Drop weight impact strength of porous concretes investigated with a measurement technique using laser doppler velocimetry

Abstract

Porous concrete is used in many applications that require permeability, noise absorption or thermal insulation. However, its response under dynamic loading is generally not considered. Porous concrete has a characteristic of forming multiple cracks and subsequently fracturing into small fragments when exposed to impact loading. Therefore, with the aim of designing a special type of cementitious material for building protective structures, porous concrete was investigated. To be able to analyze the dynamic properties of the different types of porous concretes produced, an experimental configuration that reveals the dynamic response of porous concretes in a drop weight impact test was designed. Through the measurement of particle velocity at the interface between the impactor and the concrete target, the dynamic response was obtained. Laser Doppler velocimetry was used in monitoring the time history of the particle velocity at the interface which was subsequently analyzed using a special reverberation application of the impedance mismatch method. Measurements were conducted to demonstrate how the proposed experimental technique can be used on porous and normal concretes. The consistency of the results from the experiments that were performed while testing the same porous concrete materials with different impactors are presented for the verification of the experimental configuration and the analysis method. The analyses of the particle velocity time histories of different porous concretes and a normal concrete are also demonstrated which showed that the measurement technique was sufficient to determine the impact strengths of different types of porous concretes as well as a normal concrete with a moderate strength. As the results are compared, it was observed that the aggregate properties and compaction, coupled to porosity, are the main factors that affect the impact strength of porous concrete.