What Should Be Noted During UHPC Construction?

The success of UHPC construction depends on precise control of a series of key details. Negligence at any stage can lead to substandard strength, surface defects, or even cracking. Based on extensive project experience, Qinglong Group has summarized four core precautions that must be given top priority in UHPC construction: "raw materials and mix proportions, mixing techniques, pouring and vibration, and curing and protection." These are special requirements that distinguish UHPC construction from ordinary concrete construction.

Control of raw materials and mixing water is the lifeline. Raw materials must meet specifications; arbitrary substitution or use of damp, caked materials is strictly prohibited. The amount and temperature of mixing water must be precisely controlled—small variations can have a huge impact on workability and strength. Qinglong's UHPC products are typically supplied in pre-mix form; on site, simply add water and mix according to the specified ratio. Be sure to use measuring containers and never estimate by experience. Mixing equipment must be clean and free of any residue from other materials.

The mixing and pouring process must be precise and orderly. A forced-action mixer must be used, and mixing time should strictly follow the technical instructions to ensure fibers are evenly dispersed. The mixing batch should not exceed 60% of the equipment capacity. UHPC mix is viscous and should be poured as soon as possible after discharge to prevent loss of flowability. Pouring should be continuous to avoid cold joints. Use a high-frequency poker vibrator to aid compaction, but follow the principle of "quick insertion, slow withdrawal, evenly spaced points, and no over-vibration"—stop once the surface shows laitance and no large air bubbles escape, to prevent fiber floating or segregation.

Early curing is the key to crack resistance. Once UHPC has initially set (usually within 1-2 hours after pouring), curing should begin immediately. The most effective method is covering the surface with plastic film to prevent moisture evaporation. After final set, water curing or mist spraying can begin, keeping the surface continuously moist for at least 7 days. During curing, avoid wind exposure, direct sunlight, and drastic temperature changes. Formwork removal time should be determined based on the strength of test blocks cured under the same conditions, and should not be too early. Formwork should be made of materials with smooth surfaces and coated with high-quality release agent. The temperature at each stage of construction (material temperature, placement temperature, and ambient temperature) should be controlled between 5°C and 30°C; special measures are required beyond this range. Strictly following these precautions is the prerequisite for achieving high-quality UHPC structures.