chapter 4 materials investigation -...
TRANSCRIPT
42
CHAPTER 4
MATERIALS INVESTIGATION
4.1 INTRODUCTION
Samples of each and every constituent material are tested in
laboratory for their physical and chemical properties. This results of various
tests conducted are presented in this chapter.
4.2 ORDINARY PORTLAND CEMENT
Ordinary Portland cement was used to produce a control mix
concrete in this research. The total requirement was calculated and was
purchased from local dealers and stored in a dry place inside casting yard and
kept covered with tarpaulin sheets, to avoid clotting. RAMCO 43-grade
cement has been used throughout this investigation. The physical properties
of the cement obtained from the tests conducted as per relevant IS codes are
shown in Table 4.1.
Table 4.1 Physical properties of cement
Sl.
No.Physical property
Tested
value Reference Code
1. Specific gravity 3.10Le-Chatelier flask
IS : 1727-1967
2. Standard consistency 30% IS : 4031-1968 part 4
3.
Setting time
Initial
Final
57 minutes
4 hours
IS : 4031-1968 part 5
IS : 4031-1968 part 5
4. Soundness test 0.95 mm Le-Chatelier’s apparatus
5. Compressive strength (28 days) 44.37MPa -------
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The cement has magnesium oxide (MgO), sulfuric anhydride (SO3),
free lime and alkaline oxide below the permissible limit specified by AS 3972
and ASTM C150. Excessive content of those chemicals could change the
cement soundness. Magnesium oxide and sulfuric anhydride in excessive
levels contribute to a long-term expansion of cement. High alkaline oxide
content in the cement is prone to cause alkali-silica reaction with reactive
aggregates in the mixture. Chloride found in the cement is normally added to
accelerate early strength and reduce setting time. The chemical composition
of the OPC cement is presented in Table 4.2.
Table 4.2 Chemical characteristics of Ramco 43 grade Portland cement
(manufacturer’s data)
Chemical Compound Average % Permissible limits
Silica (SiO2) 20.99 ------
Alumina (Al2O3) 6.05 6%, max (ASTM C150)
Ferric oxide (Fe2O3) 6.01 6%, max (ASTM C150)
Calcium oxide (CaO) 62.74 ---------
Magnesium oxide (MgO) 1.33 5% max (BIS)
Sulphuric anhydride (SO3) 1.82 3.5% max (AS 3972)
Loss on ignition (LOI) 1.14 5%, max (BIS)
Alkalies 0.8 1.5%, max(BIS)
Chlorides 0.015 ------
Lime saturation
factor(LSF)0.88 0.66-1.02, max(BIS)
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4.3 FINE AGGREGATE
The fine aggregate used in this investigation was clean river sand
passing through 4.75 mm sieve with fineness modulus 3.0, the specific gravity
2.60 and the bulk density was 1.72 and 1000 gm of sample was taken for test.
The particle size distribution is given in Table 4.3. The tests on sand were
carried out as per IS: 2386-1963(III). The sand used belonged to Zone II. The
grading curve is given in Figure 4.1.
Table 4.3 Sieve analysis of fine aggregate
Sieve size
(mm)
Weight of
material
retained
(gm)
% Weight of
material
retained
Cumulative
% weight of
material
retained
% Weight of
material
passing
4.75 0 0 0 100
2.36 74 7.4 7.4 92.6
1.18 367 36.7 44.1 55.9
0.60 132 13.2 57.3 42.7
0.30 317 31.7 89 11
0.15 110 11 100 0
4.4 COARSE AGGREGATE
Locally available crushed blue granite metal aggregate of size 20
mm and below was used and various tests were carried out to ascertain the
physical properties of coarse aggregate which are listed in Table 4.4.
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0
20
40
60
80
100
120
0.1 1
pe
rce
nta
ge
pa
ssin
g (
%)
Sieve size(mm)
Figure 4.1 Grading curve of fine aggregate
Table 4.4 Physical properties of coarse aggregate
Sl.
No. Physical property
Tested
value Reference code
1. Specific gravity 2.75 IS: 2386-1963 part 3
2. Fineness modulus 7.12 IS: 2386-1963 part 3
3. Percentage voids 39.02% ----
4. Crushing value 27.07% IS: 2386-1963 part 4
4.5 FLY ASH
Figure 4.2 Picture of Indian fly ash used
46
Fly ash is pozzolonic and reactive mineral admixture generated by
combustion of coal in thermal power plants, and comprises of fine particles
that rise with the flue gases and assumes the prime role in the manufacture of
Geopolymer concrete which is shown in Figure 4.2 Fly ash is generally
captured by electrostatic precipitators or other particle filtration equipments
before the flue gases reach the chimneys of coal-fired power plants. For this
experimental work, fly ash obtained from the Tuticorin Thermal Power
Station, Tamilnadu, India was used. The SEM image of fly ash is given in
Figure 4.3. The specific gravity of the fly ash was determined by density
bottle method and was found to be 2.03. Fly ash produced from anthracite
coal is low calcium ASTM class F fly ash which is glassy but there are some
traces of sulfur trioxide. It is greyish white in colour which is in contrast to
the dark colour of Australian fly ashes.
Table 4.5 Chemical composition of fly ash
Type of Chemicals % by Weight** % by Weight
Silica (SiO2) 50.20 63.53
Alumina (Al2O3) 26.30 27.40
Calcium oxide (CaO) 2.27 1.26
Ferric oxide (Fe2O3) 14.40 3.67
Potassium oxide (K2O) 0.58 0.85
Magnesium oxide (MgO) 1.48 0.35
Sodium oxide (Na2O) 0.36 0.19
Phosphorus pentoxide (P2O5) 1.57 ----
Sulfuric anhydride (SO3) 0.32 0.01
Loss on ignition (LOI) 0.58 0.9
Titanium Dioxide ------ 1.84
** Australian fly ash (Typical)
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Figure 4.3 SEM image of Class F fly ash
It has a bulk density 1047 kg/m3, specific gravity 2.2 and moisture
content less than 0.3%. The chemical composition of fly ash is obtained by
XRF method of analysis and is tabulated in Table 4.5. The residue of fly ash
retained on 45µm IS sieve was reported as 7.27%. The Tuticorin fly ash could
be classified into class F or low calcium fly ash based on its chemical
composition. According to IS: 456-2000, the maximum and minimum
quantities of chemical compounds present in the fly ash were checked. The
total sum of the silica, alumina and iron oxide of class F fly ash should be
greater than 70% with sulfuric anhydride (SO3) less than 2.75% and loss on
ignition less than 12%. The available magnesium oxide was less than 5%,
silicon dioxide not less than 35% and sulphur trioxide less than 2.75%. All the
chemicals present were well within the requirements to be used.
4.6 WATER
Potable water was considered throughout this study for diluting
NaOH flakes, for manufacturing OPC concretes and for preparing aggressive
liquids. The amount of solids was below the permissible limits as specified by
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IS: 456-2000. The result of quality control tests done on water is presented in
Table 4.6.
Table 4.6 Results of water quality analysis
Serial
No. Description of test
Water
sample
Maximum
permissible limit
1. pH value 8.9 6.0-9.0
2. Hardness (ppm) 403 1000
3. Sulphate (ppm) 100 400
4. Chlorides(ppm) 137 500
4.7 ALKALINE LIQUIDS
A combination of sodium hydroxide and sodium silicate was used
in this study to prepare the alkaline solution. Both the chemicals are
commercially available in the local market.
4.7.1 Characteristics of Sodium Silicate (Na2SiO3)
Sodium silicate also known as water glass or liquid glass, available
in viscous translucent liquid form, was purchased from the local suppliers. Its
reactivity with sodium hydroxide depends upon the Na2O/SiO2 ratio which
was maintained as 2.2. The mass of soluble silicate (SiO2) and sodium oxide
(Na2O) present in sodium silicate liquid is 33% and 15% respectively. The
picture of sodium silicate is shown in figure 4.4.
4.7.2 Characteristics of Sodium Hydroxide (NaOH)
Sodium hydroxide is one of the alkalis commonly used in
producing Geopolymer concrete. It is usually prepared in concentration
ranging between 8M and 16M. In this investigation, sodium hydroxide
concentration of 8M, 12M and 14M were considered to manufacture various
49
specimens. 320 grams of sodium hydroxide in flake form was dissolved in
820 ml of potable water to make 8M solutions.
Figure 4.4 A glass of Na2SiO3 Figure 4.5 Picture of NaOH flakes
Handling the flakes with bare hands gave a sense of irritation, and it
necessitated the use of gloves. Initially, the solution was prepared and kept in
metal containers. Due to the exothermic heat developed during dissolution,
the metal containers started to melt. So, the solution was mixed and kept in
plastic containers. The picture of NaOH flakes is shown in Figure 4.5 and the
composition of sodium hydroxide flakes is presented in Table 4.7.
Table 4.7 Composition of sodium hydroxide flakes
Chemical compound Composition
Sodium hydroxide( NaOH) 99 % by weight, min.
Sodium carbonate (Na2CO3) 0.5 % by weight, max.
Sodium chlorides( NaCl) 0.1% by weight, max.
Iron (Fe2O3) 0.004% by weight, max.
Heavy metals 20 ppm, max.
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4.8 CHEMICAL ADMIXTURES
In order to improve the workability of stiff and fresh concrete to
some extent, a high-range water-reducing Ligno-sulphonated normal super
plasticizer for the manufacture of M30 grade Geopolymer concrete and a high
performance Polycarboxylic ether based super plasticizer purchased from
BASF under trade name GLENIUM B233 for the manufacture of M50
Geopolymer concrete were used. Though the addition of plasticizer does not
improve workability of Geopolymer concrete, (Chindaprasirt et al 2007,
Daniel Kong et al 2010), it is still mixed in Geopolymer concrete to match
with OPC concrete mix.
4.8.1 Polycarboxylic Ether Based Hyper Plasticiser
The hyperplasticiser is available in market under the trade name
GLENIUM B233. It was purchased from BASF, India which is a high range
water reducing Superplasticiser based on modified polycarboxylic ether
formulation. The product has been primarily developed for applications in
high performance concrete where the highest durability and performance is
required. GLENIUM B233 is free of chloride (< 0.2%) and low alkali. It is a
light brown colour liquid with relative density 1.09 and pH value greater than
6. The specific gravity of this GLENIUM B233 is 1.09 and solid contents not
less than 30% by weight. The product has complied with ASTM C494 Type F
and shall be free of lignosulphonates, naphthalene salts and melamine
formaldehyde when subjected to IR Spectra.
4.8.2 Lignosulphonated Based Superplasticiser
Refined Lignosulphonated based normal superplasticiser under
trade name Conplast 320 was purchased from ROFF chemicals private
limited, Chennai.
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4.9 STEEL REINFORCEMENT BAR
Hot-rolled, deformed, high yield strength bars were used as the
main reinforcements in both Geopolymer concrete beams and OPC concrete
beams. Steel reinforcement bars of different diameters ranging from 8-20mm
were used for this study. The yield strength of bars used was 500 MPa. Steel
reinforcement rods were purchased from the Vizag Steel Company. The bars
were tightly wrapped in tarpaulin sheets to avoid direct exposure to seasonal
changes, in order to prevent corrosion. The steel reinforcing bars were
subjected to standard tensile test in Universal Testing Machine to find out the
yield strength of bars. Three pieces of each diameter rods were chosen
randomly for this test.
4.10 MIXTURE PROPORTIONS
4.10.1 OPC Concrete Mix Design
Ordinary Portland cement (OPC) concrete was produced for certain
tests and all the OPC concretes produced were taken as reference concrete.
The mixture was designed according to IS Code method of design. The target
strength of the OPC concrete control mix was 30 MPa for normal strength
concrete and 50 MPa for high strength concrete. The same amount of
superplasticizer was added in the mixtures to match with Geopolymer
concretes. A detail of mix design calculation is presented in Appendix 1. The
mixture proportion of the control mix for normal strength concrete and the
mix proportion of the high strength concrete are presented in Table 4.8. The
nomenclature of concrete giving 30MPa compressive strength will be
henceforth addressed as M 30 and the same for concrete of strength 50MPa
will be addressed as M50 concrete in this report. The OPC control concretes
M30 grade and M50 grade were prepared using the mix ratios 1:1.84: 3.6
1and 1:0.94:3.07 with water cement ratio 0.38 and 0.34 respectively. The
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water cement ratio was effectively maintained and concrete was mixed in a
pan mixer for accurate results.
Table 4.8 Mix proportions of M30 and M50 grade concretes
Constituent Materials M30
in kg / m3
M50
in kg / m3
Coarse aggregate
in mm
20 380 --
12 502 809
6380 540
River sand 642 425
Cement 350 450
Superplasticizer
Lignosulpho-
nated based 7.5 --
Carboxylic based --- 8
Water 125 145
4.10.2 Geopolymer Concrete Mix Design
The Geopolymer concrete mixtures were originally designed
referring GCI report (Hardjito et al 2005) and assuming some parameters such
as aggregate content, alkaline/fly ash ratio and sodium silicate/sodium
hydroxide ratio. The calculation was used to obtain the quantity of fly ash,
aggregate, solid sodium hydroxide, sodium silicate, and water.
The primary difference between Geopolymer concrete and Portland
cement concrete is the binder. The silicon and aluminium oxides in the low-
calcium fly ash react with the alkaline liquids to form the Geopolymer paste
that binds the loose coarse aggregates, the fine aggregates and other unreacted
53
Table 4.9 Mix proportions of G30 and G50 grade concretes
Constituent Materials G30
in kg / m3
G50
in kg / m3
Coarse aggregate
in mm
20 388 --
12 543 841
6 363 360
River sand 554 647
Fly ash 378 408
Sodium Hydroxide 50 63
Sodium Silicate 124 138
Super
Plasticiser
Lignosulpho-
nated based 7.5 --
Carboxylic based --- 8
Water --- ---
materials together to form Geopolymer concrete (Hardjito et al 2005). The
materials for Geopolymer concrete are mixed according to the details given in
Table 4.9. Similar to Portland cement concrete, the coarse aggregates occupy
about 75 to 80% of the mass of Geopolymer concrete. This component of
Geopolymer concrete mixtures can be designed using the tools currently
available for Portland cement concrete. Reactive alumina was less in Indian
flyash which required more quantity of alkaline solution for higher
compressive strength. Mixture proportions of G30 concrete given by Hardjito
et al (2005) was adopted, and the strength ranged between 27 MPa and
38.6 MPa, and the mean strength was taken as 32.8MPa with a standard
deviation of 1.46. Mixture proportion for G50 concrete was slightly modified
54
from that of the proportion adopted by Vijaya Rangan to suit the properties of
Indian fly ash.
4.11 PRELIMINARY STUDY ON GEOPOLYMER MORTAR
The prime difference between OPC concrete and Geopolymer
concrete is the binding phase. This is the main constituent of concrete which
binds coarse aggregates together to make a strong concrete. This binder could
be prepared from silicates and hydroxides of sodium or potassium, but to
achieve the desirable strength and durability properties of concrete, it was
carefully chosen in such a way that all the combinations of sodium and
potassium salts were tried.
The mixture proportion for mortar was selected based on Table 3.4
in GC-1 report by Hardjito et al (2005). For this preliminary study, 70.6 mm
size mortar cubes of 1:1 ratio were produced. Four different types of mixtures
were tried.
The mortar cubes cast with silicates + hydroxides of sodium,
potassium silicate + sodium hydroxides, silicates + hydroxides of potassium
and sodium silicate + potassium hydroxide were designated as N1, N2, K1
and K2 respectively. Out of the four combinations, the best combination was
chosen for further study, keeping in mind not only strength but also
economical factors. The best combination was salts of sodium. Further,
Geopolymer mortar cubes of various molarity of sodium hydroxide were tried
for fixing the concentration of molarity. All the four combinations that were
tried out are tabulated in Table 4.10.
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4.12 GEOMETRY AND REINFORCEMENT CONFIGURATION
OF TEST SPECIMENS
4.12.1 Mortar Cubes
All the Geopolymer mortar cubes for this research work was
70.6mm x 70.6mm x 70.6mm in size, confirming to IS: 10080-1982. These
specimens were used to study the strength of the mortar and consequently, the
concrete. Totally 12 numbers of specimens were cast for this purpose. The
concentration of NaOH solution used for this test was 14M.
Table 4.10 Combinations of mortar
Sl.
No.
Designation
of cubes
Combination of
salts
Mortar Mix Proportion
MaterialsMass
(kg/m3
)
1. N1
Sodium hydroxide
and Sodium
Silicate
Sand
Flyash
Sodium silicate
Sodium hydroxide
Super Plasticiser
1052
774
196
78
12
2. N2
Sodium hydroxide
and Potassium
Silicate
Sand
Flyash
Potassium silicate
Sodium hydroxide
Super Plasticiser
1052
774
196
78
12
3. K1
Potassium
hydroxide and
Potassium Silicate
Sand
Flyash
Potassium silicate
Potassium
hydroxide
Super Plasticiser
1052
774
196
78
12
4 K2
Potassium
hydroxide and
Sodium Silicate
Sand
Flyash
Sodium Silicate
Potassium
hydroxide
Super Plasticiser
1052
774
196
78
12
56
4.12.2 Concrete Cubes
The size of both Geopolymer concrete cubes and OPC concrete
cubes cast in this research work was 150mm x 150mm x150mm, in
accordance with IS.10086-1982.
4.12.3 Concrete Cylinders
All the Geopolymer concrete cylinder specimens without insertion
of rod was cast in size 150mm diameter and 300mm height, in accordance
with IS : 5816-1999. These cylinders were cast for testing Split tensile
strength.
4.12.4 Geopolymer Concrete Disc
The rapid chloride penetration test (RCPT) test has been developed
as a quick test to measure the rate of transport of chloride ions in to concrete.
This test was conducted as per ASTM C 1202-94. Concrete discs of size
90mm diameter and 35mm thickness were cast for this study.
4.12.5 Plain Geopolymer Concrete Beams
Plain Geopolymer concrete beams of standard size 100 mm x 100
mm x 500 mm long conforming to IS: 516-1959 were cast for studying
flexural strength of Geopolymer concrete. Two sets of specimens were cast.
In the first set, 12 numbers of specimens were cast, at the rate of three
specimens per each grade of M30, M50, G30 and G50 concrete with 8M
concentration of NaOH solution. In the second set, another 12 numbers of
specimens were cast at the same rate for each grade of concrete but with 14M
concentration of NaOH solution. These specimens were tested in the
Universal testing machine of Capacity 100 tonnes.
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4.12.6 Reinforced Concrete Beams of Prototype Size
Three series, namely series-A, series-B and series-C were cast for
the study of flexural behaviour. Out of this, series-A and series-B were of real
sized beams with different percentage of steel reinforcement for studying
exclusively the flexural behaviour. The first series-A was designed as a
representation of GB II - 3 of Sumajaouw (2006) beams and the second
series-B was designed based on the results of GB II – 3 beams. Six specimens
were cast for each series at the rate of three specimens per M30 and G30
concretes. Totally, 12 numbers of beams were cast. But series-C beams of
model size were cast to evaluate flexural behaviour and durability
characteristics.
4.12.6.1 Series-A beams
8 mm Bars @ 100 mm c/c
3300 mm
2 X 12Y
LONGIDUDIANAL SECTION Scale = 1:50
200mm2 X 12Y
300mm
Scale = 1:50
3x20Y3x20Y
8Y @
100mm C/C
A
A
SEC - AA
Figure 4.6 Sectional views of series-A beam (typical)
Rectangular concrete beams 200mm wide, 300mm deep and
3300mm long were cast in steel moulds, three for each M50 and G50. The
details of the specimen are presented in Figure 4.6. Three numbers 20mm
diameter rods were placed as tensile reinforcement and two numbers 12mm
diameter rods were placed as hanger rods. Vertical two-legged 12mm
100 mm c/c
8 Y
LONGITUDINAL SECTION
58
diameter rods were used as stirrups to act as shear reinforcement. Shear
reinforcement was provided at 150mm centers throughout the span. All the
rods were of Fe500 grade. A clear cover of 25mm was provided all around the
cross section.
4.12.6.2 Series-B beams
Rectangular concrete beams 150mm wide, 200mm deep and
2000mm long were cast in steel moulds, three for each M30 and G30. The
details of the specimen are presented in Figure 4.7. Two numbers
12mm diameter rods and 1 number 10mm diameter rod were placed as
tensile reinforcement and two numbers 10mm diameter rods were placed
as
2 X 10Y
2 X 12Y +
8Y @
150mm
200mm
400 mm
LONGITUDINAL SECTION Scale = 1:50
2 X 10Y
8 mm Bars @ 75 mm c/c
8 mm Bars @ 100 mm c/c
Scale = 1:50
1200mm
2x12Y +1x10Y A
A
SEC - AA
100 mm C/C
1X 10 Y
Figure 4.7 Sectional views of series-B beam (typical)
hanger rods. Vertical two- legged 8mm diameter rods were used as stirrups to
act as shear reinforcement. Shear reinforcement was provided at 75mm
centers in the shear span of 400mm on either end and at 100mm centers at the
100 mm c/c
8 Y
8 Y
59
flexure span of the beam. All the rods used were of Fe500 grade. The clear
cover to main reinforcement was 25 mm all around.
4.12.6.3 Series-C beams
The series-C concrete beams 100mm x 100mm in cross-section and
500mm long were cast in steel moulds, three for each M30 and G30. The
details of the specimen are presented in Figure 4.8. Two numbers 8mm
diameter rods for tensile reinforcement, 2 numbers 6mm diameter hanger rods
with 6mm diameter two legged stirrups at 50mm centers were fabricated. The
grade of rods for tensile reinforcement was Fe500 and for others were Fe250.
The clear cover of the main reinforcement was 10mm all around the cross
section. These beams were cast in order to evaluate the residual flexural
strength after immersion in sulfuric acid of 10% concentration, 5% sulfuric
acid + 5% hydrochloric acid, 10% magnesium sulphate and 10% sodium
sulphates solution. The molarity of sodium hydroxide was fixed as 8M. For
each type of test, 12 numbers of specimens were cast, making 51 numbers in
total, including 3 control specimens which were not exposed to aggressive
solution.
500 mm
6 mm Bars @ 50 mm c/c
2 Nos.6 mm Bars
2 Nos.8 mm Bars
LONGITUDINAL SECTION Scale = 1:50
100mm
100mm
2 X 6R Hanger Bars
2 X 8Y Main Bars
6R @ 50 mm C/C
SEC - AAA
A
Scale = 1:50
Figure 4.8 Sectional views of series-C beam (typical)
50 mm c/c
8 Y
8 Y
6 R
60
4.13 MANUFACTURING PROCESS OF PLAIN GEOPOLYMER
CONCRETE SPECIMENS
The manufacturing process, which is the most important stage in
this research work needs careful attention. Skilled workmanship is essential in
this stage to bring the novel material to light. Unlike other concretes, this
aluminosilicate concrete is manufactured in a different way. The strength and
durability of the final structure depend on fresh and hardened concrete. This
vital part of the research work makes the fresh concrete workable and the
hardened concrete stable.
This process consists of four stages and they are; preparation of
Alkaline solution
Mixing in a pan mixer
Compaction in a Table Vibrator
Curing at an elevated temperature
4.13.1 Preparation of Alkaline Solution
Chemicals such as sodium hydroxide flakes and sodium silicate
were carefully weighed according to the requirements and then placed in
clean and dry plastic containers. The required quantity of potable water was
poured into the weighed sodium hydroxide solid flakes to make it dissolve in
water, in order to prepare the sodium hydroxide solution. The plastic container
was closed with the lid immediately to avoid the irritation caused by inhaling
hot fumes of gases liberated. The mass of NaOH solid varies according to the
molarity of concentration required. The weight of NaOH solids was 310
grams per kg of solution for 8M, 385 grams per kg of solution for 12M and
400 grams per kg of solution for 14M. The sodium silicate was poured into
the prepared sodium hydroxide solution and thus alkaline solution was
61
prepared which appeared like crystal clear water Figure 4.9 and Figure 4.10
show the sodium silicate and sodium hydroxide solutions.
Figure 4.9 Sodium silicate solution Figure 4.10 Sodium hydroxide solution
In this research, a parametric study was done on the duration of
alkaline solution kept before mixing with other ingredients to ascertain the
strength of Geopolymer concrete. The alkaline solution prepared and kept for
24 hours before manufacturing concrete resulted in slow polymerization and
consequently gave lesser compressive strength than those of the concrete
manufactured by preparing alkaline solution just before mixing it with
concrete in pan mixer. 14M NaOH, being high concentration, needs to be
handled cautiously. Safety precautions like wearing gloves and masks were
taken. Sodium silicate and sodium hydroxide solution were mixed together 24
hours prior to use when 14M NaOH solution was used in this research work.
Both solutions were stirred continuously for few seconds by a plastic pipe to
get uniform mix to avoid heterogeneity in the mix.
4.13.2 Manufacture of Fresh Concrete
The Geopolymer concrete was produced by mixing the
Geopolymer mortar with coarse aggregates. Coarse and fine aggregates were
in oven dried condition under direct sun heat. To make better binding, all the
surfaces were made wet uniformly, to make fly ash-based Geopolymer
62
concrete. The saturated surface dried fine aggregate looked damp and
appeared to be free flowing. For mixing, a rotating pan mixer of 150 kg
capacity with two rotating wheels, as shown in Figure 4.11, was used.
Because of the adequate capacity of the pan mixer, two batches of concrete
were prepared to cast three beam specimens. The fly ash and sand were first
mixed in the laboratory pan mixer for about three minutes. At the end, the
alkaline liquid was added to this mixture and the mixing continued for another
four minutes to initiate polymerization. After all the ingredients were mixed
up thoroughly, the resultant was Geopolymer mortar. To this mortar, coarse
Figure 4.11 Details of pan mixer and mixing process
63
aggregates of suitable gradation in saturated surface dry condition were added
and the mixer was allowed to get mixed for another 4 minutes. The resulting
cohesive mixer, though appears to be dry, has a shiny, glassy and grey colour
in appearance was very much workable in table vibrator which is shown in
Figure 4.12.
Thus the heroic fresh Geopolymer concrete, ready to be moulded,
was manufactured. Slump test was done to measure the workability of every
batch of Geopolymer concrete and is shown in Figure 4.13.
Figure 4.12 Shiny fresh Geopolymer concrete
64
Figure 4.13 Slump cone test
Water was sprinkled over the steel plate prior to unloading the
mixture from pan mixer to avoid absorption of water from the mix. The fresh
concrete mix was placed in three layers in Abram’s cone and 25 strokes were
applied by a steel tamping rod to each layer. When the cone was filled with
the compacted fresh mix, it was lifted and the slump value was measured.
4.13.3 Table Compaction
As strength and density are closely related to the degree of
compactness, a table vibrator was used instead of a needle vibrator for better
compaction. The sides and bottom of steel moulds were coated with crude oil
to prevent the mix sticking to the mould and for easy demoulding. The
moulds were filled with fresh concrete to one-third height and kept over the
table vibrator. The vibration was done for 12-15 seconds until the concrete
was leveled. Again concrete was put into the mould, layer by layer, up to the
top of mould and got vibrated for a few seconds. For better and uniform
65
compaction, each layer was vibrated for 12 to 15 seconds and the specimens
being vibrated is shown in Figure 4.14.
Figure 4.14 Specimens under table vibration
4.13.4 Dry Heat Curing
Compaction and good curing are normally suggested to produce
low porous concrete, which in turn, is impermeable to aggressive exposure.
Heat curing was adopted for this study, since this curing substantially assisted
the chemical reaction that occurred in the Geopolymer concrete. It was done
by two methods, namely, steam curing and dry curing. Most of the literature
showed that all the reinforced Geopolymer structural elements were cured by
steam curing and all non-structural elements were either dry cured in
laboratory ovens or steam cured. Reviewing the test data, it is interesting to
note that the compressive strength of dry-cured Geopolymer concrete was
approximately 15% greater than that of steam-cured Geopolymer concrete
(Hardito et al 2005). The curing method adopted for this study was dry-heat
curing. Rectangular steel chamber with thermostats was exclusively designed
for this research work by the author and had been installed. It was designed
by the author in such a way that the temperature inside the chamber could be
adjusted between 600C and 90
0C. Also the length and depth of the chamber
66
Figure 4.15 Heat curing chamber
Figure 4.16 Geopolymer concrete cubes to be demoulded
67
could be altered to suit the profile of the elements. The cast specimens are
kept inside this chamber at 70oC for duration of 8 hours to 24 hours. Dry
cured specimens were left in the moulds for at least six hours in order to avoid
a drastic change in the environmental conditions. After demoulding, the
specimens were air dried in the room until the day of the test. The heat curing
chamber in operation mode is exhibited in Figure 4.15 and the Geopolymer
concrete cubes kept inside the curing chamber is shown in Figure 4.16.
4.14 MANUFACTURING PROCESS OF SERIES-A
GEOPOLYMER CONCRETE BEAMS
Figure 4.17 Needle vibration Figure 4.18 Geopolymer concrete
for series-A specimens beams in heat curing
chamber
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The manufacturing process of the series-A beams was slightly
modified from the other specimen’s manufacturing process. In this series,
similar to the work done in GC3 thesis report by Sumajouw et al (2006), the
beams were compacted by a needle vibrator instead of a table vibrator. The
casting of beam with needle vibration is shown in Figure 4.17. The series-A
beams were kept inside the heat curing chamber, which is shown in
Figure 4.18, for curing.
4.15 MANUFACTURING PROCESS OF SERIES B AND
SERIES C BEAMS
The manufacturing process of these two beams namely, series-B
and series-C, was the same as that of the other manufacturing process
mentioned in clause 4.12. In these two series, the beams were compacted by a
table vibrator instead of a needle vibrator. The reinforcement cage was placed
inside the steel moulds, and all the sides and bottom were applied with oil
before the concreting was done. To maintain the cover on the reinforcements,
cement briquettes were placed below the reinforcement cage prior to
concreting. Extra care was taken to avoid the displacement of the cage while
concreting, thus maintaining the cover.
4.16 MANUFACTURING PROCESS OF REINFORCED OPC
CONCRETE ELEMENTS
Ordinary Portland cement (OPC) concrete was manufactured
according to the standard procedure. The weighed quantity of fine aggregate
was made wet to boost up the bond with other ingredients. The required
quantity of cement without lumps was put along with wet fine aggregate into
the pan mixer and initially mixed for about two minutes. The measured
amount of potable water was poured slowly into the dry mixture until it was
mixed uniformly and the mixing continued for another two minutes. At this
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stage, coarse aggregate was added to the mortar and the uniformity of the
mixing of concrete was checked. The measured quantity of superplasticiser
was added to get workability. The workability was measured by a slump test
on the fresh OPC concrete. The fresh mix was poured into the moulds that
had been coated with crude oil. Compaction was done with the aid of a table
vibrator and the specimens were manufactured. The specimens were left in
the mould overnight before demoulding. Demoulding of the OPC concrete
specimens was done on the following day. The cube and cylinder specimens
were kept in the water pond for curing. Because of the space constraint of the
water pond, large sized beam specimens were cured by covering with jute
gunny bags and cured by spraying water. This is shown in Figure 4.19. The
dampness of the jute bags was ensured throughout the 28 days curing period.
On the 28th
day, the elements were removed from the water pond and placed
in an open area to get air cured until the day of the test.
Figure 4.19 Curing of OPC concrete beams
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4.17 FINISHED GEOPOLYMER PRODUCTS READY FOR
TESTING
From Figure 4.20 to Figure 4.24 display the manufactured
specimens ready for testing.
Figure 4.20 Geopolymer concrete cubes (G50)
Figure 4.21 Geopolymer concrete cubes (G30)
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Figure 4.22 Geopolymer concrete discs
Figure 4.23 Series-C Geopolymer concrete beams
Figure 4.24 G30 and G50 Geopolymer concrete series–A beams