Study On Mechanical Properties Of Graphene Modified Sulfoaluminate Cement

As a new green building material,sulfoaluminate cement has the characteristics of fast hardening and early strength,cold resistance and impermeability,which can be used in quick repair,winter construction and ocean engineering.Graphene has high mechanical strength,high toughness and superior electrical and thermal properties,so it has broad application prospects.In this paper,the application of graphene in improving the mechanical properties of sulfoaluminate cement composite was studied,the preparation method of graphene-sulfoaluminate cement composite was studied,and the improvement effect and internal mechanism of graphene on the mechanical properties of sulfoaluminate cement were studied from both macro and micro scales.The main research contents are as follows.（1）Study the dispersion method and mix ratio design of graphene as well as the preparation method of graphene-sulfoaluminate cement composite,carry out compressive and flexural tests,and study the improvement effect of graphene on the macroscopic mechanical properties of sulfoaluminate cement composite.The internal mechanism of graphene improving mechanical properties of sulfoaluminate cement composite was studied by scanning electron microscope image morphology analysis and hydration thermal analysis.The macroscopic mechanical strength of the composites firstly increased and then decreased with the increase of graphene content,and 0.02wt%was the best graphene content.The production of ettringite increased in the composite sample,and no new hydration products were generated.The trend of hydration heat release peak of the composite sample was consistent with that of the blank sample,the second heat release peak of the composite sample was higher than that of the blank sample,and the hydration reaction rate of the composite sample was higher than that of the blank sample,and the total heat release of the composite sample was lower than that of the blank sample.（2）Nanoscale mechanical properties of graphene-sulfoaluminate cement composites were studied by nanoindentation test and phase analysis was carried out.The micro-nano mechanical strength of the graphene modified sulfoaluminate cement hydration products was tested by dot matrix method.The probability distribution diagram of the measured elastic modulus and hardness values of the samples was drawn by Gaussian mixture model,and the probability density function fitting was carried out to study the generation of hydration products of the composite materials.The addition of graphene has no significant effect on the elastic modulus and hardness values of the specific phase of sulfoaluminate cement.The pores and low-density calcium silicate hydrate after hydration of the composite sample are less than those of the blank cement sample.The addition of graphene can effectively promote the formation of high-density calcium silicate hydrate,ultra-high density calcium silicate hydrate and monosulfide calcium silicate hydrate,thus improving the macroscopic mechanical strength of the composite material.（3）Nano-indentation test was used to study the creep behavior of graphene-sulfoaluminate cement composites.The continuous stiffness test method was used to test the creep coefficient after loading to a certain load,and the influence of different water-cement ratios,curing specimens and other factors on creep behavior was studied.The creep coefficient C_IT of sulfaluminate cement samples without graphene was less than 7d after curing for 3d,and the creep behavior of cement samples was more obvious.The cement samples at two curing ages showed the same logarithmic creep trend.The C_IT fitting results of the graphene-added composite samples are within the range of the standard deviationσ-C_IT of the blank sample,and the difference between the mean value of theμ-C_IT creep coefficient is less than 3.05%.The creep behavior of sulfoaluminate cement was not affected by the addition of graphene.