Analysis of Self-Sensing Capabilities of GO and rGO Based Cementitious Composites

Abstract

The addition of steel and carbon fibers to a cementitious composite to lower the composite's resistivity and create a piezoresistive matrix has recently been used as an innovative method of detecting various structural states. As SHM sensors, smart cement-based nanomaterials of graphene derivatives like carbon fibre or carbon nanotube cementitious hybrids, or a mix of the two, are piezo-resistive, which means that resistivity varies with the given load/strain. This indicates that a cement sample or building does not require the external or additional attachment of any sensor. Instead, the cement composite is able to detect its own strain as well as several other factors. The present study describes the various tests that have been done to evaluate the mechanical and electrical properties of cementitious mortar specimens with varying percentages of GO (Graphene Oxide) and rGO (Reduced Graphene Oxide). Testing has been done after 7, 28 and 56 days of curing. Mechanical properties included compressive strength test and flexural strength test, whereas, electrical properties included electrical resistivity test and piezo resistivity test. The piezoresistive action of functional filler particles, that are spread throughout the composite phase create a conductive connection, is what gives its self-sensing ability. As a result, anytime cementitious composite is forced in a certain way, the network changes, changing the electrical resistivity. Results from various tests show that both GO and rGO increased the compressive strength and flexural strength of the cementitious mortar at 28 days and 56 days. On addition of GO and rGO at all addition percentages, FCR (Fractional Change in Resistivity) decreases on increasing the load, corresponding to increase in electrical conductivity and comes back to its original value after sample failure in monotonic loading, corresponding to decrease in conductivity. Thus, overall pattern of piezoresistive behaviour is followed. Compared to GO, in rGO specimens, cluster of rGO is more randomly distributed, this is attributed to lower surface area of rGO, compared to GO. It was found that rGO 0.06% achieved the maximum sensitivity, followed by GO 0.3%, indicating maximum contact points are formed in rGO 0.06% leading to enhanced piezoresistive behaviour. The piezoresistive performance of cementitious composites with GO and rGO confirms their ability to become intrinsic cement-based sensors.