Internal structural evolution of conductive cementitious composites subjected to multi-step ohmic heating curing strategy under severely cold temperature

Abstract

Ohmic heating (OH) curing is a novel method for winter concrete construction, a more effective strategy is required for the modification of this method to achieve the high-quality and rapid structure fabrication. In this work, a multi-step OH curing strategy was introduced to prepare Ni coated carbon fibers and nano carbon fibers reinforced conductive cementitious composites (NiCFs/NCFs-CCC) under −20 °C, detailed thermal strain evolution, mechanical strengths and microstructure of the samples were clarified. With the increasing OH curing step, NiCFs/NCFs-CCC exhibited lower thermal strain during the curing process. The thermal strains inside 1-step OH cured sample was larger than 4000 με, which was much larger than those of 2-step OH cured sample and 3-step OH cured sample (lower than 2500 με), highlighting the advantage of multi-step OH curing on reducing the potential internal damage. Moreover, 3-step OH cured sample exhibited higher compressive strength of 68.2 MPa, meeting an increase of 23.1% with that of 1-step OH cured sample. MIP analysis result showed the similar regularity that multi-step OH curing was beneficial for the densification of the pore structure with lower porosity and higher proportion of harmless pores. This work provides a new insight on the modification of OH curing method, which has been verified by the internal structural evolution of the samples, providing an effective curing strategy for high-quality winter concrete construction.