Quantum Beam Science Research

4-10 Strain Measurement on Rebars in Reinforced Concrete–Application of Neutron Diffraction to Nondestructive Strain
Measurement–

Peinforced ConcreteSample
Tensile stressronPeak shift

NeutAtomDiffraction

d0d0d

Crystal structure

Detector（Stress-free）

Fig.4-23 Principle of neutron strain measurement
Lattice strain can be measured by observing change in diffraction
angle, 2θ, which is due to change in lattice spacing.

Fig.4-25 Layout of neutron strain measurement
systemNeutrons irradiate the rebar through the concrete,
and then the diffractions from the rebar aredetected by the neutron detector.

Stress (MPa)Applied stress 309MPs
Applied stress 155MPs
stress-free

Fig.4-24 Stress distributions on the rebar
Stress distributions in axial direction (loading direction) on
a rebar with diameter of 16mm embedded in concrete ofdimensions 50mm × 50mm × 800mm.

Position (mm)It is already known that the performance of a reinforced
concrete structure is affected by the bond condition between therebar and concrete, and this bond condition has been evaluatedby evaluating the strain on the rebar. In general, strains on
the rebar have been measured using strain gauges; however,waterproofing treatment and wiring of the strain gauges affectthe bond condition, and strain gauges discretely set on therebar cannot measure strain distributions in detail. On the other
hand, the neutron diffraction method, which is nondestructive
and non-contact, can measure the lattice spacing of crystalline
materials (Fig.4-23), and residual stresses and strains insidematerials at a depth on the order of centimeters can be evaluatedfrom the change in lattice spacing with the spatial resolution on
the order of a few millimeters. Although the water in hydrated
cement and the evaporated water in the concrete structures
would decrease the neutron intensity due to high absorption
by hydrogen atoms, drying the water in the concrete makes it
possible to measure the strains on the rebar in concrete with thesize of 50mm to 100mm square.
Fig.4-24 shows the lattice stress distribution on a rebar inconcrete, derived from measurements by the neutron diffraction
method. The residual stress distributions in this figure weremeasured along the rebar under uniaxial tensile stress of 155MPa and 309 MPa, as well as the stress-free condition, asshown in Fig.4-25. Stress transferred to the rebar increased
with an increase in the applied stress, though it was less than
the applied stress because stress was shared with the concrete.
Moreover, dispersion of stress around cracks was observed due
to loss of adhesion there and also due to stress concentration
around rebars. These results clearly indicate that the neutron
diffraction method enables detailed measurement of stress
distribution on the rebar.
As indicated above, the neutron diffraction method isexpected to make possible measurement of the detailed residualstresses on the rebar nondestructively and also to measure thestress distributions around cracks in the concrete which cannot
be measured by strain gauges. There is a possibility that theneutron diffraction method will gives us new knowledge in thestructural engineering field.

Reference
Kanematsu, M., Noguchi, T., Yasuda, M., Suzuki H., Nondestructive Stress Measurement of Rebar using Neutron Diffractometer “RESA”, Proceedings ofAnnual Meeting of Japan Concrete Institute, Fukuoka, Japan, 2008, p.775-780, in CD-ROM (in Japanese).
JAEA R&D Review 200853