The Pouring of Super-flat Concrete And Steel Fiber Reinforced Concrete
Flooring engineering has been developed into a systematic engineering of floor structure, surface treatment, sealing, surface performance and combination properties. The matching applications of new materials, new techniques, new equipments and new technologies, for example, laser screed process and prefabricated building-in metallic construction joints, steel fiber, liquid hardener, represents the up-to-date direction of concrete pouring.
Parameter of Super-flat concrete floor:
Super flat grade
Shelf height
F-Number System
Approx.Tolerance
In 3 meter(mm)
Flatness(FF)
Levelness (FL)
Ultra-flat
≥150
≥100
≤1.0
Super-flat
>13m
≥60
≤1.6
General flat
1st style
8~13m
≥50
≥35
≤3.0
2nd style
6~8m
≥25
≤5.0
3rd style
1~6m
≥18
≤6.0
Executive Standard for Super-flat Concrete:
1. Floor construction: According to ACI302.1R;
2. Specification for the design of floor: ACI117&BCSTR34;
3. Measure of floor flatness and levelness: ASTME1155 F-Number profile(F-number profile-FACE Floor Profile Number:
4. There must be two independent F-numbers to state floor flatness and levelness:
1) Floor flatness F-number (FF): To represent floor flatness through the difference between successive elevation differences per 1 ft(30mm) along with the measure line in the test section.
2) Floor levelness F-number (FL): To represent floor levelness through the difference in elevation at points spaced 10 ft(3m) apart along with the measure line in the test section.
Concrete pouring process flow chart
Application process of super flat concrete:
Preparation:
Adjustment and maintenance of laser screed machine;
Set two reference leveling points according to the original leveling points.
Lay moisture barrier of plastic film;
Bundle up concrete iron bars (total bundle for large area); (possibly ignore this step if for steel fiber concrete);
Install side forms; (or install embedded metal joint/plates);
Set up laser launcher, set the reference elevation to laser screed machine according to the original leveling points;
Concrete Pouring:
In the effective range of telescopic arm of laser screed machine(3m or 6.1m), placing concrete roughly by the aid of manpower, vibrating, then compacting and leveling it in one time by laser screed machine.
Construction of wear resistance materials:
When the concrete is initial set (there is 3-5 mm deep mark when pressed with finger), floating by power trowel disk, then broadcast 2/3 the specified amount of wear resistance materials criss-crossly, and then floating by power trowel; broadcasting the rest 1/3 amount of material evenly, and finishing after multi- floating; treating by wood float for the corner areas.
This construction process will have significant influence to the improving of floor flatness.
Curing and sawn cut joints:
After finishing the construction, curing with agents, for example, spraying water and covering with plastic films, floor sealer or liquid floor hardener.
Sawn cut joints in 5-7days after completing the pouring works to prevent irregular cracks.
The interval between joints should be 6-8m (usually according to intercolumniation).
The cutting works should be according to the snap-line to assure the straightness. The deepness should be at least 1/3 thickness of the concrete slab.
Full traffic after 28 day’s curing.
Others:
1)Measurement of flatness: Test by F-meter or D-meter or the same grade measuring apparatus. Usually 3 days after concrete pouring in order to provide suggestions for improving subsequent works.
2)Grouting joints: Before the use of floor, the sawn cut joints should be grouting.
About Steel Fiber Reinforced Concrete
Steel fiber, as a kind of high quality concrete reinforcement metal type aggregate, it can significantly improve flexibilities of concrete. It provides high performance and crack resistance, have set a new standard for concrete
reinforcement with the combination of flexibility and cost-efficiency.
When mixing with 1.0%~2.0%(V/V) in concrete (but no exceed 2.0%!), compare to the common concrete without mixing steel fiber, it can improve 40-80% tensile strength, 60-120% bending strength, 50-100% shearing strength, and 0-25% compressive strength.
The cement used as steel fiber reinforced concrete is usually 425#~525# ordinary Portland cement to assure higher strength and higher wear resistance.
The maximum grain size of coarse aggregates for steel fiber reinforced concrete is no larger than 2/3 length of steel fiber, or no larger than 20mm. Fine aggregates is often applied as medium-coarse sand with an avg. grain size of 0.35mm-0.45mm.
The current construction standards for steel fiber reinforced concrete is CECS 38:2004 《Technical specification for fiber reinforced concrete structures 》, which was enacted by The Standardization Institute of Chinese Construction.
According to requirement, can refer to JGJ/T221-2010《Technical specification for application of fiber reinforced concrete》,which was enacted by MOHURD.
Low slump steel fiber reinforced concrete is appropriate for the construction of super flat flooring.
Recommend the slump range 12~14 for steel fiber reinforced concrete.
Must test the following before the use of steel fiber reinforced concrete:
Workability;
Air contents;
Dispersion of bonding steel fibers;
Uniform distribution of steel fibers in concrete.
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