What Should Be Paid Attention to in UHPC Construction? Guide to Key Control Points and Avoiding Common Mistakes

The success of UHPC construction depends on precise control of a series of key control points and resolute avoidance of common pitfalls. Based on extensive project experience, Qinglong Group summarizes the core considerations for UHPC construction as: "materials are the foundation, formwork is the prerequisite, pouring is the key, and curing is the guarantee." Negligence at any stage can lead to quality problems such as substandard strength, surface defects, or even cracking, resulting in irretrievable economic losses.

Before construction, thorough "technical preparation and briefing" must be carried out. All personnel involved, including managers, batching plant operators, pouring workers, and curing workers, must receive specialized training to understand the characteristics of UHPC and how it differs from conventional concrete. Process trials must be conducted to determine the optimal mixing procedure, pouring method, vibration technique, and formwork removal time. The formwork system must be specially designed to ensure it is sealed, sturdy, and has a flat surface, and the lateral pressure exerted by UHPC on the formwork (usually higher than that of ordinary concrete) must be accurately calculated.

Special attention is required during mixing and transportation. A high-shear forced-action mixer must be used, strictly following the trial-verified loading sequence and mixing time to ensure uniform fiber dispersion. UHPC is highly viscous, so mixer trucks should be preferred for transport, and transport time should not be too long to prevent excessive slump loss. If pumping is used, a delivery pump suitable for high-viscosity materials must be selected, and the pipelines should be laid out sensibly to minimize bends.

Pouring and vibration are the core control points. Pouring should be continuous to prevent cold joints. UHPC is self-leveling, but auxiliary vibration is still needed when necessary to expel large air bubbles and ensure compact corners. High-frequency, low-amplitude vibrators must be used, and vibration time must be short (usually 10-20 seconds) to avoid over-vibration, which can cause fiber settlement and paste segregation. After pouring, the surface should be troweled immediately or given the required texture.

Curing must be timely, sufficient, and non-damaging. This is the most easily overlooked yet crucial step. Misting for moisture retention should begin after UHPC reaches initial set but before final set, to prevent the surface from losing water too quickly. After formwork removal, the structure should be immediately and tightly wrapped with water-retaining materials (such as wet cloths or curing films) or coated with a curing agent. Curing should last no less than 7 days, with protection from direct sunlight and wind. If curing is neglected, even the best materials cannot deliver their full performance.