Design Theory And Key Technology Research Of Green Manufacturing Of Low Carbon Functional Mineral Admixture

The"Belt and Road"is a national top-level cooperation initiative proposed by China.Traditional mineral admixtures are in short supply in many countries along the southern route due to the lack of resources and inconvenient transportation.Therefore,high cement content and high water-cement ratio are used in engineering construction to ensure the workability of concrete.The concrete construction in this area also faces severe challenges such as large loss of concrete slump,concentration of hydration heat release and poor volume stability due to the hot climate.These two issues will seriously affect the development of mechanical properties and durability of concrete structures.Based on the"13th Five-Year"national key research and development plan（2016YFC0701003）,this paper proposes the concept and design method of a new type of low-carbon functional mineral admixture（LCFMA）.Based on the functional component design and surface vapor deposition technology,the local waste stone powder is surface modified and given specific functions to solve the major common problems in the construction of concrete projects under high temperature in the southward area of the“Belt and Road”area,which also provide theoretical and technical support for the production and application of low-carbon cementitious materials.The main work and innovative achievements of this paper are as follows:1.Proposed the concept,functional component design method and regulation mechanism of LCFMA.On the basis of functional component design and surface vapor deposition modification technology,the surface modification of stone powder with different components and reactivity was performed to prepare low carbon functional mineral admixture with specific functions.The regulation mechanism of initial fluidity and slump loss over time,early hydration temperature rise and volume stability of functional mineral admixtures under high temperature environment has been established.2.The development law of mechanical properties of different cement-stone powder system under different curing temperatures was systematically studied,and the mechanism was revealed based on hydration product and microstructure analysis.（1）At 20℃curing temperature,the 56 d-strength of samples incorporating 30%marble powder（MP）,granite powder（GP）and perlite powder mortar（PP）were in the order of PP30>MP30>GP30,and the 56 d-activity index was 69.1%,61.4%and85.9%,respectively.The microscopic analysis showed that MP could react with aluminum phase to form Hc/Mc and prevent the transformation of AFt to Ms;GP basically did not participate in hydration reaction and played a filling role;reactive silica and aluminum components in PP promoted the generation of Ms and C-（A）-S-H,which accelerated the development of mechanical properties.And the reaction rate of PP at 56 d reached 21.01%.（2）High-temperature curing environment accelerated the cement hydration and improved the early-stage mechanical properties,but it was not conducive to its later strength development.Microscopic analysis showed that the crystallinity of Hc/Mc in MP contained samples decreased at 40°C,while Ca Mg（CO₃）₂ would participate in the hydration and generate Ht at 60°C,and no Hc/Mc formation was observed.GP had a certain degree of reactivity at high temperature.The 56-d reaction degree of GP reached4.77%at 40℃and 35.43%at 60℃.The pozzolanic activity of PP was sensitive to the curing temperature,and its 56-d reaction degree reached 35.43%at 40℃and 51.15%at 60°C.3.The modified components design and regulation methods of functional mineral admixtures were systematically studied,and the matching of functional components and regulation mechanism of LCFMA were constructed.（1）The matching relationship and numerical model of water reducing component,slump retaining component of high-fluidity mineral admixture and the fluidity of pastes were constructed.The regulation effect of water reducing components was KH>MSF>NX,and the compatibility index was KH>>MSF>NX.The adsorption capacity of mineral admixtures for KH was in the order of PP>GP>MP.Based on the response surface methodology（RSM）,the initial and 60 min flow performance and regulation law of the components of different system was studied,and the relevant numerical simulations was conducted.The developed KH-SPA synergistically modified high-fluidity mineral admixture could ensure that the pastes had basically no loss of flowability within 180min in a high temperature environment at 40℃,with the paste flow>300 mm.（2）The mechanism for regulating the hydration temperature rise of low-heat mineral admixtures based on the modification of retarding components was constructed.Unmodified stone powder effectively reduced the hydration temperature rise of the system,which was better than that of active mineral components,but had little effect on the peak position.Among them,30%unmodified MP,GP and PP reduced the hydration temperature rise about 34.03%,31.68%and 28.96%,respectively.The modification effect of the hydration heat inhibition component was in the order of PN>>BS>SJ.Based on the synergistic effect of dilution effect and hydration heat inhibition effect,MP,GP and PP modified by 0.20%,0.24%and 0.26%PN further reduced the hydration temperature rise by 39.3%,46.3%and 45.2%,respectively.The peak position was delayed to 145.65 h,192.26 h and 199.45 h,respectively.（3）The synergistic regulation mechanism of volume stability based on the compatibility of shrinkage compensating components,shrinkage reducing components and active mineral components was established.The improvement effect of unmodified stone powder on the drying shrinkage of cement-based materials was as follows:GP>MP>PP.Drying shrinkage of cement-based materials was also significantly improved by reducing the water-binder ratio.For MP and PP,MX expansion component was more effective,while for GP,GX expansion component was more effective.The shrinkage reduction component could also effectively improve the drying shrinkage,but the shrinkage reduction effect was not improved significantly when the dosage exceeded 1.0%.Compared with the unmodified sample,the drying shrinkage of MP,GP and PP modified high-volume stable mineral admixtures at 90 d decreased by53.5%,48.09%and 48.48%,respectively,under the co-regulation of expansion component and shrinkage reduction component.4.The research of LCFMA production and application.The modified functional mineral admixture of marble powder based on the design of functional components and surface vapor deposition process effectively improved the fluidity,slump retention,drying shrinkage and durability of concrete at high temperature.The concrete prepared by functional component modified mineral admixture maintained the fluidity not less than 585 mm within 180 min at 40℃,the28-d compressive strength reached 33.4 MPa,and the 90-d drying shrinkage was reduced by 32.23%compared with the reference sample,which met the demand of concrete construction under high temperature environment and provided technical support for the preparation and application of low-carbon functional mineral admixture.