Effect of Nano-Clay on The Mechanical Properties of Fresh and Hardened Cement Mortar Comparing with Nano-Silica

Transcription

1 Effect of Nano-Clay on The Mechanical Properties of Fresh and Hardened Cement Mortar Comparing with Nano-Silica 1 Prof.Dr. Sayed Abd El-Baky 2 Dr. Sameh Yehia 3 Dr. Enas A. Khattab 4 Ibrahim S. Khalil 1 Prof. of Strength & properties of Materials, Housing & Building National Research Centre, Egypt, Cairo 2 Assistant Prof, Faculty of Engineering, Shorouk Academy, Egypt, Cairo 3 Lecturer, Housing & Building National Research Centre, Egypt, Cairo 4 Assistant Lecturer, Housing & Building National Research Centre, Egypt, Cairo, ibrahimmsobhy@yahoo.com ABSTRACT: This paper presents a parametric experimental study, which investigates the effect of nano-clay (NC) on some of the physical and mechanical properties of cement mortar having various percentage of NC, a comparison between NC and nano-silica (NS) results carried out by the same percentage of addition. The nano-clay used in this investigation was montmorillonite clay (sodium calcium aluminum silicate), nano-clay prepared by thermal activation of inactivated nano-clay for 2 hours at 750 C. The cement was partially substituted by NC of 1, 3, 5, 7 and 10% by weight of cement. Other mixes were prepared with NS using the same percentage of NC substituted. Results indicated that, the fresh mortar pastes flow decreased with the increasing of NC or NS. Whilst, compressive and flexural strengths were improved for both NS and NC compared with conventional mortar. However, compressive and flexural strength of 10% NC at 28 days was higher than 7% NS results. In addition, the Scanning Electron Microscope (SEM) analysis of the NC and NS specimens microstructures showed that the NS and NC filled the cement paste pores causing more homogeneity and densification for the cement paste and Interfacial Transition Zone (ITZ), by reacting with calcium hydroxide crystals forming more calcium silicate hydrate. However, NC has more homogenous microstructure than NS. Key words: Nano silica, nano clay, mortar. 1. INTRODUCTION: Nanotechnology is the technology that measures, manipulate, or incorporate materials and/or features with at least one dimension between approximately 1 and 100 nanometers (nm) [1]. Understanding and developing of nano-scale structures change the traditional process of producing and applying construction materials [2], [3]. Clay particles at the nano size possess some unique characteristics. Nano-clay particles are in the platelet form with thickness of just 1 nm, and width of 70 to 150 nm, it has an aspect ratio of 100 to 150 which improves some anisotropic characteristics as partial reinforcement on the construction materials nano-meta-kaolin (NMK), which is a valuable pozzolanic material, is a thermally activated aluminosilicate material obtained by calcining kaolin clay within the temperature range of C [4]. Using (NMK), improved compressive and tensile strengths of the cement mortars with NMK higher than that of the conventional cement mortar by 49%. At the same w/b ratio, NMK in cement mortar acts as a nano-fiber due to its morphology [5]. Using of pozzolanic materials such as silica fume is necessary for improving the cementitious materials. Concrete and cement mortar, because of significant improvements attained on the interfacial transition zone of cement paste-aggregate. So and for the same purpose using nano-silica, which have more effective than micro silica as its pozzolanic activity is greater [6], [7] For both silica and clay nano-particles can act as nuclei for cement phases, further promoting cement hydration due to their high reactivity, as nano reinforcement, and as filler, identifying the microstructure and the interfacial transition zone (ITZ), thereby, leading to a reduced porosity[8]. 7% nano-clay added to epoxy sample showed the highest elastic modulus at 25ºC, 5% nano-clay added give the best tensile behavior upon elevated temperature above 50ºC, result based on samples without nano-clay, as nano-clay interrupted with the polymer chains in a certain extent, making the polymer chains difficult to move [9]. 2. EXPERIMENTAL PROGRAM: 2.1 Materials and Mixture Properties: Cement: The used cement is CEM I 42,5 N complied with ES [10], and the properties shown in Table (1).

2 Oxide Composition Table (1): Chemical Composition of Materials CEM1 Wt % NC Wt % NS Wt % CaO SiO Al 2 O Fe 2 O MgO SO K 2 O Na 2 O TiO P 2 O Ignition Loss Aggregate: In this research round corner sand with specific gravity of 2.6 with particle size from 0.06 mm to 5 mm were used. It should be mentioned that aggregate were granulated based on ASTM C 136 [11] standards Water: Tap water was used in this research Nano-clay: The nano-clay used in this work is montmorillonite clay (sodium calcium aluminum silicate). It is characterized by large length to thickness ratio; it is especially favorable in matrix reinforcement but crystalline state to convert it to amorphous state. The nano clay was thermally treated at 750ºC for 2 hours to give active amorphous nano montmorillonite clay. The ingredients were homogenized in a ball miller with four balls (13mm) for 1 hour to assure complete homogeneity. Figure (1): TEM Micrograph of Inactivated Nano- Montmorillonite Clay Particles Figure (2): TEM Micrograph of Activated Nano- Montmorillonite Clay Particles

3 The effect of thermal activation of the nano montmorillonite clay is the conversion from the crystalline state to the amorphous state with the reduction in grain size, which will result in increase of the chemical reactivity of the nano montmorillonite clay, the properties shown in Tables (1) and (2). Figures (1) and (2) show TEM (Transmission Scanning Election Microscopy) micrographs of inactivated and activated nano montmorillonite clay particles. Table(2): Physical Properties of Nano Montmorillonite-Clay Color Light Cream Bulk density (gm/cm 3 ) 1.9 Surface Area (m 2 /gm) Nano-silica: The nano-silica used in this research is powder type. The chemical and physical specifications are given in Table (1) and Table (3) respectively. The morphology of nano particles studied using Transmission Scanning Election Microscopy (TEM), as Shown in Figure (3). Figure (3): TEM micrograph of Nano-Silica Table (3) - Physical Specifications of Consumed Nano-Silica Diameter of Particles (nm) Density (g/cm 3 ) Specific Surface (m 2 /g) Purity Percentage Test Program and Specimens Fabrication: The test program consists of eleven mixes with different addition of NS and NC ranged from 0% to 10% as a replacement of mortar cement content as shown in Table (4). The specimens' fabrication was done as follows. Firstly, mixing nano-powder with cement by ball miller, type PM100, using four balls (13mm) for 10 minutes, forming nano-powder and cement composite. After completing mixing process, nano-powder and cement composite prepared and placed in the mixer. After that, fine aggregate was added and mixing dry composite then gently adding mixing water. The fresh mortar is poured into oiled molds and after

4 pouring, an external vibrator is used to facilitate compaction and decrease the amount of air bubbles. The specimens are demolded after 24h and then cured in water at temperature of 20±3C Testing Methods: The compressive and flexural strength tests were performed in accordance with ASTM C109 [12], and ASTM C348 [13], respectively, cubic specimens of mm for compressive strength and prism specimens of mm for flexural strength were used. 3. TEST RESULT AND DISCUSSIONS: Mix proportions, flow test Results for all mixes, Compressive and Flexural Strengths of The Mortar are shown in Table (4). Table (4): Mix Proportions, Compressive and Flexural Strengths of Mortar Made out of Cement and NS or NC Sample Mix Proportion Flow (mm) Compressive Strength (kg/cm 2 ) flexural Strength (kg/cm 2 ) C NS NC W Sand 3d 7d 28d 3d 7d 28d % % % % % N NS NS NS NS NS NC NC NC NC NC Mortar Flow: Using ASTM C 1437 [14], the Standard Test Method for Flow of Hydraulic-Cement Mortar, determines how much a mortar sample flows. Test results refer to a reduction in mortar flow proportionally with increasing the amount of nano-powder (nano-silica or nano-clay) in the cement mortar. As apart of water added exhausted in the activation process due to nano particles that added in the cement mortar, and the large surface area helped ensure that. Figure (4): Effect of nano powder on Mortar Flow Test Results

5 However it is appear that with increasing nano-silica up to 7% in mortar, flow re-increasing, as shown in Figure (4). These results are compatible with compressive and flexure strength which re-decrease at the same percentage, so we can conclude that exist of nano-particles in the mortar without including in activation process increase lubrication in the mortar. Otherwise, no re-increasing happens with increasing nano-clay. The different between NS and NC is shown in Figures (1) and (2) Compressive Strengths: Figures (5),(6),(7) show the compressive strength of NS and NC as a cement replacement at 3, 7 and 28 days respectively. All results showed that using NS ratios from 1% to 7% gives a little increase in compressive strength value than NC for the same ratios by not more than 5% at 7 and 28 days. On the other hand, at 10% NC the compressive strength value is higher by 10% than that record for NS, this may be refer to the role of the activated NC as an amorphous materials and reacting with the calcium hydroxide at higher percentage. Finally from the analysis and results it is clear that 7% NS and 10% NC as replacement of the cement content are optimum percentage for increasing compressive strength value. Figure (5): Effect of nano powder on the 3-Day Compressive Strength Figure (6): Effect of nano powder on the 7-Day Compressive Strength Figure (7): Effect of nano powder on the 28-Day Compressive Strength

6 3.3. Flexural Strengths: Flexural strength of NS and NC as a cement replacement increase proportionally with increasing nano-powder (NS or NC) as shown in Figures (8),(9) and (10) for 3, 7 and 28 days, respectively. Results shows that 7% NS replacement of cement content improve the flexural strength more than conventional mortar by 63.5, 61.0 and 60.2,% for 3, 7 and 28 days respectively, Also NC, improve flexural strength by 76.6, 67.2, and 65.4% more than conventional mortar for 7 and 28 days. All results indicated in Table (4). All results show that, using 7% NS, flexural strength was more than 7% NC replacement by 3 % at 28th days. Otherwise the enhancement can be achieved using 10% NC more than that of the same percentage of NS by 18.7 % at 28th days. Finally, for 7 % NS and 10 % NC as replacement of cement content are optimum percentages. Figure (8): Effect of nano powder on the 3-Day Flexural Strength Figure (9): Effect of nano powder on the 7-day Flexural Strength Figure (10): Effect of nano powder on the 28-Day Flexural Strength 3.4. SEM Analysis: Figures 11(a, b, c), are SEM micrographs of reference mortar and mortar with 7% NS, through the mortar itself and at the ITZ respectively. The SEM shows that the microstructure of the NS mortar, is denser and homogeneous than of the conventional mortar because of the pozzolanic reaction by consumption of Ca(OH)2, and changed to an additional C-S-H which fill the pore system and causing packing effect which improves the microstructure of

7 mortar. Figure 11-(d, e), for SEM micrographs of mortar with 10% NC at ITZ and cement paste, respectively, Figure 11-(a) for mortar microstructure without NS or NC was found that CSH gel existed in the form of stand-alone clusters, but for Figure 11-(c, e) these is a bond with the hydrated products around the transition zone between the nano-particle and hydrate products. It is appear from Figure 11-(d) for the cement mortar with NC that have the higher strength, also have the best bond surface between cement paste and aggregate surface. From Figure 11-(b, d) for cement paste of mortar with NS and NC respectively, the texture of hydrate products was denser and compacted. NS and NC improve the microstructure and strength of cement mortar, as the nano-particles added to the cement mortar as nucleus will further promote and accelerate cement hydration due to their high activity. In the consideration of the nano-particles uniformly disperse situation, a good microstructure can formed with the uniformly distributed conglomeration as shown in Figure 11-(c, e) for cement mortar with NS and NC respectively. ITZ Aggregate CH Crack CSH Voids Figure 11-(a): SEM of Conventional mortar Figure 11-(b): SEM of mortar with 7% NS CSH Aggregate CSH ITZ Figure 11-(c): SEM for mortar with 7% NS Figure 11-(d): SEM for mortar with 10% NC

8 ITZ Aggregate Figure 11-(e): SEM for mortar with 10% NC 4. CONCLUSIONS: From all the experimental studies presented in this research, conclusions can be as follows: 1. Workability of cement mortar which detected by mortar flow, decrease by increasing the amount of nanosilica as same as nano-clay, as some of added water absorbed by nano-powder, which reducing workability. 2. Compressive and flexural strength of the cement mortar increases proportionally with increasing the amount of nano-powder, (NC or NS), but 10 % NC results were higher than that of 7 % NS especially at early ages, but 7 % NS still higher than 7%NC added to cement mortar. This increasing for NC can also be due to nano reinforcements that occur from high aspect ratio between thickness and the other dimension which affect especially at flexural strength that enhanced more than compressive strength. 3. Nano-clay cement mortar have more homogeneity binder, less pores, more adhesion than conventional mortar and that containing nano-silica especially at interfacial transition zone which appear from SEM analysis. 4. The NC in cement mortar acts as a nano fiber (nano reinforcements due to its morphology). 5. Activated nano-clay microstructure photograph of the cement paste revealed that C S H existed in the form of stand-alone clusters, lapped and jointed together by many needle like hydrates. 6. The clay reacts pozzolanically with the other primary component, calcium hydroxide (CH), to form more C- S-H, thereby improving microstructure density and thus strength. 5. REFERENCES: [1] ASTM E , Standard Terminology Relating to Nanotechnology. [2] Zhi Ge, Applications of Nanotechnology and Nanomaterials in Construction, First International Conference on Construction In [3] Ashwni K.Ranal, Significance of Nanotechnology in Construction Engineering, International Journal of Recent Trends in Engineering, Vol 1, No. 4, May 2009.

9 [4] S.Taha, Thermo Mechanical Properties of Activated Nano Clay Cement Pastes at Different Curing Temperatures, International Conference on Nano Technology for Green and Sustainable Construction March 2010 Cairo-Egypt. [5] M. S. Morsy, Effect of Nano-clay on Mechanical Properties and Microstructure of Ordinary Portland Cement Mortar, International Journal of Recent Trends in Engineering, Vol 1, No. 4, May [6] Ye Qing a,b,, Zhang Zenan, Kong Deyu, Chen Rongshen, Influence of nano-sio 2 addition on properties of hardened cement paste as compared with silica fume, Cement & Concrete Composites 26 (2004) [7] Proceedings of ACI Session on Nanotechnology of Concrete: Recent Developments and Future Perspectives November 7, 2006, Denver, USA. [8] Walid H. Awad, Material properties of nanoclay PVC composites, Polymer, Elsevier, (2009) [9] Man-Wai Ho1, Enhancement of Thermal Properties of Polymer-Based Composites Using Nanoclays, University of New Orleans,USA. [10] ES /2009 "Egyptian Standard: Composition, Specifications and Conformity Criteria for Common Cements" [11] ASTM C "Standard Test Method for Sieve Analysis for Fine and Coarse Aggregate" [12] ASTM C 109/ C 109M-12, Standard Test Method for Compressive Strength of Hydraulic Cement mortars (Using 2-in. or [50-mm] Cube Specimens). [13] ASTM C348-08, Standard Test Method for flexural strength of Hydraulic-cement mortar. [14] ASTM C230/c230M-08, Standard Test Method for Flow Table for Use in Tests of Hydraulic cement.