Preparation Of Solid-Waste-Based Ferric-Rich Sulfoaluminate Marine Engineering Cementitious Material And Research On Its Anti-erosion Property

In recent years,the strategy of "Powerful Marine Nation" has been promoted step by step,and the development of China's marine economy has a historic opportunity.The development of the marine economy is inseparable from the construction of marine concrete engineering such as cross-sea bridges.However,the traditional marine building material are prone to be destroyed after being eroded by sea water and washed by sea waves for a long time,which not only affects the normal use of marine engineering,but also causes serious waste of resources.Therefore,it is urgent to develop a new type of high durability marine engineering material to solve the problem of insufficient durability of marine engineering.The ferric-rich sulphoaluminate cementitious material not only has the characteristics of fast hardening,high early strength,high strength,high frost resistance and high anti-permeability,but also has better compactness and erosion resistance due to the hydration of its iron mineral phases.It is a kind of potential high durable marine material,but its high cost restricts its popularization and application.Therefore,this paper carried out a study on the synergistic use of industrial solid wastes to prepare ferric-rich sulphoaluminate cementitious material at low cost.Firstly,the feasibility of preparing ferric-rich sulphoaluminate cementitious material from red mud,aluminum ash,FGD-gypsum and limestone slag was explored.By designing different raw material proportions,the ferric-rich sulphoaluminate cementitious material clinker was prepared and comprehensively analyzed from the aspects of chemical composition,mineral phase composition and mechanical properties,and then the optimum synthesis temperature of the clinker was studied by using the best raw material proportion.Subsequently,the hydration characteristics of solid-waste-based sulfoaluminate cementitious material with typical mineral phase composition,including hydration heat liberation,types of hydration products,microscopic morphology of hydration products,and solidification ability of heavy metals were systematically studied.Finally,the ability,to resist the erosion of different concentrations of Na2SO4 solution and MgCl2 solution,of the solid-waste-based ferric-rich sulphoaluminate cementitious material was studied,and the mechanism of anti erosion to different different types of salt solutions was discussed based on the experimental results and previous literatureThe research results show that:(1)It is feasible to prepare ferric-rich sulphoaluminate cementitious material clinker by exclusively using red mud,aluminum ash,FGD-gypsum and limestone slag as raw materials.When the alkalinity modulus is controlled between 0.95-1.00,the prepared clinker can reach the standard of industrially prepared ferric-rich sulphoaluminate cementitious material clinker in chemical composition,mineral phase composition and mechanical property.Among them,the Fe2O3 content of the clinker is more than 9%,the main mineral phases of the clinker are ye'elimite,belite and brownmillerite,and the contents of these mineral phases are all within reasonable ranges;The compressive strength of the solid-waste-based cementitious material can meet the standard of 42.5 rapid hardening ferric-rich sulphoaluminate cement,the initial setting time is more than 30min and the final setting time is within 80min;The optimal synthesis temperature of the clinker should be controlled between 1230?-1250?.(2)The early hydration heat liberation of the solid-waste-based sulphoaluminate cementitious material is rapid and concentrated,the cumulative hydration heat of the material during the first 3 days is only 283J/g,which is lower than that of ordinary SAC under the same conditions.The main hydration products of the solid-waste-based sulphoaluminate cementitious material are ettringite and AH3,the ettringite is not only formed in large quantities in the early stage of hydration,but also gradually formed with increasing hydration age until 28d,and interlaced to form spatial frameworks in the later hydration age;The solid-waste-based sulphoaluminate cementitious material also have a good immobilization ability of heavy metals in the hydration process,with the leaching concentrations of Zn,Cr,As,and Cu much lower than the limits of Chinese National Standard,and with retention ratios of Zn,Cr,As,and Cu in solid-waste-based sulphoaluminate cementitious material pastes over 90%,at each hydration age.(3)The mechanical strength of the solid-waste-based ferric-rich sulphoaluminate cementitious material not only develops rapidly in the early stage,but also continuously increases with increasing curing age.The compressive strength of the mortars,which prepared respectively with water to cement ratio of 0.3,0.35 and 0.4,have all exceeded 42.5MPa after 3 days curing,and have all exceeded 75MPa after 28 days curing.After 28,60,90 and 120 days of erosion in different concentrations of Na2SO4 solutions and MgCl2 solutions,the anti-erosion coefficient of the mortars,prepared with different water to cement ratios(0.3,0.35 and 0.4),of the solid-waste-based ferric-rich sulphoaluminate cementitious material are all greater than 1,which indicate the solid-waste-based ferric-rich sulphoaluminate cementitious material have a good anti-erosion ability to Na2SO4 solution and MgC12 solution.