Mission: As the Nation's principal conservation 

agency, the Department of the Interior has responsibility for most of our nationally-owned public 

lands and natural and cultural resources. This 

includesfostering wise use of our land and water 

resources, protecting our fish and wildlife, preserving the environmental and cultural values of 

our national parks and historical places, and providing for the enjoyment of life through outdoor 

recreation. The Department assesses our energy 

and mineral resources and works to assure that 

their development is in the best interests of all 

our people. The Department also promotes the 

goals of the Take Pride in America campaign by 

encouraging stewardship and citizen responsibility for the public lands and promoting citizen participation in their care. The Department also has 

a major responsibility for American Indian reservation communities and for people who live in 

Island Territories under U.S. Administration. 
Report ot Investigations 9382 

Evaluation of Solid-Block and Cementitious 

Foam Seals 

By N. B. Greninger, Em S. Weiss, S. J. Luzik, and C. R. Stephan 

UNITED STATES DEPARTMENT OF THE INTERIOR 

Manuel Lujan, Jr., Secretary 

BUREAU OF MINES 

T S Ary, Director 
Evaluation of did-block and cementitious foam seals / by N.B. Greninger . . . [ct 

d.]. 

p. an. - (Report of investigations; 9382) 

Includes bibliographical references 

Supt. of Docs. no.: I 2S.U:9382. 

1. Concrete stoppings (Mining)--Testing. 2 Mine ucplosions-Prevention. 

I. Greninger, Nevin. 11. Series: Report of investigations (United States. Bureau of 

Miner); 9382. 

TN23.U43 [TN3U] 622 dcU) [622'.82] 91-16546 CIP 
Page 

Abstract ........................................................................... 1 

Introduction ........................................................................ 2 

Background ...................................................................... 2 

Purpose ......................................................................... 3 

Acknowledgments .................................................................... 3 

Experimental procedure ............................................................... 3 

Discussion of test results ............................................................... 9 

Solid-concrete-block seals ............................................................ 9 

Cementitious foam seals .......................... ; .................................. 10 

Conclusions ........................................................................ 12 

Recommendations ................................................................... 12 

ILLUSTRATIONS 

1 . PlanofLLEM ................................................................... 2 . Diagram of seal test area in LLEM ................................................... 3 . Pressure trace at 134-ft instrumentation station for seal configuration 7 ......................... 4 . Standard solid-concrete-block seal .................................................... 5 . Three stages in erecting wooden structure-brattice for cementitious foam seal .................... 6 . Feeding cementitious foam into slurry mixing-pumping unit .................................. 7 . Slurry injection at top of cementitious foam seal form ...................................... 

TABLES 

1 . Summary of test conditions and results for solid-concrete-block seals ........................... 9 

2 . Summary of test conditions and results for cementitious foam seals ............................ 11 

EVALUATION OF SOLID-BLOCK AND CEMENTITIOUS FOAM SEALS 

By N. B. ~reninger,' E. S. ~eiss,~ S. J. ~uzik? and C. R. stephan4 

ABSTRACT 

The U.S. Bureau of Mines conducted explosion tests on various full-scale cementitious bulkheads used 

in abandoned mine areas to evaluate the ability of the bulkheads to withstand gas explosion overpressures of 20 psig. 

Tests were performed on 120-ft2 solid-concrete-block seals of varying thicknesses and designs. Of the 

seven solid-concrete-block seals tested, only the standard-type seal, having a 16-in thickness, keyed at 

the floor and ribs, all joints mortared, wedged at the roof, and a center pilaster, maintained its integrity 

when subjected to a 20-psig pressure wave. After being subjected to repeated explosions, the standard 

seal only showed a small hairline crack and had an air leakage of 87 ft3/min at a pressure differential 

of 1 in H20. 

Tests were performed on cementitious foam seals of varying thicknesses and compressive strengths. 

Explosion tests have shown that 200-psi strength, 4- and 8-ft-thick seals can withstand a 20-psig pressure 

wave. At a pressure differential of 1 in H20, no air leakage was detected through the 200-psi, 8-ft-thick 

foam seal. 

'~u~emisory general engineer, Pittsburgh Research Center, U.S. Bureau of Mines, Pittsburgh, PA. 

2~ining engineer, Pittsburgh Research Center. 

3~upemisory chemical engineer, Bruceton Industrial Safety Div., U.S. Mine Safety and Health Administration, Pittsburgh, PA. 

4Mining engineer, Bruceton Industrial Safety Div. 
Safety and Health Administration (MSHA) district manager. Title 30 of the U.S. Code of Federal Regulations 

(CFR) identifies the current requirements for the construction of seals or bulkheads in Part 75.329-2 as follows: 

"Pending the development and publication of definitive 

specifications for explosion-proof seals or bulkheads, such 

seals or bulkheads may be constructed of solid, substantial, 

and incombustible materials such as concrete, brick, cinder 

block, or tile, or the equivalent, sufficient to prevent an 

explosion which may occur in the atmosphere on one side 

of the seal or bulkhead from propagating to the atmosphere on the other side; provided, however, that upon publication of definitive specifications, all such seals or 

bulkheads, including those in place at the time of such 

publication, shall be required to meet or exceed those 

specifications." 

The MSHA-Bureau program was developed to evaluate seal construction in underground coal mines. This 

program primarily evaluated the "substantial" qualities of 

 i itch ell, D. W. Explosion-Proof Bulkheads. Present Practices. 

BuMines RI 7581, 1971, 16 pp. 

%'ark done by Foster-Miller Associates, Inc.. under Dureau of Mines 

contract H0166015. 

'work cited in footnote 5. 

'work cited in footnote 5. 

ciated strata do not provide adequate key strength. The 

118-in-thick coatings that were applied to some of the 

seals utilized a fiberglass-reinforced portland cement. The 

solid-block cementitious seal configurations are as follows: 

1. Seal configuration 1.-Standard-type thick wall (wetwall), 16 in thick with mortared joints with a center pilaster of 32-in thickness; keying to the floor and ribs; 

2. Seal configuration 2.-Thick wall (wetwall), 16 in thick 

with mortared joints with a center pilaster of 32411 thickness; keying at the ribs, but no keying at the floor; 

3. Seal configuration 3.-Thin wall (wetwall), 8 in thick 

with mortared joints; center pilaster having a 24-in thickness; keying to the floor and ribs; 118-in coating on the 

inby9 side of the seal; 

4. Seal configuration 4.-Thin wall (wetwall), 8 in thick 

with mortared joints; center pilaster having a 24411 thickness; keying to the floor and ribs; 118-in coating only on 

the outby10 side of the seal; 

5. Seal configuration 5.-Thick wall (wetwall), 16 in thick 

with mortared joints; keying to the floor and ribs; no 

pilaster; 

9~n this report, the term "inby" refen to that side of the seal that is 

closest to the face area where the explosion is initiated. 

lorn this report, the tenn "outbyn refers to that side of the seal that 

is farthest from the face area where the explosion is initiated. 
6. Seal configuration 6.-Thin wall (drywall), 8 in thick; 

drywall construction (no mortared joints); center pilaster 

having a 24-in thickness; full face coating on both sides of 

seal; keying to the floor and ribs; 

7. Seal configuration 7.-Thick wall (drywall), 16 in 

thick; drywall construction (no mortared joints); center 

pilaster having a 32-in thickness; full face coating on both 

sides of seal; keying to the floor and ribs; 

8. Seal configuration &-Thin wall (wetwall), 8 in thick 

with mortared joints; center pilaster having a 24-in thickness; keying at the ribs, but no keying to the floor; 1/8-in 

coating on the outby side of the seal; 

9. Seal configuration 9.-Thick wall (drywall), 16 in 

thick; drywall construction (no mortared joints); center 

pilaster having a 32-in thickness; keying to the floor and 

ribs; 118-in coating only on the inby side of the seal; and 

10. Seal configuration 10.-Thick wall (drywall), 16 in 

thick; drywall construction (no mortared joints); center 

pilaster having a 32-in thickness; keying to the floor and 

ribs; 118-in coating only on the outby side of the seal. 

Explosion tests were not conducted on the last three 

configurations listed above since they were of weaker 

design than some of the other configurations that were 

tested first and failed. Following the testing of seven 

of the above solid-block designs, similar tests were 

conducted with several cementitious foam seal designs to 

evaluate their effectiveness against the 20-psi explosion 

overpressures. 

PURPOSE 

The objective of this research is to determine whether 

the solid-block cementitious and the cementitious foam 

seal designs can withstand a 20-psig methane-air explosion 

without losing their structural integrity. Not only must the 

seal be physically strong, but it also must effectively control gas-air exchanges between sealed and open areas. 

The tests conducted on these seals will also assist MSHA 

in characterizing an acceptable leakage rate across a seal. 

A safety and cost benefit may also result from this 

program in that some of these new seal designs require 

fewer worker-hours and less materials handling to install 

than the standard-type seal. 

Full-scale explosion-proof seal research provides input 

to MSHA for setting adequate standards and useful information to industry for the improvement of mining safety 

and economics. MSHA is currently reviewing the regulations for explosion-proof seals and needs performance data 

from full-scale dynamic tests for seals. The LLEM can 

be used to provide these data, and MSHA has requested 

Bureau assistance in this area. 

ACKNOWLEDGMENTS 

The computer analysis of the pressure pulses acting instrumentation for the tests, conducted the tests, and 

on the seals was performed by Dr. Glenn Grannemann, performed the initial evaluation of the condition of the 

physicist, Pittsburgh Research Center's Theoretical Sup- seals following the explosion. The leak-rate tests on the 

port Group. Randolf Lipscomb, physical science tech- standard and foam seals were conducted by George 

nician, and Kenneth Jackson, electronics technician, Triebsch, facility superintendent, Lake Lynn Laboratory, 

of the Bureau's Lake Lynn Laboratory, arranged the and John Perry, supervisor SSI. 

EXPERIMENTAL PROCEDURE 

All of the configurations tested were made either of ce- the LLEM are 1,700 ft long, 20 ft wide, approximately 7 ft 

mentitious foam or solid-concrete blocks. All the tests high, and closed at the inby end. Mixtures of natural gas 

were conducted in the LLEM.11J2 Figure 1 shows a map and air are prepared at the face (closed end) in C drift 

of the LLEM. The seals were erected in the crosscuts be- and confined by a thin plastic diaphragm. The 474- 

tween C drift and B drift and subjected to an approximate long gas zone contained about 6,600 ft3 of near stoichio20-psig methane-air explosion. B and C drifts (fig. 2) of metric methane-air mixture. The mixture was ignited by 

electric matches, which were placed at the face in three 

locations. Barrels filled with-water were located in the 

"~riebsch, G., and M. J. Sapko. Lake Lynn Laboratory: A State-ofthe-Art Mining Research Facility. Paper in Proceedings of International gas zone to act as turbulence generators to achieve the 

Symposium on Unipue Undermound Structures (Denver. CO. June 12- 20-~si pressure wave. The bition of this gas 'One , , li, f990). CSM P&, V. 2 ,1990, pp. 75-1 to 75121. in a reproducible 20-psi overpressure. The instruments12~attes, RH., A. Bacho, and L. V. Wade. Lake Lynn Laboratory: tion in C drift included pressure transducers and flame 

Construction, Phrical Description, and Capability. BuMines IC 8911, Sensors (refer to figures and 2 for the location of the 

1983,40 pp. --- 
g

data-gathering stations that house the instruments). Signals from the instruments were recorded on a Microvax 

1113 computer. The computer collected and prepared the 

data. Figure 3 shows a typical pressure versus time trace 

for a station located 134 ft from the face near crosscut 2. 

This diagram shows the signature for the pressure acting 

on the seal between 260 and 1,100 ms. The calculated 

impulse per area for this event is 3.17 psi-s. 

The seals, erected in the crosscuts, typically were 5 to 

8 ft from C drift. The ability of each of the various seals 

to withstand an approximate 20-psig methane-air explosion has been determined and compared with that for the 

standard seal. The standard seal (fig. 4) is a 16-in-thick 

wetwall with a 32-in pilaster and a cross-sectional area of 

about 140 ft2: It was constructed using approximately 

450 8- by 16411 solid-concrete blocks. The standard seal is 

13~eference to specific products does not imply endorsement by the 

U.S. Bureau of Mines. 

keyed to the ribs and the floor using steel angle (6- by 

6-in) and wedged at the roof. In all the comparison tests, 

the standard seal was located in crosscut 1 (first outby) 

between C drift and B drift. 

For each of the cementitious foam seals, two sets of lattice structures were constructed. Vertical wooden posts 

were first erected (figure 5, top). Additional support 

boards were added in a horizontal orientation to form a 

wooden network (figure 5, middle). The top horizontal 

board on the C-drift side had injection ports. Brattice 

material was attached to the inside of each of the wooden 

lattice structures (figure 5, bottom). A four-person Celtite 

team took about 4 h to construct the forms for each seal. 

It took about 2 h to set up the mixing machine and couple 

in the feed and transport lines. 

The feed, mixing, and pumping system selected for 

use in erecting the foam seals included a Langley skidmounted mixing machine (model I), powered by a 10-hp 
TIME AFTER IGNITION, s 

Figure 3.--Pressure trace at 134-ft instrumentation station for seal configuration 7. 
motor, and a slurry pump. This system was used to inject 

a mixture of Tek€oam1' cementitious foam (manufactured 

by Celtite Corp.), water, and air into each of the 

lightweight construction forms of lumber and brattice 

cloth. Tekseal cementitious foam, a noncombustible dry 

powder, packaged in 45-lb bags, was added to the hopper 

and fed by an auger into a mixing bin where it was mixed 

by jets of water to form a thick slurry. Another auger 

drive fed the Tekseal cementitious foam-water sIurry into 

a 2-ft-long by 6-in-diam pump whose output was then 

'%e Tekfoam cementitious foam material used in the construction 

of the LLEM test seals will be referred to in the remainder of this 

report by its new legal brand name, Tekseal. 

mixed with more water (typically delivered at 12 gpm with 

a pressure of 100 psi). In filling the form in outby crosscut 2 (8-ft-thick, 200-psi seal), the mixture was transported 

150 ft and injected at the top of the form at 18 gpm, 

requiring about 6.5 h. In filing the form in outby crosscut 3 (4-ft-thick, 200-psi seal), the slurry was transported 

80 ft and injected at the top of the form at 30 gpm, requiring 2 h. Figure 6 shows Tekseal cementitious foam 

being fed into the hopper of the sIurry mixing-pumping 

unit. The slurry was pumped to the seal and injected at 

the top of the seal into the seal cavity (fig. 7). After a 

curing time of greater than 30 days, the low-density 

cementitious foam seals were explosion tested. 
Flgure 5.-Three stages In erecting wooden structure-brattlce for cementiUous foam seal. 
Figure 7.--Slurry injection at top of cementitious foam seal form. 
DISCUSSION OF TEST RESULTS 

SOLID-CONCRETE-BLOCK SEALS 

In the fust test series, a standard-type seal (seal 1, 

table I), having a 16-in-thick wetwall with a 32-in pilaster, was positioned in crosscut 1 (fig. 2). A wetwall seal 

(seal 2, table 1) similar to the standard-type seal except 

without floor keying was in crosscut 2 (second outby). A 

wetwall seal of 8-in thickness (seal 3, table I), having a 

24-in pilaster and a coating on the explosion side of the 

seal, was keyed into the floor in crosscut 3 (third outby). 

A wetwall seal of 8-in thickness (seal 4, table I), having a 

24-in pilaster and a coating on the side opposite the 

explosion, was keyed into the floor in crosscut 4 (fourth 

outby). Of these four seals, only the standard-type seal in 

crosscut 1 maintained its integrity, clearly indicating the 

need for adequate keying of the seal to the floor and ribs. 

The results of the fust series of tests are summarized 

in table 1, which lists a maximum pressure of 22 psig 

acting on the standard seal in crosscut 1 and a pressure of 

15 psig on the &in-thick test seal in crosscut 4. 

Table 1 .--Summary of test conditions and results for solld-concrete-block seals 

Location of Maximum Impulse 20-psig 

Seal TYP~ Crosscut mid center overpressure, per area, Degree of damage test 

from face, ~sig psi-s outcome 

ft 

1 . . Standard seal, thick wall, 1 60 

wetwall, pilaster, floor 

keying.' 

2 . . Thick wall, wetwall, 2 160 

pilaster, no floor keying.' 

3 . . Thin wali, wetwali, 3 260 

pilaster, floor keying, 

coating on inby side.' 

4 . . Thin wall, wetwall, 

pilaster, floor keying, 

coating on outby side.' 

5 . . Thick wall, wetwall, no 

pilaster, floor keying.3 

6 . . Thin wall, drywall 

pilaster, floor keying, 

coating on both sides.3 

7 . . Thick wall, drywall 

pilaster, floor keying, 

coating on both sides4 

22 4.55 None. . . . . . . . . . . . . . Passed. 

2 1 4.03 Large opening at roof, Failed. 

2 large cracks at left 

outby side, bottom 

displaced about 1 in. 

19 2.98 All blocks removed Failed. 

except bottom row. 

NA Large crack at top, Failed. 

blocks missing on 

outby side, pilaster 

sheared off. 

3.74 Minor damage, Marginal at 

stopping intact, c 20-psig 

mortar removed at pressure. 

top, some half blocks 

removed at roof line, 

approx 1-ft2 leak area 

formed. 

2.45 Destroyed, only a few Failed. 

blocks remained on 

and near ribs. 

3.17 All blocks removed Failed. 

except a few along 

both ribs and on 

floor. 

NA Not available. 

'Data from LLEM test 180. 

2~ressure lower at seal 4 because of venting through the opening formed when seal 3 failed at 260-ft location. 

'~ata from LLEM test 183. 

4~ata from LLEM test 187. 
In the second series of tests, three seals were located in 

crosscuts between C and B drifts. The seals constructed 

from solid-concrete blocks were all tightly keyed into the 

ribs and wedged at the roof. The standard seal withstood 

the explosion without any apparent damage. A modified 

seal (seal 5, table 1) without a pilaster was located in 

crosscut 2 between C and B drifts. The explosion removed 

portions of the blocks in the uppermost layer, causing the 

seal to lose integrity. In crosscut 3, a thin drywall seal 

(seal 6, table 1) of 8-in thickness with a pilaster of 24-in 

thickness was positioned. A coating had been applied on 

both sides. Catastrophic failure of the seal resulted. 

To measure the leakage through the standard seal after 

it had been subjected to numerous 20-psig explosions, a 

double-brattice technique utilizing a 0.5-ft2 window in the 

measurement brattice was employed.ls A centrifugal fan 

was used to blow air from B drift through the window and 

the seal into C drift. Air velocity through the window was 

measured with a vane-type anemometer. The pressure 

differential across the seal and the measurement brattice 

was measured. 

The standard-type seal, which had been subjected to 

three 20-psig methane-air explosions and two weaker explosions, was examined for air leakage. Over the pressure 

range of 0.1 to 1 in H20, the volumetric rate of leakage 

was linear with the square root of pressure, as to be 

expected. At a pressure differential of 0.1 in H,O, the 

leakage was 22 ft3/min and at 1 in H20 it was 87 ft3/min. 

The leakage rate across the seal was not measured before 

the seal was subjected to the series of explosions. The 

other seals were not tested for air leakage since all had experienced block loss to varying degrees. 

In the third series of tests, a modified drywall seal 

(seal 7, table 1) was located in crosscut 2 between C and 

B drifts. It was 16 in thick, constructed with a 32-in 

pilaster, and coated on'both sides. No mortar was used 

between blocks. The explosion removed more than 90 pct 

of the seal, causing catastrophic failure. The standard seal 

still located in crosscut 1 between C and B drifts withstood 

the explosion without any apparent damage. 

Seal configurations 8, 9, and 10, mentioned in the 

"Background" section, were not tested. The results from 

earlier tests with inherently stronger seals implied that 

these three seal configurations would also have failed. 

CEMENTITIOUS FOAM SEALS 

Following the explosion testing and removal of debris 

from the solid-block cementitious seals, five low-density, 

cementitious foam seal designs were installed and tested. 

The seals were subjected to a nominal 20-psig explosion 

pulse on the C-drift side. The pressures obtained are 

summarized in table 2. The pressure in the vicinity of 

crosscut 2 was approximately 29 psig. The pressures at 

crosscuts 3,4, and 5 ranged from 20 to 22 psig. The pressures decreased to about 13 psig at crosscut 6, located 

550 ft from the closed end of C drift. Reasonable agreement between analog (oscillograph) and digital (computer) 

static overpressure values was obtained. 

The Tekseal cementitious foam seal in crosscut 2 (8-ftthick, 200-psi) did not show any signs of physical damage. Air-leakage tests were performed after the explosion. 

To measure the leakage through the cementitious foam 

seals after they had been subjected to a nominal 20-psig 

explosion, a single-brattice technique utilizing a 0.5-ft2 

window was employed. Mortar was applied around the 

wooden frame (along the floor, ribs, and roof) that was 

used to support the measurement brattice; this was done 

to constrain the air to flow only through the brattice window, thereby minimizing the error in leak-rate measurements. The mine's main fan was used to blow air 

from C drift through the seal and the window. A flowadjustment brattice was erected outby and beyond the last 

surviving seal. By changing the speed of the mine fan, 

various pressure differentials across the seal could be 

obtained. Two settings of pressure differentials were 

used-1.0 and 4.25 in H20. At a pressure differential of 

1.0 in H20, no leakage was detected through this seal. At 

a pressure differential of 4.25 in H20, only 31 ft3/min 

of leakage was detected; this amount was considered by 

MSHA to be insignificant. Test conditions and results are 

summarized in table 2. Based on visual observations after 

the explosion and the results of the air-leakage tests, the 

8-ft-thick, 200-psi Tekseal cementitious foam seal is considered to meet the criteria of Part 75.392-2 of the CFR. 

The Tekseal cementitious foam seal in crosscut 3 (4-ftthick, 200-psi) had a few hairline cracks along the side 

exposed (C drift) to the explosion force. At a pressure 

differential of 1.0 in H20, 52 ft3/min of air leakage was 

detected. At a pressure differential of 4.25 in H20, 

114 ft3/min of air leakage was detected. Both these 

amounts are considered insignificant. Based on visual observations after the explosion and the results of air-leakage 

tests, the 4-ft-thick, 200-psi Tekseal cementitious foam seal 

is considered to meet the criteria of the CFR. 

The Tekseal cementitious foam seal in crosscut 4 (4-ftthick, 100-psi) displayed a series of cracks on both sides 

after the explosion. Some of these cracks appeared 

continuous from one face of the seal to the other near the 

outby end of the seal at about midheight. At a pressure 

differential of 1.0 in H20, 47 ft3/min of air leakage was 

detected. At a pressure differential of 4.25 in H20, 

114 ft3/min of air leakage was detected. Although the 

leakage was considered insignificant, visual observations 

indicated that the seal's performance was marginal. Additional testing would be required on Tekseal cementitious 

foam seals of 100-psi strength to determine what thickness, 

if any, would be deemed suitable to meet the criteria of 

the CFR. 

'work cited in footnote 6. 
Table 2.--Summary of test conditions and results for cementitious foam seals 

Location Maximum Leak rate,3 

Cross- Thickness, Design of mid- overcut1 ft strengthI2 center pressure, 

psi from ~sig 

face, ft 

Degree of damage f?/min 20-psig 

1.0 in 4.25 in test 

H2O H20 outcome 

-- - 

2 .... 8 4200 160 29 None ...................... 0 31 Passed. 

3 .... 4 4200 260 22 Hairline cracks on inby side. 52 114 Passed. 

4 .... 4 00 355 22 Slight cracks occurred, appearing 47 1 14 Marginal. 

continuous through seal. 

5 .... 8 650 450 2 1 Significant cracks on both sides 1 80 420 Failed. 

of seal, having about 1/4-in 

gap. 

6 .... 4 650 550 13 Seal was totally destroyed. . . . . . NAp NAp Failed. 

NAp Not applicable. 

'A standard seal made from solid-concrete blocks occupied crosscut 1 at about 85 ft from the face. The seal has a 16-in thickness and 

pilaster; it is keyed at both the ribs and the floor; it is wedged at the roof. Leakage tests, which had been conducted earlier, indicated that 

it had a leak rate of about 87 f?/min at a pressure differential of 1.0 in H20. The seal has withstood more than 5 20-psig explosions. 

'~esi~n compressive strengths may be slightly different than actual strengths; for example, the seal in crosscut 4 was designed for 100 

psi, but testing indicated an actual strength of 78 psi. 

'pressure differentials across seal are in inches of water (pressure). . 4~ade using 12 451b bags of Tekseal cernentitious foam per cubic yard, resulting in a density of about 46.4 lb/f?. 

'~ade using 8 451b bags of Tekseal cernentitious foam per cubic yard, resulting in a density of about 30.0 lb/f?. 

6~ade using 6 45lb bags of Tekseal cementitious foam per cubic yard, resulting in a density of about 23.1 lb/f?. 

The Tekseal cementitious foam seal in crosscut 5 (8-ft- at a level below the water pipe if draining has occurred or 

thick, 50-psi) displayed severe fractures on the face of the at a higher level if the water pipe is closed. The long-term 

seal. These fractures appeared to extend through the en- effects of water buildup, in general, and acidic water, in 

tire seal. After the explosion, the air leakage at a pressure particular, against a cementitious foam seal are not known. 

differential of 1.0 in H20 was 180 ft3/min, and at 4.25 in Evaluation of the effect of water and pH level on the seal 

H20 it was 420 ft3/min, strongly indicating that crack strength is merited. Personnel from MSHA are currently 

propagation had occurred through the seal. Although a conducting tests to determine both short- and long-term 

maximum acceptable leakage rate for varying pressure effects of standing water of varying pH on Tekseal cedifferentials has not been established, these values appear mentitious foam blocks of varying strengths. The blocks 

to be significant. Based on these leakage rates and on will be immersed in acidic water (various pH values and 

visual observations after the explosion, it is recommended neutral water) for a 1- to 2-month period. Concurrent 

that 8-ft-thick or less Tekseal cementitious foam seals of tests using regular concrete block will be conducted under 

50-psi compressive strength not be constructed in under- similar conditions. Following the testing period, both the 

ground coal mines. cementitious foam and standard concrete blocks will 

The Tekseal cementitious foam seal in crosscut 6 (4-ftthick, 50-psi) was completely destroyed by the explosion. 

Seals constructed with Tekseal cementitious foam of less 

than 50-psi compressive strength are also considered unsuitable with this tested method of installation. The 

frictional forces between the cementitious foam seals and 

the mine strata may need to be enhanced to withstand the 

explosion pressures, especially when installing seals with 

materials of compressive strength less than 200 psi. These 

frictional forces may be increased sufficiently to withstand 

the explosion pressure by keying the entry ribs and floor 

prior to the foam injection or by installing bolts into the 

ribs and floor (extending into the entry) between the 

frame structures prior to the foam slurry injection. 

The lowest seal in a set of seals must have a water pipe 

installed. However, water may accumulate behind the seal 

undergo compressive strength tests to evaluate the effect 

of the (acidic) water. 

A significant amount of water is used during the construction of these cementitious foam seals. The long-term 

effects on the strength of the seal from the drying out of 

the foam are currently being studied by representatives of 

Celtite, manufacturer of Tekseal cementitious foam. Their 

research has shown no signs of shrinkage and only a very 

slight weakening of the cementitious foam in terms of its 

compressive strength. The recommendation is that the 

brattice cloth and framing be left in place for the duration 

of the seal's life to reduce the amount of drying and to 

increase the time over which drying may occur. If the 

brattice cloth-timber framing were removed for detailed 

inspection of the seal, then a suitable sealant should be 

applied to the exposed surface. 
The seals in crosscuts 2 and 3 had been erected initially 

using single-point injection for the cementitious foam 

slurry. The single-point injection technique resulted in a 

rather large gap between the slurry and the mine roof. 

However, both seals were successfully "topped off" using a 

multiple-point (three-point) injection technique. Using 

multiple-point injection, seals were erected in crosscuts 4, 

5, and 6 with good closure at the roof. 

As mentioned previously, it takes about a half day for 

a four-person crew to prepare and erect the bratticetimber forms with multiple-injection ports; and about 2 h 

to set up the slurry mixing-pump system and connect the 

slurry lines. Injection can take 2 to 6 h, depending on the 

volume of the form to be filled. Less total time is required to construct a cementitious foam seal (4-ft-thick, 

32 worker-hours; 8-ft-thick, 50 worker-hours) than a 

standard solid-concrete-block seal (using approximately 

450 blocks in a 20-ft-wide by 7-ft-high entry), which may 

require 72 worker-hours to install, depending on the 

previous experience level with this type of work. 

A reliable method must be developed to ensure that 

the construction of the cementitious foam seal conforms to 

the recommended installation procedures to obtain the 

desired strength characteristics. This entails careful monitoring of the bulk density during the slurry injection period 

by means of accurately controlling the number of bags of 

Tekseal cementitious foam and the amount of water used. 

Compressive strength tests on the completed seal should 

be conducted after the curing period. 

CONCLUSIONS 

Of the seven solid-block-concrete seals tested, only the was 22 ft3/min at a pressure differential of 0.1 in H,O and 

standard-type seal maintained its integrity. A standard- 87 ft3/min at a pressure differential of 1 in HzO. 

type seal without floor keying failed. A standard-type seal An investigation into the best method to effectively 

with no pilaster but with floor keying failed. All the thin- control gas-air exchanges between sealed and open areas 

walled seals of 8-in thickness made with mortar between needs to be pursued, The seal must be physically strong 

the blocks failed; neither the use of a pilaster nor floor to control gas-air exchanges between sealed and provided sufficient against the 'O-psig open areas. Coatings placed on high-strength seals whose explosion. The addition of coatings did not significantly physical integrity would not be impaired by a 20-psig augment the seal strength- WIen erecting solid-block explosion would help to minimize the air and gas leakage seals, the technique of full-mortar bedding needs to be 

used; the entire solid top side and vertical contact plane of through the seal. 

each block needs to receive mortar to maximize shear Explosion tests have shown that 200-psi strength, 4- and 

strength. 8-ft-thick cementitious foam seals can withstand a 20-psig 

 he leakage through the standard seal after the seal Pressure wave* 

had been subjected to more than five severe explosions 

RECOMMENDATIONS 

Cementitious foam seals should be approved in the 

ventilation plan if the seals are constructed of 200-psi 

compressive strength Tekseal cementitious foam (or other 

similar product) and are at least 4 ft thick. 

Additional testing should be carried out on cementitious 

foams in thicknesses between 4 and 8 ft and with compressive strengths between 100 and 200 psi to determine other 

suitable designs for underground coal mine seal construction (i.e., at 100-psi compressive strength, a 4-ft-thick seal 

was not proven to be totally effective and an 8-ft-thick seal 

of 100-psi compressive strength was not evaluated in this 

series of tests). 

It is strongly recommended that cementitious foam of 

50-psi compressive strength not be used to construct seals 

of any thickness at this time. 

The mine companies installing cementitious foam seals 

should collect samples of the foam slurry materials in 

standard molds for processing concretes to determine, 

through independent laboratory analyses, the effects of 

aging on the seal's strength. 

Multiple-injection ports (at least three) should be 

incorporated into the brattice-timber forms for the purpose of uniformly controlling the distribution of the foam 

cement within the form. 

If the brattice cloth and wooden framing material are 

not left in place for the duration of the seal's life (to 

reduce the amount of drying), a face coat of a suitable 

sealant should be applied to the exposed surfaces after 

removal of the brattice cloth-timber framing. 
Until further tests are conducted to evaluate the longterm effects of water buildup and acidic water against cementitious seals, cementitious foam seals should not be 

constructed in areas where water accumulations may occur 

behind a seal. Testing should be conducted to determine 

the effects of standing water of varying pH on Tekseal cementitious foam blocks of various compressive strengths. 

Research should be devoted to determine the best 

method to effectively control gas-air exchanges between 

sealed and open areas. Practical methods for use in operating mines to measure the leak rate across newly erected and old seals need to be investigated. 

Further tests on seals should be conducted in the 

LLEM. More specifically, it is suggested that the following be done: 

For the stronger modified solid-concrete-block seals, 

the pressure level at which catastrophic failure occurs 

should be determined; 

To increase the frictional forces between the cementitious foam seal and the entry, substantial 1-in-dim 

bolts should be installed into the ribs and floor on 2-ft 

intervals (extending about 1 ft into the entry) between the 

lattice frame structures prior to the foam slurry injection. 

These bolts should provide increased resistance to the 

dynamic force loadings exerted on the seal by the overpressure from the methane explosion. To what extent the 

frictional forces between the cementitious foam plug and 

the coal strata in an operating mine need to be augmented 

requires additional analyses; 

Various ways to augment the strength of other solidblock seal designs, such as the use of angle iron to augment keying, currently used in operating mines should be 

pursued; and 

Novel seal designs-uch as those involving (1) 

foams, both reinforced phenolic and cementitious, and (2) 

lightweight masonry blocks--should be evaluated. 

* U.S. GPO: 1891-51 1010/42021