The Performance High Ferrite Low Alite Portland Marine Cement And Its Concrete Products

With the proposal of"Marine Power"strategy for national security in the new era and the launch of the"The Belt and Road"cooperation initiative,China is vigorously carrying out the marine engineering construction and developing the marine economy.Concrete products is widely used in marine engineering construction due to their short production cycle,convenient transportation and high construction efficiency.However,concrete products used in the marine environment is prone to premature deterioration and destruction,owing to the harsh marine environment,which seriously threatens the safety of major engineering structures and restricts the pace of China’s marine development and construction.In view of the poor durability of Portland cement concrete products served in the marine environment,the high ferrite low alite Portland cement clinker mineral system was proposed from the perspective of the key cementitious material for preparing concrete products.Combined with the steaming technology of concrete products,it was systematically studied that the hydration reaction mechanism and erosion resistance behaviors of four mineral phases under high temperature curing condition.And the hydration performance and microstructure evolution of the high ferrite low alite Portland marine cement were also characterized.According to comprehensive evaluation of the mechanical properties and durability of the high ferrite low alite Portland marine cement based materials,a high durable Portland marine cement and concrete products was developed to adapt to the marine environment.The main work and innovative achievements of this paper are as follows:（1）A high seawater erosion resistance Portland marine cement and concrete manufacture technology is innovatively proposed.Through the break of traditional Portland cement clinker mineral composition,the high ferrite low alite Portland cement clinker mineral composition（C₄AF≥18%,C₃S≤50%）is designed with utilization of excellent seawater erosion resistance mineral C₄AF.Taking advantage of steam curing process to promote and optimize cement hydration and microstructure,the concrete products with improved mechanical properties and erosion resistance could be obtained.（2）Through the study of the corrosion resistance and thermodynamic stability of C₃A and C₄AF hydration products,the essential reasons for the high corrosion resistance of the high ferrite low alite Portland marine cement are revealed.The solid solution of Fe in the hydration product garnet not only changes the crystal structure parameters,but also changes its micro-morphology,so that the Fe-doped garnet exhibits a layer-by-layer gradient erosion process under sulphate attack conditions.The entrance of Fe in the hydrated calcium carbonate aluminate increases its exchange capacity for chloride ions.Quantum chemical calculations show that the substitution of Fe for Al reduces the hydrogen bond strength of the fixed exchangeable carbonate group in the crystal structure.Under high temperature conditions,the synthesized Fe-doped hydrated calcium sulphate aluminate from C₄AF and gypsum,has lower thermodynamic stability and is more likely to be converted to Fe-doped ettringite.（3）According to the research on the hydration reaction progress of C₃S andβ-C₂S under steam curing,the internal mechanism of microstructure acceleration in the high ferrite low alite Portland marine cement paste after high temperature curing was determined.High temperature curing promotes the polymerization of silica groups in C₃S slurry,forming long silicon chains and high polymerization degree C-S-H gels which has smaller porosity and less interlayer adsorption water.A very dense inner hydration product coating layer formed on the surface of the C₃S particles,inhibits the continuous hydration of C₃S in the subsequent curing stage.Forβ-C₂S,due to its low hydration activity,high temperature curing has a very limited acceletared effect on the hydration reaction ofβ-C₂S,but more hydrated product nucleation sites are formed on the surface ofβ-C₂S particles and reduce the subsequent hydration reaction barrier,leading to the accelerated hydrated reaction ofβ-C₂S.（4）Based on the study of hydration performance and microstructure evolution in the high ferrite low alite Portland marine cement,the process of continuous rapid hydration reaction and microstructure acceleration in the high ferrite low alite Portland marine cement after high-temperature steaming in the subsequent curing stage was analyzed.The mechanical properties and durability of steam curing the high ferrite low alite Portland marine cement based materials are evaluated comprehensively,which provides theoretical guidance for its application in the marine environment.The results show that the mechanical strength of the steam curing high ferrite low alite Portland marine cement based materials continues to increase in the late stage.At the same time,the number of capillary pores in the microporous structure of the matrix decreases,the connectivity of micropores deteriorates,and the chloride ion penetration resistance increases.Under the sulfate attack,the mechanical strength of specimen decays slower and displays excellent resistance to sulphate corrosion.Under the water flow and scour,the specimen has small mass loss and high anti-wear performance.After high-temperature steaming,the specimen has small expansion ratio and good volume stability.In summary,the high ferrite low alite Portland marine cement shows a continuous hydration ability and excellent corrosion resistance under steam curing,and has long-term service performance under severe marine environment,which can meet the demand for high durability and long life concrete in large-scale engineering construction and presents a very broad application prospect.