Influence Of Curing System And External Addition Of Metakaolin On The Properties Of High Ferrite Portland Cement-Based Materials

With the introduction and implementation of the"Maritime Power"strategy and the national"14th Five-Year Plan",the development and utilization of marine resources has gradually become an indispensable part of our country’s politics,military,economy and life.However,due to the short history of marine resources development in my country,the research on marine engineering materials has become a shortcoming of marine development and utilization in my country.At present,traditional marine engineering materials have insufficient durability such as poor abrasion resistance and poor resistance to chloride ion corrosion.,restricting the country’s long-term and safe development and utilization of marine resources.Reasonable development and modification of the existing cement-based materials to adapt them to the harsh marine service environment and improve their service life are of milestone significance for the development and utilization of marine resources.Through preliminary investigation and experimental verification,high iron phase Portland cement（C₄AF≥18%,C₃S≤50%）has low C3S content,resulting in low early hydration activity.By steam curing and other conditions,the early hydration degree of cement can be significantly improved,and the steam curing adaptability is better,but the later durability is inhibited.High Si content and high pozzolanic activity cementitious materials,as admixtures,can improve the mechanical properties and durability of cement-based materials.In this paper,based on the high iron phase Portland cement system,the benchmark cement was set as the control group.By adjusting the MK content and the curing system,the effect of the coupling of external driving forces on the microstructure and macroscopic properties of high iron phase Portland cement-based materials was explored.mechanism.At the same time,the influence of mixing water with high chlorine content on the mixing performance of cement was explored to provide technical reference for construction under coastal conditions.The main research contents and research results are as follows:（1）The steam curing adaptability of high-iron Portland cement mixed with MK was explored when pure water was mixed,and the coupling effects of two external driving forces of high-temperature steam curing and external MK on the performance of high-iron Portland cement were studied.Influence Mechanism.The study found that high temperature curing and external addition of MK have the same performance improvement effect on the benchmark cement,but the high temperature curing is insufficient to improve the macro strength and the resistance to chloride ion corrosion of the benchmark cement,and even inhibits it.High-temperature curing greatly promotes the early hydration reaction of high-iron phase Portland cement,and promotes continuous hydration in the later stage,which makes up for the disadvantage of insufficient early strength of high-iron phase Portland cement,and is beneficial to high-iron phase Portland cement.The continuous compaction and development of the microstructure of cement stone in the later stage of curing.In addition,high temperature curing promotes the subsequent dissolution of siloxy groups to aggregate on the existing silicon chains of C-S-H gels,increasing the MCL of C-S-H gels,and promoting Al to replace Si to generate C-A-S-H gels.;The incorporation of MK promotes the formation of the hydration reaction,makes up for the shortcoming of insufficient early hydration activity of the high-iron phase Portland cement,and improves the macroscopic compression performance and chloride ion erosion resistance.On the whole,the macroscopic properties and corrosion resistance durability of high iron phase Portland cement mixed with 10%MK under the condition of steam curing at 70°C are the best.（2）By using 0.5mol/L sodium chloride solution instead of pure water for mixing,the high-chlorine water source environment that may exist in coastal areas is simulated,and the coupling effects of two external driving forces of high-temperature steam curing and externally-doped MK when chloride ions are mixed in are explored.Effects of high iron phase Portland cement on properties.The study found that the high-iron phase Portland cement and the benchmark cement solidified the chloride ions mixed in by generating F salts,and the high content of C₄AF in the high-iron phase Portland cement provided sufficient Al phase for the generation of F salts,making the high iron phase Portland cement has a higher chloride setting than the benchmark cement.Increasing the curing temperature will accelerate the formation of hydration products and promote the chemical fixation of chloride ions;increasing the content of MK provides more Al phase for the formation of F salts and promotes the formation of F salts.The two factors work together to increase the production of F salts and promote the development of macroscopic strength and corrosion resistance of cement paste.