The project was structured in three main technical stages. First, several families of mesoporous silica nanoparticles (MSNs, including MCM 41, MCM 48, SBA 15 and SBA 16) were synthesised and extensively characterised using FTIR, nitrogen adsorption, XRD, SEM and related methods. Their basic reactivity and dispersibility in cementitious environments were benchmarked against commercial nano silica products, and a subset of the most promising materials was selected for detailed testing.
In the second stage, the selected MSNs were incorporated into cement pastes at different replacement levels. Isothermal calorimetry showed that MSNs accelerate hydration and increase early heat release, with optimum contents in the order of 0.2 to 0.6 percent by mass of cement depending on MSN type. Combined analysis by XRD Rietveld and TGA confirmed enhanced portlandite consumption and increased formation of C S H, indicating that MSNs act through both nucleation and pozzolanic effects. Mercury intrusion porosimetry and SEM revealed a refined pore structure with reduced volume of critical capillary pores, particularly at early ages. Ultrasonic pulse velocity and mechanical tests demonstrated significant gains in early compressive and flexural strength, without detrimental effects at later ages.
In the third stage, the use of MSNs was extended to mortar and, on a more limited scale, to concrete. Mortar tests confirmed the acceleration of hydration, microstructural refinement and strength gains observed at paste level. For example, the mix containing SBA 16 showed an increase of around 50 percent in one day compressive strength and about 15 to 20 percent at 28 days compared to the reference. Concrete trials were carried out on a few representative mixes to verify feasibility, workability and early age strength trends, which followed the positive patterns seen in mortars. A screening cradle to gate life cycle assessment compared reference mixes with MSN modified scenarios and indicated that, when MSNs enable meaningful reductions in cement content or faster formwork turnover, a reduction in embodied CO2 is plausible, although strongly dependent on MSN production routes and scale.
The main achievements of the action are a consistent experimental data set on MSNs in cement paste and mortar, a clear mechanistic understanding of their combined nucleation and pozzolanic roles, quantified optimal dosage ranges, and feasibility evidence at concrete scale together with indicative LCA results. These outcomes provide a robust technical basis for future development of MSN based admixtures and their integration into low clinker, high performance concrete systems.
