Evaluation of the Hydration Characteristics and Anti-Washout Resistance of Non-Dispersible Underwater Concrete with Nano-SiO2 and MgO

In Kyu Jeon,Byeong Hun Woo,Hong Gi Kim,Dong Ho Yoo,Jae Suk Ryou

doi:10.3390/ma14061328

Abstract

In this paper, the effect of nano-SiO2 (NS) and MgO on the hydration characteristics and anti-washout resistance of non-dispersible underwater concrete (UWC) was evaluated. A slump flow test, a viscosity test, and setting time measurement were conducted to identify the impacts of NS and MgO on the rheological properties of UWC. The pH and turbidity were measured to investigate the anti-washout performance of UWC mixes. To analyze the hydration characteristics and mechanical properties, hydration heat analysis, a compressive strength test, and thermogravimetric analyses were conducted. The experimental results showed that the fine particles of NS and MgO reduced slump flow, increased viscosity, and enhanced the anti-washout resistance of UWC. In addition, both NS and MgO shortened the initial and final setting times, and the replacement of MgO specimens slightly prolonged the setting time. NS accelerated the peak time and increased the peak temperature, and MgO delayed the hydration process and reduced the temperature due to the formation of brucite. The compressive results showed that NS improved the compressive strength of the UWC, and MgO slightly decreased the strength. The addition of NS also resulted in the formation of extra C–S–H, and the replacement of MgO caused the generation of a hydrotalcite phase.

Highlights

As bridges continue to age, experts have been increasingly concerned about their structural safety, and suggest strengthening procedures
The increase in the anti-washout resistance of the Underwater concrete (UWC) that contained Magnesium oxide (MgO) presumably occurred because the fine particles of MgO increased the cohesion of the concrete mixes. Both NS and MgO increased the cohesion of the UWC mixes due to their finer particle sizes compared to that of Ordinary Portland Cement (OPC), which enhanced the anti-washout resistance of the UWC
This study investigated the effects of NS and MgO on the hydration characteristics and anti-washout resistance of non-dispersible UWC concrete

Summary

Introduction

As bridges continue to age, experts have been increasingly concerned about their structural safety, and suggest strengthening procedures. The existing strengthening methods [1,2,3,4,5,6] for substructures are costly, traffic-disrupting, and have a long construction time To deal with these weak points of conventional strengthening methods, the FRP underwater strengthening method [7], the jacket strengthening method [8], and the precast concrete segment assembly method [9] have been proposed. UWC is generally produced using viscosity-modified admixtures (VMAs) and antiwashout admixtures (AWAs) to fabricate viscous concrete mixes [12]. It is directly poured into water, and washout resistance is a significant factor that determines its strength, durability, and workability. As UWC is based on self-compacting concrete, its rheological properties must be adequately maintained to ensure higher washout resistance

Methods

Results

Conclusion