Research Of Low Carbondioxide Hydraulic Cement

There are many problems in present cement,cementitious material system and concrete production,such as high fineness of cement,high strength in early stage but low increase of strength in late stage,poor compatibility with admixtures,fast hydration rate,high hydration temperature rise and large shrinkage.The existence of"unknown zone"in the mixture of ordinary cement leads to the existence of"unknown zone"in the cementitious material system,no good gradation,and overall SO₃ deficiency;The prepared fresh concrete has poor homogeneity,large loss of damage and poor long-term durability.On the other hand,the low carbon development of cement-based materials is the trend of today's building materials.Concrete,as the largest amount of civil engineering materials,should also be subject to the development trend of energy conservation and emission reduction,but the production process of its main raw materials?cement?is a link with a lot of carbon emissions.Therefore,in order to solve the above problems,the development and application of low carbon cementitious materials is of great significance.This topic is based on the concept of“integrated cementitious materials”and the requirements of low carbon development of Professor Lian Huizhen of Tsinghua University,overall optimization of SO₃ content.The experimental research shows that the SO₃ content is between 3.5%and 4.5%,which is beneficial to improve the strength and crack resistance of the cementitious material system,and the rheological properties are also improved.The study found that in the low carbon cementitious material system,the quality of the slag powder is extremely important,and its advantages and disadvantages directly affect the strength and durability of the concrete.Generally,the 28-day activity index should be above 105%,and the7d activity should not be too low.The specific surface area should be 520⁵70m2/kg.When high-active slag powder is used,the clinker content is between 20%and 32%,and C30^C60concrete which meets the strength requirement can be prepared,and the workability is good.When using low-carbon cementing materials to prepare concrete,the water-to-binder ratio should be slightly lower than that of the mixing station.The test shows that when using low-carbon cementing materials to prepare concrete,the water-to-gel ratio of C30 concrete should be 0.40⁰.46;The water-to-gel ratio of C50 concrete should be in the range of0.28⁰.32;7%of ultra-fine limestone powder can improve the 3d strength of concrete,improve the workability of concrete,and reduce the heat of hydration of cementitious system.Comparing the current mixing station cementing material system with the low carbon integrated cementing material system,it is found that the strength and durability of the concrete prepared by the low carbon cementing material meet the specification requirements,and the performance is generally better than the benchmark group.The project used the crack-proof mold"square crack-resistant mold"independently researched and developed by the research group to study the crack resistance of the paste,mortar and concrete of the cementitious material system.Studies have shown that the crack resistance of low carbon cementitious materials is better than the current commonly used cementitious material systems.The more the clinker is added,the more sensitive the cracking is,the higher the SO₃content is,and the addition of a certain amount of expansion agent or steel slag will improves crack resistance of cementitious materials without affecting strength.Through the mercury intrusion test,it is found that the pore structure of low carbon cementitious concrete is concentrated in the harmless pores below 20nm,and the harmful pores above 200nm are greatly reduced.Scanning electron microscopy and XRD experiments show that the commonly used cementitious material system is due to SO₃.Insufficient content,there is no ettringite in the hydration products of the commonly used cementitious material system,and in the hydration products of the low carbon cementitious material,a certain amount of ettringite is formed from the curing age of 7 days,and the generated The volume expansion of ettringite can compensate concrete shrinkage to a certain extent and improve crack resistance.The subject also studied the mix design method of low carbon cementitious concrete.The design method proposed by the project emphasizes the relationship between concrete water consumption and aggregate,admixture quality and concrete strength grade.Concrete designed using this concrete mix design method can be formulated to meet the C30^C60 strength grade of concrete.According to the research content,a pilot program was proposed.By replacing the clinker with P.II cement,it is possible to formulate concrete that meets the production application.