Behavior of Alkali-Activated Fly Ash through Underwater Placement.

Zarina Yahya,Petrica Vizureanu,Dumitru Doru Burduhos Nergis,Muhammad Aiman Asyraf Zainal Hakimi,Andrei Victor Sandu,Rafiza Abd Razak,Long-Yuan Li,Mohd Mustafa Al Bakri Abdullah

doi:10.3390/ma14226865

Abstract

Underwater concrete is a cohesive self-consolidated concrete used for concreting underwater structures such as bridge piers. Conventional concrete used anti-washout admixture (AWA) to form a high-viscosity underwater concrete to minimise the dispersion of concrete material into the surrounding water. The reduction of quality for conventional concrete is mainly due to the washing out of cement and fine particles upon casting in the water. This research focused on the detailed investigations into the setting time, washout effect, compressive strength, and chemical composition analysis of alkali-activated fly ash (AAFA) paste through underwater placement in seawater and freshwater. Class C fly ash as source materials, sodium silicate, and sodium hydroxide solution as alkaline activator were used for this study. Specimens produced through underwater placement in seawater showed impressive performance with strength 71.10 MPa on 28 days. According to the Standard of the Japan Society of Civil Engineers (JSCE), the strength of specimens for underwater placement must not be lower than 80% of the specimen’s strength prepared in dry conditions. As result, the AAFA specimens only showed 12.11% reduction in strength compared to the specimen prepared in dry conditions, thus proving that AAFA paste has high potential to be applied in seawater and freshwater applications.

Highlights

The construction of structures involving concrete underwater placement usually require additional considerations due to its unique circumstances
The current study investigated the performance of alkali-activated fly ash (AAFA) paste through underwater placement in seawater and freshwater
The AAFA can be used as binder for underwater concrete without the addition of anti-washout admixture (AWA)

Summary

Introduction

The construction of structures involving concrete underwater placement usually require additional considerations due to its unique circumstances. The effective placement of conventional concrete mixture underwater depends on two main factors: the mix design of concrete itself and placement method during concreting [1,2]. For the mix design of concrete, additions of anti-washout admixtures (AWA) and viscosity-modifying admixtures (VMAs) are necessary for conventional concrete to minimise the washout effect and the ability to self-consolidate during the underwater placement [3,4,5]. Concrete resistance against washout can be improved using mineral admixture with high fineness. The most used mineral admixture includes silica fume, ground granulated blast furnace slag (GGBS) and fly ash (FA) [2,6]. Heniegal [7] confirmed that the inclusion of

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Conclusion