Method of preparing cementitious compositions for tunnel backfill

A cementitious composition for backfilling and sealing tunnels and other underground structures comprising 12-16 parts sand, 3-6 parts cement, 1.5-3 parts water, 0.1-0.5 parts plasticizer and 0.02-0.04 parts of a pituitous water soluble polyethylene oxide thickening agent.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention pertains to a cementitious composition for use as backfill 
and annulus fill for underground pipelines constructed by boring, 
particularly or use in soil conditions wherein substantial ground water is 
encountered. 
There are many types of underground structures in which cementitious fill 
materials are used, either as the primary solid or as a binder for 
aggregates. The design and selection of suitable cementitious material is 
perhaps more difficult than for surface structures because of the variable 
conditions that can occur, and for which there is often only limited 
information. Tunnels, pipelines, oil wells, piles, caissons, control 
rooms, mines, piers, dams, and earth slide areas are examples. 
Construction must cope with ground water, unstable and low bearing 
capacity soils, subsoil voids and caverns, lithostatic pressures, 
corrosive soil chemicals, difficult placement conditions, often remote 
from the surface, high temperatures and many other conditions not 
encountered in monolithic structures built on the surface. 
2. Description of the Prior Art 
The terms "cementitious material" and "cement," as used herein, means 
compounds that in contact with water react therewith and undergo a 
crystalline transformation. Examples would be the various types of 
Portland cement, certain autoclaved gypsum stuccos, high alumina cements, 
pozzolana cements, magnesia cements and the like. In this hydration 
process, the newly formed crystals interlock to become a rigid, continuous 
mass. Such materials can be used by themselves to make structures such as 
floors, walls, beams, pipe and a vast number of well-known items, but more 
often, mainly for cost considerations, they are used as binders of 
inexpensive filler materials such as sand and gravel. When cementitious 
materials are used with sand only, the mixture is commonly called "grout" 
or "mortar." If sand and gravel both are used, the mixture is called 
"concrete." If the cementitious material alone is used, it is termed 
"neat." 
Since the conditions in which the cementitious compositions must be placed 
in underground construction vary widely and are often unpredictable, the 
design of mixes that can flow freely through long lengths of conduit and 
through forms or earth spaces that may cause the mix to dilute or dewater, 
or both, is critical. 
The backfilling of tunnels and the filling of the annular space between the 
liners used in bore-type tunnels and the pipe or conduit set therein often 
involves a variety of requirements. A high degree of fluidity or 
flowability is desired, so as to minimize the number of downholes or 
injection holes needed to insure complete filling of the space. Limiting 
the attainment of high fluidity is the prerequisite to maintain the lowest 
possible water content for strength considerations and for reasons of 
preventing stratification, since any water layer at the top of the cast 
resulting from settlement of the dense aggregates and cement will become a 
void at the point where the soil overburden requires greatest support. 
A very critical consideration is the presence of ground water, either 
ponded in the pour cavity or flowing therein. If the concrete or 
cementitious material is made fluid by use of a high water/cement ratio, 
in order to facilitate placement, it thereby also becomes more susceptible 
to dilution as it flows through ponded water, and flowing ground water 
will leach out the cementitious material as well as other fines such as 
sand or fly ash. The true strength of the final set cast thus becomes 
variable, as is the extent to which the cavity is actually filled after 
the excess water rises to the top when the concrete comes to rest. If, as 
an alternative, a fairly stiff, 2-3 inch slump concrete, cohesive enough 
to resist dilution by water, is used, this limits the distance the 
concrete will flow, hence requires a greater number of expensive downholes 
or pump hose line input points. 
The placement of tunnel fills differ from the well-known technique of 
tremie placement. Generally tremie concreting involves the filling of a 
vertical cavity, and the hose or pipe extends to and discharges at the 
bottom, so that any water standing in the vertical cavity is lifted by the 
denser concrete and only a few inches of the top surface of the concrete 
placement is degraded by the water. Tunnel backfilling usually involves 
downflow from the surface also, but then the fill material must flow 
horizontally through irregular, often narrow, cross sections, one face of 
which may be soil of unpredictable texture. If groundwater is present, it 
will be ponded or will be flowing in the lower portions of the cavity. 
Even if the incoming concrete is displacing ponded still water, it is 
obvious that the leading edge of the concrete is subjected to much more 
washing and leaching action than in the case of tremie placement, and the 
extent of degradation will be much more severe. Even more serious, 
however, are cases in which there is a continuous flow of groundwater into 
the cavity in spite of the use of external dewatering pumps. This adds the 
erosive and diluting action of running water to that of the water lying on 
the cavity bottom. The placement of the cementitious composition is often 
impaired by conditions the reverse of the above. The horizontal flow of 
the composition may be inhibited or even prevented by its passage through 
dry soil or other surfaces that dewater the composition and reduce it to a 
semisolid, nonflowing state. The general approach to preventing this is to 
add a water thickening agent. Thickeners are gelling compounds that 
physically entrap water within their long-chain, convolute molecular 
clusters, or to some degree absorb water, sometimes with weak 
hydrogen-hydroxyl bonding. The long-chain molecules also act like 
dispersed fibers to increase the fluid viscosity of the solution. Gum 
arabic and gelatin are examples of water thickeners. For oil well 
cementing, commercial type agents are used. Thus R. A. Salathiel, U.S. 
Pat. No. 2,582,459, employed bentonitic and montmorillonite clay in 1952, 
as did John V. Drummond, U.S. Pat. No. 2,876,123, 1959. The development of 
synthetic thickeners was exploited by Robert C. Martin, U.S. Pat. No. 
3,234,154, 1966, using sulfonated polyvinyl styrene and polyvinyl toluene, 
and Charles F. Weisend, U.S. Pat. No. 3,132,693, 1964, and U.S. Pat. No. 
3,359,225, 1967, using hydroxyethyl cellulose and polyvinylpyrrolidone. 
There are several other such agents used in the art. 
All of the thickeners heretofore used in oil well cementing dissolve and 
fully disperse relatively rapidly in water. Their thickening action 
increases the viscosity of the cementitious composition, an effect that 
can be countered by the addition of a dispersing agent which would, in the 
absence of the thickener, increase the fluidity of the mix. To some 
degree, the gelatinizing of the water imparts lubricity, since the 
presence of the gel, and its coating of the angular solid particles, 
reduces the friction between the slurry and the conduit or medium into 
which the slurry is flowing. The major objective, however, is to "thicken" 
the water and reduce its ability to be absorbed or dry surfaces with which 
it comes in contact during placement. 
Foamed or cellular concrete can be used as tunnel backfill under certain 
conditions. The limitation is that there be no ground water seepage in the 
cavity or any ponded or impounded free water, since water will 
disintegrate the foam of the mix and result in collapse separation into a 
top layer of foam, a middle layer of water and cement last at the bottom. 
Cellular or light-weight aggregate concrete is useful and economical in 
the 25 to 50 pounds per cubic foot density, giving strengths of 150 to 400 
pounds per square inch, because such material pumps and flows readily over 
long distances. Obviously, however, such a composition will float on a 
62.5 pounds per cubic foot liquid, such as water, hence cannot be used 
except in "dry" tunnels. At higher densities that could displace water, 
e.g. 70 pounds per cubic foot or more, the cost is almost double that of 
the conventional mortars and concretes currently used. 
Plasticizers, or water-reducing agents, have been used in cementitious 
compositions for many years. They are polymeric polyelectrolyte compounds 
that bond to the surfaces of finely comminuted solids, including many that 
are not cementitious, and create an enhanced negative surface charge 
thereon. Since all the particles thus become like charged, they tend to 
repel each other. This results in deagglomeration of clusters or 
particles, and the separated, dispersed particles are much more mobile in 
the aqueous medium than are the large, angular clumps. The tiny particles 
are themselves angular, and normally tend to interlock somewhat so as to 
reduce the fluidity of the slurry. When strongly surface charged, they 
repel each other so as to provide space for free rotation and movement in 
the water of slurry, resulting in greater fluidity. The user may confine 
his benefits from such additives to the higher slump, or workability, thus 
obtained without degrading the composition by adding excess water, or he 
may elect to reduce the amount of mixing water used, thereby improving the 
quality of his cementitious composition while maintaining normal 
workability. 
The most widely used plasticizing agents are the lignosulfonates, 
by-products of the paper industry. The principle objection to them is that 
they retard the rate of hydration, or hardening, of cementitious 
materials, hence can be used only in limited dosage. More recently, two 
synthetic polymers have found increasing popularity, mainly because they 
induce a higher level of surface charge and because they do not adversely 
affect the hydration reaction. The compounds are sodium naphthalene 
sulfonate (monomer) condensed (polymerized) with formaldehyde (U.S. Pat. 
No. 2,141,569 to George R. Tucker, 1938) and sodium melamine sulfonate 
condensed with formaldehyde, developed in Germany. It is at least 
theoretically possible to develop other equally effective plasticizers 
beginning with various monomers. Such compounds are designated as 
"superplasticizers," or "high range water reducing agents" in current 
terminology. A major advantage to their use, over lignosulfonates, is that 
they cause only a slight retardation of cement hydration. 
As noted, the superplasticizers can be used to maintain fluidity in a 
composition even when 30% to 50% less water is used. Their merit in tunnel 
backfilling is in providing high fluidity as normal or low water contents. 
As elsewhere discussed, this significantly reduces segregation and 
"bleeding," the formation of a water layer on the top of the cast that 
eventually becomes a weakening void. A further advantage is that as the 
water content of a cementitious composition is reduced the rate of 
hydration or hardening is proportionately increased, as is well understood 
in the art. The compositions generally used in tunnel backfilling are 
preferrably made as low as possible in the expensive cement fraction, 
hence normally develop strength slowly when made with the usual high water 
contents of present art. If the water content is reduced and the fluidity 
maintained by use of superplasticizer, the composition will gain strength 
much more rapidly and attain much higher strength levels. This can be 
exploited by reducing the expensive cement fraction of the composition to 
a level that has the same performance characteristics as the high water 
mixture. 
In the present invention, the enhanced fluidity is further exploited to 
permit the use of high dosages of the pituitous water thickening agent, to 
levels that would otherwise cause the composition to become too stiff for 
rapid flowing in the tunnel cavities. 
SUMMARY OF THE INVENTION 
The present invention provides a superior composition for tunnel and other 
underground backfill that remedies the shortcomings of the present art and 
a method for preparing the same. 
It is an object of this invention to provide a free-flowing cementitious 
material for use in backfilling, whereby to minimize the number of entry 
or injection points along the tunnel or cavity length. 
It is a further objective to provide a cementitious composition that will 
remain cohesive in the presence of still or running water, resisting 
dilution and segregation of its components, particularly its cementitious 
fraction. 
Yet another objective is to provide a cementitious composition that is 
highly impermeable to water penetration, even under pressure, both as it 
is being placed and after it hardens. 
Another objective is to provide a composition wherein the strength of the 
final set cast may be controlled by varying the composition, whereby to 
achieve maximum economy of the fill material. 
The present invention consists of a method of providing mortar having a low 
slump of 2 to 4 inches by virtue of limiting the water/cement ration to 
0.45 or less and which may also contain a pozzolan such as fly ash for 
reasons of economy or physical properties, adding thereto a plasticizing 
agent that enhances the fluidity of the deliberately low water content mix 
whereby to increase the slump to a level of 8 to 10 inches, then adding 
thereto a selected, slow-dissolving water thickening agent at a dosage 
rate much higher than heretofore used in the art. The ingredients of the 
composition must be combined in this specific order to produce the 
superior backfill. As a final step to obtain maximum economy, pregenerated 
foam may be added to the mortar composition whereby to reduce the density 
and enhance the fluidity. 
The compositions that can be made by the teachings of this invention will 
flow readily by gravity or pump placement through lengths of tunnel 
backfill or annulus voids not heretofore attainable by prior art. The 
strength of the composition can be easily controlled by the proportioning 
of the ingredients and use of foam so as to obtain minimum cost. The 
composition will not dilute in contact with free water flowing or ponded 
in the cavity, and the placement of the composition will displace any 
water present in the cavity without dilution or desegregation of the 
mortar. The composition then hardens or sets by hydration of the 
cementitious component while the water thickening agent continues to 
swell, so that the final set mass develops a slight expansion and becomes 
a permanent, water-impermeable seal. 
DETAILED DESCRIPTION 
Since sand/portland cement mortar or grout and sand/gravel/cement concretes 
are widely and readily available, it is advantageous to use these 
ingredients as the basis of tunnel backfilling compositions. Processed fly 
ash is also widely available for use as a cement-extending pozzolan. Such 
compositions can be satisfactorily mixed and delivered in conventional 
ready-mix concrete equipment. Cellular or foam and light weight aggregate 
concretes require special mixing equipment for best results, since foam 
and expanded perlite or vermiculite tend to float on the cement slurry in 
ready-mix equipment, and cement and water slurries themselves should be 
made with special mixing to attain lump-free uniformity. Accordingly, the 
sand/cement mortars are more convenient and less expensive to use. 
A key ingredient in the composition of the present invention is the water 
thickening agent. Agents, natural or synthetic, heretofore used in 
cementitious compositions, dissolved in and absorb water, i.e., thicken, 
relatively rapidly, e.g., 10 to 20 minutes, under the mixing action that 
must be imparted to the fluid cementitious compositions used. By contrast, 
the water thickening agents used in the present invention must absorb 
water and disperse slowly, preferably taking 6 to 36 hours to reach 
stability. 
The molecular chains of most water thickeners are relatively straight 
lined, i.e., not highly convoluted or brached, and they depend on their 
high molecular weight length to produce the thickening action in a manner 
akin to that of cellulose or cotton fiber in water, as in paper pulp. The 
molecular weights range from 25,000 to several million, and in general, 
the straighter the chain, the more rapidly the agent will dissolve and 
disperse. In their anhydrous, powdered state, the chains appear as coils, 
rolls, balls or random bundles, and these quickly and easily straighten to 
become fibrous when wetted, attaining ability in a short time. As gels, 
they impart lubricity for flow in pipelines and the like even though they 
have increased the viscosity of the solution. 
The typical characteristics of the majority of water thickeners, including 
such natural clay minerals as bentonite and montmorillinite, do not 
achieve the objectives sought by the present invention, mainly because 
they reach stable state quickly. Since the mixing, delivery and placing 
operations for a batch of tunnel backfilling mortar may require 1 to 2 
hours, development of full thickening action would obviously be 
detrimental to the fluidity or slump of the mortar and if the thickener is 
fully dissolved and dispersed prior to placement, its contact with ground 
water in the cavity would simply result in dilution, with attendant 
weakening of the mortar. 
One type of thickener has been determined to be satisfactory to produce the 
results required by the invention, namely the specially polymerized, high 
molecular weight ethylene oxides, as manufactured by UCAR (formerly Union 
Carbide and Carbon Corp.) and sold under the trademark "Polyox." 
Specifically, the most economical and effective of this class of thickener 
are WSR 301, WSR 1125, Polyox Coagulant and FRA, these having molecular 
weights of 4,000,000, 5,000,000, 7,000,000 and 7,000,000 respectively. The 
WSR 205 resin, with a molecular weight of 600,000 can also be used, but 
the dosage level required is so large as to be much less econominal, and 
it reaches stability in 4 to 8 hours compared to 8 to 24 hours for the 
higher molecular weight resins. 
The above ethylene oxide resins are particularly characterized by forming 
solutions that are stringy or pituitous, which is to say that in addition 
to thickening water, both by entrapment of water molecules and by 
hydration of the resin, the resin molecules tend to interlock to form 
continuous chains or filaments or strings. Such a wetting structure on the 
surface of solids in the aqueous mixture results in the solids becoming 
very cohesively bonded to each other, and the thus thickened water does 
not readily absorb or dilute with external free water. Accordingly, mortar 
made with the Polyox resins resists dilution and remains cohesive even 
under water jet action. 
The polymerization technique developed by UCAR is, of course, proprietary, 
but full details of the behavior of the Polyvox resins can be found, for 
example, in the UCAR General Information Bulletins such as F-40246. The 
following example illustrates the novel application in the present 
invention. 
A typical mix of the present invention for a cubic yard of tunnel backfill 
mortar would be: 
Sand, FM 2.7: 2635 lbs. 
Portland Cement, Type I: 360 lbs. 
Fly Ash: 360 lbs. 
Superplasticizer (solids): 3.0 lbs. 
Water: 335 lbs. 
This mortar would have a slump of about 9 inches when made up, absent any 
addition of water thickener. 
The dosage of water thickener would be 3.5 lbs. per cubic yard, if this mix 
is to be used in a backfill severely subject to ground water flow. This 
amounts to a 1.04% solution strength based on the 335 lbs. of water used, 
and if Polyox 301 were fully dissolved in that amount of water, the 
solution would have a viscosity of 2000 centipoises, according to the UCAR 
technical data Bulletin F-40246; the viscosity using Polyox WRS 1125 would 
be 4000 centipoises. However, if these thickeners were added predissolved, 
it would be impossible to mix the mortar with so thick a solution, and 
even if it were possible, the mix would not flow. 
Since 24 to 36 hours are required for this type thickener to fully dissolve 
and uniformly disperse, it follows that only 20% to 25% of the resin will 
be dissolved during the first 1 to 2.5 hours prior to placement of the 
mortar. At this solution strength level, the viscosity of the liquid 
fraction of the mix will reach a level of only 100 and 300 centipoises for 
the respective resins accordingly to UCAR technical data Bulletin F-40246, 
so that in the practice of the invention, the slump of the mortar is 
decreased only to the level of about 7 inches instead of to zero. 
During the first three days after placement of the mortar, roughly half of 
the free water will be removed by the hydration of the cement and 
adsorption by the fly ash. This results in doubling the concentration of 
the thickener in the free water remaining. According to UCAR Bulletin 
F-40246, at the 2% concentration, the viscosity of the WSR 301 will be 
12,000 centipoises, and for WSR 1125 it will be over 14,000 centipoises, 
and at this "paste" viscosity free water cannot penetrate the mortar or 
seep or percolate therethrough. What would have normally been free water 
in the mortar will have become an immiscible, elastic solid. In the 
unlikely event that the mortar ever reached a completely dry state, the 
resins would become plastic films in the capillary channels of the set 
cast and continue to act as barriers to the passage of free water. 
Several other important benefits derive from this discovery. The slow 
acting thickeners do not lock up the free water of the composition 
quickly, as in prior art, so that the mixture retains much of its 
important fluidity or flowability during the critical placement period. 
Much higher dosages of the agent can thus be used without workability 
impairment. Even at the initial low levels of solution and dispersion, 
these agents still impart lubricity to the composition, facilitating 
pumping and flow in narrow spaces, and will also fortify and stabilize any 
foam used in the composition. The incompletely dissolved granules 
initially resemble gelatinous, plastic balls, so that the addition of a 
very small amount of water to the mix just prior to placement can impart a 
temporary slickness to their surfaces, causing them to behave like ball 
bearings and thus inducing a highly useful and disproportionate increase 
in the fluidity of the composition. 
The presence of the long molecular chain, slow-dissolving thickening agents 
of the present invention further results in a composition having unusually 
high cohesiveness. If the composition is poured into still water, it will 
not separate or become diluted, and little of the cementitious component 
will be leached out, even though the composition is left to harden in the 
submerged state. Furthermore, if a stream of water is directed at a moving 
or stationary mass of the composition, it will not disperse it or leach 
out the fine particles of cementitious ingredient. Accordingly, the 
compositions of the present invention can be placed in cavities containing 
water or where running ground water is encountered, without loss of 
integrity or properties. 
The final, and perhaps most important contribution of the slow dissolving 
water thickening agent to this improved composition occurs after 
placement. In the delayed action, the free water in the composition 
continues to be absorbed by the growing gel, becoming immobilized against 
the migration that creates voids at the top of the cast, and against 
escaping into dry or porous soils where it would be lost to the hydration 
reaction. Furthermore, the delayed swelling creates a slight expansion 
while the composition is still in the plastic state, thereby insuring 
complete filling of all cracks and crevices in the cavity and liners. When 
the cementitious composition has fully hydrated, about twenty-six parts, 
or more than half of the original mixed water has become chemically 
combined, so that the concentration of thickener in the residual water is 
doubled. This semisolid gel completely fills all capillaries and 
intercrystalline spaces in the hardened composition, rendering it 
impermeable to water penetration, so that the set cast seals the tunnel 
walls completely. 
The compressive strength of backfill material used in tunnel and 
underground structure lining and backfilling usually need to be no greater 
than that of the surrounding earth under lithostatic pressure. This may 
range from 30 to 150 pounds per square inch. The tunnel segments and 
structures are designed and reinforced to carry both earth pressures and 
service loads, so usually do not require supplemental support from the 
fill. However, there are sometimes conditions that make it very useful to 
utilize fill compositions that will contribute to the rigidity and 
structural capacity, such as where lateral earth movement, earthquake 
potential, concentrated loading as from rock formations and other factors 
may be encountered. Accordingly, it is highly useful to be able to vary 
the strength of the fill material at will, for reasons of economy, without 
significantly changing its flow and placement characteristics. The 
sand-cement mortars and concretes commonly used can be varied in strength 
by using greater or lesser amounts of the cementitious component, but this 
alters the flow characteristics unless more water is substituted for the 
cementitious material deleted. Fly ash or other finely comminuted 
pozzolanic materials can be substituted for cement, also, at some cost 
savings return for the strength reduction. 
Concrete, mortar and neat cementitious materials, in their wet states, 
weigh 120 to 150 pounds per cubic foot, and, when placed as backfill, 
exert over twice the hydraulic and flotation pressure of water. Since the 
cavities being backfilled do not fill evenly, as they might using a low 
viscosity liquid such as water, there is a constant unbalance in the 
hydrostatic load on the structure. Pipe joints get warped out of line, 
seals become displaced, and the structures sometimes even fail under the 
stress. The usual remedy is to place the dense fill in several "lifts" or 
layered pours, allowing time between placements for the material to become 
reasonably rigid by hydration of the cementitious component. For low 
strength compositions, 50 to 200 pounds per square inch, this may entail 
several days' delay with attendant higher cost. 
Stable, aqueous foams made with a variety of continuous-output generating 
equipment well known to the art, are used extensively in the production of 
low density "concretes," these being cement-water slurries blended with 
the pregenerated foam to produce nonstructural, poured-in-place insulation 
for roof decks, foundation insulation, fireproofing for safes and similar 
applications. Such foams, weighing only 2 to 3 pounds per cubic foot, are 
much lower in cost than lightweight aggregates, such as expanded 
vermiculite and perlite, do not absorb water, and are less prone to 
flotation separation in the fluid mixtures desired for backfill work. More 
important, however, is that the foam actually improves the fluidity of the 
mix, in the same manner as air entrainment does for concrete. The lower 
the density, i.e., the more foam used per unit of volume, the lower the 
strength of the finished product, so that the foam can be used 
economically to attain the strength level desired. The lower the density, 
the less cementitious material used per unit of volume, a valuable cost 
savings since foam costs only $3.00 per cubic yard, replacing 10% to 80% 
of the more expensive solids. 
There are two important prerequisites for the foams used in tunnel backfill 
mortars. First, the foam must be stable in its environment, which consists 
of a high pH, i.e., 11.8 to 12.2, characteristic of portland cement, if 
same is used as the binder, and the presence of the strong polyelectrolyte 
superplasticizers. It must remain stably intact for whatever period of 
time is required for the cementitious material used to hydrate to a 
strength level at which the matrix is self supporting. 
Secondly, the foam must be of the discrete, or closed, cell type. Most foam 
agents form open cells in cement slurries. Since the encapsulated air can 
escape through the walls of such cells, free water can readily flow into 
the pore and progress through the entire mass. This would greatly defeat 
the objects of the present invention. Air cannot escape through the films 
of a discrete, closed-cell foam, hence, water can permeate the cast only 
by slow capillary movement through the crystal matrix of the cement. In 
the present invention, even this limited penetration is prevented by the 
presence of water thickener in said capillaries. 
In prior art practice the use of foam with mortars of sand, cement and 
water is limited to density reductions no lighter than 90 pounds per cubic 
foot, since normally at that point, the foam/cement/water fraction of the 
composition becomes too low in specific gravity to keep the sand in 
suspension. However, we have found that when the composition includes the 
water thickeners of the class disclosed for the present invention, the 
solid components are rendered cohesive and do not stratify or settle out 
until the density is decreased below 50 pounds per cubic foot. This 
discovery is important, since it permits standard mortars, widely 
available from ready-mix concrete suppliers, to be used economically and 
universally at low densities not heretofore attainable. 
Prior art practice in the simultaneous use of two or more beneficiating 
additives with cementitious compositions does not specify any order of 
assembly of the components of the mix, and the plurality of additives are 
usually introduced as a single blend at any convenient time or else 
preblended with one of the components, i.e., the water, the sand or the 
cementitious material. Typical examples are found in U.S. Pat. No. 
2,690,975 to Edward W. Scripture, Jr., U.S. Pat. No. 2,757,096to David 
Tierston, U.S. Pat. No. 2,927,033 to Stephen W. Benedict, U.S. Pat. No. 
3,215,548 to Charles A. Vollick, U.S. Pat. No. 3,689,294 to Stephen 
Braunauer, U.S. Pat. No. 3,686,133 to Kenichi Hattori et al, U.S. Pat. No. 
3,359,225 to Charles F. Weisend, and others. All of these use additives 
similar and related to those of the present invention. 
For the present invention, it was discovered that following the method 
teachings of prior art produced limited and sometimes adverse results. The 
order of assembly of all the components of the composition was found to be 
critical to the properties and success of the final product. 
In the practice of the present invention, and when using ready-mix truck or 
other batch-type mixers, all of the coarse aggregates, if any is used, but 
only 40% to 50% of the fine aggregates are introduced first, to preclude 
"balling" of the cementitious material and its caking or coating on the 
mixer walls and blades. This is followed by addition of all the 
cementitious material, including pozzolans, and all of the water. Next the 
superplasticizer is added, then the balance of the sand, and finally the 
water thickener in dry powder form. The composition is then thoroughly 
mixed, and this can be accomplished during transit to the point of use in 
the conventional ready-mix manner. If foam is to be included in the 
composition, it is added just prior to discharge of the composition from 
the mixer into the pump, downhole or other method of placement. 
There are significant reasons why this procedure must be followed to obtain 
optimium results and economy. By extensive research and testing, it was 
determined that, to be most effective, the superplasticizer should not be 
added until the surfaces of the cementitious material become wetted and 
thereby acquire a low-order negative surface charge of their own. 
Thereafter, the similar low-order positive charge sites along the 
superplasticizer molecule can reaily match with the negative charges on 
the particles, bonding the superplasticizer molecules securely thereto and 
resulting in the much stronger negative charge of those molecules creating 
the repelling/dispersing force desired. On the other hand, if the 
superplasticizer is in solution in the water first, some degree of charge 
neutralization or disorientation apparently occurs, and 50% to 100% 
greater dosage of superplasticizer is required to attain results equal to 
the teaching of the present invention at a cost of about $7.00 per cubic 
yard. 
Perhaps partly because of the high dosage used, compared to prior art 
teaching, the presence of water thickener in the mix prior to or 
concurrent with the addition of the superplasticizer renders the latter 
practically ineffective. It is not clear whether the very long chain 
thickener molecules "entangle" those of the superplasticizer, or whether 
the thickener forms a protective, nonionic colloid on the surfaces of the 
solids in the composition, or whether the superplasticizer cannot dissolve 
in thickened water, or whether some other explanation applies. Premature 
addition of the dry thickener simply results in severe loss of fluidity. 
Some types of water thickeners are occasionally used as foam "fortifiers" 
or stabilizers, reinforcing the bubble films of the foam. When so used, 
the thickeners are dissolved in the water first and allowed to reach 
stable dispersion before the foam agent is added to form the foam 
solution. However, if foam has been blended and dispersed in a plastic 
mass, e.g., a cementitious composition of the present invention, and dry, 
pulverent thickening agent is then added, the opposite result will occur. 
The hygroscopic behavior of the thickening agent will dehydrate the foam, 
causing it to collapse. Accordingly, in the practice of the present 
invention, it is specified that the foam be added as the last component, 
after all other ingredients have been thoroughly blended and there has 
formed around the thickener granules a gel film that slows down the rate 
of water absorption by the undissolved core. 
In prior art practice, water thickeners are often prepared as concentrated 
solutions for convenience of addition and dispersion in the composition to 
which it is to be added. This practice would completely defeat a major 
purpose of the use of the thickener in the present invention, wherein it 
is important that the agent accomplish a substantial fraction of its 
thickening or gelling during and after placement of the cementitious 
composition. This can be achieved only by the delayed addition of the slow 
dissolving pituitous thickener in dry powder state, as herein specified. 
Since the thickener powder is relatively light in bulk density, care must 
be exercised during its addition to insure rapid and uniform dispersion, 
as by sifting or by air stream dispersion over the turbulent surfaces of 
the mortar during mixing. The powder grains become very adhesive 
immediately upon being wetted, so can readily form clumps or balls that 
are difficult to deagglomerate. 
In the practice of this invention, it is convenient to disperse the dry 
powder thickener on the second charge of sand, if the sand is being 
introduced into the mixer by conveyor belt or bucket elevator. If the sand 
must be charged by gravity, as from an overhead silo, the powder can be 
dispersed in the stream from an air stream tube. There are other means 
known to those in the art, including the preblending of the powder with 
dry sand or fly ash bulking agents to improve the dispersion.

The following specific examples will illustrate the method and compositions 
of the present invention. The first example is for use in tunnel cavities 
having a high ground water seepage as well as considerable ponded water. 
The second example illustrates a composition ideally suited for "dry" 
tunnel cavities in which the ground water or ponded water volume is minor, 
hence suitable for compositions that contain pregenerated foam as a 
component of the mortar. 
EXAMPLE 
1. A ready-mix concrete truck is loaded with the following components, 
expressed as pounds per cubic yard, in the order shown: 
Sand: 1315 lbs. 
Portland Cement, Type I: 330 lbs. 
Fly Ash: 330 lbs. 
Water: 300 lbs. 
Superplasticizer, Active Ingredient: 3.0 lbs. 
The slump mix at this point is 11 inches or more. Next, add: 
Sand: 1315 lbs. 
WSR 301 Water Thickener 
Powder: 3.5 lbs. 
The resulting slump is 6 to 7 inches, and is suitable for free-fall or pump 
placement, and up to 400 lineal feet of tunnel backfill, at a volume of 
0.5 cubic yards per foot, can be pumped from a single downhole. This 
compares to 100 to 125 lineal feet using conventional mortars. 
The strength of the above mix design averages 1000 pounds per square inch 
at seven days and 1300 pounds per square inch at 28 days, with a wet 
density of 130 pounds per cubic foot. If the 330/330 ratio of cement to 
fly ash is reduced to 260/400, the 7-day strength will be reduced to 700 
pounds per square inch, and for a 140/520 ratio, the strength will be 450 
pounds per square inch, but these mixes will provide a cost reduction of 
$2.10 and $7.20 per cubic yard, respectively. Conversely, for a higher 
cement factor, such as 420/320, the 7-day strength will average 1300 
pounds per square inch, but the cost will be increased by $1.50. 
When the above mixes were subjected to severe washing by water streams, 
both in the laboratory and in field tests, the mortars showed a strength 
loss of 20% to 45%, being highest for the low-cement factor mix, as would 
be expected. The field samples were obtained from the pour after removal 
of the bulkheads. By contrast, conventional mortars, even made with all 
cement and no fly ash, gave 7-day strengths no higher than 200 pounds per 
square inch. Normally, such a mortar would reach levels of 4000 to 4500 
pounds per square inch at seven days, but its cost would be about $8.00 
per cubic yard higher than for the 330/330 mix design. 
It will be clear to those skilled in the art that the strength of the 
mortar can be varied in other conventional manners. The ratio of sand to a 
given cement/fly ash proportion can be decreased from the 3.55 to 1 level, 
above illustrated, to 2.5 to 1 or even 1 to 1. This will increase strength 
and, to some degree, fluidity or slump, but at high cost, since the cement 
factor per cubic yard will rise sharply, and the mixes would require 
higher dosages of both superplasticizer and thickener because of the 
increase in specific surface of the fines fraction on which the dosage is 
dependent. Increasing the proportion of sand to fines (cement plus fly 
ash) reduces the paste fraction (cement, fly ash, water) and this in turn 
reduces the basic fluidity of the mortar, hence higher dosages of 
superplasticizer are required, offsetting the savings of the lowered 
cement factor. 
Another common approach to changing the strength of a given mix design is 
to alter the water-to-cement plus fly ash ratio, or w/c. Increasing the 
w/c decreases the strength and density, in accordance with a 
well-established semiparabolic curve. Increasing the water volume will 
obviously invrease fluidity and thus would permit reduction in the amount 
of superplasticizer dosage, but to counter the increased ability for the 
various components to settle out and stratify, during the now-retarded 
setting time, the thickener dosage would have to be increased, negating 
some of the gain in fluidity and all of the gain in cost. Conversely, a 
lower w/c would require more superplasticizer and less thickener, and 
would give higher strength, which might be capitalized by using a lower 
cement-to-fly ash ratio. Such a mix would have a shorter pot life, which 
is to say it would stiffen or thicken more quickly and thereby limit the 
amount of mortar that could be placed through a given port or downhole. 
The pot life of the illustrated mix is about three hours, at 80.degree. 
F.; reducing the w/c to 0.40 would reduce the pot life to about 1.5 hours, 
so would require twice as many expensive downholes or larger, more 
expensive pumping equipment of double capacity. 
EXAMPLE 
2. When pregenerated foam is included as one of the mix components, certain 
changes in the mix design are necessary for reasons which will be 
discussed hereinafter. A typical economical mix comprises the following, 
in the order given. Weights are pounds per cubic yard of foamed mortar. 
Sand: 768 lbs. 
Portland Cement, Type I: 235 lbs. 
Fly Ash: 185 lbs. 
Water: 206 lbs. 
Superplasticizer, Active 
Ingredient: 1.2 lbs. 
The above mix has a slump of 11 inches; after 2 to 3 minutes of mixing to 
reach uniformity, add: 
Sand: 768 lbs. 
Water Thickener WSR 
301 Powder: 1.5 lbs. 
This reduces the slump to 6 to 7 inches. Mixing is continued for 4 to 5 
minutes, or can be completed during transit to the placement site in a 
ready-mix truck. Prior to placement, preferrably no more than 5 minutes, 
introduce 12.5 cubic foot of pregenerated aqueous foam made from a 4% to 
6% solution of resin base foaming agent, such as Mearlcel 3532 or 3499, 
expanded by pregeneration to a foam of 2 to 3 pounds per cubic foot 
density. The finished cubic yard of mortar will have a wet density of 80 
pounds per cubic foot, a slump of 6 to 8 inches, a 7-day strength of 200 
to 250 pounds per square inch and a 28-day strength of 400 pounds per 
square inch. It will cost about $8.00 less per cubic yard than the mix of 
example 1, above, hence about $16.00 less per cubic yard than conventional 
mortar. 
The foam mortar mix design was given a field test on a large, long tunnel 
backfill, requiring about 1 cubic yard of fill per lineal foot of tunnel. 
In a continuous pour, a total of 950 cubic yards was placed by 
free-falling the mortar down 40 feet into the cavity through a 14 inch 
diameter downhole; no pumps were used. The placement rate averaged 2.5 
cubic yards per minute. A total of 850 lineal feet of tunnel was filled 
before the flow rate fell to zero. It is believed that this may be a 
record placement for free-fall tunnel backfill flow from a single fill 
point. The cost of material was about $10.00 per cubic yard less than for 
a 45 pounds per cubic foot cellular concrete that would have the same 
strength, and which might possibly be pumped for such distances. The 
cellular concrete, however, would not provide the same water sealant 
properties; the interior of this test tunnel has remained dry and leak 
free even though flooding of a nearby river has several times resulted in 
a water level 40 to 45 feet above the level of the tunnel. 
Sampling of the concrete after removal of the bulkheads disclosed that the 
in-place density of the concrete was 90 pounds per cubic foot instead of 
the 80 pounds per cubic foot at which it was placed. This was due to the 
combination of elevation and friction head compressing the air of the 
foam. At this density the strength had increased to 600 pounds per square 
inch instead of the 400 pounds per square inch that would be typical of an 
80 pounds per cubic foot density. Obviously, an increase in the volume of 
foam added would result in a compensating lower initial density that 
would, in turn, make for an in-place density of 80 pounds per cubic foot, 
if desired. 
To illustrate the difference between the mix design of mortar intended for 
foaming for use in "dry" tunnel cavities and that used in example 1, being 
mortar for high water conditions, the above quantities are herewith 
expressed in pounds per cubic yard of mortar, unfoamed: 
Sand: 1315 lbs. 
Cement: 400 lbs. 
Fly Ash: 320 lbs. 
Water: 360 lbs. 
Superplasticizer: 2.0 lbs. 
Sand: 1315 lbs. 
Water Thickener: 2.5 a lbs. 
When 20 cubic feet of 2.5 pounds per cubic foot pregenerated foam is added 
to the above, the yield is 47 cubic feet of 80 pounds per cubic foot 
mortar. 
It will be seen that the paste fraction has been increased both as to 
solids content, from 660 pounds total to 720 pounds, and as to water 
content, from 0.45 to 0.50 w/c, i.e., 60 pounds or 7.2 gallons per cubic 
yard. This is because the foam incorporates with the paste to form a 
cellular mass in which, essentially, the sand is uniformly dispersed, and 
if there is not sufficient mass, the larger sand grains will segregate. 
The cement/fly ash ratio is increased to provide strength in the matrix to 
replace that lost by foaming to low density. The w/c is increased because 
the highly expanded foam is somewhat hygroscopic and thus competing with 
the cement for available water. It may be noted that by making the foam 
wetter, e.g., by increasing its density from 2 to 3 pounds per cubic foot 
to 4 to 4.5 pounds per cubic foot, the fluidity of the foamed mortar will 
be substantially increased with very little increase in total water 
content of the mix. 
Since the foam fluidizes the mix, the dosage of superplasticizer is reduced 
for economy. Furthermore, the discrete cell pregenerated foam specified 
for practice of the present invention will, with cement paste, make a 
fairly impermeable cellular concrete, hence its use permits reduction in 
the quantity of water thickener required. The two materials are highly 
compatible, since the long chain molecules of thickeners, especially the 
pituitous type, are structurally similar to the molecules of foam agents. 
Together they reinforce each other to produce greater foam stability. 
In the research of the present invention, it was discovered that most of 
the several hundred commercial foam agents available are not compatible 
with the strong electolyte superplasticizers that are most effective with 
cementitious maaterisla, i.e., the sodium naphthalene and melamine 
sulfonate condensates. Only three were found to be stable, to wit Mearlcel 
3532, Mearlcel 3499 and Mearlcel 3728, all manufactured by Mearl 
Corporation, Roselle Park, New Jersey as proprietary compounds, reportedly 
blends of synthetic surfactants comprising nonionic polyethylene oxide 
alkyl ethers, anionic alkyl sulfates and alkyl sulfonates. Obviously, the 
foam used in tunnel backfill operations must remain stable both during the 
turbulence of mixing and placement, and subsequently at rest until the 
cementitious material hardens to become self supporting, which is 6 to 8 
hours. Foam stability was measured by filling a vertical tube 6 inches in 
diameter by 8 feet high and measuring the cavitation or shrinkage of the 
top surface of the foamed grout. 
Having thus described the compositions of mortars superior in properties 
and cost to that of prior art, and the method for making same, what we 
claim is as follows.