1. Fire Resistive Materials: THERMAL PERFORMANCE TESTING
Performance Assessment and Optimization of Fire Resistive Materials
NIST
July 14, 2005

2. Materials Science-Based Studies of Fire Resistive Materials
Microstructure
Experimental
3-D Tomography
2-D optical, SEM
Confocal microscopy
Modeling
3-D Reconstruction
Parameters
Porosity
Pore Sizes
Contact Areas
Properties
(all as a function of T)
Thermal
Heat Capacity
Conductivity
Density
Heats of Reaction
Adhesion
Pull-off strength
Peel strength
Adhesion energy
Fracture toughness
Equipment
TGA/DSC/STA
Slug calorimeter
Dilatometer
Blister apparatus
Environmental
Interior
Temperature, RH, load
Exterior
Temperature, RH, UV, load
Performance Prediction
Lab scale testing
ASTM E119 Test
Real structures (WTC)
Materials Science-Based Studies
of Fire Resistive Materials

3. Importance of Thermal Properties
The major role of the FRM is to slow down the temperature rise of the structural steel during a fire exposure
Its effectiveness will be largely determined by its thermal properties
While heat capacity, density, and heats of reaction and phase changes do play a role, it is mainly the effective thermal conductivity of the material as a function of temperature that will dominate the performance

4. Fourier’s Law of Heat Conduction
q=-kA(∂T/∂x)
Heat transfer is proportional to temperature gradient, exposed area, and thermal conductivity k
k and thickness (x) are the variables “under our control”
k is really an effective thermal conductivity as it includes contributions of conduction, radiation, and convection

5. But, what about endothermic reactions?
Endothermic reactions and phase changes (evaporation) do absorb energy, but a couple of additional points merit consideration
1) Energy absorption will maintain a higher temperature gradient across the FRM specimen which will in turn increase the driving force for heat transfer (∂T/∂x) --- as noted to me by Prof. Fred Mowrer of Univ. of MD.
2) Steam and hot gases generated during these reactions may be transferred inward towards the steel surface, actually temporarily but significantly increasing the effective thermal conductivity
3) If the material has a low permeability, these reactions may result in (explosive) spalling (Example- high performance concrete)

6. A brief aside on “liquid” water in FRMs
Thermal conductivity of liquid water is about 0.6 W/m•K; air or water vapor is about 0.03 W/m•K (a factor of 20)
Materials with “liquid” water also have a higher propensity for spalling, etc.
Make sure that your materials are really dry before E119 (or other) testing

7. Thermal Conductivity at High Temperatures
How to measure it?
ASTM C1113: Hot wire method
High-temperature guarded hot plate (world-class facility under construction in BFRL)
Transient plane source method (Hot Disk®- will be delivered to BFRL in August 2005)
Slug calorimeter (built at BFRL in 2004 and used extensively since then)
Similar in principle to the Cenco-Fitch Apparatus used in ASTM D2214 for estimating the thermal conductivity of leather (first published by Fitch in 1935)

8. Hot Disk® System Manufactured in Sweden
Measures k in range of to 500 W/m•K
With high temperature attachments, temperature range of room temperature to 700 oC
Also provides volumetric heat capacity values

9. Slug Calorimeter Technique
Sandwich specimen of two “slabs” of FRM covering two sides of a steel slug of known mass and heat capacity
Monitor slug temperature change as entire sandwich is exposed to a heating/cooling cycle
Calculate effective thermal conductivity during multiple heating/cooling cycles
For detailed information see: Bentz, D.P., Flynn, D.R., Kim, J.H., and Zarr, R.R., “A Slug Calorimeter for Evaluating the Thermal Performance of Fire Resistive Materials,” accepted by Fire and Materials, 2005, available at .

10. Slug Calorimeter 304 stainless steel Details of slug calorimeter½”
Guard
insulation
Retaining
plate
6 “
Specimen
Slug calorimeter
Specimen
3/16” inch holes at 2”, 3”, and 4”
Details of slug calorimeter
Q direction
heating 2”
cooling 4” 6”
Guard
insulation
304 stainless steel
Experimental
setup

11. Raw Data for Exposure of Intumescents
Time for central slug to reach 538 oC varied from 52
minutes to 93 minutes for the two different materials

12. Determination of Effective k
∂2T/ ∂z2=(1/α)(∂T/∂t)
With B.C.: T(0,t)=Ft, k(∂T/∂z) +H(∂T/∂t)=0
α is the thermal diffusivity
H is the thermal capacity of one half of the slug plate
F is the rate of temperature increase/decrease of the slug
Solution: T(z,t)=F[t-(H+lC)z/k+Cz2/(2k)]
l is the specimen thickness, C its volumetric heat capacity
ΔT = (Fl/k)*[H+lC/2]
ΔT is the temperature difference across the specimen
k=Fl(H+lC/2)/ΔT=Fl(MScpS+MFRMcpFRM)/2AΔT

13. Slug Calorimeter Results: Fumed Silica Board
-Results for (non-reactive) fumed silica board in good agreement
with previous NIST (1988) measurements

14. Slug Calorimeter Results: FRM A
Good agreement with previously measured values
Differences between 1st and 2nd heating cycle provide valuable
information on influences of endothermic and exothermic
events, including reactions and phase changes
- Good repeatability in cooling curves for different runs

15. Slug Calorimeter Results: FRM C
Reasonable agreement with previously measured values
Differences between 1st and 2nd heating cycle provide valuable
information on influences of endothermic and exothermic events
- Good repeatability in cooling curves for 3 different runs

16. Slug Calorimeter Results: Comparison
k from 2nd heating curves
High variability between different FRMs especially at higher T
High T insulation boards (two lower curves) have effective k
values significantly lower than current FRMs and exhibit minimal increases at higher temperatures

17. Comparison of Time for Steel Slug to Reach 538 oC

18. Determination of Heat Capacity
Volumetric heat capacity provided directly with Hot Disk® thermal conductivity measurements
For small specimens, can measure using differential scanning calorimetry (DSC) or simultaneous thermal analysis (DSC/STA)
Both units available in BFRL at NIST
Equipment for larger sample volumes (12 mL) and temperatures up to 1000 oC is available from Setaram ($$$)

19. Heat Capacity via DSC (ASTM E1269)
Need to run a sapphire reference scan and application
of a correction (fudge) factor

20. Summary
Thermal conductivity at high temperatures is a critical performance parameter for FRMs to properly protect structural steel
BFRL/NIST labs are uniquely equipped for measuring this property and are continually upgrading our capabilities
Measurement of effective thermal conductivity provides product differentiation that can be utilized both to improve existing materials and to develop new ones