Microstructural Response of Shock-Loaded Concrete, Mortar, and Cementitious Composite Materials in a Shock Tube Setup

Abstract

Microstructural changes in concrete, mortar, and cementitious composite material were investigated to determine the efficacy of these materials subjected to shock loading. An experimental methodology with the ability to generate reproducible shock waves of specified blast pressure and decay time was used to perform repeatable experiments in the range of trinitrotoluene (TNT) explosion that is unsafe for concrete columns as specified in the FEMA (Federal Emergency Management Agency) guidelines (38 kg TNT at 3.7 m). The changes in the pore volume fraction of the samples before and after shock loading were used to determine the efficacy of the materials subjected to shock loading. The study reveals that even though percentage increase in pore volume fraction before and after shock loading is highest for cementitious materials, its absolute value is low compared to that of control samples, thereby justifying the better performance of cementitious composite materials. Moreover, the size of the pores is also observed to be lower for cementitious composite samples compared to those of the and concrete samples after shock loading in comparison to the control materials in the study. The reason for the better performance of cementitious composite materials can be attributed to an increase in tensile ductility of the sample as a result of fiber addition. Apart from development of a new cementitious material for blast load mitigation, the study also demonstrates the need to consider pore size distribution in equations relating pore volume fraction to strength.