Alkali In Sulphoaluminate Cement And Its Effect On Cement Performance

In recent years,with the rapid development of large-scale infrastructure and civil engineering in China,higher performance requirements have been put forward for cement concrete products.As the third series of cement independently developed by China,sulphoaluminate cement has gradually gained recognition both at home and abroad due to its series of excellent properties,such as early strength,high strength,and erosion resistance.However,compared with Portland cement,its history is short relatively.Many basic theories still require further systematic and in-depth research.The study on the effect of alkali on the firing mechanism of Portland cement and the performance of cement has been reported,but particularly weak for sulphoaluminate cement.How does the alkali exist in the sulfoaluminate cement?How does alkali affect the performance of cement?For some high alkali cement production enterprise,how to regulate the performance and reducing the hazards of alkali in cement to better meet the needs of China's civil engineering construction,has become an increasingly concerned issue of the industry scholars.In this paper,the existence of alkali in sulphoaluminate cement clinker was studied by X-ray diffraction,scanning electron microscopy and elemental energy spectrum analysis.The alkali content of sulphoaluminate was studied experimentally through the setting time,free expansion rate and mechanical properties.The effect of performance was analyzed microscopically by X-ray diffraction and scanning electron microscopy.The results showed that a small amount of alkali in sulphoaluminate cement clinker was dissolved in C₂S to form Na₂Ca₃Si₂O₈,and most existed in the liquid phase in the form of Na₂K_2-XSO₄.For the clinker used in this article,the suitable alkali content promotes the development of later compressive strength,but the flexural strength of cement in each hydration age decreases first and then increases by the increasing of alkali content;when the alkali content is less than 0.8%,increasing the alkali content can promote the condensation of cement;when the alkali content is high,increasing the alkali content can inhibit early swelling of the cement and promote the later expansion,but the expansion rate still less than that of the low alkali cement.In this paper,the effect of mixed material on the performance of sulphoaluminate cement under different alkali content was experimentally investigated by setting time,free expansion rate and the mechanical properties.We found:?1?when the alkali content is 0.2%,adding 15%slag can reduce the early strength of cement,increase the growth rate of late strength,and suppress the 28d flexural strength contraction;adding15%fly ash can increase the flexural strength,reduce the late free Swelling ratio;adding 5%silica fume can increase the strength of cement and reduce the free expansion rate;adding 15%limestone can promote the later strength development,while suppressing the 28d flexural strength shrinkage,but it will lead to the free expansion rate of cement slurry increase.?2?when the alkali content is 0.5%,adding15%of slag can reduce the early compressive strength,improve the late strength,and promote the development of early expansion rate;adding 15%of fly ash leads to the compressive strength decrease,and improves the free expansion rate greatlyo;adding5%silica fume can increase the compressive strength especially the late strength;add15%limestone,lead to the compressive strength decreases and the free expansion rate increases.?3?when the alkali content is 0.8%,the addition of 15%slag leads to the strength decrease and the subsequent expansion rate increase;the addition of 15%fly ash can decrease the early strength,but the later-time flexural strength develops rapidly and promotes expansion;the addition of 5%silica fume can increase the strength,especially in the later flexural strength,while increasing the expansion rate in the later period;the addition of 15%limestone can reduce the strength,but increase s the expansion rate.In other words,different alkali content,the impact of the mixture on the performance of cement is not the same,we can adjuste production according to actual needs by adding mixed materials and control the performance of cement.