Investigation of the Effect of Mixing Time on the Mechanical Properties of Alkali-Activated Cement Mixed with Fly Ash and Slag.

Taewan Kim,Choonghyun Kang

doi:10.3390/ma14092301

Abstract

This is an experiment on the effect of mixing time for alkali-activated cement (AAC) using a binder mixed with ground granulated blast furnace slag (slag) and fly ash (FA) in a ratio of 1:1 on the mechanical properties. The mixing method of ASTM C305 was used as the basic mixing method, and the following mixing method was changed. Simply adding the same mixing time and procedure, the difference in the order of mixing slag and FA, and controlling the amount of activator and mixed water were considered. As a result of the experiment, the addition of the same mixing time and procedure, pre-injection of slag, and high-alkali mixed water in which half of the activator and mixing water were mixed showed the highest mechanical properties and a dense pore structure. As a result, the design of a blending method that can promote the activation action of slag rather than FA at room temperature was effective in improving the mechanical properties of AAC. In addition, these blending factors showed a clearer effect as the concentration of the activator increased. Through the results of this experiment, it was shown that high-temperature curing, high fineness of the binder, or even changing the setting of the mixing method without the use of excessive activators can lead to an improvement of mechanical properties.

Highlights

Alkali-activated cement (AAC) has attracted considerable attention as a next-generation cement that could replace existing cement materials, and many researchers are currently conducting research on AAC [1]
The ground granulated blast furnace slag and fly ash (FA) are binary binders used in AAC, and many AAC studies using these binders have been published [2,3]
An experiment was conducted to investigate the effect of the mixing method on the mechanical properties of alkali-activated cement (AAC) in which slag and FA were mixed in a ratio of 1:1

Summary

Introduction

Alkali-activated cement (AAC) has attracted considerable attention as a next-generation cement that could replace existing cement materials, and many researchers are currently conducting research on AAC [1]. The higher the mixing ratio of slag in a slag–FA mixed binder, the higher the strength of the concrete [4,5,6,7,8,9,10], because the reaction of FA at ambient temperature is considerably low [4,5,11,12,13,14,15,16]. At ambient temperature, FA-based geopolymers exhibit long setting times and low strength [4,11,17,18,19]. At curing temperatures above 60 ◦C, FA-based geopolymers exhibit fast setting times and high strength [14,20,21,22,23,24,25,26,27]. Mixing FA and slag at high temperature can result in accelerated setting and enhanced strength [15,18,28,29,30,31]

Methods

Results

Conclusion