Influence of Na2O Content and Ms (SiO2/Na2O) of Alkaline Activator on Workability and Setting of Alkali-Activated Slag Paste.

Sung Choi,Kwang-Myong Lee

doi:10.3390/ma12132072

Abstract

The performance of alkali-activated slag (AAS) paste using activators of strong alkali components is affected by the type, composition, and dosage of the alkaline activators. Promoting the reaction of ground granulated blast furnace slag (GGBFS) by alkaline activators can produce high-strength AAS concrete, but the workability might be drastically reduced. This study is aimed to experimentally investigate the heat release, workability, and setting time of AAS pastes and the compressive strength of AAS mortars considering the Na2O content and the ratio of Na2O to SiO2 (Ms) of binary alkaline activators blended with sodium hydroxide and sodium silicate. The test results indicated that the AAS mortars exhibited a high strength of 25 MPa at 24 h, even at ambient temperature, even though the pastes with an Na2O content of ≥6% and an Ms of ≥1.0 exhibited an abrupt decrease in flowability and rapid setting.

Highlights

Environmental imperatives such as the reduction of CO2 and conservation of natural resources are becoming issues worldwide
Alkali-activated slag (AAS) concrete, which is produced by using an alkali activator on ground granulated blast furnace slag (GGBFS), is a typical zero cement concrete
It should be noted that GGBFS activated in this way has very fast reaction rates due to chemical ionic reactions [6]

Summary

Introduction

Environmental imperatives such as the reduction of CO2 and conservation of natural resources are becoming issues worldwide. In order to totally replace cement with GGBFS and FA attempts have been made to create zero-cement concrete by the alkali activation of GGBFS and FA [1,2,3,4,5]. Alkali-activated slag (AAS) concrete, which is produced by using an alkali activator on GGBFS, is a typical zero cement concrete. Alkaline (pH = 12) activators are needed to stimulate GGBFS. Alkaline activators largely impact the properties of AAS concrete and their characteristics such as the alkali concentration, the dosage, and the water-to-solid ratio should be examined prior to the mixture design of AAS concrete [7,8]. A better understanding of the effects of such alkaline activators on the reaction mechanisms of alkali-activated slag could indicate ways to optimize the use of alkaline activators

Objectives

Methods

Results

Conclusion