Clinkerless ultra-high strength concrete based on alkali-activated slag at high temperatures

This work investigates the degradation mechanisms of clinkerless alkali-activated slag based ultra-high strength concrete (AAS-UHSC) upon exposure to high temperatures up to 800 °C. The heat-induced mechanical, mineralogical, molecular, microstructural, and pore structure alterations of AAS-UHSC pre...

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Bibliographic Details
Published in:Cement and concrete research 2021-07, Vol.145, p.106465, Article 106465
Main Authors: Cai, Rongjin, Ye, Hailong
Format: Article
Language:English
Subjects:
Alkali-activated binder
Aluminosilicates
Aluminum silicates
Clinker
Cracking (fracturing)
Crystallization
Degradation
Degradation mechanisms
Dehydration
High strength concretes
High temperature
Impact resistance
Incorporation
Microcracks
Microstructure
Molecular structure
Phases
Porosity
Portland cements
Slag
Spalling
Thermal damage
Thermal resistance
Thermal stability
UHSC
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Summary:This work investigates the degradation mechanisms of clinkerless alkali-activated slag based ultra-high strength concrete (AAS-UHSC) upon exposure to high temperatures up to 800 °C. The heat-induced mechanical, mineralogical, molecular, microstructural, and pore structure alterations of AAS-UHSC prepared with various activator types, water-to-powder ratios, and fiber incorporation are studied. The results demonstrate the beneficial roles of potassium incorporation on improving the thermal stability and integrity of AAS-UHSC, via suppressing deleterious crystallization and transformation of aluminosilicate phases at high temperature. In contrast to Portland cement clinker-based UHSC, no sign of explosive spalling is observed in AAS-UHSC, likely due to the presence of microcracks that enhance the pore network connectivity. The mechanical degradation of AAS-UHSC at high temperature below 600 °C is resulted from dehydration and decomposition of phases and consecutive thermal cracking, together with enlarged porosity and coarsened pore structure. As the temperature rising to 800 °C, crystallization and transformation of phases, as well as formation of porous microstructure, considerably aggravate the mechanical degradation of AAS-UHSC. In contrast to the thermal damage mitigation by polymeric fibers in conventional UHSC, the fiber incorporation has little positive impact on the thermal resistance of AAS-UHSC.
ISSN:0008-8846
1873-3948
DOI:10.1016/j.cemconres.2021.106465