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วารสารวิชาการพระจอมเกล้าพระนครเหนือ ปีที่ 19 ฉบับที่ 3 ก.ย. - ธ.ค. 2552 The Journal of KMUTNB., Vol. 19, No. 3, Sep. - Dec. 2009
Lightweight Concrete Mixed with Superfine Crumb
Rubber Powder Part 1: Insulation Properties
Piti Sukontasukkul1*and Somyot Wiwatpattanapong2
บทคัดย่อ ในการศึกษาครั้งนี้ คอนกรีตมวลเบาผสมด้วยผง
ยางรถยนต์ชนิดละเอียดมากจะถูกนำมาศึกษาโดยเน้นในส่วนของคุณสมบัติการเป็นฉนวน ผงยางที่นำมาใช้ผลิตจากโรงงานแปรรูปยางรถยนต์ เก่าเพื่อใช้ ในอุตสาหกรรม เช่น งานถนนราดยาง บล็อกยาง วัสดุอุดรอยร้าว เชิงเพลิงทางเลือก เป็นต้น จากกระบวนการผลิตด้วยวิธีการบดละเอียดทำให้ได้ขนาดต่างๆ กัน ตั้งแต่หลายมิลลิเมตรไปจนถึงระดับไมครอน ขนาดเล็กสุดอยู่ที่ประมาณ 500-600 ไมครอน ในการทดลองนี้จะนำขนาดที่ เล็กที่สุดมาใช้ผสมคอนกรีต โดยจะแทนที่มวลรวมละเอียดในสัดส่วน 10% 20% และ 30% โดยน้ำหนัก บทบาทหลักของเม็ดยางเป็นการแทนที่มวลรวมละเอียดทำให้คอนกรีตมีหน่วยน้ำหนักเบา แต่เนื่องจากขนาดของเม็ดยางที่เล็กนี้ ทำให้เม็ดยางเข้าไปแทรกตัวอยู่ในเนื้อคอนกรีตและรวมถงึอดุชอ่งวา่งตา่งๆ สง่ผลใหค้อนกรตีมคีวามสามารถในการดูดซึมและช่องว่างลดลง และมีคุณสมบัติฉนวนด้านเสียงและอุณหภูมิที่ดีขึ้น
คำสำคัญ: ผงยางชนดิละเอยีดมาก คณุสมบตัดิา้นเสยีง
และอุณหภูมิ
Abstract
In this study, insulation properties of lightweight
concrete mixed with commercialized superfine crumb
rubber powder is investigated. Crumb rubber
produced from rubber reclaimed plant has been used
widely in several applications such as pavement,
blocks, rubber tiles, sealant, supplement fuel etc.
Because of the grinding during the manufacturing,
crumb rubbers are found in various sizes from several
millimeters to microns. The smallest size is about 500
to 600 micron. In this experiment, the superfine
crumb rubbers are mixed with concrete by replacing
fine aggregate at the rate of 10%, 20% and 30% by
weight. The main role of crumb rubbers powder is to
replace fine aggregates to produce lightweight
concrete. However, because of its small diameter and
dense property, crumb rubber powder will also act as
a filler to fill small voids in concrete to reduce water
absorption and porosity. Also, the decrease in density
results in better thermal and sound properties.
Keywords: Superfine Crumb Rubber, Sound and
Thermal Properties
1 Associate Professor, Department of Civil Engineering, Faculty of Engineering, King Mongkut’s
University of Technology North Bangkok. 2 Student, Department of Civil Engineering, Faculty of Engineering, King Mongkut’s University of
Technology North Bangkok.
* Corresponding Author, Tel.0-2913-2500, Ext. 8625, E-mail: [email protected]
Received October 16, 2008; Accepted July 20, 2009
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1. Introduction 1.1 Manufacturing Crumb Rubber
Abandoned tires has been a waste problem around the world, millions ton of tires are being
discarded every year. In Thailand, total consumption of rubber products was about 242 metric tons, this number included about 90 metric tons of vehicle
tires [1]. One way to recycle them is to grind them into small particles. Crumb rubber is widely accepted and found it ways into several applications
such as asphalt, sealants, rubber sheets or mix with cementitious materials like concrete.
In Thailand, the manufacturing of commercialized
crumb rubbers consists of three steps (Figure 1). The first step is to cut and sort out the grindable parts (parts without radial steels). Next, the rubber pieces
are fed into series of cutting wheels several times until the desired size is achieved. Finally, crumb rubbers are sorted out according to the particle size.
The grinding technique allows the crumb rubbers to be produced in various sizes (about 7 to 8 different sizes). The biggest one has a diameter of about 5 mm
while the smallest one has a diameter of about 600 micron.
1.2 Concrete Microstructure Concrete consists mainly of three components:
cement, aggregates and water. During the mixing,
when water comes in contact with cement, series of chemical reactions called “hydration reactions” begin. The hydration reactions are exothermic and involve
series of temperature changes from beginning to end (until concrete get harden).
(a)
(b)
(c)
Figure 1 Manufacturing Crumb Rubber a) Sorting,
b) Grinding, c) Sieving
In harden concrete, the micro structure can be
divided into two parts: 1) solid and 2) void (or Porosity) part. The solid part consists of hydrated cement (Calcium Silicate Hydrate (CSH), Calcium
Hydroxide (CH), etc.), aggregates, unhydrated cement
1. Introduction 1.1 Manufacturing Crumb Rubber
Abandoned tires has been a waste problem around the world, millions ton of tires are being
discarded every year. In Thailand, total consumption of rubber products was about 242 metric tons, this number included about 90 metric tons of vehicle
tires [1]. One way to recycle them is to grind them into small particles. Crumb rubber is widely accepted and found it ways into several applications
such as asphalt, sealants, rubber sheets or mix with cementitious materials like concrete.
In Thailand, the manufacturing of commercialized
crumb rubbers consists of three steps (Figure 1). The first step is to cut and sort out the grindable parts (parts without radial steels). Next, the rubber pieces
are fed into series of cutting wheels several times until the desired size is achieved. Finally, crumb rubbers are sorted out according to the particle size.
The grinding technique allows the crumb rubbers to be produced in various sizes (about 7 to 8 different sizes). The biggest one has a diameter of about 5 mm
while the smallest one has a diameter of about 600 micron.
1.2 Concrete Microstructure Concrete consists mainly of three components:
cement, aggregates and water. During the mixing,
when water comes in contact with cement, series of chemical reactions called “hydration reactions” begin. The hydration reactions are exothermic and involve
series of temperature changes from beginning to end (until concrete get harden).
(a)
(b)
(c)
Figure 1 Manufacturing Crumb Rubber a) Sorting,
b) Grinding, c) Sieving
In harden concrete, the micro structure can be
divided into two parts: 1) solid and 2) void (or Porosity) part. The solid part consists of hydrated cement (Calcium Silicate Hydrate (CSH), Calcium
Hydroxide (CH), etc.), aggregates, unhydrated cement
1. Introduction 1.1 Manufacturing Crumb Rubber
Abandoned tires has been a waste problem around the world, millions ton of tires are being
discarded every year. In Thailand, total consumption of rubber products was about 242 metric tons, this number included about 90 metric tons of vehicle
tires [1]. One way to recycle them is to grind them into small particles. Crumb rubber is widely accepted and found it ways into several applications
such as asphalt, sealants, rubber sheets or mix with cementitious materials like concrete.
In Thailand, the manufacturing of commercialized
crumb rubbers consists of three steps (Figure 1). The first step is to cut and sort out the grindable parts (parts without radial steels). Next, the rubber pieces
are fed into series of cutting wheels several times until the desired size is achieved. Finally, crumb rubbers are sorted out according to the particle size.
The grinding technique allows the crumb rubbers to be produced in various sizes (about 7 to 8 different sizes). The biggest one has a diameter of about 5 mm
while the smallest one has a diameter of about 600 micron.
1.2 Concrete Microstructure Concrete consists mainly of three components:
cement, aggregates and water. During the mixing,
when water comes in contact with cement, series of chemical reactions called “hydration reactions” begin. The hydration reactions are exothermic and involve
series of temperature changes from beginning to end (until concrete get harden).
(a)
(b)
(c)
Figure 1 Manufacturing Crumb Rubber a) Sorting,
b) Grinding, c) Sieving
In harden concrete, the micro structure can be
divided into two parts: 1) solid and 2) void (or Porosity) part. The solid part consists of hydrated cement (Calcium Silicate Hydrate (CSH), Calcium
Hydroxide (CH), etc.), aggregates, unhydrated cement
1. Introduction
1.1 Manufacturing Crumb Rubber
Abandoned tires has been a waste problem
around the world, millions ton of tires are being
discarded every year. In Thailand, total consumption
of rubber products was about 242 metric tons, this
number included about 90 metric tons of vehicle
tires [1]. One way to recycle them is to grind them
into small particles. Crumb rubber is widely
accepted and found it ways into several applications
such as asphalt, sealants, rubber sheets or mix with
cementitious materials like concrete.
In Thailand, the manufacturing of
commercialized crumb rubbers consists of three
steps (Figure 1). The first step is to cut and sort out
the grindable parts (parts without radial steels).
Next, the rubber pieces are fed into series of cutting
wheels several times until the desired size is
achieved. Finally, crumb rubbers are sorted out
according to the particle size. The grinding
technique allows the crumb rubbers to be produced
in various sizes (about 7 to 8 different sizes). The
biggest one has a diameter of about 5 mm while the
smallest one has a diameter of about 600 micron.
1.2 Concrete Microstructure
Concrete consists mainly of three components:
cement, aggregates and water. During the mixing,
Figure 1 Manufacturing Crumb Rubber a) Sorting, b) Grinding, c) Sieving.
when water comes in contact with cement, series of
chemical reactions called “hydration reactions”
begin. The hydration reactions are exothermic and
involve series of temperature changes from
beginning to end (until concrete get harden).
In harden concrete, the micro structure can be
divided into two parts: 1) solid and 2) void (or
Porosity) part. The solid part consists of hydrated
cement (Calcium Silicate Hydrate (CSH), Calcium
Hydroxide (CH), etc.), aggregates, unhydrated
cement and interface zones between cement and
aggregates. As for the porosity, there can be divided
into 3 different kinds: 1) capillary pores, 2)
gel pores, and 3) interface pores. The pores in
concrete come in various sizes. Capillary pores
caused primarily by entrapped water and are
considered the largest of all. Gel pores are consider
smallest and causes by the formation and
compaction of CSH [2], [3].
Usually, the pore structure plays a significant
role on the durability of concrete. This is because
the existing of these pores allows external
substances (moisture and gas) to migrate in and out
of concrete structures. Some substances can be
harmful and caused deterioration in concrete.
Therefore to increase concrete durability, engineers
have to deal directly with the pore structures.
Theoretically, the migrations of water and gas occur
(a) (c) (b)
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mostly through the capillary pores which are large
pores and some of them might still interconnected
[4]. To stop the migrations, the volume of large
sized pores must be reduced. This can be achieved
by using small w/c ratio or using fillers (such as
silica fume, fly ash etc.).
1.3 Need for Better Insulation
Nowadays, the design and construction
purposes of a modern house should not focus on
residential and aesthetic purpose only, but also should
consider other issues like, energy conservation and
becoming an integral part of the environment. As we
know, the earth’s average temperature is rising slowly
every year due to the effect of global warming. Cares
for the environment are urgently needed by reducing
the use of fuel energy, encouraging the use of
recycled materials, reducing the emission of carbon
dioxide gas, etc [5]. The construction industry can
help by employing site management to minimize
wasted materials, using recycled aggregates, selecting
environmental friendly materials, etc.
In the case of an individual household,
architectural design based on environmental aspect
should be considered in order to achieve such goal.
From a concrete engineer’s point of view, material
selection also plays an important role. The use of
better insulating materials can directly reduce long-
term energy consumption.
1.4 Research Significance
In the last 20 years, material properties of
crumb rubber concrete have been investigated quite
exclusively [7]-[12]. Information on the mechanical
properties of crumb rubber concrete with particle
size varied from 1 mm and larger in terms of
compressive, tensile, flexural strengths, thermal and
sound, is quite well-known. However, there is no
information on the effect of crumb rubber with
particle size smaller than 1 mm on properties of
concrete. By using smaller particle size of crumb
rubber, the internal voids inside the concrete are
expected to be filled. By filling these voids, some
micro-mechanisms inside the concrete may be
different from normal concrete and concrete mixed
with large size crumb rubber. For example, the
overall absorption of concrete which is usually very
high most of the lightweight aggregate concrete may
decrease due to the decreasing of volume of
capillary pores. Thus, it is interesting to see whether
other properties are affected by the filler effect of
superfine crumb rubber.
Therefore, the objective of this study is to
investigate on the effect of superfine crumb rubber
powder on properties of concrete such as absorption,
porosity, thermal and sound properties (such as
thermal conductivity factor, thermal resistivity, heat
transfer, sound absorption at different frequencies
and noise reduction).
2. Experimental Program
2.1 Materials
Materials used in this study consisted of
Portland cement type I, 10 mm coarse aggregate,
river sand, crumb rubber (Figure 2), water and
superplasticizer Type F (13 cc /1 kg) of cement
weight. Crumb rubber with particle size pass
through sieve No. 25; the properties and gradation
of crumb rubbers are given in Table.1 and Figure3.
The mix proportion for the control specimen (no
crumb rubber) was set at 1.00:0.45:1.64:1.95
(Cement : Water : Fine Aggregate : Coarse Aggregate).
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In the case of the superfine crumb rubber
concrete (SCRC), fine aggregate were replaced with
crumb rubber at 10% 20% and 30% by weight.
Gradation of sand and sand+crumb rubber is given
in Figure 4. Details on the casting and assigned
designations are given in Table 2.
2.2 Specimen Prepartion and Testing
Concrete was dry-mixed using pan mixer for
about 5 minutes, then added water and continued
mixing for another 5 minutes, after that it was poured
into molds. Three tests were carried out: 1) Density, Voids
and Absorption [13], 2) Steady-State Heat Flux
Measurement and Thermal Transmission Properties
[14]. (Figure 5), and 3) Acoustics Determination of
Sound Absorption Coefficient and Impedance in
Impedance Tube [15] (Figure 6). Number of
samples for each test is summarized in Table 3.
Figure 4 Gradation of Fine Aggregate+Crumb Rubber.
Figure 2 Crumb Rubber Powder.
powder on properties of concrete such as absorption, porosity, thermal and sound properties (such as thermal conductivity factor, thermal resistivity, heat transfer, sound absorption at different frequencies
and noise reduction).
2. Experimental Program 2.1 Materials
Materials used in this study consisted of Portland cement type I, 10 mm coarse aggregate,
river sand, crumb rubber (Figure 2), water and superplasticizer Type F (13 cc /1 kg) of cement weight. Crumb rubber with particle size pass through
sieve No. 25; the properties and gradation of crumb rubbers are given in Table.1 and Figure3. The mix proportion for the control specimen (no crumb
rubber) was set at 1.00:0.45:1.64:1.95 (Cement : Water : Fine Aggregate : Coarse Aggregate).
In the case of the superfine crumb rubber
concrete (SCRC), fine aggregate were replaced with crumb rubber at 10% 20% and 30% by weight. Gradation of sand and sand+crumb rubber is given
in Figure 4. Details on the casting and assigned designations are given in Table 2.
Table 1 Properties of Crumb Rubber and Aggregates
Categories Crumb Coarse Fine Rubber Agg. Agg.
Avg. Bulk SG 0.62 2.68 2.43 Avg. Bulk SG (SSD) 0.62 2.69 2.47 Avg. Apparent SG 0.62 2.70 2.55 Avg. Absorption (%) 1.05 0.25 2.04 Fineness Modulus 2.83 - 2.9
Figure 2 Crumb Rubber Powder
0102030405060708090
100
0.0010.010.11
Percent Finer by Weight
Diameter (in) Figure 3 Gradation of Crumb Rubber
0102030405060708090
100
0.0010.010.11
Percent Finer by Weight
Diameter (in.)
100% Fine
70% Fine + 30% CR (30SCRC)
80% Fine + 20% CR (20SCRC)
Figure 4 Gradation of Fine Aggregate+Crumb Rubber
Figure 3 Gradation of Crumb Rubber.
Table 1 Properties of Crumb Rubber and Aggregates
Categories Crumb Rubber
Coarse Agg.
Fine Agg.
Avg. Bulk SG Avg. Bulk SG (SSD) Avg. Apparent SG Avg. Absorption (%) Fineness Modulus
0.62 0.62 0.62 1.05 2.83
2.68 2.69 2.70 0.25
-
2.43 2.47 2.55 2.04 2.9
Table 2 Details and Assigned Designations
Designation
Weight per m3
Crumb Rubber
kg
Cement kg
Coarse Agg kg
Fine Agg kg
Water
kg
PC 0 478.7 933.5 783.8 215
10SCRC 78.4 478.7 933.5 705.5 215
20SCRC 156.8 478.7 933.5 627.1 215
30SCRC 235.2 478.7 933.5 548.7 215
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Table 3 Casting Schedule
Type of Concrete
Number of specimen
Thermal Sound Density
PC 3 8 3
10SCRC 3 8 3
20SCRC 3 8 3
30SCRC 3 8 3
Total 12 32 12
Details of each test are described briefly below:
• Density and Voids [13] The specimens are
weighed under 4 different conditions: oven-dried,
saturated after immersion, saturated after boiling
and immersed under water. Then, the obtained
weights are used to calculate the density and
permeable voids based formulas given in the
standard.
• Steady-State Heat Flux Measurement and
Thermal Transmission Properties [14] The two
concrete specimens in form of square shape (300 x
300 x 25.4 mm) are setup between the heat source
(hot plate) and two cold surface assemblies. The test
begins by increasing the temperature of the hot plate
and at the same time measuring the temperature
change of both hot and cold surface assemblies.
Continue heating up until the temperature entered
the steady-state heat flux.
• Acoustics Determination of Sound
Absorption Coefficient and Impedance in
Impedance Tube [15] (21): Two different sizes of
specimens in form of dish: dia-290 x 500 mm and
dia-990 x 500 mm were used at two different
frequency ranges: high frequency (2000 and 4000 Hz)
and low frequency (125, 250, 500 and 1000 Hz).
Measurements were carried out according to the
standing wave method in which a loud speaker sets up
a sound field in a tube terminated by the sample.
When the standing waves were produced in the tube,
the ratio between the maximum and minimum sound
pressure were measured. The absorption coefficient
of the sample for zero degree incident sound wave
was then calculated from the measured data.
Figure 5 Steady-State Heat Flux [14].
2.2 Specimen Prepartion and Testing Concrete was dry-mixed using pan mixer for
about 5 minutes, then added water and continued mixing for another 5 minutes, after that it was
poured into molds. Three tests were carried out: 1) Density, Voids and Absorption [13], 2) Steady-State Heat Flux Measurement and Thermal Transmission
Properties [14]. (Figure 5), and 3) Acoustics Determination of Sound Absorption Coefficient and Impedance in Impedance Tube [15] (Figure 6).
Number of samples for each test is summarized in Table 3. Table 2 Details and Assigned Designations
Weight per m3
Designation Crumb Rubber Cement Coarse
Agg Fine Agg Water
kg kg kg kg kg
PC 0 478.7 933.5 783.8 215
10SCRC 78.4 478.7 933.5 705.5 215
20SCRC 156.8 478.7 933.5 627.1 215
30SCRC 235.2 478.7 933.5 548.7 215
Table 3 Casting Schedule
Type of Number of specimen Concrete
Thermal
Sound
Density
PC 3 8 3 10SCRC 3 8 3 20SCRC 3 8 3 30SCRC 3 8 3
Total 12 32 12
Details of each test are described briefly below: Density and Voids [13] The specimens are
weighed under 4 different conditions: oven-dried,
saturated after immersion, saturated after boiling and immersed under water. Then, the obtained weights are used to calculate the density and permeable
voids based formulas given in the standard.
Figure 5 Steady-State Heat Flux [14]
Figure 6 Acoustics Determination of Sound
Absorption Coefficient and Impedance in Impedance Tube [15]
Steady-State Heat Flux Measurement and
Thermal Transmission Properties [14] The two
concrete specimens in form of square shape (300 x 300 x 25.4 mm) are setup between the heat source (hot plate) and two cold surface assemblies. The test
begins by increasing the temperature of the hot plate and at the same time measuring the temperature
2.2 Specimen Prepartion and Testing Concrete was dry-mixed using pan mixer for
about 5 minutes, then added water and continued mixing for another 5 minutes, after that it was
poured into molds. Three tests were carried out: 1) Density, Voids and Absorption [13], 2) Steady-State Heat Flux Measurement and Thermal Transmission
Properties [14]. (Figure 5), and 3) Acoustics Determination of Sound Absorption Coefficient and Impedance in Impedance Tube [15] (Figure 6).
Number of samples for each test is summarized in Table 3. Table 2 Details and Assigned Designations
Weight per m3
Designation Crumb Rubber Cement Coarse
Agg Fine Agg Water
kg kg kg kg kg
PC 0 478.7 933.5 783.8 215
10SCRC 78.4 478.7 933.5 705.5 215
20SCRC 156.8 478.7 933.5 627.1 215
30SCRC 235.2 478.7 933.5 548.7 215
Table 3 Casting Schedule
Type of Number of specimen Concrete
Thermal
Sound
Density
PC 3 8 3 10SCRC 3 8 3 20SCRC 3 8 3 30SCRC 3 8 3
Total 12 32 12
Details of each test are described briefly below: Density and Voids [13] The specimens are
weighed under 4 different conditions: oven-dried,
saturated after immersion, saturated after boiling and immersed under water. Then, the obtained weights are used to calculate the density and permeable
voids based formulas given in the standard.
Figure 5 Steady-State Heat Flux [14]
Figure 6 Acoustics Determination of Sound
Absorption Coefficient and Impedance in Impedance Tube [15]
Steady-State Heat Flux Measurement and
Thermal Transmission Properties [14] The two
concrete specimens in form of square shape (300 x 300 x 25.4 mm) are setup between the heat source (hot plate) and two cold surface assemblies. The test
begins by increasing the temperature of the hot plate and at the same time measuring the temperature
Figure 6 Acoustics Determination of Sound
Absorption Coefficient and Impedance in
Impedance Tube [15].
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3. Results and Discussions
3.1 Density, Absorption and Voids
As shown in Table 4 and Figure 7, the crumb
rubber concrete exhibited lighter density than that of
plain concrete. The bulk density of normal concrete
was found to be about 2330 kg/m3, the average bulk
density of 10%, 20% and 30% crumb rubber concrete
were found at 2,090, 1,970 and 1,820 kg/m3,
respectively.
The decrease in bulk density of concrete was
mainly due to the replacement of a heavier material
(fine aggregate) by a lighter one (crumb rubber).
The fine aggregate (river sand) used in this study
has an average specific gravity (oven dry) of 2.42,
while the crumb rubber has an average of about
0.61. By calculation, at 10%, 20% and 30%
replacement ratio, the overall density of concrete
was expected to decrease (due to the effect of crumb
rubber alone) by 7.5%, 14% and 19.5%, respectively.
The actual results are slightly higher than the
calculation and this, perhaps, due to the effect of
moisture in fine aggregate that did not taken into
account in the calculation.
In the case of the absorption and permeable
void (Table 4, Figure 8), unlike other lightweight
aggregated concrete, the effect of crumb rubber
adding into concrete appeared to lower both
absorption and permeable void content. For
conventional lightweight concrete, these two values
would be quite high because of the high porosity in
aggregates or large amount of air bubble in cement
paste. But when using crumb rubber powder, even
though the overall density of concrete decreased
gradually with the rubber content, the permeable
void was found to decrease instead of increase.
The decrease in permeable void and absorption
was because of 2 reasons: 1) the porosity of crumb
rubber particle and 2) the filling effect. In the case of
porosity, refer to Table 1, it could be seen that the
specific gravity of superfine crumb rubber under both
SSD and oven dry conditions were quite similar (0.61
and 0.62, respectively). The similarity implied that
crumb rubber was, in fact, not a porous material.
Therefore, by adding them into concrete, there was
no additional pore adding into the concrete pore
system. As for the filling effect, the small particle of
superfine crumb rubber (SCRC) played a significant
role in this part. With small particle size as 500-600
micron, the crumb rubbers were able to fill up some
of the capillary pores which led to the decrease in
absorption from 4.26% to 2.98% as show in Figure 8.
Figure 7 Bulk Density of Concrete vs. Crumb
Rubber Concrete.
Table 4 Bulk Density, Void and Absorption
Type Bulk Density (kg/m3)
Void (%)
Absorption (%)
PC 2330 9.35 4.26
10SCRC 2090 6.79 3.51
20SCRC 1970 5.90 3.39
30SCRC 1820 5.81 2.98
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3.2 Thermal Conductivity
By definition, the quantity of heat transmitted
through a unit thickness in a direction normal to a
surface of unit area, due to a unit temperature
gradient under steady state conditions is defined as
the thermal conductivity value (k). There are several
parameters affecting the value of k in materials,
such as density, moisture content, temperature etc.
In this case, let consider only the density.
Theoretically, the value of thermal conductivity is
directly proportional to the density; this means
materials with low density will usually exhibit low
value of k.
Based on the test results as shown in Figure 9
the k value of plain concrete was found at 0.531 W/m.K,
while those of SCRC were at 0.290, 0.275, and
0.267 W/m.K for 10SCRC, 20SCRC and 30SCRC,
respectively. Comparing in percentage, they are
lower by about 44% to 49%. The lower values of k
indicated that SCRC is essentially a better insulator
than plain concrete and is partly due to the lower
density of SCRC than that of plain concrete.
According to Thailand Industrial Standard
(TIS), the allowable values of k are specified within
the range of 0.303 to 0.476 W/m.K for conventional
lightweight concrete. The k-values of SCRC obtained
from this study were found to be less than or within
the allowable range of those specified by TIS.
3.3 Heat Transfer Rate and Heat Resistivity
The rate of heat transfer per unit time (hour)
and heat resistivity can be calculated using the
following equations:
(1)
(2)
Where q is heat transferred per unit time (W/ hour ),
r is heat resistivity (m2/kW), A is heat transfer area
(m2), k is thermal conductivity (W/m.K), dT is
Temperature difference across the material (K), t is
material thickness (m).
Using the value of k from the test and
assuming that the temperature difference between
night and day is 12oC, the area is 1 x 1 m2 and the
thickness is 0.10 m, the heat transfer and resistivity
of both plain and CR concrete can be calculated as
shown in Table 5.
Figure 8 Permeable Voids and Absorption.
Figure 9 Thermal Conductivity (k).
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วารสารวิชาการพระจอมเกล้าพระนครเหนือ ปีที่ 19 ฉบับที่ 3 ก.ย. - ธ.ค. 2552 The Journal of KMUTNB., Vol. 19, No. 3, Sep. - Dec. 2009
Table 5 Rate of Heat Transfer and Heat Resistivity
Type Heat Transfer W/h
Heat Resistivity m2/kW
PC 1,514 0.19
10SCRC 827 0.34
20SCRC 784 0.36
30SCRC 761 0.37
3.4 Sound Absorption
The ability of material to absorb sound at any
particular frequency is defined in form of the sound
absorption coefficient (α). In general, for a healthy
young person, the hearing range is 15 to 18,000
hertz [24]. According to the standard test, six
different ranges of sound frequencies were used to
measure the sound absorption of both plain and
SCRC: 125, 250, 500, 1000, 2000 and 4000 Hz.
The variation of α for each material over the
wide range of frequencies can be high or low
depending on material type. On the low side, for
example, a marble tile exhibits quite consistency
values of 0.01, 0.01, 0.01, 0.01, 0.02, and 0.02 over
the six frequency ranges. On the high side such as a
plaster board (for ceiling), it has rise and fall values
from 0.15, 0.11, 0.04, 0.04, 0.07, and 0.08 [25].
Results of both plain and SCR concrete are
shown in Figure 10. It could be seen that at the low
frequency ranges of 125 and 250 Hz, both plain and
SCR concrete exhibited similar values of α. However,
at frequencies higher than 500 Hz, those of SCRC
started to separate and became higher than that of
plain concrete (Figure 11). High α indicated that
SCRC can absorb sound better at high frequency
ranges than plain concrete.
In addition, the sound absorption of material
can be illustrated using another value so called the
noise reduction coefficient (NRC). The NCR is an
average value of α at four frequencies in the middle
range, can be calculated using the following
equation:
NCR = (α250 + α500 + α1000 + α2000)/4 (3)
Results of NCR against the density are given
in Figure 11. Clearly, the noise reduction depended
mainly on the density of material. As the density
decreased, the noise reduction increased. For SCRC
which density less than plain concrete by about
20%, the noise reduction increased by about 46%.
Figure 10 Sound Absorption Coefficient. Figure 11 Noise Reduction Coefficient.
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4. Conclusions
1. Concrete mixed with crumb rubber powder
has shown improvements on both porosity and
absorption by reducing both values up to about 38%
and 30%, respectively (at 30% replacement rate).
With small particle size, the crumb rubber is able to
fill up some capillary pores and voids in concrete.
2. With smaller specific gravity than conventional
fine aggregate, the crumb rubber can reduce the density of
concrete up to about 20% at the 30% replacement rate.
3. SCRC also provides better insulating properties
in both thermal and sound as seen by the decreasing
thermal conductivity value and increasing sound
absorption coefficient as compare to those of plain
concrete.
5. Acknowledgement
The authors would like to thank the Thailand
Research Fund-Master Research Grants (TRF-MAG)
for financially support this study and also Union
Pattanakit Co., Ltd., for providing crumb rubber.
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