Frost-resistance mechanism of multi-scale PFRC based on NMR

In order to explore the frost-resistance mechanism of multi-scale polypropylene-fibre-reinforced concrete (PFRC), the mass loss rate and relative dynamic elastic modulus variation curves of concretes made with different sizes of polypropylene (PP) fibre were analysed based on the fast freeze–thaw cycle test. Nuclear magnetic resonance testing and scanning electron microscopy were carried out to study the micropore structure of the PFRCs. The results showed that the multi-scale PFRC had excellent frost resistance. Compared with plain concrete, the concretes mixed with coarse and fine PP fibres showed a 0·242–0·427% improvement in porosity, with 75·68–84·00% of pores of radius less than 100 nm. When the total PP fibre content was held constant, but the amount of fine fibre was larger and the fibre diameter was smaller, the improvements in concrete micropore structure and spalling resistance were more obvious. For the multi-scale PFRCs studied, it was found that three sizes of fibres formed a better holistic network system as the fibres supported and complemented each other. The micropore structure and frost resistance of the concrete were improved significantly, while the cracking resistance and toughness of the specimens were adequate.