Steel fiber reinforced concrete floor construction abstract （二）

Steel fiber reinforced concrete floor construction abstract （二）

3, The construction process

3.1 When floor foundation excavation to -0.700m of replacement ,the original soil compaction roller with 15T 4-5 times speed roller 25-30 m / min, wheel tracks overlap each other 20-30cm; 500mm thick gravel of replacement twice, each time for filling 250mm, rolling each end, which sag difference must be less than 2mm, ensure that the base soil compaction is greater than 0.92.
 
3.2 steel fiber concrete surface construction

   3.2.1 Mix Design of Cement: use P.O32.5 ordinary portland cement; Gravel: Gravel particle size of not more than 2/3 of the length of the steel fibers, typically 5-20mm, clay content less than 1% ; sand: suitably coarse sand, fineness modulus 2.5-3.0, clay content less than 3%; water: the use of potable water;
  
  3.2.2 strictly controlling the quality of steel fiber
   (1) conventional steel fiber volume fraction 0.35% to 1.5%, the maximum should not exceed 2%;
   (2) must having an appropriate size range and aspect ratio, general size range is 40 to 65mm, an aspect ratio of 40 to 80, do not agglomerate when stirred, not broken, do not be pulled out when concrete damage is appropriate;
   (3) steel fiber to high strength and toughness, the general strength ≮380 MPa, when toughness to bending test, steel fiber column around 3 mm diameter round rod bent to 90 degrees will not break once appropriate;
   (4) fiber surface should not affect the bonding of oil and other impurities, there should be no rust and impede bonding with the cement matrix coating or metal plating harmful

  3.2.3 SFRC Mixing and transport 
    1) The concrete mixing ratio trial and error to find the optimum mixture ratio. Mixing ratio of steel fiber reinforced concrete is a factor in its performance ,directly affects the workability and strength.
   2) feeding sequence: gravel added to the mixer first, then add steel fibers, stirring after 30s, cement is added; stirred for 30s, water and additives, can be a drum stirred 120s. Single steel fibers longer mixing time of 2-3 minutes. As the steel fiber reinforced concrete cohesive is larger than ordinary concrete, mixer first feeding should not be greater than 80% of the nominal amount of mixing, or the mixer may be due to heavy load to leave the steel fiber concrete mixing uneven. Stirring time extended 1 ~ 2min than ordinary concrete provisions, the entire mixing time ≮3min. In order to make the steel fibers can be uniformly dispersed in the concrete, When the steel fibers are added into the aggregate with shaking screening to add by layer and layer.
    3) steel fiber concrete transport is the same method with ordinary coagulation, that is, from mixer truck shipped to the pumping station. Because of during transportation slump and air content will be losses, mixture material consistency decline, and steel fiber reinforced concrete easier to segregation, so it should be possible to shorten the transport distance and time, otherwise it will cause difficulties in unloading the quality of pouring. To avoid concrete segregation, mixer truck transported marinated SFRC to the construction site, the first high-speed rotating cylinder installed 1min make homogeneously mixing barrel, then the material into the pump. Pumping to the construction location, along the path on both sides of the longitudinal direction from one end to the other end of the back and forth of the paving.
 
3.2.4 Concrete pouring
   1)using commercial concrete, its slump of 120 ± 20 is required, before pouring concrete slump, the test of slump must be done, the concrete that does not meet the requirements should  be returned.      2) one day in advance notice mixing station before pouring concrete, mixing station should have sufficient material and convenient transport, and to be requires to select transport routes (preparing two routes to avoid the concrete cold joints caused by traffic jams).
    3) before pouring concrete, shall remove impurities on the original concrete slab surface and wet by water one day in advance (by the responsible person), before pouring, should clear water first.
     4) the places of the concrete entering into the mold, each place are equipped with two vibrators, one vibrator flat, when vibrated slowly push pull, vibration time so as not to take bubble prevail, the insertion point spacing of 300mm, was plum-shaped arrangement, when vibrating, must strictly control the vibration time, vibration isolation for too long will lead to concrete breack and steel fiber in the concrete sink to the bottom, vibration time is too short can cause the concrete is not dense.
     5) When pouring concrete, first removing the floating pulp and bleeding and then roll to flatten, then artificial leveling, etc. after initial setting by a calender calender.
     6) After the final setting of concrete cover 2-layer film again sprinkler maintenance, curing time of not less than seven days.
 
4, Conclusion
 
The impacting, anti-explosion, anti-damaged of steel fiber reinforced concrete is higher ordinary concrete, it has a good plasticity. During deformation, it can absorb large amounts of deformation energy, and damage are not unexpected, the member does not occur when a sudden crack and pieces scattered damage phenomena,
 
Therefore, steel fiber concrete spalling and shatterproof has a unique advantage. So steel fiber reinforced concrete has been widely used in industrial buildings. This construction technology practice for floor construction with reference to the same type of plant.