Effect And Mechanism Of Functionalized Nano-SiO₂ With Tannic Acid On The Properties Of Composite Cement-based Materials

Cement is the largest artificial cementitious material in the world.However,the cement production process involves the"two grinding and one burning"process,which not only consumes a significant amount of energy but also results in prominent carbon emissions and pollution problems.This process is less environmentally friendly.Therefore,finding ways to reduce carbon emissions caused by cement production and use has become a critical research topic in this field.At this stage,numerous studies and practices have demonstrated that utilizing fly ash,slag,and other industrial wastes as supplementary cementitious materials in concrete,to replace a portion of the cement,is a crucial method for conserving energy and reducing carbon emissions.However,supplementary cementitious materials have low reactivity,and their involvement in the hydration reaction process primarily depends on the formation of Ca（OH）₂ after the hydration of cement.This occurs after the secondary hydration reaction or volcanic ash reaction,which significantly dilutes the cement’s binding capacity.When the dosage is too high,it adversely affects the performance of cementitious materials.To address this problem,this paper focuses on the influence of supplementary cementitious materials on the performance of cementitious materials.Specifically,it examines the use of nanosilica（NS）as the lifting material and tannic acid（TA）as the functionalized material for NS to address the issue of particle aggregation and dispersion difficulties.The study investigates the characteristics and mechanisms of the influence of tannic acid functionalized NS on the performance of cementitious materials with different active supplementary cementitious materials.Based on the findings,the paper proposes an in-situ preparation method of NS based on tannic acid.The main works and conclusions of this paper are as follows:（1）Silica sol plays a crucial role in cementitious materials by accelerating the cement setting process through mixing.This acceleration is directly linked to the nucleation effect of silica sol.On the other hand,TA will delay the setting process of composite cement.The pre-functionalized silica sol with TA can effectively regulate the setting process of composite cement and maintain the setting time within an appropriate range.TA can significantly enhance the compressive strength of the fly ash mortar,whereas the silica sol has no noticeable effect.The TA functionalized silica sol has contributed to the improvement of the compressive strength of the fly ash mortar,resulting in a 25.96%increase compared to the control group under the optimal proportioning conditions.25.96%.Overall,the results demonstrated the enhancing effect of TA on the dispersion of silica sol nanoparticles and the functionalization of ion chelation.（2）In the slag-based composite cementitious materials,the initial setting time of the neat mortar increased slightly with the functionalization of silica sol by TA,and it further increased with the increase in TA dosage.However,the final setting time was significantly longer compared to the control group at each respective dosage.With the increase of TA doping,the 3d compressive strength of the mortar decreased,while the 28d compressive strength increased.This indicates that in the high-activity supplementary cementitious material system,TA has a stronger promotion effect on the hydration of composite cementitious materials than a retardation effect.Furthermore,the promotion effect becomes stronger with age,while the retardation effect weakens.The TA-functionalized silica-sol enhances the hydration process of the composite cement,stimulates slag activity,and promotes the overall hydration process of the composite cement.The formation of calcium hydrated silicate（CSH）enhances the development of compressive strength in mortar.（3）It is feasible to adopt in-situ preparation and functionalization of nanosilica.The NS prepared by TA/water glass premixing led to a maximum increase of 26.14%in the28d compressive strength of fly ash mortar and a maximum increase of 49.06%in the compressive strength of slag mortar.The NS prepared by TA/water glass premixing has a similar effect to the silica sol functionalized by TA,and it can promote the production of more hydration products in the composite slurry.Particularly,in the slag-based composite cement,the NS prepared by TA/water glass can enhance the activity of slag,facilitate the formation of hydration product CSH,improve the secondary hydration capacity of slag,optimize the pore distribution of the mortar,and reduce porosity.Figure[51]Table[23]Reference[224]...