Experimental Investigation on Effect of Microsilica and Nanosilica on Compressive Strength of High Strength Concrete

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1 Experimental Investigation on Effect of Microsilica and Nanosilica on Compressive Strength of High Strength Concrete Arshdeep Singh 1, Rattanjot Singh Dhillon 2 1 Assistant Professor, Civil Engineering Department, PEC University of Technology, Chandigarh, India 2 Post Graduate Student, Civil Engineering Department, PEC University of Technology, Chandigarh, India Abstract This study concerns with the use of nanosilica and microsilica to improve the compressive strength of concrete. Microsilica (MS) of much finer size then cement has been proven to be affective in improving mechanical properties of concrete. With the advancement in nanotechnology, Nanosilica of even finer size than microsilica can also be used in concrete as cement replacing material. An experimental investigation has been carried out by partially replacing the cement with Nano Silica in varying percentage (i.e. 1%,2%,3%,4% & 5%) and micro silica in varying percentage (i.e. 5%,7%,9%,11%,13% &15%). In this study, cube of sizes 150mm x 150mm x150mm were cast for M-60 grade of concrete and testing of the specimens were performed on compressive strength testing machine after curing of 7days and 28 days. From the test result it was found that even very small of amount of NS (i.e. 2 to 3%) has substantial positive effects on the compressive strength of concrete, but there was very high demand of super plasticizer. Moreover combined addition of MS and NS has significant synergistic effects on the compressive strength (CS) of concrete and on the basis of results obtained it can be advised that NS and MS should be added together to achieve the maximum strength of the concrete however the effect of these material on workability of concrete can be compensated using high range water reducing super plasticizer. Key Words: Compressive strength(cs), Nanosilica (NS), Microsilica (MS). 1. INTRODUCTION Concrete is the material of present as well as future because of its low cost as well as good mechanical properties. The wide use of concrete in structures like buildings, bridges, airports, highways etc. makes it one of the most investigated materials. Due to cater the needs aroused from rapid population explosion and the technology boom, there is an urgent need to improve the strength and durability characteristics of concrete using recent advancements like nanotechnology in concrete[1]. Concrete is defined as "high-strength" solely on the basis of compressive strength at a given age. The ACI Committee on high strength concrete revised the definition to cover mixtures with specified design strength of 55 MPa or more. High strength concretes are made with carefully selected high-quality ingredients and optimized mixture designs. The main requirement is that it should be batched, mixed, placed, compacted and cured to the high quality control. Typically, high strength concretes will have a low water-cementing materials ratio of 0.20 to Superplasticizers are usually used to make these concretes workable. Production of high strength concrete may or may not require special materials such as mineral admixtures like microsilica, fly ash, ground granulated blast furnace slag etc. The producer must know the factors affecting compressive strength and know how to vary those factors for best results. [2] Most high strength concrete applications are designed for compressive strengths of 70 MPa. Commercial availability of high-strength concrete provided an economical alternative to bulky columns of conventional concrete for the lower floors of high-rise buildings. [3] 1.1 Nanotechnology in Concrete Nanotechnology applied to concrete includes the use of nanomaterials like Nano Silica, Nano Fibers etc. By adding the nanomaterials, concrete composites with superior properties can be produced. Addition of nanosilica in concretes and mortars results in more efficient hydration of cement.[3] Due to the pozzolanic activity, 214 Arshdeep Singh, Rattanjot Singh Dhillon

2 additional calcium silicate hydrates are formed to generate more strength and to reduce free calcium hydroxide. [4] This also helps in reducing the cement requirement; NS improves the microstructure and reduces the water permeability of concrete thus making it more durable. Use of Nano Silica in High Strength Concrete and Self Compacting Concrete improves the cohesiveness between the particles of concrete and reduces segregation and bleeding. Concretes with strengths as high as 66 MPa with high workability, anti-bleeding properties and short demoulding time can be produced. Nano silica can be used as an additive to eco concrete mixtures.[5,6] In the case of eco concrete mixtures, industrial wastes such as Flyash, Blast Furnace Slag are used as admixtures at certain percentages as replacement to cement. Certain problems like longer setting time, lower compressive strength at higher percentages can be overcome by adding Nano Silica which improves these properties. Condensed Silica Fume which is a by-product of metallurgical industries when used as a partial replacement to cement has been formed to contribute towards strength increase of concrete in addition to other beneficial properties.[7-10] strength of concrete with and without siliceous material. 3. MATERIALS USED 3.1 Nanosilica Nanosilica is highly pozzolanic material which contains very fine particles approximately 1000 times smaller than the cement particles. In the present study nanosilica in colloidal form i.e. nanosilica in dispersion with water in 40:60 ratios has been used. Nanosilica used in the study has been procured from Bee Chems, Kanpur, UP India. Nanosilica is being manufactured for a range of 15% to 40% Active Nano content with particle size in the range of 5-40 nm as shown in Table 3.1. Table 3.1 Variety of Nanosilica available at different active Nano content. 2. OBJECTIVES The objective of this program is to investigate the effect of partial replacement of cement with siliceous materials i.e. nanosilica and microsilica on the compressive strength of high strength concrete. This will lead to the attainment in the increase of compressive strength even by using the byproducts such as microsilica whose cost is much lesser than cement which reduces the construction cost. The main objectives of the present study are as mentioned below: To study the effect of siliceous materials on workability of concrete. To investigate variation of compressive strength of concrete containing different percentage of microsilica i.e. 5%,7%,9%,11%,13% and 15%. To investigate variation of compressive strength of concrete containing different percentage of nanosilica i.e. 1%,2%, 3%,4% and 5%. To determine the suitable dose of nanosilica and micro silica to achieve maximum strength. To compare the test results of compressive 3.2 Microsilica The microsilica used in the present study conforms to IS 15388:2003. The micro-silica is extremely fine particle, which exists in white color powder form. Micro-silica has been procured from ELKEM Pahar Ganj, New Delhi. The properties of microsilica as provided by the manufacturer are shown in Table Table-3.2: Physical Properties of Microsilica. 215 Arshdeep Singh, Rattanjot Singh Dhillon

3 3.3 Aggregates Aggregate is the component of a composite material that resists compressive stress and provides bulk to the composite material. Both 20mm and 10 mm aggregates were available locally. Specific gravity of coarse aggregate was found to be 2.63 and water absorption was 0.48%. Sand of Zone II was used in this study. Specific gravity of fine aggregates was found to be [11,12] 3.4 Cement Ordinary Portland cement (OPC) of 53 Grade, ACC brand was procured and cement used was fresh, without any lumps with uniformity in its shading. The consistency of cement was tested to find its initial and final setting time.[14,15] Specific gravity and compressive strength for 7 and 28 days was also found as depicted in Table 3.3. Table-3.3: Properties of Ordinary Portland cement. S. Item Test As per No Result IS Normal consistency (%) Specific Gravity Initial setting time (minute) 4. Final setting time (minute) 5. Compressive strength (N/mm 2 ) 3 days 7 days 28 days 150 > < >33 >43 > Superplasticizer The superplasticizer was used for improvement in workability and to reduce water cement ratio in concrete. It was sulphonated naphthalene formaldehyde with specific gravity EXPERIMENTAL PROGRAM The test program was proposed to investigate the effect of replacement of cement by Nanosilica and Microsilica on the compressive strength of high strength concrete. In first part of study, mix design for M60 grade of concrete was prepared and casting of cubes was done by partially replacing both microsilica and nanosilica by weight of cement in varying percentages (i.e. 5%,7%,9%,11%,13% and15% for microsilica and 1%,2%, 3%,4% and 5% for nanosilica). In second phase of the study, on the basis of the test results a range of dosage was selected suitably for both NS (i.e. 1%,2%, 3%) and MS (i.e. 7%,9%,11%) for further investigation. Casting of cubes was done to find the combined dosage of Nanosilica and Microsilica in concrete showing maximum compressive strength. Workability of concrete was examined using slump cone test apparatus for each mix. Slump test was conducted as per codal provisions to investigate the workability of concrete. [13] Finally, results obtained from the study has been compared with the control mix (CM) and conclusion were drawn. Mix proportion and quantity of ingredients used in the control mix is shown in Table 4.1. Table-4.1: Mix design quantities and Proportion ratio for control mix. S.No. Water (Kg/m³) Cement (Kg/m³) Fine Aggregate s (Kg/m³) Quantity Mix Proportion Coarse Aggregates (Kg/m³) 4.1 Testing Procedure To examine the compressive strength of concrete, cube moulds of size 150 mm x 150 mm x 150 mm were cast. The test specimen were submerged in clean water for proper curing after removing them from the moulds. A 2000 kn limit Compression Testing Machine (CTM) was used for compressive strength testing at the rate of 5 kn/s and the failure load in kn was observed on the monitor screen as shown in Figure 4.1. [16] 216 Arshdeep Singh, Rattanjot Singh Dhillon

4 Table-4.2: Detail of specimens showing variation in percentage change of MS, NS and compressive strength results. S. No Mix NS (%) MS( %) Compressiv e Strength (MPa) Figure 4.1 Test Appratus for Compressive Strength Testing. 4.2 Specimen Detail and Results This experimental setup was proposed to examine the behavior of high strength concrete in terms of compressive strength after addition of nanosilica and microsilica. Trial mixes were prepared and casting of cubes of standard size of 150 mm x150 mm x 150 mm as shown in Figure 4.2, was done to finalize a control mix for investigation. A total of 21 sets of different proportion were prepared comprising both nanosilica and microsilica as shown in Table 4.2. Compressive strength for each set has been found after 7 days and 28 days curing period. Figure 4.2 Test Specimen placed after demoulding. 7 day 28 day 1 CM CM NS NS NS NS NS NS MS MS MS MS 10 MS MS MS NS1+MS NS2+MS NS3+MS NS1+MS NS+MS NS2+MS NS3+MS NS1+MS NS2+MS NS3+MS DISCUSSION OF RESULTS The workability of cement concrete was examined using slump cone test. In case of control mix, the slump obtained was mm. With the addition of small percentage (i.e. 1%) of nanosilica the slump was reduced to mm. In case of 3% nanosilica the slump was minimized and hence requirement of superplasticizer was increased. Same results were obtained for microsilica and requirement of superplasticizer dosage increased with the increase in percentage of microsilica to obtain same slump value. It was observed from the compression test results of cubes that compressive strength increases as the percentage variation of 217 Arshdeep Singh, Rattanjot Singh Dhillon

5 nanosilica and microsilica was increased. There was decrease in compressive strength when replacement of cement with nanosilica was 4-5% but for microsilica it showed an increasing pattern as shown in Figure 5.1. Improvement in the hydration process occurs due fineness of nanosilica and hence the early age strength of concrete increases. As shown in Figure 5.1, it was observed that 7 days compressive strength of concrete increases with the variation of nanosilica from 1% to 3% and there was a decrease in 28 days strength with 4% nanosilica. This may be due to the high heat of hydration or less workability of concrete at this percentage variation. Figure-5.3: Compressive strength variation of concrete at varying percentages of microsilica after 7 days and 28 days. Figure-5.1: Compressive strength variation of concrete at varying percentages of nanosilica after 7 days and 28 days. It can be observed from Figure 5.2 that with the use of nanosilica in concrete, compressive strength of concrete increases. A maximum increase of 20% was obtained in 7 days strength and 15% increase was observed in 28 days strength. However, there was decrease in strength at higher percentage of nanosilica (i.e. 5%) and it may be due to decrease in workability which leads to a harsh mix. Figure-5.4: Percentage Change in Compressive strength of concrete at varying percentages of microsilica after 7 days and 28 days. Figure-5.2: Percentage Change in Compressive strength of concrete at varying percentages of nanosilica after 7 days and 28 days. Figure-5.5: Compressive strength variation of concrete at varying percentages of both nanosilica and microsilica after 7 days. 218 Arshdeep Singh, Rattanjot Singh Dhillon

6 microsilica has significant synergistic effects on the compressive strength of concrete. ACKNOWLEDGMENT Authors would like to thank PEC University Of Technology for infrastructure facilities. Figure-5.6: Compressive strength variation of concrete at varying percentages of both nanosilica and microsilica after 28days. It can be seen in Figure 5.3 that with the use of microsilica in concrete, improvement in compressive strength found was even better than as observed with the addition of nanosilica. Also, it can be observed that overall trend of the curve is increasing for both 7 days and 28 days strength. However, as shown in Figure 5.4, the percentage change in compressive strength was showing a decreasing pattern at 15 % replacement which may be improved with the help of retarding admixture or adjustment in dosage of superplasticizer. It can be noticed from Figure5.5 and Figure 5.6 that with the use of smaller percentages of microsilica in concrete containing nanosilica, continuous improvement in compressive strength found was found. However, at higher percentages change in compressive strength was showing a decreasing pattern because of high heat of hydration produced due to increased fineness of mix. Hence, a suitable dosage of nanosilica (i.e. 2-3%) in combination with microsilica (i.e. 9-11%) may be used to obtain the improved strength. 6. CONCLUSIONS The experimental investigation presented in this paper shows the effect of nanosilica and microsilica on the compressive strength of high strength concrete. From the results obtained, it can be summarized that the compressive strength of high strength concrete increases with the incorporation of both nanosilica and microsilica. However, improvement in early age strength i.e. 7 days was found to be more as compared to 28 days strength. Moreover, combined addition of nanosilica and REFERENCES [1] A.M. Said, M.S. Zeidan, M.T. Bassuoni, Y. Tian, Properties of concrete incorporating nano-silica Construction and Building Materials, 36 (2012) [2] ACI Committee 211.4R-08 Guide for Selecting Proportions for High-Strength Concrete Using Portland Cement and Other Cementitious Materials. [3] Al-Jabri K., Shoukry H., Use of nano-structured waste materials for improving mechanical, physical and structural properties of cement mortar Construction and Building Materials,73 (2014) [4] Bjornstrom J., Martinelli A., Matic A., Borjesson L. and I.Panas Accelerating effects of colloidal nano-silica for beneficial calcium silicate hydrate formation in cement, Chemical Physics Letters, 392 (2004) [5] Palla R., Karade S.R, Mishra G., Sharma U., Singh L.P., High strength sustainable concrete using nanoparticles Construction and Building Materials,138 (2017) [6] L.P. Singh, S.K. Bhattacharyya, S. Ahalawat, Preparation of size controlled silica nanoparticles and its functional role in cementitious system J. Adv. Concr. Techol. 10 (2012) [7] L.G. Li, Z H. Huang, J. Zhu, A.K.H. Kwan, H.Y. Chen(2017) Synergistic effects of micro-silica and nano-silica on strength and microstructure of mortar" Construction and Building Materials, 140 (2017) [8] Ye Qing, Zenan Z., Deyu K. and Ch. Rongshen, Influence of nano-sio2 addition on properties of hardened cement paste as compared with silica fume, Construction and Building Materials, 21(2007) [9] G.Harshavardhan. Microstructure Analysis And Strength Properties of Concrete With Nano Sio2 International Journal of Chemtech Research CODEN (USA):IJCRGG, 6 (2014) [10] Gaitero J.J., Campillo I. and Guerrero A. Reduction of the calcium leaching rate of cement paste by addition of silica nano particles Cem. and Con. Res., 38(2008) Arshdeep Singh, Rattanjot Singh Dhillon

7 [11] IS: Specification for coarse and fine aggregates from natural sources for concrete Bureau of Indian Standards, New Delhi, India. [12] IS 2386 (Part1&3):1963 Methods of test for aggregates for concrete. [13] IS 7320:1974 Specification for concrete slump test appratus. [14] IS 12269:1987 OPC 53 grade -Specification. [15] IS 5513:1996, Vicat apparatus specification Bureau of Indian Standards, New Delhi, India. [16] IS 516:1959 Method of test for strength of concrete. 220 Arshdeep Singh, Rattanjot Singh Dhillon