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To meet the material requirements for repairing cracked components serving in cold temperatures, the differences in the setting hardening characteristics and physical and mechanical properties of fly ash-modified magnesium phosphate cement (MPC) repair mortar cured at 0 °C and 20 °C were comparatively studied in this paper. The results show that under the same fly ash content, the compressive strength of MPC repair mortar cured at 0 °C is lower than that cured at 20 °C, and the setting time, fluidity, flexural strength, interfacial bonding strength, strength retention rate, and linear shrinkage rate are not significantly deteriorated. The above properties of MPC repair mortar vary with the increase in the fly ash content but still, remain appropriate when the fly ash content is not higher than 15 wt%. The microstructure of MPC is obviously refined when the content of fly ash is 10 wt%. Therefore, the MPC repair mortar cured at 0 °C and 20 °C has good physical and mechanical properties. In particular, the flexural strength and interfacial bonding strength of the specimens cured at 0 °C are higher than that cured at 20 °C at all curing ages, and at the curing age of 3 days, those are 7.9 MPa and 5.4 MPa, respectively. [ABSTRACT FROM AUTHOR]

The purpose of this study is to investigate the changes in surface morphology and mechanical properties for carbon steel butt-welded joints by ageing in salt spray environment. The corrosion characterizations of the base metal, heat-affected zone and weld metal for the butt-welded joints were tested by employing a 3D profile measurement technology, the results showed that the pitting geometrical parameters of all three zones had a similar time-dependent evolution rule, namely mean pit depth, maximum pit depth and volume-box parameter all increased with the increasing exposure corrosion time, while pitting aspect ratio decreased. In addition, it should be noted that the pitting corrosion in the heat affected zone was more severe than that in the other two zones. Tensile tests of the corroded butt-welded joint specimens were performed, the results had shown that the strength, ductility and strain hardening of the corroded butt-welded joints decreased as the degree of pitting corrosion increased. In particular, compared with the corroded base metal specimens with the same conditions, a more significant reduction of the tensile ductility for butt-welded specimens was observed. Besides, the reasons for this above degradation phenomenon were analyzed by using the numerical simulation methods. [ABSTRACT FROM AUTHOR]