Analysis Of Properties Of Cement-based Materials By Nanoindentation Technique

The macro properties of cement-based materials are determined by their micro-scale structurecharacteristics. Several advanced test methodologies like nanoindentation, thermal gravity analysis,atomic force microscopy were used to detect the micro properties of cement-based materials.Especially the nanoindentation. As the only way for quantitative characterization of materials micromechanical properties, it was used to test the micro mechanical properties of certain phase incement-based materials, which is marked by multi-scales, multi-phases and heterogeneous characters,in favor of specific surface treatment and proper loading-unloading program. The15×15indentationgrid was used to test five cement based samples prepared with different water to binder ratio (w/bratio) and slag percentages, the data could be divided into several phases by the EM algorithm.Combined with nanoindentation results, the modulus, hardness, and the packing density of globulewere calculated based on the theory of micro-mechanics and the hydration degrees were calculatedbased on a cement paste skeleton model.It could be conclude main hydration product (C-S-H gel) contained several phases, named lowdensity C-S-H(LD), high density C-S-H(HD), and composites of HD and calciumhydroxide(HD/CH). The mechanical properties of the three phases were not influenced by themixture proportion, which had effects only on the volume fractions: specifically the lower w/b ratioled to denser products; the samples of high w/b ratios showed larger volume fraction of LD;and—further more—the samples blended with slag were found to contain less HD/CH composites.The mechanical properties of C-S-H gel particle in nano-scale were stable irrespective of the mixtureproportion. The degree of hydration was calculated in the method of recognizing the clinkers amongthe indentation data. The results were also compared with the values by thermal gravity analysis. Itwas found that the two different techniques could lead to similar results.As a conclusion, as a method of testing mechanical properties in micro scale, nanoindentation canachieve the goal of getting comprehensive information on cement-based materials. With the dataobtained in the nanoindentation, substantive characteristics of cement based materials could begrasped in the quest of improving materials’ macroscopic performance.