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AN EXPERIMENTAL STUDY ON DIFFERENT CURING METHODS OF GEOPOLYMER CONCRETE MADE WITH FLY ASH AND MANUFACTURED SAND Arumairaj P.D., 1 Abdul Aleem M.I. 2 *(Corresponding Author) 1
2
Associate Professor, Department of Civil Engineering, Governement. College of Technology, Coimbatore -641013, India.
[email protected].
*Associate Professor, Department of Civil Engineering, Sri Ramakrishna Institute of Technology, Coimbatore -641010, India.
[email protected], Ph : +91 9003589750, Fax :+914222605454.
________________________________________________________________________ ABSTRACT Geopolymer concrete is the concrete made without using any quantity of cement. Instead the waste material from the thermal power station called Fly Ash is used as the binding material. This fly ash reacts with alkaline solution like Sodium Hydroxide (NaOH) and Sodium Silicate (Na2 SiO3 ) and forms a gel which binds the fine and coarse aggregates. Similarly another artificial material called Manufactured Sand (M-Sand) is also used as the fine aggregate against the normal river sand. Concrete cubes of size 100 x 100 x 100 mm, Cylinder specimen of size 150 mm diameter and 300 mm height and Prism specimen of size 100 x100 x 400 mm were prepared and cured under various curing methods like Steam curing, Hot air curing, Ambient curing and Underground curing. The Cube compressive strength, Split Tensile Strength and Beam Flexure strength were found out at 7and 28 days. The steam curing was found to be more effective. Keywords: Geopolymer concrete, Strength parameters, Fly Ash, M-Sand, Curing Methods.
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1. INTRODUCTION As per the present world statistics, every year around 260,00,00,000 Tons of Cement is used in various construction activities. One ton of cement production approximately liberates one ton of carbon di oxide to the atmosphere which is one the major agency for atmospheric pollution. Hence it is essential to find an alternative material to the existing ordinary Portland cement concrete. Geopolymer concrete can be produced without using any quantity of cement. The name, Geopolymer cement was first coined by Davidovits [1]. It represents a broad range of materials characterized by networks of inorganic molecule. Geopolymer cement is a product resulting from fly ash with alkaline solution containing sodium hydroxide and sodium silicate. Similarly, there is a scarcity for natural sand everywhere and more over the continuous sand mining on the river beds lead to environmental problems. Therefore again it is essential to find an alternative material for the natural sand. Manufactured sand (M sand) serves this purpose. This objective of this research is to study the strength parameters of the GPCM under different curing methods, so that an effective method can be drawn. 2.
MATERIALS AND METHODS
Geopolymer concrete consists of geopolymer cement, fine aggregate and coarse aggregate. It does not require any water for matrix bonding. The polymerization process involves a substantially fast chemical reaction under alkaline condition on Si-Al minerals under elevated temperature as reported by Davidovits [2], Anuar and et al[3] and Raijiwala and Patil [4]. In this study manufactured sand (M- sand) is used as fine aggregate.
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2.1 Materials The Geopolymer concrete was prepared using the following materials : a. Fly Ash b. M- sand c. Coarse aggregates d. Sodium Hydroxide e. Sodium Silicate 2.1.1 Fly Ash: The Fly Ash of class F which has rich in Silica and Aluminium was obtained from Thermal Power Station, Mettur, Tamil Nadu, India, whose nature of appearance was observed using SEM Analysis and the image is presented in Figure-1. The constituents of fly ash were found using EDX Spectrum analysis and presented in Table- 1. 2.1.2 M- sand: There is a scarcity for natural sand everywhere and more over the continuous sand mining on the river beds leads to environmental problems. It is essential to find an alternative material. M-Sand is nothing but crushing of hard stone aggregates to the size of natural sand. The finest particles are removed by washing with water. The MSand used in this study was collected in Coimbatore, Tamil Nadu, South India. The SEM image and the constituents of M-Sand calculated from the EDX spectrum are shown in Figure-2 and Table-2. The specific gravity of M-sand was found as 2.57 by using Pychonometer and the grading was also done in the Mechanical Sieve Shaker. The fineness modulus was found as 2.26. On comparing the Specific Gravity and Particle size distribution of M- sand with natural sand, it was confirmed that the M- sand shall be used
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as an alternative material for the natural sand. The Particle size distribution of natural sand and M-sand are produced in Table 3. 2.1.3 Coarse Aggregates: Coarse aggregates are obtained by pulverising of hard rock stones. The coarse aggregates of single size of 20 mm diameter were collected in Coimbatore, Tamil Nadu, South India. 2.14 Sodium Hydroxide Solution: Analytical grade Sodium Hydroxide (NaOH) with a purity of 99% was procured from Sigma Aldrich, Bangalore. A solution of molarity 10 was prepared in distilled water and used. 2.1.5 Sodium Silicate Solution: 99% purity of Sodium Silicate (Na2 SiO 3 ) solution of grade A53containing 29.4% SiO 2 , 14.7 % Na2 O and 55.9 % of water was procured from Sigma Aldrich, Bangalore and used as such. 2.2 Experimental Methods Abdul Aleem and Arumairaj [5] had used the
mix ratios namely 1: 1.3:3.1, 1:1.4:3.2,
1:1.5:3.3 and 1:1.6:3.4.in determining the optimum mix for Geopolymer concrete using natural sand and found that 1:1.5:3.3 was the optimum mix. The same optimum mix ratio is adopted in this study. 2.2.1
Casting: Fly ash, fine aggregates (M-sand) and coarse aggregates were mixed
manually in a container in the laboratory in the dry form. Alkaline solution (NaOH and Na2 SiO 3 combined together in a ratio of 2.5) - fly ash ratio of 0.35 was added. The exact quantity of materials for 1 m3 for the chosen mix is provided in Table -4. The Geo Polymer Concrete with Manufactured sand (GPCM) thus prepared was placed in moulds in three layers and each layer was compacted by giving 25 blows with a 16mm tamping
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rod, as per the Bureau of Indian Standard guide lines. The type, size and number of test specimens are presented in Table -5. 2.2.2
Effects of Curing: An important parameter that affects the properties of
geopolymer concrete is the curing method with reference to varying curing temperature. The previous researches Siva konda etal,2011[6]; Loyd and Rangan,2009[7]; Van Chanh Bui etal,2008[8]; Hardjito etal, 2004[9] concluded that the curing temperature was a reaction accelerator in the fly ash-based geopolymers, and significantly affects the mechanical strength, with the curing time. Higher curing temperature and longer curing time were proved to result in higher compressive strength. In order to study the effect of curing on the strength parameters, the following methods are chosen. a. Steam Curing b. Hot Air Curing c. Ambient curing d. Underground curing- 0.5m, 1.0m, 1.5m and 2.0 m from the existing ground level. The underground curing was chosen to study the use of Geopolymer concrete in the under ground RC piles. 2.2.3
Steam Curing: In the Steam curing method, the geopolymer concrete test
specimens were kept in the autoclave for steam curing at 60 degree centigrade for 24 hours. The steam curing is shown in Figure-3. After the curing period, they were allowed to cool at room temperature.
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2.2.4
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Hot Air Curing: The concrete test specimens were kept in the Hot air Oven for
curing at a temperature of 60 degree centigrade for 24 hours and then they were allowed to cool at room temperature. The hot air curing setup is presented in Figure-4. 2.2.5
Ambient Curing: In the Ambient curing method, the geopolymer concrete
specimens were made to cure at the ambient temperature condition up to the test period after de-moulding. The curing arrangement is indicated in 2.2.6
Figure -5.
Underground Curing: The concrete specimens were de-moulded and cured at
underground condition at various depths such as 0.5m, 1.0m, 1.5m, and 2.0m, from the existing ground levels.
Pits were excavated to the required depths and specimens were
placed as shown in Figure -6 and then back filled with the excavated soil. The soil was classified as red sandy clay having liquid limit 35%. The moisture content was determined as 15%. Lightly deteriorate substances like iron, peat etc. were not available in the soil. The sulphates and chlorides were available only less than 0.2%. The density of soil was found as 19 kN/ m3 and the water table is much below the tested depth. This condition was maintained up to the test period by protecting the specimens. The temperature and pressure at various depths are tabulated in Table-6. 3. RESULTS AND DISCUSSIONS 3.1 Compressive Strength Test The cube specimens were tested in a compressive testing machine of having 2000kN capacity in accordance with the Bureau of Indian Standard test procedures. The results of 7 and 28 days compressive strength is presented in Figure 7 and 8 respectively. The 7 days compressive strength of hot aired curing is slightly more than the steam curing and after that the strength attaining characteristic of hot air cured sample is reduced compared
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to the steam cured samples. The underground curing revealed that the compressive strength increases with respect to depth. The higher strength with respect to the depth is obtained due to the increase in temperature and higher pressure. 3.2 Split Tensile Test The cylinder specimens were tested in a compressive testing machine having 2000kN capacity for Split Tensile Test in accordance with the Bureau of Indian Standard test procedures. The results of 7and 28 days compressive strength is presented in Figure 9 and 10. Steam cured specimens showed higher tensile strength compared to all the other types of curing. The split tensile strength also confirmed that the strength increases with respect to depth for the underground cured samples. The higher strength is achieved due to the higher earth pressure at deeper depths. 3.3 Flexure Test Flexural test is used to find out the Tensile Strength of the GPCM. The 100 x 100 x 400 mm prism specimens were tested for 7 days and 28 days in a Flexure testing machine and the results are presented in Figure 11 and 12. Flexural test results also revealed that the strength of steam cured sample is higher compared to all other types of curing. Again it is observed that the strength increases with respect to depth in the case of underground curing. 4.
CONCLUSIONS
The steam curing is the best method for GPCM. The strength parameters are more significant in the steam curing method which confirmed that GPCM can be effectively used in the prefabricated structures. The fly ash can be used in an effective manner, as no
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vacant land is required for dumping the fly ash. Since no cement is used in the GPCM, lot of energy can be saved and pollution of atmosphere can also be reduced with reduction in the production of ordinary Portland cement. Due to the high strength, environmental friendly GPCM can be used as an alternative material to the existing ordinary Portland cement concrete. 5.
REFERENCES
[1]. Davidovits J(1984),
―Pyramids of Egypt Made of Man- Made Stone, Myth or
Fact‖, Symposium on Archaeometry 1984. Smithsonian Institution, Washington. [2].
Davidovits J(1994), ―Geopolymers : Man made rock geosynthesis and the resulting development of very early high strength cement‖,International Journal of Materials Education.
[3]. Anuar K.A, Ridzuan A.R.M.and Ismail S.(2011), Geopolymer
Concrete‖,
International Journal of
―Strength Characteristic of Civil & Environmental
Engineering. [4]. Raijiwala D.B and Patil H. S. (2011) ―Geopolymer Concrete- a Concrete of next decade‖, Journal of Engineering Research and Studies. [5]. Abdul Aleem M.I. and Arumairaj P.D (2012) ―Optimum Mix for the Geopolymer Concrete‖- Indian Journal of Science and Technology. [6]. Siva Konda Reddy B., Naveen Kumar Reddy K.and Varaprasad J(2011) ―Influence of curing conditions on compressive strength of cement added low lime fly ash based geopolymer concrete‖, Journal of Engineering Research and Studies.
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[7]. Lloyd N.and Rangan B.V.(2009),
―Geopolymer Concrete—Sustainable Cementless
Concrete.‖ ACI Special Publication SP-261, 10th ACI International Conference on Recent Advances in Concrete Technology and Sustainability Issues. American Concrete Institute. [8]. Van Chanh Bui, Dang Trung and Dang Van Tuan(2008),-―Recent Research Geopolymer Concrete‖, Nguyen during the 3rd ACF Interntl.Conference. [9]. Djwantoro Hardjito, Steenie E. Wallah, Dody M.J.Sumajouw, and B.Vijaya Rangan(2004),
―On the development of fly ash–based geopolymer Concrete.‖ACI.
Material. Journal.
Figure Legend Figure 1 - Image of Fly Ash Figure 2- Image of M- Sand Figure 3- Auto clave for steam curing of GPCM Specimens Figure 4- Hot air curing of GPCM Specimens Figure 5- GPCM specimens during Ambient curing Fig ure6- GPCM specimens kept for under ground curing Figure 7- Cube Compressive strength of GPCM in 7 days Figure 8- Cube Compressive strength of GPCM in 28 days Figure 9- Split tensile strength of GPCM in 7 days Fig ure10- Split tensile strength of GPCM in 28 days Figure 11- Flexurural strength of GPCM in 7 days Figure 12- Flexurural strength of GPCM in 7 days
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TABLES
Table 1- Constituents of Fly Ash App. Element
Weight% Intensity
Weight%
Const.
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Atomic% Sigma
C
4.29
0.2747
8.34
2.52
13.15
O
82.17
0.8606
50.95
1.50
60.32
Mg
0.55
0.7768
0.37
0.09
0.29
Al
22.96
0.8770
13.98
0.46
9.81
Si
31.76
0.7869
21.54
0.67
14.53
K
1.50
0.9855
0.81
0.09
0.39
Ca
0.91
0.9496
0.51
0.08
0.24
Ti
1.90
0.8092
1.26
0.13
0.50
Fe
3.44
0.8193
2.24
0.19
0.76
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Table 2- Constituents of Manufacturing Sand App. Element
Weight% Intensity
Weight%
Atomic%
Const.
Sigma
C
0.55
0.3048
1.74
2.91
3.08
O
42.25
0.8457
48.09
1.61
63.81
Na
2.01
0.7199
2.69
0.26
2.49
Mg
1.70
0.6659
2.45
0.21
2.14
Al
6.41
0.7585
8.13
0.37
6.40
Si
14.84
0.7744
18.45
0.68
13.94
K
3.01
1.0201
2.84
0.19
1.54
Ca
3.71
0.9693
3.68
0.22
1.95
Table 3- Particle size distribution of Natural sand and M-sand
APERTURE 4.75mm 2.36mm 1.18mm 600 µ 300 µ 150 µ 75 µ
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% Finer NATURAL SAND 99.7 89.4 73.4 59.4 29.4 8.6 2.0
% Finer M SAND 99.2 84.8 71.6 65.6 40.8 11.6 3.6
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Table 4 – Quantity of Materials for 1m3 S.No. 1.
3
MATERIALS Fly ash (Class F)
Kg/ m 408.00
2.
Manufacturing sand
612.00
3. 4.
Coarse aggregate (20mm in size) Sodium silicate solution
1346.40 103.00
5.
Sodium hydroxide solution(10 Molar)
41.00
Table 5 – Type, size and number of specimens
Type
Size
Cube Cylinder Prism
100 x 100 x100 mm 150 x 300 mm 100 x100 x 400 mm
7 days 21 21 21
Number of specimens 28 days Total 21 42 21 42 21 42
Table 6- Temperature and Stress at various depths Depth (m) 0.5 1.0 1.5 2.0
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Temperature (degree Centigrade) 31 33 36 38
Total Stress (kN/m2 ) 9.5 19.0 28.5 38.0
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FIGURES
Fig 1- Image of Fly Ash
Fig 2- Image of M- Sand
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Fig 3- Auto clave for steam curing of GPCM Specimens
Fig 4- Hot air curing of GPCM Specimens
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Fig 5- GPCM specimens during Ambient curing
Fig 6- GPCM specimens kept for under ground curing
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Fig 7- Cube Compressive strength of GPCM in 7 days
Fig 8- Cube Compressive strength of GPCM in 28 days
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Fig 9- Split tensile strength of GPCM in 7 days
Fig 10- Split tensile strength of GPCM in 28 days
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Fig 11- Flexurural strength of GPCM in 7 days
Fig 12- Flexurural strength of GPCM in 28 days *****
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