Preparation And Carbonation Hardening Properties Of Self-pulverized Low-calcium Cement

In order to reduce the energy consumption of cement firing and power consumption of grinding and reduce the emission of CO₂ gas,a new type of self-pulverized low-calcium cement with C₂S as the main mineral is proposed in this paper.The content of C₂S is higher than 79.2%.The self-pulverized power of the self-pulverized low-calcium cement is the transition energy of?-C₂S into?-C₂S.And carbonation technology was accelerated to make it harden.The preparation method of self-pulverized low-calcium cement,mechanical properties and microstructure after carbonation were studied.The specific research results are as follows.1.Preparation of self-pulverized low-calcium cement by chemical reagents was firstly conducted to initially explore the rate range and calcining temperature for the preparation of the cement.The result of the exploration is that the lime saturation coefficient KH is 0.667 and the silicon rate is 2.0 to 4.0.The firing temperature is1350°C.Based on the above exploration,further industrial materials were used to explore the preparation conditions of the self-pulverized low-calcium cement.The results show that the conditions for preparing the cement from limestone,sandstone/river sand and iron ore are as follows.Lime saturation coefficient KH is 0.667and silicon rate SM is 2.50³.50.Besides sintering temperature is 1300?.Cooling rate is below 400°C/min.?-C₂S content is more tnan 57.3%and?-C₂S conversion rate is more than 70%.Free calcium oxide content in the system cement is 0.0%.So that the cement has good burnability.The surface area of the ungrinded self-pulverized low-calcium cement is about 311.08 m²/kg,and the average particle size is about 25?m.The self powdering effect of the cement is remarkable.It can be directly put into industrial application without grinding,and the power consumption of cement clinker is saved.2.Because that?-C₂S has almost no hydration activity,the cement is hardened by carbonation.The accelerated carbonation device is a CO₂ reactor.After exploration,the suitable conditions for the carbonation reaction are as follows.The partial pressure of CO₂ in the reactor is 0.3 MPa and the temperature is 25°C.When the test blocks are molded,the water-cement ratio is 0.1 and the forming pressure of the preform of the extrusion test blocks is 4 MPa.The carbonation time is 8h.3.The compressive strength of the extruded pulp block for 8 hours is 76.8 MPa,and the 240 d compressive strength is 89.5 MPa.The compressive strength of the injection molded pulp block for 8 h is 56.9 MPa,and the compressive strength for 240days is 62.6MPa.Mortar specimens with the size of 40mm×40mm×160mm were prepared with the cement.After carbonation of 8h,The bending strength was 8.2MPa and the compressive strength was 51.6 MPa.Standard curing was used for Mortar specimens for 180d after carbonation.The bending strength at 240d was 14.0MPa and the compressive strength could achieve 71.2MPa.The cement exhibits excellent mechanical properties.In the microstructure of carbonated mortar test pieces,the cementitious carbonation product has good adhesion to the aggregate,which reduces the side effects of the interface transition zone on the self-pulverized low-calcium cement performance.4.The carbonated products are CaCO₃ and SiO₂ gels,and the combined effect of the two results in excellent physical and mechanical properties of the self-pulverized low-calcium cement..Compared with ordinary Portland cement,the cement production process saves limestone by 10%.CO₂ emission reduction is over 28%.