Optimizing Sonication Time and Solid to Liquid Ratio of Nano-Silica in High Strength Mortars

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1 e-issn Volume 3 Issue 4, April 217 pp Scientific Journal Impact Factor : Optimizing Sonication Time and Solid to Liquid Ratio of Nano-Silica in High Strength Mortars Kamal G. Sharobim¹, Hassan Mohammedin¹, Nagy F. Hanna², M.S. El-Feky³, E. Khattab 4, A. Maher El-Tair 5 ¹Professor of Testing and Properties of Materials, Suez Canal University ² Professor of Concrete Structures, Helwan Uniersirty ³ Researcher at National Research Center 4 Assistant Professor, Housing and Building Research Center 5 Assistant Lecturer, German University in Cairo Abstract: Many researchers investigated the effect of using nano-silica particles as a partial replacement of cement on the fresh and hardened properties of cement mortars. One of the main concerns related to the use of nano materials in cement composites is that they get highly agglomerated specially when mixed with water. Sonication is one of the methods used to deagglomerate nano-silica particles and to improve the dispersion of nano-silica in cement matrix. This research aims to reach the optimum indirect sonication time and solid to liquid ratio that enhances the dispersion of nano-silica and consequently increases its reactivity in high strength cement mortars. Particle size distribution of the sonicated nano-silica particles and the corresponding specific surface area were the main keys governing the optimization process of the studied parameters. Using the optimum solid to liquid ratio with the corresponding sonication time, cement mortars were prepared and their compressive strength as compared to a control mix (without nanosilica addition) were measured as an indication to the reactivity of nano-silica, in addition the microstructural analysis using SEM, and XRD helped in confirming the compressive strength results. The results revealed that the optimum solid to liquid ratio is 1:1. Moreover for every concentration, there is an optimum indirect sonication time. The optimum sonication time found to be 5 minutes for solid to liquid ratio 1:1. By using the optimum concentration an improvement in compressive strength of 39.8% and 25.37% after 7 and 28 days were reached as compared to the control mix. I. INTRODUCTION Many researchers investigated the influence of nano-silica on the mechanical properties of cement composites. The results indicated that nano-silica can improve the strength and durability characterizes of cement and concrete [3-4-1]. This improvement was due to their fine size which can fill the pores of the cement matrix. Also, due to the nucleation site effect and the pozzolnaic reactivity of the nano-silica which improves the microstructure of the cement composites [6]. A proper dispersion method should be applied to nano-silica to de-agglomerate its particles, in order to optimize the utilization of the nano-silica particles within the cement matrix. Sonication is one of the dispersion methods used to improve the effectiveness of nano-silica to modify its granulometric distribution and to improve its densification [5-7]. Serag et al [8] have studied the reactivity of nanosilica using different techniques; homegenizier, stirrer and indirect sonication. The results indicated that the reactivity significantly enhanced by the use of indirect sonicator. Type of sonication; direct or indirect, the frequency of the sonicator, liquid to solid ratio, and time of sonication are factors affecting the dispersion of nano-particles [11]. Elkady et al [11] investigated the effect of changing the indirect sonication time on the dispersion and the reactivity of nano-silica as a cement substation in concrete mixes. The results showed that 5 minutes of indirect sonication to nano-silica prior being added to concrete leads to an improvement in workability and a gain in compressive strength reached 33% than the control mix. The effect of solid to liquid ratio, and the time of sonication weren t taken into consideration as factors affecting the sonication process. Where Janani et al [12] have All rights Reserved 6

2 the effect of using nano-silica as a partial replacement of cement in cement mortars. Nano silica used was produced by the ball mill technique to convert silica fume to nano-silica. The results obtained that the optimum replacement was 23% of the cement content which it gave an improve in strength by 32.69% than the control mix. The proposal aims to optimize the dispersion of Nano-Silica particles, through studying the effect of different solid to liquid ratios on the particle size distribution and specific surface area of the sonicated nano-silica particles. The compressive strength of nano-silica cement mortars produced using the optimum solid to liquid ratio will be then compared to that of the control mix. In addition microstructure analysis (XRD, SEM) will be introduced to study in depth the effect of sonicated nano-silica on the micro structure of the cement mortars. II. EXPERIMENTAL WORK 2.1 Materials: Ordinary Portland Cement (OPC) confirming to ASTM C15 standard was used. Silica fume used was brought from the Egyptian ferro-alloys company in Aswan, Egypt. Chemical and physical properties of the used cement and silica fume are listed in table 1. Nano-silica used was produced from the physic depatement in the national research and housing center in Egypt, with average particles size 3 nm. The properties of of nano-silica are shown in table 2. Transmission electron micrographs (TEM) and powder X-ray diffraction (XRD) diagrams of nano-silica particles are shown in figs. (1and 2). Sand free of alkali-reactive materials brought from Suez area, in Egypt. The mix proportions are shown in table 3. Sika viscorete 3425 was used as a polycarboxilic ether additive. Table 4 shows some of the physical and chemical properties of the used admixture in this study. Figure 1: TEM Microscophy of Nano-Silica Figure 2: XRD Analysis of Nano-Silica Table 1: Chemical Composition of Portland cement, Silica Fume, and Nano-Silica Element SiO2 Al2O3 Fe2O3 CaO MgO So3 Na2O K2O P2O L.O.I Cement Silica Fume Nano-Silica Table 2: Physical and Chemical characteristics of Viscocrete 3425 Base Polycarboxylates Appearance Clear Liquid Density 1.8 kg/l ph Value All rights Reserved 7

3 2.2 Experimental Program: The experimental program is divided into two phases; the first phase aims to optimize the liquid to solid ratio of nano-silica using indirect sonication on different durations. Where a group of 4 different concentrations of nano-silica; 1:3, 1:15, 1:1, and 1:7.5, were sonicated for 4 different durations;, 5, 1, and 15 minutes. The optimum concentration was chosen based on the optimum particle size distribution, and specific surface area of the sonicated samples. In the second phase the effect of nano-silica on the compressive strength was studied using the optimum concentration and with the corresponding indirect sonication time. Ten mixtures were prepared to investigate the influence of nano-silica on the compressive strength. The mortar cubes used were 5 x 5x 5 cm³. The cubes were tested after 7 and 28 days of water curing. Cubes were manually compacted in 3 layers according to ASTM C19. Then, the specimens were vibrated for 3 minutes using the vibrating table. Then the cubes were de-molded after 24 hours and cured in water at room temperature until the day of testing. The mixture proportions are shown in table 3, with constant cement content 6 kg/m³ and with water to binder ratio.26. The silica fume was used with a percentage of 2% of the cement content. The chemical admixture used with a ratio of 4% of the binder content. Nano-silica used with a percentage of 1, 2, and 3% replacement of cement content at 2 different solid to liquid ratios; 1:1 and 1:7.5. In the indirect sonication the power was fixed at 135 Watt and the frequency was at 4 KHz. The mixing procedures were as follow: (a) Weight the mix components, (b) add the nano-silica to the needed water for sonication according to the required concentration, (c) place cement and silica fume in the mixer and make a dry mixing for 1 min, (d) add the concentration of water and nano-silica to the dry mix and rotate the mixer for 2 min, (e) add the remaining of mixing water with the superplasticizer to the mix and make it mix for 3 mins, (f) add fine aggregate (sand) to the mix and make it to mix for 3 mins. While for the unsonicated nano-silica the procedures will be as follow: (a) place cement, silica fume, and nano-silica and make the mixer rotate for 1 mins as dry mix, (b) add part of the mixing water to the dry components and mix for 3 mins, (c) add the remaining of the water with superplasitizer to the mix for 3 mins, (d) add sand and mix for 3 mins. Table 3: Mix Proportions by weight Mix Silica Fine Nano- Cement Water Superpalstizier (Lit./m³) fume Agg. Silica Concentartion Sonication (kg/m³) (kg/m³) (kg/m³) (kg/m³) (kg/m³) time C as receive Control OS as receive mins OS as receive mins OS as receive mins SS :1 5 mins SS :1 5 mins SS :1 5 mins MS : mins MS : mins MS : All rights Reserved 8

4 Volume Density (%) Volume Density (%) Volume Density (%) Volume Density (%) International Journal of Current Trends in Engineering & Research (IJCTER) III. RESULTS AND DISCUSSION 3.1 Optimum Sonication time for each concentration: Form the data shown below in figure (3) and in table (4), as the indirect sonication time increased the nano- particle content to reach an optimum value, differs in every concentration, while by increasing the indirect sonication time above the optimum duration the nano-particle decreased. In solid to liquid ratio 1:3, at zero time sonication the D5 was 1.23 nm and a specific surface area was 8829 m²/kg and after 5 minutes of indirect sonication the D5 was decreased to.57nm and a specific surface area was increased to 1368 m²/kg. However, at solid to liquid ratio 1:1 the D5 was.572 nm and with a specific surface area was 1372 m²/kg. Where by increasing the indirect sonication time to 5 minutes the optimum results was obtained at a D5 equals to.423 nm and with a specific surface area 1648 m²/kg. 1:3 5 mins 15 mins 1 mins mins :15 5 mins 15 mins 5 1 mins 4 mins Size (µm) (a) Size (µm) (b) 1:1 6 5 mins 15 mins 5 1 mins 4 mins Size (µm) 1 1 (c) 1:7.5 5 mins 6 15 mins 5 1 mins 4 mins Size (µm) (d) Figure 3: Particle size distribution of nano-silica samples (a) concentration at 1:3, (b) at concentration 1:15, (c) at concentration 1:1, and (d) at concentration All rights Reserved 9

5 Table 4: Specific surface area and mean particle size distribution for each sonication time and concentration by the master sizer 3 Concentration 1:3 1:15 1:1 1:7.5 surface area (m²/kg) Time (min.) D5 (nm) surface area (m²/kg) D5 (nm) surface area (m²/kg) D5 (nm) surface area (m²/kg) D5 (nm) Effect of Sonication on Compressive Strength: A comparison was carried out between the optimum solid to liquid ratio 1:1 which gives the optimum a specific surface area of 1648 m²/kg and the below value solid to liquid ratio 1: m²/kg. nano silica was sonicated using the corresponding duration for each solid to liquid ratio. The results show that solid to liquid ratio 1:1 gives the higher strength than 1:7.5, as shown in figure [4-5]. Where the optimum ratio of nano-silica was 2% of the cement content, which gives a compressive strength after 28 days 77.3 MPa with an improvement 25.4% than the control mix, while for solid to liquid ratio 1:7.5 gives MPa with an improvement All rights Reserved 1

6 11.4% 8.9% 5.% Compressive Strength (MPa) 12.3% 25.4%.9% 2.4% 25% 16.8% Compressive Strength (MPa) 34.5% 39.2% 21.2% International Journal of Current Trends in Engineering & Research (IJCTER) Conc. 1:1 Conc. 1: Control Nano-Silica (%) Figure 4: Comparison between Compressive Strength after 7 days for Nano-Silica concentrations at 1:1 and 1:7.5 Conc. 1:1 Conc. 1: Control Nano-Silica (%) Figure 5: Comparison between Compressive Strength after 28 days for Nano-Silica concentrations at 1:1 and 1:7.5 Another comparison was carried out to study the effect of sonication on the strength of cement mortars, between an unsonicated nano-silica cement mortars and a sonicated nano-silica cement mortars using the optimum solid to liquid ratio 1:1 and with an optimum sonication time 5 minutes. In unsonicated nano-silica samples. The compressive strength for unsonicated nano-silica samples was 51MPa using 1% nano-silica with an improvement by 11.45% while by using sonicated nanosilica the strength was improved by 35% at the same nano-silica dosage. As shown in figures [6-7]. The optimum nano-silica dosage obtained was at 2% for both sonicated and unsonicated nano-silica as the strength was improved after 28 days by 25% and 15% All rights Reserved 11

7 16.3% 15.6% 12.4% Compressive Strength (MPa) 12.3% 25.4%.9% 11.5% 21.2% 18.9% Compressive Strength (MPa) 34.5% 39.2% 21.2% International Journal of Current Trends in Engineering & Research (IJCTER) unsonicated NS Sonicated NS Nano-Silica (%) Figure 6: Compressive Strength for sonicated and unsonicated Nano-Silica cement mortars after 7 days unsonicated NS 77.3 Sonicated NS Nano-Silica (%) Figure 7: Compressive Strength for sonicated and unsonicated Nano-Silica cement mortars after 28 days 3.3 Microstructure Test: Microstructure test was carried out using both Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD) as shown in figures (8) and (9), respectively. Figure (8) shows the SEM of mortar samples without nano-silica (a), with unsonicated nano-silica (b), with sonicated nano-silica (c) with age 28 days. From the figures below, it is more obvious that the mortar samples with nano-silica are denser than samples without nano-silica, also, the effect of sonication on the microstructure on the mortar samples. Nano-silica caused a secondary reaction between the silica oxide located in nanosilica and Ca(OH)2 crystals existing in the paste. Sonication makes the cement paste more homogenous than unsonicated nano-silica through the filler effect and the good dispersion of nanoparticles in the matrix. XRD analysis was performed to detect changes in the hydration products due to the presence of nano-silica. Nano-silica addition resulted in a significant decrease in the calcium hydroxide peaks specially in the sonicated nano-silica sample, figure (9-c), compared to the both unsonicated nano-silica sample, figure (9-b), and the control mix, figure All rights Reserved 12

8 (a) (b) (c) Figure 8: SEM pictures of (a) cement mortar without nano-silica, (b) with unsonicated nano-silica, and (c) with sonicated All rights Reserved 13

9 (a) All rights Reserved 14

10 (c) Figure 9: XRD analysis of (a) cement mortar without nano-silica, (b) with unsonicated nano-silica, and (c) with sonicated nano-silica IV. CONCLUSIONS From the experimental works the following conclusions can be drawn: The optimum solid to liquid ratio of nano-silica is 1:1 and with an indirect sonication time 5 minutes, which results in the optimum specific surface area and particle size distribution. Indirect sonication for 5 minutes and with a concentration 1:1 gives higher compressive strength improvement as compared to the control mix by 39% and 25% after 7 and 28 days, respectively. Using sonicated nano-silica improves the microstructure of the cement matrix and consumes calcium hydroxide crystals to produce more and denser C-S-H crystals. The optimum nano-silica replacement percentage is 2% of the cement weight. Within the range studied, changing the solid to liquid ratio of nano-silica more or less than 1:1 will results in a decrease in the strength gained, as an increase in the re-agglomeration occurred. Microstructure analysis reveals that nano-silica improve the microstructure of the cement paste and produce a denser and more homgenous matrix than without nano-silica. REFERENCES [1] Sobolev, K., Flores, I. and Hermosillo, R. Nanomaterials and Nanotechnology for High-performance cement composites, Proceedings of ACI Session on Nanotechnology of Concrete: Recent Developments and Future Perspectives, November 7, 26, Denver, U.S.A., pp: [2] Khanzadi, M., Tadayon, M., Sepehri, H. and Sepehri, M. Influence of nano-silica particles on mechanical properties and permeability of concrete, Proceedings 2 nd International Conference on Sustainable Construction Materials and Technologies, Universita Ploitecnica delle Marche, Ancona, Italy, 21, pp. All rights Reserved 15

11 [3] Li, G. Properties of high-volume fly ash concrete incorporating nano-sio2, Cement and Concrete Research 34, 24, pp [4] Maghsoudi, A.A. and Arabpour-Dahooei, F. Effect of Nano Scale Materials in Engineering Properties of Performance Self-Compacting Concrete, Proceeding of the 7 th International Congress on Civil Engineering, Iran, 27, pp: [5] Martinez-Velandia D, Paya J, Monzo J and Borrachero M. V. Granulometric Activation of Densified Silica fume (CSF) by Sonication, Advances in Cement Research 2(3), 28, pp: [6] Jo BW, Kim CH, Tae G, Park JB., Characteristics of Cement Mortar with Nano- SiO2 Particles. Construction Building Material, 21(6):1351 5, 27. [7] Martínez, D., Payá, J., Monzó J. M., and Borrachero M. V. "Effect of Sonication on the Reactivity of Silica Fume in Portland Cement Mortars" Adv Cement Res, 23(1), 211, [8] Serag M.I., Elkady H. and Elfeky M.S., "Effect of Nano Silica Deagglomeration, and Methods of Adding Superplasticizer on the Compressive Strength, and Workability of Nano Silica Concrete", Civil and Environmental Research, Vol.3, No.2, 213. [9] Mostafa Khanzadi, Mohsen Tadayon, Hamed Sepehri, and Mohammad Sepehri, Influence of Nano-Silica Particles on Mechanical Properties and Permeability of Concrete, 2 nd International Conference on Sustainable Construction Materials and Technologies, Ancona, Italy, June 21. [1] Zhang, M. H. Islam, J. Peethamparan, S. "Use of nano-silica to increase early strength and reduce setting time of concretes with high volume of slag." Cem Concr Compos, 34(5), 212, pp: [11] Elkady H., Serag M. I. and Elfeky M. S., "The Effect of Indirect Sonication on the Reactivity of Nano Silica Concrete", International Journal of Scientific & Engineering Research, Volume 5, Issue 12, 214. [12] P. Janani, S. Ganeshkumar, M. Harihananth, Mechanical Properties of Nano Silica Concrete, International journal of innovative research in science, engineering and technology, ISO 3297, Vol. 5, Issue 3, March All rights Reserved 16