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Nanoparticles for enhancing mechanical properties of fly ash concrete
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ScienceDirect Materials Today: Proceedings 3 (2016) 2387–2393
www.materialstoday.com/proceedings
Recent Advances In Nano Science And Technology 2015 (RAINSAT2015)
Nanoparticles for enhancing mechanical properties of fly ash concrete Kalpana Kumaria,*, R.Preethaa, D. Ramachandranb, Vinita Vishwakarmab, Rani.P.Georgec, C.Sundaramurthya, U.Kamachi Mudalic, C.Sivathanu Pillaia a
Civil Engineering Group, IGCAR, Kalpakkam-603102 Centre for Nanoscience and Nanotechnology, Sathyabama University, Chennai-600119 c Corrosion Science and Technology Group, IGCAR, Kalpakkam-603102
b
Abstract Fly ash is used in concrete industry to reduce the amount of cement and to enhance durability of concrete. Some early-age performance issues of fly ash concrete are, delayed setting time, low early-age strength, and a more stringent curing conditions. To overcome this deficiency, nano modifications are adopted. This study is attempted to understand the effect of nano TiO2 (NT), nano CaCO3 (NC) particles and a combination of NT and NC particles (NTC) on various properties like compressive strength, workability and durability of fly ash concrete by partial replacement of cement. NT and NC particles with average diameter of 50-70 nm were used with six different contents ranging from 0.5 to 3% by weight of cement, with an increment of 0.5%. The results showed that addition of NT particles up to a maximum replacement level of 3.0% produced concrete with improved strength, whereas addition of NC and NTC particles in the mix showed higher strength up to 2% and thereafter it decreased. Workability of fresh concrete increased at 0.5% addition of all the three nano particles and thereafter, though it decreased for given water to powder content, the mixes were workable. This was confirmed with consistency tests. The fresh and hardened properties along with low rapid chloride penetration values and high pH values highlight the advantages of nano modification of flyash concrete. © 2015Elsevier Ltd.All rights reserved. Selection and Peer-review under responsibility of [Conference Committee Members of Recent Advances In Nano Science and Technology 2015.]. Keywords: Fly ash;compressive strength;workability;TiO2;CaCO3.
* Corresponding author. E-mail address: [email protected], [email protected]
2214-7853© 2015 Elsevier Ltd.All rights reserved. Selection and Peer-review under responsibility of [Conference Committee Members of Recent Advances In Nano Science and Technology 2015. ].
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1. Introduction The utilization of fly ash in concrete as a raw material for cement production, for use in blended cements and as a partial replacement of cement in concrete is well established. The mechanical and durability properties of fly ash concrete have been well researched and documented but a few properties like slow set and low early strength has caused a reduced percentage of this material in concrete. Recently, new developments on incorporation of nanoparticles in concrete in order to improve the physical and mechanical properties have been researched and most of them have focused on using SiO2 nanoparticles [1- 4], TiO2 nanoparticles [5], nano-Fe2O3 [6], nano-Al2O3 [7, 8], and nano CaCO3 particles [9, 10]. It has been shown that utilizing nanoparticles in concrete improves the mechanical properties of concrete and also shows improvement in its microstructure and pore structure. It is suggested that nanoparticles can act as heterogeneous nuclei for cement pastes, further accelerating cement hydration because of their high reactivity, as nano-filler, densifying the microstructure, thereby, leading to a reduced porosity[11]. Because of ultrafine size, nanoparticles show unique physical and chemical properties different from those of the conventional materials. As a result of their unique properties, nanoparticles have gained good attention and been applied in many fields . The combination between fly ash and nano materials can tightly bond the hydration product which is regarded as an important factor for accelerating the pozzolanic reaction as it compensates for the increased early strength development [12-15]. Some studies have suggested a potential benefit of incorporation of nano-CaCO3 in high volume of supplementary cementitious materials [15]. Most of the investigations evaluated the effects of specific percentages of nanoparticles on the hydration, setting, microstructure, compressive strength of concrete but there has been limited progress on the effect of addition of nano TiO2and CaCO3 individually and in combination in fly ash concrete in terms of early and long-term strength and durability properties. Therefore, the objective of the present work is to evaluate the optimum replacement level of these nanoparticles and also to study the effectiveness of these nanoparticles not only on strength development but also its influence on the durability properties through rapid chloride penetrability and pH. 2. Experimental 2.1 Materials Ordinary Portland cement (43 grade) conforming to IS 8112 [16] was used in this study. Fly ash (FA) used was Siliceous type conforming to IS 3812 [17] and was used as a partial (40%) cement replacement material. Crushed sand (CS) with a maximum size of 4.75 mm was used as a partial (30%) replacement material for fine aggregate (river sand, RS). The Coarse aggregate (CA) used in the mix was black Granite with maximum size 20 mm and 12.5mm. All the aggregates complied with the requirements of IS 383[18]. Chemical admixture (A) used, was of high range water reducer type, having Sulphonated Naphthalene Formaldehyde as base. NT particles with average size 50-60nm and NC particles with average size of 50-70nm was used. NT and NC particles had a specific gravity of 3.76 and 2.69 respectively. 2.2 Mix proportioning Six series of concrete mixes of grade M35 were prepared in the laboratory by replacing cement with NT, NC and NTC particles. The various percentage of nanoparticles replaced by weight of cement were 0.5%, 1.0%, 1.5%, 2.0%, 2.5% and 3% . F0 concrete mix was referred as control mix consisting of cement, flyash, natural aggregate, crushed sand, super plasticizer and water. The concrete containing NT, NC and NTC particles were labelled under the mix series T1 to T6 (T-series), C1 to C6 (C-series), and TC1 to TC6 (TC-series) respectively. The total powder content (cement + flyash + nanoparticles) for all mixes was 375 kg/m3.Water to powder ratio was 0.44, fly ash content was 150 kg/m3, river sand 549 kg/m3, crushed sand 235 kg/ m3, aggregate 1130 kg/ m3 and chemical admixture was 4.5 kg/ m3. The proportions of the mixtures are presented in Table 1.
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Table 1: Mix proportion of concrete
Sample designation
Nanoparticles (%)by wt. of cement
Quantities (kg/m3) Cement
TiO2
CaCO3
TiO2 + CaCO3
T- Series
C - Series
TC - Series
F0
0
225
0
0
0
T1,C1,TC1
0.5
223.875
1.125
1.125
1.125 (0.5625+0.5625)
T2,C2,TC2
1
222.75
2.25
2.25
2.25 (1.125+1.125)
T3,C3,TC3
1.5
221.625
3.375
3.375
3.375 (1.6875+1.6875)
T4,C4,TC4
2
220.5
4.5
4.5
4.5 (2.25 + 2.25)
T5,C5,TC5
2.5
219.375
5.625
5.625
5.625 ( 2.8125+2.8125)
T6,C6,TC6
3
218.25
6.75
6.75
6.75 (3.375 +3.375)
2.3 Preparation of Test Specimens The concrete was prepared in a laboratory concrete drum mixer. Cement, fly ash and aggregates were mixed in dry condition for one minute and then for another two minutes after adding water and chemical admixture. The nano particles were mixed with part of mix water using a handheld mixer for one minute to disperse the agglomerates. This prepared solution was poured in the drum mixer and mixed for two minutes along with the other ingredients. Slumps of the fresh concrete were determined immediately to evaluate the workability [19]. Cubes of 150 mm size and cylinders of height 200mm and diameter 100mm were cast as per the procedure laid in IS 516 [20] and thereafter cured for 28 days in a laboratory curing tank filled with water at a temperature of 28±1o C. To determine the consistency [24], cement pastes with 0% to 3% nanoparticles as mentioned above were made. 2.4 Testing methodology Compression tests of 150 mm cube concrete specimens were carried out according to IS 516[20] at the age of 7 and 28 days of sample. The split tensile strength test was carried out on the cylindrical specimens as per IS 5816 [21] at 28 days. Three specimens were tested in each condition for all the mixes. Crushed specimens were utilized further for determining the pH value. 10grams of the crushed sample was diluted in 100ml distilled water, stirred for ten minutes and thereafter the solution was tested for pH using a pH meter. The Rapid Chloride Penetrability Test was conducted as per the procedure laid in ASTM C1202 [22] by slicing the cylindrical specimen in the required size. Microanalysis was carried out for the 2% substitution from all the mixes. Small pieces from fractured surface of tested specimens were used for the investigation. The examination was carried out using a scanning electron microscope (SEM). 3. Results and Discussions All the results obtained from the experimental investigations are shown in Table 2. All the values are the average of three specimens in each condition. The results are discussed as follows in Table 2. 3.1 Compressive and tensile strength Comparing the 7 days compressive strength results for all the mixes it is noticed that 0.5% replacement showed a higher value than the 1 %, in all the mixes. The T- series mix showed a gradual increase in strength from 1 to 3% substitution. In C and TC- series mix, increase in strength was seen from 1 to 2% substitution and thereafter the
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strength started decreasing. It is predicted that, in the case of concrete with NT particles an improved filler effect would have been the reason for the increase in strength with the increase in nanoparticles. In NC particles a higher strength was observed at lower percentage of nanoparticles. For the T series mix the 28 days compressive strength showed a gradual increase till 3.0 % and decreased at 2.5 % and thereafter increased and the same was reflected in the split tensile strength value. In the C and TC series mix the 28 days compressive strength started decreasing with increase in the percentage of nano CaCO3 till 1.5 % but showed an increased strength at 2% and thereafter decreased slowly. The split tensile values were found to follow similar pattern in all the mixes. The ratio of split tensile strength to compressive strength was in the range of 0.08 to 0.09 as expected [23].With respect to mix of fly ash concrete , C&TC mixes showed higher early strength (ie.7 days) especially at 2% replacement, whereas T mix showed higher early strength at replacement of 0.5%, 2.5% and 3%. Table 2: Strength, pH and RCPT values for different mixes TiO2 & CaCO3 Nanoparticles (%)
Compressive Strength (N/mm2) 7 days
28 days
F0
Control
23.17
49.13
3.83
10.44
243
T1
0.5
27.00
45.70
2.85
10.58
172.8
T2
1
20.65
48.76
2.95
11.02
233.1
T3
1.5
21.39
49.47
3.57
11.22
216
T4
2
22.36
49.93
3.35
11.35
129.6
T5
2.5
27.06
47.55
3.58
11.18
179.1
T6
3
27.58
50.97
3.61
9.85
181.8
C1
0.5
27.05
49.74
3.69
9.05
191
C2
1
24.79
47.64
3.38
11.03
207.9
C3
1.5
26.35
44.95
3.86
11.89
224.1
C4
2
26.09
48.71
3.52
12.45
189
C5
2.5
24.07
43.74
3.16
9.65
195.7
C6
3
21.11
42.79
3.57
9.53
196.2
TC1
0.5
30.20
54.49
3.43
9.28
169.2
TC2
1
21.94
40.53
3.39
9.95
303.2
TC3
1.5
24.48
38.02
3.39
10.08
255.6
TC4
2
38.38
58.14
3.64
11.25
149.4
TC5
2.5
34.72
54.03
3.89
11.02
144
TC6
3
25.64
40.29
3.55
10.34
181.8
Mix series
Split tensile str. (N/mm2) 28 days
Crushed pH 28 days
RCPT value (Coulombs) 28 days
3.2 Rapid Chloride Penetrability Test (RCPT) and pH Values The RCPT values were in the range of 100 – 500 coulombs for all the mixes, which indicated very low chloride ion penetrability [21] .The lowest value among all the mixes was observed at 2% substitution. There was an increase in pH value of concrete as the percentage substitution of nanoparticles increased up to 2%, and thereafter the value gradually decreased. 3.3 Workability and Consistency values The workability (slump values) of all the concrete mix series are presented in Figure 1.
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Fig.1. Slump value variation
The figure shows the influence of nanoparticle content on the workability of mixtures at constant water to binder ratio of 0.44. The water content and admixture dosage were kept constant in order to understand the fluidity and water demand of the mix. The results show that all the mixes blended with nanoparticles showed a decline in slump value as the percentage of nanoparticles increased in the mix. The decrease in the slump was most evident in C series mix. As the percentage of addition of NC particles increased, there was a decrease in the fluidity and increase in water demand in the mix. This was confirmed in the consistency tests [24] which showed an increase in percentage of water required to meet the consistency limits [Figure2].
Fig. 2. Consistency value variation
3.4 Scanning electron microscopy results As the strength, pH and RCPT results were encouraging for the specimens with 2% modification; these fractured specimens were subjected to microanalysis using SEM (Fig.3). While comparing the images of T4, C4 and TC4 with F0, it appears that a homogenous dense microstructure is attained in the given order of mixes. This justifies the mechanical as well as penetrability properties for the above mixes as given in Table 2. Dense appearance of hydrated products in C4 justifies the high pH .This will be further verified using EDAX and XRD analysis.
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F0
C4
T4
TC4
Fig. 3. SEM images
4. Conclusion •
• • •
The addition of nanoparticles of TiO2, CaCO3 and their combination greatly enhanced the early and higher age strength of fly ash concrete. It was observed that a 0.5 % substitution of nanoparticles gave an appreciably higher strength and also an increase in percentage of NT particles showed an increase in strength (with maximum at 3%). The NTC particles showed a maximum strength at 2% substitution. The 2% substitution of NT and NC particles yielded slightly lower strength when compared to the maximum strength attained but the RCPT values were very low at this percentage indicating a good impermeable concrete. Though the workability of fresh concrete showed a decline in slump value as the percentage of nanoparticles increased, these slump values as such gave a workable concrete. When seen from durability point of view a 2 % substitution of nanoparticles showed a very good resistance to chloride ion penetration and also a high pH value. Comparing all the results it was found that 2% is the optimum level of nanoparticle substitution which could yield a durable and strong concrete. This was further verified using SEM.
Acknowledgements The paper is the outcome of the projects done with BRNS. Authors are grateful to the management of BRNS for financing the project. The authors also wish to thank, Director, Indira Gandhi Centre for Atomic Research, without whose support, this work would not have been possible.
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References [1] Ji T. Preliminary study on the water permeability and microstructure of concrete incorporating nano-SiO2.Cement and Concrete Research. 2005 [2] Jo B-W, Kim C-H, Tae G-h, Park J-B. Characteristics of cement mortar with nano-SiO2 particles. Construction and Building Materials. 2007 [3] Qing Y, Zenan Z, Deyu K and Rongshen C. Influence of nano-SiO2 addition on properties of hardened cement paste as compared with silica fume. Construction and Building Materials. 2007 [4] Lin DF, Lin KL, Chang WC, Luo HL and Cai MQ. Improvements of nano-SiO2 on sludge/fly ash mortar. Waste Management. 2008 [5] Ali Nazari, Shadi Riahi, Shirin Riahi, Seyedeh Fatemeh Shamekhi and A. Khademno. Assessment of the effects of the cement paste composite in presence TiO2 nanoparticles .Journal of American Science 2010 [6] Ali Nazari*, Shadi Riahi, Shirin Riahi, Seyedeh Fatemeh Shamekhi and A. Khademno. Benefits of Fe2O3 nanoparticles in concrete mixing matrix Journal of American Science 2010 [7] Z. Li, H. Wang, S. He, Y.Lu, M. Wang. Investigations on the preparation and mechanical properties of the nano-alumina reinforced cement composite. Materials Letters, 60 (3) (2006), pp. 356–359 [8] Ali Nazari, Shadi Riahi. Al2O3 nanoparticles in concrete and different curing media. Energy and Buildings 43 (2011) 1480–1488 [9] Sato T, Beaudoin JJ. Effect of nano-CaCO3 on hydration of cement containing supplementary cementitious materials. Adv Cement Res 2011. [10] Faiz U.A. Shaikh , Steve W.M. Supit. Mechanical and durability properties of high volume fly ash (HVFA) concrete containing calcium carbonate (CaCO3) nanoparticles. Construction and Building Materials 70 (2014) [11] Sanchez F, Sobolev K. Nanotechnology in concrete – a review. Constr Build Mater 2010; 24:2060–71. [12] Li G. Properties of high volume fly ash concrete incorporating nano-silica. Cem Concr Res 2004 [13] Shaikh FUA, Supit S. A study on the effect of nano silica on compressive strength of high volume fly ash mortar and concrete. Material and Design 2014 [14] Supit S, Shaikh FUA, Sarker PK. Effect of nano silica and ultrafine fly ash on compressive strength of high volume fly ash mortar. Appl Mech Mater 2013; 368–370 [15] Supit S, Shaikh FUA. Durability properties of high volume fly ash concrete containing nano silica. Mater Struct 2014 [16] IS 8112- 2013- Ordinary Portland Cement, 43 grade - Specification [17] IS 3812 - 2003 - Pulverized Fuel Ash - Specification (Part 2) - For use as admixture in Cement Mortar and Concrete [18] IS 383 -1970 (Reaffirmed 2002) - specification for coarse and fine aggregates from natural sources for concrete [19] IS 1199-1959- Indian Standard Methods of Sampling and Analysis of Concrete. [20] IS 516- 1959 (Reaffirmed 2004) - Methods of Tests for Strength of Concrete [21] IS 5816:1999(Reaffirmed 2004) - Splitting Tensile Strength of Concrete – Method of Test [22] ASTM C1202-10 – Standard test method for Electrical Indication of Concrete’s Ability to Resist Chloride Ion Penetration [23] P.Kumar Mehta, Paulo J.M.Monteiro, Concrete, Mc Graw Hill, 2006. [24]IS 4031-1988 (Reaffirmed 2005) - Methods of physical tests for hydraulic cement, Part 4: Determination of consistency of standard cement paste.
ScienceDirect Materials Today: Proceedings 3 (2016) 2387–2393
www.materialstoday.com/proceedings
Recent Advances In Nano Science And Technology 2015 (RAINSAT2015)
Nanoparticles for enhancing mechanical properties of fly ash concrete Kalpana Kumaria,*, R.Preethaa, D. Ramachandranb, Vinita Vishwakarmab, Rani.P.Georgec, C.Sundaramurthya, U.Kamachi Mudalic, C.Sivathanu Pillaia a
Civil Engineering Group, IGCAR, Kalpakkam-603102 Centre for Nanoscience and Nanotechnology, Sathyabama University, Chennai-600119 c Corrosion Science and Technology Group, IGCAR, Kalpakkam-603102
b
Abstract Fly ash is used in concrete industry to reduce the amount of cement and to enhance durability of concrete. Some early-age performance issues of fly ash concrete are, delayed setting time, low early-age strength, and a more stringent curing conditions. To overcome this deficiency, nano modifications are adopted. This study is attempted to understand the effect of nano TiO2 (NT), nano CaCO3 (NC) particles and a combination of NT and NC particles (NTC) on various properties like compressive strength, workability and durability of fly ash concrete by partial replacement of cement. NT and NC particles with average diameter of 50-70 nm were used with six different contents ranging from 0.5 to 3% by weight of cement, with an increment of 0.5%. The results showed that addition of NT particles up to a maximum replacement level of 3.0% produced concrete with improved strength, whereas addition of NC and NTC particles in the mix showed higher strength up to 2% and thereafter it decreased. Workability of fresh concrete increased at 0.5% addition of all the three nano particles and thereafter, though it decreased for given water to powder content, the mixes were workable. This was confirmed with consistency tests. The fresh and hardened properties along with low rapid chloride penetration values and high pH values highlight the advantages of nano modification of flyash concrete. © 2015Elsevier Ltd.All rights reserved. Selection and Peer-review under responsibility of [Conference Committee Members of Recent Advances In Nano Science and Technology 2015.]. Keywords: Fly ash;compressive strength;workability;TiO2;CaCO3.
* Corresponding author. E-mail address: [email protected], [email protected]
2214-7853© 2015 Elsevier Ltd.All rights reserved. Selection and Peer-review under responsibility of [Conference Committee Members of Recent Advances In Nano Science and Technology 2015. ].
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1. Introduction The utilization of fly ash in concrete as a raw material for cement production, for use in blended cements and as a partial replacement of cement in concrete is well established. The mechanical and durability properties of fly ash concrete have been well researched and documented but a few properties like slow set and low early strength has caused a reduced percentage of this material in concrete. Recently, new developments on incorporation of nanoparticles in concrete in order to improve the physical and mechanical properties have been researched and most of them have focused on using SiO2 nanoparticles [1- 4], TiO2 nanoparticles [5], nano-Fe2O3 [6], nano-Al2O3 [7, 8], and nano CaCO3 particles [9, 10]. It has been shown that utilizing nanoparticles in concrete improves the mechanical properties of concrete and also shows improvement in its microstructure and pore structure. It is suggested that nanoparticles can act as heterogeneous nuclei for cement pastes, further accelerating cement hydration because of their high reactivity, as nano-filler, densifying the microstructure, thereby, leading to a reduced porosity[11]. Because of ultrafine size, nanoparticles show unique physical and chemical properties different from those of the conventional materials. As a result of their unique properties, nanoparticles have gained good attention and been applied in many fields . The combination between fly ash and nano materials can tightly bond the hydration product which is regarded as an important factor for accelerating the pozzolanic reaction as it compensates for the increased early strength development [12-15]. Some studies have suggested a potential benefit of incorporation of nano-CaCO3 in high volume of supplementary cementitious materials [15]. Most of the investigations evaluated the effects of specific percentages of nanoparticles on the hydration, setting, microstructure, compressive strength of concrete but there has been limited progress on the effect of addition of nano TiO2and CaCO3 individually and in combination in fly ash concrete in terms of early and long-term strength and durability properties. Therefore, the objective of the present work is to evaluate the optimum replacement level of these nanoparticles and also to study the effectiveness of these nanoparticles not only on strength development but also its influence on the durability properties through rapid chloride penetrability and pH. 2. Experimental 2.1 Materials Ordinary Portland cement (43 grade) conforming to IS 8112 [16] was used in this study. Fly ash (FA) used was Siliceous type conforming to IS 3812 [17] and was used as a partial (40%) cement replacement material. Crushed sand (CS) with a maximum size of 4.75 mm was used as a partial (30%) replacement material for fine aggregate (river sand, RS). The Coarse aggregate (CA) used in the mix was black Granite with maximum size 20 mm and 12.5mm. All the aggregates complied with the requirements of IS 383[18]. Chemical admixture (A) used, was of high range water reducer type, having Sulphonated Naphthalene Formaldehyde as base. NT particles with average size 50-60nm and NC particles with average size of 50-70nm was used. NT and NC particles had a specific gravity of 3.76 and 2.69 respectively. 2.2 Mix proportioning Six series of concrete mixes of grade M35 were prepared in the laboratory by replacing cement with NT, NC and NTC particles. The various percentage of nanoparticles replaced by weight of cement were 0.5%, 1.0%, 1.5%, 2.0%, 2.5% and 3% . F0 concrete mix was referred as control mix consisting of cement, flyash, natural aggregate, crushed sand, super plasticizer and water. The concrete containing NT, NC and NTC particles were labelled under the mix series T1 to T6 (T-series), C1 to C6 (C-series), and TC1 to TC6 (TC-series) respectively. The total powder content (cement + flyash + nanoparticles) for all mixes was 375 kg/m3.Water to powder ratio was 0.44, fly ash content was 150 kg/m3, river sand 549 kg/m3, crushed sand 235 kg/ m3, aggregate 1130 kg/ m3 and chemical admixture was 4.5 kg/ m3. The proportions of the mixtures are presented in Table 1.
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Table 1: Mix proportion of concrete
Sample designation
Nanoparticles (%)by wt. of cement
Quantities (kg/m3) Cement
TiO2
CaCO3
TiO2 + CaCO3
T- Series
C - Series
TC - Series
F0
0
225
0
0
0
T1,C1,TC1
0.5
223.875
1.125
1.125
1.125 (0.5625+0.5625)
T2,C2,TC2
1
222.75
2.25
2.25
2.25 (1.125+1.125)
T3,C3,TC3
1.5
221.625
3.375
3.375
3.375 (1.6875+1.6875)
T4,C4,TC4
2
220.5
4.5
4.5
4.5 (2.25 + 2.25)
T5,C5,TC5
2.5
219.375
5.625
5.625
5.625 ( 2.8125+2.8125)
T6,C6,TC6
3
218.25
6.75
6.75
6.75 (3.375 +3.375)
2.3 Preparation of Test Specimens The concrete was prepared in a laboratory concrete drum mixer. Cement, fly ash and aggregates were mixed in dry condition for one minute and then for another two minutes after adding water and chemical admixture. The nano particles were mixed with part of mix water using a handheld mixer for one minute to disperse the agglomerates. This prepared solution was poured in the drum mixer and mixed for two minutes along with the other ingredients. Slumps of the fresh concrete were determined immediately to evaluate the workability [19]. Cubes of 150 mm size and cylinders of height 200mm and diameter 100mm were cast as per the procedure laid in IS 516 [20] and thereafter cured for 28 days in a laboratory curing tank filled with water at a temperature of 28±1o C. To determine the consistency [24], cement pastes with 0% to 3% nanoparticles as mentioned above were made. 2.4 Testing methodology Compression tests of 150 mm cube concrete specimens were carried out according to IS 516[20] at the age of 7 and 28 days of sample. The split tensile strength test was carried out on the cylindrical specimens as per IS 5816 [21] at 28 days. Three specimens were tested in each condition for all the mixes. Crushed specimens were utilized further for determining the pH value. 10grams of the crushed sample was diluted in 100ml distilled water, stirred for ten minutes and thereafter the solution was tested for pH using a pH meter. The Rapid Chloride Penetrability Test was conducted as per the procedure laid in ASTM C1202 [22] by slicing the cylindrical specimen in the required size. Microanalysis was carried out for the 2% substitution from all the mixes. Small pieces from fractured surface of tested specimens were used for the investigation. The examination was carried out using a scanning electron microscope (SEM). 3. Results and Discussions All the results obtained from the experimental investigations are shown in Table 2. All the values are the average of three specimens in each condition. The results are discussed as follows in Table 2. 3.1 Compressive and tensile strength Comparing the 7 days compressive strength results for all the mixes it is noticed that 0.5% replacement showed a higher value than the 1 %, in all the mixes. The T- series mix showed a gradual increase in strength from 1 to 3% substitution. In C and TC- series mix, increase in strength was seen from 1 to 2% substitution and thereafter the
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strength started decreasing. It is predicted that, in the case of concrete with NT particles an improved filler effect would have been the reason for the increase in strength with the increase in nanoparticles. In NC particles a higher strength was observed at lower percentage of nanoparticles. For the T series mix the 28 days compressive strength showed a gradual increase till 3.0 % and decreased at 2.5 % and thereafter increased and the same was reflected in the split tensile strength value. In the C and TC series mix the 28 days compressive strength started decreasing with increase in the percentage of nano CaCO3 till 1.5 % but showed an increased strength at 2% and thereafter decreased slowly. The split tensile values were found to follow similar pattern in all the mixes. The ratio of split tensile strength to compressive strength was in the range of 0.08 to 0.09 as expected [23].With respect to mix of fly ash concrete , C&TC mixes showed higher early strength (ie.7 days) especially at 2% replacement, whereas T mix showed higher early strength at replacement of 0.5%, 2.5% and 3%. Table 2: Strength, pH and RCPT values for different mixes TiO2 & CaCO3 Nanoparticles (%)
Compressive Strength (N/mm2) 7 days
28 days
F0
Control
23.17
49.13
3.83
10.44
243
T1
0.5
27.00
45.70
2.85
10.58
172.8
T2
1
20.65
48.76
2.95
11.02
233.1
T3
1.5
21.39
49.47
3.57
11.22
216
T4
2
22.36
49.93
3.35
11.35
129.6
T5
2.5
27.06
47.55
3.58
11.18
179.1
T6
3
27.58
50.97
3.61
9.85
181.8
C1
0.5
27.05
49.74
3.69
9.05
191
C2
1
24.79
47.64
3.38
11.03
207.9
C3
1.5
26.35
44.95
3.86
11.89
224.1
C4
2
26.09
48.71
3.52
12.45
189
C5
2.5
24.07
43.74
3.16
9.65
195.7
C6
3
21.11
42.79
3.57
9.53
196.2
TC1
0.5
30.20
54.49
3.43
9.28
169.2
TC2
1
21.94
40.53
3.39
9.95
303.2
TC3
1.5
24.48
38.02
3.39
10.08
255.6
TC4
2
38.38
58.14
3.64
11.25
149.4
TC5
2.5
34.72
54.03
3.89
11.02
144
TC6
3
25.64
40.29
3.55
10.34
181.8
Mix series
Split tensile str. (N/mm2) 28 days
Crushed pH 28 days
RCPT value (Coulombs) 28 days
3.2 Rapid Chloride Penetrability Test (RCPT) and pH Values The RCPT values were in the range of 100 – 500 coulombs for all the mixes, which indicated very low chloride ion penetrability [21] .The lowest value among all the mixes was observed at 2% substitution. There was an increase in pH value of concrete as the percentage substitution of nanoparticles increased up to 2%, and thereafter the value gradually decreased. 3.3 Workability and Consistency values The workability (slump values) of all the concrete mix series are presented in Figure 1.
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Fig.1. Slump value variation
The figure shows the influence of nanoparticle content on the workability of mixtures at constant water to binder ratio of 0.44. The water content and admixture dosage were kept constant in order to understand the fluidity and water demand of the mix. The results show that all the mixes blended with nanoparticles showed a decline in slump value as the percentage of nanoparticles increased in the mix. The decrease in the slump was most evident in C series mix. As the percentage of addition of NC particles increased, there was a decrease in the fluidity and increase in water demand in the mix. This was confirmed in the consistency tests [24] which showed an increase in percentage of water required to meet the consistency limits [Figure2].
Fig. 2. Consistency value variation
3.4 Scanning electron microscopy results As the strength, pH and RCPT results were encouraging for the specimens with 2% modification; these fractured specimens were subjected to microanalysis using SEM (Fig.3). While comparing the images of T4, C4 and TC4 with F0, it appears that a homogenous dense microstructure is attained in the given order of mixes. This justifies the mechanical as well as penetrability properties for the above mixes as given in Table 2. Dense appearance of hydrated products in C4 justifies the high pH .This will be further verified using EDAX and XRD analysis.
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F0
C4
T4
TC4
Fig. 3. SEM images
4. Conclusion •
• • •
The addition of nanoparticles of TiO2, CaCO3 and their combination greatly enhanced the early and higher age strength of fly ash concrete. It was observed that a 0.5 % substitution of nanoparticles gave an appreciably higher strength and also an increase in percentage of NT particles showed an increase in strength (with maximum at 3%). The NTC particles showed a maximum strength at 2% substitution. The 2% substitution of NT and NC particles yielded slightly lower strength when compared to the maximum strength attained but the RCPT values were very low at this percentage indicating a good impermeable concrete. Though the workability of fresh concrete showed a decline in slump value as the percentage of nanoparticles increased, these slump values as such gave a workable concrete. When seen from durability point of view a 2 % substitution of nanoparticles showed a very good resistance to chloride ion penetration and also a high pH value. Comparing all the results it was found that 2% is the optimum level of nanoparticle substitution which could yield a durable and strong concrete. This was further verified using SEM.
Acknowledgements The paper is the outcome of the projects done with BRNS. Authors are grateful to the management of BRNS for financing the project. The authors also wish to thank, Director, Indira Gandhi Centre for Atomic Research, without whose support, this work would not have been possible.
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