Influence of Activator Na₂O Concentration on Residual Strengths of Alkali-Activated Slag Mortar upon Exposure to Elevated Temperatures.

Tai Tran,Hyug-Moon Kwon

doi:10.3390/ma11081296

Abstract

The mechanical strength variation of ambient cured Alkali-activated mortar (AAS) upon exposure to elevated temperatures from 200 to 1200 °C was studied in this article. Slag was activated by the combination of sodium silicate liquid (Na2SiO3) and sodium hydroxide (NaOH) with different Na2O concentrations of 4%, 6%, 8%, and 10% by slag weight. Mechanical properties comprising compressive strength, flexural strength, and tensile strength before and after exposure were measured. Thermogravimetric analysis (Thermogravimetric analysis (TGA) and Derivative thermogravimetric (DTG)), X-ray diffraction (XRD), scanning electron microscope (SEM), and energy-dispersive X-ray spectroscopy (EDS) were also used for strength alteration explanation. The results indicated that Na2O concentration influence on strength variation of AAS mortar was observed clearly at temperature range from ambient temperature to 200 °C. The melting alteration of AAS mortar after exposed to 1200 °C was highly dependent on concentrations of Na2O.

Highlights

Blast furnace slag is a by-product that is formed by rapidly cooling the slag liquid from the furnace in cast iron manufacture [1]
Based on above experimental results and discussion, the study reveals the following conclusions: conclusions: The Na2 O concentration of alkaline activator has a great influence on mechanical strength of
The Na2O concentration of alkaline activator has a great influence on mechanical strength of unexposed alkali-activated slag mortar, higher compressive strength with higher concentration of unexposed alkali‐activated slag mortar, higher compressive strength with higher concentration of

Summary

Introduction

Blast furnace slag is a by-product that is formed by rapidly cooling the slag liquid from the furnace in cast iron manufacture [1]. Non-Portland cement binder, named as alkali activated slag (AAS), which is synthesized by mixing blast furnace slag with alkali hydroxide, carbonate, or silicate attracted a great deal of attention of many scientists due to its high strength, durability, and low environmental impact [2,3]. When compared with sodium carbonate or sodium hydroxide activator, slag activated by sodium silicate liquid possessed the highest compressive strength [5]. The activation products are predominantly composed of sodium and calcium aluminosilicate hydrates (C-A-S-H and N-A-S-H), as well as some hydrotalcite-like products when using sodium hydroxide or sodium silicate as activator [7,8,9,10]. Urban and industrial glass waste was investigated to be used as a potential alkaline activator for blast furnace slag [11,12,13]

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