Durability analysis of nanocarbon black-based self-strain sensing ultra-high-performance concrete (UHPC): Effects of moisture content and sea-salt solution exposure

Abstract

Equipping ultra-high-performance concrete (UHPC) with intrinsic strain sensing capability has received significant research interest. Previously, the authors introduced a self-strain sensing UHPC mixed with cost-effective nanocarbon black (nCB-UHPC). Since it is known that the strain sensing performance of smart cementitious composites may be affected by various environmental factors and that the mechanical properties of UHPC depend significantly on curing condition and may change under environmental exposure, this paper presents a recent study aiming to investigate the properties of the new nCB-UHPC under different curing and working conditions. The test results indicate that the mechanical properties of the nCB-UHPC can be improved by prolonged curing duration, and also by dry curing at 105 ℃ due to the accelerated hydration activity at an elevated temperature. However, exposure to sea-salt solution is shown to decrease the mechanical properties due to the formation of cracks by secondary hydration products. On the other hand, the fractional change in resistivity of the nCB-UHPC exhibits a distinct synchronization to the applied compressive stress. Nonetheless, the strain sensitivity decreases with an increase of moisture content due to increasing contact resistance between nCB particles. Furthermore, exposure to the sea-salt solution increases the strain sensitivity of fully saturated nCB-UHPC specimens, thanks to the high mobility of the dissolved ions from the saline solution – an important finding in the context of marine construction. This study lays a foundation for the large-scale implementation of the nCB-UHPC as a field-deployable solution for monitoring the condition of concrete structures.