio of 0.40) was added to homogenous
146
dry WVA-MgO and RVA-MgO mixes, yielding workable pastes. The details of mixing
147
proportions are reported in Table 2. The fresh pastes were transferred to stainless steel
148
molds of 50 x 5 x 50 mm, followed by curing in humidity chamber with 99±1% relative
149
humidity (RH) at 23±2ºC. After 24h of curing, the hardened cubes were demolded and
150
cured at the same conditions for 28-days to achieve considerable compressive strength.
151
The 28-days cured samples (zero time of carbonation) were transferred to
152
stainless steel CO2-champer with RH of 75%. To ensure the medium with 100% CO2
153
environment before conducting accelerated carbonation test, the open chamber was
154
flashed with CO2 for 2 min. After CO2-flushing, the top outlet of the chamber was closed
155
to proceed the accelerated carbonation of the hardened materials. The CO2-pressure
156
adjusted at 20 atm. using dial gauge contented to CO2 cylinder. At different time intervals
157
such as 1, 14, and 28-days, the carbonated samples were taken out and kept for 24h at
158
50±5 % RH and 23±2ºC before conducting strength measurements and solid phase
159
identification using XRD, thermo-gravemetric (TG/DTG) analysis, and Fourier transform
160
infrared (FTIR) spectroscopy.
161
2.3. Experimental methods
162
Compressive strength testing was carried out on the hardened cubes following the
163
procedure described by (C109M, 2016). The compressive strength value was taken as an
164
average of 5-specimens readings. In order to remove irregularities, the surface of the
165
specimen was carefully polished by filter paper. Compressive strength measurements
166
were carried out using five tones German Brüf Pressing Machine with a maximum load 7
167
capacity of 175kN. Mercury intrusion data from an Auto Pore IV 9500 porosimeter was
168
applied to determine the change in the total porosity of the hardened materials before and
169
after carbonation reaction.
170 171
2.4. Phase identifications
172
XRD-analysis was used to determine the crystalline phases in the cured and carbonated
173
samples using Philips PW3050/60 diffractometer with 5 to 60 (2θº) scanning range,
174
1s/step scanning speed, and 0.05°/step resolution. All the obtained peaks were identified
175
according to powder diffraction file (PDF). A DT-50-Thermal Analyzer (Schimadzu Co-
176
Kyoto, Japan), which provided by cryostat for cooling process, was used to perform the
177
TGA of carbonated and cured samples. The weight percentage of CO2-sequestrated (CO2
178
wt. %) by the hardened samples during CO2-exposure was calculated by dividing the
179
weight loss of MgCO3-phase (WL) by the total weight loss (TWL) of sample as follow: 2,
.% =
∗ 100
180
FTIR-analysis was carried out on some selected samples in order to identify the
181
functional groups of hydration products via KBr discussing Genesis-IIFT-IR
182
spectrometer at the wavenumber range of 400-4000 cm-1.
183 184
3. Results and discussion
185
Interestingly, reactive magnesium oxide-volcanic ash blends can react with water to yield
186
hardened materials with acceptable mechanical properties. The exposure of the hardened
187
materials to accelerated carbonation causes a significant changes their performances.
188
3.1. XRD-analysis 8
189
The X-ray diffractograms (Fig. 3) proved that brucite {Mg(OH)2}, and periclase (MgO),
190
quartz, and albite are the main phases of the hardened M-WVA mixture at zero time. The
191
exposure of hardened material to CO2 has resulted in the formation of nesquehonite
192
(MgCO3. 3H2O: PDF # 20-669). Same observation was reported by the previous work
193
(Liska et al., 2008; Vandeperre and Al-Tabbaa, 2007; Dung and Unluer, 2017) as the
194
nesquehonite phases has been formed in MgO-fly ash-Portland cement (PC) system. In
195
contrast, Abdel-Gawwad et al., (2018c) have reported that magnesium carbonate was
196
formed during accelerated carbonation of hardened PC-MgO blends. The increase of
197
exposure time leads to the enhancement of nesquehonite formation accompanied by the
198
increase of Mg(OH)2 consumption. Mg(OH)2 acts as an active site for CO2 capture as it
199
can interact with hydrated CO2 to yield nesquehonite mineral. It’s worth mentioning that
200
magnesium silicate hydrate (MSH: as the main binder of this system) is characterized by
201
low crystallinity; so, it cannot be detected by XRD. This is in consistence with previous
202
works (Abdel-Gawwad et al., 2018b). As represented in Fig. 4, there is no difference
203
between the mineralogical compositions of the hydration and carbonation products of M-
204
WVA and M-RVA samples. Nevertheless, the pattern affiliated to M-RVA sample
205
exhibits brucite mineral with lower peak intensity compared to that identified in the case
206
of M-WVA one. This gives strong evidence on the high efficacy of M-RVA in the
207
sequestration of CO2.
208
3.2. FTIR-spectroscopy
209
The FTIR spectra also confirmed that the transmittance bands affiliated to stretching
210
vibration of CO32- (at 1479 cm-1) in the case of carbonated M-WVA was appeared with
211
higher intensity compared to that identified in the case of zero time-hardened samples 9
212
(Fig. 5). The intensity of band characteristics for stretching vibration of OH within
213
Mg(OH)2 (at 3694cm-1) decreases with CO2 exposure time up to 28-days accompanied by
214
an enhancement in CO32- band intensity. This perfectly proves that the consumption of
215
Mg(OH)2 and the formation of carbonate containing phase are ongoing with time. It is
216
important to note that, the intensity of transmittance bands related to bending vibration of
217
HOH within MSH decreases with exposure time in the case of spectrum affiliated to
218
hardened samples exposed to CO2 gas for 28-days. This highlights the fact that the
219
probability of MSH carbonation enhances with the increase of exposure time. The
220
intensity of a symmetric stretching vibration band of Si-O-Si(Al) (at 1043cm-1) in the
221
case of M-WVA seems to be with higher intensity comparing with that appeared in the
222
spectrum of M-RVA (Fig. 6). This proves the higher reactivity of WVA in the interaction
223
with Mg(OH)2, resulting in an enhancement in MSH formation. Complementary, the M-
224
RVA spectrum exhibits OH band with Mg(OH)2 with lower intensity compared with that
225
identified in the case of M-WVA one. This is an indication of the high efficiency of M-
226
RVA sample in the capture of CO2.
227
3.3. DTG-analysis
228
Fig. 7 represents the DTG-thermograms of M-WVA and M-RVA hydrated for 28-days
229
(zero time). Different weight losses can be observed at different temperatures. The weight
230
loss affiliated to the dehydration of combined water within MSH are detected at
231
temperature range of 50-200 ºC (Abdel-Gawwad et al., 2018a, b). The weight loss
232
related to the dehydroxylation of Mg(OH)2 was identified at 300-400 ºC (Abdel-
233
Gawwad et al., 2018c). A small peak which appeared at 600-700 ºC is mainly referred to
234
the decomposition of carbonate group within MgCO3 (Abdel-Gawwad et al., 2018a,b,c). 10
235
The M-WVA demonstrates combined water weight loss within MSH greater than that of
236
determined in the case of M-RVA at the same curing time. The sample with the higher
237
MSH-weight loss (M-WVA) possesses the lower Mg(OH)2 content and vice versa,
238
confirming the strong relation between MSH formation and Mg(OH)2 consumption
239
during hydration process (before carbonation). This synergistic effect mainly depends on
240
the amorphous content in volcanic ash. The reactivity of volcanic ash in the consumption
241
of Mg(OH)2 enhances with the increase of amorphous content in its microstructure. This
242
is in line with previous work (Abdel-Gawwad et al., 2018a), which reported that the
243
silicate-rich-waste with high amorphous content has high efficacy on the consumption of
244
Mg(OH)2 and the formation of MSH.
245
The exposure of M-WVA to accelerated carbonation (Fig. 8) has resulted in the
246
formation of new peak related to the dehydration of combined water (at 200-300ºC)
247
within nesquehonite mineral (MgCO3.3H2O) accompanied by the increase of weight loss
248
related to decarbonation of MgCO3. With increasing exposure time, the weight loss of
249
these phases increases associating with a noticeable decrease in Mg(OH)2 weight loss.
250
This should be explained by the capture of CO2 by Mg(OH)2 in the formation of
251
carbonate-containing-phases. The M-WVA mixtures exposed for 28-days was found to
252
exhibit the lowest MSH weight losses and the formation of the highest nesquehonite
253
content. This is an indication of the potential impact of CO2 on the carbonation of MSH
254
resulting in the formation of carbonate-containing-phases. Comparing of the carbonated
255
M-WVA, the exposure of M-RVA to CO2 leads to the formation of higher nesquehonite
256
weight loss (Fig. 9). This could be related to the high availability of Mg(OH)2, in the
11
257
hydrated M-RVA at zero time (See Fig. 7) which acts as an active site for the capture of
258
CO2.
259
Generally the increase of weight loss (estimated by TGA) of hydrated and
260
carbonated phases is an indication of the increment of their content. As reported in Table
261
2, the M-WVA mixture demonstrate MSH weight loss at zero time 35% higher than that
262
recorded in the case of M-RVA one, indicating the significant role of amorphous content
263
within volcanic ash in the uptake of hydrated magnesia and the formation of MSH-binder
264
(Abdel-Gawwad et al., 2018a). Both hydrated mixtures at zero time exhibit low
265
carbonate loss, confirming the fact that the hydration is the dominant reaction which
266
occurs during the curing of the hardened sample in 99±1 % RH, complying with previous
267
work (Abdel-Gawwad et al., 2018c). A considerable increase in MgCO3 weight loss in
268
parallel with a remarkable decrease in Mg(OH)2 weight loss was detected with the
269
increase of exposure time of the hydrated samples to CO2. This demonstrates the
270
carbonation process of the hydrated magnesia is ongoing with time. The weight loss of
271
MSH slightly changes during the first 14-days of carbonation process, followed by a
272
significant decrease in its value after 28-days of CO2-exposure time. This means that after
273
the first 14-days of accelerated carbonation, the MSH (responsible for the strength of
274
hydrated samples) is carbonated by CO2, yielding MgCO3 (with lower binding capacity
275
compared to MSH) and SiO2 (Eikeland et al., 2015; Wang et al., 2019). This explains
276
why the compressive strength of the carbonated samples shift toward lower value at 28-
277
days of curing (See later Fig. 10). At all carbonation ages, The M-RVA demonstrates
278
CO3 weight losses higher than those recorded in the case of M-WVA. This should be
279
explained by the high availability of Mg(OH)2 within the hydrated M-RVA (caused by
12
280
the low pozzolanic activity of RVA) which represents active sites for carbonation
281
reaction. The mathematical calculations prove that the intrusion of CO2 sequestration by
282
the hardened materials enhances with time. At 28-days of exposure time, the M-WVA
283
and M-RVA samples absorb ~ 22 and 26% CO2, respectively. This means that each ton
284
of the prepared materials absorb ~220 and 260 kg/ton, respectively. This strongly
285
contributes to the mitigation of the global warming potential (GWP) resulted from
286
different industrial activities.
287
3.4. Physical and mechanical properties
288
The relationship between compressive strength development and porosity of the
289
carbonated samples at different ages is displayed in Fig. 10. Firstly, the hardened M-
290
WVA and M-RVA at zero time demonstrate compressive strength values of 62 and
291
49MPa, respectively. This variation in strength is mainly due to the change in amorphous
292
content in each volcanic ash, meaning that the physical nature of volcanic ash plays a
293
circular role in the performance of the hardened material (Abdel-Gawwad et al., 2018a).
294
As proved by Rietveld XRD-quantitative analysis, WVA represents amorphous content
295
(72 %) higher than that recorded by RVA (39 %). The ash with high amorphous content
296
exhibits high capability to interact with Mg(OH)2, yielding excessive content of MSH
297
binding phase, complying with TG/DTG and FTIR-analyses. At the first 14-days of
298
carbonation, a significant increase in compressive strength associating with porosity
299
reduction has been recorded. The positive role of accelerated carbonation on strength
300
development and porosity reduction has been observed in the case of different
301
cementitious systems having MgO (Morrison et al., 2016). The reason behind this effect
302
is the increase of CO2-capture (See Fig. 11), yielding carbonate-containing-phases. 13
303
The accumulation of carbonate phases mainly contributes to the reduction of pore
304
volume of the hardened material. Moreover, the CO2-capture has no effect on MSH-
305
binder formed in the hardened matrix at this period (Fig. 11). Interestingly, the hardened
306
M-WVA mixture exposed to CO2 for 14-days represents compressive strength value
307
higher than that of the hydrated sample (at zero time) by ~47 % accompanied by the
308
lower porosity. Although the hardened M-RVA mixture shows compressive strength
309
values lower than those of M-WVA one, it records compressive strength development
310
higher than that of M-WVA mixture, especially at 14-days of CO2-exposure (55 %). This
311
should be explained by the higher zero-time porosity (32 %) of the hardened M-RVA
312
compared to that of M-WVA one (24%). The higher porosity has potential impact on the
313
acceleration of carbonation rate including the fast intrusion of CO2-gas into the hardened
314
materials (Morrison et al., 2016). The high porosity of the hardened M-RVA mixture at
315
zero time is due to the low amorphous content in RVA as it has low efficacy in the
316
interaction with hydrated magnesium oxide, resulting in the formation of low MSH-
317
content. Moreover, the high crystallinity of RVA causes the formation of excessive
318
Mg(OH)2 content which in turn easily transforms to nesquehonite after exposure of
319
hardened material to CO2.
320 321
It is postulated that the rate of CO2 diffusion into the hardened material enhances
322
with the increase of its pore volume, confirming the higher CO2-capture in the case of M-
323
RVA sample as compared with M-WVA one. The 28-days carbonated samples
324
demonstrate the highest CO2-capture (Fig. 11). Nevertheless, they represent compressive
325
strength lower than those of 14-days carbonated ones (Fig. 10). This is likely derived
14
326
from the fact that the continuous exposure of hardened samples to CO2 has resulted in a
327
significant reduction in MSH-content within hardened matrix, complying with TG/DTG
328
results. It can be said that regardless the role of amorphous content in volcanic ashes in
329
prepared materials, it potentially affects the rate of CO2 capture within hardened
330
materials.
331
3.5. Mechanism of accelerated carbonation
332
The reaction mechanism of CO2-sequestration by the fabricated materials is shown in
333
Fig. 12 (Fernández Bertos et al., 2004). The capture process initiates by the diffusion
334
and penetration of CO2-gas through the hardened materials, followed by transformation
335
of CO2 from gas state to liquid one (H2CO3: as intermediate step). This transformation is
336
caused by the high moisture content within hardened materials. Carbonic acid (H2CO3) is
337
unstable compound which immediately ionized to H+, HCO3-, and CO32-. Carbonate ions
338
interact with Mg(OH)2 (as a byproduct of the hydration of MgO-volcanic ashes
339
mixtures), yielding nesquehonite (MgCO3.3H2O). At later ages, MSH (as the main binder
340
of the hardened materials) can be carbonated to form silicate hydrate and MgCO3.3H2O,
341
resulting in a significant loss in mechanical properties. As shown in Fig. 13, a noticeable
342
change in the color of hardened materials was recorded when they exposed to accelerated
343
carbonation, confirming the formation of carbonate phase caused by CO2-caprture by
344
these materials.
345
3.6. Beneficial use of the prepared materials
346
The above mentioned outcomes proved that the designed hardened materials from
347
naturally occurring volcanic ashes and MgO were found to have high efficacy in the CO2-
348
capture accompanied a remarkable change in their physical and mechanical properties. 15
349
Moreover, the proposed method in the present study can be beneficially applied in the
350
sustainable disposal aluminosilicate and magnesia-rich-wastes in the cleaner production
351
of cementitious materials with high performance and efficacy in the sequestration of
352
CO2-gas. This not only strongly contributes to the conservation of naturally-occurring
353
resources used in construction, but also reflects on the mitigation of global warming
354
potential caused by industrial and human activities.
355 356
4. Conclusions
357
The work focused on the impact of accelerated carbonation on the performance of the
358
hardened magnesium silicate cement under humidity and accelerated carbonation
359
conditions. These materials were fabricated by mixing magnesium oxide-volcanic ashes
360
blends with water, followed by humidity curing. As proved by different analyses,
361
magnesium silicate hydrate and magnesium hydroxide are the main hydration products
362
within fabricated materials. Magnesium hydroxide was found to be the active site for
363
CO2-capture, resulting in the formation of nesquehonite phase in the open pores of the
364
hardened mixtures. The amorphous content in volcanic ashes plays a circular role in the
365
performance of the fabricated materials and their ability to CO2-capture. The fabricated
366
material containing volcanic ash with low amorphous content represented the higher
367
effectiveness in the CO2-sequestration compared to that having high amorphous content.
368
The main reasons behind this criterion are the formation of porous hardened material and
369
the enhancement of magnesium hydroxide availability. The beneficial use of these
370
materials in different engineering projects is not only based on their high efficacy in the
16
371
CO2-capture, but also due to the enhancement of their physical and mechanical properties
372
with CO2-exposure.
373 374
Acknowledgment
375
I would like to give my deepest appreciation to my wife Dr. Fatma A. M. Abdel-aal,
376
Lecturer in pharmaceutical analytical chemistry department, Faculty of Pharmacy,
377
Assiut University, Egypt for her faithful and honest efforts with me. She supported and
378
stands by my side in every moment in this research. A special gratitude to the Consejo
379
Nacional De Ciencia Y Tecnologia (CONACYT) for their support and faithful efforts
380
to accomplish this work. A faithful important thankful to Prof. Dr. Ricardo Morales
381
Estrella, and Senorita Griselda Ledesma Lopez Michoacan State University,
382
Mexico, for their faithful support and efforts to perform this research.
383
A special gratitude to the president of New Valley University Prof. Dr. Abdel Aziz
384
Tantawy, Prof. Dr. Mohamoud Mohamed Ahmed and Dr. Mohamed Osman for
385
their faithful support during this project. As well as, I would like to thank Profs.
386
Abdalla M. El Ayyat and Nageh A. Obaidalla, Assiut University, Egypt, for their
387
support during my scientific career. Finally, a special gratitude to Prof. J.L. Rico & Mr.
388
Manuel Robles Laboratorio de Catalisis, Faultad de Ingenieria Quimica, Edificio
389
VI, for their support in the lab works.
390 391 392 17
393
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Table 1: Chemical compositions and physical properties of starting materials
496
Table 2: Mixing proportions of magnesium silicate-based cement
497
Table 3: TG-weight losses and calculated CO2 content sequestrated by the prepared materials at different CO2-exposure times
498 499 500 501
Fig. 1. XRD-patterns of white and red volcanic ashes (WVA and RVA)
502
Fig. 2. Basic diagram of the preperation, hydration, and carbonation processes
503
Fig. 3. XRD-patterns of the hardened carbonated M-WVA mixtures at different times of
504 505 506
CO2-exposure Fig. 4. XRD-patterns of the carbonated M-WVA and M-RVA mixtures at 28-days of CO2-exposure
507
Fig. 5. FTIR-spectra of the carbonated M-WVA mixtures at different times of CO2-
508
exposure
509
Fig. 6. FTIR-spectra of the carbonated M-WVA and M-RVA mixtures at 28-days of
510 511 512
CO2-exposure Fig. 7. DTG-thermograms of the hardened M-WVA and M-RVA mixtures at 28-days of curing in humidity
21
513 514 515 516 517 518 519 520 521 522 523
Fig. 8. DTG-thermograms the carbonated M-WVA mixture at different times of CO2exposure Fig. 9. DTG-thermograms of the hardened M-WVA and M-RVA mixtures at 28-days of CO2-exposure Fig. 10. Relationship between strength and porosity of the carbonated samples exposed to CO2-gas at different times Fig. 11. Relationship between CO2-capture and MSH content of the carbonated samples exposed to CO2-gas at different times Fig. 12. Proposed reaction mechanism of the accelerated carbonation adapted from (Fernández Bertos et al., 2004) Fig. 13. Digital photos of hardened samples before and after accelerated carbonation
524
22
Table 1: Chemical compositions and physical properties of starting materials
Mixtures notations
Chemical compositions, wt. %
Physical properties
SiO2
CaO
MgO
WVA
71.30
2.39
0.45
4.60
13.10
1.17
5.01
0.91
0.83
2.65
72
White
RVA
47.32 10.81
2.32
15.61
15.30
2.30
1.84
1.29
2.52
2.83
39
Red
99.57
-
-
-
-
-
-
1.92
-
White
MgO
-
-
Fe2O3 Al2O3 Na2O K2O P2O5 TiO2 Specific gravity
Amorphous Color content
Table 2: Mixing proportions of magnesium silicate-based cement WVA
RVA
MgO
Mixture notation
W/P ratio wt. %
WVA-MgO
25
-
75
0.40
RVA-MgO
-
25
75
0.40
Table 3: TG-weight losses and calculated CO2 content sequestrated by the prepared materials at different CO2-exposure times Mixtures notations
M-WVA
M-RVA
Exposure time (day)
Weight loss wt. % CO2 wt. % ratio in the sample
MSH
Mg(OH)2
MgCO3
Total loss
0
3.20
4.12
0.38
10.49
3.62
1
3.31
3.54
1.65
13.38
12.33
14
3.39
2.16
2.89
14.75
18.09
28
2.54
1.75
3.54
15.97
22.16
0
2.36
5.16
0.45
11.25
4.01
1
2.41
3.28
2.19
13.51
16.21
14
2.45
2.14
3.26
14.99
21.74
28
2.01
1.86
4.19
16.04
26.12
Fig. 1. XRD-patterns of white and red volcanic ashes (WVA and RVA)
1
Fig. 2. Basic diagram of the preperation, hydration, and carbonation processes
2
Fig. 3. XRD-patterns of the hardened carbonated M-WVA mixtures at different times of CO2exposure
3
Fig. 4. XRD-patterns of the carbonated M-WVA and M-RVA mixtures at 28-days of CO2exposure
4
1-d
14-d
28-d
Transmittance, %
Zero time
4000
3400
2800
2200
1600
1000
400
Wavenumber, cm-1 Fig. 5. FTIR-spectra of the carbonated M-WVA mixtures at different times of CO2-exposure
5
M-WA
Transmittance, %
M-RA
4000
3400
2800
2200
1600
1000
400
Wavenumber, cm-1 Fig. 6. FTIR-spectra of the carbonated M-WVA and M-RVA mixtures at 28-days of CO2exposure
6
2
DTG, mg/min
1.6 CO32- within carbonate phase
1.2
0.8 H2O within MSH
0.4
M-WA M-RA
OH within Mg(OH)2
0 0
100
200
300
400
500
600
700
800
Temperature, ºC Fig. 7. DTG-thermograms of the hardened M-WVA and M-RVA mixtures at 28-days of curing in humidity
7
2
DTG mg/min
1.6
1.2
H2O within nesquehonite
0.8 CO32- within nesquehonite
H2O within MSH
0.4 OH within Mg(OH)2
Zero time
0 0
100
200
300
400
500
600
700
800
Temperature, ºC Fig. 8. DTG-thermograms the carbonated M-WVA mixture at different times of CO2-exposure
8
2
DTG mg/min
1.6
1.2
H2O within nesquehonite H2O within MSH
0.8 OH within Mg(OH)2
0.4
CO32- within nesquehonite
M-WA M-RA 0 0
100
200
300
400
500
600
700
800
Temperature, ºC Fig. 9. DTG-thermograms of the hardened M-WVA and M-RVA mixtures at 28-days of CO2exposure
9
Fig. 10. Relationship between strength and porosity of the carbonated samples exposed to CO2gas at different times
10
Fig. 11. Relationship between CO2-capture and MSH content of the carbonated samples exposed to CO2-gas at different times
11
Fig. 12. Proposed reaction mechanism of the accelerated carbonation adapted from (Fernández Bertos et al., 2004)
12
M-RVA
M-WVA
Before
Before
After After
Fig. 13. Digital photos of hardened samples before and after accelerated carbonation
13
Highlights ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ Eco-friendly Cementitious material with high CO2 capture Capacity.
Two naturally volcanic ashes and reactive magnesium oxide are the main raw materials
The amorphous content plays an important role in the performance of CO2 absorption
The absorption capacity of CO2 was ranging from (~260- 220 kg/ton) in 28 days
1
Declaration of Interest Statement
The authors confirms that there is no conflict of interest
Best Regards, Hassan Soltan Hassan Corresponding author Cleaner Production Author & Reviewer