Supported ITZ Modification Efficiencies via Surface Coating Nanoparticles on Aggregate and its Influence on...

Concrete durability is closely tied to the microstructure of the interfacial transition zone (ITZ) between aggregate and cement paste. Prior research has shown that ITZ porosity influences chloride penetration and mechanical strength. No prior work had resolved how specific nanoparticle coatings affect both microstructure and macroscopic properties. This gap motivated an investigation into how surface coatings alter ITZ characteristics. Existing methods of ITZ modification often lack precision in controlling coating thickness and material distribution. Researchers have proposed that nanoparticle coatings may alter ITZ porosity but have not confirmed how this affects concrete performance. The need for a controlled, scalable method of ITZ modification remains unmet. This study addresses the uncertainty by evaluating three coating materials and three thicknesses.

The study aimed to assess how nanoparticle coatings on aggregate surfaces influence ITZ microstructure and concrete properties. Researchers focused on compressive strength and chloride resistance as key performance indicators. They selected three coating materials—slag, nano-CaCO3, and nano-SiO2—to compare their effects. The goal was to determine optimal coating thicknesses that balance performance metrics. The team hypothesized that coating material and thickness would significantly affect ITZ characteristics. They sought to quantify how these variables influence concrete durability. The study also aimed to clarify whether inert nanoparticle coatings improve or degrade concrete properties. By analyzing ITZ microstructure, the researchers hoped to link microscale changes to macroscale outcomes.

The team applied coatings of varying thicknesses (5, 10, and 15 μm) to aggregate surfaces using nanoparticles. They selected three materials—slag, nano-CaCO3, and nano-SiO2—for coating experiments. Compressive strength tests measured the mechanical performance of coated concrete samples. Chloride penetration resistance was evaluated using pre-loading and sound samples. Backscattered electron (BSE) imaging quantified ITZ microstructure changes. The researchers used image analysis to assess porosity and phase distribution near aggregate surfaces. They controlled coating thickness through deposition techniques and verified it via microscopy. The study compared the effects of each coating material across all thickness levels.

Coating thickness and material significantly influenced concrete properties. Slag and nano-SiO2 coatings increased chloride resistance but reduced compressive strength. Nano-CaCO3 coatings led to a significant decline in both properties. Thicker coatings (15 μm) showed greater resistance but lower strength compared to thinner ones. BSE imaging revealed that coatings altered ITZ porosity within 30 μm of aggregate surfaces. The most effective coatings were those that filled ITZ pores without disrupting particle packing. Slag and nano-SiO2 improved ITZ density but introduced microcracks under load. Nano-CaCO3 coatings failed to enhance ITZ structure and instead weakened it. The results suggest that coating material and thickness must be optimized for specific performance goals.

The study found that nanoparticle coatings can modify ITZ microstructure but do not always improve concrete properties. Slag and nano-SiO2 coatings enhanced chloride resistance at the expense of compressive strength. Nano-CaCO3 coatings reduced both strength and durability. Coating thickness influenced performance, with thicker coatings generally offering better resistance. The ITZ region within 30 μm of aggregate surfaces was most affected by coatings. The results suggest that material selection and coating design are critical for achieving desired outcomes. Coating inert particles may disrupt initial packing and degrade performance. The findings support the need for material-specific optimization of coating parameters. These conclusions align with the authors' hypothesis that coating effects depend on both material and thickness.