Non-destructive detection of hollow-particle-mixed filler put into concrete cracks using infrared thermography and heat flux simulation

Filler into concrete cracks is one of the repair methods for in-service concrete structures.Applying epoxy-based filler to the structures combines concrete material with epoxy resin and protects re-degradation.However, the insufficient filling of the filler into cracks can reduce the repair effectiveness.By the authors, epoxy-based filler mixed with hollow particles has been developed for improving mechanical properties of the repaired concrete and inspecting the insufficient filling well.In particular, this study focuses on non-destructive detection of the insufficient filling of the mixed filler into an artificial concrete crack using active infrared thermography.In lab experiment, we performed active infrared thermography with 20-minute heating and 40-minute cooling for four concrete samples.The concrete samples had an artificial crack that was filled with epoxy-based filler mixed with hollow particles.Each filling proportion into the crack was set to 20%, 50%, 80%, and 100%.The volume ratio of the epoxy resin to the hollow particles in the filler was 2 to 1.In analysis, we analyze the surface temperature fields of the samples using thermal images and the inner temperature fields using a two-dimensional heat conduction simulation.As a result, in the 20%-filling sample, which has the smallest filling proportion, the standard deviations of the filler temperatures during first 60 seconds of the cooling are largest in the samples.Additionally, in the same sample, changes of the heat flux in the depth direction around the surface, which is determined by the simulation, are also largest.The characteristics of the temperature variation and heat conduction probably depend on the hollow particles.The filler mixed with the hollow particles enables us to detect the filling into the crack accurately, quickly, and remotely.Thus, this study provides the non-destructive method for monitoring the repair using the hollow particle mixed filler.