Civil and Project

Assessment of the Effect of Fly Ash and Nanosilica on the Geotechnical Properties of Forest Road Subgrade

10.22034/cpj.2025.527515.1373
Volume 7, Issue 5 - Serial Number 75
August 2025
Civil and Project

Document Type : Research Article

Authors

Sadegh Ghavami 1
Amin Hallaji 2
Yashar Sandooghsaz 3

1 Faculty of Civil Engineering, Sahand University of Technology, Tabriz, Iran.

2 Faculty of Civil Engineering, Sahand University of Technology, Tabriz, Iran

3 Department of Civil Engineering, Shabestar Branch, Islamic Azad University, Shabestar, Iran

Abstract
This study aims to investigate the effect of nanosilica on the geotechnical parameters of soil stabilized with class C fly ash. For this purpose, the soil of a forest road subgrade in northern Iran was studied, and tests of Atterberg limits, standard compaction, unconfined compressive strength, and California bearing ratio were performed on the soil stabilized with class C fly ash. The optimal amount of fly ash to improve soil strength was found to be 25%. Subsequently, experiments were conducted on soil-fly ash mixtures containing 0.5%, 1%, and 2% nanosilica. The results showed that adding up to 1% nanosilica improves strength, while a further increase in nanosilica leads to a decrease in strength. With 1% nanosilica, the compressive strength and soaked California bearing ratio of the sample containing 25% fly ash increased from 741 kPa to 926 kPa and from 27.4% to 36.2% after 28 days of curing, respectively. The reactivity and high specific surface area of nanosilica lead to accelerated hydration and an increase in cementitious products, which enhance the strength of the samples. The results also show that fly ash and nanosilica improve soil stiffness.

Keywords

Forest Road Subgrade
Soil Stabilization
Geotechnical Properties
Class C Fly Ash
Nanosilica
Strength Parameters
Subjects
  • Receive Date 30 April 2025
  • Revise Date 07 June 2025
  • Accept Date 08 June 2025
  • First Publish Date 08 June 2025
  • Publish Date 23 July 2025

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