High strength and high performance concrete (abbreviated to HS-HPC) is a kind of high performance concrete with strength degree over C80, possessing the advantages of high strength and durability, applied to foundation column and beam of ultra high-rise building. It has the same reinforcement ratio with normal concrete, can decrease structure section to enlarge using area and space, and achieves higher durability.
1. Main Technology
Water-binder ratio of HS-HPC is no more than 28%, water consumption is no less than 200kg/m, cementing agent consumption is 650~700kg/m, cement content is 450~500kg/m, dosage of silicon and mineral fine powder is 150~200kg/m, coarse aggregate is 900~950kg/m, fine aggregate is 750~800kg/m, and it adopts polycarboxylate or amino-sulfonic based superplasticizer. When used in reinforced concrete structure, HS-HPC needs fiber (volume fraction: 2.0~2.5%) like polypropylene fiber, steel fiber and so on.
2. Technical Indexes
(1）The workability of fresh HS-HPC impacts strongly the concrete construction, with the characteristics of high viscosity, low liquidity, not available to ultra high pumping. Technical indexes of concrete mixture mainly include slump (≥240mm), slump flow (≥600mm), and delivery time of inverted slump cone (≤10s), without gravity segregation and weeping of concrete mixture.
(2）The mixture design of HS-HPC should follow the formula: f cu ,o = 1.15 f cu ,k
(3）HS-HPC should be of great durability with compacting inter structure and proper pore structure. Durability of freezing resistance, carbonation and so on can be exempted from inspection, or tested in accordance with Regulations on High Performance Concrete Applied Technology: CECS207; the electric conductivity should be below 500C; for resistance to sulfate corrosion, cement containing C3A ( 5%) is better; and there being latent reaction of alkali-active aggregate, non-alkali-active one should be used.
(4）Autogenous Shrinkage of HS-HPC
1) Autogenous Shrinkage and Solutions
When fresh HS-HPC is enclosed in a certain volume, for the hydration of cement, it would absorb water from capillary tube and cause certain tension of the latter, so large that the concrete cracks, which is called autogenous shrinkage cracking. Water-cement ratio is lower, the shrinkage is more violent.
Generally, the amount of aggregates should not be too low, and the amount of binding material not be too high; adding steel fiber could compensate the loss of toughness, except the corrosion situation, and in the corrosion situation organic fiber like polypropylene fiber is needed. The shrinkage and cracking of HS-HPC could be controlled by adding ultra-fine zeolite powder of 5% saturation and adequately maintaining.
2) Test for Autogenous Shrinkage
The test can be referred to Test Standards for Normal Concrete Persistence and Durability: GB/T50082 and Regulations on High Performance Concrete Applied Technology: CECS207 by China Association for Engineering Construction Standardization. The crash width of HS-HPC should be less than 0.2mm. When the strain rate of normal concrete is 3‰, the bearing capacity can still keep more than half. If the strain rate of HS-HPC is also 3‰, the real bearing capacity is near zero, meaning that only can cracking be observed and then rapid destruction.
3. Scope of Application
HS-HPC is applicable to structural engineering in which concrete strength is demanding.