Ductal - An Ultra-High Performance Material for Resistance to Blasts ...

1 st Specialty Conference on Disaster Mitigation1ère conférence spécialisée sur l’allégement des désastresCalgary, Alberta, CanadaMay 23-26, 2006 / 23-26 mai 2006Ductal ® - An Ultra-High Performance Material for Resistance to Blastsand ImpactsB. Cavill 1 , M. Rebentrost 2 and V. Perry 31 VSL Australia Pty Ltd, Sydney, NSW, Australia2 VSL Australia Pty Ltd, Melbourne, Victoria, Australia3 Lafarge North America, Calgary, AB, CanadaAbstract Reactive Powder Concrete (RPC) is a cementitious material consisting of cement, sand, silicafume, silica flour, superplastizer, water and high strength steel fibres. The material was developed byBouygues, the parent company of VSL, Lafarge and Rhodia and is marketed under the brand name ofDuctal ® .Ductal ® is almost self-placing, has a compressive strength of 160-200 MPa and a flexural strength of 30-40 MPa. It has exceptionally high-energy absorption capacity and resistance to fragmentation, making itideal for panels and components that need to perform under explosives, impact or shock loads. Theflexural toughness is greater than 200 times that of conventional fibre reinforced concrete.In May 2004, the performance of seven panels was evaluated in two large explosive trials performed atWoomera (South Australia). The panels performed remarkably well, exhibiting high levels of ductility andno signs of fragmentation. In further tests, 100mm thick Ductal ® blast resistant panels have effectivelyresisted explosions from close charge blasts, projectile impacts from ballistic tests, and impacts caused byblast produced fragments using fragment simulated projectile tests.In June 2005, the first Ductal ® protective panels manufactured to provide resistance to blast were suppliedto the Australian Government and installed on an Australian Government building in a high risk,international location.1. Properties of Ductal ® for DesignDuctal ® production in Australia commenced in January 2003. Initially, development and testing of theproduction mix were undertaken by University of New South Wales (UNSW), and are reported in detail inGowripilan et al. (2003). Ductal ® is a family of products with a range of properties, custom formulated foreach application or market segment. The properties shown in this paper represent those properties for theparticular mix utilized for this application.Table 1 lists the properties of Ductal ® used in design. Figure 1 shows a typical stress-strain responseobtained from a compression test, with 100mm diameter by 200mm long cylinders and the stressdeflectionresponse for a typical four-point flexure test from 100×100×500mm prisms.DM-003-1

Table 1. Design properties for Ductal ®Property Standard Heat Treated Ductal ®FluidityASTM C230Between 190 and250mm after 20 dropsCompressive strength AS 1012.9 160 MPaFlexural Tension: Modulus of Rupture AS 1012.11 24 MPaFlexural Tension: First cracking AS 1012.11 20 MPaModulus of Elasticity AS 1012.17 47 GPaShrinkage AS 1012.13< 500 µ strain after 56 days0 after heat treatmentDensity 2,450 kg/m 3Stress [MPa]2001501005000 3 5 8 10 13Compression strain [10 -3 ]Bending stress [MPa]4030201000 2 4 6 8Deflection [mm]Figure 1. Typical force deformation response of Ductal ® in compression and flexureHeat treatment consists of curing in steam at a temperature of 90°C for a period of 48 hours afterdemoulding. This results in rapid strength gain and substantially reduced creep, and causes almost all theshrinkage to occur during the period of the heat treatment. The strength of heat treated Ductal ® is 15%greater than non-heat treated, and durability properties are also improved. The use of heat treatment isoptional and depends on the application. Table 2 lists the durability properties of Ductal ® in generalcompared with high performance concrete, as reported by Roux et al. (1996). The extremely highresistance to the penetration of aggressive agents, due to the absence of capillary porosity, correspondsto excellent durability characteristics.Table 2. Durability Properties (Following Heat Treatment)Durability IndicatorValueDuctal ® with Metallic Fibrescompared withHigh Performance ConcreteTotal porosity 2-6% 1/4 to 1/5 of HPCMicroporosity (>10µm) < 1% 1/10 to 1/30 of HPCPermeability (air) 2.5×10 -18 m 2 1/50 of HPCWater absorption < 0.2 kg/m 2 1/50 of HPCChloride ions diffusion 0.02×10 -12 m 2 /s 1/50 of HPCElectrical resistance (excl. fibre) 1.13×10 3 kΩ.cm12 to 17 times HPCElectrical resistance (incl. fibre)137 kΩ.cm1.5 to 2 times HPCAbrasion resistance coefficient 1.3 2 to 3 times HPCFatigue, impact and blast resistance - Far superior to HPCWhile the ultra-high strength of Ductal ® puts it outside the direct provisions of national design standards,design recommendations have been prepared in France (BFUP, AFGC 2002) and Australia (Gilbert et al.2000), in accordance with the intent of national standards.DM-003-2

A prestressed beam or slab made from Ductal ® has between 35-45% of the volume of a conventionalprestressed beam or slab. The depth is approximately the same as a conventional prestressed member inorder to provide stiffness for deflection control.Flexural strength for large span beams and slabs is achieved through prestressing in combination with thehigh compressive strength of Ductal ® . Short span beams and slabs generally need no reinforcement.Shear strength is provided by the tensile strength of Ductal ® . No additional shear reinforcement isrequired. The compression stresses, due to the prestressing, add to the material tensile strength tocounter the principal tensile stresses.2. Conventional Uses of Ductal ®Ductal ® has been used worldwide to create precast elements from thin (20mm) fascia and soundabsorption panels to pedestrian bridges with spans up to 120m and other innovative architectural andstructural applications. Details of applications can be found in Behloul and Lee (2002), Cavill and Chirgwin(2004), Acker & Behloul (2004), Cavill and Rebentrost (2005), Rebentrost (2005), Graybeal(2005) andPerry et al (2005).3. Protective Panels Research & DevelopmentConcrete panels (slabs and walls) play an important part in protecting buildings against the extremeloading conditions caused by blast, shock and impact. The high-energy absorption capacity of Ductal ®was known from static strength tests, however the performance of Ductal ® elements under severeimpulsive loading had not been investigated. The flexural toughness measured as the area under theflexural bending stress-deformation curve (Figure 1) is greater than 200 times that of conventional fibrereinforced concrete.3.1 Blast Testing at Woomera, May 2004In a joint project between VSL Australia Pty Ltd and the Advanced Protective Technologies forEngineering Structures (APTES) group at the University of Melbourne, Ductal ® panels were tested underextreme explosions at blast trials performed at Woomera in South Australia. The Woomera trial in May2004 consisted of two separate blasts equivalent to six (6) tonnes of TNT. Each detonation consisted of abare charge of 5 tonnes of the explosive Hexolite.A total of seven panels were tested at 30m, 40m and 50m from the blast. One conventional, reinforcedconcrete panel was tested at 40m from the blast. Calculated reflective blast pressures were 2000, 800 and400kPa, respectively, for these distances. The panels had a span of 2m and were 1m wide, with athickness of 50mm, 75mm and 100mm. Five of the panels contained an identical arrangement of highstrength (tensile breaking strength 1840MPa) prestressing strands. The details are confidential. The othertwo panels were unreinforced. Deflections were recorded on five of the panels using a simple pen onpaper apparatus. The other two panels had a laser system installed with the intent of recording thedeflection and time history. Unfortunately the system malfunctioned and provided no information.The test data and observations showed that the panels performed remarkably well, displaying highductility and no signs of fragmentation. The stressed panels were able to absorb substantial energythrough their ability to sustain considerable deflection up to span/28 without fracture. The fact that theDuctal ® panels displayed no fragmentation in any of the tests, even at fracture, is a major advantagecompared to conventional concrete. Fragmentation poses great danger to both people and infrastructure.Table 3 lists the main observations from the tests.DM-003-3

PANEL TYPEStressed 100mmStressed 100mmStressed 75mmStressed 50mmTable 3. Main observations, Woomera blast trialStand-offDistance30m40m40m50mRecordedDeflection50mm in37mm out0mmLaserNo record0mm72mm in55mm out18mm inLaserNo record0mmMain observationsVirtually undamaged, no permanentdeflection. Several vertical hairlinecracks in front face of 0.1 to 0.2mmwidth. No fragmentation.Basically undamaged, no permanentdeflection, No fragmentation.Intact, cracked with small permanentdeflection, no fragmentation.Intact, shallow crack, no permanentdeflection, no fragmentation.Unreinforced 50mm 50m >300mm Fractured, no fragmentationStressed 75mm 30m >300mm Fractured, no fragmentationUnreinforced 100mm 40m 280mm Fractured, no fragmentationReinforced conventionalconcrete (40MPa) 100mm40m>300mmFractured, severe damage,fragmentation from back faceThe series of photos in Figures 2and 3 show; a typical 2 × 1m panel being installed into a concrete testframe; the test panels before a blast; one of the two blasts; the crater caused by a blast and two of thepanels after being subjected to extreme blast loading.Installing panels into concrete framesPanels ready for blastBlast, equivalent to 6t of TNTCrater (17m dia) caused by the blastFigure 2. Protective panel tests, Woomera blast trialDM-003-4

100mm panel at R=30m after the blast;undamaged50mm panel at R=50m after the blast, shallowcrack, no spalling or fragmentationFigure 3. Protective panel tests, Woomera blast trialThe 100mm thick stressed panel at 30m after the blast is shown in Figure 4 bottom left. The panel haddeflected inwards 50mm, then outwards 37mm and come to rest with no permanent deflection. The blastresulted in an average reflected impulse at the panel surface of 3771 kPa.msec with a peak reflectedpressure of 1513 kPa. The panel was basically undamaged. The 50mm thick stressed panel at 50m afterthe blast, also shown in Figure 4 (bottom right), withstood significant deflection and had no permanentdeflection. The panel was basically intact, and had a shallow crack on the front face.The results of the blast trials demonstrated the suitability of Ductal ® for blast resistance and confirmed thedesign methods.3.2 Constitutive Model for Ductal ® at High Loading RatesThe response of concrete to very high strain rates needs to be known in order to properly designstructures subjected to blast or impact effects. At high strain rates, the strength of concrete can increasesignificantly. The response for Ductal ® was determined by a series of impact tests carried out using theSplit Hopkinson Pressure bar (SHPB) setup on large-diameter test cylinders. A range of loading rates andpressures were used.Figure 4 shows the stress-strain curves at different strain rates of 50mm diameter Ductal ® cylinders. It canbe seen that the compressive strength increases up to 1.5 times at the strain rate of about 267.4/sec. Thiscorresponds to a strength Dynamic Increase Factor of 1.5. Table 4 summarises the test results of 3 RPCspecimens. It was found that RPC is less rate sensitive compared to both NSC and HSC (Ngo 2005).250200RPC-3Stress (MPa)150100StaticRPC-1RPC-25000 0.002 0.004 0.006 0.008 0.01 0.012 0.014 0.016 0.018 0.02StrainFigure 4. Stress-strain curves of RPC (Ductal ® ) at different strain-ratesDM-003-5

Table 4. Dynamic Compressive Strength of RPC (Ductal ® )Concrete Impact Average StrainDynamicUltimate StrengthSpecimen Velocity Rate (1/sec)Increase FactorStatic Test - - 159.8 MPa -RPC-1 11.6 m/s 80.7 187.2 MPa 1.17RPC-2 16 m/s 187.3 226.1 MPa 1.41RPC-3 20 m/s 267.4 240.9 MPa 1.5Based on the results of the experimental program using the Hopkinson Bar apparatus and through arigorous calibration process, a new strain-rate dependent constitutive model has been proposed by theAPTES group at the University of Melbourne for concrete under dynamic load. The model can take intoaccount the strain-rate effect by incorporating multiplying factors for increases in the peak stress andstrain at peak strength. This model is applicable to concrete strengths varying from 32 MPa to 160MPawith a strain rate up to 300 s-1. A detailed report is given in Ngo, et al. (2005).3.3 Fragment Impact Simulation TestsOn June 9, 2005, two 100mm thick Ductal ® blast resistant panel pieces were subjected to fragmentsimulated projectile (FSP) loading. Tests were carried out at a NATA (National Association of TestingAuthorities) approved projectile testing lab in Melbourne, Australia.Test pieces were sourced from the production of high-performance blast resistant Ductal ® panels. Thepieces had a thickness of 100mm and were reinforced with high strength steel (tensile breaking strength1840MPa) prestressing strands. Details of the strands are confidential. The test pieces were cut from asingle larger panel. In accordance with Australian Standard AS/NZ 2343 (1997) for Bullet Resistant Panelsand Elements, all test pieces had a plan dimension of 420 x 420mm.During production of the project panels, Ductal ® cylinders and prism were tested and strength results ofapproximately 170 MPa in compression and 30 MPa in tension (flexural) recorded.Testing procedure followed AS/NZ 2343 and consisted of firing projectiles at the target piece with anintended speed. Each test piece was mounted in a frame and a witness (paper) card was placed behind itto record fragmentation impacts. The test was considered to be passed if no fragment penetrated throughthe witness paper; see Figure 5.Figure 5. Testing frame and 420 x 420 x 100mm Ductal ® panel ready for testDM-003-6

Two types of steel projectiles were used: 50 caliber (13mm diameter) and 20mm diameter. The projectileswere fired at the test panels with different target speeds. Figure 6 shows the projectiles.13mm dia 20mm diaFigure 6. 50 caliber and 20mm FSP, before and after impactThe tests were the first of their type to be undertaken using Ductal ® high performance blast protectionpanels. The results of these simulated fragment projectile tests show that a specifically designed 100mmthick Ductal ® blast resistant panel will resist the impact of a 50 caliber FSP at 1164m/s and 20mm FSP at821 m/s without fragmentation on the non-impact side. Figure 7 shows the test pieces after impact andtest observations are summarized in Table 5.Panel 1after impacts from 50 caliber FSP at 715 Panel 2 after impact from 20mm FSP at 821 m/s.m/s and 1164 m/s.(crater depth is 25mm)Figure 7. Test pieces after impactTable 5. FSP tests observationsPanel 150 CaliberFSP at 715 m/sPanel 150 CaliberFSP at 1164 m/sPanel 220mmFSP at 821 m/s• FSP did not cause spalling of the panel on the non-impact face• No micro cracking observed behind impactPanel passed impact test successfully (witness paper undamaged)• FSP did not cause spalling of the panel on the non-impact face• Micro cracking observed behind impact• Impact crater larger diameter and depth than in shot 1Panel passed impact test successfully (witness paper undamaged)• FSP did not cause spalling of the panel on the non-impact face• Cracking observed behind impact but no spallingPanel passed impact test successfully (witness paper undamaged)In comparison with standard mortar fragments, the results compare favourably with impact data for 81mmmortar, general purpose (GP) and US 4.2 inch mortar fragments. The impact energy of the projectiles thatcaused no spalling on the non-impact face and repelled the fragment (20mm at 821m/s), are at least amagnitude of almost two greater than the impact energy data for the mortars.DM-003-7

3.4 Close Charge TestsIn July 2005, two Ductal ® panels (panels 1 & 2) were tested with close charges of the plastic explosiveC4at a laboratory in England. In November 2005, one Ductal ® (panel 3) and one conventional reinforcedconcrete panel (panel 4) were subjected to close charges of composition B. The tests were performed bya laboratory in Australia.The panels were manufactured at the VSL Ductal ® factory in Melbourne. The panels were reinforced withhigh strength steel strands with the same arrangement as used in the FSP tests. The reinforced concretepanel 4 was designed to have a similar static flexural capacity to the Ductal ® panel 3.Table 7. Panel details for close Charge TestsPanel Dimensions m Material Reinforcement Explosive Stand-off1 1.0 x 1.0 x 0.1 Ductal ® High strength steel strands 3kg C-4 1.0m2 1.0 x 1.0 x 0.15 Ductal ® High strength steel strands 5kg C-4 0.5m3 1.3 x 1.0 x 0.1 Ductal ® High strength steel strands 0.5kg Comp B 0.1m4 1.3 x 1.0 x 0.1Concrete50MPaN20 at 75mm back faceN20 at 150mm front face0.5kg Comp B 0.1mThe three panels (1, 2 and 3) performed very well under the very severe loading. Panels 1 and 2 had onlyminor hairline cracks appearing on the back face. Photos and observations of panels 3 and 4 are shown inFigure 8.Panel 3 (Ductal ® ) front surface after explosionNo cracksPanel 4 (conventional reinforced concrete) frontsurface after explosion - Slight cracksPanel 3 rear surface after explosion- Very slight scabbing at the surface of the panel.- Minor cracks through the panel.- Structurally undamaged.Panel 4 rear surface after explosion- Heavy scabbing, reinforcing bars exposed.- Cavity approximately 480 mm x 300 mm, with amaximum depth of 50 mm (1/2 section depth).Figure 8. Test panels 3 and 4 after close charge explosionDM-003-8

3.5 Ballistic TestsIn September 2005, three 100mm thick panels were tested at a NATA registered laboratory in Melbourne,for resistance to attack by NATO standard 7.62/9.3g full metal case bullets at 850m/s. All panels werereinforced with high strength steel strands with the same arrangement as used in the FSP tests. The testswere performed in accordance with AS/NZS 2343. All panels passed the test, with no fragments beingdislodged from the back face or penetrating the witness paper, and achieved an R2 ballistic rating. Figure9 shows the panels following the test.Figure 9. Two test specimen after three impacts from 7.62mm full metal case bullet at 850m/s4. Protective Panel Project ExamplePanels for the first structure to utilize Ductal ® to provide resistance to blasts were manufactured inMarch/April 2005 at the VSL plant in Melbourne. The client was the Department of Foreign Affairs andTrade of the Australian Government. The panels are part of a blast protection system designed by VSLAustralia and APTES.The panels are up to 4.5m long x 2.0m wide x 100mm thick. They are being used to provide blastresistance to an existing building in a high risk international location. The panels were installed on site inJuly. Photos of the panels prior to shipment from the VSL factory and as installed on site are shown inFigure 10. Project specifics have been classified.Precast Ductal ® blast resistant panels in storage.Installed Panel system.Figure 10. Ductal ® protective panels with 100mm thicknessDM-003-9

5. Concluding RemarksLarge scale blast tests, close charge blast tests, fragment simulation tests, and ballistic tests haveconfirmed that panels made with Ductal ® are an effective solution for blast and impact resistance. Panelscan be much thinner than those made from conventional concrete, and the risk of injury or damagecaused by concrete fragments is virtually eliminated.6. ReferencesAcker, P and Behloul, M (2004). “Ductal ® Technology: A Large Spectrum of Properties, A Large Range ofApplications”, International Symposium on Ultra-High Performance Concretes, Kassel, Germany, Sept2004.Australian Standard for Bullet Resistant Panels and Elements AS/NZS 2343. 1997, Australia.Australian Standard for Testing Concrete AS 1012-1 to 13. Various dates, Australia.BFUP, AFGC, “Ultra-High Performance Fibre-Reinforced Concretes”, Interim Recommendations, AFGCpublication, France, 2002.Behloul, M. and Lee, K. (2002). “Innovative Footbridge in Seoul – Seonyu Footbridge”, First FIB Congress,Osaka, Japan, October 2002Cavill, B. and Chirgwin, G. (2004). “The World’s First RPC (Ductal ® ) Road Bridge at Shepherds Creek,NSW”, Austroads 5th Bridge Conference, Hobart, May 2004.Cavill, B. and Rebentrost, M. (2005). “Ductal ® – An Ultra-High Performance Material for InnovativeStructures and Resistance to Hazardous Environments”, Australian Structural Engineering Conference2005, Newcastle NSW, September 2005.Gilbert, I., Gowripalan, N. and Cavill, B. (2000). “On the Design of Precast, Prestressed Reactive PowderConcrete (Ductal ® ) Girders”, Austroads 4th Bridge Conference, Adelaide, November 2000.Gowripalan, N., Watters, R., Gilbert, I. and Cavill, B. (2003). “Reactive Powder Concrete (Ductal ® ) forPrecast Structural Concrete – Research and Development in Australia”, 21st Biennial Conference of theCIA, Brisbane, July 2003.Graybeal, B.(2004). “Fabrication of an Optimized UHPC Bridge”, 2004 PCI National Bridge Conference,USA.Ngo, T., Mendis, P., Lam, N. and Cavill, B. (2005). “Performance of Ultra-High Strength Concrete Panelssubjected to Blast Loading”, The 2005 Science, Engineering and Technology Summit, Canberra, July2005Ngo, T. (2005). “Behaviour of High Strength Concrete subjected to Impulsive Loading”, PhD Thesis,Department of Civil & Env. Engineering, University of Melbourne, Australia, 2005Perry, V., Zakariasen, D., Chow, T., Vincenzino, E.,and Culham, G. (2005), “First Use of UHPFRC in ThinPrecast Concrete Roof Shell for Canadian LRT Station”, PCI Journal, October 2005, USA.Rebentrost, M. (2005). “Design and Construction of the First Ductal ® Bridge in New Zealand”, 22ndBiennial Conference of the Concrete Institute of Australia, October 2005, Melbourne.Roux, N., Andrade, C. and Sanjuan, M.A. (1996). “Experimental Study of Durability of Reactive PowderConcretes”, Journal of Materials in Civil Engineering, Feb 1996.DM-003-10