Research On High Performance Materials By Carbonation Of Rankinite And Curing Equipment

Since Portland cement was invented,there have been inherent defects of low flexural strength and self shrinkage.On the other hand,CO₂utilization is an important way to realize the"two-carbon"strategy.Therefore,the low carbon and energy saving calcemite cement invented by our research group reacts with CO₂to form a building material with high flexural strength,which not only has multiple functions of CO₂utilization,reducing the amount of steel in concrete and reducing the self-shrinkage of concrete,but also can avoid cracks caused by self-shrinkage.Based on the above considerations,the following three aspects of research are carried out in this project:（1）taking calcite 3Ca O·2Si O₂（C₃S₂）as raw material,in the process of carbonation reaction with CO₂,through crystal type regulation formation,calcite is transformed into stone,and then high bending strength building materials are prepared;（2）Based on the reaction of C₃S₂and CO₂to generate Ca CO₃and calcium-modified silica gel,the volume change of C₃S₂in the carbonation process with different water-cement ratios was studied,and the influence of the volume change of C₃S₂on the performance of mortar test blocks was studied by changing its cemilar-sand ratio.（3）According to the carbonation property of C₃S₂and CO₂,a curing kiln equipment which can use the tail gas of cement kiln to conserve the brick composed of C₃S₂is designed.（1）Because C₃S₂ has high carbonation reactivity and generates a high proportion of calcium carbonate on the basis of carbonation,the transformation of aragonite to calcite is inhibited by crystal regulator during the formation of calcium carbonate and the formation of aragonite is promoted.The flexural strength of C₃S₂cement clincher is improved by in-situ growth of aragonite.Therefore,C₃S₂the main mineral component of C₃S₂cement clinker,was used as the experimental raw material,and the type,crystal shape and microscopic morphology of carbonated products were analyzed by XRD,SEM and FTLR.The product was quantitatively analyzed by Rietveld refining method,and it was determined that the crystal form of calcium carbonate carbonated product of C₃S₂net pulp was mainly calcite and a little aragonite,while containing a large amount of calcium-modified silica gel,and it was found that increasing temperature was conducive to the formation of aragonite.After the temperature was determined to be favorable to the formation of aragonite,inorganic ion Mg²⁺was added into the C₃S₂pure pulp as the crystal regulator.The formation of aragonite was observed by changing the molar ratio of Mg²⁺/Ca²⁺.Finally,it was found that when the reaction temperature was 70℃and the molar ratio of Mg²⁺/Ca²⁺was 0.1,the content of aragonite reached 36%and the content of calcite was 12%.Aragonite becomes the main crystalline form of calcium carbonate.Applying this condition to C₃S₂mortar test block,it is found that after carbonation for 28d,the bending strength and compressive strength of the mortar test block with Mg²⁺are 15.6 MPa and 71MPa,respectively.Compared with the bending strength（6.1 MPa）and compressive strength（65.6 MPa）of the mortar test block without Mg²⁺,The flexural strength of C₃S₂was greatly improved by 155%and 8%respectively.（2）By carbonation C₃S₂ clean pulp（1）to determine the C₃S₂ carbonated product,the volume change of test block of C₃S₂clean pulp under the condition of changing water-cement ratio and temperature was studied.According to the expansion calculation formula,the volume change of C₃S₂single mineral during carbonation was studied.It was found that at 0.35 water-cement ratio,The maximum expansion rate of C₃S₂test block can reach 0.149%,and the carbonation reaction degree is also the largest among the three water-cement ratios of 0.44,0.40 and 0.35.After determining the influence of water-cement ratio on C₃S₂test block,it is found that the volume change can occur during the carbonation process of C₃S₂.Therefore,the influence of volume change of C₃S₂on mechanical properties was studied by changing the cemilar-sand ratio.The results showed that the cemilar-sand ratio of 0.37,0.33 and 0.30 and the water-cement ratio of 0.45.It was found that the strength of the test block increased with the increase of the dosage of cemilar-sand at 3d,5d and 7d in the early stage,while the strength of the test block showed a trend of decline at the condition of 0.37 cemilar-sand ratio at 28.However,the strength of 0.33 and0.30 increases with the increase of time,and the mechanical strength of 0.33 cement-to-sand ratio is the best one under the four conditions.The compressive strength and flexural strength of the 0.33 cement-to-sand ratio reach 84 Mpa and 9.6 Mpa respectively at 28d,and the solid phase theoretical calculation shows that the volume of C₃S₂can expand by74.49%after complete carbonation.（3）According to the degree of 60%carbonation of C₃S₂,it is calculated that each kilogram of C₃S₂can absorb 240g during carbonation.Therefore,aiming at the consolidation of 50,000 tons of CO₂,a kind of curing equipment is designed through optimization,which can use the tail gas of cement kiln.The length of this curing kiln is380m,the height is 2.5m and the width is 8m.The brick billet is made by extrusion molding with C₃S₂and aggregate,and then transported to the curing kiln by transportation equipment for curing,so that the brick can absorb CO₂in the process of carbonation and hardening.