Effect Of Composite Nanomaterials On Rheology,Mechanical Properties And Microstructure Of Cement-Based Materials

With the progress of society and the development of science and technology,the use of nano-materials to adjust the microstructure of cement matrix to improve the comprehensive properties of cement matrix has become the current research focus.As a typical two-dimensional nano-material,graphene oxide（GO）has excellent physical and chemical properties,which can significantly improve the mechanical properties and microstructure of cement-based materials.However,the poor dispersion of GO in cement-based materials restricts its wide application.In this paper,GO was hybridized with nano-silica（nano-silica NS）by the sol-gel method to form GO-NS（GOS）,which improved the dispersion of GO and NS in the cement matrix.At the same time,the rheological properties,mechanical properties and,microstructure of GO,GO@NS（GN）and,GOS nano-cement-based composites were compared and analyzed.The specific research contents and conclusions are as follows:（1）GO was obtained by the Hummers method through oxidation,purification,and exfoliation.GO and tetraethyl orthosilicate（TEOS）were stirred in an alkaline aqueous alcohol solution at 40℃for 48 h,and GO-NS（GOS）nanohybrids were obtained.The active functional groups and micro-morphologies of GO and GOS were characterized by XRD,TEM,XPS,and FTIR.The test results show that GO has obvious folds,and GOS is covered with a dense NS layer,both of which have oxygen-containing functional groups.（2）GO,and NS were mechanically mixed into GO@NS（GN）by ultrasonic method.The degree of clarity of GO,GN,and GOS in deionized water（DI）,saturated calcium hydroxide（Ca（OH）₂）solution,and pore solution（PS）was compared and analyzed to judge the dispersion of nanomaterials in solution.The results showed that GO and GN accumulated and precipitated in the three solutions at 12 h and completely precipitated at 7 d,but there was no precipitation in the GOS solution,and it had good dispersibility.（3）The spreading,marsh cone flow time,and rheological parameters of GO,GN,and GOS cement pastes are compared and analyzed.The results show that GOS has the least effect on the rheological properties of cement paste at low content（0.01%-0.03%）.The spreading,yield stress,equivalent plastic viscosity,and thixotropic ring area of cement paste containing GOS decreased by 4%～12%,37%～84%,3%～13%,and 9%～24%,respectively,compared with the control group.The pseudoplasticity index decreased by 1%～5%.（4）based on the comparative analysis of the mechanical properties of GO,GN and GOS cement paste,it is found that the strength of cement matrix is the highest when the content of GO,GN and GOS is 0.01%,and the mechanical properties of cement-based materials are improved most obviously by GOS.Compared with the control group,the compressive strength of 3 d,7 d,and 28 d GOS cement-based materials increased by 43.27%,39.26%,and 34.10%respectively,and the flexural strength increased by 88.64%,50.72%,and 61.63%,respectively.（5）the hydration products and micro-morphology of GO,GN,and GOS cement matrix were compared and analyzed by XRD,TG-DTG,and SEM.GOS and GN contain NS to facilitate the pozzolanic reaction.After consuming extra calcium hydroxide（CH）,more C-S-H gels are formed.GOS has a denser microstructure than GN.