Spectral induced polarization for monitoring the hydration process of cements with zeolites as a supplementary cementitious material

SUMMARY Portland cement remains the most widely used construction material globally, valued for its well-documented properties and performance. However, its production generates substantial CO₂ emissions, mainly due to the decomposition of limestone (CaCO₃) into calcium oxide during clinker formation. In response to these environmental concerns, researchers have been actively exploring ways to lower cement’s carbon footprint and improve its sustainability. One effective strategy involves reducing the clinker content by incorporating supplementary cementitious materials (SCMs). To ensure SCMs enhance performance without compromising safety, it is essential to investigate the properties of blended cements. Natural zeolites have emerged as promising SCMs. Although they do not possess inherent cementitious properties, finely ground zeolites can react with calcium hydroxide in the presence of water, contributing to strength development. This study examines the potential of natural zeolites as SCMs and utilizes the spectral induced polarization (SIP) method to monitor cement hydration and reaction mechanisms. Portland cement mortars containing 25 per cent zeolite were prepared and compared against two reference mixes. Zeolites were analysed using scanning electron microscopy (SEM) and X-ray diffraction (XRD), while SIP monitoring was conducted continuously over 28 d. Our results reveal that SIP responses are influenced by the specific chemical composition of the mortar. The incorporation of SCMs alters cement chemistry, significantly influencing SIP signals. Over time, we observed an increase in the imaginary conductivity component and a decrease in the real conductivity component. SEM analysis showed the formation of new fibrous mineral habits in zeolite-blended samples, alongside a reduction in pore fluid content. These observations suggest a strong connection between SIP signals and mineralization processes, likely associated with the formation of secondary gels and calcium monosulfoaluminate. The interaction of zeolites with calcium hydroxide promotes the development of calcium aluminate hydrates, which then react with ettringite to form calcium monosulfoaluminate. These results emphasize the importance of studying SIP behaviour in cement systems containing SCMs, as assumptions based on ordinary Portland cement may lead to misinterpretations. Our research underscores the potential of SIP as a valuable tool for monitoring cement hydration while offering new insights into the chemical transformations in zeolite-containing mortars. Ultimately, this work contributes to the advancement of more sustainable cement formulations, supporting environmentally responsible construction practices.