Facility Maintenance Division of Kukje Chemical & Construction Co., Ltd.
Fire Resistance Mortar
MLM(Ministry of Land, Transport and Maritime Affairs) New Technology No. 647 (Fire resistant method for concrete structures, casting the fire resistant mortar with the dedicated spray equipment and applying fire resistant coating
Patent no. 10-1016156 (Fire resistant method for concrete structures, using the fire resistant mortar)
Heat load is removed from existing spherical concrete to form concavo-convex and secure adhesive force. Then, dusts and foreign matters are eliminated from the substrate by water jet cleaning, and the fire resistant mortar is sprayed with dedicated equipment. Then, the material is finished with fire resistant coating agent to block external deterioration elements, improve aesthetic features and form new fire resistant protective layer so as to improve durability of existing structures and prevent recurrence of deterioration. In that way, sudden heat can be prevented during the fire to ensure safety of existing structures.
Large-scale fire in structures, such as Daegu Subway Jungangro Station fire(2003), fire in the section of Onsu Station on Seoul Metropolitan Railway(2005), and fire on the elevated bridge at Jungdong IC in Bucheon, causes damage to the structures, bringing social infrastructures, such as transportation networks, to a standstill for a prolonged time, as well as casualties, due to degradation of structural strength. The International Tunnelling. Association, European countries, Japan, etc., have established and operated the fire resistant design standards for underground facilities to minimize damage to structures, prevent casualties, and ensure undisrupted operation of transportation networks in case of large-scale fire. In Korea, the fire resistant design standard is yet to be established, and as a result, overseas fire resistance-related laws have been used as references.
Inadequate fire resistant performance
Degradation adhesive force in humid regions
Occurrence of raising phenomenon
Low strength
Vulnerability to impact and low wear-resistance
Low durability and strength
Risks of peeling and dropping
Low resistance temperature, resulting in damage
Existing fire resistant materials provide lower fire resistant performance, causing cracks, peeling, exfoliation, and sudden heat, which increases the risk of large-scale disasters such as collapse of structures.
Mont Blanc Tunnel fire
Fire in Euro Tunnel
Gotthard Tunnel fire(collapse of lining concrete)
Name of Tunnel | Mont Blanc | Railroad tunnel linking England and France under the Strait of Dover | Gotthard Tunnel | Gotthard Tunnel |
---|---|---|---|---|
Location | France | England, France | Austria | Austria |
Year | 1999 | 1996 | 2001 | 1997 |
Extension | 11.6Km | 49.4Km | 16.9Km | 16.9Km |
Highest Temperature | 1000℃ / 53 hours | 1100℃ / 9 hours | 27 hours | 30 minutes |
Damage in structures | The lining ceiling was destroyed due to the explosive fracture as large as up to 70cm at the ceiling part in the 900m section. | The concrete linings were peeled off in the 9.0km section. Within the range of 300m to 500m, segments with a thickness of 40cm were severely destroyed, making the bedrocks exposed. | Collapse due to explosive fracture of concrete at the ceiling part in the 250m section | Damage was caused to the ceiling part in the 50m section due to explosive fracture measuring 100m2 in size |
Ensuring the safety of structures from fire
The polypropylene[PP fiber] is mixed with fire resistant mortar to prevent explosive fracture, exfoliation, and peeling.
Using the lightweight aggregates and hollow aggregates, the thermal conduction rate can be lowered and the quality of structure can be maintained even at high temperatures.
Explosive fracture, peeling, and exfoliation occur due to high temperature.
Quality is degraded drastically due to low strength, low durability, and vulnerability to external vibrations and impacts.
· Prevention of fiber entanglement and nozzle clogging
· Improved dynamic performance and durability, ensuring the workability
The mixing device for fire resistant mortar performs mixing automatically with the mixing device inclined at about 45º in the primary mixing unit, and has the discharge unit at the top to prevent the fire resistant mortar from being stuck or discharged in a clumped state, unlike the existing mixing device installed horizontally for measuring the mixing water manually.
Agitator for fire resistant mortar was developed because fire resistant mortar containing large amount of polypropylene cannot be used for a long time although ordinary mortar can be applied using the existing agitator. The clogging caused by fiber was prevented by transferring the material toward the pump and generating the whirlpool.
· Maintain the quality at a constant level and decrease the rebound rate to ensure safety
· Increase eco-friendliness by using industrial by-product slag micropowder and silica fume
· Improve the maintainability by increasing the durability
Design stage | Installation stage | Maintenance stage |
---|---|---|
Ensuring the safety of structure by conducting the fire experiment based on the ISO and RABT fire resistant curve | Ensuring the quality based on the installation guideline for each process[fire resistant mortar, fire resistant coating agent] | Ensuring the durability based on water absorption coefficient test, etc. |
Dead load reflected in the design to accommodate to the increase in self-weight | Ensuring the safety based on the quality and site management | Ensuring the resistance to fire based on the fire resistant test results conforming to the standards and preparation of maintenance guide |
Applicability to the sites | Distributability | Structural safety |
---|---|---|
Development of fire resistant mortar and double mixing device | Meeting the fire resistant performance and quality standards | Fire resistance test results meeting the standards |
Development of fire resistant method | Ensuring the reliability and consistency with public interest | Preparation of installation guide and achievement of high durability |
Fire resistant test was conducted for 170 minutes by applying the fire resistant mortar to the surface of concrete block test piece(1,850 X 1,250 X 300mm) under the heating condition according to the RABT-fire curve(Train). The temperature on the concrete surface of test piece and internal temperature were measured. In the test, the concrete with the standard strength of 27MPa was used. The fire resistant mortar was applied to a thickness of 30mm.
Fire resistant mortar application and curing
RABT(Train) fire curve test
No explosive fracture occurred. The RABT(Train) fire curve test showed that the maximum temperature on the interface was 228℃, which conforms to the European fire resistance standard(concrete interface temperature of 380℃ or less) and Japan’s fire resistance standard(concrete interface temperature of 350℃ or less), thus proving excellent fire resistant performance. After completion of the test, no exfoliation of fire resistant mortar occurred. So, the material is considered to help prevent degradation of fire resistant performance of existing structures and promote structural stability.
Surface of testpiece prior to fire resistant test
내화시험 후 시험체 표면
· Adjustment of water and cement ratio
· Ensuring the diffusability of powder and polypropylene fiber(PP fiber)
Concrete chipping
water jet cleaning
fire resistant mortar spray coating
fire resistant coating agent application
Application of surface coating material
Concrete interface temperature of 350℃ or less
0.2 or higher
5.0 or higher
2.0 or higher
Damage caused to bridge due to fire
Fire resistant repair of bridge
Exfoliation and peeling caused by fire
Fire resistant repair of tunnel
Concrete chipping
water jet cleaning
Application of anti-rust agent
Application of spherical reinforcing agent
Fire resistant mortar spray coating
Fire resistant coating agent coating
Surface coating agent application
Concrete interface temperature of 350℃ or less
1.0 or higher
20.0 or higher
6.0 or higher
PC Beam fire resistant repair works(July 2011)
Damage is caused by the fire at the lower part of bridge, such as concrete peeling from the PC beam
By applying the FRM method, the load-bearing capacity of structure is increased and original structure is protected from fire.
Fire resistant repair of box structures(June 2011)
Concrete peeling, exfoliation, crack, rebar exposure, etc., were detected. Countermeasures against fire are needed.
By applying the FRM method, the load-bearing capacity of structure is increased and original structure is protected from fire.
Test-purpose coating of fire resistant mortar (May 2011)
There are risks to the safety of upper structures in case of fire due to inflammable materials at the lower part of bridge.
By applying the FRM method, the load-bearing capacity of structure is increased and original structure is protected from fire.