Experimental and theoretical studies of hydrolysis of nerve agent sarin by binuclear zinc biomimetic catalysts

Article abstract of DOI:10.1016/j.chemphys.2015.05.011

A complex (ZnL1) of 2,2-(2-hydroxy-5-methyl-1,3-phenylene)bis(methylene)bis ((pyridin-2-ylmethyl)azanediyl)diethanol (this ligand is named by L1) functionalized with two Zn(II) centers, has been previously suggested to be a structural model for binuclear

Full text of DOI:10.1016/j.chemphys.2015.05.011

Construction and Building Materials 91 (2015) 133–137
Contents lists available at ScienceDirect
Construction and Building Materials
journal homepage: www.elsevier.com/locate/conbuildmat
Preparation and characterization of high porosity cement-based foam
material
⇑
Guochen Sang , Yiyun Zhu, Gang Yang, Haobo Zhang
State Key Laboratory Base of Eco-hydraulic Engineering in Arid Area (Xi’an University of Technology), Xi’an 710048, China
h i g h l i g h t s
ꢀ
ꢀ
ꢀ
ꢀ
A physical air-entraining method has been reported.
The properties of high porosity cement-based foam materials have been investigated.
Influence of water–cement ratio and HPMC on material properties has been analyzed.
Pore structure formation mechanism has been clarified.
a r t i c l e i n f o
a b s t r a c t
Article history:
High porosity cement-based foam materials were prepared through physical air-entraining method and
the pore structure and the properties of materials were characterized. The results show that water–ce-
ment ratio and Hydroxypropyl Methyl Cellulose (HPMC) content have crucial influence on material prop-
erties. When the water–cement ratio was 0.9 and the content of HPMC was 0.4%, the cement-based foam
material with the porosity of 94.33% and thermal conductivity value of 0.049 W/(m K) could be obtained.
The formation mechanism of pore structure was analyzed that water–cement ratio and HPMC content
affect the bubble film toughness which influence on material properties.
Received 18 October 2014
Received in revised form 2 April 2015
Accepted 1 May 2015
Available online 16 May 2015
Keywords:
Cement-based foams
Mechanical air-entraining method
Pore structure
Ó 2015 Elsevier Ltd. All rights reserved.
Porosity
Thermal conductivity
1. Introduction
not only are raising porosity but also optimizing pore structure [6].
The conventional methods for preparing cement-based foam mate-
Cement-based foam material is more attractive than polymer
foam materials for its unique a set of properties: they have high
heat capacity, excellent fire resistance and low cost [1,2]. In field
of building energy efficiency, cement-based foam material could
substitute the combustible organic thermal insulation materials
so as to reduce the occurrence of fire disasters effectively [3]. But
compared with organic thermal insulation materials, the thermal
conductivity of conventional cement-based foam materials is
higher. The opinion of Lysenko and Raed [4,5] is that the materials
could obtain the extremely low thermal conductivity value when
the pore diameters of porous thermal insulation materials drop
to nanometer grade. However, achieving nano-grade pore is
greatly difficult for cement-based thermal insulation material.
The methods usually adopted to improve the mechanical property,
meanwhile thermal performances of cement-based foam materials
rials mainly include chemical foaming method and physical prepa-
ration foam method [7]. Chemical foaming method is to mix
foaming agents such as aluminum powders, hydrogen peroxide
solution and modified cement paste to stir evenly for preparing
material paste to be poured into mold, in which foams are pro-
duced via chemical reactions. Foam materials prepared by this
method could get a porosity reaching as high as 50–90%. Physical
method for preparing foam material is to inject preformed foam
into cement paste. Tony and Gibson [9] have used this method to
prepare foam materials with the density of 160–1600 kg/m3.
Akthar and Evans [8] prepared
a
high porosity (92%)
cement-based foam by using the similar foaming method for high
temperature ceramics [10]. Researchers have been exploring a
variety of methods to improve the properties of cement-based
foam materials. Verdolotti et al. [11] prepared the composite
cement–polyurethane foams by mixing the inorganic cement pow-
der to the polyurethane precursors. Polystyrene granules were
used as the filler in a light-weight thermal-insulation foam cement
⇑
Corresponding author. Tel./fax: +86 29 8231 2519.
E-mail address: sangguochen@xaut.edu.cn (G. Sang).
http://dx.doi.org/10.1016/j.conbuildmat.2015.05.032
0950-0618/Ó 2015 Elsevier Ltd. All rights reserved.

134
G. Sang et al. / Construction and Building Materials 91 (2015) 133–137
composite and the density in the region of 150–170 kg/m3 [12].
The methods above mentioned are considerably complicated.
Foam collaboration is easy to appear if these methods are
employed to prepare high porosity cement-based foam material
[13,14].
A simple mechanical air-entraining method is adopted to pre-
pare cement-based foam material, which is using mechanical stir-
ring to bring a great quantity of air into a modified cement paste
with foaming admixture. After the setting and hardening of cement
paste, foams solidified gradually. Some correlated researches on
adopting mechanical mixing air-entraining method to prepare high
porosity cement-based foam material are still under the explora-
tory stage so that few research achievements have been reported.
In this research, the porosity, strength, water absorption, thermal
conductivity and other relevant properties of foam materials were
tested. Microstructure of pore was also observed by electronic
microscopy. Some relevant effective factors on the properties of
cement-based foam materials were investigated in this paper.
2.4. Test of compressive strength and water absorption
Pressure testing machine was adopted to estimate the compressive strength.
The load was added to cubic dried samples with the side length of 70.7 mm at
the speed of (10 1) mm/min till the testing sample was damaged.
Water absorption was measured as follows: weighed the mass of the cubic
dried sample with side length of 70.7 mm, and then soaked the sample into water
for 2 h under the room temperature. Water surface must be higher 25 mm than the
surface of testing sample. When soaked process finished, the residual water of the
samples taken out of water was absorbed by sponge. The water absorption can be
calculated in terms of Eq. (1) as follows:
m1 ꢁ m0
W
¼
ꢃ 100%
V0 qw
ꢃ
ð1Þ
v
where, W – water absorption, %; m0 – the mass of dried testing sample, g; m1 – the
v
mass of sample saturated with water, g; V0 – the sample volume, cm3; qw – water
density, taking 1 g/cm3.
2.5. Thermal conductivity test
Samples of specification with size of 300 ꢂ 300 ꢂ 30mm3 were dried to con-
stant weight at the temperature of 100–110 °C and cooled to the room temperature
for thermal conductivity measuring. Thermal conductivity was measured using
TPMBE-300 flat plate thermal conductivity meter and the steady-state guarded
hot plate method according to the Chinese Standard [17]. A JEOL JSM-6700F scan-
ning electronic microscope (SEM) was utilized to observe the microstructure of
the samples after hydration for 3 days. The samples were dried to reach constant
weight at the temperature of 100–110 °C. Fracture surfaces were sputter coated
with gold.
2. Experimental
2.1. Materials
Grade 42.5 rapid-hardening sulfate aluminate cement was used and its perfor-
mance is shown in Table 1. When mechanical mixing air-entraining method was
used to prepare cement-based foam material, cement type had some influences
on the pore structure. The rapid-hardening sulfate aluminate cement is character-
ized by fast setting, hardening and micro-expansion. Compared with Portland
cement, these characteristics are more helpful to shorten solidification time and
form small and uniform cells in cement matrix [15]. Modified sodium alcohol ether
sulfate was used as foaming agent. The addition of superplasticizer was necessary
to ensure foaming cement paste with a low water volume. The pore structure of
the hardened foam material was optimized by using additive Hydroxypropyl
Methyl Cellulose (HPMC) with viscosity value of 400 mPa S. Foaming agent to
cement ratio by weight was 6% and superplasticizer was 0.2%.
3. Results and discussion
3.1. Influence of water–cement ratio upon material properties
When mechanical mixing air-entraining method was used to
prepare cement-based foam material, water–cement ratio has cru-
cial influence on the material pore structure and properties, due to
the variable water–cement ratio was taken to prepare the
cement-based foams material. The physical and mechanical prop-
erties of samples are shown in Table 2.
It can be seen from Table 2 that the porosity of each group is
higher than 80% and the porosity increase with the water–cement
ratio increase. When water–cement ratio is 0.95, porosity can
reach as high as 93.3%, while the water absorption increased grad-
ually, inversely the apparent density, compressive strength and
thermal conductivity values decreased gradually. The water
absorption to porosity can reflect the pore connectivity of foam
material [18].
It can be seen from Fig. 1 that the ratio of water absorption to
porosity changes little when water–cement ratio is between 0.75
and 0.85. The ratio of water absorption to porosity increases when
water–cement ratio is over 0.85. Connected pores can be filled with
water when sample is soaked into water. The numerical value of
water absorption is equal to the numerical value of connected
porosity. The ratio of water absorption to porosity means the ratio
of connected porosity to the total porosity. The curve in Fig. 1 indi-
cates that pore connectivity increases with the increasing of
water–cement ratio.
2.2. Preparation of high porosity cement-based foam material
The procedure of sample preparation is described as follows. (1) Cement and
other dry powder materials were weighed accurately and poured into a mixer.
(2) Making the mixer run to stir the materials for 3 min at the speed of
140 5 r/min to obtain the dry powder mixture, where the weighed water with
foaming agent was then added into. (3) After stirring the mixed material paste
evenly for 10 s at the speed of 140 5 r/min, and then continually stirring the
mixed material paste for 5 min at the speed of 285 10 r/min, the mixed material
paste was full foamed, and then poured into molds which were removed after cur-
ing at room temperature for 8 h. (4) The materials were further cured for 3 days in
the standard curing condition. According to the Chinese Standard [15], the 3 days
age compressive strength of this kind of cement exceeds the 28 days age compres-
sive strength 90%.
2.3. Porosity test
Before testing, the samples should be dried until the constant weight was
obtained under the temperature of 100–110 °C. The porosity of cement-based foam
ꢀ
ꢁ
material was calculated using P ¼ 1 ꢁ q
ꢂ 100% with apparent density
apparent
qth
From Fig. 2 the relation curve of strength-apparent density rate
and water–cement rate is obtained. It can be seen that the decrease
rate of strength is larger than that of apparent density and the
decreasing rate of strength is aggravated when water–cement ratio
is over 0.85. The above mentioned results show a high pore con-
nectivity which could aggravate the stress concentration when
foam material was subjected to loads.
derived from weighing a known volume of dried foam material, and theoretical
P
n
density qth
nent i) [16].
¼
i¼1viqi
(
vi = volume fraction of component i, qi = density of compo-
Table 1
Physical performances of grade 42.5 rapid-hardening sulfate aluminate cement.
Setting time (min)
Compressive
Flexural
strength (MPa)
strength (MPa)
Initial setting
time
Final setting
time
1d
3d
28d
1d
3d
28d
3.2. Influence of cellulose ether on material properties
29
48
35.2 46.5 48.8 6.7 7.1 8.0
When mechanical mixing air-entraining method was used to
prepare cement-based foam materials, the stability of air bubbles

G. Sang et al. / Construction and Building Materials 91 (2015) 133–137
135
Table 2
The mix proportion and testing results at different water–cement ratios.
Nos.
Experiment matching rates
Testing results
Water–cement
ratios
Cement
(g)
Foaming agent
(g)
Porosity
(%)
Water absorption
(%)
Apparent density
(kg/m3)
3d com. strength (kPa)
Thermal conductivity
(W/(m K))
1
2
3
4
5
0.75
0.80
0.85
0.90
0.95
500
3.0
84.78
88.67
90.37
92.56
93.30
14.87
15.30
13.57
42.99
56.49
409
306
260
201
181
682
485
401
304
223
0.078
0.072
0.069
0.058
0.059
70.0
60.0
50.0
40.0
30.0
20.0
10.0
0.0
46.00
45.00
44.00
43.00
42.00
0.75
0.80
0.85
0.90
0.95
0.2
0.3
0.4
0.5
Water-Cement Ratio
HPMC weight fraction /%
Fig. 1. Ratio of water absorption to porosity changes with water–cement ratio
variation.
Fig. 3. Ratio of water absorption to porosity changes with HPMC weight fraction.
It can be seen from Table 3 that, with the increase of HPMC
weight fraction, apparent density decreases, while porosity
increases. The addition of HPMC improved the ability of cement
paste containing entrained air. The data in the Table 3 shows that
the of HPMC weight fraction increasing from 0.2% to 0.3%, 0.4% and
0.5% causes the porosity increase from 93.48% to 94.11%, 94.33%
and 94.41%, respectively. It is worthwhile to note that the variation
of water absorption and compressive strength are not consistent
with the change of the porosity and apparent density, respectively.
Fig. 3 shows the ratio of water absorption to porosity decrease
gradually although there is no great variation in water absorption.
Fig. 4 shows the ratio of compressive strength to apparent density
enlarge when HPMC weight fraction increases.
1.80
1.60
1.40
1.20
1.00
0.75
0.80
0.85
0.90
0.95
Water-Cement Ratio
Cellulose ether (HPMC) is widely used as water-retention
agents, thickeners, and film formers in cement-based materials
[23–26]. Controlling the porosity of cement-based material is
important, since the matrix porosity is fundamental for thermal
conductivity and strength. Due to accumulation of HPMC at the
Fig. 2. Ratio of strength to apparent density changes with water–cement ratio.
depended on the ability of cement paste inhibiting foam breakage
and escaping [19]. Cellulose ether is a polymer containing polar
groups and surface active groups which are widely applied in
cement-based materials [20–22]. Cellulose ether (HPMC) was
employed in this experiment to improve the flexibility and
mechanical strength of the cement paste liquid film, which are
favorable for reducing air bubble breakage and escaping.
Based on Table 2 tests results, HPMC was used to modify
cement paste at 0.9 water–cement rate. The mix proportion and
test results are shown in Table 3.
air-void interfaces, air voids are stabilized in
a
fresh
cement-based foam paste [27]. In addition to the entrained air
pores, HPMC may impact the microstructure of the matrix by
affecting the hydration process of cement in different ways.
Foamed paste is underwent the most severe moisture loss condi-
tions when it is poured into molds in the preparation of
cement-based foam material. HPMC agent can reduce the rate of
water evaporation for its water-retention property, therefore, the
Table 3
Mix proportion and testing results with HPMC admixture.
Nos.
Mix proportion
Testing Results
Cement
(g)
Foaming agent
(g)
HPMC mixture
(%)
Apparent density
(kg/m3)
3d com. strength
(kPa)
Porosity
(%)
Water absorption
(%)
Thermal conductivity values
(W/(mꢃK))
1
2
3
4
500
3.0
0.2
0.3
0.4
0.5
180
159
153
151
262
243
232
230
93.48
94.11
94.33
94.41
42.42
41.15
41.53
40.96
0.055
0.051
0.049
0.050
Note: HPMC mixture refers to HPMC mass percentage of cement mass.

136
G. Sang et al. / Construction and Building Materials 91 (2015) 133–137
1.55
1.50
1.45
1.40
0.2
0.3
0.4
0.5
HPMC weight fraction /%
Fig. 4. Ratio of strength to apparent density changes with HPMC weight fraction.
Fig. 6. SEM image of fracture surface of pores at water–cement ratio of 0.8.
shrinkage and cracking in hardening foam material is controlled
[28]. Furthermore, during evaporation, a polymer-enriched layer
may form at the cement–air interface. The cracks and holes in
the modified high porosity cement-based foam material could be
repaired and reinforced through the formation of flexible polymer
film which could improve the micro tensile strength and macro
compressive strength. As expected, an increase in total porosity
and the ratio of strength to apparent density was evident when
HPMC was added (see Fig. 4). Moreover, the ratio of water absorp-
tion to porosity decrease slightly with increasing HPMC dosage
(see Fig. 3). The testing results show that the addition of HPMC
agent can improve the foam structure and properties of high poros-
ity cement-based foam material.
significantly from 13.57% to 56.49%, when porosity increases from
90.37% to 93.30% by reflecting from Tables 2, 3 and Fig. 5.
The curves in Fig. 5 show that the porosity and foam structure
are improved by HPMC modification. When HPMC mixture
increase from 0% to 0.4%, the porosity increases from 93.30% to
94.33% and the thermal conductivity value decreases from 0.059
to 0.049 W/(m K). Nevertheless, with the further increase of
HPMC from 0.4% to 0.5%, porosity and thermal conductivity value
all increase slightly. It is possible that ultra-high porosity degrades
foam structure.
3.4. Formation mechanism of pore structure
The formation of foam in cement paste is just the process of bal-
ancing the paste pressure, that is foam internal pressure and
cement paste surface tensile force of three interactions with each
other. Based on Young–Laplace formula [29] (Eq. (2)), that is,
3.3. Influence of porosity and pore structure on thermal conductivity
Thermal conductivity is an important property for
cement-based foam material. Water–cement ratio and HPMC can
apparently affect the material porosity and pore structure,
whereby affecting thermal conductivity value of material. The cor-
relation among thermal conductivity, porosity and foam connec-
tivity are illustrated in Fig. 5.
Fig. 5 shows that porosity affects cement-based foam material
thermal conductivity greatly. Thermal conductivity value
decreases with increase of porosity, but thermal conductivity value
is not in agreement with porosity varying law when cement paste
without HPMC modification. When porosity increases from 92.56%
to 93.30%, the thermal conductivity value does not further
decrease but increase slightly. This change may be caused by the
intensifying of pore connection. The increase of pore connection
can be reflected by the change of the ratio of water absorption to
porosity. The ratio of water absorption to porosity increase
2
R
r
P1 ꢁ P2
¼
ð2Þ
where, P1, P2 – the foam internal and external pressures; R – radius
of curvature; – cement paste surface tensile force coefficient.
r
The pressure difference between two neighboring air bubbles is
as follows (they can be viewed as locating in the same depth in
cement paste):
ꢂ
ꢃ
1
1
D
P ¼ 2r
ꢁ
ð3Þ
R1 R2
In an assumed ideal model, the cement paste surface tensile
force coefficient is a fixed value and the radius of curvature of
two neighboring air bubbles is R1 and R2, respectively. Due to the
80.00
60.00
40.00
20.00
0.090
Ratio of water absorption to
porosity
0.080
Thermal conductivity
0.070
0.060
0.050
Modified by HPMC
0.040
Without HPMC modification
0.00
84.78 88.67 90.37 92.56
93.3
93.48 94.11 94.33 94.41
Porosity˄%˅
Fig. 5. Ratio of water absorption to porosity and thermal conductivity changes with porosity.

G. Sang et al. / Construction and Building Materials 91 (2015) 133–137
137
Research and Development Program of Shaanxi Provincial
(2011K07-33), Scientific Research Program Funded by Shaanxi
Provincial Education Department (2013JK0945).
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This work was supported by the National Natural Science
Foundation of China (51278419), the Science
& Technology