MODIFIED PROPERTIES OF CEMENTITIOUS MATERIALS WITH Cr 2 O 3 AND AL 2 O 3 NANOPARTICLES

International Conference on Advances in Structural and Geotechnical Engineering ICASGE 15 6-9 April 15, Hurghada, Egypt MODIFIED PROPERTIES OF CEMENTITIOUS MATERIALS WITH Cr 2 O 3 AND AL 2 O 3 NANOPARTICLES E.E. Etman 1, A.M. Atta 1, M.H. Taman 1, N.A.Ali 2, A. M. Wahba 2 1 Department of Structural Engineering, Tanta University, Egypt. E-mail: emadetman@gmail.com E-mail: Drahmedatta03@yahoo.com E-mail: mohamed.taman@f-eng.tanta.edu.eg 2 Department of Engineering Physics and Mathematics, Tanta University, Egypt. E-mail: nehalzr@gmail.com E-mail: a_m_wahba@yahoo.co.uk In this study, the effect of nano-cr 2 O 3 and different-phase Al 2 O 3 nanoparticles addition on the fresh and hardened properties of cement mortar has been investigated. Ordinary Portland cement was replaced by nano powder at 0.5%, 1.% and 2.5%wt percent. Nano Cr 2 O 3 and Al 2 O 3 nanoparticles were prepared via citrate-precursor autocombustion method. The structure of the prepared nanoparticles was characterized using X-ray diffraction (XRD). The results illustrate that the obtained powders have a single phase structure. The morphology and the size of the synthesized nano-particles were analyzed using Transmission Electron Microscope (TEM). Photographs confirmed nanoscale crystallized structure. Properties of fresh density and flow percentage were evaluated in fresh state. The compressive strength along age of the cement paste was the evaluated property in hardened state. Different mixing methods to uniformly disperse the nanoparticles within the cement matrix were explored and a suitable mixing technique was suggested. Scanning electron microscope (SEM) revealed that the microstructure of the composites with -phase Al 2 O 3 nanoparticles were more compact and dense than that of plain composite. Keywords: Nano-Cr 2 O 3, Nano-Al 2 O 3, cementitious materials. 1 Introduction In the field of nanotechnology, tailored nano-composites have the prime focus as one of the most major and significant areas of research. There is a particular interest in developing nanotechnology for cement and concrete. Not only the chemistry that forms cement hydration products but also the physical behaviour of those products are acceptable for manipulation through nanotechnology. The mechanical properties of nanoparticles depict their immense potential for use as reinforcements in composite materials. Most of the published studies on the use of nano-particles in cement and concrete have utilized nano-oxides, especially SiO 2 and Fe 2 O 3 (Li 04, Li et al. 04, Korpa et al. 05, Lin et al. 08, Abbas 09, Qing et al. 09). The early work of Li (Li 04) showed that nano- 1

SiO 2 could significantly increase the early compressive strength of concrete containing large amounts of fly ash (Kopra et al. 05), and improve pore size distribution by filling the pores between large fly ash and cement particles at the nano-scale. Also, the slurry of amorphous nano-silica was used to improve the segregation resistance of self-compacting concrete. Another nano-sized oxide of interest in construction is titanium oxide (TiO 2 ) (Han et al. 04, Xiong et al. 06). To our knowledge, there are few works on incorporating nanoparticles into cementitious materials to achieve improved physical and mechanical properties. There are several reports on incorporation of nanoparticles in normally vibrated concretes, most of which have focused on using SiO 2 nanoparticles (Bjornstorm et al. 04). In addition, some of the works have utilizednano-al 2 O 3 (Li et al. 06, Campillo et al. 07), and zinc iron oxide nanoparticles (Flores-Velez and Dominguez 02). Previously, the effects of ZnO 2 (Nazari and Riahi 10e, Nazari and Riahi 10d) nanoparticles on different properties of self-compacting concrete have been studied. In addition, the works investigating the effects of several types of nanoparticles on properties of concrete specimens (Nazari 10, Nazari and Riahi 10a, Nazari and Riahi 10b, Nazari and Riahi 10c) which are cured in different curing media have been reported. Incorporation of other nanoparticles is rarely reported. Therefore, introducing some other lab-made nanoparticles, which probably could improve the mechanical and physical properties of cementitious composites, taking into considerations the low cost of the additives would be interesting. The use of different-phase Al 2 O 3 nanoparticles had not been examined in previous work. So the main aim of this study is preparing -phase Al 2 O 3, -phase Al 2 O 3, in addition to Cr 2 O 3 nanoparticles by laboratory method and incorporating them into cement matrix as a replacement to study its impact to the fresh and hardened properties of cementitious materials. Several specimens with fixed amounts of superplasticizer have been prepared and their physical and mechanical properties have been considered. 2 Materials and Methods 2.1 Preparation of the nanoparticles Aluminium nitrate (99%) was diluted in distilled water and the calculated amount of citric acid (99%) (molar ratio of citric acid/metal was set at 1:1) were dissolved in distilled water. Both solutions were mixed together to form stable metal citrate complexes. This mixture was heated until 100 C for 1 h under magnetic stirring to evaporate excessive water and converted to a gel. The gel was heated in muffle furnace. Its thermal decomposition, which results in a powder, was processed at 350 C for 3 h (Bezerra and Dissertação 07). The high temperature ignited the gel to swell into foam, undergoing a strong self-propagating combustion reaction with the evolution of large volume of gases in several minutes. The processed powder was milled, sieved and calcinated at different temperatures to obtain different phases of Al 2 O 3. The Cr 2 O 3 nanoparticles were prepared using the same procedure. The X-ray diffraction (XRD) data was collected using K radiation. Approximately 0 mg of powder was transferred to a glass XRD sample holder. This sample holder was then placed inside an X Pert Graphics X-Ray Powder Diffractometer. Transmission Electronic Microscopic (TEM) analysis was carried out using a microscope type JEOL JEM 1230 providing x60000 magnification. 2

2.2 Materials Ordinary Portland cement CEMI-42.5N in compliance with EN196-1 was used in this study. Table 1 shows the chemical and physical properties of cement. Sand with bulk density of 2.55 and fineness modulus 2.2 was used. Water to cement ratio of 0.40 and superplasticizer type F were used according to ASTM C494 of dose 0.7% of cement mass based on polycarboxylate ether. Table 1: The chemical composition and physical properties of the conducted cement 2.3 Sample preparation Chemical composition (%) CEM I-42.5N Cao 65.4 SiO 2.4 Al 2 O 3 4.9 Fe 2 O 3 3.1 MgO 1.7 Na 2 O 0.28 K 2 O 0.24 SO 3 3.6 Specific gravity (gm/cm 3 ) 3.15 Blaine fineness (cm 2 /gm) 3400 Cement mortar was mixed according to ASTM C305 with mixing proportions as shown in Table 2. Water-binder ratio of 0.4 was used. Nanoparticles were used as a replacement for cement with 0.5%, 1.%, and 2.5%. The dispersion process included mixing of water, superplasticizer, and nanomaterials together. Stirring the previous solution for min then sonication process started for 45 min. The dry mix powder of cement and sand 2 min in a drum mixer, and nally the mixture of water, nanoparticles and the superplasticizer was added. The mixing process continued for min. The flow test was conducted according to ASTM C230M-14. Three groups of each nano component containing 0.5%, 1., and 2.5% in 5 cm 5 cm 5 cm cubes were casted. The comparative study was provided using two different control specimens, one of them with superplasticizer and the other without. The mix proportion of the hole specimens is shown in table 2. After 24 hours of batching, the samples were demolded and cured in normal tap water until required for testing. The compressive strength of the cubes was measured at the ages of 7, 28 and 180 day. Each testing age accomplished three cubes. 3 Results and Discussion 3.1 Characterization of nanoparticles The XRD diffraction patterns of the prepared samples are illustrated in Fig. 1. No impurities of or secondary phases was recorded. The crystallite size for the three samples was estimated using Williamson-Hall method (Prabhu et al. 14) and were found to be 58.3, 21.7, and 167.5 nm for Cr 2 O 3, -phase Al 2 O 3 and -phase Al 2 O 3, respectively. TEM was carried out to study the morphology and to find out exact particle size of synthesized nanoparticles. Fig. 2 shows the TEM images and particle size distribution of the synthesized Cr 2 O 3 NPs. The images show that Cr 2 O 3 NPs were regular in size and shape. We 3

can observe a large quantity of uniform nanoparticles (NPs) with average particle size of 40-90 nm, indicates that our synthesis process is an easy method for the preparation of this nanoparticles. Mix No. Sample Table 2: Mix proportion of the specimens Nanoparticles replacement (%) Cement (gm) Sand (gm) Water (gm) Nanoparticles (gm) Superplasticizer (gm) 1 Control without SP 0.0 500 1375 242 0.0 0 2 Control with SP 0.0 500 1375 242 0.0 3.5 3 0.5 497.5 1375 242 2.5 3.5 4 Al 2 O 3 1. 493.75 1375 242 6. 3.5 5 2.5 487.5 1375 242 12.50 3.5 6 0.5 497.5 1375 242 2.5 3.5 7 Al 2 O 3 1. 493.75 1375 242 6. 3.5 8 2.5 487.5 1375 242 12.50 3.5 9 0.5 497.5 1375 242 2.5 3.5 10 Cr 2 O 3 1. 493.75 1375 242 6. 3.5 11 2.5 487.5 1375 242 12.50 3.5 Cr 2 O 3 Intensity (a. u.) Al 2 O 3 ( ) Al 2 O 3 ( ) 30 40 50 60 70 2 Figure 1. XRD for Cr 2 O 3, Al 2 O 3 nanoparticles Fig. 3 shows the TEM images and histograms of (a) -alumina and (b) -alumina nanoparticles. Electronic Microscopic images reveal that severe agglomeration occurred at high temperatures, and the size distribution of nanoparticle is mostly uniform. Due to the agglomeration, the determination of the average diameter was difficult because individual particle boundaries were not clearly distinguishable. But with more accuracy the size of crystallites (not particles) before 4

the severe agglomeration is possible to estimate. From TEM images, and the distribution of the -alumina particles are about 400-700 nm, and those -alumina nanoparticles are about 10 40 nm as shown in the histogram fig.3. Percentage, % 15 10 5 0 1.3 (a) TEM images for Cr 2 O 3 nanoparticles 3.1 4.4 14.1 11.0 19.8 21.6 16.7 Cr 2 O 3 4.4 2.2 0.9 0.4 30 40 50 60 70 80 90 100 110 1 130 Particles size, nm (b) Particle size distribution of Cr 2 O 3 nanoparticles Figure 2. (a) TEM images and (b) Particle size distribution of Cr 2 O 3 nanoparticles (a) TEM images for -Al 2 O 3 nanoparticles 5

Percentage, % 15 10 5 9.3 9.8 14.5 16.6 17.1 7.8 6.2 5.2 Al 2 O 3 (alpha) 2.6 4.7 6.2 0 0 300 400 500 600 700 800 900 1000 1100 10 Particles size, nm (b) Particle size distribution of -Al 2 O 3 nanoparticles Percentage, % 15 10 5 (c) TEM images for -Al 2 O 3 nanoparticles Al 2 O 3 (gamma) 13.2 14.4 15.6 13.6 12.3 10.7 11.1 4.1 2.9 2.1 0 5 10 15 30 40 50 60 70 Particles size, nm (d) Particle size distribution of -Al 2 O 3 nanoparticles Figure 3. TEM images and particle size for (a), (b) - Al 2 O 3 and (c), (d) - Al 2 O 3 nanoparticles 3.2 Consistency Fig. 4 shows the flow ability of cement mortar. Where the initial flow percentage indicates the spreading value of the cement mortar after lifting the conical mold without chaking the table. The final flow percentage measured after standard number of chaking cycles equal to. The 6

high concentration of nanoparticles additives reduces the flow significantly due to its high specific area. The final flow value also reduced with increasing the dose of nanoparticles except for -Al 2 O 3. The -Al 2 O 3 nano particles replacements show the minimum flow values between nanoparticles. This may be due to the smaller size of such nano as shown from TEM results, thus increase the ability of filling the spaces of the produced specimens. 3.3 Compressive strength It is clear that the control samples without using superplasticizer have larger compressive strength compared to that one with SP as shown in Fig. 5. For other tested samples with using of both nanoparticles as a replacement and SP, it was found that, 1.% had the maximum compressive strength value. Using 1.% of -Al 2 O 3 nanoparticles as a replacement raised compressive strength up to 16%. 264 Initial flow, % 231 198 Final flow, % 5 5 5 0 184 216 195 Flow, % 165 132 99 66 68 132 121 111 100 74 163 53 137 105 89 153 33 0 5 11 21 Figure 4. Effect of using different nanoparticles on cement mortar consistency 3.4 Scanning electron microscopy Specimens were broken of the compressive strength testing using a hammer to small pieces. The microscope used was operated with high vacuum and accelerated voltages of 5 kv. Specimens were coated with platinum. Several regions were examined. Fig. 6 represents the scanning electron microscope images of control specimen without SP, that with 1.% nano - Al 2 O 3, and that with 1.% nano Cr 2 O 3 nanoparticles. 7

50 50 50 Compressive strength, MPa 45 40 35 30 Control without SP Control with SP Al2O3- - 0.5% Al2O3- - 0.5% Cr2O3-0.5% 0 60 1 180 Age, days 45 40 35 30 Control without SP Control with SP Al2O3- - 1.% Al2O3- - 1.% Cr2O3-1.% 0 60 1 180 Age, days 45 40 35 30 Control without SP Control with SP Al2O3- - 2.5% Al2O3- - 2.5% Cr2O3-2.5% 0 60 1 180 Age, days Figure 5. Compressive strength of cement replaced with 0%, 0.5%, 1.% and 2.5% examined nanoparticles The structure was found to have more and larger voids compared with control specimen without SP. SEM analysis reveals formation of much denser microstructure using both nano - Al 2 O 3, and nano Cr 2 O 3. Images revealed that the nano-particles were not only acting as a ller, but also as an activator to promote hydration proves. Agglomerations of nano -Al 2 O 3, and nano Cr 2 O 3 particles were also observed as represented by the white circles in the SEM images. (a) control without SP (b) 1.% nano -Al 2 O 3 8

(c) 1.% nano Cr 2 O 3 Figure 6. SEM of (a) control without SP, (b) 1.% nano -Al 2 O 3, and (c) 1.% nano Cr 2 O 3 4 Conclusions From the experimental results obtained, the following conclusions are drawn: Using 1.% of -Al 2 O 3 nanoparticles as a replacement raised compressive strength up to 16%. Addition of nano-cr 2 O 3 does not improve the compressive strength of cement paste. SEM con rms the formation of much denser microstructure with nano - Al 2 O 3 addition and agglomeration of nano- Al 2 O 3 particles. Further study in this direction is recommended. 5 References Abbas, R. (09). Influence of nano-silica addition on properties of conventional and ultra-high performance concretes. HBRC Journal, 5(1): 18-30. Bezerra, M. J. O. S. Dissertação, UFRN, Natal/RN, 104, (07). Bjornstrom J, Martinelli A, Matic A, Borjesson L and Panas I. (04). Accelerating effects of colloidal nanosilica for beneficial calcium silicate hydrate formation in cement, Chem. Phys. Lett. 392(1 3): 242 248. Campillo I, Guerrero A, Dolado J S, Porro A, Ibáñez J A and Goñi S. (07). Improvement of initial mechanical strength by nanoalumina in belite cements, Mater. Lett. 61: 1889 1892. Flores-Velez L M and Dominguez O. (02). Characterization and properties of Portland cement composites incorporating zinc-iron oxide nanoparticles, J. Mater. Sci. 37: 983 988. Han, B., Guan, X. and Ou, J. (04). Specific resistance and pressure-sensitivity of cement paste admixing with nano-tio2 and carbon fiber. Journal of Chinese Ceramics Society, 32: 884 887. Korpa, A., Trettin, A. and Pyrogene, R. (05). Nano-oxides in modern cement-based composites. Proceedings of 2nd International Symposium on Nanotechnology in Construction, Bilbao, Spain, pp. 313 3. Li Z, Wang H, He S, Lu Y and Wang M. (06). Investigations on the preparation and mechanical properties of the nano-alumina reinforced cement composite, Mater. Lett. 60: 356 359. Li, G. (04). Properties of high-volume fly ash concrete incorporating nano-sio2. Cement and Concrete Research, 34: 1043-1049. 9

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