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Application of nano-silica in cement mortar and concrete
Application of nano-silica in cement mortar and concrete
27
Sakshi Gupta Department of Civil Engineering, Amity University Haryana, Haryana, India
Chapter outline 1. Introduction 601 2. Nano-materials and cementitious composites 2.1 2.2
602
Use of nano-silica in paste/mortar 603 Use of nano-silica in concrete 605
3. Mortar containing nano-silica: a case study 606 3.1 3.2 3.3 3.4 3.5
Preparative method 606 Fresh properties 607 Compressive strength study 607 Ultra-sonic pulse velocity study 610 Concluding remarks 612
4. Concrete containing nano-silica: a case study 4.1 4.2 4.3 4.4
612
Preparative method 612 Compressive strength study 612 Ultra-sonic pulse velocity study 613 Concluding remarks 613
References
614
1. Introduction Now-a-days, the status of the cementitious materials in the built environment and construction industry is beyond any question. They have a variety of applications and therefore, their complexity is also not hidden from anyone in the industry. They are certainly composite materials with truly multi-scaled internal structures that keep on developing over the years (Gupta, 2014, 2017; Gupta and Garg, 2017). The cement paste matrix is fundamentally a porous material comprising of calcium hydroxide (portlandite), un-hydrated cement (clinker) and aluminates surrounded by an amorphous nano-structured hydration product called calcium silicate hydrate (CeSeH) gel. This gel is of utmost importance as a hydration produce of the cement paste, because it is the ample constituent (50%e70% by volume) and also due to its remarkably good mechanical properties (Gaitero et al., 2008).
Smart Nanoconcretes and Cement-Based Materials. https://doi.org/10.1016/B978-0-12-817854-6.00027-1 Copyright © 2020 Elsevier Inc. All rights reserved.
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Smart Nanoconcretes and Cement-Based Materials
Nanotechnology is swiftly becoming the industrial revolution of 21st era (Siegel et al., 1999) and it is going to disturb nearly every single facet of one’s life (IWGN, 1999). Nanotechnology is much less definite and well-structured in comparison to other technologies. The sense of nanotechnology differs from field to field and nation to nation and therefore, best reproduced as a ‘catch-all’ portrayal of tasks at the nanometric scale having vast applications in the real world (Saxl, 2001). Till date, the applications of nanotechnology and its advancements in the field of built environment and building materials have been jagged (Bartos, 2009). Nanoparticles have a high ratio of surface area to volume and are therefore, very reactive (Wiesner and Bottero, 2007). The first document (report RILEM TC 197-NCM) related to nanotechnology in construction materials by Zhu et al. (2004), standardized in a logical way the potentiality of nanotechnology in the growth of construction and building materials. It stated the following: •
• • • • •
The utilization of high performance structural materials such as the nanostructure modification of steel/metals, nanoparticles, nanotubes and nano-admixtures enhances the strength and durability of cementitious materials (Zhan et al., 2003; Bigley and Greenwood, 2003; Li et al., 2004a; Man, 2006; Mitchell, 2009; Gupta, 2013, 2014, 2015 and 2015a) Developing innovative techniques to comprehend phenomena at nanoscale (e.g hydration, shrinkage, durability, strength, etc.) Production of functional thin films/coatings to improve the performance and diminish energy consumption on abrasion resistance, optical, thermal and other applications (Harrington et al., 2010). Development of new sensors, devices and smart structures to improve the monitoring of structural conditions and their abilities at nano-level. Use of nano-materials for sustainable energy, environmental applications, pollution reduction and enhanced performance. Understanding the phenomena of conventional construction materials like concrete, asphalt, plastic and steel, at nanoscale (Gupta, 2014, 2015; Ghaly et al., 2017; Khan, 2018).
Nanotechnology is an empowering technology that permits the development of materials with enhanced or completely new properties. Today, appealing the engineers, especially the civil engineers, to implement nanotechnology could allow them to deliver revolutionary answers to the difficult problems of construction industry. It is a known fact that materials are the fundamental parts of construction industry which could be developed (enhanced) by the utilization of nanotechnology. Though the soaring costs of nano-materials could impede their widened application in today’s time but it is projected that these costs will drop in the near future and would provide beneficial advantages over conventional materials (Gupta, 2013, 2014; 2015).
2.
Nano-materials and cementitious composites
Widespread research is being conducted in the built environment sector for refining the efficiency of many building materials and evolution of durable and sustainable concrete is one of them. Nano-silica is the utmost extensively utilized material in the cement and concrete among all the nano-materials to enhance its efficiency due to
Application of nano-silica in cement mortar and concrete
603
its pozzolanic reactivity and the pore filling effect (Li, 2004; Berra et al., 2012; Gupta, 2013, 2014; 2015, 2015a). The utilization of nano-silica has been studied in various cementitious materials and in this chapter we will look into two main aspects (i) Pastes/mortars, and (ii) Concrete.
2.1
Use of nano-silica in paste/mortar
There have been various researches been conducted throughout the world with respect to the use of nano-silica in paste and mortar. Some of the works have been discussed as follows: Haruehansapong et al. (2014) through their study found the compressive strengths of mortars incorporating nano-silica (nS) and silica fume (SF) and a comparison of the two. The nS used in the study with sizes ranging from 12 to 40 nm. Nine different mixes were prepared with water/binder ratio of 0.65; one control mix, four for nS and other four for SF (3%, 6%, 9% and 12% for both). Test results revealed noteworthy enhancement in strength but were dependent on size of nano particles. 40 nm sized nano-particles exhibited higher strength than others because of their agglomeration and unproductive dispersion. The optimum content was found to be 9% in both the cases. Shaikh et al. (2014) through their study found out the effect of nano-silica on mortars and concretes by conducting various experiments. Eight different mixes were prepared with 1%e6% (by wt.) of nS as a replacement of cement. Compressive strength was found at 7 and 28 days. It was found that 2% nano-silica content exhibited highest enhancement in strength in both 7 and 28 days. Adak et al. (2014) experimentally considered the effect of nano-silica on cement mortars. Colloidal nano-silica with altering percentages of fly ash was added. Adding 6% nano-silica in the fly ash, revealed an enhanced compressive strength at 7 and 28 days. Also, at the same percentage flexural strength and split tensile strength increased from the control value. Oltulu and Sahin (2013) investigated the effect on compressive strength and capillary water absorption on the addition of nano-SiO2 (nS), nano-Al2O3 (nA) and nanoFe2O3 (nF) powders plus the binary and ternary combinations of these materials on cement mortars containing fly ash (FA). Powder quantities were utilized i.e. 0.5, 1.25 and 2.5 wt % of the binder for all mixtures. The results presented that the addition of any type of oxide powders (nS, nA and nF) at 1.25% enhanced compressive strength of the mortars than the other proportions. The utilization of nS þ nA powders at 1.25% enhanced the compressive strength as compared to the control mix. Among all the combinations, the finest results were found for the mortar at 1.25% weight of cement with nS þ nA þ nF powders. Hou et al. (2013) through their experiments stated a reduction in the permeability when mix was more durable. The reason for this was found by researchers that there was an obstruction to migration of aggressive agents. Nano-silica changed the pore structure of mortar leading to lesser transport property, thereby reducing the pore volume.
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Hou et al. (2012) carried out the experiment to assess the consequence of addition of nano-SiO2 on the cement hydration process, gel structure and nanoscale mechanical properties of the cement paste. Cement pastes mixed with and without 5% (colloidal nano-silica/silica fume) at a w/b ratio of 0.4 were prepared and investigated. Results revealed that pozzolanic activity of colloidal nano-silica is higher than that of silica fume and its hydration acceleration outcome was higher in the early age, but this result at the later ages was comparable to that of silica fume. Berra et al. (2012) investigated the influence of nano-size particles of amorphous nano-silica on the rheological behavior and mechanical strength progress of cementitious mixes. Fourteen different mixes were casted using three dosage levels. Cement paste workability was found to be considerably lower than likely for the adopted water/binder ratios. The result of instant interactions between the solution of nano-silica and the liquid phase of cement pastes, which demonstrated the development of gels characterised by an important capacity of water retention in the cementitious mixes. Lucas et al. (2012) reported the usage of nano-SiO2 (nS) and nano-TiO2 (nT) in cement pastes and mortars. Samples with 0e3 wt % nS, 0e12 wt % nT and 0.5 water/binder weight ratio were set and investigated. The results revealed that the flow table values were lessened but the mechanical properties were not considerably influenced by nano-particles in the range taken for the above study. Stefanidou and Papayianni (2012) introduced nano-particles into cement pastes to enhance their properties and generate materials having superior performance. NanoSiO2 manufactured by pyrolysis was incorporated at various percentages (0%, 0.5%, 1%, 2% and 5%) to high-strength cement pastes. These pastes were then tested for their mechanical as well as structural properties at different ages. The addition of superplasticizer in 1% weight by weight of cement decreased the water demand but the strength enhanced varying from 30% to 35%. Even at low dosage of nano-silica, the mechanical and structural properties were affected. Aly et al. (2012) compared the micro-structural, alkaliesilica reaction and the mechanical properties of cement mortars containing waste glass powder (WG) as a replacement of cement with and without colloidal silica (CS). Five different mixes were casted with 20% and 40% replacement with glass powder and 3% CS. The results revealed that the addition of WG has a positive effect on the mechanical properties of cement mortars especially when CS was present. Senff et al. (2010) reported the impact of nano-silica (nS) and silica fume (SF) on the rheology, spread on flow table, compressive strength, water absorption, apparent porosity, unrestrained shrinkage and weight loss of mortars. Samples with nS (0e7 weight %), SF (0e20 wt %) and water/binder ratio between 0.35 and 0.59, were explored through tests. The results revealed that during the rheological measurements, nano-silica with 7 wt% lead to the formation of structures in a faster manner. Senff et al. (2009) incorporated amorphous nano-silica (nS) particles by cement in cement pastes and mortars. The influences of these materials on the fresh properties were studied. Fresh mortar was equipped with binder/aggregate weight ratio of 1:2 and water/binder ratio of 0.35. Even the cement paste was equipped with the same water/binder ratio. The dosage of nS was taken as 0%, 1.0%, 1.5%, 2.0% and 2.5% by the weight of cement. X-ray diffraction test revealed the occurrence of calcium hydroxide
Application of nano-silica in cement mortar and concrete
605
after 9 h in the sample with 2.5 wt% nS. The air content improved by 79% and apparent density reduced by 2.4% when nS was incorporated in the mix. Qing et al. (2007) carried out a study on the influence of addition of nano-SiO2 (nS) on the characteristics of hardened cement paste (hcp) as compared with silica fume (SF). Eight different mixes were cast. For all the pastes, a ratio of 1:0.22:0.025 (cement: water: superplasticizer) was used. Experimental data has revealed that compressive strengths of hcp enhanced with increment in the dosage of nano-SiO2, particularly at early ages. Though, the strengths of hcp decreased somewhat with the increase in the dosage of silica at early ages, but increased at later ages. Ltifia et al. (2001) studied the properties of cement mortars with nano-SiO2 experimentally. Mortar mixes were prepared for 0%, 3% and 10% dosage of nano-silica by weight of cement with the same w/b ratio. From the results, it was seen that nano-SiO2 made the cement paste thicker and the cement hydration process was accelerated. Compressive strengths improved on more addition of the dosage of nano-SiO2.
2.2
Use of nano-silica in concrete
Jalal et al. (2015) investigated the properties like chloride penetration, water absorption and electrical resistivity which are identified with the durability of high strength self-compacting concrete (SCC) by utilizing nano-silica and silica fume. Portland cement was substituted by various dosage of micro silica (10%), nano-silica (2%) and a blend of micro as well as nano-silica (10% þ 2%). Twelve concrete blends were taken into account with a consistent water/binder ratio of 0.38. Both water and capillary retention results revealed substantial enhancement with the inclusion of admixtures, specifically the mixture of micro and nano materials for binder content of 500 kg/m3. Ghafari et al. (2014) carried out an exploratory investigation on the effect of nanosilica on the characteristics of ultra-high performance concrete. Compressive strength enhanced with the increment in the nano-silica content, exclusively at early ages. The optimum content was found to be 3% by weight. Proper dispersion was a critical parameter to enable the integration of greater fractions of nano-silica into the cement pastes. Zhang and Islam (2012) considered experimentally the impact of nano-silica (nS) on the setting times and early age strengths of high volume slag mortar and concrete. The influence of nS quantities, size and dispersion approaches on the strength development of high volume slag mortars were examined. It was found that the addition of a small dosage of nS decreased setting times, and enhanced 3 and 7-day compressive strengths of high-volume slag concrete, substantially, in contrast with the reference slag concrete with zero dosage of silica. Said et al. (2012) studied the impact of colloidal nano-silica on concrete including single (ordinary cement) and binary (ordinary cement þ Class F fly ash) binders. Six blends were arranged and Class F fly ash was utilized in three blends. The nano-silica utilized was in a colloidal type of an aqueous solution with 50% amount of SiO2. So as to accomplish a consistent level of workability, a high-range water reducing admixture (HRWRA) was utilized at diverse amounts for all the blends. Coarse aggregates used
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in the blends was well-graded natural gravel. Significant improvement was seen in the blends including nano-silica regarding reactivity, development of strength, pore structure refinement and interfacial transition zone densification. Micro-structural and thermal analyses demonstrated that the influence of pozzolanic and filler impacts the pore structure refinement that relied upon the amount of nano-silica. Quercia and Brouwers (2010) experimentally carried out an investigation and devised a methodology to decrease the amount of the cement content in concrete mixes by the utilization of silica fines. A new nano-silica (nS) can be generated in high amounts and for low costs allowing for large-scale application in concrete. Concrete become financially more attractive by the utilization of nS. With the utilization of nS, the CO2 footprint of the produced concrete products is also reduced to great extent. This leads to a concrete which gives better efficiency, reduced costs and enhanced ecological footprints. Givi et al. (2010) explored the influence of the size of SiO2 nano-particles on various properties such as compressive, flexural and tensile strength of binary blended concrete. Two distinctive SiO2 nano-particles with the diameter of 15 and 80 nm (average) were utilized. An aggregate of three arrangements of blends were set up in the research facility premises. The control specimens (C0) comprised of natural aggregates, cement and water. Series FN (15 nm) and CN (80 nm) were prepared with diverse quantities of SiO2 nano-particles. The results revealed that SiO2 nanoparticle advantageously replaced the amount of cement by up to maximum of 2.0%. Despite the fact that the ideal substitution level of nano-SiO2 particles for 15 and 80 nm size were picked up at 1.0% and 1.5%, respectively. Ji (2005) experimentally found the water permeability resistant behavior and microstructure of concrete with nano-SiO2. NC (normal concrete) and SC (nano-silica concrete) were the mix proportions prepared and tested in this work. Results revealed that SC was stickier than NC because the specific surface area is large. Also, the water permeability test showed that the SC has better water permeability resistant behavior than NC. Li et al. (2004b) experimentally studied the properties of high-volume fly ash highstrength concrete including nano-SiO2 (SHFAC). Portland cement was utilized in the mix formation. The water/binder ratio was kept constant throughout having value of 0.28 for the concrete mixes with diverse dosage of superplasticizer. This was done to keep the fluidity of concretes intact because of the impact of various mineral admixtures. The results revealed that fly ash has low initial reactivity, but the pozzolanic reactivity expressively improved after addition of a very small amount of nanoSiO2. It was also found that by adding nano-SiO2 to high-volume high-strength concrete, there is a significant rise in short-term and long-term strengths.
3.
Mortar containing nano-silica: a case study
3.1
Preparative method
Ordinary Portland cement (OPC) 43 grade having specific gravity: 3.15; consistency: 29%; fineness: 2%; soundness: 1 mm; initial setting time (IST): 120 min; and final
Application of nano-silica in cement mortar and concrete
607
setting time (FST): 175 min has been used in this work. Fine aggregate is river sand conforming to grading Zone-II of IS:383e1970 (spherical structure; maximum grain size: 2 mm; specific density: 2.65). Twelve cement mortar mixtures M0 to M5 (without super plasticizer) and MS0 to MS-5 (with super plasticizer) were prepared with varying nano-silica from 0.5% to 1.5% at the interval of 0.25% as given in Table 27.1. Nano-silica might not show an even spreading in the mixture because of its large surface area. It may directly disturb the physical and mechanical properties of the mortars. After numerous pilot tests, the procedure for the manufacture of specimen was then finalized for the study. The final mixture was poured into molds of 70.6 mm 70.6 mm 70.6 mm and after vibration for 2 min, the specimens were left to harden. After 24 h, the demoulded mortar specimens were stockpiled in curing tanks holding water at a temperature of 20 2 C until testing was carried out. Three specimens were set for each mixture. The compressive strength tests, water absorption tests and ultra-sonic pulse velocity tests were carried out on the hardened specimens. Compression tests were done at a rate of loading of 0.5 MPa/s at early ages (1, 3 and 7 days), at standard age (28 days), and at later ages (90 and 180 days) conforming to IS: 516e1959. Ultrasonic pulse velocity (UPV) technique is used to study the relationships between internal structure, mechanical properties and dynamic modulus of elasticity (Ed) of numerous materials. UPV measurements of all the mortars were determined according to the standard of IS: 13311-(part-1)-1992 (Reaffirmed, 2004). UPV is used to forecast and assess the mechanical properties of several materials by non-destructive means. UPV tests were carried out at same ages as of compressive strength and on the same samples. Longitudinal wave measurements were taken by using PUNDIT non-destructive ultrasound equipment (transducer frequency of 54 kHz) (Fig. 27.1). The investigations were carried out for replacement of cement with nano-silica varying from 0.5% to 1.5% at the interval of 0.25%. Results obtained through the replacements of cement with of nano-silica in cement mortars are presented with the analysis of various properties.
3.2
Fresh properties
The consistency of cement pastes for mixes M0 to M5 was observed to increase from 29% to 32%, with 29% for control mix (M0) and similar trend of increase was observed for mixes MS-0 to MS-5 from 22% to 25% with 22% for control mix with super plasticizer (MS-0). Decrease in IST and FST was also observed for both M and MS mixes, on increasing the percentages of nano-silica (Table 27.1).
3.3
Compressive strength study
Table 27.2 give the results for mortars containing nano-silica, while the distinction of compressive strength with respect to the ages (1, 3, 7, 28, 90 and 180 days) is given in Fig. 27.2. It is clearly evident from the figure that the strength of all mortar mixes encompassing nano-silica increased with age from 1 day to 90 days. Still, the rate
608
Table 27.1 Mix design of 12 mortar samples. Mortar mixes M-0
M-1
M-2
M-3
M-4
M-5
MS-0
MS-1
MS-2
MS-3
MS-4
MS-5
Cement (gm)
200
199
198.5
198
197.5
197
200
199
198.5
198
197.5
197
Sand (gm)
600
600
600
600
600
600
600
600
600
600
600
600
w/b ratio
0.3
0.3
0.3
0.3
0.3
0.3
0.23
0.23
0.23
0.23
0.23
0.23
Nano-silica %
0
0.5
0.75
1.0
1.25
1.5
0
0.5
0.75
1.0
1.25
1.5
SP %
0
0
0
0
0
0
1
1
1
1
1
1
31
32
28
33
32
34
32
34
31
33
29
31
Mortar temp C
31
34
30
35
35
38
31
36
33
36
32
34
Relative humidity %
70
63
74
61
61
72
61
51
67
59
75
62
o
Air temp C o
Here, SP¼ Superplasticizer; w/b ratio ¼ water to binder ratio; temp ¼ temperature.
Smart Nanoconcretes and Cement-Based Materials
Properties
Application of nano-silica in cement mortar and concrete
609
Fig. 27.1 Specimen testing using Ultrasonic pulse velocity method equipment.
Table 27.2 Compressive strength values of mortars containing nano-silica. Compressive strength (MPa) Sr. no.
Mix
1 day
3 days
7 days
28 days
90 days
180 days
M0
17.70
23.46
41.46
47.41
49.87
51.94
M1
18.12
26.32
45.18
52.90
55.38
57.29
M2
18.30
27.04
44.51
51.63
54.25
55.31
M3
17.89
25.32
44.30
49.29
52.7
53.78
M4
17.09
24.97
42.24
48.98
51.24
53.14
M5
16.80
24.15
41.86
48.22
50.98
52.91
MS0
17.91
28.64
42.63
51.86
54.35
56.17
MS1
21.23
35.13
48.08
54.81
57.82
59.51
MS2
23.13
35.97
51.37
59.27
61.88
63.28
MS3
25.61
36.79
52.76
63.69
65.91
67.83
MS4
24.97
35.42
49.71
60.64
62.35
64.11
MS5
24.51
34.28
47.14
58.04
60.13
61.59
of increment in the strength varied with the quantity of the nano-silica as compared to that for the control mixes. It is evident from Fig. 27.2 that the highest compressive strength was obtained for the mixes designated as M1 and MS-3. Results revealed that the addition of nS improves the compressive strength of cement mortars added with/without superplasticizer, optimized at 0.5% for mortars mix without super plasticizers and 1.0% for mortar mix with super plasticizer. This is in accordance with the similar study being conducted by Ji (2005) where the filler consequence was displayed by nS and its
610
Smart Nanoconcretes and Cement-Based Materials 80.00
1 day M Compressive Strength (MPa)
70.00
1 day MS
60.00
3 day M 3 day MS
50.00
7 day M 40.00
7 day MS 28 day M
30.00
28 day MS
20.00
90 day M 10.00 0.00 1
2
3
4
5
6
Mixes
Fig. 27.2 Compressive strength values of various mortar mixes with respect to the ages (without and with superplasticizer).
capability to make a further strong matrix and aggregateecement paste interface. The results of this study are compatible with existing literature.
3.4
Ultra-sonic pulse velocity study
Ultra-sonic pulse velocity (UPV) test was carried out on all the specimens to find the homogeneity, quality and dynamic elastic modulus of concrete. Propagation speed of sound waves within material structure depends on the type and inner characteristics of the material. This property helps to provide information about the inner structure of the material. A high transmission rate of sound means less pores and, thus higher strength. When pulse is transferred to the material by a transducer, it endures multiple reflections at the boundaries of diverse phases within the material. Assessing the quality of materials by UPV measurements is done by an apparatus that generate appropriate pulses and precisely measures the time of transmissions. The velocity of a pulse of longitudinal ultrasonic vibrations traveling in an elastic solid is given by Eq. (27.1). V2 ¼
Eð1 uÞ pð1 þ uÞð1 2uÞ
where. V: pulse velocity (m/s) E: dynamic elastic modulus (N/mm2) p: density (kg/m3), u: Poisson’s ratio which was taken as 0.24 as per IS: 13311-(part-1)-1992
(27.1)
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Table 27.3 Elastic modulus values of various mortar mixes. Elastic modulus (MPa) Sr. No.
Mix
1 day
3 day
7 day
28 day
90 day
180 day
M0
45622
47097
50263
53836
53980
54136
M1
47426
47985
51467
55121
56603
56997
M2
48341
49207
52623
54594
55559
55719
M3
47235
48576
51062
54552
56809
55914
M4
46713
48111
49546
53114
55013
55314
M5
44796
47013
47628
51649
54326
54763
MS0
47667
50427.
52752
54533
55818
56118
MS1
50260
51367.
53587
56574
57263
57648
MS2
51375
51791.
54291
58382
58873
59147
MS3
50894
52758
56062
58926
59110
59934
MS4
49667
50961
54789
57980
57666
58051
MS-5
49386
49091
53116
57455
55757
56040
The dynamic modulus was assessed on the basis of Eq. (27.1), where density was obtained experimentally. The UPV tests were carried out on same specimens as used for compressive strength. Table 27.3 and Fig. 27.3 show the results of the ultra-sonic pulse velocity on mortar specimens. Compared to the control specimen (M0), the increase in elastic modulus values was observed for all ages of the specimens. 65000 1 day M 1 day MS
Elastic Modulus (MPa)
60000
3 day M 3 day MS 7 day M
55000
7 day MS 28 day M
50000
28 day MS 90 day M 45000
90 day MS 180 day M 180 day MS
40000 1
2
3
Mixes
4
5
6
Fig. 27.3 Elastic modulus values of various mortar mixes with respect to the ages (without and with superplasticizer).
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The optimum results were obtained for the specimen designated as M-1(early ages), M2 (later ages) and MS-3 mortars. The increase in elastic modulus of mixes without super plasticizer at 0.5% and 0.75% were may be due to higher particle packing because of the use of nano-silica but on increasing the content of nano-silica to 0.75%, the workability decreased causing small cracks in the structure, leading to lower elastic modulus. Similarly, because of the use of super-plasticizer the workability of the mixes enhanced, with mix MS-3 (with nS 1.0%), having the highest elastic modulus as compare to the control mix.
3.5
Concluding remarks
The main effects of nano-silica on properties of cement mortars are: - The compressive strength of all the mixes containing nano-silica was observed to be higher than the control mix. - Addition of nano-silica (with super-plasticizer), further enhanced the workability of the mortar mix resulting in better particle packing at higher proportions and higher compressive strength as compared to mixes without super-plasticizer. - Nano-silica percentage 0.5% (without super-plasticizer) and 1.0% (with super-plasticizer) were observed to be the optimum percentages. - The elastic modulus of all the mixes containing nano-silica was found to be higher than that of the control mix. The increase in elastic modulus may be due to the increase in the particle packing density due to presence of nano-silica but after certain percentages, low workability is observed as mixes are not compacted properly, leading to cracks in the structure, causing reduction in elastic modulus and strength of the specimen.
4.
Concrete containing nano-silica: a case study
4.1
Preparative method
The concrete with grade M25 has been used with ordinary Portland Cement 43 grade (normal consistency: 32%). For aggregates, their specific gravities are 2.65 and 2.72 for fine and coarse aggregates, respectively. Mix ratio of (cement: sand: aggregate: water) is (1: 1.41: 2.75: 0.43). This mix proportion was designed taking into consideration all the material properties and in accordance with Indian Standard code IS: 102622009. Nano-silica particles have the average size of 230 nm. The content of nano-silica in concrete varies from 0.3 % to 1% by weight of cement.
4.2
Compressive strength study
For carrying out the compressive strength test on concrete, cubes of size 150 150 150 mm were casted. Their compressive strength values were presented in Table 27.4. As seen in Table 27.4, there is an increment in the compressive strength of concrete on adding of a definite minimum amount of nano-SiO2 (NS). The increment in compressive strength has a maximum value for NS at 1% by weight of cement,
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Table 27.4 Compressive strength values of concrete samples. 7 days compressive strength (MPa)
28 days compressive strength (MPa)
Control mix (0% nano-silica)
26.30
35.4
2
M1 (0.3% by weight of cement)
27.6
35.2
3
M2 (0.6% by weight of cement)
31.1
36.5
4
M3 (1% by weight of cement)
34.6
39.8
S.No.
Specimen
1
and minimum value for NS at 0.3% by weight of cement. There is a considerable increment in the early-age strength of concrete as compared to the 28 day increase in the strength on addition of NS. It is shown from the results that there is an enhancement in the early strength of concrete with the replacement of cement with nano-silica but later the increment in the strength is reduced. This is because of the micro-filling effect of the nano-silica particles. The more the silica particles, the more they will inhabit the pores in the gel and makes the microstructure even and consistent. The increment in the strength is because of the presence of adequate amount of silica making the microstructure denser and consistent.
4.3
Ultra-sonic pulse velocity study
Table 27.5 presents the data obtained from UPV test for these concrete samples. From the results of the UPV test, it was evident that the quality of concrete was very good. The results clearly revealed that the 28-days quality of concrete is better than that of the 7-days. The control mix specimen was found to have better quality in comparison to the blended concrete specimen. 0.3 % nano-silica means a better packed microstructure whereas for 1% nano-silica in concrete, the microstructure is more dense, and therefore enhances the strength of concrete. On addition of the NS, it was seen through the UPV test that there is a slight impact on the quality of concrete but the overall quality of concrete gets preserved.
4.4
Concluding remarks
The main effects of nano-silica on properties of concrete are: - There is an increment in the compressive strength of concrete on adding of a definite minimum amount of nano-SiO2 (NS). The increment in the compressive strength is maximum for NS at 1% by weight of cement and least for NS at 0.3% by weight of cement. - There is a considerable increment in the early-age strength of concrete as compared to the 28 day increase in the strength on addition of NS.
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Smart Nanoconcretes and Cement-Based Materials
Table 27.5 UPV values of concrete samples (7 and 28 days test).
S.No.
Concrete samples
1
Control mix (0% nano-silica)
2
3
4
M1 (0.3% by weight of cement)
M2 (0.6% by weight of cement)
M3 (1% by weight of cement)
7 days velocity (m/s)
7 days time (ms)
28 days velocity (m/s)
28 days time (ms)
4675
32.1
4808
31.2
4704
31.9
4854
30.9
4777
31.5
4777
31.5
4491
33.3
4673
32.1
4491
33.3
4732
31.8
4389
34.3
4856
31.0
4630
32.5
4704
31.9
4630
32.5
4777
31.5
4704
31.9
4777
31.5
4491
33.3
4658
32.3
4360
34.5
4704
31.9
4560
33.0
4808
31.2
- The increment in the strength is because of the presence of adequate amount of silica making the microstructure denser and consistent. - The quality of concrete was very good as per the ultrasonic pulse velocity test as per the codal provisions. The results clearly revealed that the 28-days quality of concrete is better than that of the 7-days. - In terms of UPV test, the control mix specimen was found to have better quality in comparison to the blended concrete specimen. - On addition of the NS, it was seen through the UPV test that there is a slight impact on the quality of concrete but the overall quality of concrete gets preserved.
Thus, it can be concluded that the use of nano-structured materials in both cement mortar and concrete can complement several advantages directly related to the various properties such as fresh, mechanical and durability properties of these materials. It also makes it possible to decrease the quantities of cement in the composites, thereby, opening new avenues for the utilization of nano-particles in the construction industry.
References Adak, D., Sarkar, M., Mandal, S., 2014. Effect of nano-silica on strength and durability of fly ash based geopolymer mortar. Construction and Building Materials 70, 453e459. Aly, M., Hashmi, M.S.J., Olabi, A.G., Messeiry, M., Abadir, E.F., Hussain, A.I., 2012. Effect of colloidal nano-silica on the mechanical and physical behaviour of waste-glass cement mortar. Materials & Design 33, 127e135.
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Bartos, P.J.M., 2009. Nanotechnology in construction: a roadmap for development. In: Bittnar, Z., Bartos, P.J.M., Nemecek, J., Smilauer, V., Zeman, J. (Eds.), Nanotechnology in Construction: Proceedings of the NICOM3, Prague, Czech Republic, pp. 15e26. Berra, M., Carassiti, F., Mangialardi, T., Paolini, A.E., Sebastiani, M., 2012. Effects of nanosilica addition on workability and compressive strength of Portland cement pastes. Construction and Building Materials 35, 666e675. Bigley, C., Greenwood, P., 2003. Using Silica to Control Bleed and Segregation of SelfCompacting Concrete, pp. 43e45. Concrete. Gaitero, J.J., Campillio, I., Guerrero, A., 2008. Reduction of the calcium leaching rate of cement paste by addition of silica nanoparticles. Cement and Concrete Research 38, 1112e1118. Ghafari, E., Costa, H., Julio, E., Portugal, A., Duraes, L., 2014. The effect of nano-silica addition on flowability, strength and transport properties of ultra-high performance concrete. Materials & Design 59, 1e9. Ghaly, A., Attia, A., Mostafa, H., Sammour, K., Ghobrial, M., Fathy, A., Abou-Zeid, M., 2017. The effect of nano-silica on cementitious materials. In: Leadership in Sustainable Infrastructure May 31 e June 3, 2017, Vancouver, Canada MAT614, pp. 1e10. Givi, A.N., Rashid, S.A., Aziz, F.N.A., Salleh, M.A.M., 2010. Experimental investigation of the size effects of SiO2 nano-particles on the mechanical properties of binary blended concrete. Composites Part B: Engineering 41, 673e677. https://doi.org/10.1016/ j.compositesb.2010.08.003. Gupta, S., 2013. Application of silica fume and nanosilica in cement and concrete e a review. Journal on Today’s ideas-Tomorrow’s Technologies 1 (2), 85e98. Chitkara University. Gupta, S., 2014. A review on the use of nano-silica in cementitious compositions. International Journal of Concrete Technology 1 (1), 1e15. Gupta, S., 2015. Use of nano-silica in concrete: a review. New Building Materials & Construction World 20 (10), 118e135. Gupta, S., 2015a. Use of triangular membership function for prediction of compressive strength of concrete containing nano-silica. Cogent Engineering 1 (2). Gupta, S., 2017. A critical evaluation of the role of micro silica and nano-silica in cementitious materials. International Journal of Recent Development in Civil & Environmental Engineering 3 (1), 1e13. Gupta, S., Garg, D., 2017. Using GA to predict the compressive strength of concrete containing nano-silica. International Journal of Energy Sector Management VII (I), 37e43. Harrington, M., Masic, A., Holten-Andersen, N., 2010. Iron-clad fibers: a metal-based biological strategy for hard flexible coatings. Science 216e220. Haruehansapong, S., Pulngern, T., Chucheepsakul, S., 2014. Effect of the particle size of nanosilica on the compressive strength and the optimum replacement content of cement mortar containing nano-SiO2. Construction and Building Materials 50 (15), 471e477. Hou, P., Kawashima, S., Kong, D., Corr, D.J., Qian, J., Shah, S.P., 2012. Modification effects of colloidal nano SiO2 on cement hydration and its gel property. Composites Part B: Engineering 45 (1), 440e448. Hou, P., Kawashima, S., Wang, K., Corr, D.J., Qian, J., Shah, S.P., 2013. Effects of colloidal nanosilica on rheological and mechanical properties of fly-ash cement mortar. Cement and Concrete Composites 35, 12e22. IS: 13311-(part-1)-1992(Reaffirmed 2004) Indian Standard Non e Destructive Testing of Concrete -methods of Test e Part 1 : Ultrasonic Pulse Velocity, Bureau of Indian Standards, New Delhi.
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IS: 383 -1970 (Reaffirmed 2002) Indian Standard Specification for Coarse and Fine Aggregates from Natural Sources for Concrete (Second Revision), Bureau of Indian Standards, New Delhi. IS:10262-2009. Indian Standard Concrete Mix Proportioning e Guidelines (First Revision). Bureau of Indian Standards, New Delhi. IS:516e1959 (Reaffirmed 2004) Indian Standard Method of Tests for Strength of Concrete. Bureau of Indian Standards, New Delhi. IWGN, 1999. National science and technology council, committee on technology, interagency working group on nanoscience, engineering and technology (IWGN). In: Nanotechnology: Shaping the World Atom by Atom’, September 1999. Jalal, M., Pouladkhan, A., Harandi, O.F., Jafari, D., 2015. Comparative study on effects of Class F fly ash, nano-silica and silica fume on properties of high performance self- compacting concrete. Construction and Building Materials 94, 90e104. Ji, T., 2005. Preliminary study on the water permeability and microstructure of concrete incorporating nano-SiO2. Cement and Concrete Research 35, 1943e1947. Khan, M.I., 2018. Nanosilica/silica fume. In: Waste and Supplementary Cementitious Materials in Concrete, pp. 461e491. Li, G., 2004. Properties of high-volume fly ash concrete incorporating nano-SiO2. Cement and Concrete Research 34 (6), 1043e1049. Li, H., Gang, H., Jie, X., Yuan, J., Ou, J., 2004a. Microstructure of cement mortar with nanoparticles. Composites Part B: Engineering 35 (2), 185e189. Li, X., Chang, W.C., Chao, Y.J., Wang, R., Chang, M., 2004b. Nanoscale structural and mechanical characterization of a natural nano-composite Material: the shell of red abalone. Nano Letters 4 (4), 613e617. Ltifia, M., Guefrech, A., Mounanga, P., Khelidj, A., 2001. Experimental Study of the Effect of Addition of Nano-Silica on the Behaviour of Cement Mortars. Procedia Engineering, Elsevier Ltd., pp. 900e905 Lucas, S., Senff, L., Hotza, D., Ferreirac, V.M., Labrincha, J.A., 2012. Effect of nano-SiO2 and nano-TiO2 addition on the rheological behavior and the hardened properties of cement mortars. Materials Science and Engineering A 53, 354e361. Man, S., 2006. Nanotechnology and Construction. Nanoforum Report. Institute of Nanotechnology. Mitchell, S., 2009. Capturing carbon. Concrete and Construction-World Concrete 54, 104. Oltulu, M., Sahin, R., 2013. Effect of nano-SiO2, nano-Al2O3 and nano-Fe2O3 powders on compressive strengths and capillary water absorption of cement mortar containing fly ash: a comparative study. Energy and Buildings 58, 292e301. Qing, Y., Zenan, Z., Deyu, K., Rongshen, C., 2007. Influence of nano-SiO2 addition on properties of hardened cement paste as compared with silica fume. Construction and Building Materials 21 (3), 539e545. Quercia, G., Brouwers, H.J.H., 2010. Application of nano-silica (nS) in concrete mixtures. In: Proc: 8th Fib PhD Symposium in Kgs. Lyngby, Denmark, 20-23 June, 2010. Said, A.M., Zeidan, M.S., Bassuoni, M.T., Tian, Y., 2012. Properties of concrete incorporating nano-silica. Construction and Building Materials 36, 838e844. Saxl, O., 2001. Opportunities for Industry in the Application of Nanotechnology. The Institute of Nanotechnology, UK. Senff, L., Hotza, D., Repette, W.L., Ferreira, V.M., Labrincha, J.A., 2010. Mortars with nanoSiO2 and micro-SiO2 investigated by experimental design. Construction and Building Materials 24, 1432e1437.
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Senff, L., Labrincha, J.A., Ferreira, V.M., Hotza, D., Repette, W.L., 2009. Effect of nanosilica on rheology and fresh properties of cement pastes and mortars. Construction and Building Materials 23, 2487e24891. Shaikh, F.U.A., Supit, S.W.M., Sarker, P.K., 2014. A study on the effect of nano-silica on compressive strength of high volume fly ash mortars and concretes. Materials & Design 60, 433e442. Siegel, R.W., Hu, E., Roco, M.C., 1999. Nanostructure Science and Technology: A Worldwide Study. IWGN. September 1999. Stefanidou, M., Papayianni, I., 2012. Influence of nano-SiO2 on the Portland cement pastes. Composites Part B 43, 2706e2710. Wiesner, M.R., Bottero, J.Y., 2007. Environmental Nanotechnology: Applications and Impacts of Nanomaterials. McGraw-Hill, New York. Zhan, G.D., Kuntz, J.D., Garay, J.E., Mukerjee, A.K., 2003. Electrical properties of nanoceramics reinforced with ropes of single-walled carbon nanotubes. Applied Physics Letters 83, 1228e1230. Zhang, M.H., Islam, J., 2012. Use of nano-silica to reduce setting time and increase early strength of concretes with high volumes of fly ash or slag. Construction and Building Materials 29, 573e580. Zhu, W., Bartos, P., Porro, A., 2004. Application of nanotechnology in construction. Summary of a state-of-the-art report. RILEM TC 197-NCM. Materials and Structures 37, 649e658.
27
Sakshi Gupta Department of Civil Engineering, Amity University Haryana, Haryana, India
Chapter outline 1. Introduction 601 2. Nano-materials and cementitious composites 2.1 2.2
602
Use of nano-silica in paste/mortar 603 Use of nano-silica in concrete 605
3. Mortar containing nano-silica: a case study 606 3.1 3.2 3.3 3.4 3.5
Preparative method 606 Fresh properties 607 Compressive strength study 607 Ultra-sonic pulse velocity study 610 Concluding remarks 612
4. Concrete containing nano-silica: a case study 4.1 4.2 4.3 4.4
612
Preparative method 612 Compressive strength study 612 Ultra-sonic pulse velocity study 613 Concluding remarks 613
References
614
1. Introduction Now-a-days, the status of the cementitious materials in the built environment and construction industry is beyond any question. They have a variety of applications and therefore, their complexity is also not hidden from anyone in the industry. They are certainly composite materials with truly multi-scaled internal structures that keep on developing over the years (Gupta, 2014, 2017; Gupta and Garg, 2017). The cement paste matrix is fundamentally a porous material comprising of calcium hydroxide (portlandite), un-hydrated cement (clinker) and aluminates surrounded by an amorphous nano-structured hydration product called calcium silicate hydrate (CeSeH) gel. This gel is of utmost importance as a hydration produce of the cement paste, because it is the ample constituent (50%e70% by volume) and also due to its remarkably good mechanical properties (Gaitero et al., 2008).
Smart Nanoconcretes and Cement-Based Materials. https://doi.org/10.1016/B978-0-12-817854-6.00027-1 Copyright © 2020 Elsevier Inc. All rights reserved.
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Smart Nanoconcretes and Cement-Based Materials
Nanotechnology is swiftly becoming the industrial revolution of 21st era (Siegel et al., 1999) and it is going to disturb nearly every single facet of one’s life (IWGN, 1999). Nanotechnology is much less definite and well-structured in comparison to other technologies. The sense of nanotechnology differs from field to field and nation to nation and therefore, best reproduced as a ‘catch-all’ portrayal of tasks at the nanometric scale having vast applications in the real world (Saxl, 2001). Till date, the applications of nanotechnology and its advancements in the field of built environment and building materials have been jagged (Bartos, 2009). Nanoparticles have a high ratio of surface area to volume and are therefore, very reactive (Wiesner and Bottero, 2007). The first document (report RILEM TC 197-NCM) related to nanotechnology in construction materials by Zhu et al. (2004), standardized in a logical way the potentiality of nanotechnology in the growth of construction and building materials. It stated the following: •
• • • • •
The utilization of high performance structural materials such as the nanostructure modification of steel/metals, nanoparticles, nanotubes and nano-admixtures enhances the strength and durability of cementitious materials (Zhan et al., 2003; Bigley and Greenwood, 2003; Li et al., 2004a; Man, 2006; Mitchell, 2009; Gupta, 2013, 2014, 2015 and 2015a) Developing innovative techniques to comprehend phenomena at nanoscale (e.g hydration, shrinkage, durability, strength, etc.) Production of functional thin films/coatings to improve the performance and diminish energy consumption on abrasion resistance, optical, thermal and other applications (Harrington et al., 2010). Development of new sensors, devices and smart structures to improve the monitoring of structural conditions and their abilities at nano-level. Use of nano-materials for sustainable energy, environmental applications, pollution reduction and enhanced performance. Understanding the phenomena of conventional construction materials like concrete, asphalt, plastic and steel, at nanoscale (Gupta, 2014, 2015; Ghaly et al., 2017; Khan, 2018).
Nanotechnology is an empowering technology that permits the development of materials with enhanced or completely new properties. Today, appealing the engineers, especially the civil engineers, to implement nanotechnology could allow them to deliver revolutionary answers to the difficult problems of construction industry. It is a known fact that materials are the fundamental parts of construction industry which could be developed (enhanced) by the utilization of nanotechnology. Though the soaring costs of nano-materials could impede their widened application in today’s time but it is projected that these costs will drop in the near future and would provide beneficial advantages over conventional materials (Gupta, 2013, 2014; 2015).
2.
Nano-materials and cementitious composites
Widespread research is being conducted in the built environment sector for refining the efficiency of many building materials and evolution of durable and sustainable concrete is one of them. Nano-silica is the utmost extensively utilized material in the cement and concrete among all the nano-materials to enhance its efficiency due to
Application of nano-silica in cement mortar and concrete
603
its pozzolanic reactivity and the pore filling effect (Li, 2004; Berra et al., 2012; Gupta, 2013, 2014; 2015, 2015a). The utilization of nano-silica has been studied in various cementitious materials and in this chapter we will look into two main aspects (i) Pastes/mortars, and (ii) Concrete.
2.1
Use of nano-silica in paste/mortar
There have been various researches been conducted throughout the world with respect to the use of nano-silica in paste and mortar. Some of the works have been discussed as follows: Haruehansapong et al. (2014) through their study found the compressive strengths of mortars incorporating nano-silica (nS) and silica fume (SF) and a comparison of the two. The nS used in the study with sizes ranging from 12 to 40 nm. Nine different mixes were prepared with water/binder ratio of 0.65; one control mix, four for nS and other four for SF (3%, 6%, 9% and 12% for both). Test results revealed noteworthy enhancement in strength but were dependent on size of nano particles. 40 nm sized nano-particles exhibited higher strength than others because of their agglomeration and unproductive dispersion. The optimum content was found to be 9% in both the cases. Shaikh et al. (2014) through their study found out the effect of nano-silica on mortars and concretes by conducting various experiments. Eight different mixes were prepared with 1%e6% (by wt.) of nS as a replacement of cement. Compressive strength was found at 7 and 28 days. It was found that 2% nano-silica content exhibited highest enhancement in strength in both 7 and 28 days. Adak et al. (2014) experimentally considered the effect of nano-silica on cement mortars. Colloidal nano-silica with altering percentages of fly ash was added. Adding 6% nano-silica in the fly ash, revealed an enhanced compressive strength at 7 and 28 days. Also, at the same percentage flexural strength and split tensile strength increased from the control value. Oltulu and Sahin (2013) investigated the effect on compressive strength and capillary water absorption on the addition of nano-SiO2 (nS), nano-Al2O3 (nA) and nanoFe2O3 (nF) powders plus the binary and ternary combinations of these materials on cement mortars containing fly ash (FA). Powder quantities were utilized i.e. 0.5, 1.25 and 2.5 wt % of the binder for all mixtures. The results presented that the addition of any type of oxide powders (nS, nA and nF) at 1.25% enhanced compressive strength of the mortars than the other proportions. The utilization of nS þ nA powders at 1.25% enhanced the compressive strength as compared to the control mix. Among all the combinations, the finest results were found for the mortar at 1.25% weight of cement with nS þ nA þ nF powders. Hou et al. (2013) through their experiments stated a reduction in the permeability when mix was more durable. The reason for this was found by researchers that there was an obstruction to migration of aggressive agents. Nano-silica changed the pore structure of mortar leading to lesser transport property, thereby reducing the pore volume.
604
Smart Nanoconcretes and Cement-Based Materials
Hou et al. (2012) carried out the experiment to assess the consequence of addition of nano-SiO2 on the cement hydration process, gel structure and nanoscale mechanical properties of the cement paste. Cement pastes mixed with and without 5% (colloidal nano-silica/silica fume) at a w/b ratio of 0.4 were prepared and investigated. Results revealed that pozzolanic activity of colloidal nano-silica is higher than that of silica fume and its hydration acceleration outcome was higher in the early age, but this result at the later ages was comparable to that of silica fume. Berra et al. (2012) investigated the influence of nano-size particles of amorphous nano-silica on the rheological behavior and mechanical strength progress of cementitious mixes. Fourteen different mixes were casted using three dosage levels. Cement paste workability was found to be considerably lower than likely for the adopted water/binder ratios. The result of instant interactions between the solution of nano-silica and the liquid phase of cement pastes, which demonstrated the development of gels characterised by an important capacity of water retention in the cementitious mixes. Lucas et al. (2012) reported the usage of nano-SiO2 (nS) and nano-TiO2 (nT) in cement pastes and mortars. Samples with 0e3 wt % nS, 0e12 wt % nT and 0.5 water/binder weight ratio were set and investigated. The results revealed that the flow table values were lessened but the mechanical properties were not considerably influenced by nano-particles in the range taken for the above study. Stefanidou and Papayianni (2012) introduced nano-particles into cement pastes to enhance their properties and generate materials having superior performance. NanoSiO2 manufactured by pyrolysis was incorporated at various percentages (0%, 0.5%, 1%, 2% and 5%) to high-strength cement pastes. These pastes were then tested for their mechanical as well as structural properties at different ages. The addition of superplasticizer in 1% weight by weight of cement decreased the water demand but the strength enhanced varying from 30% to 35%. Even at low dosage of nano-silica, the mechanical and structural properties were affected. Aly et al. (2012) compared the micro-structural, alkaliesilica reaction and the mechanical properties of cement mortars containing waste glass powder (WG) as a replacement of cement with and without colloidal silica (CS). Five different mixes were casted with 20% and 40% replacement with glass powder and 3% CS. The results revealed that the addition of WG has a positive effect on the mechanical properties of cement mortars especially when CS was present. Senff et al. (2010) reported the impact of nano-silica (nS) and silica fume (SF) on the rheology, spread on flow table, compressive strength, water absorption, apparent porosity, unrestrained shrinkage and weight loss of mortars. Samples with nS (0e7 weight %), SF (0e20 wt %) and water/binder ratio between 0.35 and 0.59, were explored through tests. The results revealed that during the rheological measurements, nano-silica with 7 wt% lead to the formation of structures in a faster manner. Senff et al. (2009) incorporated amorphous nano-silica (nS) particles by cement in cement pastes and mortars. The influences of these materials on the fresh properties were studied. Fresh mortar was equipped with binder/aggregate weight ratio of 1:2 and water/binder ratio of 0.35. Even the cement paste was equipped with the same water/binder ratio. The dosage of nS was taken as 0%, 1.0%, 1.5%, 2.0% and 2.5% by the weight of cement. X-ray diffraction test revealed the occurrence of calcium hydroxide
Application of nano-silica in cement mortar and concrete
605
after 9 h in the sample with 2.5 wt% nS. The air content improved by 79% and apparent density reduced by 2.4% when nS was incorporated in the mix. Qing et al. (2007) carried out a study on the influence of addition of nano-SiO2 (nS) on the characteristics of hardened cement paste (hcp) as compared with silica fume (SF). Eight different mixes were cast. For all the pastes, a ratio of 1:0.22:0.025 (cement: water: superplasticizer) was used. Experimental data has revealed that compressive strengths of hcp enhanced with increment in the dosage of nano-SiO2, particularly at early ages. Though, the strengths of hcp decreased somewhat with the increase in the dosage of silica at early ages, but increased at later ages. Ltifia et al. (2001) studied the properties of cement mortars with nano-SiO2 experimentally. Mortar mixes were prepared for 0%, 3% and 10% dosage of nano-silica by weight of cement with the same w/b ratio. From the results, it was seen that nano-SiO2 made the cement paste thicker and the cement hydration process was accelerated. Compressive strengths improved on more addition of the dosage of nano-SiO2.
2.2
Use of nano-silica in concrete
Jalal et al. (2015) investigated the properties like chloride penetration, water absorption and electrical resistivity which are identified with the durability of high strength self-compacting concrete (SCC) by utilizing nano-silica and silica fume. Portland cement was substituted by various dosage of micro silica (10%), nano-silica (2%) and a blend of micro as well as nano-silica (10% þ 2%). Twelve concrete blends were taken into account with a consistent water/binder ratio of 0.38. Both water and capillary retention results revealed substantial enhancement with the inclusion of admixtures, specifically the mixture of micro and nano materials for binder content of 500 kg/m3. Ghafari et al. (2014) carried out an exploratory investigation on the effect of nanosilica on the characteristics of ultra-high performance concrete. Compressive strength enhanced with the increment in the nano-silica content, exclusively at early ages. The optimum content was found to be 3% by weight. Proper dispersion was a critical parameter to enable the integration of greater fractions of nano-silica into the cement pastes. Zhang and Islam (2012) considered experimentally the impact of nano-silica (nS) on the setting times and early age strengths of high volume slag mortar and concrete. The influence of nS quantities, size and dispersion approaches on the strength development of high volume slag mortars were examined. It was found that the addition of a small dosage of nS decreased setting times, and enhanced 3 and 7-day compressive strengths of high-volume slag concrete, substantially, in contrast with the reference slag concrete with zero dosage of silica. Said et al. (2012) studied the impact of colloidal nano-silica on concrete including single (ordinary cement) and binary (ordinary cement þ Class F fly ash) binders. Six blends were arranged and Class F fly ash was utilized in three blends. The nano-silica utilized was in a colloidal type of an aqueous solution with 50% amount of SiO2. So as to accomplish a consistent level of workability, a high-range water reducing admixture (HRWRA) was utilized at diverse amounts for all the blends. Coarse aggregates used
606
Smart Nanoconcretes and Cement-Based Materials
in the blends was well-graded natural gravel. Significant improvement was seen in the blends including nano-silica regarding reactivity, development of strength, pore structure refinement and interfacial transition zone densification. Micro-structural and thermal analyses demonstrated that the influence of pozzolanic and filler impacts the pore structure refinement that relied upon the amount of nano-silica. Quercia and Brouwers (2010) experimentally carried out an investigation and devised a methodology to decrease the amount of the cement content in concrete mixes by the utilization of silica fines. A new nano-silica (nS) can be generated in high amounts and for low costs allowing for large-scale application in concrete. Concrete become financially more attractive by the utilization of nS. With the utilization of nS, the CO2 footprint of the produced concrete products is also reduced to great extent. This leads to a concrete which gives better efficiency, reduced costs and enhanced ecological footprints. Givi et al. (2010) explored the influence of the size of SiO2 nano-particles on various properties such as compressive, flexural and tensile strength of binary blended concrete. Two distinctive SiO2 nano-particles with the diameter of 15 and 80 nm (average) were utilized. An aggregate of three arrangements of blends were set up in the research facility premises. The control specimens (C0) comprised of natural aggregates, cement and water. Series FN (15 nm) and CN (80 nm) were prepared with diverse quantities of SiO2 nano-particles. The results revealed that SiO2 nanoparticle advantageously replaced the amount of cement by up to maximum of 2.0%. Despite the fact that the ideal substitution level of nano-SiO2 particles for 15 and 80 nm size were picked up at 1.0% and 1.5%, respectively. Ji (2005) experimentally found the water permeability resistant behavior and microstructure of concrete with nano-SiO2. NC (normal concrete) and SC (nano-silica concrete) were the mix proportions prepared and tested in this work. Results revealed that SC was stickier than NC because the specific surface area is large. Also, the water permeability test showed that the SC has better water permeability resistant behavior than NC. Li et al. (2004b) experimentally studied the properties of high-volume fly ash highstrength concrete including nano-SiO2 (SHFAC). Portland cement was utilized in the mix formation. The water/binder ratio was kept constant throughout having value of 0.28 for the concrete mixes with diverse dosage of superplasticizer. This was done to keep the fluidity of concretes intact because of the impact of various mineral admixtures. The results revealed that fly ash has low initial reactivity, but the pozzolanic reactivity expressively improved after addition of a very small amount of nanoSiO2. It was also found that by adding nano-SiO2 to high-volume high-strength concrete, there is a significant rise in short-term and long-term strengths.
3.
Mortar containing nano-silica: a case study
3.1
Preparative method
Ordinary Portland cement (OPC) 43 grade having specific gravity: 3.15; consistency: 29%; fineness: 2%; soundness: 1 mm; initial setting time (IST): 120 min; and final
Application of nano-silica in cement mortar and concrete
607
setting time (FST): 175 min has been used in this work. Fine aggregate is river sand conforming to grading Zone-II of IS:383e1970 (spherical structure; maximum grain size: 2 mm; specific density: 2.65). Twelve cement mortar mixtures M0 to M5 (without super plasticizer) and MS0 to MS-5 (with super plasticizer) were prepared with varying nano-silica from 0.5% to 1.5% at the interval of 0.25% as given in Table 27.1. Nano-silica might not show an even spreading in the mixture because of its large surface area. It may directly disturb the physical and mechanical properties of the mortars. After numerous pilot tests, the procedure for the manufacture of specimen was then finalized for the study. The final mixture was poured into molds of 70.6 mm 70.6 mm 70.6 mm and after vibration for 2 min, the specimens were left to harden. After 24 h, the demoulded mortar specimens were stockpiled in curing tanks holding water at a temperature of 20 2 C until testing was carried out. Three specimens were set for each mixture. The compressive strength tests, water absorption tests and ultra-sonic pulse velocity tests were carried out on the hardened specimens. Compression tests were done at a rate of loading of 0.5 MPa/s at early ages (1, 3 and 7 days), at standard age (28 days), and at later ages (90 and 180 days) conforming to IS: 516e1959. Ultrasonic pulse velocity (UPV) technique is used to study the relationships between internal structure, mechanical properties and dynamic modulus of elasticity (Ed) of numerous materials. UPV measurements of all the mortars were determined according to the standard of IS: 13311-(part-1)-1992 (Reaffirmed, 2004). UPV is used to forecast and assess the mechanical properties of several materials by non-destructive means. UPV tests were carried out at same ages as of compressive strength and on the same samples. Longitudinal wave measurements were taken by using PUNDIT non-destructive ultrasound equipment (transducer frequency of 54 kHz) (Fig. 27.1). The investigations were carried out for replacement of cement with nano-silica varying from 0.5% to 1.5% at the interval of 0.25%. Results obtained through the replacements of cement with of nano-silica in cement mortars are presented with the analysis of various properties.
3.2
Fresh properties
The consistency of cement pastes for mixes M0 to M5 was observed to increase from 29% to 32%, with 29% for control mix (M0) and similar trend of increase was observed for mixes MS-0 to MS-5 from 22% to 25% with 22% for control mix with super plasticizer (MS-0). Decrease in IST and FST was also observed for both M and MS mixes, on increasing the percentages of nano-silica (Table 27.1).
3.3
Compressive strength study
Table 27.2 give the results for mortars containing nano-silica, while the distinction of compressive strength with respect to the ages (1, 3, 7, 28, 90 and 180 days) is given in Fig. 27.2. It is clearly evident from the figure that the strength of all mortar mixes encompassing nano-silica increased with age from 1 day to 90 days. Still, the rate
608
Table 27.1 Mix design of 12 mortar samples. Mortar mixes M-0
M-1
M-2
M-3
M-4
M-5
MS-0
MS-1
MS-2
MS-3
MS-4
MS-5
Cement (gm)
200
199
198.5
198
197.5
197
200
199
198.5
198
197.5
197
Sand (gm)
600
600
600
600
600
600
600
600
600
600
600
600
w/b ratio
0.3
0.3
0.3
0.3
0.3
0.3
0.23
0.23
0.23
0.23
0.23
0.23
Nano-silica %
0
0.5
0.75
1.0
1.25
1.5
0
0.5
0.75
1.0
1.25
1.5
SP %
0
0
0
0
0
0
1
1
1
1
1
1
31
32
28
33
32
34
32
34
31
33
29
31
Mortar temp C
31
34
30
35
35
38
31
36
33
36
32
34
Relative humidity %
70
63
74
61
61
72
61
51
67
59
75
62
o
Air temp C o
Here, SP¼ Superplasticizer; w/b ratio ¼ water to binder ratio; temp ¼ temperature.
Smart Nanoconcretes and Cement-Based Materials
Properties
Application of nano-silica in cement mortar and concrete
609
Fig. 27.1 Specimen testing using Ultrasonic pulse velocity method equipment.
Table 27.2 Compressive strength values of mortars containing nano-silica. Compressive strength (MPa) Sr. no.
Mix
1 day
3 days
7 days
28 days
90 days
180 days
M0
17.70
23.46
41.46
47.41
49.87
51.94
M1
18.12
26.32
45.18
52.90
55.38
57.29
M2
18.30
27.04
44.51
51.63
54.25
55.31
M3
17.89
25.32
44.30
49.29
52.7
53.78
M4
17.09
24.97
42.24
48.98
51.24
53.14
M5
16.80
24.15
41.86
48.22
50.98
52.91
MS0
17.91
28.64
42.63
51.86
54.35
56.17
MS1
21.23
35.13
48.08
54.81
57.82
59.51
MS2
23.13
35.97
51.37
59.27
61.88
63.28
MS3
25.61
36.79
52.76
63.69
65.91
67.83
MS4
24.97
35.42
49.71
60.64
62.35
64.11
MS5
24.51
34.28
47.14
58.04
60.13
61.59
of increment in the strength varied with the quantity of the nano-silica as compared to that for the control mixes. It is evident from Fig. 27.2 that the highest compressive strength was obtained for the mixes designated as M1 and MS-3. Results revealed that the addition of nS improves the compressive strength of cement mortars added with/without superplasticizer, optimized at 0.5% for mortars mix without super plasticizers and 1.0% for mortar mix with super plasticizer. This is in accordance with the similar study being conducted by Ji (2005) where the filler consequence was displayed by nS and its
610
Smart Nanoconcretes and Cement-Based Materials 80.00
1 day M Compressive Strength (MPa)
70.00
1 day MS
60.00
3 day M 3 day MS
50.00
7 day M 40.00
7 day MS 28 day M
30.00
28 day MS
20.00
90 day M 10.00 0.00 1
2
3
4
5
6
Mixes
Fig. 27.2 Compressive strength values of various mortar mixes with respect to the ages (without and with superplasticizer).
capability to make a further strong matrix and aggregateecement paste interface. The results of this study are compatible with existing literature.
3.4
Ultra-sonic pulse velocity study
Ultra-sonic pulse velocity (UPV) test was carried out on all the specimens to find the homogeneity, quality and dynamic elastic modulus of concrete. Propagation speed of sound waves within material structure depends on the type and inner characteristics of the material. This property helps to provide information about the inner structure of the material. A high transmission rate of sound means less pores and, thus higher strength. When pulse is transferred to the material by a transducer, it endures multiple reflections at the boundaries of diverse phases within the material. Assessing the quality of materials by UPV measurements is done by an apparatus that generate appropriate pulses and precisely measures the time of transmissions. The velocity of a pulse of longitudinal ultrasonic vibrations traveling in an elastic solid is given by Eq. (27.1). V2 ¼
Eð1 uÞ pð1 þ uÞð1 2uÞ
where. V: pulse velocity (m/s) E: dynamic elastic modulus (N/mm2) p: density (kg/m3), u: Poisson’s ratio which was taken as 0.24 as per IS: 13311-(part-1)-1992
(27.1)
Application of nano-silica in cement mortar and concrete
611
Table 27.3 Elastic modulus values of various mortar mixes. Elastic modulus (MPa) Sr. No.
Mix
1 day
3 day
7 day
28 day
90 day
180 day
M0
45622
47097
50263
53836
53980
54136
M1
47426
47985
51467
55121
56603
56997
M2
48341
49207
52623
54594
55559
55719
M3
47235
48576
51062
54552
56809
55914
M4
46713
48111
49546
53114
55013
55314
M5
44796
47013
47628
51649
54326
54763
MS0
47667
50427.
52752
54533
55818
56118
MS1
50260
51367.
53587
56574
57263
57648
MS2
51375
51791.
54291
58382
58873
59147
MS3
50894
52758
56062
58926
59110
59934
MS4
49667
50961
54789
57980
57666
58051
MS-5
49386
49091
53116
57455
55757
56040
The dynamic modulus was assessed on the basis of Eq. (27.1), where density was obtained experimentally. The UPV tests were carried out on same specimens as used for compressive strength. Table 27.3 and Fig. 27.3 show the results of the ultra-sonic pulse velocity on mortar specimens. Compared to the control specimen (M0), the increase in elastic modulus values was observed for all ages of the specimens. 65000 1 day M 1 day MS
Elastic Modulus (MPa)
60000
3 day M 3 day MS 7 day M
55000
7 day MS 28 day M
50000
28 day MS 90 day M 45000
90 day MS 180 day M 180 day MS
40000 1
2
3
Mixes
4
5
6
Fig. 27.3 Elastic modulus values of various mortar mixes with respect to the ages (without and with superplasticizer).
612
Smart Nanoconcretes and Cement-Based Materials
The optimum results were obtained for the specimen designated as M-1(early ages), M2 (later ages) and MS-3 mortars. The increase in elastic modulus of mixes without super plasticizer at 0.5% and 0.75% were may be due to higher particle packing because of the use of nano-silica but on increasing the content of nano-silica to 0.75%, the workability decreased causing small cracks in the structure, leading to lower elastic modulus. Similarly, because of the use of super-plasticizer the workability of the mixes enhanced, with mix MS-3 (with nS 1.0%), having the highest elastic modulus as compare to the control mix.
3.5
Concluding remarks
The main effects of nano-silica on properties of cement mortars are: - The compressive strength of all the mixes containing nano-silica was observed to be higher than the control mix. - Addition of nano-silica (with super-plasticizer), further enhanced the workability of the mortar mix resulting in better particle packing at higher proportions and higher compressive strength as compared to mixes without super-plasticizer. - Nano-silica percentage 0.5% (without super-plasticizer) and 1.0% (with super-plasticizer) were observed to be the optimum percentages. - The elastic modulus of all the mixes containing nano-silica was found to be higher than that of the control mix. The increase in elastic modulus may be due to the increase in the particle packing density due to presence of nano-silica but after certain percentages, low workability is observed as mixes are not compacted properly, leading to cracks in the structure, causing reduction in elastic modulus and strength of the specimen.
4.
Concrete containing nano-silica: a case study
4.1
Preparative method
The concrete with grade M25 has been used with ordinary Portland Cement 43 grade (normal consistency: 32%). For aggregates, their specific gravities are 2.65 and 2.72 for fine and coarse aggregates, respectively. Mix ratio of (cement: sand: aggregate: water) is (1: 1.41: 2.75: 0.43). This mix proportion was designed taking into consideration all the material properties and in accordance with Indian Standard code IS: 102622009. Nano-silica particles have the average size of 230 nm. The content of nano-silica in concrete varies from 0.3 % to 1% by weight of cement.
4.2
Compressive strength study
For carrying out the compressive strength test on concrete, cubes of size 150 150 150 mm were casted. Their compressive strength values were presented in Table 27.4. As seen in Table 27.4, there is an increment in the compressive strength of concrete on adding of a definite minimum amount of nano-SiO2 (NS). The increment in compressive strength has a maximum value for NS at 1% by weight of cement,
Application of nano-silica in cement mortar and concrete
613
Table 27.4 Compressive strength values of concrete samples. 7 days compressive strength (MPa)
28 days compressive strength (MPa)
Control mix (0% nano-silica)
26.30
35.4
2
M1 (0.3% by weight of cement)
27.6
35.2
3
M2 (0.6% by weight of cement)
31.1
36.5
4
M3 (1% by weight of cement)
34.6
39.8
S.No.
Specimen
1
and minimum value for NS at 0.3% by weight of cement. There is a considerable increment in the early-age strength of concrete as compared to the 28 day increase in the strength on addition of NS. It is shown from the results that there is an enhancement in the early strength of concrete with the replacement of cement with nano-silica but later the increment in the strength is reduced. This is because of the micro-filling effect of the nano-silica particles. The more the silica particles, the more they will inhabit the pores in the gel and makes the microstructure even and consistent. The increment in the strength is because of the presence of adequate amount of silica making the microstructure denser and consistent.
4.3
Ultra-sonic pulse velocity study
Table 27.5 presents the data obtained from UPV test for these concrete samples. From the results of the UPV test, it was evident that the quality of concrete was very good. The results clearly revealed that the 28-days quality of concrete is better than that of the 7-days. The control mix specimen was found to have better quality in comparison to the blended concrete specimen. 0.3 % nano-silica means a better packed microstructure whereas for 1% nano-silica in concrete, the microstructure is more dense, and therefore enhances the strength of concrete. On addition of the NS, it was seen through the UPV test that there is a slight impact on the quality of concrete but the overall quality of concrete gets preserved.
4.4
Concluding remarks
The main effects of nano-silica on properties of concrete are: - There is an increment in the compressive strength of concrete on adding of a definite minimum amount of nano-SiO2 (NS). The increment in the compressive strength is maximum for NS at 1% by weight of cement and least for NS at 0.3% by weight of cement. - There is a considerable increment in the early-age strength of concrete as compared to the 28 day increase in the strength on addition of NS.
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Smart Nanoconcretes and Cement-Based Materials
Table 27.5 UPV values of concrete samples (7 and 28 days test).
S.No.
Concrete samples
1
Control mix (0% nano-silica)
2
3
4
M1 (0.3% by weight of cement)
M2 (0.6% by weight of cement)
M3 (1% by weight of cement)
7 days velocity (m/s)
7 days time (ms)
28 days velocity (m/s)
28 days time (ms)
4675
32.1
4808
31.2
4704
31.9
4854
30.9
4777
31.5
4777
31.5
4491
33.3
4673
32.1
4491
33.3
4732
31.8
4389
34.3
4856
31.0
4630
32.5
4704
31.9
4630
32.5
4777
31.5
4704
31.9
4777
31.5
4491
33.3
4658
32.3
4360
34.5
4704
31.9
4560
33.0
4808
31.2
- The increment in the strength is because of the presence of adequate amount of silica making the microstructure denser and consistent. - The quality of concrete was very good as per the ultrasonic pulse velocity test as per the codal provisions. The results clearly revealed that the 28-days quality of concrete is better than that of the 7-days. - In terms of UPV test, the control mix specimen was found to have better quality in comparison to the blended concrete specimen. - On addition of the NS, it was seen through the UPV test that there is a slight impact on the quality of concrete but the overall quality of concrete gets preserved.
Thus, it can be concluded that the use of nano-structured materials in both cement mortar and concrete can complement several advantages directly related to the various properties such as fresh, mechanical and durability properties of these materials. It also makes it possible to decrease the quantities of cement in the composites, thereby, opening new avenues for the utilization of nano-particles in the construction industry.
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