Abstract
The high-temperature mechanical behaviour of a pre-industrial hybrid alkaline cement (HYC) was studied. The HYC in question contained 30 % Portland clinker and 70 % of a blend of slag, fly ash and a solid activator (mix of alkaline salts with a predominance of Na2SO4). The material was tested during exposure to high temperatures to establish its compressive and bending strength and elastic modulus, as well as fracture toughness, analysed using an innovative methodology to notch the hydrated cement paste specimens. Post-thermal treatment tests were also run to assess residual mechanical strength after 2 h of exposure to temperatures ranging from 400 °C to 1000 °C. TG/DTA, MIP and SEM were deployed to ascertain heat-induced physical-chemical changes in the structure. The higher mechanical strength during and after treatment exhibited by the hardened hybrid alkaline cement than the CEM I 42.5R ordinary portland cement (OPC) paste used as a reference was associated with the lower water and portlandite content found in HYC. Pseudo-plastic behaviour was observed at high temperatures in the loaded HYC in the tests conducted during exposure.
Highlights
RESUMEN: Efecto de las elevadas temperaturas en el comportamiento mecánico de un cemento híbrido
Mass loss at 200 °C was greater in ordinary Portland cement (OPC) (11 %) than in hybrid alkaline cement (HYC) (9 %)
That lower water loss may be due to a lesser degree of hydration in HYC than OPC, the authors deem that the differences are largely attributable to the lower water content in the highly polymerised gels forming in HYC
Summary
RESUMEN: Efecto de las elevadas temperaturas en el comportamiento mecánico de un cemento híbrido. Alkaline cements based on activated fly ash have been observed to behave pseudo-plastically when loaded [19, 20] at temperatures ranging from 500 °C to 700 °C, with stress-induced softening and considerable strain Such behaviour affects residual strength after the material is exposed to high temperatures, with compressive strength values rising as a rule and bending strength declining for reasons of dimensional stability. Hybrid alkaline cements (HYCs) are a new group of cements, developed by combining knowledge of traditional Portland and alkaline cement chemistry [11, 20,21,22,23,24] They are characterised by low clinker content (20 % to 30 %) and a high proportion of supplementary cementitious materials (SCMs). The need to add water only constitutes an advantage over traditional alkaline cements, which generally require a highly alkaline, normally viscous, unwieldy solution that is costly to ship and calls for pre-curing at temperatures of 65 °C to 85 °C [25]
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