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Thermogravimetry analysis, compressive strength and thermalconductivity tests of non-autoclaved aerated Portland cement–flyash–silica fume concrete
Chalermphan Narattha1• Pailyn Thongsanitgarn1
• Arnon Chaipanich1
Received: 7 July 2014 / Accepted: 20 April 2015 / Published online: 22 May 2015
� Akademiai Kiado, Budapest, Hungary 2015
Abstract This paper reports the investigated thermo-
gravimetry analysis, compressive strength and thermal con-
ductivity tests of non-autoclaved aerated Portland cement–fly
ash–silica fume concrete. The mixes were cured in water and air
for 3, 7 and 28 days. Thermogravimetry results showed that
calcium silicate hydrate (C–S–H), ettringite, gehlenite
(C2ASH8), calcium hydroxide [Ca(OH)2] and calcium car-
bonate (CaCO3) phases were detected in all mixes. The com-
pressive strength and thermal conductivity of aerated Portland
cement–fly ash–silica fume concrete increased when compared
with aerated Portland cement–fly ash concrete after 28 days.
The compressive strength and thermal conductivity of aerated
concrete cured in water had higher values than air-cured spe-
cimens. X-ray diffraction and thermogravimetry showed that
Ca(OH)2 decreased with increased silica fume content. This is
due to the increased pozzolanic reaction when compared with
the Portland cement–fly ash mixes, which corresponds to an
increase in compressive strength and thermal conductivity.
Keywords Thermogravimetry � Fly ash � Silica fume �Compressive strength � Thermal conductivity
Introduction
The cement industry is one of the most energy-consuming
industries. The carbon dioxide (CO2) emissions rate is re-
sponsible for approximately 5 % of global man-made CO2
emissions [1]. The production of greenhouse gases by the
cement industry can be reduced by using pozzolanic ma-
terials, such as fly ash and silica fume, as partial replace-
ments for Portland cement (PC) to create a blended cement
[2]. The main reasons for using pozzolanic materials are
not only the cost-effectiveness but also to improve the
properties of concrete [3].
Fly ash (FA) is a by-product of coal combustion in
thermal power plants and contains partially active glass
silica and alumina [4]. FA is widely used in blended ce-
ment and is normally used to replace Portland cement up to
30 % by mass [5–8]. The benefits of using FA in cement
are improved properties such as lower heat of hydration,
increased workability, improved resistance to sulfate at-
tack, lower shrinkage characteristics and reduced expan-
sion in mortar/concrete [9–11]. However, FA has a slow
rate of strength development compared with normal con-
crete [12, 13]. FA requires water and calcium hydroxide
[Ca(OH)2] to react (pozzolanic reaction) to form binding
materials similar to PC [14, 15]. This reaction with
Ca(OH)2 proceeds slowly since Ca(OH)2 is formed from
the hydration reaction of PC.
Silica fume (SF) is a by-product of the ferrosilicon in-
dustry. SF consists of very small spherical particles of non-
crystalline silica (&100 nm) and has a high content of
amorphous silicon dioxide (more than 80 %), characteris-
tics which account for its high pozzolanic reactivity [16].
SF can improve the properties of cement-based materials,
providing increased strength, modulus and ductility
[17, 18]. Korpa et al. [19] found that SF accelerated the
early cement hydration phases by providing large amounts
of reactive siliceous surface, which serves as a site for early
precipitation of hydration products. Kohno et al. [20] re-
ported that SF increased the strength of normal cement.
Other recent studies found that a combination of SF and FA
& Arnon Chaipanich
[email protected]; [email protected]
1 Advanced Cement-Based Materials Research Unit,
Department of Physics and Materials Science, Faculty of
Science, Chiang Mai University, Chiang Mai 50200,
Thailand
123
J Therm Anal Calorim (2015) 122:11–20
DOI 10.1007/s10973-015-4724-8
improved the properties of concrete better than the addition
of FA alone [21, 22]. Valipour et al. [23] reported that
7.5–10 % SF is optimum amount for cement replacement.
Li et al. [24] also reported that blended cement pastes with
30 % FA and 10 % SF give the optimal mix, which con-
tribute to higher compressive strength than blended cement
pastes with FA.
Curing is an essential procedure of cement samples to
give desirable mechanical properties and endurance. The
procedure provides samples with adequate water for the
hydration reaction and avoids from drying phenomena.
Therefore, 28-day water-cured samples are used for stan-
dard tests. However, in real practice, concrete buildings are
exposed to air after mixing and depositing [25]. Aerated
concrete (or foam concrete [26]) is a cement or lime
mortar, classified as lightweight concrete, in which air
voids are entrapped in the mortar matrix by means of a
suitable aerating agent. Aerated concrete can be non-au-
toclaved (NAAC) or autoclaved (AAC) [27]; the properties
depend on the method and duration of curing. The ad-
vantages of aerated concrete are its lightweight, high de-
gree of thermal insulation and considerable savings in
energy consumption [28]. New options for the application
of aerated concrete in manufacturing processes have arisen
from utilizing a combination of chemical foaming (alu-
minum powder) and air curing. These new aerated con-
cretes as structural lightweight concrete are innovative
building materials which can be used in load-bearing
structures [29].
Most of aluminum-added aerated concrete is normally
autoclaved [30–33]. Little is known on the properties and
phase characterization of non-autoclaved aerated concrete
using aluminum especially with FA and SF. Thus, this
work investigated the compressive strength, thermal con-
ductivity and phase characterization by thermal analysis of
non-autoclaved aerated concrete containing FA and SF (air
and water cured) as structural lightweight concrete which
can be used in load-bearing structures.
Experimental
Portland cement type 1 (PC) was used in this study. Fly ash
(FA) was obtained from Mae Moh power plant in Lam-
pang, Thailand, and undensified silica fume (SF), grade
920-U, was produced by Elkem (Norway). The non-auto-
claved aerated PC–FA–SF concrete studied was produced
from cement mortar. River sand, with specific gravity of
2.65 and maximum size of 5 mm, was used as a fine ag-
gregate in concrete, according to ASTM standard C33 [34].
Aluminum powder (Al), a pore-forming agent that reacts
with calcium hydroxide to form hydrogen gas, was sup-
plied by HiMedia Laboratories, India. The reaction
between aluminum with calcium hydroxide to form hy-
drogen gas is shown in the following equation [35].
2Al þ 3Ca OHð Þ2þ6H2O ! 3CaO � Al2O3 � 6H2O þ 3H2
Alumimium powder þ Hydrated lime
! Tricalcium hydrate þ Hydrogen
The superplasticizer (SP) used was obtained from Sika
(Thailand). The chemical composition of materials used in
this research was obtained by means of X-ray fluorescence
and is given in Table 1. FA and SF were used in different
compositions by mass as a partial replacement for PC. The
replacement levels of FA were 20, 25 and 30 %, while SF
was 5 and 10 % by mass of PC. Al was added at 0.2 % by
mass of binders. The mix proportions are summarized in
Table 2. Mixes were designed to have a constant water-to-
binder ratio of 0.475. The flow of mortar at 110 ± 5 mm
was kept constant by the use of a superplasticizer. A fine
aggregate-to-binder ratio of 2.5 was used. Concrete mixes
were mixed and cast in 50 9 50 9 50 mm cubic molds for
compressive strength testing and 125 9 /25 mm cylin-
drical molds for thermal conductivity testing. Concrete
mixes were compacted using a vibration table. The samples
were stored in molds at room temperature for 24 h.
Afterward, the samples were demolded and then cured in
air and water at room temperature for 3, 7 and 28 days.
After the curing process, three specimens were investi-
gated for compressive strength, according to ASTM stan-
dard C109 [36]. In addition, three samples were
investigated for density and three samples were investi-
gated for thermal conductivity in accordance with ASTM
D5930-01 [37]. The microstructure of samples was inves-
tigated using scanning electron microscopy (SEM;
JEOLJSM-840A, Japan). Thermogravimetry (TG) and
Table 1 Chemical composition and physical properties of raw
materials
PC FA SF
Chemical composition/%
SiO2 20.64 45.37 93.543
Al2O3 4.848 20.65 0.556
CaO 63.62 10.43 1.128
Fe2O3 3.17 12.31 0.172
MgO 1.137 2.127 0.747
Na2O 0.51 1.331 0.137
K2O 0.812 1.496 1.047
P2O5 0.32 0.245 0.531
TiO2 0.213 0.517 0.002
SO3 2.753 2.526 1.006
Specific gravity 3.15 2.1 2.2
Average particle size/lm 8.31 5.22 0.1
12 C. Narattha et al.
123
derivative thermogravimetric (DTG) were carried out using
a Mettler–Toledo TGA/SDTA 851e. The samples were
heated from 30 to 1000 �C at a heating rate of 10 �C min-1
under nitrogen atmosphere. The nitrogen flowing rate is
60.0 mL min-1. Moreover, phase identification of the
samples was performed using an X-ray diffractometer
(XRD; Rigaku MiniFlex II, Japan). For XRD and TG
studies, samples were taken from the middle part of the
broken paste cube (&15 mm in size) after compressive
strength test. The samples were immersed in acetone for
3 days to stop hydration reaction after the curing process.
The samples were dried in an oven at 60 �C for 24 h. The
samples were placed in sealed bags. Powder for XRD and
TG studies was prepared from dried sample after grinding
and sifting through a No. 200 mesh sieve. For XRD tests,
room-temperature XRD measurements using CuKa ra-
diation (k = 1.5418 A) operating at 40 kV, 35 mA were
taken. XRD measurements were taken for 2h between 5�and 60� with increment of 0.01� step-1 and scan speed of
3 s step-1. The diffraction peaks were analyzed using
JCPDS software. For SEM test, low vacuum mode was
used. Sample was placed on brass stub with carbon tape.
Sample was dried using infrared light for 5 min. Then,
sample was coated with gold approximately 20 A thick
using blazer sputtering coater. Micrograph was recorded
with magnifications of 1009 at 15 kV. All SEM, XRD and
TG characterizations were carried out on 28-day samples
as standard test age.
Results and discussion
Compressive strength
The compressive strength results after curing for 3, 7 and
28 days are shown in Fig. 1. It was found that in binary
phase (30FA mix), the compressive strength of aerated
concrete with FA was lower than that of the PC control.
The FA content contributes to slow pozzolanic reaction
rate, which is inadequate for pre-28-day compressive
strength development [12, 13, 38]. The compressive
strength of aerated concrete containing FA can be im-
proved by adding SF as a cement replacement. The
20FA10SF mix had compressive strength values similar to
the PC control mix after 28 days of curing. SF particles are
finer and their pozzolanic reactivity is higher compared
with FA particles. SiO2 in SF reacted with Ca(OH)2 from
hydration reaction to give C–S–H formation to supplement
bonding strength. Furthermore, interior microstructure
pores were filled with SF [39]. Thus, aerated concrete with
both FA and SF has increased compressive strength [21,
22]. Nochaiya et al. [40] reported that 28-day compressive
strength of PC–FA–SF concrete was found to increase by
45 % of compressive strength at 28 days when compared
with PC–FA concrete. Guneyisi et al. [41] also reported
that the ternary blended cement with FA and SF, especially
in 15FA10SF, had slightly higher compressive strength
than binary blended cement with FA. Moreover, water
curing of aerated concrete resulted in higher compressive
strength than air curing, due to quicker and fuller hydration
induced by a sufficient water supply [42]. The major ce-
mentitious compounds in cements, belite (C2S:Ca2SiO4)
and alite (C3S:Ca3SiO5), had completely reacted with wa-
ter to form calcium silicate hydrates (C-S–H) [26]. Aerated
concrete was having compressive strength at 28 days in the
range of 13–23 MPa. These results can be used for mod-
erate-strength concrete and structural concrete [43].
Density
The density of non-autoclaved aerated concrete with FA
(30FA mix) was lower than that of the PC control mix
(Fig. 2). Also, the density of aerated concrete that con-
tained SF replacement was higher than that of the 30FA
mix and tended to increase with increased SF content. This
is because SF improves the pore structure; its small particle
size results in a filler effect, in which the SF particles
bridge the spaces between cement grains and the spaces
between cement grains and aggregate particles. SF also
reacts pozzolanically with Ca(OH)2 to produce a greater
solid volume of the C–S–H phase, leading to an additional
reduction in capillary porosity during hydration [44]. The
Table 2 Mix proportion of non-autoclaved aerated concrete
Mix w/b ratio Proportions/kg m-3 SP/% Al powder/%
PC Water Sand FA SF
PC 0.475 576 288 1440 – – 0.12 0.2
30FA 0.475 403 288 1368 173 – – 0.2
25FA5SF 0.475 403 288 1369 144 30 0.15 0.2
20FA10SF 0.475 403 288 1371 115 60 0.25 0.2
Thermogravimetry analysis, compressive strength and thermal conductivity tests of… 13
123
density of the 20FA10SF mix was higher than that of the
PC control mix. The density of aerated PC–FA–SF con-
crete cured in saturated limewater was higher than that of
air-cured specimens. This is due to hydration of cement can
occur only in water-filled capillary porosities [26]. There-
fore, the specimens under water curing were supplied with
sufficient water, leading to the continuous hydration of
specimens (with less porous structure) than air-cured spe-
cimens. These findings are in agreement with the test re-
sults for compressive strength, which increased with
increased SF content.
Thermal conductivity
The thermal conductivity results of water-cured and air-
cured aerated PC–FA–SF concrete are shown in Fig. 3. The
thermal conductivity of the 30FA mix was lower than the
PC control mix and had the lowest values for both water-
cured and air-cured specimens. The thermal conductivity
was increased when SF was added as a cement replacement
in ternary phase. The thermal conductivity values for
25FA5SF and 20FA10SF mixes were higher than the PC
control mix. Thermal conductivity increased with increas-
ing SF content as a result of the denser microstructure of
the cement paste matrix [38]. Albayrak et al. [45] reported
a decrease in thermal conductivity is relation to the de-
crease in density of autoclaved aerated concrete. Demir-
boga and Gul [46] also reported that a decrease in density
leads to a decrease in thermal conductivity. The thermal
conductivity of 25FA5SF and 20FA10SF mixes and bulk
density increased when replacing SF instead of FA [47].
Aluminum added in aerated concrete resulted in higher
porosities and lower thermal conductivity due to large
volume of air voids [43]. Moreover, thermal conductivity
values of water-cured specimens were higher compared
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30FA 25FA5SF 20FA10SF PC 30FA 25FA5SF 20FA10SF PC
30FA 25FA5SF 20FA10SF PC
Mixes Mixes
Mixes
WaterAir
WaterAir
WaterAir
(a) (b)
(c)
Fig. 1 Compressive strength of aerated PC–FA–SF concrete under water cured and air cured at a 3 days, b 7 days and c 28 days
14 C. Narattha et al.
123
with air-cured specimens. Water curing provided sufficient
moisture to maximize the hydration reaction which gives a
denser matrix resulting in a higher conductivity than air-
cured specimens [48].
Microstructure
The microstructure of aerated PC–FA–SF pastes can be
seen from scanning electron microscope (SEM) micro-
graphs of PC mixes cured for 28 days (Fig. 4). Water-
cured PC specimens (Fig. 4a) are noticeably denser than
air-cured specimens (Fig. 4b) and have smaller pore
sizes. This indicates that water curing aided hydration of
PC mixes by maintaining sufficiently moist conditions
[48]. This was because water is the most important factor
in the hydration reaction. Figure 5 shows SEM micro-
graphs of aerated PC–FA–SF pastes of 30FA mix and
25FA5SF mix after curing for 28 days. In general, larger
pore size and more pores can be seen in air-cured
samples than water-cured samples. This relates to the
higher density of water-cured samples compared to air-
cured samples. Some remaining unreacted FA particles
(&50–100 lm) can be detected (spherical shapes) in
Fig. 5, which indicates that some of the FA has already
reacted with Ca(OH)2, while the remaining of larger
([50 lm) unreacted FA particles represent an incomplete
reaction of FA. This confirms that fly ash is a slow-
reacting material. In contrast, silica fume particles would
have already reacted to form hydration products, as de-
tected by the DTG curve [20]. Water cured and air cured
of 25FA5SF pastes microstructure appear to be denser
than 30FA pastes.
XRD
The X-ray diffraction (XRD) patterns of aerated PC–FA–
SF pastes cured for 28 days are shown in Fig. 6. In all
mixes cured in water and air (Fig. 6a, b), peak of calcium
2000
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Den
sity
/kg
m–3
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Den
sity
/kg
m–3
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1900
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1700
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1400
1300
1200
Den
sity
/kg
m–3
30FA 25FA5SF 20FA10SF PCMixes
30FA 25FA5SF 20FA10SF PCMixes
30FA 25FA5SF 20FA10SF PCMixes
WaterAir
WaterAir
WaterAir
(a) (b)
(c)
Fig. 2 Density of aerated PC–FA–SF concrete under saturated limewater curing and air curing at a 3 days, b 7 days and c 28 days
Thermogravimetry analysis, compressive strength and thermal conductivity tests of… 15
123
hydroxide [Ca(OH)2] phase can be seen. In addition, the
peaks of belite (C2S:Ca2SiO4) and alite (C3S:Ca3SiO5)
phases (unhydrated products from Portland cement) were
detected. This study found that the intensity of Ca(OH)2 in
ternary aerated cement pastes was lower than in binary
aerated cement paste that incorporated only FA. The in-
tensity of Ca(OH)2 decreased with increasing SF content.
This indicated that SiO2 reacted with Ca(OH)2. Moreover,
the reaction between CO2 and Ca(OH)2 to form CaCO3 in
carbonation reaction when samples are exposed to the air is
another reason in the decreased Ca(OH)2 [49]. Thus,
Ca(OH)2 may also be partly reduced due to the reaction of
Ca(OH)2 with CO2 when samples are exposed briefly in air
during the curing and drying process.
0.60
0.55
0.50
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0.30
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0.00
The
rmal
con
duct
ivity
/W m
–1 K
–1
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0.55
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0.25
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0.00
The
rmal
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duct
ivity
/W m
–1 K
–1
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0.55
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0.25
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0.15
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0.05
0.00
The
rmal
con
duct
ivity
/W m
–1 K
–1
30FA 25FA5SF 20FA10SF PCMixes
30FA 25FA5SF 20FA10SF PCMixes
30FA 25FA5SF 20FA10SF PCMixes
WaterAir
WaterAir
WaterAir
(a) (b)
(c)
Fig. 3 Thermal conductivity of aerated PC–FA–SF concrete under saturated limewater curing and air curing at a 3 days, b 7 days and c 28 days
Fig. 4 SEM micrograph of PC mix cured at 28 days: a water cured and b air cured
16 C. Narattha et al.
123
Thermogravimetry
Thermogravimetry (TG) results of non-autoclaved aerated
PC–FA–SF pastes cured for 28 days are shown in Figs. 7
and 8. The results were plotted as derivative thermo-
gravimetric (DTG) to observe each phase, as shown in
Figs. 9 and 10. The main mass loss transition of all pastes
occurred in three temperature ranges. The first main mass
loss up to &350 �C was through dehydration of several
hydrate phases, such as calcium silicate hydrate (C–S–H),
ettringite and gehlenite (C2ASH8). The second main mass
loss from &350–500 �C was due to dehydroxylation of
calcium hydroxide [Ca(OH)2] [50]. The third main mass
loss from &500–1,000 �C occurred from decarbonation of
calcium carbonate (CaCO3) [51–53]. DTG results of all
pastes after 28 days showed the following detected phases:
ettringite at &79–83 �C, C–S–H at &108–119 �C,
C2ASH8 at &156–165 �C and Ca(OH)2 at &457–465 �C.
CaCO3 presented two dominant peaks at &680–713 �Cand &871–893 �C for water-cured pastes. For air-cured
pastes, the detected phases from DTG results are ettringite
at &70–93 �C, C–S–H at &108–121 �C, C2ASH8 at
&157–168 �C and Ca(OH)2 at &456–467 �C. CaCO3 also
presented two dominant peaks at &699–748 �C and
&879–905 �C. The first CaCO3 peak occurred due to de-
composition of ordinary calcite, and the second peak is
likely to be shifted due to difference in surface area, par-
ticle size, partial pressure of CO2 and impurities such as
magnesium which affected the decomposition of calcite
[54]. The higher intensity of the CaCO3 peak of the 30FA
Fig. 5 SEM micrograph of
non-autoclaved aerated PC–FA–
SF pastes: a 30FA mix water
cured, b 30FA mix air cured,
c 25FA5SF mix water cured,
d 25FA5SF mix air cured
10 20 30 40 50 60
2θ/°10 20 30 40 50 60
2θ/°
Ca(OH)2 C3S C2S
20FA10SF
25FA5SF
30FA
PC
20FA10SF
25FA5SF
30FA
PC
Inte
nsity
/a.u
.
Inte
nsity
/a.u
.
Ca(OH)2 C3S C2S(a) (b)
Fig. 6 XRD pattern of aerated cement pastes cured at 28 days: a water cured and b air cured
Thermogravimetry analysis, compressive strength and thermal conductivity tests of… 17
123
mix may be because the more FA content in the mix re-
sulted in greater porosity; thus, atmospheric CO2 could
diffuse more easily than in other mixes. Pandey and
Sharma [55] reported total porosity increased with the in-
crease in the addition of fly ash. The peak intensity of C–S–
H curves of mixes that contained SF was higher than of
mixes that contained only FA. The C–S–H curves in-
creased with increased SF content due to the higher poz-
zolanic reaction rate when SF was added. This result
agreed with the increase in compressive strength of aerated
concrete.
The mass loss of non-autoclaved aerated PC–FA–SF
pastes cured for 28 days is shown in Table 3. The mass
loss of C–S–H ? ettringite ? C2ASH8 phases for all
pastes increased with increased SF content. The mass loss
for PC–FA–SF pastes was higher than for PC–FA pastes.
This was because SF improved the pozzolanic activity of
aerated cement pastes. The mass loss of the Ca(OH)2 phase
of pastes tended to decrease when SF was added as a ce-
ment replacement because Ca(OH)2 was consumed by FA
and further by SF in the pozzolanic reaction. In all cases,
when comparing water- and air-cured specimens, the mass
loss of C–S–H ? ettringite ? C2ASH8 and Ca(OH)2 for
water-cured mixes was higher than for air-cured mixes.
The mass loss of CaCO3 for air-cured mixes was higher
than for water-cured mixes because air-cured samples were
directly exposed to carbonation during curing while water-
cured samples were not exposed during curing but only
during the drying process. Moreover, there are more in-
terconnected channels and large pores size in air-cured
samples which resulted to more diffusion of CO2 which
increase carbonation [56]. The mass loss of CaCO3 for
30FA air-cured mixes had the highest value. This was
because part of Ca(OH)2 phase being used by the car-
bonation reaction with atmospheric CO2 (exposure during
storage), forming CaCO3 [57, 58].
100
95
90
85
80
75
70
Mas
s/%
0 200 400 600 800 1000
Temperature/°C
20FA10SF25FA5SF30FA
Fig. 7 TG curves of aerated PC–FA–SF pastes water curing at
28 days
100
95
90
85
80
75
70
Mas
s/%
0 200 400 600 800 1000
Temperature/°C
20FA10SF25FA5SF30FA
Fig. 8 TG curves of aerated PC–FA–SF pastes air curing at 28 days
0 200 400 600 800 1000
Temperature/°C
20FA10SF25FA5SF30FA
0.0000
–0.0002
–0.0004
–0.0006
–0.0008
–0.0010
–0.0012
–0.0014
–0.0016
Der
ivat
ive
mas
s lo
ss/°
C–1
Fig. 9 DTG curves of aerated PC–FA–SF pastes water curing at
28 days
0 200 400 600 800 1000
Temperature/°C
20FA10SF25FA5SF30FA
0.0000
–0.0002
–0.0004
–0.0006
–0.0008
–0.0010
–0.0012
–0.0014
–0.0016
Der
ivat
ive
mas
s lo
ss/°
C–1
Fig. 10 DTG curves of aerated PC–FA–SF pastes air curing at
28 days
18 C. Narattha et al.
123
The compressive strength and density of non-auto-
claved aerated PC–FA–SF concrete were
&1765–1869 kg m-3 and &13–23 MPa, respectively.
These results of products were sufficient to ACI Com-
mittee 213 standard [43] for use as moderate-strength
concrete and structural concrete. Thus, aluminum-added
non-autoclaved aerated PC–FA–SF concrete can be con-
veniently cast into any desirable size using less energy
than autoclaved method. This study focussed on the me-
chanical and thermal properties of non-autoclaved aerated
PC–FA–SF concrete. Durability properties such as freeze–
thaw of non-autoclaved aerated PC–FA–SF concrete are
recommended for future studies.
Conclusions
Aluminum-added aerated concrete was cast and tested
(density &1765–1869 kg m-3) having compressive
strength at 28 days in the range of 13–23 MPa. These
results can be used for moderate-strength concrete and
structural concrete. Non-autoclaved aerated PC–FA–SF
concrete has considerable advantages such as reducing the
cost of products, accommodating the production process
and low energy consumption compared with autoclaved
aerated concrete. The compressive strength and thermal
conductivity decrease with the use of binary FA cement
but were found to increase when SF was incorporated
with FA for both water- and air-cured samples. This is
due to the increase in the hydrated product (C–S–H) and
less Ca(OH)2 in the ternary (PC–FA–SF) mixes as de-
tected by TG and XRD, but more hydration products were
formed in water-cured samples. The pozzolanic reaction
was thus affected by the air curing method where TG
results showed that C–S–H, ettringite and C2ASH8 in
water-cured samples were higher than in air-cured sam-
ples, while Ca(OH)2 and CaCO3 in water-cured samples
were lower than in air-cured samples.
Acknowledgements The authors gratefully acknowledged the Of-
fice of the Higher Education Commission (OHEC), the Thailand
Research Fund (TRF), Department of Physics and Materials Science,
Faculty of Science, Chiang Mai University, and the Graduate School
of Chiang Mai University.
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