Transport kinetics of internal curing water in cement-based materials using broadband dielectric spectroscopy

Early age cracking in concrete is a serious durability issue that is primarily due to autogenous shrinkage. One of the effective and viable ways of mitigating against this durability issue without any compromise is by introducing internal curing material. Internal curing materials for concrete are moisture-rich materials that are introduced to the fresh concrete mixture with objective of providing an adequate internal reservoir of water to concrete at a later age for the completion of hydration process within the cementitious systems. Materials such as light-weight-aggregates, cellulose and thermo-mechanical fibers have been found to perform adequately against this durability issue. However, there is still a need to determine the rate and the distribution of this released water in other to ensure that an optimum hydration is achieved.;To improve the present state of knowledge on water transport kinetics in concrete, broadband dielectric spectroscopy an inexpensive, non-destructive, non-ionizing and low-cost in-situ nano scale characterization technique was applied to dielectric measurements of four selected internal curing materials of concrete (Solite, Stalite, Perilite and Thermo-mechanical fibers) and the results were evaluated. The complex dielectric permittivities were measured between 300 MHz and 13.5 GHz frequencies at 23 °C continuously for seven day from the time water was added to the mixture.;The research shows that fast measurements could be done easily for materials having multiple relaxations such as concrete. Broadband dielectric spectroscopy could be used to monitor continuously the chemical state of water in hydrating concrete materials containing internal curing materials and the profiles of their distributions could be used to determine the rate of water release at any particular time. The results further show that Solite and Stalite released stored water at a later age while Perlite and Thermomechanical pulp fibers release their stored water right from the onset of hydration process. The recorded spectra are well described by combination of both the Cole–Cole and Cole–Davidson spectral functions. A procedure of extracting individual spectra from the complicated complex permittivity was adopted in determining the relaxation times for the system.