Study On Interface Microstructure Of Cementbased Materials Based On High Resolution X-CT

It is well-known that the interfacial transition zone(ITZ)of cement-based materials is a bridge,connecting aggregates and cement paste.The structure and performance of ITZ is different from aggregates and cement paste.Compared with cement paste,ITZ with defects such as crystal orientation,large crystal size,large number of pores,large pore size,is a weak link of cement-based materials.It is directly affects the transport of mass and energy in materials.This will further influence the macroscopic performance and service life of materials.Therefore,it is important to study ITZ for improving the macroscopic properties of cement-based materials.In the thesis,the high resolution X-CT is used to obtain the three-dimensional internal structural information of the ideal sample without loss.The ideal sample(sand/ cement powder deposit sample and single aggregate cement paste)is used to simplify the ITZ.The geometric magnification method is used to solve the problem that the ITZ statistical unit is too small to be representative.Combined with digital image processing techniques,the related information of the wall-effect is quantitatively characterized,and the effects of W/C ratio,particle size of the gel material,the curvature of the aggregate and curing time(hydration time)on the ITZ and wall-effect were studied.The main conclusions are as follows: 1)Geometric magnification is an effective method to expand the statistical unit and conduct ITZ analysis.It solves the problem that the ITZ statistical unit is too small to be representative.2)The W/C ratio affects the grain size of unhydrated cement particles in the ITZ.When the curing conditions stay the same and the curing age is 7 days,at the same distance from the aggregate,the average diameter of unhydrated cement particles in the single-aggregate hardened cement with a W/C ratio of 0.40 is less than that with a W/C ratio of 0.53.In the entire statistical range,the unhydrated cement particles of P40 have a volume average diameter of 11.8?m and P53 of 16.6?m.3)The width of ITZ increases with the increase of W/C ratio.When the W/C ratio increases from 0.40 to 0.53,the ITZ width of hardened cement increases from 9.00?m to 20.4?m.4)The ITZ width is related to the average diameter(or median particle diameter)of initial gel particles.The ITZ width of the sand carbon rod sample is about 600?m,which is similar to the median particle diameter(median particle diameter is about 600?m).The ITZ width of the cement powder sample is about 16.8?m,which is similar to the average diameter of the cement powder particles of about 15.8?m.