MICROSTRESS FLUCTUATIONS IN CEMENT PASTE
AS A GRANULAR MATERIAL
29th Our World in Concrete and Structures (OWICs) - 2004
S.M.F. Asmus*, Oegussa Construction Chemicals, Shanghai, P.R. China
G. Pezzotti, Kyoto Institute of Technology, Japan
cement, piezospectroscopy, Raman spectroscopy, micro stress, granular material
The formation of force chains and concomitant fluctuation of microstress values are specific and well-known features of granular materials. Though mortar is sometimes regarded as a granular system, as well as cemented rocks are eventually considered, cement paste is hardly perceived as a granulate.
In the present paper, an experimental method to measure micro stresses in cement paste was developed employing a fluorescence microprobe spectroscopy method. Stresses were recorded with a fluorescence spectrometer making use of a lumina and, in an evolutionary step, organic molecules as piezospectroscopic stress sensors. In a two-dimensional stress map, fluctuations in the stress distribution led to stress chains, indicating the granular character of cement paste. Due to these fluctuations, micro forces much higher than the macroscopic strength of the material existed. The presented technique is proposed as a general tool to analyze stresses
in cementitious systems. In practice, the method supports the development of
toughening additives to materials like cement paste, concrete, etc, and is anticipated to give a major contribution to the understanding of the tensile failure of cementitious systems.