Feasibility of using concrete for lunar-base construction has been discussed recently without relevant data for the effects of vacuum on concrete. Experimental studies performed earlier at Los Alamos have shown that concrete is stable in vacuum with no deterioration of its quality as measured by the compressive strength. Various considerations of using concrete successfully on the moon are provided in this paper along with specific conclusions from the existing data base

Cullingford, Hatice S.

Keller, M. Dean

English

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A major purpose of the Techni-
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1989001689
https://ntrs.nasa.gov/search.jsp?R=19890001689 2020-03-20T05:48:47+00:00Z
LUNAR BASES & SPACE AGT_VIT_E$
|_] THE 21St CENTURY
LA-UR--88-2405
April $ - 7, 1988 DE88 014391
Westin Galleria Hotel
Houston, Texas
LUNAR CONCRETE FOR CONSTRUCTION
* **
Hatice S. Cullingford and M. Dean Keller
** NASA/Johnson Space Center, Houstou, TX 77058
Los Alamos Natlonal Laboratory, Los Alamos, NM 87545
Paper No. LBS-88-7271
Symposium sponsoredby NASA,AIAA, the Lunar & Planetary Institute, the
American GeophysicalUnion, the AmericanNuclear Society, the American
Society of Civil Engineers,the Space Studies Institute and the National SpaceSociety.
1989001689-002
LUNARCONCRETEFOR CONSTRUCTION
Hatice S. Cullingford
NASA/JohnsonSpace Center, Houston, TX 77058
M. Dean Keller
Los Alamos, National Laboratory,Los Alamos, NM 87545
Feasibility of using concrete for lunar-basecorstruction has been discussed
recently without relevant data for the effects of vacuum on concrete. Our
experimentalstudies performed earlier at Los Alamos have shown that
concrete is stable in vacuum with no deteriorationof Its quality as
measured by the compressive strer_th. Various considerationsof using
concrete successfullyo_,the moon are provided In this paper along with
specific conclusions from the existing data base.
INTRODUCTION
Concrete is probably the most widely used of all the man-made materials of
construction. It does not require expensive,hlgh-temperatureshape-forming
processes; develops its strength at ambient temperatures; has low density
and high thermal and electrical insulationproperties; and is noncombustible
and generally nontoxic (Double, 1981). Based on a historlcally-long
i Lunar Concrete : le_t
1989001689-003
successful experience with concrete, it is natural that lunar applications
have been suggested by Lin (19B4) and others.
Concrete is by definition a polyphase material that consists of particles of
aggregate connected by a matrix of hardened cement (Lott and Kesler, 1967).
According to a scenario proposed by Lin, cement could be obtained by high-
temperatureprocessing of lunar rocks while aggregateswould be obtained by
physical processing of lunar rocks and soils (Lin, 1984).
The purpose of this paper is to discuss the authors' experimentalwork with
concrete as it relates to lunar base construction.
NOVEL TESTING PROGRAM
Very little informationexists in the vacuum or concrete literatureon the
¢
behavior of concrete in vacuum even though there has been a continued
interest over the years in using concrete for vacuum applications. On the
other hand, the stability of concrete in vacuum Is intuitivelyquestioned
without data (Cullingfordand Fox, 1980). Because there was a need to know
the vacuum's effect on concrete's strength for a linear-acceleTatorllne at
the Los Alamos National Laboratory (LANL), we designed earlier a test
program to investigate both outgassing and compressive strength of concrete
in high vacuum (Cullingfordet al., 1982).
Lunar Concrete:Text
1989001689-004
Outgassing characteristicsof vacuum materials are typically reported in the
vacuum science literature (for example, Perkins, 1973). Our study of
concrete, however, involveda multidisciplinarytreat_t with an
engineeringapproach to the problem of concrete's behavior in vacuum. To
begin with, all concrete used was prepared as a mix given in Table I; the
local aggregate with the composition shown in Table II came from the San
lldefensoPueblo. Relevant engineeringstandards were applied for concrete
preparation,curing, and testing. (See Cullingfordet al., 1982). Concrete
samples thus prepared (cylindersof B-inch diameter by 12-inches high) were
designated by "test" or "control." The test cylinderswere placed in high-
vacuum environmentfor specified periods of time after air curing while the
control cylinders were not.
Figure I shows the experimental vacuum apparatus for the outgassing studies.
The clean-systembase pressure was 3wi0-6 torr (3.99x1D-4Pa) after 160-h
pumping time. The test program involved a progressionof air curing,
weighing, vacuum treatment, weighing, and then breaking for compressive
strength as represented in Figure 2. All tests involvedmultiple cylinders
for a more representativeaverage behavior. This is an important point
because of the nonhomogenousnature of concrete.
Mass loss, compressive strength, and outgasslngmeasurementswere made
during the test program. An increase in compressive strength with time is
observed, reaching an equilibrium value of 6500 psi with or without vacuum
exposure (Cullingfordet al., 1982). (See Figure 3.) Significance of this
3 Lunar Concrete:Text
1989001689-005
TABLE I. CONCRETE DESIGN MIX
Mass Percentage
Material (Ib) (%)
Water 2.0 7.05
Portland Cement 4.1 14.47
Fine Aggregate 9.0 31.54
Coarse Aggregate 13.3 46.94
Total 28.3 100.00
4 Lunar Concrete:Text
1989001689-006
TABLE II. COMPOSITIONOF LOCAL AGGREGATE
Fine Aggregate 0.25-0/75 in. 0.75-1.50 in.
Quartzite 2 45 36
Acid Volcanic 16 28 23
Granite tO 13 22
Basic Volcanic i 8 II
Quartz 57 4 7
Feldspar* 9 - -
Chert** 3 - -
i Residue _22 _22 _!I
Total 100 100 100
where
Basic Acid
Granite Volcanic Volcanic Quartzite
Si02 77.0 49.1 75.6 97.05
A1203 12.0 15.7 12.7 1.39
Fe203 0.8 5.4 1.2 1.25
FeO 0.9 6.4 0.34 -
MgO - 6.2 0.12 0.13
CaO 0.8 9.0 0.59 0.18
Na20 3.2 3.1 4.0 -
K20 4.9 1.5 4.6 -
H20 0.3 1.6 0.46 -
Other 0.1 2.0 0.39 -
* Feldspar is assumed to be 50% KAISi308 and 50% NaAISi308.
**Chert is predominatelySi02.
5 Lunar Concrete: Text
..... 1989001689-007
result is that structures for vacuum use can be designed without additional
safety margins.
The predominantpumped species in concrete outgassingwas not a diatomic
gas, but water vapor as studied by mass spectrogramof the.residual gas in
the test chamber (Cullingfordet al., 1982). During the first several days
of pumping, the outgassing rate is approximately10-6 torr.L/cm2.s. The
empty chamber throughput,at this time, is about three orders of magnitude
lower than the gross throughputwith concrete samples in the chamber.
The mass-loss informationwas reduced to water content as percent of
concrete dry mass and is also plotted in Figure 3. Concrete became stronger
as it aged. A faster drying rate was observed, as expected, under vacuum
exposure. A final water content of 6.6 and 4.93% was calculated on dry-mass
basis for the control and test samNles, respectively. The total amount of
water lost from the concrete cylinders was 0.13 and 0.35 Ibm/ft2 for control
and test cylinders, respectively. Thus, about 2.1 times the mass of water
was released overall under vacuum treatment without a reduction in
compressive strength. The next section discusses further the effect of
vacuum on concrete's water.
VACUUM EFFECT ON CONCRETE'SWATER
Water is present in concrete in three states: chemically bonded water in
the hydration product, adsorbed water on the surface of gel particles, and
6 Lunar Concrata :TaMt
1989001689-008
condensedwater in the capillarypores. Whenwater is added to a mixtureof
Portlandcementand aggregateto prepareconcrete,hydrationreactionsoccur
betweencalciumsilicatesand the water. Thishydrationprocesscontinues
for severaldays,and the concretebecomesstrongerand harder. The drying
phaseduringthe air cureinvolvesreleaseof the free (notchemically
bound)waterfromthe concrete(LottandKesler,1967).
The LosAlamosdata showthatvacuumexposureproducedfasterreleaseof
thisfreewaterfrom the concretesamples. However,the factthat
compressivestrengthdoes notworsenundervacuumtreatmentsuggeststhat
cementdehydrationreactionsdo not occur. In addition,a constantrate of
moistureloss (0.04%per day)was experienceduringthe earlypartof
vacuumexposureregardlessof the lengthof air curingperiodpreceeding.
(SeeFigure3.)
The waterevaporationratecorrespondingto thisconstantrateof
evaporationundervacuumis 3.g7x10-8g/s.cN_'.On the otherhand,the
controlsamplesunderwentan evaporationrateof o.g2x10-8g/s.cm2. These
rateswere comparedwiththe calculatedrateof freeevaporationof water at
the testconditionsfromthe followingequationderivedfromthe kinetic
theoryof gases (Roth,1976;Kaldis,1980).
W = 5.83,10-?a Pv (MIT)-I/2
where W - rateof evaporation(gls.cm2),
a - evaporationcoefficient(1.0for free evaporation),
Pv = saturationvaporpressure(torr),
7 Lunar Concrete:Text
1989001689-009
M = molecularweight,and
T = surfacetemperature(K)
Thiscomparisonshowedthatan evaporationcoefficientof 1.59xi0-7 is
attributableto the vacuum'seffecton concrete.
Finally,the evaporationratescalculatedfor concretein air or vacuum(i_
the orderof 10-8g/s.cm2)suggesta smallsurfacecoolingand,thus, little
uncertaintyin the surfacetemperatureof concrete(Kaldis,1980). This
assuresa higherconfidencein the constant-temperatureanalysisof the
concretedata.
DISCUSSION
The experimentaldataobtainedat Los Alamoson concreteare significantin
planningfor lunarconstructionwith concrete.The followingspecific
conclusionsare derivablefromour study.
• Concreteis stablein vacuumwith no deteriorationof concretequalityas
measuredby compressive strenlth. (Ours was about 6500 psi,)
• Water lessfromthe concretecylinderswas 0.13 and 0.35 Ibmlft2for
control{withoutvacuumexposure)and for test {withvacuumexposure)
samples,respectively.
8 Lunar Concrete:Text
1989001-689'010
• An evaporationcoefficientof 1.59,107 is attributableto the vacuum's
effecton concreteduringconstantrate of drying.
• An outgassingrateof 10-6torr.I/cm2.swas observedafter 7_-hvacuum
pumping. The predominantgas specieswas water vapor.
• A highvacuumof 2xi0-4torrwas maintainedv_Iththe mechanicalpumping
systemusedin the experimentalapparatus.
Variousconsiderationsof usingconcreteor the moonare listedbelow.
i. The moon gravitationis lessthanthatof the earth. Therefore
concretewouldbe betterableto handlestressesof largestructures.
I(oweverthe forceswouldnot alwaysbe actingin the ways thatwe are
accustomedto.
2. Any dome structureon the moonwouldprobablyhavepressureon the
insideand vacuumon the outside. The domewould thereforehaveto act
in tension. However_concreteIs weak in tension.
3. Reinforcingwould thenrequirethe manufactureof steelon, or shipment
of steelto the moon. Fiberreinforcing,especiallyof a type that
couldbe manufacturedlocally,wouldaid in providingtensilestrength
for concrete.
9 Lunar Concrete: Text
1989001689-011
4. Assumethe pressureinsidea dome is about10 psia. Thiswould require
1440psF of pressureexteriorto the dome to resistby "deadweight."
_;i_nthemoon gravityas it is, thiswou]dbe a highbackfillover the
dome. The anchoringproblemaroundthe perimeterwould haveto be
solved.
5. Excavatedundergroundwith linedwallswould be anotherpossibility.
Thiswouldalsoofferprotectionfrmumeteroidswhich do not burnup
due to lackof atmosphere.A combinationof cement,lunarrocksand
soils,and fiberreinforcingcouldprovidea coatingon wallsfor
protectionagainstrockslides.
6. At entrancesand shafts,preplacedaggregatecouldbe formedand a
groutbe pumpednextIntothe voidsto constructvariousconcrete
shapes. Considerationwill haveto be givento shapesto assurethat
the low lunargravityand the internalpressureare actingto placethe
concretein compression.
7. Formenclosureswouldhaveto be air-tightto assurethatwater is not
lostbeforethe hydrationprocessis complete. Vacuumwould thenbe
directedso thatmoisturecouldbe capturedwhen it is withdrawnfrom
the hardenedconcrete.
8. Concretecan be formedby usingan air filleddome. If two domesare
constructedone withinthe other so that theyare concentric,for
example,by abouttwo feet;the interiorair bag couldbe inflatedto
10 Lunar Concrete : Text.
f1989001689-0fl2
about10 psiawiththe differentialbetweenthe innerand the outerbag
to be about2 psia. Strapscouldbe used so thatthe bagswill always
remainseparatedby about2 feet. Concretecan thenbe placedin the
annulusbetweenthe two bags. Concreteoperationscan be carriedout
withinthe innerbagwhilethe lunaraggregatei_ alsomined insidethe
bag. The waterneededcouldbe alsomanufacturedinside, Problemsto
solveincludethe breakingof the bag materialby penetrationof flying
objectsand the anchoringat the perimeter.The bagscouldbe
fabricatedon earthcompletewitha floorand _ numberof airlock
alreadyformedin th? wallsof the bag.
g. Theair bagsmentionedin item8 would supplythe tensilestrength.
Theconcretecastwithinthe annuluswouldprovideresistanceto
penetrationand radiationprotection.
I0. We don'tknowhow firmthe rock structureison the moon, or how deep
isthe loosetop material. Unlessan enclosedtube is constructedwith
pressurein all directions(therebyeliminatingany vectorforcesin
the verticaldirection)we couldlookforwardto beingforcedto remain
deepbelowground.
11, Air bags,in concertwithconcrete,couldprovld¢a viablealternative
givingus an abovegroundstructurewhichwouldbe stable. Geometric
shapesand sizeswouldhaveto be carefullystudied,
11 Lunar Concrete:Text
19890U1689-013
CONCLUSION
The experimentaldata discussed in this paper are significant for lunar-base
constructionwith concrete. Having studied the effect of vacuum on
concrete, we find that additional safety margins are not needed for vacuum
use. Additonal future inquiry should be focused on ueveIoping structural
options with concrete for lunar habitation.
ACKNOWLEDGEMENTS
rhis work was supported by the U.S. Department of Energy. The help received
from The Zia ConKoany,Los A1amos, New Mexico, is appreciated by the authors.
R. W. Higgins of the LANL was a team member of this experimentaleffort.
W. E. Fox, also of LANL, brought up first the problem of vacuum's effect on
concrete's strength to H. S. Cullingfordwho later led this work.
REFERENCES
Cullingford,H. S. and W. E. Fox (1980), in Proc 16th Annual Symposium,
American Vacuum Society, New Mexico Chapter.
Cullingford,H. S., M. O. Keller, and R. W. Hlgglns (1982), J. Vacuum
Science Technology,Vol. 20, No. 4.
Double, D. D. (1981),Nature, 289, p. 29.
12 Lunar Concrete:Text
|
1989001689-014
Kaldis, E. (Ed) (1980), Current Topics in Materials Science, Vol. 5, North-
Holland PublishingCompany, New York.
Lin, T. D. (19B4), in Lunar Bases and Space Activities of the 21st Century,
p. 381, Lunar and Planetary Institute, Houston.
Lott, J. L. and C. E. Kesler (1967), Material Res. Std., p. 375.
Michaelis, M. M. (1978), Vacuum, Vol. 28, No. 8/9.
Perkins, W. G (1973), J. Vacuum Science Technology,Vol. 10, No. 4.
Roy, D. M. (19B7), Science, Vol. 235, p. 651.
Roth, A. (1976), Vacuum Technology, North-HollandPublishing Company,New
York.
l_ Lunar Concrete : Text
1989001689-015
FIGURES
Figure I Layout of vacuum pumping chamber for concrete samples•
Figure 2 Sequence of testing for typical control (air cured) and test
(vacuum treated) cylinders.
Figure 3 Water content of concrete based on dry mass and compressive
strength for air-cured and vacuum-treatedcylinders.
14 Lunar Concrete:Te_t
1989001689-016
e1989001689-017
CONTROLCYLINDER
CAST CURE WEIGH CURE WEIGH
Ill m
• • v
WATER AIR BREAK
TESTCYLINDER
CAST CURE WEIGH CURE WEIGH VACUUM WEIGH
Y • • _1'
WATER AIR TREAT BREAK
TIME
Figure 2
eT.
7' v^G_u,-. v^_, .-, v^_._.-, vAo_
i OOMPRE881VERTREN_TH _ Vf__ATEO ,I I I I I , I
o 40 8O _o leo 200 240 elm
T1ME(OAYS)
FIQURE$ 08071leO.ART;1
1989001689-018
DISCLA.I_[ER
This report was prepared as an account of work sponsored by an agency of the
United States Government. Neither the United States Government nor any agency
thereof, nor any of their employees, makes any warranty, express or implied, or
assumes any legal liability or responsibility for the accuracy, completeness, or use-
fulness of any information, apparatus, product, or proceu disclosed, or represents
that its use would not infringe privately owned rights. Reference herein to any spe-
cific commercial product, process, or service by trade name, trademark, manufac-
turer, or otherwise does not necessarily constitute or imply its endorsement, recom-
mendation, or favoring by the United States Government or any agency thereof.
The views and opinions of authors expressed herein do not necessarily state or
reflect those of the United States Government or any agency thereof.
1989001689-019


Lunar concrete for construction

Feasibility of using concrete for lunar-base construction has been discussed recently without relevant data for the effects of vacuum on concrete. Our experimental studies performed earlier at Los Alamos have shown that concrete is stable in vacuum with no deterioration of its quality as measured by the compressive strength. Various considerations of using concrete successfully on the moon are provided in this paper along with specific conclusions from the existing data base. 10 refs., 3 figs., 2 tabs

Cullingford, H. S.

Keller, M. D.

UNT Digital Library

A major purpose of the Techni-cal Information Center is to providethe broadest dissemination possi- -ble of- information contained inDOE’s Research and DevebpmentReports to business, industry, theacademic community, and federal,state and local governments.Although a small portion of thisreport is not reproducible, it isbeing made available to expeditethe availability of information on the. research discussed herein. ~‘1Pr@LUNAR BASES & SPAICE$vCTMVITMESoh!THE 2tSt ICENITLJRY/\LA-UR--88-2405April 5 - 7, 1988 DE88 014391Westin Galleria HotelHouston, Texas( LUNAR CONCRETEFOR CONSTRUCTIONHatice S. Cullingford***and M. Dean Keller;y,,:,,!*NASA/Johnson Space Center, Houeton, TX 77058,:,,>(,.,.,:,●*LOS Uamos National Laboratory, Loa Uamos, NM 87545.$,,:,.,,,,/:,,,+.‘%:$;*Symposium sponsored by NASA, AlAA, the Lunar & Planetary Institute, theAmerican Geo h sical Union, the American Nuclear Society, the Americanrisociety of Clv I ngineers, the Space Studies Institute and the National SpaceSociety.. .LUNAR CONCRETE FOR CONSTRUCTIONHatIce S. CullingfordNASA/.JohnsonSpace CPnter, Houston, TX 77058M. Dean KellerLos Alamos, National Laboratory, Los Alamos, NM 87545Feasibility of using concrete for lunar-base construction has been discussedrecently without relevant data for the effects of vacuum on concrete. Ourexperimental studies performed earlier at Los Alamos have shown thatconcrete Is stable in vacuum with no deteriorutlon of its quality asmeasured by the compressive strength. Various considerations of usingconcrete successfully on the moon are provided In this paper along withspecific conclusions from the existing data base.INTRODUCTIONConcrete IS probably the most widely used of all the man-made materials ofconstruction. It does not require expensive, hlgh-temperature shape-form!ngprocesses; develcrps its strength at ambient temperatures; has low densityAnd high thermal and electrical Insulation properties; and Is noncombustibleand generally nontoxic (Oouble, 1981). Based on a historically-long1 Lunar ConcrOtw:r@itsuccessful experience with concrete, It is natural thathave been suggested by Lin (1984) and others.Concrete is by definition a poljphase material that consaggregate connected by a matrix of hardened cement (LottAccording to a scenario proposed by Lin, cement could beunar appllcaclonssts of particles ofand Kesler, 1967).obtained by high-temperature processing of lunar rocks while aggregates would be obtained byphysical processing of lunar recks and soils (Lln, 1984).The purpose of this paper is to discuss the authors’ experimental work withconcrete as it relates to lunar base construction.NOVEL TESTING PROGRAMVery little information exists in the vacuum or concrete literature on thebehavior of concrete in vacuum even though there has been a continuedInte-est over the years in using concrete for vacuum applications. On theother hand, the stability of concrete in vacuum Is intuitively questionedwithout data (Cullfngford and Fox, 1S80). Because there was a need to knowthf?vacuum’s effect on concrete’s strength for a linear-accelerator line atthe Los Aiamos National Laboratory (LANL), we designed earlier a testprogram to investigate both outgass!ng and compressive strength of concreteIn high vacuum (Cullingfordet al., 1982).2Clutgassingcharacteristics of vacuum materials are typically reported in thevacuum science literature (for example, Perkins, 1973). Our study ofconcrete, however, involved a multidisciplinary trea~nt with anengineering approach to the problem of concrete’s behavior In vacuum. Tobegin with, all concrete used was prepared as a mix given In Table 1; thelocal aggregate with the composition shown in Table II came from the SanIldefenso Pueblo. Relevant engineering standards were applied for concretepreparation, curing, and testing. (See Cullingford et al., 1982). Concretesamples thus prepared (cylinders of 6-inch diameter by 12-inches high) weredesignated by “test” or “control.” The test cylirders were placed in hlgh-vacuum environment for specified periods of time after air curing while thecontrol cylinders were not.Figure 1 shows the experinmtal vacuum apparatus for the outgassing studies.The clean-system-base pressure was 3x1o-6 torr (3.99x1O-4 Pa) after Ml-hpumping time. The test program involved a progression Df air curing,weighing, vacuum treatment, weighing, and then break’strength as represented in Figure 2. All tests invo’for a more representative average behavior. This ISbecause of the nonhomogeneousnature of concrete.ng for compressiveved multiple cylindersan important pointMass loss, compressive strength, and outgassing wasure’ments were madeduring the test program. An increase in compressive strength with time isobserved, reaching an equilibrium value of 6500 psi with or without vacuumexposure (Cullingford et al., 1982). (See Figure 3.) Significance of this3 Luntr Concrets:lcxtTABLE 1. CONCRETE DESIGN MIX.—.—————. .——..—— _—— — .. ——:——— _——_— — .Material Mass(lb)Percentage(%)Mater 2.0 7.05Portland Cement 4.1 14.47Fine Aggregate 9.0 31.54Coarse Aggregate 13.3 46.94Total 28.3 100.00—— —4 lunar Concrete: lgxtTABLE II. COFIPOSITIONOF LOCAL AGGREGATE—Fine Aggregate 0.25-0/75 in. 0.75-1.50 in.Quartzite 2Acid Volcanic 16Granite 10Basic Volcanic 1Quartz 57Feldspar* 9Chert** 3Residue ~Total 100whereGranltqSI02 77.0A1203 12.0Fe203 0.8FeO 0.9MgoCaO 0.8Na20 3.2K20 4.9H20 0.3Other 0.1BasicVolcanic49.115.75.46.46.29.03.11.51.62.045201384100AcidVolcanic75.612.71.20.340.120.594.04.60.460.39362322117J100Quartzit~97.C51.391.250.130.18● Feldspar is assured to be 50% KAlS1308 and 50% NaA1Si308.●*Chert Is predominately SIOZ.result is that structures for vacuum use can be designed without additionalsafety margins.The predominant pumped species in concrete outgassing was not a dlatomicgas, but water vapor as studied by mass spectrogram of th~ residual gas inthe test chamber (Cullingford et al., i982). During the first several daysof pumping, the outgnssing rate is approximately IO-6 torr.L/cm2.s. Theempty chamber throughput, at this time, Is about three orders of magnitudelowtr than the gross throughput with concrete samples in the chamber.The mass-loss information was reduced to water content as percent ofconcrete dry mass and is also plotted In Figure 3. Concrete became strongeras It aged. A faster drying rate was observed, as expected, under vacuumexposure. A final water content of 6.6 and 4.93% was calculated on dry-massbasis for the control and test samples, respectively. The total amount ofwater lost from the concrete cylinders was 0.13 and 0.35 1~/ft2 for controland test cylinders, respectively. Thus, about 2.7 times the mass of waterwas released overall under vacuum treatment without a reduction incompressive strength. The next section discusses further the effect ofvacuum on concrete’s water.VACUUM EFFECT ON CONCRETE’S HATERMater is present in concrete in three states: chemically bonded water inthe hydration product, adsorbed water on the surface of gel particles, andcondensed water in the capillary pores. Mhen water is added to a mixture ofPortland cement and aggregate to prepare concrete, hydration reactions occurbetween calcium silicates and the water. This hydration process continuesfor several days, and the concrete becomes stronger and harder. The dryingphase during the air cure involvt?srelease of the free (not chemicallybound) water from the concrete (Lott and Kesler, 1967).The Los Aldmos data show that vacuum exposure produced faster release ofthis free water from the concrete samples. However, the fact thatcompressive strength does not worsen under vacuum treatment suggests thatcement dehydration reactions do not occur. In addition, a constant rate ofmisture loss (0.04% per day) was experienced during the early part ofvacuum exposure regardless of the length of air clming period preceedlng.(See Figure 3.)The water evaporation rate corresponding to this constant rate ofevaporation under vacuum is 3.97x10-8 g/s.cn#. On the other hand, thecontrol samples underwent an evaporation rate of o.92x1o-8 g/s.cm2. Theserates were compared with the calculated rate of free evaporation of water atthe test conditions from the following equation derived from the kinetictheory of gas~s (Roth~ 1976; KaldW 1980).H = 5.83’ 10-2a Pv(M/T)-l/2where H ■ rate of evaporation (g/s.cm2),n ■ evaporation coefficient (1.0 for free evaporation),Pv ■ saturation vapor pressure (torr),Lunar Concrct@:TastM = molecular weight, andT = su~face temperature (K)This comparison showed that an evaporation coefficient of 1.59x1O-7 isattributable to the vacuum’s effect on concrete.Finally, the evaporation rates calculated for concrete in air or vacuum (inthe order of 10-8g/s.cm2) suggest a small surface cooling and, thus. littleuncertainty in the surface temperature of concrete (Kaldis, 1980). Thisassures a higher confidence in the constant-temperature analysls of theconcrete data.DISCUSSIONThe experlmenttl data obtained at Los Alanm on concrete are significant inplanning for lunar construction with concrete. The following specificconclusions are derivable from our study.● Concrete is stable In vacuum with no deterioration of concrete quality asmeasured by compressive strength= (Ours was about 65~ Psi.). Mater loss from the concrete cylinders was 0.13 and 0.35 1~/ft2 forcontrol (without vacuum exposure) and for test (with vacuum exposure)samples, respectively.8 Lunar Concrote:Tast. An evaporation coefficient of 1.59M1O-7 is attributable to the vacuum’seffect on concrete during constsnt rate of drying.. An outgassing rate of 1o-6 torr.1/cm2.s was observed after 73-h vacuumpumping. The predominant gas species was water vapor.● A high vacuum of ZXIO-4 torr was maintained with the mechan’system used in the experimental apparatus.cal pump-rigVarious considerations of using concrete on the moon are listed below.1. The moon gravitation is less than that of the earth. Thereforeconcrete would be better able to handle stresses of large structures.However the forces would not always be acting In the ways that we areaccustomed to.2. Any dome structure on the mon would probably have pressure on theinside and vacuum on the outside. The dome would therefore have to actIn tension. However, concrete is weak In tension.3. Reinforcing would then require the manufacture of steel on, or shipmentof steel to the moon. Fiber reinforcing, especially of a type thatcould be manufactured locally, would aid in providing tensile strengthfor concrete.9 Lunar Concr@tO;~ext4. Assume the pressure inside a dome is1440 psf of pressure exterior to theUith the moon gravity as it 1s, thisabout 10 psia. This would requiredome to resist by “dead weight.”would be a high backfill over thedome. The anchoring problem around the perimeter would have to besolved.5. Excavated underground with lined walls would be another possibility.This would also offer protection from meteroids which do not burn updue to lack of atmosphere. A combination of cement, lunar rocks andsoils, and fiber reinforcing could provide a coating on walls forprotection against rock slides.6. At entrances and shafts, preplaced aggregate could be formed and agrout be pumped next into the voids to construct various concreteshapes. Consideration will have to be given to shapes to assure thatthe low lunar gravity and the Internal pressure are acting to p;ace theconcrete in compression.7. Fom enclosureslost before thewould have to be air-tight to assure that Watel” Is nothydration process is complete. Vacuum would then bedirected so that moisture could be captured when it is withdrawn fromthe hardened corcrete.8. Concrete can be formed by using an air filled dome. If two domes areconstructed one within the other so that they are concentric, forex~le, by about two feet; the interior air bag could be inflated to10 Lunar Concrotc:Toxtabout 10 psia with the differential between the inner and the outer bagto be about 2 psia. Straps could be used so that the bags wI1l alwaysremain separated by about Z feet. Concrete can then be placed in theannu’withbag.us between the two bags. Concrete operations can be carried outn the Inner bag while the lunar aggregate Is also ml~?ed Inside theThe water needed could be also manufactured Inside. Problems tosolve Include the breaking of the bag material by penetration of flyingobjects and the anchoring at the perimeter. The bags could befabricated on earth complete with a floor and a number of airlockalready formed in the walls of the bag.9. The air bags mentioned in item 8would supply the tensile strength.The concrete cast within the annulus would provide resistance topenetration and radiatiorlprotection.10. Ue don’t know how firm the rock structure is on the moon, or how deepis the loose top material. Unless an f!nClOSed tube is constructed withpressure in all directions (thereby eliminating any vector forces inthe vertical direction) we could look forward to being forced to remaindeep below ground.11. Air bags, in concert with concrete, could provide a viable alternativegiving us un above ground structure which would be stable. Geometricshapes and sizes would halveto be carefully studied.11 Lunar Concreto:Tc~tCONCLUSIONThe experimental dat~ discussed in this paper are significant for lunar-baseconstruction with concrete. Having stud{ed the effect of vacuum onconcrete, we find that additional safety margins are not needed for vacuumuse. Additonal future inquiry should be focused on developing structuraloptlollswith concrete for lunar habitation.ACKNOWLEDGEMENTSThis work was supported by the U.S. Department of Energy. The help receivedfrom The ZR. H. Higg’Id.E. fox,concrete’sa Company, Los Alamos, New Mexico, is appreciated by the authors.ns of the LANL was a team member of this experimental effort.also of LANL, brought up first the prcblem of vacuum’s effect onstrength to H. S. Cullingford who later led this work.REFERENCESCullingford, H. S. and W. E. Fox (1980), in Proc 16th Annual Symposium,American Vacuum Society, New Mexico Chapter.Cullingford, H. S., d. D. Keller, and R. W. Higgins (1982), J. VacuumScience Technology, Vol. 20, No. 4.Double, D. 0. (1981), Naturq, 289, P. 29.12 Lunar Concrotc:ltntKaldis, E. (Ed) (1980), Current Topics in Materials Science, Vol. 5, North-Holland Publishing Company, New York.Lin, T. D. (1984), In Lunar Bases and Space Activities of the 21st Century,p. 381, Lunar and Planetary Institute, Houston.Lott, J. L. and C. E. Kesler (1967), Material Res. Std., p. 375.Michaells, M. M. (197G), Vacuum, Vol. 28, No. 8/9.Perkins, Ii.G (1973), J. Vacuum Science Technology, Vol. 10, No. 4.Roy, 0. M. (1987), Science, Vol. 235, p. 651.Roth, A. (1976), Vacuum Technology, North-Holland Publishing Company, NewYork.13FIGURESFigure 1 Layout of vacuum pumping chamber for concrete samples.Figure 2 Sequence of testing for typical control (air cured) and test(vacuum treated) cyllnders.Figure 3 Water content of concrete based on dry mass and compressivestrength for air-cured and vacuum-treated cylinders.14.NASA-S-88-01246THERMOCOUPLE GAUGE\ . ~PYREX VACUUM CHAMBERTUREK3MOLROUGHIMG-CDIAPHRAGM GAUGESCONTROL CYLINDERCAST CURE WEIGH CURE WEIGHWATER AIR BREAKTESTCYLINDERCAST CURE WEIGH CURE WEIGH VACUUM WEIGHWA’lER AIR TREAT BREAKTIMEFigure2OOWRES8NE STRENGTH 4 VAW TREATEOO AIROIMEO1 I .i .—L_L--l,ooo71160nART;lDISCLAMERThis repfi was preparedw tn sccountofwork qmntord by ●n agency of theUniM Stdea Government. Neither he UnitedStatwGovernmentnor ●ny ●gencythcmf,nor ●ny of their employees, makes any warranty, oxpruu or implied, orassumti any I@ liability or responsibility forIhcaczurmy, mmplotenas, or use-fulnms of tfiy information, appar~tu~ pduct,orpnxxu diwld, or represwmthat its usc would not infringe privately owned rlghc. Rafercn=herein10anysp-cificcommercialpralucl,pr~, orwwice by trade rmma, trademark, manufac-turer, or otherwise doss not necaasarily canslitute or imply its endorsement, ramm-mendation, or favoring by the ( Initcd Smt- Government or My agency thereof.The views and opinions of authort expreuod herein do not noowurily state orreflect themeof the UnitedSt~loaGovernmentoranyagencythereof.

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Lunar concrete for construction

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