Will UHPC Components Deform or Crack Under High-Temperature Sun Exposure?

Will UHPC Components Deform or Crack Under High-Temperature Sun Exposure? Industry Field Test Data Gives a Clear Conclusion

Since the onset of summer, extreme high-temperature weather has occurred frequently across most regions of China, and the weathering stability of outdoor building components has become a key concern for many project parties. For UHPC components, which are commonly used on the facades of landmark buildings and high-end public buildings, many project parties raise the core question: will long-term high-temperature sun exposure cause UHPC components to deform or crack? As a leading intelligent manufacturing enterprise with nearly 30 years of UHPC R&D and production experience, we draw on field test data from over a thousand completed projects to provide the industry with clear assessment criteria and solutions.

I. Key Factors Influencing Deformation and Cracking of UHPC Components Under High-Temperature Sun Exposure

First, it must be made clear that qualified UHPC components inherently possess extremely strong weathering properties, but if the production or installation processes fall short of standards, quality issues may indeed arise under prolonged high-temperature sun exposure. Based on our project data spanning nearly 30 years, extreme outdoor summer heat typically tests UHPC component performance in three dimensions: first, the thermal stability of the material itself. Ordinary concrete has high thermal conductivity and thermal deformation coefficients and is prone to internal stress accumulation under long-term temperature variations, whereas the core characteristic of UHPC is the dense structure provided by fiber reinforcement, giving it heat deformation resistance more than 10 times that of ordinary concrete. Second, mix ratio control in production. Many small and medium-sized manufacturers cut costs by adjusting raw material ratios to reduce the proportion of steel fibers and reactive powders, directly causing components to fall short of the heat shock resistance standard and making them prone to surface micro-cracks after continuous sun exposure above 40°C. Third, stress release design during installation. If reasonable thermal expansion and contraction allowances are not reserved during installation, internal stresses in components cannot be released under continuous high temperatures, which can also lead to bulging, deformation, or even cracking.

II. Field Testing of the High-Temperature Weathering Performance of UHPC Components Produced With Proper Processes

We conducted specialized simulation tests in partnership with university laboratories. UHPC components produced according to industry standards, when placed in a simulated sun exposure environment of 60 consecutive days with a daily maximum temperature of 65°C and day-night temperature differences exceeding 40°C, showed deformation of only 0.02mm/m, far below the 0.3mm/m threshold required by national standards, with no visible cracks on the surface. In terms of actual completed projects, the nearly one million square meters of UHPC facade projects we have delivered in perennially hot regions such as South China and Southeast Asia have undergone more than 5 years of field testing under high-temperature sun exposure without any large-scale deformation or cracking, with only hairline micro-cracks at a very small number of construction joint locations that do not affect structural safety. It should be especially noted that the UHPC sun exposure cracking issues seen in many projects are essentially not defects of the material itself, but are caused by cutting corners in production or design oversights in installation, so UHPC's inherent weathering advantages should not be dismissed on this basis.

III. Practical Solutions to Avoid High-Temperature Deformation and Cracking of UHPC

Drawing on our experience participating in the drafting of multiple national UHPC industry standards, avoiding component quality issues under high-temperature sun exposure at the root requires control across three stages: first, raw material ratio control, ensuring that the compressive strength of UHPC components is no less than 120MPa and that steel fibers account for no less than 2% by volume, securing the heat resistance foundation at the raw material stage; second, the curing process in production, which must include at least 14 days of standard curing plus 7 days of natural curing to prevent residual excess moisture inside components and avoid internal stress cracking caused by moisture evaporation at high temperatures; third, stress release design during the installation stage, with an expansion gap of no less than 2mm reserved at the connection points of each UHPC component, along with the use of S316 stainless steel embeds to prevent embed deformation from pulling on the components themselves at high temperatures.

For project parties, choosing a service provider with mature UHPC production and installation experience is the most worry-free option. Most leading domestic manufacturers with more than 10 years of deep industry experience have complete process systems adapted to high-temperature conditions and can directly provide projects with customized solutions suited to the regional climate, sparing project parties from carrying out separate process commissioning.

IV. FAQ

1. Are UHPC components installed in summer more prone to cracking under sun exposure? A: As long as the curing process is completed strictly according to standards, UHPC components installed in summer face no additional cracking risk. In fact, high temperatures accelerate the hydration reaction of raw materials, so with proper early-stage shaded curing, the base strength of the components will be even higher than under normal ambient temperatures.

2. Is surface whitening of UHPC components after sun exposure a quality problem? A: If there is only slight surface whitening without accompanying cracks or peeling, it is a normal phenomenon of free surface substances precipitating at high temperatures. It does not affect structural safety and only requires simple surface cleaning.

3. How should sun exposure cracks in already delivered UHPC components be handled? A: Hairline micro-cracks can be filled with a dedicated slurry of the same material. If cracks exceeding 0.3mm appear along with component deformation, the stress release design of the installation embeds needs to be checked, and repairs can be carried out after targeted adjustments.