584840

research-article2015

WMR0010.1177/0734242X15584840Waste Management & ResearchMukharjee and Barai

Original Article

Development of construction materials using nano-silica and aggregates recycled from construction and demolition waste

Waste Management & Research 1­–9 © The Author(s) 2015 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/0734242X15584840 wmr.sagepub.com

Bibhuti Bhusan Mukharjee and Sudhirkumar V Barai

Abstract The present work addresses the development of novel construction materials utilising commercial grade nano-silica and recycled aggregates retrieved from construction and demolition waste. For this, experimental work has been carried out to examine the influence of nano-silica and recycled aggregates on compressive strength, modulus of elasticity, water absorption, density and volume of voids of concrete. Fully natural and recycled aggregate concrete mixes are designed by replacing cement with three levels (0.75%, 1.5% and 3%) of nano-silica. The results of the present investigation depict that improvement in early days compressive strength is achieved with the incorporation of nano-silica in addition to the restoration of reduction in compressive strength of recycled aggregate concrete mixes caused owing to the replacement of natural aggregates by recycled aggregates. Moreover, the increase in water absorption and volume of voids with a reduction of bulk density was detected with the incorporation of recycled aggregates in place of natural aggregates. However, enhancement in density and reduction in water absorption and volume of voids of recycled aggregate concrete resulted from the addition of nano-silica. In addition, the results of the study reveal that nano-silica has no significant effect on elastic modulus of concrete. Keywords Colloidal nano-silica, compressive strength, density, recycled aggregate concrete, water absorption, volume of voids

Introduction The increase in the use of concrete in various sectors requires a huge quantity of natural aggregates, as aggregates are the key filler materials in concrete. The worldwide aggregates consumption is about 20,000 billion kg per year, with a forecasted annual growth rate of 4.7% (Pacheco-Torgal, 2013). Therefore, Japan and several other countries around the world have been facing shortages of natural aggregates (Otsuki et al., 2003). To mitigate this problem, aggregates have been produced artificially, or from other sources such as various recycled waste materials. To reduce the impact on the environment, several waste materials have been utilised as a replacement of cement in various works (Del Río Merino et al., 2010). The waste materials generated from demolition of old buildings or construction of civil engineering infrastructures are generally termed as construction and demolition waste (CDW), which if not properly managed can cause several problems, like environmental pollution and shortage of lands for disposing of such materials (Tam and Tam, 2009; Coelho and de Brito, 2011). Simultaneously, setting up of a new source of aggregates is urgently required, as the natural sources of aggregates will be depleted in the long run (PachecoTorgal and Jalali, 2011a). Therefore, utilisation of this waste concrete as recycled aggregates (RAs) for production of new concrete can lessen the use of non-renewable materials and

provide an alternate, and more eco-friendly, destination to this waste, thereby proving beneficial from the viewpoint of environmental protection and preservation of natural resources (Hansen, 1986; Hao et al., 2008; Lin et al., 2010). As RAs are generally manufactured by crushing and grinding, the adhered cement paste of RAs are not properly removed. The coarse fraction of RA used for replacement of natural coarse aggregate (NCA) is termed recycled coarse aggregate (RCA). RCA can be considered as a small piece of concrete since it is composed of original coarse aggregates and adhered mortar. Therefore, these aggregates exhibit higher water absorption, lower density and higher porosity compared with NCA (de Juan and Gutiérrez, 2009; Simultaneously, setting up Nixon, 1978; Tam and Tam, 2009). Previous studies concluded that compressive strength (CS) of fully recycled aggregate concrete (RAC) decreased up to

Department of Civil Engineering, Indian Institute of Technology Kharagpur, Kharagpur, India Corresponding author: Bibhuti Bhusan Mukharjee, Department of Civil Engineering, Indian Institute of Technology Kharagpur, IIT Kharagpur, Kharagpur 721302, India. Email: [email protected]

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25% as compared with NACs (Ajdukiewicz and Kliszczewicz, 2002; Rahal, 2007; Rakshvir and Barai, 2006; Rao et al., 2011). The decrease in split and flexural tensile strength of RAC was in the order of 10% when compared with those values of NAC (Ajdukiewicz and Kliszczewicz, 2002). It was observed that a modulus of elasticity (E) of 100% RAC was 45% lower than that of concrete with virgin aggregates (Ajdukiewicz and Kliszczewicz, 2002; Xiao et al., 2005). In addition, drying shrinkage, creep and water absorption of concrete increased up to 50% when NCA is replaced with RCA (Domingo et al., 2010; Li, 2008). Freezing and thawing resistance was also reduced when aggregates are replaced with RAC (Salem et al., 2003; Zaharieva et al., 2004). However, the carbonation depth behaviour of RAC was found to be similar with normal concrete (Levy and Helene, 2004; Otsuki et al., 2003). Similarly, the chloride penetration of RAC was similar or slightly increased as compared with that of natural aggregate concrete (NAC) (Ann et al., 2008; Otsuki et al., 2003). Previous studies reported that mechanical and durability behaviours of RAC were inferior to those of normal concrete. Several techniques were adopted for enhancing the qualities of RCA, including various mixing methods. For instance, RCAs were soaked in three different acids (hydrochloric acid, sulphuric acid and phosphoric acid) for a period of 24 h at temperatures around 24 °C. The results showed that the values of water absorption of the pre-treated RCA significantly reduced and improvement in mechanical properties for the RAC was observed (Tam et al., 2007a). In addition to the soaking approaches, a two-stage mixing approach (TSMA) was developed for improvement of RAC, in which the total quantity of mixing water was divided into two parts. One half of the required water was utilised for mixing during the first stage of mixing leading to the development of a thin layer of cement slurry on the surface of RCA, which would permeate into the porous old cement mortar, filling up the old cracks and voids. In the second stage of mixing, the residual amount of water was added to complete the concrete mixing process (Tam et al., 2007b). A novel triple mixing method was adopted to realise surface coating of RCA with silica fume and fly ash for further improvement of microstructure and properties of RAC (Kong et al., 2010). Enhancement of mechanical and durability properties of RAC could be achieved by incorporating various pozzolanic materials in concrete mixes (Kong et al., 2010; Tangchirapat et al., 2008). The newly developed nano-sized particles have significantly improved properties from traditional grain-size materials with similar chemical composition. The application of newly developed nano-materials in cement-based materials has grown considerably since these particles are very effective in filling the empty spaces of the C–S–H, augmenting the rate of hydrations by acting as nucleation centres and diminishing the size of Ca(OH)2 crystal (Pacheco-Torgal et al., 2013). Silica nanoparticles are most popular nano-particles among all available nano-materials to be applied in the field of cement and concrete (Pacheco-Torgal and Jalali, 2011b). In this study, ‘NS’ was used

as an abbreviated form for silica nano-particles or nano-silica. Previous investigation confirmed that NS had a higher pozzolanic activity than silica fume (SF) during early days owing to the higher rate of consumption of Ca(OH)2 crystals; hence, the strength of cement paste containing NS was higher than that of SF incorporated paste (Qing et al., 2007). Moreover, the mechanical properties of cement mortar improved with the addition of NS (Lin et al., 2008). Previous studies revealed that concrete containing NS had better water permeability resistant behaviour and CS than concrete without NS. This was because silica nano-particles filled the minute pores of the C–S–H gel structure and acted as nucleus to tightly bond with C–S–H gel particles, making the binding paste matrix dense (Ji, 2005). Incorporation of colloidal NS enhanced compressive and tensile strength of concrete along with reduction of porosity of concrete, which was attributed to the physical filler effect in the cementitious matrix (Said et al., 2012). The addition of 3% NS led to an increase in CS of RAC and a reduction in water absorption (Hosseini et al., 2011). This improvement of behaviour of concrete was attributed to the fact that NS filled the pores present in the attached mortar RCA and improved microstructure of RAC. From the detailed review of literature available in the field of RA concrete and application of nano-materials in cement and concrete the following general observations were found. •• RCA had lower density, higher water absorption, and inferior physical and mechanical properties as compared with that of virgin aggregates. •• Experimental studies showed that up to 30% RCA had no significant effect on the CS of RAC; however, thereafter reduction of strength occurred with increasing percentages of RCA. •• Although split tensile strength, flexural strength, abrasion resistance and other engineering properties of RAC were inferior to that of NAC, these values were found to be within permissible limits. •• Improvement of properties of RAC could be brought by either improving aggregate characteristics or strengthening the bonding between the aggregates and paste. •• Increasing the crushing stages, presoaking with acids and ultrasonic cleaning techniques could be useful in enhancing the quality of RCA. •• The properties of RAC could be improved with adopting a two-stage or three-stage mixing approach, modified TSMA or addition of pozzolanic materials. •• Application of nano-technology was quite useful in devolving new nano-materials to be applied in cement and concrete products. •• Mechanical and durability characteristics of cement mortar and paste could be improved with the addition of NS. •• Comparisons of experimental values of elastic modulus with different numerical proposals. •• Study of water absorption, density and volume of voids of RAC mixes containing NS.

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Mukharjee and Barai Table 1.  Properties of colloidal NS. Colour

Specific gravity

pH value

Solid content

Particle size

SiO2 content

White

1.12

10.11

39%

8–20 nm

99.1%

Experimental programme Materials Ordinary Portland Cement (OPC) of 43 Grade, having a consistency of 32%, specific gravity 3.12 and fulfilling the requirements of the Bureau of Indian Standard Specifications (BIS) (IS 8112, 1989), was used to cast all concrete specimens in the experimental work. The experimental programme was completed within one month of receipt of cement. Standard tests have been performed to characterise the cement and the results of those tests are presented in Table 1. The NS used in this experimental programme was commercially available colloidal NS that was a suspension of fine amorphous, non-porous and typically spherical particles in liquid phase. The cost of colloidal NS was the equivalent to the cost of superplasticiser, as per manufacture’s information. The properties of NS are illustrated in Table 1. Transmission electron microscope (TEM) analysis of NS has been conducted and the obtained image is presented in Figure 1. TEM is one of the microscopic techniques engaged for determination of particle size of nano-particles, since direct measurement of nano-particles is not practically feasible. The TEM image of NS presented in Figure 1 has been taken in bright field mode. It was also observed from the picture that the particles were spherical in shape and present in non-agglomerated form. The analysis TEM picture revealed that the particle size of the colloidal NS was found to be varying between 8 to 20 nm, which was analogous to the results of the X-Ray Diffraction (XRD) analysis. Crushed dolerite of 20 mm nominal size was employed as NCAs for producing concrete mixtures. The RCAs were prepared from the waste concrete collected from a 30-year-old demolished building of Jhargram, West Bengal (a city of Eastern India). Locally available river sand conforming to Zone II specification of IS 383 (1970) was used as a natural fine aggregate (NFA) in concrete mixes. Standard tests have been performed to characterise aggregates and results of those tests are presented in Table 2.

Concrete mixtures The details of quantities of materials for mix proportioning of one metre cubed of concrete containing RCAs and different amount of NS as a replacement of cement are presented in Table 3. The water cement ratio was kept constant as 0.4 for all mixes and three different amounts of NS (0.75%, 1.50% and 3.00%) by weight of cement were used for production of concrete mixes. The amount of water present in colloidal NS should be taken into account while finding out the total quantity of water required for production concrete mixtures. Normal tap water, available in laboratory confirmed to fulfil the standards of drinking water, was used for

Figure 1.  TEM of NS.

the manufacture of concrete mixtures. Two sets of concrete mixtures were produced: one set incorporating NCA and another set using fully RAC. The reference concrete or control concrete containing NCA without NS was designed along with the above mixes. To mitigate the additional water requirements of RCA, additional 10% water along with a stipulated amount of water was added in the RAC mixtures.

Specimen casting and curing Initially, colloidal NS was mixed with water and stirred properly (mixed in a small concrete mixer) to avoid agglomeration of particles and to achieve uniform dispersion of silica nano-particles. After that, the cement, sand and coarse aggregates were mixed at a low speed for 2 min in a concrete rotary mixer. After mixing for 2 min, the mixture of NS and water was slowly poured in and stirred at a low speed for another 2 min to achieve desired workability (slump value 50 mm to 80 mm). The fresh concrete was collected from the mixer, poured in to the specified moulds and kept for 24 h under a controlled environment. After 24 h, the specimens were removed from the moulds, and traditionally cured by storing them under water.

Testing of specimens The CS test was carried out on standard cubes of size 150 and 100 mm, and on cylindrical specimens of 150 mmФ × 300 mm height using a 3000  kN compressive testing machine in

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Table 2.  Properties of aggregates. Apparent specific gravity

Type of aggregate

Bulk density (kg m−3)



Loose

Compact

FA NCA RCA

1525 1504 1321

1698 1654 1418

Specific Gravity

Impact value (%)

Los Angeles abrasion value (%)

Crushing value (%)  

2.66 2.81 2.67

2.62 2.72 2.46

– 15.35 34.85

– 19.72 36.56

– 15.11 31.52

NFA: natural fine aggregate; NCA: natural coarse aggregate; RCA: recycled coarse aggregate.

Table 3.  Proportions of mixtures per cubic metre of concrete. Mixture

Cement (kg)

NCA (kg)

RCA (kg)

NFA (kg)

NS (kg)

Water (kg)

NAC 1 NAC 2 NAC 3 NAC 4 RAC 1 RAC 2 RAC 3 RAC 4

450.000 446.625 443.250 436.500 450.000 446.625 443.250 436.500

1180 1180 1180 1180 – – – –

– – – – 1067 1067 1067 1067

640 640 640 640 640 640 640 640

– 3.375 6.750 13.500 – 3.375 6.750 13.500

180 180 180 180 180 180 180 180

NAC: natural aggregate concrete ; NCA: natural coarse aggregate; NFA: natural fine aggregate; NS: nano-silica; RAC: recycled aggregate concrete; RCA: recycled coarse aggregate.

accordance with the procedures given in BIS (IS 516, 1959). The CS of 100 cubes was determined at 3, 7 and 28 days, and the CS of 150 mm cubes and cylinders were found out after 28 days curing. The modulus of elasticity or elastic modulus of concrete at 28  days was determined on cylindrical specimens of 150 mmФ × 300 mm height using a 3000 kN compression testing machine according to the procedure given in ASTM C469 (2002). The density, water absorption and volume of voids of hardened concrete were determined on samples of 100 mm cube as per the procedures given in ASTM C 642 (2006). Initially, the dry mass (M1) of the sample was determined by drying the samples in an oven at 100 °C to 110 °C. Then the samples were immersed in water for 48 h and saturated surface dry weight (M2) was determined by allowing them to dry in natural air for a period of 24 h. After that, the samples were boiled for at least 5 h in tap water and allowed to cool by natural loss of heat for not less than 14 h and surface dry mass (M3) was recorded. Finally, the specimens were suspended in water and dry weight was measured (M4). The density, water absorption and volume of voids were calculated using the following equations:

Bulk density =

M1 ×ρ M3 − M 4

(1)



Volume of voids =

M 3 − M1 × 100 M3 − M 4

(2)



Water absorption =

M 2 − M1 × 100 M1

(3)

where ρ is the density of water.

Results and discussion Compressive strength The results of the CS test for different percentages of NS are presented in Figure 2(a). It can be seen that 3 days CS of control concrete is 31.35 MPa and increases to 35.37 MPa with the addition of 3% NS, which indicates an increase of CS of 10%. The early gain of strength could be attributed to the high pozzolanic action of colloidal NS. It can also be indicated that the 3-day CS of fully RAC is 28.34 MPa which shows a 10% reduction of the CS as compared with the control concrete. This reduction of strength is because of the inferior quality of the RCA compared with NCA (Ajdukiewicz and Kliszczewicz, 2002). However, the addition of NS to RAC enhances the CS and with 3% NS the CS value is more than that of the control concrete. The previously mentioned improvement of early strength of RAC with the incorporation of NS is owing to the filling of voids of the porous aggregate–cement matrix (Pacheco-Torgal et al., 2013). It can be seen that 7 days CS of NAC with 3% NS improves 14% compared with the control concrete, which signifies that incorporation of NS improves quality of concrete. However, the CS of 100% RAC is 14% lower than that of the control concrete, which is owing to the poor quality of aggregates. On the other hand, the CS improves with the addition of NS and the strength of RAC containing 3% NS is similar to that of the normal concrete. The 28 days CS of concrete containing NS is similar to 3 and 7 days CS. The CS of NAC with 3% NS is 25% more than that of the control concrete. The 14% decrease of CS of the concrete owing to replacement of natural aggregates by RCA is compensated by adding 3% NS and CS of 3% NS-incorporated RAC is more than that of control concrete. The improvement of the CS of both

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Mukharjee and Barai 3 days strength

0 % NS

40

7 days strength 50

0.75 % NS 35

28 days strength

Moduls of Elasticity (GPa)

Compressive Strength (MPa)

60

40 30 20 10

1.5 % NS 3 % NS

30 25 20 15

0 NAC1 NAC2 NAC3 NAC4 RAC1 RAC2 RAC3 RAC4

10 NAC

Mix Type

Compressive Strength (MPa)

60

(a)

Cylinder 150 mm cube

50

RAC Mix Type

100 mm cube

40

Figure 3.  Variation of modulus of elasticity of concrete mixes.

NS: nano-silica.

Modulus of elasticity

30 20 10 0 NAC1 NAC2 NAC3 NAC4 RAC1 RAC2 RAC3 RAC4 Mix Type

(b) Figure 2.  (a) Variation of CS of cubes. (b) Comparison of 28day CS of cubes and cylinders.

NAC: natural aggregate concrete; RAC: recycled aggregate concrete.

NAC and RAC owing to the addition of NS is primarily because of filling of nano-pores of cement matrix by nano-sized particles, which makes the concrete strong compared with the concrete without NS (Hosseini et al., 2011). It is observed that strength development is uniform from 3 days to 28 days for all cases, but development of the CS from 3 days to 28 days for the mixes containing NS is slightly more than other percentage of NS. This difference could be attributed to a high percentage of NS, which is sufficient to fill all voids present in the concrete. Figure 2(b) shows the comparison of the CS of cubes and cylinders of concrete mixtures. It is observed that for the control concrete mix, the CS of cylinders is 32.17 MPa and that of 100 mm cubes is 42.16 MPa; whereas the CS of 150 mm cubes is 40.67 MPa, which indicates that the CS of 100 mm cubes are highest and that of cylinders lowest. Similar types of observation are found for all other mixes. This difference of the CS of cubes and cylinders is owing to the size effect of specimens, which states that an increase in the aspect ratio leads to a decrease in the CS (Neville, 2006). Similar type variations of results of cubes and cylinders could be observed from the previous studies (Bhanja and Sengupta, 2002).

Figure 3 presents the results of the elastic modulus of concrete (E) containing RCA and NS. It can be observed that elastic modulus GPa, which increased to of the control concrete is 32.763  34.06 GPa with the addition of 3% NS. However, this increment is not so significant as compared with that of the CS of concrete because the elastic modulus value of concrete is not significantly influenced by the presence of mineral additions (Corinaldesi and Moriconi, 2009). A RAC mix without NS has an elastic modulus value of 23.081 GPa, which is about 30% lower than that of control mix. The reduction of elastic modulus could be attributed to the fact that the modulus of elasticity of RAs is lower than that of natural aggregates. Moreover, a 50% reduction in modulus of elasticity was reported when the NCAs of concrete were replaced by RAs (Rao et al., 2011). It can be seen that the elastic modulus of RAC increases slightly with the addition of NS, which illustrates that addition of NS to RAC mixes had no significance effect on the modulus of elasticity. It is well known that static modulus of elasticity is primarily governed by coarse aggregate characteristics rather than the addition of minerals (Neville, 2006). The plot between elastic modulus and CS as observed in the present study and in comparison with previous studies (given in Table 4) are presented in Figure 4. It should be noted that the formula for calculating the elastic modulus from CS given in NBR 6118 (2003) and Hueste et al. (2004) is based on a 28 cylinder CS; therefore a correction of 0.8 is adopted for converting cube strength to cylinder strength. For other formulations 28 days CS of 150 mm cubes is used (Neville, 2006). The results of the present study depict that significant difference exists between the elastic modulus of NAC mixes and RAC mixes owing to a difference in quality of aggregates used. Moreover, the reduction of elastic modulus value owing to the replacement of NCA by RCA could not be fully restored by incorporating NS. Therefore, it can be observed that relationships commonly used for relating CS and modulus of elasticity for normal concrete cannot be applied to RA concrete, which

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Table 4.  Formulations for predicting modulus of elasticity (E) from CS (fc). Reference

Formulation

Ravindrarajah and Tam (1985)

E=7770×

Dillmann (1998)

E = 634.43 × f + 3057.6

Dhir et al. (1999)

E = 370 × f + 13100

Mellmann (1999) IS 456 (2000)

E = 378 × f + 8242 E = 5000 × √f

NBR 6118 (2003)

E = 5600 × √f

Hueste et al. (2004)

E = 5230 × √f

√f

c

c

c

c

c

c

c

Ravindrarajah and Tam (1985) Dillmann (1998) Dhir et al.(1999) Mellmann (1999) IS 456 (2000) NBR 6118 (2003) Huesete et al. (2004) Present study

45 40

0 % NS 0.75 % NS 1.5 % NS 3 % NS

7 6 Water Absorption (%)

50

Modulus of Elasticity (MPa)

0.33

35 30

5 4 3 2 1

25

0 NAC

20 35.1

37.48 39.18 41.32 40.67 44.36

45.7

Compressive Strength (GPa)

Figure 4.  Relationship between modulus of elasticity and CS.

has also been reported in previous investigations (Xiao et al., 2005).

Water absorption The variation of water absorption of concrete mixes containing NS is presented in Figure 5. The water absorption of NAC without NS is 4.74%, which decreases to 3.21% owing to the addition of 3% NS. The water absorption of NAC with 3% NS has a water absorption value 32% lower than that of the control concrete. This reduction is mainly owing to the lessening of voids present in the concrete after the addition of NS in the concrete mixes (Said et al., 2012). However, the water absorption increases from 4.74% to 6.60% when the natural aggregates are replaced by RAs. This increase is because of higher water absorption of the RAs than natural aggregates (Nixon, 1978). The addition of NS improves the quality of concrete by filling the voids present in it as indicated from Figure 5. The addition of NS reduces the water absorption from 6.60% to 4.58%; hence, the characteristics of RAC improved owing to incorporation of the NS. This improvement of the RAC water absorption with the addition of NS is because of the filling of minute pores present in the interfacial transition zone of the

RAC Mix Type

49.89

Figure 5.  Variation of water absorption of concrete mixes.

NAC: natural aggregate concrete ; NS: nano-silica; RAC: recycled aggregate concrete.

concrete (Hosseini et al., 2011). The relation between CS and water absorption is shown in Figure 6, which illustrates that the CS decreases with an increase in water absorption. A second degree is used to express this relationship and a high value of determinant coefficient (0.93) indicates the existence of a strong correlation between water absorption and CS. The concrete having less CS contains more voids, hence, absorbs more water. In other words, concrete with a higher strength absorbs less water.

Density The variation of density of concrete mixes with different percentages of NS is shown in Figure 7. It is observed that the density of concrete mixes (both NAC and RAC) is enhanced with the addition of NS and density increases with an increasing percentage of NS. The density of NAC without NS is 2389 kg m−3, which increases up to 2505 kg m−3 with an addition of 3% NS. The increase in density indicates that the concrete becomes dense and voids are minimised owing to incorporation of NS in concrete (Ji, 2005). The density of RAC without NS is 2214.90 kg m−3, which is lower than that of the control concrete. This reduction of density could be owing to the lower density of RAs compared with natural aggregates. The density of RAs is less than natural aggregates as

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60

60

50

50

Compressive Strength (MPa)

Compressive Strength (MPa)

Mukharjee and Barai

40 30

y = 0.8078x2 - 12.511x + 84.034 R² = 0.93

20 10 0 2

3

4 5 6 Water Absorption (%)

7

40 30 20

y = 0.0001x2 - 0.6473x + 740.9 R² = 0.94

10

8

0 2100

2200

Figure 6.  Relation between CS and water absorption.

2300 2400 Density (kg/m3)

2500

2600

Figure 8.  Relation between CS and density. 0 % NS

2600

0.75 % NS 1.5 % NS

16

2400

14 Volume of Voids (%)

Density (kg/m3)

0 % NS 0.75 % NS 1.5 % NS 3 % NS

18

3 % NS

2200

2000 NAC

RAC Mix Type

12 10 8 6 4 2 0 NAC

NAC: natural aggregate concrete; NS: nano-silica; RAC: recycled aggregate concrete.

the mortar attached to RAs are porous and lightweight (Nixon, 1978). However, the addition of NS to RAC mixes improves the density of the mixes and this improvement in density of RAC could be attributed to the filling of voids of old mortar as well as new cement mortar by NS and making the aggregate–cement interface dense and strong (Ji, 2005). Figure 8 demonstrates the relation between CS and density of concrete mixes containing NS. It can be found that the CS increases with increasing density because concrete having a higher density can have the potential to sustain a higher load, hence stress generated will be higher. The relationship between the parameters can be expressed in terms of a quadratic equation and higher value of determination coefficients (0.94) indicates that good correlation exist between two parameters.

Volume of voids The volumes of voids of concrete mixes with different percentages of NS are shown in Figure 9. It can be noticed that the volume of voids in the concrete decreases from 13.1% to 9.36 % with an addition of 3% NS. This decrease in volume of voids is owing

RAC Mix Type

Figure 7.  Variation of density of concrete mixes.

Figure 9.  Variation of volume of voids of concrete mixes.

NAC: natural aggregate concrete ; NS: nano-silica; RAC: recycled aggregate concrete.

to the filling of voids by silica nano-particles (Pacheco-Torgal et al., 2013). Under normal circumstances, the volume of voids of RAC without NS is 16.1%, which is higher than that of the control concrete. This increase in volume of voids is owing to the voids present in the attached mortar of the RAs (Nixon, 1978). However, the addition of NS substantially reduced the volume of voids to 13.29% by filling them with the help of nano-particles (Hosseini et al., 2011). The relation between 28 days CS and volume of voids is shown in Figure 10. The best-fitted line between 28 days CS and volume of voids is a quadratic curve and it indicates that CS decreases with an increasing volume of voids. The determination coefficient is found to be 0.94, which states that strong correlation exists between the CS and volume of voids.

Conclusion This research demonstrates an experimental approach to investigate the combined effects of partial replacement of cement with

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Waste Management & Research References

Compressive Strength (MPa)

60 50 40 30

y = 0.0809x 2 - 4.3693x + 86.057 R² = 0.95

20 10 0 8

10

12 14 16 Volume of Voids (%)

18

Figure 10.  Relation between CS and volume of voids.

colloidal NS and substitution of NCAs by the RCA on the behaviour of concrete. CS, modulus of elasticity, water absorption, density and volume of voids of both NAC and RAC containing different percentages of NS (0, 0.75, 1.50 and 3) have been determined and the conclusions drawn from the analysis of the results of the study are summarised as follows. •• The 3 days CS of concrete was significantly enhanced with the incorporation of colloidal NS owing to the higher pozzolanic activity of NS. The CS of RA concrete at 3, 7 and 28 days was lower than that of the control concrete. However, this loss could be recovered by adding NS. The results of the effect of specimen size on the compressive study of concrete containing RAs and NS was found to be similar to that of normal concrete. •• The reduction of elastic modulus by RA concrete was in the order of 30%, which was owing to the inferior quality of aggregates used. Furthermore, incorporation of NS could not make any significant improvement in the modulus of elasticity of concrete as elastic behaviour of concrete is primarily dependent upon the characteristics of the aggregates rather than on addition of pozzolanic materials. •• Increase in water absorption and volume of voids, and reduction of density was observed for RA concrete mixes prepared without NS owing to the increase in quantity of voids by the use of more porous RAs. However, the addition of NS reduced the water absorption and volume of voids in addition to the enhancement of density, which may be attributed to the fact that silica nano-particles are quite effective in filling the pores present in the old attached mortar of aggregates as well as in the new mortar matrix.

Declaration of conflicting interests The authors declare that there is no conflict of interest.

Funding This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.

Ajdukiewicz A and Kliszczewicz A (2002) Influence of recycled aggregates on mechanical properties of HS/HPC. Cement and Concrete Composites 24: 269–279. Ann KY, Moon HY, Kim YB and Ryou J (2008) Durability of recycled aggregate concrete using pozzolanic materials. Waste Management 28: 993–999. ASTM C469-02 (2002) Standard test method for static modulus of elasticity and Poisson’s ratio. West Conshohocken, USA: American Society for Testing and Materials. ASTM C642-06 (2006) Standard test method for density, absorption, and voids in hardened concrete. West Conshohocken, USA: American Society for Testing and Materials. Bhanja S and Sengupta B (2002) Investigations on the compressive strength of silica fume concrete using statistical methods. Cement and Concrete Research 32: 1391–1394. Coelho A and de Brito J (2011) Distribution of materials in construction and demolition waste in Portugal. Waste Management & Research 29: 843–853. Corinaldesi V and Moriconi G (2009) Influence of mineral additions on the performance of 100% recycled aggregate concrete. Construction and Building Materials 23: 2869–2876. de Juan MS and Gutiérrez PA (2009) Study on the influence of attached mortar content on the properties of recycled concrete aggregate. Construction and Building Materials 23: 872–877. Del Río Merino M, Gracia PI and Azevedo ISW (2010) Sustainable construction: construction and demolition waste reconsidered. Waste Management & Research 28: 118–129. Dhir RK, Limbachiya MC and Leelawat T (1999) Suitability of recycled aggregate for use in BS 5328 designated mixes. Proceedings of Institute of Civil Engineering 134: 257–274. Dillmann R (1998) Concrete with recycled concrete aggregate. In: Proceedings of international symposium on sustainable construction: Use of recycled concrete aggregate, London, UK, 11–12 November 1998, pp.239–253. Domingo A, Lazaro C, Gayarre FL, et al. (2010) Long term deformations by creep and shrinkage in recycled aggregate concrete. Materials and Structures 43: 1147–1160. Hansen TC (1986) Recycled aggregate and recycled aggregate concrete, second state-of-the-art report, developments from 1945–1985. Materials and Structures 19: 201–246. Hao JL, Hills MJ and Tam VW (2008) The effectiveness of Hong Kong’s construction waste disposal charging scheme. Waste Management & Research 26: 553–558. Hosseini P, Booshehrian A and Madari A (2011) Developing concrete recycling strategies by utilization of nano-SiO2 particles. Waste Biomass Valorization 2: 347–355. Hueste MBD, Chompreda P, Trejo D, et al. (2004) Mechanical properties of high-strength concrete for prestressed members. ACI Structural Journal 101: 457–465. IS 383 (1970) Indian Standard Specification for coarse and fine aggregate from natural sources. New Delhi, India: Bureau of Indian Standards. IS 456 (2000) Indian Standard plain and reinforced concrete code of practice. New Delhi, India: Bureau of Indian Standards. IS 516 (1959) Indian Standard methods of tests for strength concrete. New Delhi, India: Bureau of Indian Standards (Reaffirmed in 1999). IS 8112 (1989) Indian Standard Specification 43 Grade ordinary Portland cement specification. New Delhi, India: Bureau of Indian Standards. Ji T (2005) Preliminary study on the water permeability and microstructure of concrete incorporating nano-SiO2. Cement and Concrete Research 35: 1943–1947. Kong D, Lei T, Zheng J, et al. (2010) Effect and mechanism of surfacecoating pozzalanics materials around aggregate on properties and ITZ microstructure of recycled aggregate concrete. Construction and Building Materials 24: 701–708. Levy SM and Helene P (2004) Durability of recycled aggregates concrete: A safe way to sustainable development. Cement and Concrete Research 34: 1975–1980. Li X (2008) Recycling and reuse of waste concrete in China; Part I. Material behaviour of recycled aggregate concrete. Resources Conservation and Recycling 53: 36–44.

Downloaded from wmr.sagepub.com at UNIV PRINCE EDWARD ISLAND on July 11, 2015

9

Mukharjee and Barai Lin KL, Chang WC, Lin DF, et al. (2008) Effects of nano-SiO2 and different ash particle sizes on sludge ash–cement mortar. Journal of Environmental Management 88: 708–714. Lin KL, Wu HH, Shie JL, et al. (2010) Recycling waste brick from construction and demolition of buildings as pozzolanic materials. Waste Management & Research 28: 653–659. Mellmann G (1999) Processed concrete rubble for the reuse as aggregate. In: Proceedings of the international seminar on exploiting waste in concrete, Dundee, Scotland, 7 September 1999, pp.171–178. London, UK: Thomas Telford publishing, Thomas Telford Limited. NBR 6118 (2003) Brazilian Association of technical standards: Design of concrete structures, Rio de Janeiro (In Portuguese). Neville AM (2006) Properties of Concrete. 4th ed. New Delhi: Person Education Limited. Nixon PJ (1978) Recycled concrete as an aggregate for concrete-a review. Materials and Structures 11: 371–378. Otsuki N, Miyazato SI and Yodsudjai W (2003) Influence of recycled aggregate on interfacial transition zone, strength, chloride penetration and carbonation of concrete. Journal of Materials in Civil Engineering 15: 443–451. Pacheco-Torgal F (2013) Introduction to the recycling of construction and demolition waste (CDW). In: Pacheco-Torgal F, Labrincha J, De Brito J, et al. (eds) Handbook of Recycled Concrete & Other Demolition Wastes. Cambridge, UK: Woodhead Publishing. Pacheco-Torgal F and Jalali S (2011a) Eco-efficient Construction and Building Materials. London, UK: Springer. Pacheco-Torgal F and Jalali S (2011b) Nanotechnology: Advantages and drawbacks in the field of construction and building materials. Construction and Building Materials 25: 582–590. Pacheco-Torgal F, Miraldo S, Ding Y and Labrincha JA (2013) Targeting HPC with the help of nanoparticles: An overview. Construction and Building Materials 38: 365–370. Qing Y, Zenan Z, Deyu K and Rongshen C (2007) Influence of nano-SiO2 addition on properties of hardened cement paste as compared with silica fume. Construction and Building Materials 21: 539–545.

Rahal K (2007) Mechanical properties of concrete with recycled coarse aggregate. Building and Environment 42: 407–415. Rakshvir M and Barai SV (2006) Studies on recycled aggregates-based concrete. Waste Management & Research 24: 225–233. Rao MC, Bhattacharyya SK and Barai SV (2011) Influence of field recycled coarse aggregate on properties of concrete. Materials and Structures 44: 205–220. Ravindrarajah RS and Tam CT (1985) Properties of concrete made with crushed concrete as coarse aggregate. Magazine of Concrete Research 37: 29–38. Said AM, Zeidan MS, Bassuoni MT and Tian Y (2012) Properties of concrete incorporating nano-silica. Construction and Building Materials 36: 838–844. Salem RM, Burdette EG and Jackson NM (2003) Resistance to freezing and thawing of recycled aggregate concrete. ACI Material Journal 100: 216–221. Tam VW, Tam CM and Le KN (2007a) Removal of cement mortar remains from recycled aggregate using pre-soaking approaches. Resources, Conservation and Recycling 50: 82–101. Tam VWY, Tam CM and Wang Y (2007b) Optimization on proportion for recycled aggregate in concrete using two-stage mixing approach. Construction and Building Materials 21: 1928–1939. Tam VW and Tam CM (2009) Parameters for assessing recycled aggregate and their correlation. Waste Management & Research 27: 52–58. Tangchirapat W, Buranasing R, Jaturapitakku C, et al. (2008) Influence of rice husk–bark ash on mechanical properties of concrete containing high amount of recycled aggregates. Construction and Building Materials 22: 1812–1819. Xiao J, Li J and Zhang C (2005) Mechanical properties of recycled aggregate concrete under uniaxial loading. Cement and Concrete Research 35: 1187–1194. Zaharieva R, Buyle-Bodin F and Wirguin E (2004) Frost resistance of recycled aggregate concrete. Cement and Concrete Research 34: 1927–1932.

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Development of construction materials using nano-silica and aggregates recycled from construction and demolition waste.

The present work addresses the development of novel construction materials utilising commercial grade nano-silica and recycled aggregates retrieved fr...
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