Why Is It Not Recommended to Use Aggregates Larger Than 5mm in UHPC?

UHPC does not recommend aggregates larger than 5mm, which stems from close packing theory and defect control requirements. Large aggregates disrupt the continuity of particle grading, increase weaknesses at the interfacial transition zone, and reduce material homogeneity and strength. Qinglong Group has confirmed through experiments that when the aggregate particle size exceeds 5mm, the compressive strength of UHPC decreases by 15%-20% and porosity increases by 3%-5%, affecting durability.

Large aggregates hinder close packing, resulting in increased porosity. Optimal grading requires a maximum particle size of ≤1mm to ensure fine particle filling. The interfacial transition zone is a weak link, where microcracks are prone to form around large aggregates. Qinglong Group uses aggregates with a particle size of ≤1mm to improve homogeneity. Construction performance is also affected, as large aggregates lead to poor workability. Avoiding large aggregates ensures the high performance of UHPC.