How Long Should UHPC Be Mixed? An In-Depth Analysis of Qinglong's UHPC Mixing Process

UHPC mixing time is critical to material performance. According to extensive test data, the optimal mixing time is 4-6 minutes, comprising 1 minute of dry mixing and 3-5 minutes of wet mixing. This time range ensures uniform fiber distribution without over-mixing.

For the mixing process, a forced-action mixer must be used with the rotation speed controlled at 30-40rpm. First, add the dry materials (cement, silica fume, quartz sand, etc.) and mix for 60 seconds to preliminarily blend the materials; then add the water solution containing water reducer in batches and continue mixing for 3-5 minutes. In a project in Guangzhou, precise control of mixing time achieved a fiber distribution uniformity of over 95% and kept the strength coefficient of variation within 5%. Over-mixing causes fiber damage, while insufficient mixing leads to uneven distribution—both affect the final performance.

Importance of Dry Mixing Time Control

60 seconds of dry mixing ensures the powders are preliminarily and uniformly blended; too short a time easily causes clumping, while too long leads to segregation; this stage lays the foundation for wet mixing.

Precise Control of Wet Mixing Time

The 3-5 minutes of wet mixing is the critical period for fiber distribution; add water in batches during the first 2 minutes, then mix thoroughly for the remaining 1-3 minutes; insufficient time causes fiber agglomeration, while excessive time damages fibers.

Mixing Speed Optimization

The linear velocity is best controlled at 1.5-2.0m/s; too fast damages fibers, too slow is inefficient; this speed ensures gentle yet effective mixing.

Mixing Equipment Selection Requirements

A forced-action mixer must be used; the capacity must match production requirements; the gap between the blades and drum wall must be ≤5mm. Equipment performance affects mixing results.

The mixing process requires fine control. Trial mixing is recommended to determine the optimal parameters. Qinglong UHPC provides process guidance.