Estimation method of stress and strain history in cement-based composite materials and calcite particle aggregates
For measuring the stress history in a simple form, which is widely applicable to various types of structural materials which the elastic modulus is different from each other, a large number of calcite particles is embedded as a stress sensor in a cement-based composite material that can be elastically deformed after receiving an external. A twin-crystal density of the calcite particles is measured after an external force is applied to the composite material, to convert the twin-crystal density to a strain by an approximate formula set in terms of a strain ε (%) generated in the composite material and a twin-crystal density Dtw (lines/mm) of the calcite particles, and further to convert this strain to a stress by the elastic modulus of the composite material, whereby to estimate the history of stress and strain. The approximate formula between strain and twin-crystal density is independent of the modulus of the composite material and is used in a common form.
1 . An estimation method of stress and strain history regarding to an object to be measured ( 50 ) in which a plurality of calcite particles ( 11 ) having a particle diameter of a predetermined size are embedded as a stress sensor,
wherein a plurality of the calcite particles ( 11 ) are calcite particles with no twin crystals that are mixed in a predetermined mixing ratio in a cement composite material ( 12 ) prepared in advance so that an elastic modulus becomes a predetermined value in a solidified state to be formed into a predetermined shape of a calcite particle aggregates ( 10 ) as a whole, and one or more of the calcite particle aggregates ( 10 ) are removably embedded in the object to be measured ( 50 ) with non-shrinkage mortar ( 60 ), and
the calcite particle aggregates ( 10 ) after receiving an external force are processed to be extracted as a portion of the non-shrinkage mortar ( 60 ) from the object to be measured ( 50 ), and to be cut out to expose crystal planes of the calcite particles ( 11 ) so that a twin-crystal density (Dtw) thereof is measured, wherein the twin-crystal density (Dtw) is to be converted into strain (ε) based on an approximate formula showing a relationship between strain (ε) and twin-crystal density (Dtw), and the strain (ε) is to be converted into stress (σ) based on the elastic modulus.
2 . An estimation method of stress and strain history in cement-based composite materials as set forth in claim 1 wherein the said shape is polyhedron.
3 . An estimation method of stress and strain history in cement-based composite materials as set forth in claim 1 , wherein the calcite particles ( 11 ) contained in the calcite particle aggregates ( 10 ) are colored.
4 . An estimation method of stress and strain history in cement-based composite material as set forth in claim 1 , wherein the calcite particle aggregates ( 10 ) contain non-twin-crystal synthetic calcite particles ( 11 ) having a particle size of 5 μm to 1.50 mm.
5 . An estimation method of stress and strain history in cement-based composite material as set forth in claim 1 , wherein the mixing ratio of the non-twin-crystal synthetic calcite particles ( 11 ) in the calcite particle aggregates ( 10 ) is 0.3 to 10% by volume.
6 . An estimation method of stress and strain history in cement-based composite material as set forth in claim 1 , wherein the calcite particle aggregates ( 10 ) collected from the object to be measured ( 50 ) are to have surfaces polished to such an extent that the twin crystals of the calcite particles ( 11 ) can be observed.
7 . An estimation method of stress and strain history in cement-based composite material as set forth in claim 6 wherein the twin-crystal density (Dtw) of the calcite particles are measured on one or more surfaces of the polished calcite particle aggregates ( 10 ).
8 . An estimation method of stress and strain history in cement-based composite material as set forth in claim 7 wherein a relationship between the twin-crystal density (Dtw) of the calcite particles and the stress history (σ) generated in the object to be measured ( 50 ) is configured to correspond to each other on one to one for each elastic modulus of the cement composite material ( 12 ) or the non-shrinkage mortar ( 60 ).
9 . An estimation method of stress and strain history in cement-based composite material as set forth in claim 8 , wherein when the elastic modulus of the cement composite ( 12 ) or the non-shrinkage mortar ( 60 ) is uniquely fixed, the relationship between the twin-crystal density (Dtw) of the calcite particles and the stress history (σ) is configured to be linearly approximated.
10 . An estimation method of stress and strain history in cement-based composite material as set forth in claim 8 , wherein the stress history (σ) generated in the object to be measured ( 50 ) is estimated, in a conversion from the twin-crystal density (Dtw) of the calcite particles to the stress history (σ), by using a following approximate formula (1) set in terms of the strain (ε) generated in the object to be measured ( 50 ) and typical values of the twin-crystal density (Dtw) of the calcite particles
ε=0.0094 Dtw− 0.2 (1)
to convert the measured twin-crystal density (Dtw) of calcite particles to strain (ε), and further to convert the strain (ε) to stress by the elastic modulus of the cement composite ( 12 ) or the non-shrinkage mortar ( 60 ).