Damage characteristics of hybrid fiber reinforced concrete under the freeze-thaw cycles and compound-salt attack

This paper presents an experimental investigation on the damage characteristics and microstructures of hybrid fiber reinforced concrete (HFRC) subjected to the freeze-thaw（F-T）cycles and compound- salt attack. The effect of steel fiber content and steel-polypropylene fiber hybridization on the apparent morphology, mass loss, relative dynamic elastic modulus (RDEM), mechanical strengths in terms of compressive and flexural strengths were studied. The damage mechanism was explored based on an analysis of pore structures of specimens. The results showed that the F-T cycle has adverse effect on the physical and mechanical properties of specimens. The addition of fibers alleviates the damage degree of concrete, and the fiber hybridization shows more pronounced effect. Results from the porosity analysis indicate the pore sizes of 1.2HFRC are mainly distributed within 40 nm and those of OC are within 60 nm. The volume of larger pore size of 1.2HFRC increases less than the others after salt F-T cycles. Finally, based on Weibull distribution function, evolution equations for the salt-frozen damage of HFRC are developed by a combination of strength attenuation and RDEM degradation. The research results provide theoretical basis and reference for the practical application and building maintenance of fiber reinforced concrete.