-
DEVELOPMENT OF STRUCTURAL LIGHTWEIGHT FOAMED CONCRETE USING
POLYMER FOAM AGENT
K.-J. Byun, H.-W. Song* and S.-S. Park Department of Civil
Engineering, Yonsei Univ., Seoul 120-749, Korea
Y.-C. Song
Korea Electric Power Co., Daejeon, Korea ABSTRACT
Lightweight foamed concrete is a concrete made by cement slurry
mixed with prefoamed
foams so that foam concrete is lighter than conventional
concrete. The objectives of this study is to develop optimal
prefoamed lightweight foamed concrete possessing improved
lightness, flowability and strength by using polymer foam agent,
admixtures and industrial by-products such as styrofoam,
silica-fume and fly-ash. In this paper, extensive test data on
lightweight foamed concrete are presented. This paper also presents
the mechanical characteristics of developed lightweight foamed
concrete including long-term behaviors and their improvement. It is
expected that this study provides an important guide to manufacture
structural lightweight foamed concrete using polymer foam agent. 1.
INTRODUCTION
Lightweight foamed concrete is a kind of lightweight concrete,
which is lighter than
normal concrete by mixing foams into cement slurry [1].
According to foaming type, lightweight foamed concrete is
classified as pre-foaming type foamed concrete which is mixed by
prefoamed foams in cement slurry, after-foaming type foamed
concrete which is mixed with foaming agents such as aluminum powder
and zinc powder, and mixed-foaming type foamed concrete which is
mixed with surface active agent into cement slurry during mixing
[2]. In this study, lightweight foamed concrete is manufactured by
the pre-foaming type because of its advantages for controlling the
quantity of the foam and easiness of placing during construction.
The foam agent is the most important factor for the foamed concrete
and foam agents are classified as polymer foam agent, protein foam
agent and surface active agent. Protein foam agent compounded of
animal blood and gelatin is made of several kinds of amino acid and
makes about 0.20.8mm size of a pore in the cream at the time of
foaming. Surface active agent is made of alkyl benzene sulfonate
and is hard to obtain stable foams in cement slurry at the time of
foaming. In this study, polymer
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* Correspondence to : H.-W.Song, Dept. of Civil Eng., Yonsei Univ.,
Seoul 120-749, Korea [email protected]
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foam agent is used since the polymer foam agent does not have
the defect due to corrosion and bad smells due to chloride and
zinc, and also the polymer foam agent develops stable pores films
surrounding the foam. As a polymer compounded of water repelling
hydrocarbon and water attaching hydrocarbon, the polymer foam agent
has neutral PH and makes about 0.10.4mm size of a pore in the state
of white cream at the time of foaming. In order to use industrial
by-product for the partial substitution of the foam, expanded
polystyrene bead (so-called styrofoams) is also used. Styrofoams,
which is used to have brown color and round shape, are normally
manufactured by expanding petroleum, coal-tar and polystyrene in
heat. Styrofoams do not absorb water because it is consist of about
million closed cellulars. In manufacturing processes of the foamed
concrete as shown in Fig.1, the foams are made by compressed air in
pre-foaming method. Dilute water and foam agent with ratio of 50:1
are used to make foams at foaming instrument. Omnimixer which has
250l capacity is used for mixing, and only vibrated compaction is
performed to minimize antifoaming. Curing is performed in curing
room at the normal temperature for at least 48 hours and then
continued in curing tank at 202 for 28 days. In this study, we
define the optimal lightweight foamed concrete as a foamed concrete
which has more than 180mm flow value, more than 30kg/cm2
compressive strength, and about 0.5t/m3 unit volume weight.
Fig.1 Manufacturing process of foamed concrete
2. DEVELOPMENT OF OPTIMUM FOAMED CONCRETE For the purpose of
developing the optimum foamed concrete, influencing mixing
factors
are analyzed and optimum mix proportions are obtained for
required flowability, unit volume weight and compressive strength.
In this study, styrofoam is used as partial substitution for the
foam. The specific weight of styrofoam is 0.03 which is less than
that of foam (0.05). Fig.2 shows compressive strengths for
different substitution ratios of styrofoam. When the ratio of
styrofoam B to foam F is 3:7, i.e. B:F=3:7, the compressive
strength [kg/cm2] is 36.6kg/cm2 which is larger than that of pure
foamed concrete (24kg/cm2) for the case of 0.55t/m3 of unit volume
weight. Therefore, the optimum substitution ratio of styrofoam is
30% of the foam. It is found that 5% of silica-fume replacement for
cement increases the strength of the foamed concrete most
effectively for the case of 30% styrofoam substitution. It is also
found that fly-ash affects durability of the foamed concrete which
will be discussed later but it does not increase the strength of
the foamed concrete. According to test result, mixing ratio of fine
aggregate does not affect to the strength of the foamed concrete.
When unit weight of cement is 450520 kg/cm2 and water cement ratio
is 0.5, foamed concrete is satisfied to required compressive
strength and unit volume weight. Thus optimum mix proportions are
summarized at Tab.1.
Compressedair
foaming instrument
foam agent, dilute water
cement
admixtures
styrofoam
water (3/4)
foam
water (1/4)
foamed concrete
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Tab.1 Optimum mix proportions
* B:F = the ratio between styrofoam (B) and foam (F) Fig.3 shows
compressive strength normalized by compressive strength without
pore ( 0) for
different pore ratios P which can be expressed as eq.1 and eq.2
by regression analysis. These equations are similar with those by
Balshin and Ryshkewitch [3][4].
= 0(1-P)4 (1) = 0e-6P (2)
The pore ratio has also direct relationship with unit volume
weight of the foamed concrete. The relationship between pore ratio
and unit volume weight con [t/m3] by regression analysis is
obtained as eq.3.
con = 2.1 - 2.3P (3) Flowability is estimated from flow values.
The flow value 180 is regulated as standard
value to acquire sufficient flowability because it enables 500m
pumping without material segregation [5]. Foamed concrete with
styrofoam is verified to have more than 180 flow value when
water-cement ratio is more than 0.5.
Fig. 2 Compressive strength change Fig. 3 Relationship between
pore ratio and
by substitution ratio of styrofoam compressive strength
3. MECHANICAL CHARACTERISTICS OF FOAMED CONCRETE 3.1 Compressive
strength
From the experiments, the relationship between unit volume
weight and compressive strength ck of lightweight foamed concrete,
when water-cement ratio is 0.5 and sand-cement ratio is 0, is
obtained as shown in Fig.4 and can be expressed as eq.4.
ck = 1.5 e5 con (4) Fig.5 shows the relationship between
compressive strength at the age of 7 days (7 )
and compressive strength at the age of 28 days (28 ) of
lightweight foamed concrete, which can be also expressed as
eq.5.
28 = 1.277 + 2.57 (5)
factor ratio comment factor ratio comment water-cement ratio 0.5
- fine aggregate 0 - unit weight of cement C ()
450520 460, if *B:F 5:5
pore ratio (P) 0.550.6 -
amount of styrofoam (P %)
30 - amount of silica-fume (C %)
5 20, if no styrofoam is used
/0 10 Eq. 1 Eq. 2
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Fig. 4 Relationship between unit weight Fig. 5 Relationship
between 7 and 28 days
and compressive strength strength by unit weight 3.2 Young's
modulus and Poisson's ratio
In this study, secant slope which connects origin of
stress-strain curve and point of 50% ultimate strength is defined
as Young's modulus E. Tab.2 shows the Young's modulus for different
unit volume weights.
Tab. 2 Unit weight, compressive strength, Young's modulus of
foamed concrete
It can be seen that Young's modulus of foamed concrete is about
0.33104 kg/cm2, which
is 115% of that of normal concrete. From the regression
analysis, an equation to derive the Young's modulus can be
expressed as eq.6.
E = 6326 (con)1.5 ck (6) The average Poisson's ratio of
lightweight foamed concrete is measured as 0.2.
3.3 Tensile strength For 1020cm cylindrical specimens of foamed
concrete with W/C=0.5, tensile strength
is obtained by splitting test method. Tensile strength of foamed
concrete is about 1.48.1kg/cm2 when con = 0.380.75t/m3. Fig.6 shows
relationship between compressive strength and tensile strength t ,
which can be expressed as eq.7.
t = 1.03 ck (7) While the ratio of tensile strength to
compressive strength is 0.080.11 in normal
concrete, the ratio in lightweight foamed concrete is 0.20.4.
3.4 Flexural strength
Flexural-strength tests of foamed concrete for W/C=0.5 are
performed for 4416cm beam specimens by three points bending test.
Flexural strength b of foamed concrete is about 314kg/cm2. The
ratio of the flexural strength to the compressive strength of
foamed concrete is about 0.30.6. Fig.7 shows relationship between
compressive strength and flexural strength, which can be expressed
as eq.8.
b = 1.74 ck (8)
unit weight (t/m3) compressive strength (kg/cm2) Young's
modulus(104kg/cm2) 0.39 7.38 0.4 0.49 15.4 0.8 0.55 36.6 1.6 0.64
47.0 2.3
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Fig. 6 Relationship between compressive strength Fig. 7
Relationship between compressive
and splitting tensile strength strength and flexural strength
3.5 Pores of lightweight foamed concrete
Decrease of pore size of the foamed concrete generally increases
strength. In general, the pores are composed of macro pore and
micro pore. Macro pore is measured by image analysis and micro pore
is measured by mercury inserting method [6]. For eight specimens of
the foamed concrete without styrofoams which have pore ratio of
0.76, 0.72, 0.69, 0.65, 0.61, 0.59, 0.58, 0.51 and 1010cm sectional
area, image analyses are performed to measure average size and
distribution of macro pore. Average pore size is 250460. Fig.8
shows relationship between average pore size D () and compressive
strength, which can be expressed as eq.9.
ck = 243e-0.01D (9) Fig.8 and Fig.9 show relationship between
pore ratio and average pore size, which can be expressed
as eq.10. It shows that average pore size increases as pore
ratio increases. D = 663P2 - 113P (10)
PORE SIZE () (D)
Fig. 8 Relationship between mean pore size Fig. 9 Relationship
between mean pore ratio and compressive strength and mean pore
size
4. IMPROVEMENT OF MATERIAL PROPERTIES 4.1 Improvement of
compressive strength
A method to improve the compressive strength, while maintaining
the unit weight constant, is to intensify strength of cement paste
by replacing some portion of cement by silica-fume. Fig.10 shows
compressive strengths for different amount of silica-fume
replacements. Specimens of no.6 show that 86 kg/cm2 of compressive
strength, when con = 0.86t/, is obtained by replacing 30% of cement
by silica-fume and maintaining W/C = 0.2 by using super
plasticizer. Fig. 11 shows that lightweight foamed concrete
developed in this study has maximum 4 times of improvement in
compressive strength than
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conventional one.
No.1 No.2 No.3 No.4 No.5 No.6
-120-100-80-60-40-20
020406080
100120
1.21.00.80.60.40.2
12010080604020
0
UNIT
WEI
GHT(
t/) C
OMPR
ESSI
VE S
TREN
GTH(
/
)
N o .1 : W /C 0.25 SF 0%N o.2 : W /C 0.30 SF 15%N o.3 : W /C
0.35 SF 20%N o.4 : W /C 0.35 SF 25%N o.5 : W /C 0.30 SF 30%N o.6 :
W /C 0.20 SF 30%
1 2 3 4 50
20
40
60
80
IMPROVEMENT STRENGTH
MONOCRETECOPPER COM
NORMAL FOAM CONC.
JEWOS
COM
PRES
SIVE
STR
ENGT
H (
/)
Fig 10 Compressive strength Fig 11 Comparison of compressive
strength
and unit weight per mixing of foamed concrete 4.2 Properties of
foamed concrete with flash-setting agent
For the practical use of lightweight foamed concrete, it is
sometimes necessary to obtain required strength in early age [7].
In this study, time to reach 8cm of critical flow value in flow
test of fresh concrete by using different mixing ratio of
flash-setting agent are compared for the cases of both pure foamed
concrete and styrofoam-mixed concrete. As shown at Fig.12(a),(b),
setting time becomes shorter when mixing ratio of flash-setting
agent becomes higher. When mixing ratio of flash-setting agent is
10%, setting time is shortened to 7080%. Adding styrofoam also
makes the setting time shorter, but it leads to decrease of
flowability. So, it is desirable to increase styrofoam replacing
ratio and flash-setting agent mixing ratio only for urgent
construction. Fig.13 shows change of compressive strength with
respect to the age of normal foamed concrete and 8% flash-setting
agent mixed foamed concrete. Normal foamed concrete shows 40% of
strength increase within 3 days, but foamed concrete with
flash-setting agent shows 70% of increase.
0 100 200 300 400 500 600 700 800
8
10
12
14
16
18 Flash-setting agent 0% Flash-setting agent 6% Flash-setting
agent 8% Flash-setting agent 10%
FLOW
(cm
)
MIN.0 100 200 300 400 500 600 700 800
8
10
12
14
16
18 Flash-setting agent 0% Flash-setting agent 6% Flash-setting
agent 8% Flash-setting agent 10%
FLOW
(cm
)
MIN. 0 5 10 15 20 25 30
0
4
8
12
16
20
Normal foam concrete Flash- setting agent
mixing rate (8%)
COM
PRES
SIVE
STR
ENGT
H (
/)
AGE (day) (a) pure foamed concrete (b) foamed concrete with
styrofoam
Fig. 12 Flow change as adding Fig. 13 Change of compressive
flash-setting agent strength as aging
4.3 Improvement of strength by fiber reinforcement To improve
the flexural strength and the tensile strength of lightweight
foamed concrete, vynylon
fibers are mixed with cement paste as fiber reinforcer. For 28
days tensile strength, we obtained 1.97 times improvement effect of
tensile strength with 19mm vynylon fiber and 2.04 times with 30mm
vynylon fiber. We obtained 1.44 times improvement of tensile
strength with 30mm vynylon fiber in splitting test. For flexural
strength, we obtained 1.3 times of improvement with 30mm vynylon
fibers. 4.4 Impact behavior
Resistance to impact are estimated with impact hammer and F.F.T.
analyzer to study dynamic properties of lightweight foamed
concrete. As seen in Tab.3, natural frequency and damping time of
each specimen are compared by estimating properties of acceleration
and transmission function of acceleration at each frequency.
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Tab. 3 Dynamic properties of lightweight foamed concrete
specimens
Damping effect decreases as pore ratio decreases due to increase
of the damping time. And
impact coefficient which is obtained by static amplitude to
dynamic amplitude ratio at the time of impact decreases as pore
ratio decreases. Thus it is founded that more pore ratio of foamed
concrete decrease, more resistance of impact increase and absortion
of impact decrease. Fig.14 and Fig.15 compare transmission function
of acceleration and acceleration element for specimen 1 and 4.
0 100 200 300 400
0.0
0.5
1.0
1.5
2.0
2.5
No.1 specimen No.4 specimen
ACCE
LERA
TION
()
FREQUENCY (Hz) 0.50 0.55
0
2
4
6
8
10
No.4 specimen
No.1 specimen
4
2
0
4
2
0
ACCE
LERA
TION
()
TIME (10- 3 sec) Fig. 14 Transmission function of acceleration
Fig. 15 Acceleration element of
of foamed concrete foamed concrete 5. PROPERTIES OF LONG TERM
BEHAVIORS
For the improvement of durability, fly-ash is used as partial
replacement of cement.
5.1 Shrinkage Fig.16 shows shrinkage properties of lightweight
foamed concrete with different mixing
factors. It can be seen that styrofoam and fly-ash (FA) reduce
shrinkage and shrinkage strain more than 50%. 5.2 Heat of
hydration
Temperature due to heat of hydration in the center of
lightweight foamed concrete in the field, rises up to 95 at highest
and kept over 60 after 150 hours by thermal insulator effect of
foamed concrete. But, few cracks by temperature occurs due to relax
confinement of foams. 5.3 Freezing and thawing
Properties of freezing and thawing of lightweight foamed
concrete are obtained by quick test in water. Tab.4 shows weight
change, relative dynamic-elastic coefficient and durability index.
Durability index of lightweight foamed concrete to freezing and
thawing are about 524, and it shows that lightweight foamed
concrete does not have enough resistance to freezing and thawing.
From the Tab.4, it can be seen that the resistance to freezing and
thawing is improved by using styrofoam and fly-ash.
no. 1 no. 2 no. 3 no. 4 type dynamic properties pore ratio 0.71
pore ratio 0.63 pore ratio 0.55 pore ratio 0.47natural frequency ()
198 194 192 174 damping time (10-3sec) 194 278 326 365 impact
coefficient (i) 0.13 0.097 0.055 0.032
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Tab. 4 Freezing and thawing test results
5.4 Permeability
From permeability test, permeability coefficients are obtained
as 9.510-87.210-4 cm/sec, the range is similar to that of
coarse-grained silt and coarse-grained clay, and it is more than 50
times larger than that of normal concrete. Fig. 17 shows that the
permeability coefficient of lightweight foamed concrete is
proportional to unit weight and inversely proportional to pore
ratio.
10 20 30 40 50 60
-500
0
500
1000
1500
2000
Styrofoam Styrofoam Styrofoam + fly ash Styrofoam + fly ash Only
foam Only foamSH
RINK
AGE
STRA
IN (
)
AGE (day) 0.60 0.65 0.70 0.75
10-7
10-6
10-5
10-4
10-3
PERM
EABI
LITY
COE
FFIC
IENT
(cm
/sec
)
PORE RATE Fig. 16 Shrinkage strain as mixing factors Fig. 17
Change of permeability
coefficient as pore ratio 6. CONCLUSIONS
By using the polymer foam agent, we develop a lightweight foamed
concrete which has more than 180 flow value and increased
compressive strength than conventional one. Compressive strength of
the developed lightweight foamed concrete is 36.6/ when unit volume
weight is 0.55t/ and 86/ for 0.86t/. From the experiments for
different mixing factors, optimum mix proportion of lightweight
foamed concrete is presented and the mechanical characteristics
including long term behavior and the durability of developed foamed
concrete with different mix proportions are also presented.
REFERENCES [1] Watson, K. L., Eden, N. B. and Farrant, J. R.,
"The Effect of Admixture on the Relationship between Compressive
Strength and Density of Autoclaved Aerated Concrete made from Slate
Powder and Portland Cement", Silicates Industrials, Vol. 43, 1978,
pp. 57-64. [2] Short, A. and Kinniburgh, W., "Lightweight
Concrete", 3rd Ed., Applied Science Publishers Ltd., London, 1978,
pp. 1-14. [3] Watson, K. L., "Autoclaved Aerated Concrete from
Slate Waste, Part 2 : Some
no. note weight change (%) relative dynamicelastic coefficient
(%)
durability index (DF)
1-1 109.36 89.30 16.07 1-2
B:F=3:7 110.37 92.75 22.06
2-1 118.48 87.64 21.03 2-2
B:F=3:7 FA=10% 122.14 96.29 23.11
3-1 115.58 95.44 5.09 3-2
B:F=1:9 118.34 85.91 4.58
4-1 98.87 96.38 5.14 4-2
B:F=2:8 112.33 81.85 20.06
-
Property/Porosity Relationships", The International Journal of
Lightweight Concrete, Vol. 3, No. 2, 1980, pp. 121-123. [4] Edan,
N. B., Manthorpe, A. R., Miell, S. A., Szymanek, P. H. and Watson,
K. L.,"Autoclaved Aerated Concrete from Slate Waste, Part 1 : Some
Property/Density Relationships", The International Journal of
Lightweight Concrete, Vol. 2, No. 2, 1980, pp. 95-100. [5] Zhang,
M. H. and Gjorv, O. E., "Permeability of High-Strength Lightweight
Concrete", ACI Material Journal, Vol. 88, No. 5, 1991, pp. 463-469.
[6] Neville, A. M., "Properties of Concrete", Pitman, 3rd Ed., pp.
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