Matrix Optimization of Ultra High Performance Concrete for Improving Strength and Durability

Current research on concrete materials has established that ultra-high performance concrete (UHPC) can achieve high compressive strength and durability. However, the precise matrix optimization needed to consistently achieve these properties remains unclear. Prior studies have shown that adding silica fume and superplasticizers improves performance, but the role of nano silica and metakaolin in UHPC is less understood. This gap motivated the current study to explore how different combinations of additives affect UHPC properties. Existing literature has not resolved the optimal mix proportions for maximum mechanical and durability outcomes. The need for a systematic approach to matrix optimization is evident in the field. This study addresses the lack of clarity on the most effective additive combinations for UHPC. By focusing on specific mix designs, the paper contributes to filling this knowledge gap.

The aim of this study is to evaluate how specific combinations of additives influence the mechanical and durability properties of UHPC. The specific problem addressed is identifying the most effective mix proportions to enhance UHPC performance. The motivation stems from the need to improve structural materials for long-term durability and strength. The researchers propose to test various combinations of nano silica, metakaolin, and silica fume. This approach allows for a focused investigation of matrix optimization. The study seeks to determine the most effective additive combinations for UHPC. The goal is to provide a framework for future UHPC formulations. This research contributes to the broader field of advanced concrete materials.

Concrete specimens were prepared using a binder content of 1100 kg/m³ and a water/binder ratio of 0.20. Silica sand and a superplasticizer were included in all mixtures. The study tested the effects of adding silica fume, metakaolin, and two types of nano silica. Some mixtures also included 13 mm long OL steel fibers. Mechanical properties were assessed using compressive strength tests. Durability was evaluated through electrical resistivity and mercury intrusion porosimetry. Thermal analysis was conducted using differential and thermogravimetric methods. These methods allowed for a comprehensive evaluation of UHPC performance under various conditions.

The best mechanical and durability outcomes were observed in mixtures containing a binary combination of nano silica and metakaolin. A ternary combination of nano silica, metakaolin, and silica fume also showed superior performance. These mixtures achieved compressive strengths exceeding typical UHPC standards. Electrical resistivity values indicated improved resistance to chloride ion penetration. Mercury intrusion porosimetry revealed reduced pore volume and improved microstructure. Thermal analysis confirmed enhanced stability under varying temperatures. The inclusion of OL steel fibers contributed to additional mechanical benefits. These findings suggest that specific additive combinations significantly enhance UHPC properties.

The authors propose that the binary and ternary combinations of nano silica, metakaolin, and silica fume are most effective for UHPC matrix optimization. These findings suggest that such mix designs improve both mechanical and durability properties. The results align with the hypothesis that additive combinations influence UHPC performance. The study supports the idea that specific matrix compositions can enhance structural materials. The findings may guide future UHPC formulations in construction applications. The researchers suggest that these combinations could be used to develop more durable concrete structures. The study does not claim that these additives are essential for all UHPC applications. The conclusions are based on the observed performance of the tested mixtures.