| In order to cope with global climate change and reduce carbon emissions,China strives to reach the peak of carbon dioxide emissions by 2030 and achieve carbon neutrality by 2060.As an important building material,the problem of high carbon emissions has received great attention,so the research and application of green high-performance cement has become the main development direction.High belite sulphoaluminate cement(HBCSA)is a new type of low-carbon cement.Compared with traditional cement,it has the characteristics of rapid hardening,high strength,low shrinkage and corrosion resistance.However,the high production cost has limited the development and application of high belite sulphoaluminate cement.In order to reduce its use cost,improve ecological benefits,economic benefits and application prospects,this topic aims to prepare a low-carbon,environment-friendly high belite sulphoaluminate mud based multi-component cementitious material.In this paper,the influence of additives on the performance of high belite sulphoaluminate cement is preliminarily explored,ordinary Portland cement and gypsum are introduced to prepare the high belite sulphoaluminate slurry based ternary cementation system,and the influence of the addition of fly ash and mineral powder and their amount on the basic performance,hydration products and morphological characteristics of the high belite sulphoaluminate slurry based ternary cementation system is studied,And explore the corrosion degradation mechanism of multi-component cementitious materials in sulfate environments.The research results indicate that:(1)By studying the effect of admixtures on the properties of High-belite sulphoaluminate cement and taking 1.4% as the saturated content of cement net slurry fluidity,it is found that the three retarders have different degrees of retarding effect and do not affect the types of cement hydration products.β-cyclodextrin combined with polycarboxylic acid water reducing agent,compared with the use of water reducing agent alone,the initial fluidity of cement slurry is not much different,the dispersion is more stable,the early and late strength of cement are reduced.After the combination of citric acid or borax and polycarboxylic acid superplasticizer,the initial fluidity and Zeta potential analysis of cement slurry were reduced,but borax did not affect the strength of cement mortar.When citric acid and borax were mixed with β-cyclodextrin,the fluidity of the mixture was improved,but it was not beneficial to the development of cement strength.Therefore,it also inhibited the development of AFt,the main hydration product of cementite,and changed its morphology.(2)By adding ordinary Portland cement and gypsum to High-belite sulphoaluminate cement,the High-belite sulphoaluminate cement-Portland cement-gypsum terpolymer system was prepared.The mechanical properties of the terpolymer system were studied.When the ratio of High-belite sulphoaluminate cement,Portland cement and gypsum was 7:2:1,the strength development of the terpolymer system was more beneficial.The basic properties,types of hydration products and microstructure of fly ash and mineral powder were studied by adding different amounts of fly ash and mineral powder into the ternary cementing system based on High-belite sulphoaluminate.The addition of fly ash and mineral powder can improve the fluidity of the composite system,reduce the loss of fluidity,and improve the shrinkage resistance of the cement-based composite system.However,the effect of extending the setting time of the ternary cementative system is not obvious.After the addition of fly ash and mineral powder,the setting time of the multicomponent cementative material is only extended by 6min at most.With the increase of fly ash and mineral powder content,the compressive strength of the cementing material decreases continuously,especially when the content of all the admixture components reaches 30%.Scanning electron microscopy showed that the morphology of ettringite developed slowly and the total amount of ettringite was reduced.According to the thermal analysis,the hydration degree of the ternary gelling system in blank group is the highest,and the hydration reaction of the multicomponent gelling material mixed with fly ash and mineral powder is weakened.From the analysis of hydration products,it can be seen that the main hydration product of multi-cementite material mixed with fly ash and mineral powder is still ettringite.(3)The effect of fly ash and mineral powder on the corrosion resistance of High-belite sulphoaluminate cementified ternary cementification system was studied.The quality change of multicomponent cementified material cementified sand test block was relatively obvious after immersion in sodium sulfate solution.The mass change rate of cement cementified sand mixed with admixture was significantly higher than that of blank group,and the mass change rate of cement cementified sand increased linearly at the early soaking stage.In the later period,the mass change rate changed little and tended to be stable.The compressive strength increased gradually with the increase of soaking age,and began to decline after soaking for 240 days.The relative dynamic elastic modulus increased within 120 days and decreased after 120 days,and the decrease was most obvious in blank group.Under the condition of semi-immersion,the mass change rate of the cement mortar test block increased slightly and remained in an increasing state,while the strength of the lower part of the test block soaked also changed significantly.Microscopic tests showed that the diffraction peak of ettringite AFt was significantly enhanced after 240 days of sulfate erosion,which was also the reason for the strength increase in the process of erosion.Scanning electron microscope images showed that the generated ettringite crystal was relatively coarse,and micro-cracks appeared in the test block,resulting in the strength decline after 240 days of erosion.When fly ash and mineral powder are mixed,the resistance to sulfate attack of the ternary cementing system based on High-belite sulphoaluminate can be improved. |
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