Analysis of steel fiber reinforced concrete technology: the secret of increasing compressive strength by 188%

This article analyzes the performance differences between end hook steel fibers and bonded row steel fibers from the perspective of steel fiber type comparison; the standardized construction process proposes a 5-step mixing method (feeding in batches, controlling time, etc.) to avoid fiber agglomeration, and emphasizes the use of a twin-shaft mixer.

 

Zhang Ji's team at Huazhong University of Science and Technology has experimentally confirmed that when the end hook steel fiber content is 4%, the compressive strength increases by 188% (DOI: 10.1038/s41598-024-60391-1).

 

Comparison of the core performance of steel fiber concrete vs. traditional concrete

 

Performance indicators	Traditional C30 concrete	Steel fiber reinforced concrete	Improvement	Test standards
Compressive strength	34.5 MPa	38-42 MPa (end hook fiber)	10%-20%	ASTM C39
Tensile strength	2.5-3.0 MPa	4.5-6.0 MPa (copper-plated microwire)	80%-100%	ASTM C496
Flexural strength	4.0-5.0 MPa	7.0-9.0 MPa (bonding fiber)	75%-80%	EN 14651
Crack width control	0.3-0.5 mm	≤0.1 mm	Reduction 60%-80%	ACI 544
Impact toughness	1.5-2.0 kJ/m²	8.0-10.0 kJ/m²	4-5 times	ACI 544.2R
Freeze-thaw cycle life	150 times (5% mass loss)	300 times (mass loss <3%)	Extension 100%	ASTM C666

 

 

1. Compressive strength

Traditional concrete: The standard compressive strength of C30 is 34.5MPa. Steel fibers mainly improve toughness through three-dimensional support, and the improvement of compressive strength is limited (usually 10%-20%).

 

2. Tensile and crack resistance

Core advantages: Steel fibers transfer stress by bridging cracks, and the tensile strength is increased by more than 80%, which significantly inhibits the expansion of cracks (see the figure below).

 

3. Durability and life

Salt spray corrosion test: In 5% NaCl solution, the corrosion time of steel bars in copper-plated steel fiber concrete is extended from 10 years to 25 years.

Wear resistance: The use of steel fibers in industrial floors reduces the surface wear rate by 40%-50%.

 

Analysis of the correlation between steel fiber type and performance

1. End hook steel fiber vs. bonded row steel fiber: mechanical performance comparison)

Indicators	End hook steel fiber (dosage 4%)	Bonded steel fiber (dosage 4%)
Compressive strength improvement	188%	142%
Tensile strength	6.8MPa	5.2MPa
Crack control level	Grade I	Grade II

 

Standardization Guidelines for Steel Fiber Concrete Construction Process

1. Raw Material Control and Mix Ratio Design

(1). Raw Material Requirements

Steel fiber: length 20-60mm, diameter 0.3-0.9mm, aspect ratio 30-80, tensile strength ≥600MPa (end hook type ≥700MPa). Copper-plated steel fiber must meet the salt spray test ≥500 hours without rust245.

Cement: grade not less than 425, preferably silicate or ordinary silicate cement, water-cement ratio ≤0.526.

Aggregate: coarse aggregate particle size ≤ 2/3 of steel fiber length (generally ≤25mm), fine aggregate should be medium-coarse sand (fineness modulus 2.6-3.0), mud content <3%2610.

Admixture: Chloride salt is strictly prohibited, water reducer must be compatible with cement, and the dosage is determined by test610.

 

2. Mix design

Steel fiber volume ratio: 0.5%-2% for conventional projects, and can be increased to 1.5%-1.8% for important projects26.

Sand ratio and water consumption: Sand ratio is 40%-46%, and for every 0.3% increase in steel fiber volume ratio, water consumption increases by 3kg/m³56.

Slump control: 20mm less than ordinary concrete, Vebe consistency remains consistent 610.

Example mix ratio:

Project type	Steel fiber content (%)	Sand ratio (%)	Water-cement ratio	Cement (kg/m³)	Steel fiber (kg/m³)
General casting	0.5-1.2	40	0.45	400	78
Important project	1.5-1.8	46	0.45	450	120

 

3. Mixing process: 5 key steps to avoid fiber agglomeration

Step list:

● Dry mix aggregate and cement for 60 seconds

● Add steel fiber three times (30 seconds interval)

● Wet mix for 90-120 seconds after adding water

● Add water reducer before discharging (polycarboxylic acid is best)

● It is strictly forbidden to use forced mixer (twin-horizontal shaft model is recommended)