CAREER: Antiquity-Inspired Novel Stratlingite-Based Cementitious Binder (StraCem): A Lesson from Ancient and Modern Civilizations

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This Faculty Early Career Development (CAREER) award will advance the fundamental understanding of the kinetics and thermodynamics of stratlingite precipitation and its interaction with calcium silicate hydrate phases, to enable the design of a new eco-efficient stratlingite-based cementitious binder (StraCem) that mimics the chemistry and mineralogy of ancient Roman concretes, while integrating the benefits of modern concrete designs. Many ancient structures have withstood aggressive seawater environments for over 2000 years testifying to their high durability and resilience, while most modern structures tend to deteriorate slowly under similar environments. However, modern concrete technology enables the design of concretes for specific applications with impressive properties that were not possible in the ancient era. The performance and durability of concretes are known to be strongly linked to the chemistry and microstructure of the hardened matrix, and recent studies have disclosed the mineral phase assemblage and microstructure of existing Roman structures, wherein the distribution of tobermorite-like calcium silicate hydrate and stratlingite phases are postulated to be contributory to their durability and resilience. This project will harness the chemistries of ancient concretes and modern ones to facilitate the design of StraCem that features at least 50% lower carbon footprint than Portland cement, while ensuring superior performance, chemical resilience, and durability in land and marine environments. The lower carbon footprint of the materials contributes to the mitigation of climate change. The program integrates educational activities to help inspire, train, and equip future cement material scientists and engineers through local K-12 outreach activities, provision of experiential learning opportunities for underrepresented minority undergraduate and graduate students, and the outcome of the study will enrich new and existing courses on the chemistry of cement-based materials. The specific research goal of this project is to investigate the pathways and energetics of stratlingite nucleation and growth together with tobermorite-like calcium silicate hydrate gels in cementitious systems. The effort will unlock the compositional drivers, including aqueous pore solution chemistries, and the energy landscapes to facilitate rapid coprecipitation of stable stratlingite and Al-tobermorite-like calcium silicate hydrate gels. The study will be curated with relevant nucleation and growth theories, and the insight thereof will be applied to design a novel low-carbon StraCem clinker that will yield an optimum balance of stratlingite and calcium silicate hydrate gel during hydration, mimicking reported beneficial mineralogy of ancient Roman concretes, while minimizing less beneficial hydrate phases. The performance and durability of the designed StraCem-based pastes, mortars, and concretes will be investigated in air and simulated marine conditions. It is hypothesized that StraCem will feature superior performance and durability than Portland cement under terrestrial and marine environments, due to the space-filing properties of strätlingite and binding ability of calcium silicate hydrate gel. Also, the new cement will present significantly lower CO2 emissions due to its lower calcareous content and clinkering temperature than Portland cement. To actualize the objectives, a combination of wet chemistry, solid-state chemistry, in-situ and ex-situ multiscale characterization, and thermodynamic computation will be employed. This project will establish multi-disciplinary research and mentorship at the intersection of chemistry, chemical engineering, materials science, and civil engineering.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.