A Complete Guide to Steel Fibre Concrete Construction: Answers to Selection, Admixture Control, Mixing Process, Crack Prevention and Acceptance Criteria Reducing Shrinkage and Improving Crack Resistance!
Top Ten Challenges in Steel Fibre Reinforced Concrete Construction: Selection to Acceptance
I. Steel Fibre Selection: Comparison of 4 Major Types of Performance and Scenario Adaptation
1.1 How to Select Steel Fibre Type?
Cold-drawn steel wire fibre: tensile strength 380-3000MPa, suitable for high crack-resistant pavement (e.g. airport runway)
Milled wave fibre: crescent-shaped surface to enhance concrete anchorage, preferred for tunnel spraying (rebound rate ↓12%)
Bonded row fibre: hydrosol pre-bonding technology, mixing efficiency ↑40%, optimal solution for precast components
Heat-resistant fibre: 380MPa tensile strength, core material for fire-resistant construction.
1.2 Selection Decision Table
|
Project Scenario |
Recommended Type |
Key Indexes |
|
Bridge seismic structure |
end hook type |
flexural strength ↑50%~80% |
|
Tunnel wet shotcrete |
milled wave type |
rebound rate ≤12% (EN 14487) |
|
Industrial flooring |
bonded cluster type |
crack resistance class I |
|
Military blast wall |
copper plated micro-wire type |
impact resistance toughness ↑20 times |
II. Admixture control: scientific proportioning and cost balance
2.1 What is the optimum dosage?
Golden range: 1.5%-4.5% (v/v), no significant reduction in flexural rigidity above 3%.
Data support:
Doping 1.5% → cracking strength 7.4MPa, ultimate strength 44.5MPa
Dosage 3.0% → cracking strength 9.6MPa (↑30%), ultimate strength 57.6MPa
Doping 4.5% → Ductility coefficient is obviously reduced, and economy decreases.
2.2 Anti-freezing programme for winter construction
Critical measures: water-cement ratio ≤ 0.50 + early-strengthening agent (sodium sulphate 2% of cement dosage)
Shrinkage control: ↓7%-9% shrinkage after mixing steel fibre, with triple anti-freezing process:
Material preheating: aggregate heating to ≥ 5 ℃, into the mould temperature> 2 ℃
Air-entraining and ice reduction: Doped rosin thermopolymer air-entraining agent, reduce the destructive force of ice crystal expansion
Layered cover (-5℃ environment)
Bottom layer: plastic film sealing moisture
Middle layer: three layers of cotton felt insulation (>5 ℃ temperature difference buffer)
Outer layer: rock wool anti-freezing layer8
III. Mixing process: elimination of agglomeration and performance guarantee
3.1 Precautions for mixing steel fibre concrete?
Fatal taboo: manual mixing is strictly prohibited! Forced mixer required for small projects
Five-step standardised process:
Dry mix cement + aggregate + steel fibre (≥1.5min)
Add water in three stages (30s interval)
Extend wet mixing by 20-30s (total time ≥ 3min)
Add water reducing agent (polycarboxylic acid system is the best)
Water washing method to detect fibre dispersion (deviation ≤±15%)
IV. Acceptance standards: authoritative testing methods and indicators
4.1 What are the acceptance testing indicators?
Four items must be inspected:
Mechanical properties: compressive strength (≥115% of design value), flexural strength (↑50%~80%)
Fibre distribution: CT scan uniformity ≥95% (prefabricated components)
Durability: frost resistance (quality loss of 300 freeze-thaw cycles ≤5%)
Content deviation: washing and sun-drying weighing, single sample deviation ≤±20%, mean value deviation ≤±5%
4.2 On-site quick inspection toolkit
Item Tool Qualification standard
Fibre length 0.1mm precision caliper Deviation ≤10% of nominal value
Bending resistance Diameter 3mm steel rod 90° bending without breakage
Surface quality Alcohol wiping test No oil residue
V. Crack prevention: material + process dual control
5.1 Material-level solutions
Copper-plated micro-wire fibre: Salt spray test >1000 hours (ASTM B117), corrosion rate <0.5%
Shrinkage compensation formula: Calcite expansion agent + steel fibre to offset temperature difference stress
5.2 Key points of construction process
Timing of secondary plastering: compaction of micro-cracks before initial setting (8-12 hours) when finger-pressing to leave traces
Conditions for demoulding: Strength ≥1.2MPa + ambient temperature difference ≤20℃ (to prevent surface brittle cracking)