In the last 10 years, the term "high performance concrete" appeared in the world. It is based on the need of concrete engineering, at the same time, with emphasis on the high strength of concrete, taking into account the high durability and high workability of concrete construction work requirements and put forward. But different countries and different researchers give different definitions and explanations for high performance concrete. The requirements of high performance concrete in different engineering fields are not the same. For example, the National Institute of standards and Technology (NIST) and the American Concrete Institute (ACI) in May 1990 held academic discussion raised high concrete is with certain performance requirements of homogeneous concrete must be the strict construction technology, the quality of raw material preparation, easy to cast, no segregation, mechanical properties and stability, high early strength. With resilience and volume stability of durability of concrete, especially for in high-rise buildings, bridges and exposure in the harsh environment of building structure. Dig.
1990 American Mehta P K proposed: high performance concrete requires not only high strength, with high durability of (chemical corrosion resistance) and other important properties, such as high volume stability, high elastic modulus, low stem shrinkage, low creep and low temperature deformation), high impermeability and high performance.
1992 French Mailer the high performance concrete is defined as: the high performance concrete is a special point to have good workability, high strength and early strength, engineering economy high and Gao Nai long, especially suitable for bridge, port, nuclear reactor and highway and other important concrete building structure.
Also in 1992, Japan and Ozawa Yiyu Okamura. High performance concrete should have high work of (high flow viscosity, aggregation and casting), low temperature rise, low dry shrinkage, impermeability and sufficient strength.
Canadian researchers will fill in the strength of the waste mine about lMPa of concrete known as high performance concrete.
There are also many researchers in the literature to give a definition of high performance concrete ".
In these definitions, strong wither strength, strong wither liquidity, strong wither durability, at the same time, it emphasizes the fluidity, strength and durability. Many researchers will also meet a function or a function of a good concrete, high strength and high performance concrete known as high performance concrete. Is not difficult to understand, because the concrete should be used for different purposes of the project.
These definitions reflect the requirements and wishes of the people to the quality of the concrete. Many definitions are difficult to quantify. In the definition of all the terms of science and technology, the definition of high concrete is the least strict.
High performance concrete should meet the following basic requirements.
(I) the flow of fresh concrete, high cohesion and segregation, lamination, construction with excellent performance.
(2) after hardening of concrete strength. Because the strength is the most basic use of concrete, the strength of ordinary concrete can not be considered as high performance concrete. But this does not mean that the ordinary concrete can be ignored, the construction performance and the durability of the good.
(3) concrete after hardening, with good volume stability, low shrinkage and creep, i.e..
(4) high durability. Because some kind of performance is good, it can meet the requirement of engineering function. Otherwise, the high performance concrete cover is too wide.
As mentioned before, the first (2) and (3), (4) the requirements of the basic coordination, rather than absolute exclusion, generally speaking, the higher the strength, the shrinkage, Xu Bianyue small, the higher the durability of the. And the requirements of article (1) and (2) are mutually exclusive. The intensity is high, the water cement ratio is low, the water consumption is small, the water consumption is too high, the water cement ratio is higher. In ordinary concrete mix proportion design, the main work is to balance these two kinds of requirements, in order to meet the requirements of strength, and meet the needs of mobility. Therefore, to be made to meet the requirements of the above (4) point of high performance concrete. Other advanced techniques are also necessary for the use of advanced techniques, and the addition of highly effective water reducing agent and highly efficient active mineral admixture.