Frost Resistance of Magnesium Oxychloride Cement Mortar Added with Highland Barley Straw Ash

Abstract

In order to study the influence of highland barley straw ash (HBSA) prepared under certain conditions on the durability of magnesium oxychloride cement mortar (MOCM) under freeze-thaw damage, rapid freeze-thaw cycle tests were carried out firstly. The relative mass evaluation parameters and the relative compressive strength evaluation parameters, which represent the degradation of freeze-thaw resistance, were used as the indices to study the degradation rule of MOCM. Secondly, nuclear magnetic resonance (NMR) tests were carried out on MOCM under different freeze-thaw cycles to analyze the pore diameter changes in the freeze-thaw process. The microstructure of MOCM was tested by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and scanning electron microscopy (SEM), and then the effect mechanism of HBSA on the anti-freezing performance of MOCM was revealed. Finally, the two-parameter Weibull distribution function was used to analyze the reliability of durability degradation of MOCM added with HBSA under freeze-thaw cycles. The specific conclusions are as follows: With the increase of HBSA’s addition, the freeze-thaw resistance of MOCM increase firstly and then decrease. When the addition of HBSA is 10%, the decay rate of relative mass evaluation parameters and relative compressive strength evaluation parameters is the slowest, and the frost resistance is the best. The proportion of harmful pores and more harmful pores in MOCM added with 10% HBSA decreases by 25.11% and 21.34%, compared with that without HBSA before and after freeze-thaw cycles. A lot of magnesium silicate hydrate (M-S-H) gels are generated in MOCM with HBSA content of 10%, which fills part of the pores, so that the proportion of harmful pores and more harmful pores is the lowest. The Weibull function can be effectively applied to the reliability analysis of the freeze-thaw cycle of MOCM added with HBSA, and the theoretical results are in good agreement with the experimental results.

Keywords

magnesium oxychloride cement / highland barley straw ash / freeze-thaw resistance / pore diameter distribution / microstructure / reliability