What material is UHPC?

What is UHPC？The UH in UHPC is an abbreviation of the phrase Ultra-High, which means the highest order of magnitude;The word P(Performance) means performance, efficacy;C is for Concrete.UHPC stands for "Ultra-High Performance Concrete".

How strog is the UHPC

Since UHPC is ultra-high performance concrete, how high can its performance really be? In terms of the most important compressive performance of concrete, the compressive strength of ordinary concrete is almost 15Mpa-30Mpa, while the high hardness of pig iron in our daily life is generally 200Mpa, and it is said that the highest compressive strength of UHPC can reach 810Mpa. It can be said that ordinary concrete is "war five slag" in front of UHPC.

The "Three Heights" of UHPC

"Ultra-high performance concrete" is mainly known for "three high" : high strength, high durability, high workability.

"High intensity"

As mentioned above, the maximum compressive strength of UHPC can reach 810Mpa, because the technological level of each country is quite different, the minimum pressure of UHPC is also required to reach more than 150Mpa, the shear resistance is more than 25Mpa, and the high heat insulation, high waterproof, fine texture, basically can isolate all harmful media. It can be described as the giant white jade pillar, the sea purple gold beam, independently carrying a day.

▲ Zhonghai · Zuoan Lanting, Architectural design: Shanghai Tianhua, UHPC Construction: Nanjing Berida © Wang Xiao, © Yiran Architectural Photography

"High durability"

Traditional concrete, inevitably, has many gaps of its own. In the case of high temperature or low temperature, continuous rain or sunny cracks will further magnify the low service life, and UHPC itself basically does not have any cracks, even if affected by external forces to produce subtle cracks, UHPC also has a magical self-healing ability.

UHPC was first used in bridge construction to reduce the weight of the structure and improve the service life and durability of the structure. The service life can reach more than 100 years.

"High workability"

Unlike traditional concrete, which is "thick, stupid, thick and heavy", UHPC relies on its own strong physical characteristics to make the structure extremely lightweight and has a strong visual beauty. Designers with its excellent performance can completely put the unrestrained imagination into practice.

UHPC density, high surface finish, fine texture has a warm jade feeling, ordinary concrete in front of UHPC is completely a rough man. Not only that, the ultra-low porosity also makes the UHPC not easy to be polluted, and the cleaning and maintenance work is easy to do.

Why is UHPC so powerful

Traditional concrete is generally composed of cement, admixture, sand, water and other components according to a certain proportion of preparation, after mixing and in a certain maintenance to form the aggregate (sand) and cement slurry based composite material. However, the physical and mechanical properties of traditional concrete aggregate and cement slurry are quite different, which are mainly restricted by the following three aspects:

The first cement slurry water at high or low temperature thermal expansion and contraction of the role of the first, the aggregate and the cement slurry will naturally create a gap.

Second, the hardness of aggregate based on sand and stone is not high and the volume is large. Under the use of external force, the gap will be further enlarged. In general, the larger the volume of aggregate, the larger the crack.

Third, the traditional concrete is rough in the mixing process, so that the distribution of supporting aggregates in the cement slurry is not very uniform and the porosity is relatively high, which greatly reduces the compressive ability of concrete.

As a result, the traditional concrete has great brittleness, poor compressive resistance and low durability. The pressure resistance is only 20Mpa-30Mpa.

Improve the performance of concrete mainly from the following three points:

1 Reduce the moisture content of concrete as much as possible.

2 Look for smaller and harder materials as aggregates.

3 Reduce porosity and make the aggregate, media and other parts more uniform.

"Water Reducers reduce moisture content"

"Ultrafine powder improves densification"

In the 1970s, the Danes greatly increased the strength of concrete by adding water-reducing agents and ultra-fine powders. The water-reducing agent greatly reduces the moisture content in concrete. Ultrafine powder powder is added to the concrete mixture as an admixture to effectively reduce the gaps between the aggregates and minimize the quality of the mixed air to improve the compactness of the material through full mixing.

▲UHPC is fully stirred

The concrete treated by the above method is called HPC(high strength concrete), and the compressive strength of HPC can theoretically reach 120MPA (120 tons of force per square meter).

"Steel fiber increases strength"

"Active Powder improves fusion"

Around the 1990s, active mineral powder such as silica ash and mineral powder was used as the admixture of concrete, and ultra-fine steel fiber was used to replace the traditional coarse aggregate, and the ultra-fine active powder was added to minimize the internal defects of the material. The strength of steel fiber is higher and the volume is smaller, and the active mineral powder such as silica fume and mineral powder can make the integration degree between materials higher in the chemical sense, and make the concrete achieve the optimal microstructure after a long time curing in the environment of high temperature and pressure. Even small cracks in the material can slowly heal themselves under the action of active mineral powder.

"High pressure molding"

"High temperature curing"

Because the main role of the whole process is active mineral powder, the Concrete at this time is called RPC (Reactive Poeder Concrete) reactive powder concrete, which has been able to have ultra-high physical properties and has begun to be called UHPC.

Generally RPC (reactive powder concrete) can be divided into two grades according to different curing conditions, in the case of 20℃-90℃ curing for about 3 days, the compressive strength of RPC can reach 200MPA (200 tons per square meter can be stressed), such concrete is called PRC200. If the RPC is formed by high pressure (the porosity of UHPC is lower under high pressure), the compressive strength of RPC can reach 500MPA-800MPA under the condition of 250℃-400℃, and this kind of concrete is called PRC800.

There are great differences in the production level and science and technology among countries, and the evaluation standards of UHPC among countries also have great differences. Generally speaking, concrete with compressive strength of more than 150MPA can be called ultra-high performance coagulation (UHPC).

"Relative Limitations of UHPC"

Generally speaking, if the UHPC wants to achieve relatively high strength, it needs a certain high temperature and high pressure thermal curing as a necessary condition, on the other hand, the steel fiber is easy to cluster during the mixing process, which requires large professional mixing equipment. These are basically difficult to achieve for the construction conditions of on-site pouring. As a result, UHPC is mostly prefabricated parts that need to be prepared in advance in the factory.

UHPC application case

"Qatar National Museum"

The Qatar Museum, which opened in 2019, takes the unique natural intention of "desert Rose" as its design inspiration, and the vertical structure serves as the main load-bearing structure, supporting a criss-crossing disc, which is full of futuristic feeling. Architect Jean Nouvel used the UHPC's superior mechanical properties to create a unique experience that combines architecture, outdoor and sensory integration by using the overhanging disc as the primary shading system in a tropical desert environment.

"Hangzhou Yuhang Grand Theatre"

Hangzhou Yuhang Grand Theatre is the first case of UHPC application in Chinese architecture. The whole building adopts the structural form of "frame shear + steel concrete (concrete)" to meet the design inspiration of ice cracking, and the building is integrated with a strong visual effect. The surface of UHPC is delicate, and it also provides a lot of convenience for later maintenance.

Louvre ABU Dhabi

The Louvre ABU Dhabi is also the work of Pritzker Prize winner Jean Nouvel, and the facade of the complex is made of 3,900 high performance fiber concrete (UHPC) to form a unique domed structure. Under the strong performance of ultra-high concrete, the whole dome mechanism basically no longer needs other structural components, pure and transparent, with the surrounding water environment, light and shadow patchy is very charming.

Louvre ABU Dhabi/Jean Nouvel

Shanghai Opera House

The building facade of Shanghai Opera House is made of UHPC wall panel and GRC wall panel. The whole is hollowed-out, and the brickwork pattern is the main design source. The simple texture and color are in step with the surrounding environment, which is clear, quiet and elegant.

▲ Shanghai Opera House Photographer: Shao Feng

"The bridge over the D 'R etovice River"

The hyperbolic geometric structure of the bridge has a span of 10 meters and a curvature of 0.4 meters. The bridge uses UHPC to break through the limitations of traditional Bridges with its extremely simple and lightweight structure. The colleagues with a fascinating sense of science and technology, as if from myths and legends, take us to the unknown secret corner.

▲D 'Etovice River bridge, Czech Republic

The genius architect Rudy Ricciot1 once said of UHPC (ultra-high performance concrete), "We don't know how far this material will take us, but together we can certainly change the world." Indeed, the power of technology is more like a bridge, leading designers to the kingdom of creativity.

This article is reproduced from the public number: landscape school