UHP in UHPC is the abbreviation of the phrase (ultra-high), which refers to the highest magnitude of P (performance), the word means performance, efficacy, C refers to concrete, and UHPC refers to ultra-high performance concrete
Since UHPC is ultra-high-performance concrete, how high can its performance be?
In terms of the most important compressive properties of concrete, the compressive strength of ordinary concrete is about the same15mpa-30mpa, and pig iron, which has a high hardness in our daily life, generally has compressive strength200mpaIt is said that UHPC has the highest compressive strength but can be achieved810mpa
It can be said that ordinary concrete is "five scum" in front of UHPC.
[Example]: Monkey King's Ruyi Golden Hoop Stick, weighing 13,500 catties (about 6.).75 tons), the highest strength UHPC is still easy to put a hundred or so Dinghaishen needles on one square meter.
The "high" of UHPC is more than just a single compressive capacity
UHPC"Three highs"
Ultra-high performance concrete] is mainly known for its "three highs": high strength, high durability and high workability.
1. High strength
As mentioned above, the maximum compressive strength of UHPC can reach 810MPa, because the process level of each country is quite different, and the minimum compressive strength of UHPC is also required to reach more than 120MPa, and the shear resistance is more than 25MPa, and it has high heat insulation, high waterproof, delicate texture, and can basically isolate all harmful media. It can be described as the white jade pillar of the sky, the purple gold beam of the sea, and the independent carrying of a piece of the sky.
2. High durability
Traditional concrete inevitably has many gaps of its own. In the case of high temperature or low temperature, continuous rain or high sunshine, the gap will be further amplified, and the service life is low, and UHPC itself basically does not have any gap, even if it is affected by external forces to produce subtle gaps, 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.
sunyudo footbridge
3. High workability
Different from the characteristics of traditional concrete, such as "coarse, clumsy, thick and heavy", UHPC relies on its strong physical characteristics to make the structure extremely lightweight and has a strong visual beauty. With its excellent performance, designers can completely implement their imaginations.
UHPC has high density, high surface finish, delicate texture and a feeling of warmth like jade, ordinary concrete is completely rough in front of UHPC. Not only that, the ultra-low porosity also makes UHPC less susceptible to contamination and easy to clean and maintain.
Why UHPC is so strong
Traditional concrete is generally prepared by cement, admixture, sand, water and other components in a certain proportion, and after mixing and curing to a certain extent, cement-based composite materials based on aggregate (sand and gravel) and cement slurry are formed. However, there is a big difference between the aggregate and the cement slurry of traditional concrete in terms of physical and mechanical properties, which are mainly restricted by the following three aspects:
First:The water content of cement slurry expands and contracts at high or low temperature, and there will naturally be gaps between the aggregate and the cement slurry.
Second:The hardness of the aggregate based on sand and gravel is not high and the volume is large, and the gap will be further enlarged under the use of external force, generally speaking, the larger the volume of the aggregate, the larger the crack.
Third:The traditional concrete is rough in the mixing process, so that the distribution of the supporting aggregate in the cement slurry is not very uniform and the porosity is relatively high, which greatly reduces the compressive capacity of the concrete.
Concrete batching as well as concrete pouring
This makes traditional concrete brittle, poor compressive and not durable. The compressive capacity is only 20MPa-30MPa.
To improve the performance of concrete, we mainly start from the following three points:
1. Reduce the moisture content in the concrete as much as possible.
2. Look for substances with smaller volume and higher hardness as aggregates.
3. Reduce porosity and make aggregates, media, etc. more uniformly distributed.
Water reducer reduces moisture content
Ultra-fine powder improves compactness
In the 70s of the last century, the Danes greatly improved the strength of concrete by adding superplasticizers and ultrafine powders to concrete. Superplasticizers make the moisture content in concrete greatly reduced. Ultrafine powder powder is added to the concrete ingredients as an admixture, and the gap between the aggregates is effectively reduced and the quality of the mixed air is minimized through sufficient stirring, so as to improve the compactness of the material.
UHPC stirring thoroughly.
The concrete treated by the above methods is called HPC (high-strength concrete), and the compressive capacity of HPC can theoretically reach a strength of 120MPa (120 tons of force per square meter).
Steel fibers increase strength
The active powder improves the degree of confluence
Around the 90s of the last century, people used silica fume, mineral powder and other active mineral powders as admixtures for concrete, and used ultra-fine steel fibers to replace the traditional coarse aggregates, and incorporated ultra-fine active powders to minimize the internal defects of the materials. The strength of steel fibers is higher and the volume is smaller, and the active mineral powders such as silica fume and mineral powder can make the fusion between materials higher in a chemical sense, and after long-term curing in a high-temperature and high-pressure environment, the microstructure of concrete can be optimized. Even if there are microscopic cracks in the material, they can slowly heal themselves under the action of active mineral powders.
Ultra-fine steel fibers in concrete.
UHPC admixture with steel fibers added.
High pressure molding
High temperature curing
Because the whole process plays a leading role in the active mineral powder, the concrete at this time is called RPC (Reactive Poeder Concrete) active powder concrete, which can already have ultra-high physical properties and is also called UHPC.
General RPC (active powder concrete) can be divided into two grades according to different curing conditions, curing for about 3 days in the case of 20 -90, the compressive strength of RPC can reach about 200MPa (200 tons per square meter), this kind of concrete is called PRC200. If the RPC is formed under high pressure (the porosity of UHPC is lower under high pressure) and cured at 250 -400 °C, the compressive strength of RPC can reach 500MPa-800MPa, and this kind of concrete is called PRC800.
There are great differences in the level of process production and science and technology between countries, and the evaluation standards for UHPC in various countries are also very different. Generally speaking, concrete with a compressive strength of more than 150MPa can be called ultra-high performance concrete (UHPC).
Relative limitations of UHPC
Generally speaking, if UHPC wants to achieve relatively high strength, it needs a certain high temperature and high pressure heat curing as a necessary condition, on the other hand, steel fibers are easy to agglomerate during the mixing process, and large professional mixing equipment is required. These are basically difficult to achieve for the construction conditions of on-site pouring. As a result, UHPCs are mostly prefabricated parts that need to be prepared in advance at the factory.
UHPC prefabricated components of Lanting project on the left bank of China Shipping (**Source: Shanghai Tianhua).
UHPC application examples
National Museum of Qatar
Opened in 2019, Qatar Museums is inspired by the unique natural intention of the "Desert Rose", with a vertical structure that plays the main load-bearing structure and supports a staggered disc for a futuristic look. Architect Jean Nouvel used the superior mechanical properties of UHPC to use the disc as the main shading system in the tropical desert environment, creating a unique experience that integrates architecture, exterior and sensory.
Hangzhou Yuhang Grand Theater is the first case of UHPC application in China's architecture, and the building is adopted as a whole".Frame shear + steel concrete (concrete).The structural form meets the design inspiration of ice cracking, and the building is integrated with a strong visual effect. The delicate surface of UHPC also provides a lot of convenience for later maintenance.
Shanghai Opera House
The façade materials of the Shanghai Opera House are UHPC exterior wall hanging board and GRC hanging board, which are hollow as a whole, with brickwork patterns as the main design, and the simple texture and color are in step with the surrounding environment, quiet and elegant.
Shanghai Opera House Photographer: Shao Feng.
The hyperbolic geometry of the bridge has a span of 10 meters and a span of 0With a curve of 4 meters, the bridge uses UHPC to break through the limitations of traditional bridges with an extremely simple and lightweight structure, with a charming sense of science and technology, and at the same time, it seems to originate from myths and legends, taking us to unknown hidden corners.