Utilization of Nano Silica & Fly Ash on the Workability and Compressive Strength of Ordinary Portland Cement

Abstract

This paper focusses on studying the utilization of nano silica and flyash on the compressive strength of concrete containing different percentage of nano silica (NS) ranging from 0.3 to 1% (by weight) and a fixed proportion of fly ash (20% by weight) as a partial replacement of cement. The compressive strength of concrete is measured at 7 days & 28 days respectively. The effects of NS in microstructure development and pozzolanic reaction of pastes containing above fly ash content are also studied through Field Emission Scanning Electron Microscope (FESEM).Result shows that the maximum compressive strength is obtained with 20% of fly-ash and 0.75% of nano silica by weight of cement for both M20 & M30 grades of ordinary concrete. The strength found to be 20.76 MPa and 27.11 MPa for 7 days and 28 days respectively for M20 grade of nano silica & fly ash mixed concrete while the compressive strength of ordinary concrete of M20 grade comes out to be 15.06 MPa and 24.88 MPa for 7 days and 28 days respectively. Hence the maximum percentage increase in the compressive strength comes out to be 8.96 % for M20 grade of concrete in 28 days also the compressive strength found to be 31.73 MPa and 40.10 MPa for 7 days and 28 days respectively for M30 grade of nano silica & fly ash mixed concrete while the compressive strength of ordinary concrete comes out to be 23.17 MPa and 34.91 MPa for 7 day and 28 days respectively. Hence the maximum percentage increase in the compressive strength comes out to be 14.86 for M30 grade of concrete at 28 days.The test conducted on it shows a considerable increase in early-age compressive strength and a small increase in the overall compressive strength of the ordinary concrete.The FESEM analysis also supports the above findings.

Introduction

Concrete is a fundamental construction material used across infrastructure—from roads and bridges to buildings and airports. Its wide usage is primarily due to the binding properties of Portland cement, which, although effective, is energy-intensive and environmentally taxing. To improve strength, durability, and sustainability, researchers have explored partial replacement of cement with materials like fly ash, blast furnace slag, silica fume, and nano-silica.

Key Findings from Research Studies

• Nano-Silica Enhancements:
  Studies by Min-Hong Zhang et al. (2012) and AM Said et al. (2012) show nano-silica improves early strength, setting time, and reduces porosity. Strength gains up to 22% were observed with 2% nano-silica and 50% slag mix.

• Fly Ash Blending:

  • Shaikh et al. (2014) noted that adding 2% nano-silica to high-volume fly ash (HVFA) mixes enhances compressive strength, especially at 40–50% fly ash content.

  • Alvin Harison (2014) found compressive strength peaks at 20–30% fly ash replacement.

  • Rishabh Joshi (2017) concluded 30% fly ash gives optimal workability and durability, but more than that decreases compressive strength.

• Combination Materials:

  • Yanqun Sun et al. (2020) showed a mix of fly ash (20%) and nano-CaCO? (1%) with a 0.4 w/c ratio gave the best performance.

  • Behzadian and Shahrajabian (2019) reported that adding nano-silica to concrete with recycled PET improved tensile, compressive, and flexural strength.

• Fracture Properties with Nano-TiO? and GGBS:

  • Pathak and Vesmawala (2023) observed improvements in fracture toughness and energy with nano-TiO? (1–3%) and GGBS (30%).

Current Study Objective

The present study focuses on assessing the compressive strength of concrete by:

• Replacing 20% of cement with fly ash

• Varying nano-silica from 0.3% to 1%

• Conducting tests after 7 and 28 days

• Using Field Emission Scanning Electron Microscopy (FESEM) to analyze pore structures

Materials Used

• Cement: OPC 53 grade (IS: 12269-1987)

  • Initial setting: 1 hr 22 min

  • Final setting: 5 hr 40 min

  • Specific gravity: 2.9

  • Fineness: 7%

  • Consistency: 33.5 mm

• Fine Aggregate (Sand): Crushed limestone

  • Specific gravity: 2.66

  • Water absorption: 0.84%

  • Fineness Modulus: 2.63 (Zone II)

• Coarse Aggregate: Crushed limestone

  • Sieve analysis conducted with standard methodology

Conclusion

From the test results obtained from the experimental investigations, following conclusions can be drawn. 1) Increase in the compressive strength for both the type of concrete mix (M20 and M30 grades) with the increased percentage of nano-silica up to 0.75% and fly-ash 20% by weight of cement and then strength is getting reduced with the increased percentage of nano-silica. The maximum 28 days strength of modified concrete is obtained as 27 MPa and 40 MPa for M20 and M30 grades of concrete respectively with nano-silica of 0.75% and 20% of fly-ash by weight of the cement. 2) Workability of concrete increases on addition of small percentage of nano-silica whereas workability starts decreasing with the increased percentage of nano-silica. 3) It is observed that on addition of nano-silica there is considerable increase in 7 days strength of cement concrete mix compared to 28 day`s increase in strength. 4) Microstructure of the concrete specimens becoming dense on addition of nano-silica.

References

[1] A study of the mechanical properties of ground ceramic powder concrete incorporating nano-SiO2 particles Ali Heidari,DavoudTavakoli Department of Civil Engineering, University of Shahrekord, Shahrekord, Iran, Department of Civil Engineering, Najafabad Branch, Islamic Azad University, Najafabad, Iran (2012) [2] Properties of concrete incorporating nano-silica A.M. Said, M.S. Zeidan, M.T. Bassuoni, Y. Tian, Department of Civil and Environmental Engineering, University of Nevada, Las Vegas, USADepartment of Civil Engineering, University of Manitoba, Winnipeg, Canada (2012) [3] Use of nano-silica to reduce setting time and increase early strength of concretes with high volumes of fly ash or slag Min-Hong Zhang Jahidul Islam, Department of Civil and Environmental Engineering, National University of Singapore, Engineering Drive 2, 117576 Singapore, Singapore (2011) [4] Effect of Fly Ash on Compressive Strength of Portland Pozzolona Cement Concrete,Alvin Harison, Sam Higginbottom University of Agriculture, Technology and Sciences (2014) [5] Experimental Study of the Effect of Nano-silica on the Mechanical Properties of Concrete/PET Composites, RohamBehzadian* and HamzehShahrajabian** (2019) [6] Effect of Nano-CaCO3 on the Mechanical Properties andDurability of Concrete Incorporating Fly Ash, Yanqun Sun , Peng Zhang , WeinaGuo, JiuwenBao, and Chengping QuSchool of Civil Engineering, Qingdao University of Technology, Qingdao 266033, China (2020) [7] A study on the effect of nano silica on compressive strength of highvolume fly ash mortars and concretes F.U.A. Shaikh, S.W.M. Supit, P.K. Sarker Department of Civil Engineering, Curtin University, Perth, Australia (2014) [8] Effect of fly ash and nanosilica oncompressive strength of concrete at early age, N. M. Garcia, L. E. Zapata, O. M. Suarez3 and M. Cabrera-Rios (2015) [9] Influence of Nano-TiO2 and water to cement ratio on fracture parameters of concrete, Pathak, S.S., Vesmawala, G.R.Asian J CivEng 24, 1969–1979 (2023). https://doi.org/10.1007/s42107-023-00616-2 [10] Revised AASTHO T84 [11] AASTHO T85

Copyright

Copyright © 2025 Shivam Srivastava, Umesh Kumar Maheshwari. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.