The Dispersion Behavior Of Graphene Oxide And The Effect On The Hydration Performance Of Cement

Graphene oxide（GO）has significant reinforcing and toughening effects on cement-based composites,but the dispersion behavior and hydration effects have been bottlenecks limiting the wide application of GO cement-based composites.How to achieve good dispersion of GO in cement paste?What is the impact of GO on cement hydration process and hydration products?Based on the above problems,the relationship between the molecular structure of polycarboxylic acid water reducing agent（PCE）and the dispersion of graphene oxide was established from the dispersion behavior of graphene oxide.On this basis,the influence of GO on the hydration process and hydration products of C₃S,C₃A and cement systems was investigated in collaboration with a variety of characterization tests to reveal the regulatory mechanism and enhanced toughening mechanism of GO on the hydration behavior of cement.The main conclusion are as follows.The optimal dispersion parameters were determined by visual observation,UV-Vis absorption spectroscopy and Raman spectroscopy as PCE:GO mass ratio=3:1,ultrasonic power 150w,and ultrasonic time 10min to ensure adequate GO dispersion and avoid damage to the sheet structure.On this basis,the dispersion of GO in cement pore solution and cement paste treated with different structured PCE was further characterized by optical microscope observation,dynamic light scattering test,cement paste fluidity and cement mortar mechanical properties.From this,PCE6 with a large charge density that is most favorable for GO dispersion.On the one hand,PCE6 complexes free Ca²⁺in the solution to reduce the concentration of Ca²⁺to avoid GO agglomeration.On the other hand,PCE6 maintains the dispersion stability of GO through the steric hindrance effect of side chains.The effects of GO on the early dissolution process of clinker and the precipitation process of hydration products were investigated by heat of hydration,ICP-OES and SEM in four hydration systems of cement,C₃S,C₃A and C₃A+gypsum.The results show that GO can promote the C₃S dissolution process,and the-COO^-of the GO sheet provides a greater dissolution driving force to promote the dissolution of C₃S particles by complexing the free Ca²⁺in the solution.In cement and C₃S systems,the effect of GO on the promotion of product precipitation process is governed by the dispersion state of GO.GO in a well-dispersed state provides a much larger number of crystalline nucleation sites than agglomerated GO,which is more conducive to the rapid crystalline nucleation growth of hydration products.GO would inhibit the dissolution process and precipitation process of C₃A system.However,due to the adsorption of SO₄^2-on the surface of C₃A particles,GO can promote the dissolution process and precipitation process of C₃A+gypsum system.The effects of GO on C₃S and cement hydration products were investigated by XRD,TG-DTA,Nanoindentation,²⁹Si MAS NMR and XPS.The results showed that GO did not affect the physical phase composition of the hydration products,but could promote the increase of calcium hydroxide content,and the increase of calcium hydroxide content was related to the dispersion state of GO.GO can form good bonds with C-S-H gels,insert between C-S-H gels,refine the pore structure,fill the capillary pores,promote the regular arrangement of C-S-H gels,and induce the conversion of low-density C-S-H gels to high-density C-S-H gels.There are two main reasons for GO reinforced and toughened cement-based composites.On the one hand,well-dispersed GO can accelerate the hydration process,provide a large number of additional nucleation sites,promote the rapid crystallization and precipitation of hydration products,and increase the amount of hydration products.On the other hand,GO can influence the C-S-H gel properties,fill the pores between C-S-H gel layers and increase the high-density C-S-H gel content.Meanwhile,GO can form good interfacial bonding with C-S-H,reduce the generation and development of microcracks and improve the macroscopic properties of cementitious composites.