CEE April-June 2012

Nanoindentation technique The technique was developed in 1970s in order to measure the hardness of small volume elements. The indentation on the surface of the material is obtained by a diamond indenter and the relationship between the load applied through the indenter and the dimensions of the indentation is obtained as Hardness, H = PMax I A, (P: Max. Load, A Indentation Area) [11 , 14]. The indenter used has a triangular pyramid shape. It is known as "Berkovich tip". First the depth of indentation is measured then , by using the geometry of the indenter, the area of indentation is calculated. Finally, from the load-penetration curve, various mechanical properties can be estimated. Furthermore, the indentation can be observed by AFM. Several computer programmes that relate moduli of elasticity to indentation geometry had been developed. However, they are applicable to linear elastic, isotropic materials. For cement pastes, besides various elastic properties, phases of different densities (low-, high-, or ultra-high- density) can be differentiated by this method. The nano indentation technique had shown that the elastic moduli of cement paste in concrete are not related with the distance from the aggregate– matrix interface but with the degree of heterogeneity of the interface. information obtained by NMR clearly confirmed that the structure of silicon dimmers and higher order polymerized chains and the associated calcium layers in a hydrated cement paste are highly dependent on the Ca-Si ratio of the system the production method used and the presence of chemical and mineral admixtures [3]. Recently NMR is used to reveal the defects in silicate structures, to investigate hydration kinetics, to determine the relative amounts of free water, C-S– H interlayer water and C-S-H gel water and to study changes in early hydration due to internal curing [3,20]. Neutron ve X-ray scattering techniques SANS and SAXS experiments have permitted to research on the evolution of the microstructure in cement systems during hydration at the nanometer scale as well as on the composition, solid density, and dimensions of nanoscale C-S-H. These techniques provide direct data on particle morphology, surface area and pore size distribution and have been applied to better understand creep, shrinkage, and the effects of aging. It was observed that the aging of cement paste due to external influences can be related to changes in the orientation and packing of the nano sized C-S-H particles. QENS technique helps to see the movement of water near the surface. Gives information about the situation of water; allowing to get data about chemically bound water, physically bound water that interacts with the lndentttr surface of gel pores, and unbound water confined within capillary pores of cement paste. In studies of hydrating and hardened cement pastes, QENS helped to determine the rate of conversion of free water to bound water and has shown that a greater degree of hydration is achieved at lower initial curing temperatures. Since getting information about cement phases p L y 0 u • d k (a) h, Pent>tra,.yon O.rinligt h.,. , h Matrix (b) Matrl!'> I - -r n' faz ·r I Figure 1b. An indentation formed by a nano indenter and calculation methods [21] and interaction of water, many Nuclear techniques (NMR) Nuclear Magnetic Resonance (NMR) technique is being used to obtain information on both hydrated and non-hydrated phase structures and properties of cement. Besides, it gives information about the pore structure of the cementitious materials. NMR allows for the quantification of Si- and AI- substituted tetrahedral chain lengths and structural positioning and identification of nearest and next-nearest neighbouring elements. Together with XRD spectra, critical properties of which are becoming clear. In addition to this, "Neutron Scattering Technique" is also used for investigating deformation and early hydration stages in alkali– silica reactions. Deformation state, particle size, development of the settlement in granitic rocks effect the alkali-silica reactions. Advantages of this type of analysis method are rapid data collection , high resolution, non-destructive testing and properties of sample is determined easily at room or lower temperatures [3, 21, 22]. 12