High performance concrete is made through conventional technology and its strength grade is from C50~C80. It is composed of cement, sand, stone, superplasticizer and other additives, fly ash, superfine slag, silica fume and other mineral admixtures. As a new kind of building material, high performance concrete has the advantages of high compressive strength, high resistance to deformation, high density and low porosity. Its application range is wide, covering bridge engineering, high-rise building, concrete products, water conservancy and hydropower engineering, port and marine engineering, etc.
Production & Construction Process
One is the production and construction of mixing plant, including high performance concrete’s raw materials, preparation technology and transportation. Another is the site construction, involving pouring and curing of high performance concrete. The construction technology of high performance concrete is basically the same as ordinary concrete, but the construction requirements of high performance concrete are more strict.
Cement: When you produce high performance concrete, the specific dosage should be based on the variety and fineness of cement, the size of the concrete slump, the shape and gradation of the aggregate and so on; Fly ash, silica fume and other mineral admixtures; Stone, sand and other aggregates (The maximum size of coarse aggregate is generally limited below to 20mm, and the maximum should be not more than 25mm, and it should adopt continuous gradation; the fineness modulus of sand should be controlled between 2.6-3.3. The higher the fineness modulus is, the thicker the sand is); Water: High performance concrete’s requirement for water is the same as ordinary concrete; Superplasticizer, retarding water reducer, air-entraining water-reducing agent and other additives.
Note: Raw materials should be separately stored according to variety, specification, quality level, strength level, manufacturers and production place. At the same time, you should take appropriate measures to prevent raw materials from sun, rain, moisture, freeze and so on.
When the raw materials have been prepared, they should be sent to the central mixing station according to the pre-set formula. The most important machine of central mixing station is one or more mixers. Raw materials stored in barrel will be sent into the mixer by screw conveyor ( it is advisable to use a twin-shaft compulsory mixer). The central control room can control the proportion of raw materials and the time of mixing (see the below table). After the raw materials are stirred and mixed, the next step can go on.
High performance Concrete Mixing Time
Concrete Strength Grade
Mixing Time (s)
Note: High performance concrete’s production requirements: 1. use selected cement, aggregates and other raw materials; 2. add superplasticizer to reduce water consumption and water-cement ratio; 3. add high-quality mineral admixtures to improve the microstructure of cement stone and interface region, and to improve the compactness and bond strength; 4. carefully select the material mix proportion and determine the reasonable sand ratio and water-cement ratio to reduce the dosage of cement and improve the strength of concrete.
The time between high-strength concrete was loaded the concrete mixer to be discharged should not be more than 90 minutes. When the truck mixer reaches the pouring site, the stirred pot should be rotated at high speed for 20s-30s before unloading the concrete.
Note: When the discharged concrete mix has a high consistency and the time from loading to discharging is within 90 minutes, you can add some water reducer to improve the fluidity of concrete. Water reducer should meet following standard requirements: 1. same variety 2. dosage should be determined by the test plan 3. after water reducing agent is added into the concrete mix, the mixing tank should be rotated at high speed for not less than 90 seconds.
High performance concrete structure adapts layered casting technics. Layer thickness should not be too large and each layer pouring time interval should not be too long, which are conducive to ensuring the concrete pouring quality of each layer and the homogeneity of the overall structure. (Layer thickness should not be larger than 500mm; Time interval of the same pouring location of the upper and lower layers should not be more than 120 minutes.) The high performance concrete can be machined with a vibrator, and the insertion point spacing should not be greater than the vibrating radius of the vibrator. The vibrating time of pumping high performance concrete should not be too long so as to avoid the layering of stone and slurry. The vibrating time of each insertion point is not more than 20 seconds. When the surface of concrete mixture appears pulp and almost no bubbles, it can be regarded as having been tamped; as for the continuous multi-layer pouring, the vibrating bar should be inserted into the lower mixture 50mm to vibrate.
After the high performance concrete pouring process is finished and the concrete has been molded, you should take measures to cover the exposed surface timely. Before the final concretion, you should use trowel to rub the surface at least twice and cover it again after flatting. High performance concrete can take many curing ways such as moister curing, water storing, watering, water spraying and covering to preserve moisture. The temperature difference between curing water and concrete surface should not be greater than 20 ℃ and water curing time should not be less than 10 days.