Effect And Mechanism Of Nano-materials On Hydration Properties Of Tricalcium Silicate

Cement-based materials have become the world's largest and most widely used basic building materials.The service environment of cement-based materials is complex.Freeze-thaw cycle,chloride ion erosion and mechanical damage will reduce the durability of materials and cause economic losses.Nanometer materials have the characteristics of small particle size,large specific surface area and high activity.Put the nanophase materials into cement-based materials,which can affect the hydration rate,morphology and composition of hydration products and can improve the capability of cement-based materials effectively.At present,the research of nanophase materials in cement-based materials mainly focus on the modification of cement paste,mortar and concrete.Adding some nanometer materials can increase the strength of cement-based materials and reduce the porosity of the paste.Based on the above problems,this paper takes C₃S as the research object and selects three nano-materials:nano-Al₂O₃,graphene oxide and multi-walled carbon nanotubes,which has explored the influence of nano-materials on the macro-physical properties of C₃S,such as setting time,water requirement for standard consistency and compressive strength of hardened body.By using the XRD analysis,SEM-EDS analysis,comprehensive thermal analysis of hydration and pore structure analysis,the effects of three nano-materials on the composition,microstructure,heat release rate of hydration and pore structure of C₃S hydration products are studied.The main conclusions are as follows:?1?In the nano-Al₂O₃-C₃S hydration system,with the increasement of nano-Al₂O₃ content,the initial and final setting time of C₃S is prolonged obviously.As a filling material,nano-Al₂O₃ can fill the micropore in the paste,increase the density of the paste and improve the compressive strength of C₃S paste.When the content of nano-Al₂O₃ is 1%,the 28 days compressive strength is 54 MPa,and the compressive strength of blank sample is 46 MPa.The results of isothermal calorimetry show that nano-Al₂O₃ could accelerate the hydration rate of C₃S in initial hydration period,meanwhile delay the hydration of C₃S in acceleration period.The hydration product C-A-S-H don't promote the nucleation of C-S-H.The small size and large specific surface area of nano-Al₂O₃ could promote the hydration of C₃S.The cumulative exothermic amount and hydration rate in subsequent three days are higher than those in blank group.The relative contents of C-S-H and Ca?OH?₂ are calculated by TG thermal analysis method.The content of C-S-H and Ca?OH?₂ in C₃S hydration products is increased by nano-Al₂O₃ significantly.Scanning electron microscopy show that the addition of nano-Al₂O₃ makes the structure of C₃S paste compact.Pore structure analysis show that the addition of GO reduce the total porosity of C₃S paste.?2?In the GO-C₃S hydration system,the addition of GO has little effect on the water requirement and stability of C₃S paste.With the increasement of GO content,the initial setting time and final setting time of C₃S paste decrease.GO can improve the compressive strength of C₃S paste significantly.When the GO content is 0.2%,the 28d compressive strength is 51.23 MPa,and the 28d compressive strength of the blank sample is 46 MPa.The carboxyl on the surface of GO combines with the hydration product C-S-H,which becomes the nucleation point of C₃S hydration,accelerating the hydration of C₃S.The cumulative heat release and hydration rate of C₃S during hydration for 3 days are higher than those of blank samples.The cumulative heat release from hydration increases with the increasement of GO content.TG data shows that the content of C₃S hydration product C-S-H and Ca?OH?₂ is increased by the addition of GO.When the content of GO is 0.2%,the content of 28d hydration product Ca?OH?₂ is increased by 26%comparing with the blank sample,and the content of C-S-H is increased by 5.8%.Scanning electron microscopy shows that the addition of GO makes the structure of C₃S hardened paste compact and hydrate highly.The pore structure analysis shows that the total porosity of C₃S hardened slurry decrease with the addition of GO.?3?In the MWNTs-C₃S hydration system,the addition of MWNTs reduces the initial setting time and final setting time of C₃S paste.The more the MWNTs are added,the shorter the setting time of the C₃S slurry are.MWNTs can improve the compressive strength of C₃S paste significantly.When the content of MWNTs is 0.1%,the 28d compressive strength is 54.15MPa,while the 28d compressive strength of blank sample is 46 MPa.Meanwhile the compressive strength of C₃S paste increases by 17.7%.As a kind of nano-material,MWNTs can provide nucleation point of C₃S hydration,which can improve the hydration rate and cumulative exothermic amount of C₃S samples.When MWNTs content is 0.1%,the cumulative amount of 3d hydration exothermic heat is 274.28 J/g,while the blank sample is252.17 J/g.Scanning electron microscopy shows that the addition of MWNTs makes the hydrated product C-S-H gel bridge with nanotubes and form a dense network structure to have the slurry paste more dense.Pore structure analysis shows that after adding MWNTs,the total pore size of C₃S hydration slurry decrease,and the density of hardened paste is increased,and the paste structure is improved,and the physical properties of C₃S paste are improved.