Pumpable roof supports: an evolution 

in longwall roof support technology

T.M. Barczak and S.C. Tadolini

Senior research engineer and chief rock safety engineer, respectively, Pittsburgh Research Laboratory, 

National Institute for Occupational Safety and Health (NIOSH), Pittsburgh, Pennsylvania

Abstract

Pumpable roof supports provide an alternative approach to secondary support in underground mining. 

Unlike all other supports that are either partially or fully prefabricated prior to being transported into 

the mine, the pumpable support is fabricated in place in the mine entry. This reduces the underground 

material handling efforts and thus the injuries historically associated with in-mine support construction. 

On-site fabrication also facilitates application of the support in areas that are inaccessible to transportation equipment such as scoops or rail cars, making it ideal for many bleeder applications. One of the 

main advantages of the pumpable support is that it fully bridges from the mine floor to the roof, thereby 

eliminating the requirement of “topping off” the support with wooden wedges or crib blocks that soften 

most other support responses. This report examines the development of modern pumpable roof support technology and provides a full description of the performance capabilities of each of the support 

products now on the market. 

Introduction

The search for the optimum roof support system continues 

with more than 50 standing roof support products now on the 

market for longwall tailgate and bleeder applications. Overall, 

the Can support manufactured by Burrell Mining Products 

Inc.1,

 1 Reference to company name or product does not imply endorsement by the National Institute for Occupational Safety 

and Health.

 shown in Fig. 1, is the most widely used standing support 

system in the United States for longwall tailgate applications. 

About a third of the longwall tailgates in the United States are 

supported using the Can, with the highest percentage found 

in western U.S. mines, where timber products are scarce and 

expensive. The Can provides a high-deformation support 

system and consistent loading through as much as 50% strain, 

thereby improving ground support in many applications where 

lower capacity, less stiff and less stable supports, such as wood 

cribbing, have been utilized. Equally important is the fact 

that the Can supports are installed with a machine that avoids 

much of the material handling associated with conventional 

crib construction.

Despite the success of the Can support, there are some disadvantages. First, the support must be topped off with something, 

usually timbers, to establish roof contact. This will typically 

“soften” the support response due to the contact compatibility 

of the timbers with the uneven roof, requiring wedges or small 

pieces of wood to provide a tight fit (see Fig. 1). “Soften” 

means that roof convergence can occur with minimal resistance. 

When less than full support contact with the Can is achieved, 

the wood response alone can cause a softer response. Finally, 

poor construction practices, in which multiple timber layers 

are placed on top of the Can, may provide hinge points that can 

also reduce the overall stability of the support system.

There are several different cementitious materials used in 

pumpable roof support technology. The first modern pumpable 

roof support installed in the United States was by FOSROC 

Inc. in the Southern Ohio Coal Company’s Meigs No. 2 Mine 

in southeastern Ohio in 1993. The support employed foamed 

cement similar to that used in Tekseal seal construction. Today, the most common material in pumpable roof supports 

is a calcium sulfo-aluminate (CSA) cement, which relies on 

ettringite formation to provide a high-yield, fast-setting grout. 

More than 110,000 of these supports have been installed in 

the past five years in several different mines, primarily in the 

eastern United States. The CSA material has traditionally been 

imported from England, contributing to the very high cost of 

this support technology, but it is now obtained from Mexico 

by Heitech Corporation. The CSA-based grout has been the 

most effective and commonly used grout for pumpable supports, but it remains an expensive support system in terms of 

material costs.

Considerable research has been done during the past few 

years to develop an alternative to CSA grouts to reduce costs. 

The Minova Tekpak support uses a high-alumina cement 
instead of the imported CSA cement to provide the ettringite 

formation. Other products rely on portland-based cements in an 

effort to reduce the cost of the system. One such support is the 

Tekpak-P product developed by Minova. Full-scale laboratory 

testing has shown that the Tekpak-P support is comparable to 

the supports using CSA grout, but far fewer supports using 

Tekpak-P material have been installed. The Mesh Pack support 

developed by Strata Products was successfully demonstrated 

at a Jim Walters Resource’s mine, although the pumping was 

more difficult and considerably slower by comparison to the 

CSA systems used elsewhere because the materials had to be 

Figure 1 — The Can is a commonly used tailgate support 

in the United States.

pumped from an underground location. 

Pumpable roof support technologies were developed to 

compete with the Can support and overcome some of its 

deficiencies. Because these supports are filled in place in the 

mine entry, they eliminate transportation into the mine and 

material-handling bottlenecks associated with the bulky Can 

support. They also eliminate the need for a secondary material 

to establish roof contact (see Fig. 2). The pumpable supports 

easily conform to the mine roof and floor, providing a stiffer 

initial response than the Can supports with wood topping. 

In addition, the pumpable supports provide the potential for 

limited active roof loading. 

Figure 2 — Pumpable roof support in longwall tailgate 

showing how the support can achieve full contact with 

mine roof.

By definition, a pumpable support involves the support 

material being pumped from a remote location to the supported 

area in the underground mine. The material is some form of 

cementitious grout, which is typically pumped into a flexible 

bag that is hung from the mine roof to form a supporting 

column. The cementitious material and size of support vary 

depending on the manufacturer and application, but they all 

share this basic concept. 

History of pumpable supports in coal mining

Coal mining applications of pumpable support systems date 

back to the development of packwalls for advancing longwall 

operations in European mines. Unlike retreating longwall 

operations, where the gate roads are developed in advance 

of the panel mining, in advancing longwall mining the gate 

roads are developed as the panel is mined as shown in Fig. 3. 

A fabricated “packwall” is formed to establish a single-entry 

roadway that is developed in advance of the longwall face 

and protected from the forming gob. The first system was 

developed in Germany using anhydrite, which was blown by 

compressed air to the longwall site. The material would harden 

on contact with water. Anhydrite has a high compressive 

strength but does not yield, and these non-yielding packwalls 

would not work well in weaker strata conditions. This system 

also required large amounts of compressed air for dispersion 

of the anhydrite, in volumes not available at these locations 

underground. The British developed a two-component monolithic pack in which one component, composed of a filler slurry 

of bentonite and coal fines with water, was pumped by a large 

reciprocating piston pump to a shuttered packhole behind the 

face. Meanwhile, the second component, rapid setting cement 

slurry, was prepared and injected to harden the mass (Kellet 

and Mills, 1980). An improvement to this system was the addition of accelerators to a prehydrated bentonite-coal slurry 

waste to improve pumping life.

The first pumpable roof supports for U.S. longwall tailgate 

applications were installed by FOSROC Inc. (now Minova) 

at the Southern Ohio Coal Company’s Meigs No. 2 Mine in 

southeastern Ohio in 1993 (Amick et al., 1993). At that time, 

the only available supports were conventional wood cribbing 

and concrete cribbing. FOSROC had been doing cavity-filling 

work in the mine and asked to install a test area using the 

pumpable (Tekcrib) support. Ten supports were installed in 

the longwall tailgate and their performance was thought to 

be an improvement over conventional wood cribbing. At the 

time, the No. 31 mine had severe problems in a four-entry 

longwall tailgate, where excessive roof falls in the middle 

two entries had left only the active tailgate to provide ventilation and secondary escape. Because the area was not readily 

accessible, the situation was ideal for taking advantage of 

the pumpable support. Seventy-five Tekcribs were installed 

in conjunction with mechanical jacks. The tailgate survived 

without any roof falls. This test demonstrated the flexibility of 

pumpable supports being installed in inaccessible areas, which 

remains a major incentive for many applications of pumpable 

roof support systems. 

Despite the success of this initial trial, pumpable supports 

were not used again until Heitech began installing a new generation of supports at Foundation Coal Company’s Emerald 
mine in southwestern Pennsylvania in 1999 (Barczak et al., 

2003). The supports have provided good ground control in 

areas where conventional wood cribbing performed poorly in 

the past. Emerald continues to use pumpable roof supports in 

both the tailgate and bleeder entries today, and Heitech remains 

a leader in the installation of pumpable roof support systems 

in the United States, having installed more than 130,000 supports in 13 different mines (see Figs. 4 and 5) since this initial 

application in 1999. Micon, in partnership with Minova, has 

also installed thousands of pumpable cribs in several different 

mines. The major drawback to increased utilization of this support technology has been the high material cost of the support 

due to the cement and the containment bag. It is still the most 

expensive support used for tailgate and bleeder applications. 

This limitation has spurred current research to develop less 

costly cementitious materials for this application. 

Figure 3 — Packwalls in advancing longwall operations were the first systematic use of pumpable materials for support.

Figure 4 — Installation of Heitech pumpable roof supports 

by year from 1999 to 2006.

Figure 5 — Heitech pumpable support installations by mine 

site during the period 1999 to 2006.

Application and design requirements of pumpable supports

The application of pumpable supports for longwall mining 

can be categorized into three areas: bleeder applications, tailgate support and predriven recovery room or mine-through 

entries. 

Bleeder applications.The first major use of pumpable support 

systems in U.S. longwall operations was in the support of bleeder 

entries. Bleeder entries are established around the perimeter 

of a set of longwall panels and are used to control methane 

liberation. The support of bleeder entries is ideal for pumpable supports that can be remotely installed, because access 

to these areas is generally restricted due to power constraints, 

presence of belt and track structures, or previously installed 

standing support. The support design requirements for bleeder 

applications are generally long-term support stability (5 years 

or more), broad roof coverage and stiff support response. Stiff 

support response is needed because main roof loading activity 

is likely to be limited, and the primary requirement is to control 

the time-dependent deformation of the immediate roof. 

Tailgate applications.The success of bleeder applications using 

pumpable supports led to extended trials in longwall tailgate 

applications. Here, the support duration is much shorter, but the 

load conditions are much greater due to the development of the 

side and front pressures associated with the panel extractions. 

Recent studies have shown that much of the tailgate loading is 
derived from the main roof activity and elastic responses of the 

strata and pillars to the stress increases (Barczak et al., 2005). 

This response can be considered “uncontrollable convergence,” 

meaning that the support system cannot prevent the convergence 

from occurring. The support system must be able to sustain 

roof loading through this range of convergence to be able to 

provide support of damaged rock structures at the longwall 

face or localized roof failures that occur outby. The degree of 

convergence will depend on the mine site and conditions. For 

example, the specification currently required by Foundation 

Coal for the western Pennsylvania mines operating below 180 

to 240 m (600 to 800 ft) of cover is a minimum support load 

of 136 t (150 st), with no significant load shedding occurring 

before 25.4 mm (1 in.) of convergence. In other words, the 

support must be able to survive 25.4 mm (1 in.) of convergence 

without failing or sacrificing load carrying capacity. 

Predriven recovery room or mine-through entries. Predriven 

recovery rooms or mine-through entries provide a specialized 

set of load conditions. Pumpable supports are used in predriven 

recovery rooms largely because the longwall shearer can easily 

cut them out for easy removal as the longwall advances into 

the room. They are also easy to install, providing flexibility 

to the timing of the support installation. As the longwall panel 

approaches the predriven recovery room, yielding of the panel 

fender causes uncontrollable convergence, resulting in yielding 

of the shield supports and the standing supports prior to the 

advancement of the shields into the recovery room (Barczak 

et al., 2006). However, unlike with the tailgate design criteria 

described above, the uncontrollable convergence in the recovery 

room is likely to exceed the yield load rating of the pumpable 

support; hence, the residual loading capacity and length of 

time the support can sustain this load during convergence 

establishes the support design criteria. Because pumpable 

supports do provide a residual load capacity through several 

inches of convergence, they offer an advantage over concrete 

support systems that use timber to soften the support response 

to survive the uncontrollable convergence but provide very 

little useful residual load once the concrete members fail (see 

Fig. 6). 

Figure 6 — Failure of concrete cribbing in longwall predriven recovery room.

Pumpable support technologies

The differences in the cementitious grout define the various 

types of pumpable support technologies as well as their performance capabilities. Most construction cements are based 

on ordinary portland cement (OPC), which is primarily formulated from limestone, certain clay minerals and gypsum 

in a high-temperature process that drives off carbon dioxide 

and chemically combines the primary ingredients into new 

compounds. As a hydraulic cement, these compounds hydrate 

when combined with water and then slowly harden to gain 

strength. They retain their strength and stability but remain 

insoluble in water as this process is completed. Those pumpable support systems that are not based on portland cements 

use a radically different chemistry and a completely different 

hydration process.

Aerated cements. Aerated cements are formed by incorporating foaming agents into the cement to create air bubbles 

that are stable and able to resist the physical and chemical 

forces imposed during mixing, placing and hardening of the 

foamed cement. The foamed cement is similar to that used in 

constructing ventilation seals. The air voids are easily visible 

to the naked eye. For the mining application of pumpable 

supports, the cement product blended with the foaming agent 

is typically provided as a powder in bags. The powder, when 

mixed with the proper amount of air and water in a specially 

designed placer unit, begins to gel within minutes of discharge 

and forms a non-toxic, non-combustible product with a density 

of less than 593 kg/m3 (1,000 lbs per cu yd). It cures to a final 

strength ranging from 0.69 to 3.45 MPa (100 to 500 psi), which 

is much lower than ordinary portland cement, which can achieve 

a compressive strength of several thousand pounds per square 

inch. The aerated cements for mining applications are designed 

to allow reasonably long pumping distances >300 m (>1,000 ft) 

without destroying the integrity of the void formation, which 

is more common with portland-based foamed cements because 

of their more fragile cell structure. 

Figure 7 — Tekcrib support. Version of this support was 

first pumpable support installation in longwall tailgate in 

the U.S. in 1993. 

Developed by Minova USA, the Tekcrib, as shown in Fig.

7, is an example of a pumpable support made from this material. The Tekseal material has been pumped 1,070 m (3,500

ft), using combinations of surface equipment and strategically
drilled boreholes, for underground mine support installation. 

As mentioned above, the Tekcrib was the first successful 

pumpable support used in a longwall tailgate. An example of 

the performance curve for a 1.07-m (42-in.-) diameter Tekcrib 

developed from full-scale testing in the NIOSH Mine Roof 

Simulator is shown in Fig. 8. The support begins to yield at 

about 109 t (120 st) of load and 12.7 mm (0.5 in.) of displacement, providing a maximum load capacity of about 163 t (180 

st) at 140 mm (5.5 in.) of displacement. The support then 

sheds load through several inches of convergence, resulting 

in a final residual load capacity of about 90 t (100 st) after 300 

mm (12 in.) of displacement. While this curve is considered 

to be representative of the product, the residual load response 

can vary depending on the nature of the grout fracturing and 

bag confinement.

Figure 8 — Full-scale performance curve for Tekcrib pumpable support taken from NIOSH STOP software.

Portland fly ash cement. Basically, this is a portland cement 

blend with fly ash added to reduce the portland cement and 

water content and help preserve early strength. The strength 

can be varied depending on the amount of portland cement 

used in the mix. For longwall gate road support, the singlecomponent mix is likely to be pumped from an underground 

location due to the limited pumping distance of less than 910 

m (3,000 ft). Bleeder entries could be pumped from a surface 

location if a borehole is within the vicinity. 

An example of this type of cement application is the Mesh 

Pack Support developed by Strata Products USA, as shown 

in Fig. 9. The hardened grout that is used for support capacity 

is shown in Fig. 10. The containment bag does not need to be 

waterproof, but must provide a high degree of confinement 

because of the brittle nature of the OPC concrete. This requirement is satisfied by 25.4 mm (1-in.-) wide steel bands spaced 

about one foot apart (see Fig. 9) and wire mesh to enhance 

the confinement provided by the bag fabric. The performance 

curve for a Mesh Pack pumpable support as acquired from 

STOP is shown in Fig. 11.

Figure 9 — Mesh Pack pumpable support showing laboratory 

test specimen on left and in mine trials on right (courtesy 

of Strata Products USA).

Figure 10 — Portland fly ash cement product used in Mesh Packs support.

Portland pozzolan cement.This cement is made from portland 

cement with various pozzolan components, typically fly ash and 

ground-granulated blast-furnace slag and a retarding agent to 

provide adequate pumping time. These components allow the 

cement to be mixed with large quantities of water, generally 

more water than solids. This slurry is then combined with an 

alkaline activator to overcome the retarding action near the 

location where the support bag is filled. The two-component 

approach, where each component is pumped separately to the 

support site, is designed for simplicity of use and allows for 
long pumping distances because the curing process is delayed 

until the material is inside the support containment bag. The 

final product is generally dark gray to black in color.

Figure 11 — Full-scale performance curve for Mesh Pack 

pumpable support taken from NIOSH STOP software.

An example of this type of cement is the Tekpak P and Tekpak F formulations developed by Minova (see Fig. 12). Both 

use a symmetrical (equal volume), two-component approach 

as described above to allow for pumping distances greater than 

3,000 m (10,000 ft), because the two slurries are not joined 

until they are near the support location. The two components 

are labeled Tekpak P or F and Tekbent P or F. The P and F 

designations primarily represent strength variations, with the 

F series designed to have a higher strength than the P series. 

The Tekcem portion represents the portland cement side and 

is a noncombustible brown powder that forms easy-to-pump 

slurry with water. It has a minimum 12-hour pumping life. The 

Tekbent portion consists of the alkaline activator. It is in liquid 

form and has an indefinite pumping life. The components can 

be mixed in any standard batch or continuous mixer, requiring 

about three minutes of mixing time. Once the two slurries are 

combined, they set very rapidly (in a few seconds) and cure 

quickly, developing compressive strength of 4.14 MPa (600 

psi) within the first 24 hours and 5.86 MPa (850 psi) within 

the first 7 days. Figure 13 shows the STOP performance chart 

for a 610-mm- (24-in.-) diameter Tekpak P support. As seen 

in the graph, the support is capable of producing a maximum 

support capacity of 136 t (150 st) in less than 25.4 mm (1 in.) 

of convergence. The residual load decreases with continued 

convergence due to loss of confinement, reaching 45 t (50 

st) at 150 mm (6 in.) of convergence in this example. These 

results represent the average of two full-scale tests conducted 

in the NIOSH Mine Roof Simulator. Figure 14 is a photo of 

the support at 200 mm (8 in.) of convergence being subjected 

to 43 t (47 st) of load.

Figure 12 — Tekpak P grout is an example of this portland pozzolan cement category. It is dark, almost black, in color.

Figure 13 — Full-scale performance curve for Tekpak P 

pumpable support taken from NIOSH STOP software.

Ettringite-based cements. Ettringite as a natural mineral is 

found in only a few areas of the world. It was first discovered 

near Ettringen, Germany, from which it got its name. The other 

locations where the mineral is mined include South Africa 

and Ireland. Figure 15 is a photo of the ettringite mineral. It 

is bright yellow in color and is formed as a precipitate from 

hydrothermal solutions by the underground burning of an 

alumina-rich oil-bearing stratum that is overlain by limestone. 

Calcium aluminates are formed during the burning. Following 

the burning, the ground eventually cools to the point where 

the sulfate-saturated ground waters can pass into the shrinkage 

fissures, forming ettringite crystals that grow on the surface 

of aeolean sand grains. This natural process has been taking 

place for thousands of years. A defining feature of ettringite 

is that four out every five atoms in this mineral is either part 

of a water molecule or a hydroxide. Thus, ettringite is almost 

all water and, as such, is the key ingredient in the high-yield, 

rapid setting grouts used for the pumpable roof support systems. However, the mineral itself is not used directly; rather 

ettringite is formed as part of the chemical process in the 

hydration and formation of the cement products. Ettringitebased grouts can be subdivided into the four types detailed 

below based on the components used to produce the ettringite 

(Mangabhai, 1990): 

Types I and II: These early ettringite-based cements were 

used in the development of packwalls for gate road protection 

in advancing longwall systems and in retreat mining to reuse 

roadways in British coal fields in the 1970s (Nixon and Mills, 
1981). Both of these cements utilized ordinary portland cement (OPC) in combination with high alumina cement (HAC) 

and calcium sulfate and lime to produce the ettringite. These 

cements had very rapid strength development as desired and 

were high yield; meaning high water content could be used. 

The high water content was a huge advantage over previous 

non-ettringite cements, but the Type I product still had a short 

pump life. 

Figure 14 — Photo of Tekpak P pumpable support after 

150 mm (6 in.) of convergence carrying a load of about 

45 t (50 st).

The development breakthrough for the Type II cement came 

from the idea of transferring the accelerator, sodium carbonate, 

from the cement slurry to the bentonite slurry (Mills, 1988). 

This improved the pumping life to about 20 minutes because 

the cement did not harden nor activate until the two components 

were mixed together, followed by the slurry mixing. Another 

improvement was that the high level of ettringite formation 

in this process allowed the aggregate materials (coal fines) to 

be replaced by water. The slurries were pumped in separate 

pipes and mixed at the desired location curing to a compressive 

strength of about 5.00 MPa (725 psi). These slurries could also 

be pumped up to 460 m (1,500 ft).

Type III: The Type III mine cement developed in 1982 

removed the portland cement and relied solely on the high 

alumina cement (HAC) to formulate the ettringite (Beale and 

Viles, 1982). The sodium carbonate was also replaced by a 

small amount of lithium carbonate in the “bent” slurry to act 

as an accelerator. The high content of HAC and calcium sulfate 

led to the formation of greater quantities of ettringite with the 

final product composed of 90% water by volume compared 

to about 85% for the Type II cement product. 

Figure 15 — Ettringite mineral. Ettringite is a key component that provides high yield (more water than solids) and 

facilitates fast setting and high strength.

Figure 16 — Full-scale performance curve for Tekpak pumpable support taken from NIOSH STOP software.

Minova currently uses a version of Type III, ettringite-based 

cement in the Tekpak pumpable support for longwall tailgates 

and bleeders (Mills and Long, 1989). Again, the key factor is 

that HAC is used to formulate the ettringite. The cured grout 

material is light gray to white in color. The pumpable support 

material is a two-component system consisting of the Tekcem 

component and the Tekbent component, which are mixed with 

water and pumped as slurries separately, then mixed together 

at the support installation location. Both are blended powder 

materials packaged in bags for transport. The Tekcem portion is a non-combustible dark brown powder, which forms 

milky alkaline slurry with water. The Tekbent component is 

a non-combustible off-white powder that, when mixed with 

water, results in a mildly alkaline slurry with a creamy milk 

appearance. Each material has more than 24 hours of pumping life. Type III ettringite-based cement can be pumped 

more than 4,500 m (15,000 ft) horizontally through low-cost, 

small-diameter pipe or hose. The performance characteristics 

of the 610- and 760-mm (24- and 30-in.) Minova Tekpak 

supports are illustrated in the STOP chart shown in Fig. 16. 
A 760-mm- (30-in.-) diameter Tekpak provides a maximum 

support capacity of about 136 t (150 st) at about 15.2 mm (0.6 

in.) of convergence, with a residual load of about 64 t (70 st) at 

150 mm (6 in.) of convergence in this representative full-scale 

test in the NIOSH Mine Roof Simulator.

Type IV: Type IV ettringite-based cements utilize calcium 

sulfo-aluminate (CSA), also known as Klein’s compound, as the 

primary ingredient in the ettringite production instead of the HAC 

used in the Type III cement. This product has a close relationship to Type K expansive cements. Calcium sulpho-aluminates 

are manufactured from limestone, bauxite and gypsum under 

oxidizing conditions using a rotary calcining kiln (Fig. 17). 

Figure 17 — Illustration of the process of making calcium sulpho-aluminate 

(CSA) cement.

It takes less energy to produce CSA than 

HAC cements; however, CSA cements are 

produced in only a few locations throughout 

the world. Much of the CSA material used 

in the United States for mining cements 

has been imported from England and 

manufactured by Blue Circle Cement (now 

owned by La Farge) at the Barnstone facility in Nottingham. Recently, CSA cement 

has been delivered from Mexico through 

CTS Cement Manufacturing Corporation 

in Cypress, California. The United States 

experimented with CSA cements several 

years ago, but China pioneered the largescale manufacture of CSA cements and 

continues to produce the product, although it 

is not routinely imported for mine use in the 

United States. The CSA (Type IV) cement 

provides the highest water content, exceeding 85% by volume, for water to solids ratio 

of 1.75 to 1, which is typically used in the 

mining applications. Like all the ettringitebased cements, it sets and cures rapidly. The 

CSA-based grouts have high compressive 

strengths, with the mining mixes typically 

above 6.9 MPa (1,000 psi).

The pumpable support system developed by Heitech Corporation (subsidiary 

of Heintzmann Corporation) is made from 

CSA or Type IV cement. These Heitech 

supports have been the most commonly 

used longwall pumpable supports since 

their inception into the U.S. industry in 

1999. As was indicated in the Introduction, 

more than 130,000 supports in 13 different mines have been installed. The two 

components used to make pumpable cribs 

are typically packaged in 25-kg (55-lb) 

bags, although a batch system, whereby 

the material is transported in bulk on rail 

cars to storage silos or for bulk bagging, is 

now under development at the Foundation 

Coal site in Waynesburg, Pennsylvania. The 

aluminous cement constituent is packed 

separately from the sulfate, lime source 

and aluminous cement accelerators. One 

is a white powder and the other is a dark 

powder. Each of the two parts is mixed 

with half the total water requirement and 

pumped through separate lines (Fig. 18), 

typically down a 150- to 200-mm- (6- to 

8-in.-) diameter borehole to the support 

installation areas up to 9 km (30,000 ft) 

away (Fig. 19). 

Figure 18 — The two-components (powders) used to produce the CSA grouts 

are packaged separately in bags and delivered to the pumping site where they 

are mixed with water. 

Here the two slurry lines are joined together 

through a tee section a few feet before entering the bag (Fig. 

20). The splash mixing of the two slurries as they enter and fill 

the bag is sufficient to provide a consistent concrete structure 

once the bag is filled. The hydration reactions of the minerals 

are considerably exothermic, which creates heat as the cement 

hydrates. Heat can be felt on the support bags within minutes 

after being filled and they remain warm for several hours as 

the hydration continues. The final product is lightweight, brittle 

and has a light color, as shown in Fig. 21.

The 600-mm- (24-in.-) diameter Heitech pumpable support provides over 113 t (125 st) of support capacity, while 
the 760-mm- (30-in.-) diameter support provides more than 

180 t (200 st) of support capacity. The performance curves 

developed from full-scale testing as recorded in the NIOSH 

STOP software are shown in Fig. 22.

Figure 19 — Cement slurries are pumped down the borehole 

in separate lines (pump mixing station in background).

Figure 20 — Components are pumped in separate lines and 

joined together just prior to entering the bag.

Figure 21 — The final product produced from CSA grout 

is light in color and lightweight.

Figure 22 — Full-scale performance curves for Heitech 

pumpable supports taken from NIOSH STOP software.

Performance characteristics of pumpable supports

In general, pumpable supports provide a very stiff loading 

characteristic, typically reaching peak loading between 12.7 

and 25.4 mm (0.5 and 1.0 in.) of convergence. The peak load 

is followed by a load-shedding behavior, often with sudden 

dramatic drops in load as the grout fractures from the induced 

stress of the convergence, followed by a useful residual load being maintained through 150 mm (6 in.) or more of convergence, 

depending on the confinement and integrity of the bag as the 

convergence continues. Factors that affect these generalized 

performance characteristics are examined below.

Maximum support load. The maximum support capacity is 

obviously controlled largely by the compressive strength of 

the cementitious grout, with greater grout strength providing 

higher maximum support capacity. However, the full material 

strength is never realized in full-scale support constructions, 

implying that there are other factors involved that affect the 

maximum support capacity. Depending on the cement type, 

as discussed above, the compressive strength of the material 

can vary. For Type IV cement (CSA-based ettringite), the 

laboratory-measured strength determined from 150-mm- 

(6-in.-) diameter samples is typically around 6.9 MPa (1,000 

psi). However, full-scale testing of the support indicates that 

the full compressive strength of the grout is not achieved. 

Two factors account for the observed degraded full-scale 

strength. First, uneven ends (top and bottom) of the support 

can contribute to non-uniform loading of the specimen in the 

stiff mine roof simulator, where the large steel platens of the 

load frame are positioned to remain parallel to each other prior 

to and during load application. The second, and believed to be 

more significant factor, is the presence of hairline preexisting 

fractures, probably due to expansion during the hydration 
of the cement components as the grout cures and hardens in 

the support bag. These preexisting fractures can be seen on 

the surface of the support and appear to control the fracture 

behavior of the grout during load application (see Fig. 23), 

resulting in failure at far less stress than the material strength 

would suggest.

Figure 23 — Fracture planes developed as grout strength 

is exceeded often occur along preexisting fractures developed during curing

Confining pressure provided by the containment bag can 

significantly offset these weaknesses. Table 1 shows results 

from three full-scale tests comparing the maximum support 

capacity with the containment bag as normal and with the 

containment bag removed after the support was pumped and 

the grout fully cured. On average, the support capacity was 

increased by 282% by the confinement of the bag compared 

to the capacity achieved without the bag.

A considerable amount of development, particularly by ABC 

Industries in Warsaw, Indiana, has been made in producing the 

bag containment system for the pumpable roof supports. The 

current production containment bag is constructed by a spiral 

wrap of high-tenacity fabric with woven polyester yarn in a grid 

to provide tensile strain resistance in two orthogonal directions 

(see Fig. 24). 

Figure 24 — Bag construction showing polyester yarn and 

waterproof fabric on a section of bag that ripped open during 

performance testing in NIOSH Mine Roof Simulator.

The seams are strengthened by overlapping and 

welding the fabric together to provide a strength equivalent 

to that of the bag fabric. The polyester fibers provide a tensile 

strength of up to 8,900 kg per meter width of fabric (500 lbs 

per inch width of fabric) and can elongate about 25% before 

breaking. The bag also incorporates a 10- to 12-gage metal 

wire that is spiraled from the top to the bottom of the bag, 

secured either in the seam or externally to preserve the seam 

strength, with the heavier gage wire as shown in Fig. 25. For 

the bag system to improve the maximum support capacity, it 

must provide active confinement in conjunction with the filling of the bag. For adequate confinement to be achieved, once 

the bag is full and contacts the mine roof, the grout must be 

pressurized to cause the bag to expand slightly.

Figure 25 — Bag construction showing inlet tube, breather 

tube, wire pitch and reinforcement wire.

The confinement, as described above, can be enhanced, 

thereby causing higher support capacity in the following 

ways:

• Heavier gage wire: The benefit of the wire can be seen 

in a Fig. 26, which shows the performance for a bag with 

a vertical seam without the wire reinforcement that is 

used in the spiral wrap bag construction. Both the peak 

load and the residual load are increased in the support 

with the wire-wrap construction. A test using a prototype 

high-strength wire and containment bag is also shown in 

this chart. It is seen that this system provided the largest 

peak load of the three supports. Heavy-gage wire can 

provide higher initial confining forces in the sense that 

larger-diameter wire will develop more tensile stress with 

less deformation than smaller diameter wire. However, 

the impact on the peak load is thought to be rather small 

for the range of wire diameters practical to install.
Table 1 — Comparison of maximum support capacity with and without the containment bag.

 Maximum support capacity, t (st) Loading stress at peak capacity, MPa (psi)

Test With bag Without bag With bag Without bag

1 223 (246) 24 and 43 (26 and 47) 4.80 (696) 0.51 and 0.92 (74 and 133)

2 164 (181) 83 (92) 3.53 (512) 1.79 (260)

3 122 (135) 29 (32) 2.63 (382) 0.63 (91)

Average 170 (187) 44 (49) 3.66 (530) 0.97 (140)

Figure 26 — Peak-load capacity of the support is increased by the wire wrap. 

Figure shows comparison between bag with wire and one without wire. 

Figure 27 — Closer wire spacing can also provide higher peak capacity due to 

the increased confinement. Chart compares 150- and 250-mm (6- and 10-in.) 

wire spacing.

• Tighter wire spiral: Reducing the 

spacing between the wire wrap can 

increase the total system confinement and thereby increase the support capacity. Figure 27 shows the 

improvement in both stiffness and 

support capacity from an early developmental test using a South African 

manufactured bag comparing a 150 

mm (6-in.) and a 250 mm (10-in.) 

wire pitch. The standard pitch (wire 

spacing) of the most commonly used 

bag manufactured by ABC Industries 

is 150 mm (6 in.). The company also 

provides a 10-gage, 100-mm (4-in.), 

wire/seam pitch that also has been 

shown to increase support capacity 

beyond that provided by the standard 

150-mm- (6-in.-) pitch bag.

• Stronger/enhanced bag fabric: The 

primary function of the bag is to 

contain the material between the wire 

wraps. However, the bag does provide 

secondary confinement and can contribute to the peak support capacity. 

Figure 28 compares developmental 

testing of two prototype bags showing that the stronger bag with thicker 

wire provided higher support capacity 

than the weaker bag.

Support stiffness. The support stiffness 

(K

 K = (A × E)/L (1)

where

A is the support area, 

E is the material modulus and 

L is the support height.

 Assuming that the material modulus 

does not change, the diameter of the support will largely control its stiffness. Table 

2 compares the loading stiffness of 761- and 

610-mm- (30- and 24-in.-) diameter supports. A 60% increase in loading stiffness 

was observed with a 63% increase in load-

) is theoretically defined by 

ing area when the two support diameters 

were compared, confirming the proportionality between the 

stiffness and loading area. To put the stiffness into perspective, 

the pumpable support stiffness of 10.5 to 17.4 t/mm (293 to 

486 st per in.) compares to a stiffness of only 0.89 t/mm (25 

st per in.) for a 4-point wood crib structure. 

Residual load. The residual load capacity is highly dependent 

on the confinement provided by the containment bag. Pumpable 

supports typically shed load after reaching their peak support 

capacity because the confinement provided by the bag/wire 

is insufficient to prevent this from occurring. The initial load-
shedding event is often very dramatic due to the brittle nature 

of these cementitious grouts. This is difficult to control, but 

higher active confinement during pumping appears to limit the 

onset of the initial load-shedding event. An example is shown 

in Fig. 29, which compares the load-displacement relationship 

for a bag with a 150-mm (6-in.), 12-gage wire pitch and one 

with a 100-mm (4-in.), 10-gage wire pitch. The 100 mm (4-

in.) wire pitch also appears to increase the residual loading as 

the convergence continues beyond the initial load-shedding 

event up to the point where the wire system is failing, which 

in this case occurs at about 200 mm (8 in.) of convergence. 

Even passive confinement, meaning that the confinement 

does not occur until the grout fractures and bulks, can significantly improve the residual loading capacity by extending the 

amount of convergence and load that the 

support can sustain. This was proven by 

experimental trials where the support bag 

after filling was wrapped with additional 

material including “house wrap” (material 

used to wrap residential houses to minimize 

air leakage) and chain link mesh. Although 

these materials are not used in production 

bag designs, these trials show the advantage 

of such passive confinement. 

Figure 28 — Peak load capacity of the support can be increased by additional 

confinement provided by the bag/wire system.

Figure 29 — Comparison of 100-mm (4-in.), reinforced, and 150-mm (6-in.), 

standard, wire pitch bags. Reinforced bag delayed major load shedding and 

increased residual load capacity.

Installation and safety-related 

performance comparisons

The installation of pumpable supports reflects a good safety record. Heitech reports 

238 lost workdays installing pumpable 

supports over a five-year period from 2002 

to 2006. During this time, approximately 

110,000 supports were installed. This translates into approximately 21 lost workdays 

per 10,000 supports installed. The injuries 

are primarily due to sprains resulting from 

slips or falls while handling the grout material, with occasional chemical burns. Most 

injuries have been minor with lost time 

less than 15 days. Overall, the average is 

2.5 lost days per incident. This compares 

to 41 lost workdays per incident in U.S. 

coal mines in 1990 based on MSHA accident statistics, when wood cribbing was 

primarily installed. It is anticipated that 

the injuries can be further reduced by the 

application of a batch system, which would 

eliminate some of the material handling of 

the cement at the pump site. 

Conclusions

Pumpable roof supports provide a new 

alternative to conventional standing support application in underground coal mines. 

The support consists of a bag made from 

fabric that can be transported in a collapsed 

form and then hung from the mine roof to 

create a form for filling with cementitious 

grout. The desirable feature of this support technology is that it can be installed 

in place in the mine as opposed to being 

pre-fabricated and brought into the mine 

as a unit. Furthermore, because the main 

component of support, the cementitious 

grout, can be pumped from the surface 

in most cases, the support can be installed in areas that are 

inaccessible to equipment. This makes the support ideal for 

longwall bleeder and tailgate applications. 

There are several pumpable support products now on the 

market. Although they all pump material into a fabric bag and 

thus can look very similar to each other, there are significant 

differences in the grout materials used. These materials are categorized into four main groups: aerated cements, portland fly ash 

cement, portland pozzolan cement and ettringite-based cement. 

Of these, the ettringite-based cements, calcium sulfo-aluminate 

(or CSA) cements in particular, have been the most successful 

and by far the most widely used material. These cements have 

several superior qualities that, so far, have not been matched by 

the other grouts. The CSA-based grout has the highest water 
content (+85% by volume with water-to-solids ratio of 1.75 or 

2.00 to 1). Essentially, the support is mostly water, making the 

slurry the most fluid and easiest to pump. It also has the most 

practical set-up time. Once the two-component grout is mixed 

together at the underground support installation location, the 

grout sets in 10 to 15 minutes. This provides some flexibility 

in the final pumping phase, but still allows the support to be 

completely formed in just a few lifts. The ettringite-based grouts 

have provided consistent in-mine capacity for the support, but 

ettringite formation — more specifically, the control of its 

formation — requires a finely balanced mix with the proper 

constituents. Failure to control these parameters can degrade 

the support performance. Therefore, it is a rather sophisticated 

grout that is much more complex than the common Portlandcement products. The major disadvantage of the CSA product 

is that no domestic source of the component is available and 

importation is expensive.

Table 2 — Comparison of support loading stiffness for 

two support sizes.

 Stiffness, t/mm (st per in.)

 Diameter, Diameter, 

 Test number ~760 mm (~30 in.) 1 ~610 mm (~24 in.) 2

1 16.5 (462) 9.6 (268)

 2 18.2 (510) 11.4 (318)

 Average 17.4 (486) 10.5 (293)

1 Area = 0.492 m2 (763 in.2)

2 Area = 0.301 m2 (467 in.2)

There has been extensive research conducted in the past few 

years to develop portland-based alternatives to the ettringitebased products, ideally alternatives that can be produced domestically. Conventional portland cements have been around 

for a long time, and this technology is well-proven. The mining 

application is also expected to be reliable, but the pumping 

of conventional fly ash/sand mixtures is considerably more 

problematic in that the material can plug the lines if allowed 

to set and it cannot easily be pumped very long distances. The 

pumping also requires higher pressures and stronger pipe. 

Therefore, conventional fly ash/sand mixtures may be a viable 

alternative, but their limitations are likely to make them less 

attractive than the ettringite-based grouts. Nevertheless, some 

applications such as bleeder installations do not require long 

pumping distances, and there is likely to be a role for a material 

than can be reliably pumped 900 m (3,000 ft), particularly if 

it is a lower cost material. It is likely that additional research 

will continue in this area.

One hybrid portland-based product that has had some success is the Tekpak P/F product developed by Minova. Like the 

ettringite-based cements, this system is a two-component mix 

utilizing an accelerator to overcome the retarding agents necessary to provide long pumping life with fast setting times once the 

components are mixed together. The strength of this grout can 

be designed to exceed that of the ettringite-based grouts, but the 

current mine applications provide similar strengths. Here, too, 

the accelerator and hydration chemistry is critical to providing 

consistent strength and desired in-mine performance. Aerated 

or foamed cements have some desirable qualities in terms of 

sustaining peak loading through a larger convergence prior to 

severe load shedding. However, their strengths are considerably 

weaker, requiring more material to provide equivalent strength 

to the ettringite-based or portland-based supports. As a result, it 

is not likely that aerated or foamed cements will replace these 

grouts on any large-scale installation. 

Disclaimer

The findings and conclusions in this report have not been formally disseminated by the National Institute for Occupational 

Safety and Health and should not be construed to represent 

any agency determination or policy.

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