Influence of fly ash on mechanical properties and hydration of calcium sulfoaluminate-activated supersulfated cement.

Zhengning Sun,Hui Li,Jian Zhou,Qiulin Qi,Ru Mu,Na Zhang

doi:10.3390/ma13112514

Abstract

This paper aimed to report the effects of fly ash (FA) on the mechanical properties and hydration of calcium sulfoaluminate-activated supersulfated cement (CSA-SSC). The CSA-SSC comprises of 80% granulated blast furnace slag (GBFS), 15% anhydrite, and 5% high-belite calcium sulfoaluminate cement (HB-CSA) clinker. The hydration products of CSA-SSC with or without FA were investigated by X-ray diffraction and thermogravimetric analysis. The experimental results indicated that the addition of FA by 10% to 30% resulted in a decrease in the rate of heat evolution and total heat evolution of CSA-SSC. As the content of FA was increased in the CSA-SSC system, the compressive and flexural strengths of the CSA-SSC with FA after 1 day of hydration were decreased. After 7 days of hydration, the compressive and flexural strength of CSA-SSC mixed with 10 wt.% and 20 wt.% of FA rapidly increased and exceeded that of ordinary Portland cement (OPC), especially the flexural strength. Moreover, the compressive strength of CSA-SSC mixed with 30 wt.% of FA after 90 days of hydration was close to that of OPC, and flexural strength of CSA-SSC mixed with 30 wt.% of FA after 7 days of hydration was close to that of OPC. The hydration products of the CSA-SSC and CSA-SSC mixed with FA were mainly ettringite and calcium silicate hydrate (C-S-H).

Highlights

Ordinary Portland cement (OPC) is the most widely used cementitious material in civil engineering construction
The hydration reaction of ordinary Portland cement (OPC) paste is accompanied by the release of a vast amount of hydration heat, which enhances the internal temperature of the mass concrete structure
The calcium sulfoaluminate-activated supersulfated cement (CSA-SSC) consisted of 80 wt.% granulated blast furnace slag (GBFS), 15 wt.% anhydrite, and 5 wt.% high-belite calcium sulfoaluminate cement (HB-CSA) clinker

Summary

Introduction

Ordinary Portland cement (OPC) is the most widely used cementitious material in civil engineering construction. The hydration reaction of OPC paste is accompanied by the release of a vast amount of hydration heat, which enhances the internal temperature of the mass concrete structure. When the thermal deformation is restrained, it is easy to cause cracking of the concrete surface and, seriously affect the durability and safety of the mass concrete structure. Weakening the temperature rising inside the mass concrete structure is a critical key to prevent the development of cracks from the mass concrete structure [1,2,3]. The cementitious material with low heat evolution should be widely used in mass concretes [4,5,6]

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