Study Of The Effect Of Graphene Oxide On Cement Performance And Its Mechanism

Graphene oxide,as a two dimensional nanomaterials,has been wildly used in cement based materials for application research.However,the effect mechanism of graphene oxide on the performance of cement base material is not clear.In this paper,different type of cement paste and mortar with different GO dosage or size was prepared,then the effect of graphene oxide on the rheological behavior and the hydration process and hydration products and a variety of performance of cement based materials were studied.Furthermore,we analyzed the mechanism of graphene oxide in cement base material.The lamellar stucture and the oxygen containing functional group of graphene oxide we used were characterized by AFM,TEM,XPS,and FTIR.That the GO sheets exhibit irregular shapes with a dimension of about a round 1-10 ?m and a thickness of about 1 nm.GO sheets is almost transparent nanosheet with many wrinkled and folded feature in liquid phase.The oxygen containing functional group including hydroxyls(-OH),carbonyls(-C=O),and sp3 carbon with C-O bonds(-C-O),and oxygen content of GO is about 48%.The rheological property and flocculation morphology of fresh cement pastes with various contents of graphene oxide were studied quantitatively by rheometer and Laser Confocal Scanning Microscope.Results show that at the presence of GO,the re-agglomeration of cement particles occurs and new flocculation structures are generated,although cement particles have been homogeneously dispersed under the action of polycarboxylate superplasticizer.The new flocculation structures lead to the unique rheological properties of the cement paste.The hydration degree and hydration products of hardened cement paste with different GO dosage or size were characterized by isothermal calorimeter,XRD,TG-DTA and ICP.Results show that graphene oxide on the hydration process of cement had no obvious effect.But graphene oxide has a significant influence on the morphology of calcium hydroxide,which is one of the main product of cement hydration.The presence of graphene oxide not only has obvious inhibitory effect for the crystal calcium hydroxide,but it is able to refine crystal size of calcium hydroxide.We also tested a variety of performance of hardened cement paste and mortar,including mechanics performance,pore structure,shrinkage performance and anti-penetrability.Results show that the presence of graphene oxide can effectively improve the flexural strength and compressive strength of cement base materials.Graphene oxide is able to increase the number of gel pores and capillary pores in hardened cement paste,leading to a significantly increased drying shrinkage.The permeability resistance of mortar has certain improvement when mortar was mixed with graphene oxide.Electron microscopy images show that the graphene oxide we used had no obvious effect on the crystal configuration.This paper argues that the enhance effect of graphene oxide in the properties of cement-based materials have three main reasons:(1)The refine effect of graphene on material's pore structure;(2)The refine effect of graphene oxide on crystal calcium hydroxide;(3)Graphene oxide sheets which is in block have inhibition effect for the internal micro cracks generate and extend in the process of destruction.