How Long Should UHPC Be Mixed? Process Control and Qinglong Group's Precision Mixing Technology

The mixing time of UHPC is not a fixed value but a dynamic parameter determined jointly by "mixer type, mix proportion characteristics, and ambient temperature," typically ranging from 5 to 15 minutes. Qinglong Group has determined the optimal mixing time through extensive testing: approximately 8-10 minutes for planetary mixers and 5-7 minutes for single-shaft forced mixers, to ensure uniform fiber distribution and thorough wetting of the paste. Too short a time results in uneven mixing, while too long a time may introduce air bubbles or cause fiber bending. At our Nanning production base, we use a fully automatic mixing system with second-level time control accuracy to ensure consistent performance of every batch. Precise mixing is the first gateway to unlocking UHPC performance.

Mixing Equipment Differences Lead to Different Times

Planetary mixers have strong shear force and are suitable for high-viscosity UHPC, requiring slightly longer time (8-10 min). Single-shaft forced mixers are more efficient, requiring shorter time (5-7 min). Qinglong production lines are equipped with sensors that monitor torque changes in real time and automatically determine the mixing endpoint, avoiding human error.

Mix Proportion Components Affect Mixing Duration

When fiber content is high (e.g., 3%) or ultrafine materials such as silica fume are abundant, the mixing time needs to be extended to ensure dispersion. We optimize the process through pre-mixing fibers and step-by-step feeding (dry mixing first, then adding liquid). High-range water reducers can improve workability and appropriately shorten the time.

Ambient Temperature and Mixing Speed Must Be Coordinated

In hot summer, the mixing time can be slightly shortened to prevent moisture from evaporating too quickly; in winter it needs to be extended to promote material integration. We recommend controlling the mixing speed at 30-50 rpm, as excessive speed easily entraps air. Qinglong provides seasonal construction guidelines.

Determining the Mixing Endpoint Is Crucial

Visually, the paste should be uniform and glossy, with no fiber clumping. A more reliable method is to monitor it with a torque meter or rheometer. We require the paste to achieve a spread of 600-700 mm and meet homogeneity standards upon delivery. A simple on-site method: take a sample and spread it—it is acceptable if there are no dry powder lumps or fiber clusters.

Scientifically mastering the mixing time is the first step to ensuring UHPC quality. With rigorous craftsmanship, Qinglong Group lays a solid foundation for subsequent processes.