Effects of bacteria-based self-healing nutrients on hydration and rheology of cement pastes

Crack openings in concrete lead to a reduction in its lifespan. Many authors have analysed different techniques that could repair cracks autonomously, being the use of bacteria one of the most promising approaches. Bacteria are often introduced with nutrients in the concrete mixes, and they may alter the cement hydration. In this study, the effects that calcium lactate, calcium nitrate, and yeast extract have on cement pastes during the early hours of hydration were analysed. To accomplish this, calorimetry, in situ X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Vicat and rheology techniques were employed. The results demonstrated that the addition of calcium lactate led to higher values of ettringite, which altered the rheological behaviour of the pastes. Moreover, when added at 4%, calcium lactate also delayed the setting time by inhibiting the reaction of silicates, a similar effect was observed when yeast extract was added. Lastly, the incorporation of nitrate accelerated the setting time.