Construction and Building Materials 52 (2014) 189–193

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Construction and Building Materials

journal homepage: www.elsevier .com/locate /conbui ldmat

Effects of nano-Al2O3 on early-age microstructural propertiesof cement paste

0950-0618/$ - see front matter � 2013 Elsevier Ltd. All rights reserved.http://dx.doi.org/10.1016/j.conbuildmat.2013.11.010

⇑ Corresponding author. Address: Department of Civil Engineering, Curtin Uni-versity of Technology, GPO Box U1987, Perth, WA 6845, Australia. Tel.: +61 8 92662392; fax: +61 8 9266 2681.

E-mail addresses: Salim.Barbhuiya@curtin.edu.au (S. Barbhuiya), shaswataa@gmail.com (S. Mukherjee), Hamid.Nikraz@Curtin.edu.au (H. Nikraz).

Salim Barbhuiya a,⇑, Shaswata Mukherjee b, Hamid Nikraz a

a Curtin University of Technology, Australiab Jadavpur University, Kolkata, India

h i g h l i g h t s

� Early-age microstructural properties of cement paste containing nano-Al2O3.� No changes noticed in the early-age compressive strength with nano-Al2O3 addition.� No new crystalline phase was developed with nano-Al2O3 addition.� Formation of much denser microstructure with nano-Al2O3 addition.

a r t i c l e i n f o

Article history:Received 24 September 2013Received in revised form 17 October 2013Accepted 2 November 2013Available online 5 December 2013

Keywords:Nano-Al2O3

CementXRDFTIRSEMCompressive strength

a b s t r a c t

The effects of nano-Al2O3 addition on the early-age microstructural properties of cement paste isreported in this paper. The study was limited to evaluation of properties of cement paste hydrated upto an age of 7 days. Ordinary Portland cement was replaced by nano-Al2O3 powder at 2% and 4% byweight. The water–binder ratio was fixed at 0.4. No changes were noticed in the early-age compressivestrength with nano-Al2O3 addition. XRD analysis confirmed that no new phase developed due to the addi-tion of nano-Al2O3 powder. However, FTIR analysis shows a shift in water associated band to lower fre-quency mostly with 4% nano-Al2O3 addition. Scanning electron microscopy reveals the formation ofmuch dense microstructure with larger crystals of portlandite within the cement matrix.

� 2013 Elsevier Ltd. All rights reserved.

1. Introduction Al O during cement hydration was found to responsible for

Concrete is one of the common and widely used building mate-rials in the world and it is a nano-structured, multi-phase, compos-ite material that ages over time [1]. The concept of incorporatingnanomaterials in cement matrix is a new and promising researchfield. Various nano-materials such as nano-SiO2, nano-TiO2, nano-Al2O3, nano-Fe2O3, carbon nano-tubes, carbon nano-fibres andnano-clay have recently being used in cement and concrete to im-prove their mechanical, physical, durability and several others no-vel properties [2]. Recent research by Li et al. [3] has found that theuse of nano-Al2O3 has no change in compressive strength, but itsuse can increase the elastic modulus of cement mortar by 143%at 28 days with 5% nano-Al2O3. Densification of the ITZ by nano-

2 3

increment of the elastic modulus. If the replacement level was in-creased more than 5%, agglomerations of nano-Al2O3 particles de-creased the elastic modulus by ineffective densification.

Achieving a high-quality concrete may not be possible if ade-quate attention is not paid to its early-age properties. For instance,the mechanical performance and long-term durability of concretecan be seriously affected due to inadequate curing or insufficientcompaction during placement. Moreover, accelerated constructionschedules aiming at economic gains have led to tragic failures dur-ing construction due to inadequate knowledge of the concretebehavior at the early age. Therefore, a fundamental understandingof the behavior of concrete at early age is essential to ensure safetyduring construction, as well as adequate durability and long-termproperties.

Ali and Shadi [4] studied the heat of hydration, up to 70 h, bypartially replacing the binder materials (Portland cement + slag)with nano-Al2O3 at levels of 0%, 1%, 2%, 3% and 4%, by weight. Addi-tion of nano-Al2O3 in cement pastes was found to accelerate thepeak times and drop the heat release. The highest drop in the heat

190 S. Barbhuiya et al. / Construction and Building Materials 52 (2014) 189–193

release was more prominent for 3% nano-Al2O3 content mix. Aliet al. [5] reported a decrease in workability and reduction in set-ting time with nano-Al2O3 addition. However, a detailed study onthe effects of nano-Al2O3 on the microstructure and changes inquality and quantity of hydration product is missing in the litera-ture. This experimental study focuses on the microstructural prop-erties of cement pastes with nano-Al2O3 addition. This is neededfor better understanding the effects of nano-Al2O3 addition incement.

20 30 40 50 60 70 802 Theta (deg.)

Fig. 1. XRD analysis of nano-Al2O3 and cements.

40080012001600200024002800320036004000

Cement

Nano Alumina

2. Materials and methods

2.1. Materials

Cement used was ordinary Portland cement. Nano-Al2O3 powder was suppliedby Nanostructured & Amorphous Material Inc., USA. The chemical composition ofcement is presented in Table 1, and the properties of nano-Al2O3 powder are givenin Table 2. Fig. 1 represents the XRD analysis of cement and nano-Al2O3. It can beseen that corundum is the major mineral present in nano-Al2O3 powder whereasalite and belite are the major minerals in cement. The absolute spectra of nano-Al2O3 powder and dry Portland cement are shown in Fig. 2. Possible assignmentto some of the peaks of dry cement at different wavenumber (cm�1) are: 2100–2300 due to CaCO3, 1400–1500 due to CO3, 1100–1200 due to v3 of SO4, 1011–1080 due to polymerized silica, 877–878 due to v2 of CO3, 847–848 due to Al–O,Al–OH and 656–658 due to v4 of SiO4. The infrared spectrum which characterizesnano-Al2O3 powder is in the wave number range from 400 to 1000 cm�l.

2.2. Sample preparation

Portland cement was replaced by nano-Al2O3 powder at 0.2% and 4% by weight.The nano-Al2O3 powder was mixed with cement in dry condition and the dry mixwas sieved several times for proper dispersion of the nano-Al2O3 powder. Thewater-binder ratio (W/B) used was 0.4. Cement paste cubes of 50 mm size were castand vibrated in table vibrator. Specimens were then demoulded and cured in nor-mal tap water until required for testing. Microstructural properties of hydratedcubes were evaluated at the age of 1, 3 and 7 day.

2.3. Test methods

The compressive strength was measured for 50 mm cube specimens. At eachtest date, after crushing the specimens, they were ground manually and sievedthrough 150 lm sieve for XRD analysis. For this, XRD machine, using Cu Ka radia-tion (Wavelength = 1.5405 Å) was used. Spectra were collected on a FTIR machinefitted with a single-bounce diamond ATR. Sixty-four background and 64 samplespectra were co-averaged and ratioed to generate the transmission spectrum.Two levels of zero filling (3 additional data point between each pair of data pointsin the interferogram), Norton-Beer strong apodization (to minimize side-lobes), andMertz phase correction were employed. The spectral resolution was 4 wavenum-bers. Specimens were broken with a hammer into small pieces for SEM. The micro-scope used was operated with high vacuum and accelerated voltages of 5 kV.Specimens were coated with platinum with a thickness of 10 lm. Several regionswere examined and finally the reported figures are selected at 30,000�magnification.

Table 1Chemical composition of cement.

Oxides (%)

SiO2 20.4Al2O3 4.3Fe2O3 2.5CaO 62.6MgO 2.4SO3 2.2LOI 1.0

Table 2Properties of nano-Al2O3 powder.

Constituents Crystal phase Purity Average particle size

Nano-Al2O3 a 99.5% 27–43 nm

3. Results and discussion

3.1. Compressive strength

Compressive strength of cement paste containing 2% and 4%nano-Al2O3 was found to increase slightly at 1 and 7 day. Thechanges in compressive strength at 1, 3 and 7 day is very smalland it was found that addition of nano-Al2O3 in cement paste doesnot have any direct effect on the compressive strength of pastesamples. However, the long-term compressive strength of cementpaste containing nano-Al2O3 may be more than the control. There-fore, there is a need to investigate the long-term compressivestrength (see Fig. 3).

Wave Number (cm-1)

Fig. 2. FTIR analysis of nano-Al2O3 and cement.

0

10

20

30

40

50

60

1 day 3 day 7 day

Com

pres

sive

stre

ngth

(MPa

)

0% nano alumina

2% nano alumina

4 % nano alumina

Fig. 3. Compressive strength of cement replaced with 0%, 2% and 4% nano-Al2O3.

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3.2. X-ray diffraction

Figs. 4–6 illustrate the XRD analysis of cement paste replacedwith 0, 2% and 4% nano-Al2O3 at 1, 3 and 7 day respectively.Ettringite, portlandite, Alite, Belite and Gypsum were found to bemajor phases for all the mixes. Changes in peak height and forma-tion of new peaks were found at 7 day. Intensity of Alite and Belitephase decreased and new peak of portlandite (2 theta deg. �34, 47,51, etc.) were found at 7 day. A new peak of Gypsum was foundafter 7 day curing (2 theta deg. �11) and is more prominent for

5 10 15 20 25 30 35 40 45 50 55 60 65

2 Theta (deg.)

Fig. 4. XRD analysis of cement replaced with 0%, 2% and 4% nano-Al2O3 at 1 day.

5 10 15 20 25 30 35 40 45 50 55 60 652 Theta (deg.)

Fig. 5. XRD analysis of cement replaced with 0%, 2% and 4% nano-Al2O3 at 3 day.

5 10 15 20 25 30 35 40 45 50 55 60 652 Theta (deg.)

Fig. 6. XRD analysis of cement replaced with 0%, 2% and 4% nano-Al2O3 at 7 day.

4% nano-Al2O3 content mix. However, no other new crystallinephase was found with nano-Al2O3 addition.

3.3. Fourier transform infrared spectroscopy

Vibrational frequencies of 0%, 2% and 4% nano-Al2O3 contentmix at 1, 3 and 7 day measured by FTIR (Figs. 7–9) generally givean indication of changes in silicate, sulfate, hydroxide andcarbonate phases. The silicate condensation reaction can bestudied by silicate infrared bands. Out of plane Si–O bending(V4SiO4�

4 ), Asymmetric Si–-O stretching (V3SiO4�4 ) and in plane

Si–O bending (V2SiO4�4 ) typically centred at around wavenumber

508, 941 and 440 cm�1. The % transmittance was found to bedecrease at 1 and 3 day for 4% nano-Al2O3 content mix. Some

40080012001600200024002800320036004000Wavenumber (cm-1)

0% Alumina, Day 1

2% Alumina, Day 1

4% Alumina, Day 1

Fig. 7. FTIR analysis of cement replaced with 0%, 2% and 4% nano-Al2O3 at 1 day.

40080012001600200024002800320036004000

Wavenumber (cm-1)

0% Alumina, Day 3

2% Alumina, Day 3

4% Alumina, Day 3

Fig. 8. FTIR analysis of cement replaced with 0%, 2% and 4% nano-Al2O3 at 3 day.

40080012001600200024002800320036004000

Wavenumber (cm-1)

0% Alumina, Day 7

2% Alumina, Day 7

4% Alumina, Day 7

Fig. 9. FTIR analysis of cement replaced with 0%, 2% and 4% nano-Al2O3 at 7 day.

Fig. 10. 1 Day SEM of 0% nano-Al2O3.

Fig. 11. 1 Day SEM of 2% nano-Al2O3.

Fig. 12. 1 Day SEM of 4% nano alumina.

Fig. 13. 3 Day SEM of 0% nano alumina.

Fig. 14. 3 Day SEM of 2% nano alumina.

Fig. 15. 3 Day SEM of 4% nano alumina.

Fig. 16. 7 Day SEM of 0% nano alumina.

192 S. Barbhuiya et al. / Construction and Building Materials 52 (2014) 189–193

possible assignments of peaks are given by Ylmen et al. mostlymatches for our samples and are taken as Ref. [6]. The bands at3640 cm�1 is due to the presence of calcium hydroxide and theband at 3397 cm�1 is because of v3H2O and capillary water. Othermajor bands at wavenumber 1655 cm�1 is due to v2H2O,1414 cm�1 is due to CO3, 1109 cm�1 is due to v3SO4, 872 cm�1 isdue to v2CO3 and 621 cm�1 is due to v4SiO4. With the incrementof nano-Al2O3 content in the mix, water associate bands haveshifted slightly to lower frequencies. No such changes were noticedfor sulfate, silicate and hydroxide associated bands with nano-Al2O3 addition.

3.4. Scanning electron microscopy

Figs. 10–18 represents the scanning electron microscope imagesof 0%, 2% and 4% nano-Al2O3 content mix cured up to 1, 3 and

Fig. 17. 7 Day SEM of 2% nano alumina.

Fig. 18. 7 Day SEM of 4% nano alumina.

S. Barbhuiya et al. / Construction and Building Materials 52 (2014) 189–193 193

7 days. Formation of C–S–H and ettringite is found for 1 day curedspecimens for 0%, 2% and 4% nano-Al2O3 content mix specimens.The structure was found to be with fewer voids with 4% than 0%and 2% nano-Al2O3 content specimens. Formation of larger crystalof portlandite was found for 2% and 4% at 7 day compared to 0%

nano-Al2O3 content specimens. Agglomerations of nano-Al2O3 par-ticles were also noticed with 2% and 4% nano-Al2O3 content spec-imens that are represented by the white circles in the SEMimages. SEM analysis reveals formation of much denser micro-structure with nano-Al2O3 addition.

4. Conclusions

From the experimental results obtained, the following conclu-sions are drawn:

i. Addition of nano-Al2O3 does not improve the compressivestrength of cement paste at early age.

ii. XRD analysis confirms that no new crystalline phase wasdeveloped with nano-Al2O3 addition within 7 days of curing.

iii. From FTIR analysis water associated bands were found to beshifted to lower frequency with nano-Al2O3 addition and nosuch major changes in sulfate, carbonate or silica associatedband were noticed. The % of transmittance was found to bedecreased with 4% nano-Al2O3 addition.

iv. SEM confirms the formation of much denser microstructurewith nano-Al2O3 addition and agglomeration of nano-Al2O3

particles.

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