Performance of waste-based marine concrete subject to carbonation curing: Mechanical properties, microstructural development, durability, molecular dynamics simulation, and its engineering application

Hong Kong is facing an increasing disposal pressure of municipal solid waste incineration bottom ash (MSWIBA) after 2025. Therefore, there is an urgent demand to upcycle MSWIBA as a value-added material to avoid landfilling. Additionally, commercial ground-granulated blast-furnace slag (GGBS) is a commonly used supplementary cementitious material (SCM) in casting concrete for green construction practice in Hong Kong, but the reality is often associated with a lower replacement ratio due to the low early strength of GGBS. In contrast, carbonation curing (CO2 curing) can usually improve concrete's early strength. Consequently, the project will provide an effective solution to recycle waste materials (MSWIBA and GGBS) and will develop three innovations. The first innovation is the production of carbonation-cured MSWIBA-GGBS-OPC marine green concrete. We will integrate both pretreated MSWIBA(successfully verified by the preliminary results) and GGBS as SCMs, targeting 50 % of cement replacement, into producing green concrete through early-age carbonation curing. This combined approach will enhance mechanical properties (i.e., high early strength) and improve microstructure (i.e., refined pore structure and densification of the interfacial transition zone) for green concrete. The second innovation is the combination of accelerated laboratory tests and real-time splash-zone field exposure tests to assess the durability of carbonation-cured MSWIBA-GGBS-OPC marine green concrete under accelerated chloride ingress, wet–dry cycling, and coupled exposures since Hong Kong is a coastal city, and its coastal infrastructure is experiencing severe deterioration in the marine environment. It is believed that carbonation curing can potentially create numerous nucleation sites from the generation and precipitation of nano-scale carbonates for a synergetic reaction effect of MSWIBA, GGBS, and cement, contributing to the improved performance. Given the fact that durability tests are always time-consuming, to elucidate degradation mechanisms and support service-life prediction, molecular dynamics and reaction–transport modelling together with a Weibull reliability framework will be integrated to establish an accurate service life Prediction Model, which will be considered our third innovation. Lastly, small-scale precast units such as armour blocks will be fabricated for field trial use in Hong Kong’s coastal infrastructure with the support of different governmental and industrial partners. Technical guidelines will be established to facilitate industrial adoption and commercialization. In summary, the project will advance fundamental understanding of carbonation-cured concrete systems and deliver a practical pathway for waste valorization, emission reduction, resource conservation, and resilient marine construction in high-density urban regions, contributing to the sustainable development and environmental protection.