Effects Of Nano-materials On Hydration And Hardening Properties Of C₃S Mineral

Cement based materials have become the largest and most widely used building materials.However,the durability of cement-based materials is affected by carbonation,chloride ion erosion,freeze-thaw cycle,etc.,which seriously affect the service life.In recent years,nanomodified cement based materials have become a new method to improve their mechanical properties and durability.The nano-materials have small particle size and high activity.When nano-marterails are added into cement based materials,they can promote the hydration,optimize pore structure and improve hydration product content due to filler effect,nucleation effect and pozzolanic effect.Up to now,however,research is mainly focus on paste,motar and concrete,the relative lack of research on C₃S mineral of cement clinker.In order to further study the effect of nano-materials on hydration and hardening properties of cement,this paper chooses C₃S?the main mineral composition of cement clinker?as the research object and the effects of nano-SiO₂,nano-CaCO₃ and nano-TiO₂ on hydration and hardening properties of C₃S have investigated.The influences of nano-marterails on hydration,rheological and hardening properties of C₃S have investigated by early hydration heat,setting time,Ca?OH?₂ content and C-S-H relative content,shear stress,yield stress,apparent viscosity,plastic viscosity,pore size distribution,microstructure and compressive strength.Based on the experimental data,the main conclusions are as follows:1.Effect of nano-materials on the hydration properties of C₃SNano-SiO₂,nano-CaCO₃ and nano-TiO₂ can improve the hydration exothermic rate and total hydration heat within 3 days,which means that the early hydration of C₃S is promoted by nano-materials,but there are differences among 3 nano-marterials in hydration promoting effect of C₃S.Under the optimal amount of nano-materials?SiO₂: 3%;CaCO₃: 1%;TiO₂: 5%?,the promotion on C₃S hydration: nano-SiO₂ > nano-TiO₂ > nano-CaCO₃.Nano-SiO₂,nano-CaCO₃ and nano-TiO₂ can promote the condensation of C₃S,but there are differences in the accelerating coagulation.The initial setting time is shortened by 58 min,34 min and 23 min and final setting time is shortened by 41 min,21 min and 17 min when 1% nano-SiO₂,nano-CaCO₃ and nano-TiO₂ is added,illustrating the acceleration effect of nanomaterials on C₃S condensation: nano-SiO₂ > nano-TiO₂ > nano-CaCO₃.The results of Ca?OH?₂ content and the relative content of C-S-H indicate that the nanoSiO₂ promotes the hydration of C₃S in 3 days,and the more content of nano-SiO₂,the better the hydration promotion effect;however,the hydration rate of C₃S gradually decrease with the increase content of nano-SiO₂ after 3 days;the addition of nano-SiO₂ improves the relative content of C-S-H,which is of great benefit to improve the strength and durability of C₃S hardened paste.Under the optimal dosage of nano-CaCO₃ and nano-TiO₂,the content of Ca?OH?₂ and CS-H is the highest in nano-TiO₂ modified C₃S samples at 3 and 28 days,followed by nanoCaCO₃ modified C₃S samples and the content of Ca?OH?₂ and C-S-H is the lowest in pure C₃S sample.It can be seen that both nano-CaCO₃ and nano-TiO₂ can promote the hydration of C₃S,but the promotion effect of nano-TiO₂ is better than that of nano-CaCO₃.2.Effect of nano-materials on rheological properties of C₃S pasteNano-SiO₂,nano-CaCO₃ and nano-TiO₂ can thicken the C₃S paste,and the thickening effect of nano-materials on C₃S paste is more and more obvious with the increase content of nano-materails;the thickening effect of different nano-materials on C₃S paste is different due to the difference of the specific surface area of nano-materials and the promotion effect on early hydration of C₃S,nano-SiO₂ > nano-TiO₂ > nano-CaCO₃.3.Effect of nano-materials on C₃S hardened pasteNano-SiO₂,nano-CaCO₃ and nano-TiO₂ can improve the compressive strength of C₃S hardened pastes,the optimum amounts are 3%,1% and 5%,respectively.However,improvements in compressive strength among nano-materials are different: nano-SiO₂ > nanoTiO₂ > nano-CaCO₃.When nano-SiO₂,nano-CaCO₃ and nano-TiO₂ under the optimal amount,the compressive strengths of C₃S are 40.06 MPa,18.71 MPa,28.25 MPa at 3 days and 61.41 MPa,54.94 MPa,58.56 MPa at 28 days.Nano-SiO₂,nano-CaCO₃ and nano-TiO₂ can reduce the total porosity of C₃S hardened paste,increase the density and improve the pore structure.When nano-SiO₂,nano-CaCO₃ and nano-TiO₂ under the optimal amount,the total porosity of C₃S hardened pastes is 17.14%,18.62% and 17.87%,respectively;the density of harded pastes is 1.73 g/cm3,1.67 g/cm3 and 1.69 g/cm3,respectively;the pore content less than 20 nm was 71.85%,14.63% and 23.25%,respectively,which reflect the optimization effect of nano-marterials on pore structure: nano-SiO₂ > nanoTiO₂ > nano-CaCO₃.Morphologies of C₃S hydration products show that the addition of nano-SiO₂,nanoCaCO₃ and nano-TiO₂ can change the morphology of C-S-H in C₃S hardened pastes,which makes C₃S hardened pastes more compact,and reduces the porosity.C-S-H gel in nano-SiO₂ incorporated C₃S has lower Ca/Si ratio in comparison to pure C₃S at 3 and 28 days,which is beneficial to improve the permeability resistance of C₃S.