Instruction for Use of Steel Fibers in Concrete
Material reference of steel fiber reinforced concrete
Steel fiber: The mechanical properties of the selected steel fibers should not be lower than the requirements of first-grade carbon steel, and its geometric parameters should meet the requirements of the table below.
|Structure Type of Concrete||Length (mm)||Equivalent Diameter (mm)||Aspect Ratio|
|Ordinary cast structure||25-50||0.3-0.8||40-100|
|Earthquake resistant frame||40-50||0.4-0.8||50-100|
Cement: Ordinary Portland cement is preferred.
Coarse aggregate: Crushed stone or pea gravel with a size no more than 20mm or 2/3 of the length of steel fibers is preferred.
Fine aggregate: Clean river sand with a fineness modulus of 2.3 to 3.0 is preferred, and clay content should be less than 3%. The use of sea sand is strictly prohibited.
Water: Clean water should be used; Seawater should not be used.
Admixture: Use high-quality superplasticizers; Admixtures containing chloride ions should not be used.
Inspection of raw materials
Mix ratio design
Calculating the construction mix ratio
In the mixing process, adding cement, fine aggregate, coarse aggregate, admixtures, steel fibers sequentially
Testing mechanical properties of concrete
Set out survey
Sampling and testing volume fraction
1. Use a forced action mixer for mixing steel fiber reinforced concrete, and the mixing volume at one time should not exceed 80% of its rated mixing volume, and the mixing time is 1 to 2 minutes longer than that of ordinary concrete.
2. When mixing, the allowable errors of measurement of various materials are as follows: coarse and fine aggregate ±3%, steel fibers, cement and admixtures ±2%, water ±1%.
3. The feeding sequence is based on the principle that steel fibers are uniformly dispersed and do not agglomerate during the mixing process. The method of mixing is as follows:
cement, fine & coarse aggregates, admixtures
mix for 2 min
add steel fibers while mixing
mix for 2 min
add water and mix for 2 min
4. Steel fibers are added by machine dispersedly. The method is to set up a platform above the hopper of the mixer, put a steel fiber disperser on the platform and install a movable chute under the disperser. After the cement, fine and coarse aggregates, and admixtures enter the mixer from the hopper, put down the hopper, put the platform setup into the mixer, and start the disperser while the mixer is mixing. Manually and gradually add steel fibers through the chute.
5. The transportation of steel fiber reinforced concrete is the same as that of ordinary concrete, but the time should be shortened as much as possible, and the segregation of the mixture should be avoided during the transportation. If segregation has occurred, the concrete should be mixed again before pouring.
6. Before pouring the steel fiber reinforced concrete, the slab should be treated and prepared, and the reliability of formwork joints, supports, other structures, the position and size of the embedded parts should be checked.
7. The corners of the form should be curved, and the steel fibers should not expose at the concrete surface.
8. The pouring of steel fiber reinforced concrete should ensure the continuity and the uniform distribution of steel fibers. The time between the discharge of mixture from the mixer to the completion of pouring should be within 30 minutes. And it is strictly forbidden to add water during the pouring process.
9. The height of free fall should not exceed 2 meters when the steel fiber reinforced concrete is poured.
10. The pouring of steel fiber concrete should be carried out in layers, and the pouring thickness should be determined according to the mixing capacity, transportation conditions, pouring speed, tamping capacity, etc.
11. The steel fiber reinforced concrete should be vibrated mechanically instead of manually. The moving distance of the internal vibrator should not exceed 1.5 times the radius of action of the vibrator, and the depth into the lower layer is 5-10cm. The moving distance of the surface vibrator should cover the edge of the compacting part. The use of the attached vibrator should ensure the compactness of the concrete.
12. When the vibrator is working, it is not allowed to lean against the steel bars, nor to hit with the steel bars and buried parts. The vibration duration of the vibrator at each position should ensure that the concrete has sufficient compactness (the concrete does not sink, no bubbles appear, and the surface starts bleeding). It is also necessary to prevent excessive vibration from affecting the steel fibers distributed.
13. The curing method of steel fiber reinforced concrete is the same as that of ordinary concrete.