Blast-resistant characteristics of ultra-high strength concrete
and reactivepowder concreteNa-Hyun Yia, Jang-Ho Jay Kima,,
Tong-Seok Hana, Yun-Gu Chob, Jang Hwa LeecaSchool of Civil and
Environmental Engineering, Yonsei University, Engineering Building
#A, 134 Shinchon-dong, Seodaemun-gu, Seoul 120-794, South
KoreabMaterial Division, Hyundai Institute of Construction
Technology, Mabuk-dong, Gihung-gu, Yongin-si, Gyunggi-do 446-716,
South KoreacStructural Engineering & Bridges Research Division,
Infrastructure Research Department, Korea Institute of Construction
Technology, 1190, Simindae-Ro, Ilsanseo-Gu, Goyang-Si,Gyunggi-do
411-712, South Koreaarti cle i nfoArticle history:Received 7
October 2010Received in revised form 2 September 2011Accepted 28
September 2011Available online 29 November 2011Keywords:Ultra-high
performance concrete (UHPC)Ultra-high strength concrete
(UHSC)Reactive powder concrete (RPC)Material
propertiesBlast-resistant capacityANFO blast chargeTNT blast
chargeabstractRecent advances in nanotechnology research have been
applied to improve the durability,serviceabil-ity, andsafetyof
ultra-highperformanceconcrete(UHPC). Furthermore,
improvementsinthecom-pressivestrengthof
concretehaveallowedconcretestructural member sizeandself-weight
tobesignicantlyreduced,
whichhasinturnresultedincostreductionandstructural
aestheticenhance-ment. Amongmany UHPCs
currentlyavailableonthemarket,themostrepresentativeones
areultra-highstrengthconcrete(UHSC)andreactivepowderconcrete(RPC).
EventhoughUHSCandRPChavecompressivestrengthsofover100 MPa,
theirsafetyhasbeenquestionedduetopossibleultra-brittlefailure
behavior and unfavorable cost-to-performance efciency. The
blast-resistant capacities of
UHSCandRPCwereexperimentallyevaluatedtodeterminethepossibilityofusingUHSCandRPCincon-crete
structures susceptible to terrorist attacks or accidental impacts.
Slump ow, compressivestrength, splittensilestrength,
elasticmodulus, andexurestrengthtestswerecarriedout. Inaddi-tion,
ANFOblasttestswereperformedonreinforcedUHSCandRPCpanels. Incidental
andreectedpressures, as well as maximum and residual displacements
and the strains of rebar and concrete weremeasured. Blast
damageandfailuremodes of thereinforcedpanel specimens wererecorded.
OurresultsshowedthatUHSCandRPChavebetterblastexplosionresistancethannormal
strengthcon-crete. Thestudyresultsarediscussedindetail. 2011
Elsevier Ltd. All rights reserved.1. IntroductionTherecent
construction trendsof building super-span bridgesand mega-height
high-rises mandate the use of ultra-highperformance concrete (UHPC)
because of its outstanding safety, ser-viceability, durability,and
economical advantages[1,2]. Thecon-structionof newandoldconcrete
structures using UHPCcanimprove their service life beyond 100 years
with minimal mainte-nancerequirementsandlowlifecyclecosts[1,3].
Furthermore,recent ndings in nano-material science have been used
to improvethecompressivestrengthof
concretewhilesimultaneouslyreducingmember size and self-weight,
resulting in cost reduction and struc-turalaestheticenhancement.
UHPCsaredenedascementitiouscompositeswithsuperiormaterialpropertiesthatcanwithstandcompressive
stresses of up to 150 MPa and tensile stresses of up to8
MPawhileexhibitingstrain-hardeningbehaviorunderuniaxialtension
[1,4,5]. The extremely low permeability of UHPC, attribut-able to
its dense matrix, allows it to be used as a waterproong layerin
bridge decks [6] and a non-penetrable cover protection for
rein-forced concrete (RC) structures under marine environments
[79].UHPCis the mainmaterial inthe
non-reinforcedSeon-Yufootbridge,a pedestrianbridge inKorea withthe
worlds highest slenderness ra-tio (120 mspan to 130 cmdepth) [8].
Among many UHPCs availableonthemarket,
ultra-highstrengthconcrete(UHSC)andreactivepowder concrete (RPC)
are the most widely used [1]. However,
be-causeoftheirultra-highstrengthsandmanufacturingcosts,
theuseofUHSCandRPChasbeenquestioned, withconcernsraisedabout
possible ultra-brittle failure and unfavorable cost-to-perfor-mance
efciency. This study was performed to evaluate the blastresistance
capacities of UHSC and RPC to determine whether thesematerials are
suitable for use instructures susceptible toterrorist at-tacks or
accidental impacts.In2009, theKoreanbuildingcodewas
modiedtorequireterror-resistant designs for any high-riseslocated
within the citylimits of Seoul with an above-ground height of over
200 m or 50or more oors above ground [10,11]. This code regulation
reectsthepublicconcern regarding
possibleterrorattacksonbuildingsandstructuresinKorea.
Becauseoftheultra-highstrengthsandenergyabsorptioncapacitiesofUHSCandRPC,
theyareoptimal0950-0618/$ - see front matter 2011 Elsevier Ltd. All
rights reserved.doi:10.1016/j.conbuildmat.2011.09.014Corresponding
author. Tel.: +82 2 2123 5802; fax: +82 2 364 1001.E-mail address:
[email protected] (J.-H.J. Kim).Construction and Building
Materials 28 (2012)
694707ContentslistsavailableatSciVerseScienceDirectConstruction and
Building Materialsj our nal homepage: www. el sevi er . com/ l ocat
e/ conbui l dmatmaterials for use in structures that are potential
targets of terrorattacksoraccidental impacts. However,
becauseUHSCandRPCarefairlynewmaterials,
theirblast-resistantcapacitieshavenotyet been investigated in
detail. To correctly and efcientlyincorporate UHSC and RPC into a
protective design scheme, theirblast-resistant capacities needtobe
known. Therefore, inthisstudy,
wefocusedonevaluatingtheblast-resistantcapacitiesofUHSCandRPCdevelopedatHyundaiEngineeringandConstruc-tion
Co. in Korea. The static material properties of UHSC and RPCwere
measured by performing slump ow, compressive
strength,splittensilestrength,exurestrength,andelastic
modulustests,andANFOblast testswerecarriedout
onreinforcedUHSCandRPC panels to assess blast-resistant capacity.2.
Previous UHSC and RPC studies2.1. Material research
studiesSincetheinitial development of UHSCandRPCintheearly1980s
inDenmark[4,12], numerous studies havebeencarriedTable 1Mix
proportion design of normal strength concrete (NSC).Max. size of
coarseaggregate (mm)Target strength(MPa)Slump(mm)W/B (%) S/a (%)
Unit water(kg)Unit binder(kg)Unit ne aggregate (kg) Unit
coarseaggregate (kg)AE admixture (kg)Cement Fly-ash S1 S225 24 100
49.8 47.7 163 294 33 616 264 957 2.45Table 2Mix proportion design
of ultra-high strength concrete (UHSC).W/B (%) lessthanS/a (%)
lessthanUnit water (kg) lessthanUnit binder (kg) lessthanUnit ne
aggregate (kg) lessthanUnit coarse aggregate (kg)less thanAE
admixture (%)range of20 39.1 140 1300 450 700 13Table 3Mix
proportion design of reactive powder concrete (RPC).W/B (%)
lessthanCement (kg)less thanUnit water (kg)greater thanSilica fume
(%)range ofUnit ne aggregate (kg)range ofFiller (2.2200 lm)
(kg)greater thanAdmixture (%)range ofSteel ber(%)20 800 200 1030
8001000 200 13 2Fig. 1. Photos of ow test for UHSC and RPC: (a)
UHSC slump-ow test, (b) RPC ow table test.N.-H. Yi et al. /
Construction and Building Materials 28 (2012) 694707 695out to
evaluate and improve these materials. Due to their extraor-dinary
strength and energy absorption capacity compared to
con-ventionalconcrete,
UHSCandRPChaveattractedstronginterestfromresearchersinothereldsaswell
[1,4,5]. AUHSCmixturecontains homogeneous silica aggregates and
cement-replacing sil-ica fume binders, which are responsible for
the incredible strengthof this material [4,13,14]. RPC is
reinforced with special short steelbers to improve its ductility.
Furthermore, UHSC and RPC both
re-quirehightemperaturecuringtoobtainhighearly-agestrength[2,13,1517].Numerous
studies to improve the material properties of UHSCand RPC have
resulted in the current availability of various UHSCsand RPCs with
compressive strengths ranging from 120 to 400 MPa[1,12,14]. UHSCs
and RPCs with tensile strengths ranging from 8 to30 MPa and elastic
moduli ranging from 60 to 100 GPa have alsobeen developed
[1,5,12,14]. The effects of curing on the compres-sive strength of
UHSC and RPC according to curing age have beeninvestigated[4,6].
Typical stressstrainandexural stress-dis-placement
relationshipsforUHSCandRPChavebeenproposedand compared to those of
typical high strength concrete for designapplications[1,18,19].
Recently,
stressstrainrelationshipsunderdynamiccompressivestrainratewerereportedfor
bothUHSCand RPC [2025]. Yang and Joh (2010) predicted the exural
capac-ity of plain UHSC beams using modied ACI-recommended
equa-tions andHableetal. (2006)proposedmaterial property
modelsbasedonexperimental data[6,26]. TheabovementionedUHSCand RPC
studies indicate that the material properties and behaviorof UHSC
and RPC can vary according to mixture proportions, curingFig. 2.
Photos from compressive strength and elastic modulus tests: (a)
compression test, (b) elastic modulus test.050100150200250NSC UHSC
RPCCompressive Strength
(MPa)010,00020,00030,00040,00050,00060,000Elastic Modulus
(MPa)Compressive StrengthElastic ModulusFig. 3. Average compressive
strength and elastic modulus test results of NSC, UHSC, and
RPC.Table 4Poissonsratio, shearmodulusofelasticity,
andbulkmodulustestresultsof NSC,UHSC, and RPC.Specimen Poisson
ratio Shear modulus ofelasticity, G (GPa)Bulk modulus, K (GPa)NSC
0.17 6.99 8.13UHSC 0.22 21.8 31.1RPC 0.19 21.3 26.9ConcreteSteel
fiberFig. 4. CohesivecrackmodelofRPC[21]:(1)Stressfreezone,
(2)Fiberbridgingzone, (3) Micro-crack zone, (4) Undamaged zone.696
N.-H. Yi et al. / Construction and Building Materials 28 (2012)
694707conditions, and loading rates. Therefore, in this study, we
directlymeasured the blast-resistant material properties of UHSC
and RPC.2.2. Blast resistanceConcrete structures with blast
protection must have sufcientstructural strength, stiffness, and
energy absorption capacity to re-sistblastloads.
Concreteisgenerallyknowntohavearelativelyhigherblast-resistantcapacitythanotherconstructionmaterials[27,28],
but the blast-resistant capacity of concrete structures de-signed
without blast protection needs to be improved by retrot-ting during
their service life [29,30]. Retrotting by attachingextra structural
members or supports to increase blast resistanceis inefcient,
because it eliminates useable space and incurs extraexpenses
[27,28,31]. Furthermore, the retrotting method does
notgreatlyimprovetheoverall structural resistanceagainst
ablastload. A more feasible method of blast resistance retrotting
wouldbe to use advanced materials such as UHSC or RPC [30].Past
studies have shownthat beams andslabs
constructedusinghighstrengthconcrete(HSC)havebetterimpactresistantcapacity
than beams and slabsmade using normalstrength con-crete (NSC).
However, due to social and governmental
constraints,thesetypesofcomparisonstudieshavenotbeencarriedovertostructural
blast resistance improvement studies, resulting in a lackof
dataconcerningtheblast-resistant capacityof HSC[32]. Re-cently,
several researchers have pursued static and impact capacitystudies
on ber-reinforced concrete members under time-depen-dent
loadingconditions[33,34]. However, fewimpact or blast-loaded UHSC
or RPC studies have been performed, and data fromthe studies that
have been performed are not publically available.3. UHSC and RPC
material propertiesIn this study, we evaluated the material
properties of UHSC andRPCunder staticloading.
Theselectedmixproportionsof NSC,UHSC, andRPCaretabulatedinTables13,
respectively. Specialshort steelbersat2%volumewere
usedintheRPCspecimens.Duetothepatent copyright of thedeveloper of
thematerials,Hyundai EngineeringandConstructionCo.,
themixproportionsof RPC and UHSC are listed as range values. The
specic mixturecontentsarereportedintheKoreanpatent[35].
UHSCandRPCspecimens were steam-cured for 3 days at 90 C.3.1. Slump
ow and ow
testsUHSCandRPCmusthavesufcientworkabilityforconstruc-tionusage.
Forworkabilitytestingoffreshconcretemixes,
con-creteslumpowandmortar
owtabletestswerecarriedoutaccordingtoKSF2594(2009)andKSL5111(2007)standards,respectively[36,37].
UHSCandRPCslumpowsweremeasuredby averaging the maximumowdiameter
and perpendiculardiametertothemaximumowdistanceassuggestedbytheKSF
2594 (2009) and KS L 5111 (2007) standards [36,37]. The slumpowsof
UHSCandRPCwere635and200 mm, respectively, asshownin Fig. 1.3.2.
Compressive strength and elastic modulus testsCompressive strength
tests were carried out on 100 200 mmcylindrical specimens according
to KS F 2405 (2005) as shown inFig. 2a [38]. The average
compressive strengths of the NSC, UHSC,and RPC specimens were 25.6,
202.1, and 202.9 MPa, respectively,as shown in Fig. 3. The
compressive strengths of the UHSC and
RPCspecimenswereapproximately7.9-foldgreaterthanthatof
theNSCspecimen. Theelasticmodulusofeachspecimenwasmea-sured using a
compressometer according to the KS F 2438 (2002)standard as shown
in Fig. 2b [39]. The average elastic modulus ofthe NSC, UHSC, and
RPC specimens was 16300, 53143, and50511 MPa, respectively, as
shown in Fig. 3. The elastic moduli
ofUHSCandRPCwereapproximately3.093.26-foldgreater thanthat of the
NSC specimen. The UHSC specimen had a higher elasticmodulus than
the RPC specimen for two reasons. Firstly, UHSC has0510152025NSC
UHSC RPCSplit Tensile Strength (MPa)Fig. 5. Split tensile strength
test results of NSC, UHSC, and RPC.Fig. 6. Photos of exural test
for RPC.Fig. 7. Photo of the buried supporting frame setup.N.-H. Yi
et al. / Construction and Building Materials 28 (2012) 694707 697a
higher material rigidity than RPC, because UHSC is denser thanRPC,
andsecondly, RPCismoredeformablethanUHSC, becauseRPCcontainsshort
steel berswhichcreatemultipleinterfaces(similar to voids) in the
material.Test results for Poissons ratio, shear modulus, and bulk
modulusaretabulatedinTable4.
PoissonsratiowasmeasuredusinganextensometeraccordingtotheKSF2438(2002)
standard[39].The average Poissons ratios of the NSC, UHSC, and RPC
specimenswere 0.166, 0.216, and 0.187, respectively, calculated
according tothewidth-to-lengthstrain.
TheUHSCspecimenhadthehighestPoissons ratio, indicating that more
damage can occur in the lateraldirection in this material, leading
to a brittle failure. Due to a steelber bridging effect, the RPC
specimen developed less cracks andhad higher ductility than theUHSC
specimen as shown in Fig. 4.Eqs. (1) and (2) were used to calculate
the shear and bulk modulus,respectively,
usingthemeasuredelasticmodulusandPoissonsratio:G E21 t1K E31
2t2where G is the shear modulus; K is the bulk modulus; E is the
elasticmodulus; and t is Poissons ratio. The shear and bulk modulus
val-uesof UHSCandRPCwere3.03.8-foldgreater
thanthecorre-spondingNSCvaluesasshowninTable4. Inparticular,
thebulkmodulus (volume expansion resistant capacity under
compression)of UHSCwasgreater thanthat of RPC,
indicatingpossiblecata-strophic brittle failure in UHSC.3.3. Split
tensile strengthSplit tensile strength tests were carried out on
100 200 mmcylindrical specimens according to the KS F 2423 (2006)
standard[40]. Theaveragesplit tensilestrengthsof theNSC, UHSC,
andRPC specimens were 2.2, 9.2, and 21.4 MPa, respectively, as
shownin Fig. 5. RPC had a higher split tensile strength than UHSC,
becausethe short steel bers in RPC control crack openings in the
tensilestress direction. Due to the ber crack control effect, the
ductilityof RPC was also signicantly higher than that of UHSC.3.4.
Flexural strength testsAs shown in Fig. 6, tests of the exural
strength of RPC were
car-riedoutonunnotchedprismaticspecimenswithdimensionsof100 100 400
mmusinga4-pointloadingsetupaccordingtothe KS F 2408 (2000) standard
[41]. The load was applied by forcecontrol loading at a rate of 2.4
kN/s. The exural strengths of threeRPC specimens were 33.16, 32.50,
and 33.94 MPa, giving an aver-ageexural strengthof33.20 MPa.
Bendingcracksinitiatedandpropagated at a location approximately 100
mm from the supportFig. 8. Measurement sensor locations: (a)
pressure-meter placement setup photo, (b) strain gauge
locations.698 N.-H. Yi et al. / Construction and Building Materials
28 (2012) 694707asshowninFig. 6,
indicatingacombinedexural-sheartypeoffailure.4. Blast-resistant
capacityWeevaluatedtheblast-resistantcapacityofreinforcedUHSCand
RPC panels under ANFO blast loading. The experiments werecarried
out at the test site of the Agency for Defense
DevelopmentofKorealocatedneartheMilitaryDemarcationLine(MDL).
Twosets of tests, preliminary and main tests, were performed
indepen-dently. In the preliminary test, the required blast charge
weight foranNSCpanel specimenwasestimated. Theblastchargeweightand
standoff distance for the main test were based on the
resultsobtained in the preliminary test. In the preliminary test,
4.08 and15.88 kg of TNT were used as blast charges on a reinforced
NSC pa-nel (acontrol specimen). Afterthepreliminarytest, 15.88
kgofANFO and a standoff distance of 1.5 m were selected for the
maintest.4.1. Blast test detailsA steel frame was buried in the
ground as a xture for specimenplacement as shown in Fig. 7, because
ground surface placementeliminates blast wave
reection[10,11,31,42]. The steel
framewasmadeusing7-mmthickSM520withstiffenersataspacingof250
mmtopreventframedistortionduringblastloading. Thespecimen was
clamped on all four sides with two clamps per sideto prevent
uplifting during the experiment. The panel dimensionswere 1000 1000
150 mm. Two layers ofD10 mesh reinforce-ments with 82 mm spacing in
both directions were placed in theNSC and UHSC panel specimens.
Theyield and ultimate strengthof the D10 reinforcement was 400 and
600 MPa, respectively[30,42]withanominal cross-sectional
areaof71.33 mm2andaunit weight of 0.56 kg/m. Thereinforcement
ratiosof NSCandUHSCspecimenswerethesame, whereas2%volumeof
specialshort steel bers were used in the RPC specimens. The mix
propor-tions of NSC, UHSC, and RPC are tabulated in Tables
13,respectively.Free-eldincidentpressureandreectedpressureweremea-sured
at distances of 5 m and 1.5 m away from the center of thespecimen,
respectively, as shown in Fig. 8a. The reected pressuretransducers
were placed on the top surface of the specimens, at thecenter and
at 230 mm from the center, 1/3 of the diagonal distancefrom the
center to the corner as shown in Fig. 8b. To measure waveimpact
acceleration, anaccelerometer wasattachedonthetopcenter of the
specimens and linear variable differential transform-ers (LVDTs)
were placed on the bottom surface to measure maxi-mum and residual
vertical displacements. Details of
themeasurementsystemset-upareprovidedinFig. 9.
Signalsfromgaugesweretransferredusingltersandampliers, andstoredin
a data acquisition (DAQ) system as digital data [10,42].4.2. Blast
test resultsBlast pressures, deections, strains, and wave impact
accelera-tions of the NSC, UHSC, and RPC panel specimens were
measuredunder blast loading.4.2.1. Surface examination and crack
patternsWhen the tests were completed and safety was insured, the
sur-faces of the specimens were examined. Crack patterns,
fragmenteddimple locations, and gauge survival were assessed. The
NSCFig. 9. Data acquisition system descriptions.Fig. 10. Specimen
appearance before and after the preliminary blast test: (a) before
blasting, (b) after blasting with 4.08 kg TNT, (c) after blasting
with 15.88 kg TNT.N.-H. Yi et al. / Construction and Building
Materials 28 (2012) 694707 699NSC2NSC1NSC2UHSCNo crackUHSC1
UHSC2RPCNo crackRPC1 RPC2(a) (b) (c)(d) (e) (f)(g) (h) (i)NRC :
Normal Strength Concrete, UHSC : Ultra High Strength Concrete, RPC
: Reactive Powder ConcreteFig. 11. Surface crack patterns of
blasted specimens: (a) top of NSC2 specimen (ANFO charge), (b)
bottom of NSC1 specimen (TNT charge), (c) bottom of NSC2
specimen(ANFO charge), (d) top of UHSC1 and UHSC2 specimens, (e)
bottom of UHSC1 specimen, (f) bottom of UHSC2 specimen, (g) top of
RPC1 and RPC2 specimens, (h) bottom ofRPC1 specimen, (i) bottom of
RPC2 specimen.700 N.-H. Yi et al. / Construction and Building
Materials 28 (2012) 694707specimens were photographed before
blasting as shown in Fig. 10a,afterblastingwith4.08
kgTNTasshowninFig. 10b, andafterblasting with 15.88 kg TNT as shown
in Fig. 10c. A drastic differ-ence inthe magnitude of damage
between4.08and15.88 kgTNTblastswasevidentcomparingFig. 10bandc.
However, thedamage to the top surface of the specimen blasted with
15.88 kgof TNT was mostly due to TNT metal capsule fragments rather
thanthe blast pressure. The damage caused by blast fragments is
depen-dent of the fragment shape, mass, initial velocity, standoff
distance,andimpactangleof thefragments[10,11]. Inparticular,
aTNTblast charge that explodes in air creates hundreds of sharp
metalfragments with an initial velocity and impact force dependent
onthe charge
amount.Schematicdrawingsofthetopandbottomsurfacecrackpat-terns of
NSC, UHSC, and RPC panel specimens are shown inFig. 11. All of
these specimens were loaded with 15.88 kg of ANFOcharge except for
the NSC 1 specimen as shown in Fig. 11b, whichwas loaded with 15.88
kg of TNT. The bottom surfaces of NSC spec-imens were
photographedafter loading with15.88 kg TNT asshown in Figs. 11b and
15.88 kg ANFO as shown in Fig. 11c. Seriousshell fragment damage
was observed from TNT loading, but almostnodamagefromANFOloading,
becauseanANFOblastproducespure wave pressure without shell fragment
impact. Well-dispersedturtle-back types of crack patterns were
observed in the NSC spec-imens as shown in Figs. 11b and c and 12a.
Macro-crack lines sim-ilar to a cone prism type of plastic yield
line were observed fromthe center to the four corners, indicating a
two-dimensional (2D)membraneplasticfailuremode.
Itisimportanttonotethatthediagonal shear cracks that
formedonthesidesurfaces of theFig. 12. Photos of bottom surface of
the blasted specimens: (a) NSC, (b) UHSC, (c) RPC.Fig. 13.
Free-eldincident pressure versus time measurements fromthe
pre-liminary test: (a) 4.08 kg TNT, (b) 15.88 kg TNT.Table 5Blast
pressure and impulse measurements from the main tests (15.88 kg
ANFO).Specimen NSC UHSC1 UHSC2 RPC1 RPC2 ConWEPEnvironmentTemp. 5 8
NR 9 NR Humid(%) Up 51 56 NR 39 NR Reected pressureCenterRP_C 1st
(MPa) NR NR 16.92 NR 21.99 17.02RP_C 2nd (MPa) NR NR 25.28 NR
28.1Duration (ms) NR NR 1.176 NR 0.374 1.412Impulse (MPa ms) NR NR
3.87 NR 2.83 2.42230 mmRP_2_1st (MPa) 26.58 NR 18.76 22.62 22.1
16.53RP_2_2nd (MPa) 26.58 NR 18.76 22.62 22.41Duration (ms) 1.212
NR 0.564 0.424 1.524 1.468Impulse (MPa ms) 3.26 NR 3.02 2.03 3.29
0.01Free eld pressure1st Peak (MPa) 0.161 0.249 0.191 0.16 0.191
0.1702nd Peak (MPa) 0.26 0.249 0.191 0.217 0.191Duration (ms) 3.102
3.1 3.194 3.056 3.212 4.628Impulse (MPa ms) 0.23 0.191 0.23 0.229
0.21 0.205NR: Data not recorded due to strain gauge malfunctioning.
RP_C: Reected pressureat the top surface center. RP_2: Reected
pressure at 230 mm location from the topsurface center. CFRP: NSC
retrotted with CFRP sheet.N.-H. Yi et al. / Construction and
Building Materials 28 (2012) 694707 701specimen indicated that the
panel was susceptible to shear failure.This shear
failuresuggestedthat todesignblast-resistant NSCstructures, shear
resistance must be taken into account.We did not observe any damage
or cracks on the top surfaces ofUHSC and RPC specimens as shown in
Fig. 11d and g. These resultsindicated
thattheultra-highcompressivestrengths
ofUHSCandRPCconferredgreaterresistancetoblast loadingthanNSC.
We2observed crack patterns on the bottom surface of the UHSC
spec-imens as shown in Figs. 11e and f and 12b. The crack patterns
weresimilarinappearancetotheyieldlinefailurepatternexpectedbased on
2Dmembrane theory, and the cracks were
mostlymacro-cracksconcentratednearorontheyieldlines. Crackpat-terns
on the bottom surfaces of the RPC specimens are shown inFig. 11h
and i. One-directional multiple chopped macro-cracks bi-sected the
middle of the RPC specimens. This crack pattern was
ex-pectedforRPC, becauseRPCisacementmortarreinforcedwithshort steel
bers; crack control by the bers
preventedcata-strophicmacro-crackpropagations,
resultingintheformationofchoppedmacro-cracks onlyinthedirection
perpendiculartotheprinciple tensile strain direction as shown in
Fig. 12c. Because bothUHSC and RPC specimens failed due to
macro-cracks, it is safe toassume that they failed in a
quasi-brittle manner even under theexuremodebecauseof
theirultra-highcompressivestrengths.The lack of shear cracks on the
specimens led us to conclude thatthe shearcapacities of UHSC and
RPCare sufcient towithstandblasts. In summary, the failure patterns
of UHSC and RPC indicatethat they are much more resistant to blast
loading than NSC andhave superior blast-resistant capacities.
Furthermore, because rel-atively fewer cracks were found in these
specimens than in the NSCspecimens,
itwouldrequirelesseffortandcosttorepairblast-damaged UHSC and RPC
members than NSC members.4.2.2. Blast pressure measurementsWe were
not able to measure the compressive blast pressure
inthepreliminarytest becausemetal capsulefragmentsfromtheTNT blast
impacted and damaged the pressure gauge installed atthe center top
surface of the specimen. Therefore, in the prelimin-ary test, we
measured the pressure from a free-eld incident pres-sure meter
placed 5 mfromthe center of the
specimenandcomparedtheresultswiththosecalculatedusingConWEPsoft-ware.
ConWEP software is an analytical program used to calculatethe blast
loadings of blast pressure, fragmentation, surface impact,etc.
based on Unied Facilities Criteria (UFC) 3-340-01. The pres-sure
comparison results are shown in Fig. 13. The rst peak
pres-sureobtainedfromtheexperimentwassimilarinmagnitudetothat
predicted by ConWEP. However, the second peak of reectedpressures
from the 4.08 kg and 15.88 kg TNT charges were approx-imately 40%
and 56% less than that predicted by ConWEP, respec-tively.
Theseresults indicatedthat reectedpressureis highlydependent on
experimental variabilities and environmental condi-tions,
validatingtheimplementationofamagnicationfactorinthe ConWEP
calculation [11,31]. The experimental data wereinconsistent
duetoexperimental variations andenvironmentalconditions (i.e.,
charge shape, charge angle, wind velocity, humid-ity, etc.) as
shown in Table 5 and Fig. 11. However, the overall blastpressure
data agreed well with the ConWEP results.The free eld and reected
pressures were measured with pres-sure meters for all specimens as
shown in Table 5. A second peakoverpressure followed the rst peak
overpressure at the center ofthe specimen for both reected and free
eld pressures. This couldbe ascribed to the nite time duration of
the explosion of an ANFOcharge, unlike an incidental TNT explosion,
resulting in a relativelyslower detonation speed. Due to the
continuous explosion charac-teristics of an ANFO charge, the
reected and re-reected pressuresare combined, creatingdifferent
appliedpressures andseveralpeak overpressures as shown in Fig. 14.
Because an ANFO chargeof 15.88 kg isequivalent toa TNTcharge
of13.02 kg interms ofblast pressure magnitude, the expected free
eld incident pressureandimpulseofa15.88
kgANFOchargewouldbeapproximately15.9% and 13.5% less than those of
a 15.88 kg TNT charge.The approximate ranges of the expected strain
rates for differ-entloadingconditionsareshownin Fig. 15. Blast
loadstypicallyproduce very high strain rates in therange of
102104s1, whileFig. 14. Reectedpressures versus time measurements
of various topsurfacelocationsfromthemaintest(15.88
kgANFO):(a)thecenter, (b)230 mmradiallocation from the center.Fig.
15. Strain rate ranges for various loading types [43].702 N.-H. Yi
et al. / Construction and Building Materials 28 (2012)
694707ordinary static strain rate is within the range of
106105s1[43].Thestrainraterangemeasuredfromthis blast test was
278457 s1. Inthepreliminarytest,
themeasuredstrainratewasapproximately750 s1,
whichis1.642.7-foldgreaterthanthatfromthemaintests.
Themeasuredstrainratesforblastloadingwere similar to previously
reported strain rates [43]. When a loadwith high strain rate is
applied to a structure, its dynamic mechan-ical properties and
damage mechanisms itself change. Evaluationdata can be used to
characterize the dynamic damage mechanisms.4.2.3. Deection
measurementsInthepreliminarytestsusing4.08and15.88
kgTNTcharges,themaximumverticaldeectionsmeasuredatthecenteroftheNSCspecimens
were7 mmandexceeding25 mm(theLVDTsmaximummeasurement capacity is 25
mm), respectively. TheNSCspecimenwitha 15.88 kg TNTcharge
showedsignicantresidual deection,
butbecausetheLVDTwasdestroyedduringthe experiment, the exact
deection was not measured.Thecenter point deection historiesofNSC
specimens witha15.88 kgTNTand15.88 kgANFOchargeareshowninFig.
16aandb, respectively, whilethecenterpointdeection
historiesoftheUHSCandRPCspecimenswithanANFOchargeof 15.88 kgare
shown in Fig. 16c and d, respectively. The maximum and resid-ual
deectionsof theNSC, UHSC, andRPCspecimensfromthe15.88 kg ANFO
charge were 18.57 and 5.79 mm, 15.14 and5.86 mm, and 13.09 and 5.41
mm, respectively, as shown in Table6 and Fig. 16. These results
indicate that RPC has the best-30-25-20-15-10-5050 50 100 150
200Time (msec)Displacement (mm)TNT 15.88 kg, NSC Max. displacement=
over 25 mmResidual displacement = 12.618 mmOver LVDT
range-20-15-10-5050 50 100 150 200Time (msec)Displacement (mm)ANFO
15.88 kg, NSC Max. displacement= 18.565 mmResidual displacement =
5.790 mm-20-15-10-50510Time (msec)Displacement (mm)UHSC_1UHSC_2ANFO
15.88 kg, UHSCMax. displacement= 10.517 mm, 15.140 mmResidual
displacement = 1.856 mm, 5.860 mm-20-15-10-505100 50 100 150 200 0
50 100 150 200Time (msec)Displacement (mm)RPC_1RPC_2ANFO 15.88 kg,
RPCMax. displacement= 10.730 mm, 13.090 mmResidual displacement =
3.202 mm, 5.410 mm(a) (b)(c) (d)Fig. 16. Center displacement versus
time measurements from blast loading: (a) NSC under 15.88 kg TNT
loading, (b) NSC under 15.88 kg ANFO loading, (c) UHSC, (d)
RPC.Table 6Maximum and residual displacement measurements from
blast loading.Specimen Experiment results
(mm)Max.displacementResidualdisplacementNSC Case 1 Over 25
12.26Case 2 18.57 5.79UHSC Case 1 10.52 1.86Case 2 15.14 5.86RPC
Case 1 10.73 3.20Case 2 13.09 5.41N.-H. Yi et al. / Construction
and Building Materials 28 (2012) 694707 703blast-resistant capacity
followed by UHSC and then RPC. This is areasonableresult
becausetheblast resistanceof RPCissigni-cantly enhanced by the
presence of short steel bers which provideimproved crack-bridging
characteristics and energy absorptioncapacity. In contrast to the
other two types of specimens that arereinforced only with ordinary
rebar, the RPC specimens are proneto having smaller deections and
cracks. Furthermore, it is
impor-tanttonotethatdifferentresultsobtainedfromidentical
speci-mens tested with a 15.88 kg ANFO charge is due to differences
inthetestingconditionssuchashumidity, temperature,
andwind.BecausethespecimenslabeledCase1andCase2weretestedafew
months apart, the Case 1 group data (UHSC and RPC) and theCase 2
group data (NSC, UHSC, and RPC) have different range val-ues.
Manypreviousstudieshavedemonstratedthesensitivityofblasttestresultstoenvironmentalconditions.
ThedifferencesindataforCase1and2(approximately50%difference)arewithintherangeofdifferencesthatcanbeconsideredtobecausedbyenvironmental
conditions.4.2.4. Strain measurementsStrain data are generally
better at reecting specimen behaviorcompared to deection data. The
strains measured in this study aretabulated in Table 7. Because RPC
specimens do not have reinforc-ing bars, steel strain measurements
were only obtained from theNSCandUHSCspecimens.
Thestraindataindicatebottomrein-forcement yielding in all
specimens, with higher strains
occurringinthereinforcementstowardsthecenter of thespecimen.
Themaximumstrains measuredfrombottomreinforcement of theNSC and
UHSC specimens were approximately 28,000 and10,000 le,
respectively, as shown in Fig. 17. These results indicatedthat
smaller displacements occurred in the UHSC specimens thanin the NSC
specimens and conrmed that UHSC has better blast-resistant capacity
than NSC.Concrete strains were measured from six strain gauges
attachedto the bottom and top surfaces (three for each surface) of
the spec-imens. Three strain gauges on the top and bottom surfaces
mea-suredmostlycompressiveandtensilestrains, respectively.
Thebottomcenterconcretestrainswereover16,000 lefortheNSC,UHSC, and
RPC specimens as shown in Fig. 18. The horizontal linedata for the
NSC specimen indicated that the tensile strain
exceededthegaugecapacityanddestroyedthegauge. Comparisonof
thestrains of the NSC, UHSC, and RPC specimens showed that the
strainat the center of the RPC specimen tended to be less than that
of theNSC and UHSC specimens because of the presence of short steel
-bersin theRPCspecimen that controlledcrack opening by
crackbridging. In contrast, reinforcement of the NSC and
UHSCspecimens did not control cracks, but rather caused larger
strainstooccur. Ifaspecimenbehaveselastically,
thenspecimenstresscan be calculated using Hookes Law and strain
data, allowing indi-rect calculation of the strength magnication
factor due to strainrate.4.2.5. Wave acceleration
measurementsSpecimenblast behaviorcanbeanalyzedbasedondataob-tained
from LVDT or accelerometers. Specimen acceleration
mea-surementsfortheNSC, UHSC, andRPCspecimensareshowninFig. 19ac,
respectively. Waveaccelerationswerefoundtorangebetween 1000 and
2500 times gravity (g). However, these acceler-ationmeasurements
aremixedvalues, andrepresent
boththespecimenandimpulseaccelerations. Thesensorinstalledonthetop
concrete surface of the UHSC1 specimen was detached whenblast
pressurewasapplied, givingresultswithimprecisenoise.Therefore, the
UHSC1 data was considered unt for analysis.The NSCand UHSCspecimens
showed similar accelerationbehavior, but the acceleration behavior
of the RPC specimen wasmarkedlydifferent, andwas
characterizedbylargeoscillationsand magnitude. Two factors could
account for this nding. One isthat rebar in the NSC and UHSC
specimens controlled theTable 7Maximum strain measurements from
blast loading.Specimen NSC UHSC1 UHSC2 RPC1 RPC2Steel strainCh. 1
TC 5964 2796 2832 Ch. 2 T2 2052 1549 2192.47 Ch. 3 BC 28,113 6711
7553.6 Ch. 4 B2 4831 3452 3622 Concrete strainCh. 5 TC 11,848 4502
12,821 11,198 NRCh. 6 T1 5336 3479 6243 9247 NRCh. 7 T2 2518 NR
3745 5967 1951Ch. 8 BC NR 16,025 18,081 NR 4903Ch. 9 B1 2581 9768
454 NR 3571Ch. 10 B2 28,274 4692 878 708 2269TC: Top surface
center. T1: 100 mm from the top surface center. T2: 230 mm fromthe
top surface center. NR: Data not recorded due to strain gauge
malfunctioning.BC: Bottomsurface center. B1: 100 mmlocation fromthe
bottom surface center. B2:230 mm location from the bottom surface
center. : Strain gauge not installed.Fig. 17. Reinforcement bar
strain versus time measurements from blast loading: (a)NSC, (b)
UHSC.704 N.-H. Yi et al. / Construction and Building Materials 28
(2012) 694707structural accelerationbehavior(i.e.,
oscillationandmagnitude),but because the RPC specimen was
reinforced only with short steelbers without rebar, it was unable
to control acceleration behavior.Another possible explanation of
the results is that RPC with steelbers is more exible than UHSC,
and thereby absorbs more blast-1400-70007001400210028003500Time
(msec)Acceleration (g)RPC 1RPC 2ANFO 15.88 kg, RPCMaximum
acceleration , RPC1= 2844.6 gMaximum acceleration,RPC 2= 2465.2
g-5000500100015002000250030003500Time (msec)Acceleration (g)NSCANFO
15.88 kg, NSCMaximum acceleration = 1815.5
g-50005001000150020002500300035000 2 4 6 80 3 6 9 12 150 3 6 9 12
15Time (msec)Acceleration (g)UHSC 2ANFO 15.88 kg, UHSCMaximum
acceleration , UHSC1 = Not ReportedMaximum acceleration, UHSC 2 =
1420 g(a)(b)(c)Fig. 19. Specimen acceleration versus time
measurements from blast loading: (a)NSC, (b) UHSC, (c) RPC.Fig. 18.
Concrete strain versus time measurements from blast loading: (a)
NSC, (b)UHSC, (c) RPC.N.-H. Yi et al. / Construction and Building
Materials 28 (2012) 694707 705energy. Even though the acceleration
of the RPC specimen had thelargest magnitude among the three tested
specimens, damping ofthe RPC specimen reduced the oscillation
period by approximately2 ms compared to a 4 ms reduction in the NSC
and UHSCspecimens.The Fast Fourier Transform (FFT) spectrum
analysis results forblast loaded specimens are shown in Fig. 20.
The specimens(NSC, UHSC, RPC) all showedthreeidentical resonant
frequen-ciesunderblastloading, withrst, second,
andthirdmodefre-quenciesof5.197, 10.39, and15.593 kHz,
respectively. However,the magnitude of the amplitude differed. RPC
specimens
hadamplitudesof0.392and0.356foritssecondmodeofvibration,vibratingwithhighaccelerationoverashorttimeduration.
Theshort steel bersof RPCwithout rebar reinforcement makesitvery
exible. Therefore, during its free vibration process, it
oscil-lates withlarger amplitudeandhigher blast
energyabsorbingcapacity.5. ConclusionsIn this study, the material
properties and blast-resistant
capac-itiesofultra-highstrengthconcrete(UHSC)andreactivepowderconcrete
(RPC) were experimentally evaluated. The results showedthat they
have outstanding material properties and blast-resistantcapacities.
The conclusions of this study are summarized asfollows:(1)The
compressive strength, split tensile strength, elastic mod-ulus, and
Poissons ratio values of UHSC and RPC are 3.07.9-fold higher than
the corresponding NSC values. The Poissonsratio of UHSC is 1.2-fold
greater than that of RPC because ofthe short steel bers used in
RPC. RPC has a higher split ten-silestrengththanUHSCbecauseof
thecrack-controllingeffect of the short steel bers.(2)The
blast-resistant capacities of UHSC and RPC were
veriedbyblasttestsusinga15.88 kgANFOchargewitha1.5
mstandoffdistance, applyingablastloadwithstrainrateof278457 s1.
Deection, strain, and accelerometer measure-ments from the blast
tests revealed that UHSC and RPC
panelspecimenshavehigherblast-resistantcapacitiesthanNSCspecimens.(3)Rebar
and short steel bers used in the UHSC and RPC spec-imens,
respectively, negate the brittle material characteris-tics of UHSC
and RPC members, provide sufcient ductility,and confer outstanding
energy absorption and crack control-ling capacities to these
materials.AcknowledgementsThisstudywascarriedoutwithnancialassistancefromtheNuclear
Research and Development Division of the Korea Instituteof Energy
Technology Evaluation and Planning (KETEP) grantFig. 20. FFT (Fast
Fourier Transform) spectrum of the specimens under blast loading:
(a) NSC, (b)UHSC, (c) RPC1, (d) RPC2.706 N.-H. Yi et al. /
Construction and Building Materials 28 (2012) 694707funded by the
Korea government Ministry of Knowledge Economy(No. 2010-1620100180)
andaNational
ResearchFoundationofKorea(NRF)grantfundedbytheMinistryofEducation,
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