Nanoindentation as a tool to measure and map mechanical properties of hardened cement pastes
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Research Letters
Nanoindentation as a tool to measure and map mechanical properties of hardened cement pastes Chuanlin Hu, Nano and Advanced Materials Institute, The Hong Kong University of Science and Technology, Hong Kong, China Address all correspondence to Chuanlin Hu [email protected] (Received 25 October 2014; accepted 11 February 2015)
Abstract Regarding the significance of cement paste in construction materials, the present paper aims to use nanoindentation to measure and map mechanical properties of hardened cement pastes. The mechanical properties of involved phases were extracted from grid nanoindentation on the cement paste. The results suggested that nanoindentation can be used as a tool to measure and map mechanical properties of hardened cement pastes, and can identify the phases, including outer product, inner product, calcium hydroxide (or interface of residual cement clinker), and residual cement clinker.
Introduction Concrete is the most widely used building material in the world and responsible for 5–10% of total greenhouse gases emission. The mechanical properties of concrete such as elastic parameters, strength, ductility, creep, shrinkage, and fracture behavior largely depend on the material structure at the nano- and microscale. To understand and improve the macroscopic mechanical performance of concrete, it is essential to study its microstructural mechanical properties. As an effective and powerful tool to detect the local elastic properties and hardness of the material microstructure, nanoindentation has been used to interpret the local elastic properties and hardness of such cement-based material at the nano- and microscale. Previously, many works have been done in studying the mechanical properties (indentation modulus, M, and hardness, H ) of cement pastes by nanoindentation. In most studies,[1–11] statistical analysis was used to deconvolute the mechanical properties of active phases from large arrays of nanoindentation tests on the polished cement paste. Statistical analysis exhibits some advantages in the study of such multi-phase material, e.g. the researchers do not need to know the location or material phase where each nanoindentation test was performed. The identified phases of the order of indentation modulus and hardness from low to high were considered as low-density C–S–H (calcium– silicate–hydrates), high-density C–S–H, ultra-high-density phase, and residual cement clinkers.[6,7,10] Ultra-high-density phase was a composite of high-density C–S–H and calcium hydroxide nanocrystals.[12] Some other studies considered the third phase as calcium hydroxide rather than ultra-high-density phase.[4,8,9] Regarding the significance of the microstructural mechanical information of hardened cement paste in concrete science and technology, this study aims to use nanoindentation
to measure and map mechanical properties of the hardened cement pastes at different water-to-cement ratios, and reveal the identified phases of grid nanoindentation.
Materials and experiments For the sake of
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