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TESTS AND ANALYSIS OF THE LOCALIZED RESPONSE OF SLURRY INFILTRATED FIBER CONCRETE (SIFCON) AND CONVENTIONAL REINFORCED CONCRETE (CRC) SUBJECTED TO BLAST AND FRAGMENT LOADING K. Marchand, P. Nash, P. Cox

To cite this version: K. Marchand, P. Nash, P. Cox. TESTS AND ANALYSIS OF THE LOCALIZED RESPONSE OF SLURRY INFILTRATED FIBER CONCRETE (SIFCON) AND CONVENTIONAL REINFORCED CONCRETE (CRC) SUBJECTED TO BLAST AND FRAGMENT LOADING. Journal de Physique Colloques, 1988, 49 (C3), pp.C3-327-C3-332. .

HAL Id: jpa-00227770 https://hal.archives-ouvertes.fr/jpa-00227770 Submitted on 1 Jan 1988

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JOURNAL DE P H Y S I Q U E Colloque C 3 , Supplement au n 0 9 , Tome 49, septembre 1988

TESTS AND ANALYSIS OF THE LOCALIZED RESPONSE OF SLURRY INFILTRATED FIBER CONCRETE (SIFCON) AND CONVENTIONAL REINFORCED CONCRETE (CRC) SUBJECTED TO BLAST AND FRAGMENT LOADING K.A.

MARCHAND, P.T.

NASH and P.A. COX

Southwest Research Institute, PO Drawer 28510, San Antonio, TX 78284, U.S.A. Resum6 - Des analyses et des essais ont Cte men6s sur des panneaux structuraux de b6ton arm6 de type CRC et SIFCON sous chargement local et dynamique dans un environnement combine de souffle et d'bclats. La rbponse des panneaux met en evidence les differences intrinseques de comportement au choc de ces mat6riaux. L'absence de ductilite de la reponse du SIFCON souleve le probleme de ses possibilites d'applications dans des environnements de chargements s6vhres.

Abstract - Analysis and tests of locally and dynamically loaded CRC and SIFCON structural panels were tested under simultaneous blast and fragment loading environments. The response of the panels indicate the inherent difference in shock resistance of the construction materials. The absence of ductility in the SIFCON response raises questions as to its applicability in severe loading environments. 1 - Introduction

Structural designs for barrier systems to be used for the prevention of propagation of explosive detonation through fragment impact or rigid body impact must specify materials and configurations which will retain complete integrity during severe blast and shock loading. Heavily reinforced concrete and SIFCON provide inherent capability to achieve this goal. 2 SIFCON Material Descri~tion SIFCON, an acronym for Slurry Infiltrated Fiber Concrete, has recently (1983) been introduced as a high strength impact resistant material. It consists of high strength steel fiber and a low viscosity slurry. Several fiber sizes and shapes have been used and the fiber selection fixes the fiber density of the cast material. Construction practice is simply, "rain in" the fiber, by hand or machine, to fill the form and then pour in the slurry. The slurry, consisting of water, cement, fly ash, su er plasticizer, and micro silica, infiltrates the voids between fibers and the end result is a ratherRigh strength ductile composite. It is reported to be especially resistant to dynamic loads in Reference 1. Motetial Properties The "rained in" fibers take on a preferred orientation and produce an anisotropic material from the macroscopic viewpoint. Based on data presented in Reference 1, the preferred orientation is for fibers to Ile in a plane with their longitudinal axis perpendicular to the force of gravity. If the fiber direction is truly random in the plane normal to direction of gravity then the material stiffnesses might be transversely isotropic. However, tests reported in Reference 2 show sii ht orthotro y. Not enough data are available to make an adequate judgement on material stiffness classi&ation. Differences in compressive strength are also qulte evident in the three principal material directions of a cast block of the material. Most especially, the compresslve strength for loads in the direction normal to the preferred lane are 60 - 70 percent greater than Compressive strengths for specimens loaded in the plane o the preferred direction. For the higher strength SIFCON material, a major compressive strength as high as 13,000 psi and a minor compressive strength of 7,800 are reported in Reference 2. At strain rates of 100 200/sec. these compressive strengths show a dynamic increase factor (ratio of compresslve strength at strain rate to f c ) of 1.4 to 1.0. In comparison these compressive data are not much better than static and dynamic strengths reported for high strength concrete of various aggregate

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Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1988347

C3-328

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size and strength reported in Reference 3. However, there is one particular property of SIFCON that is very interesting and important. The compressive moduli of the various types of SIFCON vary fro? 1.0 to 1.75 X 106 SI. In comparison, other concrete material moduli range from 4.0 to 5.0 X 10 psi. This means tRat SIFCON will absorb much more strain energy than conventional high strength concrete materials. Recent tensile tests at SwRI using ASTM standard tensile specimens for cementitious materials (Reference 4) indicate that a major tensile strength of 1000 psi and a minor tensile strength of 300 psi can be expected. The major tensile strength is approximately twice that expected for standard concrete (approximately 10-15% of the compressive strength, and is much more ductile, exhibiting its maximum at 2.5% strain. 3 - Structural Res~onseAnalvses FIerural Capacity An ASTM beam of SIFCON DRAMIX 30150 was tested and reported in Reference 2. The maximum load for a beam tested with loads perpendicular to the referred fiber orientation plane was approximately 13,500 lbs. For a beam tested with loads paralfel to the plane of preferred fiber orientation the maximum load was approximate!^ 4,000 lbs. The modulus of rupture is defined as

where P = center load, lb. b = beam width = 4 in. d = beam depth = 4 in. L = distance between end loads = 10 in. The moduli of rupture for the 13,500 and 4,000 Ib. loads are respectively 2,200 psi and 630 psi. The maximum moment may be defined as

where I = planar moment of inertia, in4 C = maximum fiber distance, in. Using this equation the maximum moment for the two loads become 23,320 in.-lb and 6,670 in.-lb. The plastic moment Mp equation for conventional reinforced concrete is given as A4,=0.9bd2 f X c q ( l - 0 . 5 9 q )

where b = beam width, in. d = distance from bottom of beam to center line of tensile reinforcement, in. strength of concrete, psi

6

yield strength of reinforcement, psi .005 the plastic moment For the same sire beam with f c = 5,000 psi, fy = 50,000 psi, and! becomes, Mp = 13,980 in-lbs. Of course, doubling the amount o re~nforcementalmost doubles the plastic moment. This comparison then shows that SIFCON may be only as effective in bending as a conventional reinforced concrete beam with a 0.75-1.0 percent effective tensile reinforcement ratio. Recent tests of beams at SwRI have also shown that for equal moment capacity beams of conventional reinforced concrete and SIFCON, the SIFCON specimen exhibits much less ductility past maximum capacity. Figure 1 shows the loss of ductility in the SIFCON past maximum moment.

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REINFORCED C O N C R m BEAM - 6.0 1n.X 6.0 In. 28 DAY CONCRETE STRENGTH = 5300 psi 1.4 % 60 ksi REINFORCEMENT EACH FACE SIFCON BEAM - 6.0 in. X

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Figure 1. Comparison of CRC and SIFCON Flexural Response. Load Definition for Combined Blast and Fragment Impuke Fragment Impulse - When velocity and spatial distribution for fragments produced b a munition 1s known, momentum ap lied to the target can be calculated. Relating this calm ated momentum with the catcher bundL sire used in fragment tests performed at SwRI additionally allows s ecific momentum or momentum per unit area (specific fragment impulse on the target) to be d m l a t e d . Tests of the munition considered in this study produced the following data: Specific Impulse at 120 in. -- 0.0055 psi-sec. Specific Impulse at 7 in. -- 1.6229 psi-sec. The impulse at 7.0 in. is the scaled standoff observed in testin . This impulse can be scaled to full scale (impulse scales as a function of the scale factor, 2.0). e scaled up impulse becomes (2)*(1.6229) or 3.25 psi-sec. as determined from the cased charge tests. Pressure Records and Impulse Calculations - The s ecific impulse measured in testing of the munition at its scaled standoff was a maximum of 2.2fpsi-sec. At full scale, the blast impulse becomes 4.5 psi-sec. The total local impulse delivered to the section then becomes 7.75 psi-sec. Shear Response/Critical Impuke Failure Based on a method described in Reference 5 for edge shear failure of ductile metals, the SIFCON bamer will be checked for a shear failure that may occur prior to flexural response. Consider a rather localized impulsive load is applied as shown in Fi re 2. Here the assumption is that a cylindrical volume of some radius R will be removed y the applied specific impulse I, if that ap lied specific impulse exceeds a critical impulse Icr where Icr is based on material pPoperties orthe material. The applied average impulse over some area is given by

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where tcr is some critical time taken as the quarter period of the fundamental frequency of the slab. The critical specific impulse is given by

where p is the slab density, h is the slab thickness and vcr is the critical velocity defined in Reference 5 as

JOURNAL DE PHYSIQUE

where a,, = tensile s t r e s s of t h e slab material The failure criterion as given in Reference 6 used here sugests that if the applied specific im ulse I for an area exceeds the critical specific impulse I, wthin a given time to then a voLme ofpadius R and thickness h will be sheared throu the thickness of the slab. For this study the applied impulse will include both the blast and ra ent loading. This total im ulse is based on the loading of a cased charge of 18.0 pounds of 8 a t a distance of 1.33 feet. h e design is based on an applied impulse of 7.75 psi-sec. average over an area of 12 X 24 inches. The minimum thickness required to resist the maximum applied specific impulse obtained by setting Ia = Iap and solving for the thickness is

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Using the tensile strength and density of Table 1 the minimum thickness becomes h m.l n

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d2(2.8)(.33) h,,, = 8.6inches

TABLE 1. PROPERTIES OF DRAMIX 30150 SIFCON, Reference 7 Volume fraction of steel:

0.11

Density:

2.40 g/cm3 7.80 g/cm3 3.0 g/cm3 187 lb.Ift.3 13000psi 2200 psi

Slurry Steel SIFCON Specific Weight SIFCON Compressive Strength (28 day), f c Tensile Strength (Mod. of Rupture) Dynamic Strengths (DIF = 1.5 @ = 100/sec.): Compressive Tensile Modulus of Rupture

19,500 psi 3,300 psi 3,300 psi

4 - Dynamic Load Tests SIFCON and Conventional Reinforced Concrete Designs Two 6.0 inch thickness (half scale) designs were generated for the SIFCON and conventional reinforced concrete (CRC) barrier concepts based on the critical impulse requirements as presented above. Figure 3 shows the concrete panel design used in testing during this program and is illustrative of the details of the 6.0 ft. by 6.0 ft. barrier conce t considered in this analysis. The SlFCON barrier concept is sinpie by comparison to the ~ ~ ~ % a r concept r i e r and is of the same overall dimensions. Modijied SIFCON Barrier Design The modified design includes centerline flexural reinforcement in the form of no. 3 bars placed 6 in. on center both ways. This centerline flexural steel is actually near the center of the tensile zone of a bending panel and will increase the ductility of the system, and reduce the probability of a catastrophic failure of the panel during loading.

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Figure 3. Detail of CRC Test Section.

Conventional Reinforced Concrete Barrier Response The shock generated in the barrier from the fra ment impact caused significant spall around the edges of the barrier. This spall was generated as t e initial lateral shock wave was reflected at the free surfaces. The fr nt face fragment penetrations had an average de th of 0.5 in. The spall zone in this test was 4 ft. in area. The depth of the spall observed was we 1 past the cover reinforcement at points as deep as one half the barrier thickness, or 3.0 in. SIFCON Banier Response The fragment impact damage on the SIFCON barrier front face was significant (at oints 0.5 in. deeper than the conventional concrete barrier fragment penetrations) yet none of t i e edge s all could be seen in this test. The structural response in this test was observed to be different tRan the concrete. A centerline flexural crack, perpendicular to the charge axis, was pro agated through the barrier thickness. Some s all can be observed, and, as in the uncased test, tRe cosmetic cover produced the spall. d e deepest spall depth measured was 0.25 in. Thus, the overall damage to the barrier wall was significantly less than for the conventional reinforced concrete wall. Reinforced SIFCON Bam'er Response The munition did considerable damage to the barrier in this test, but depth of fragment penetration was limited to approximately 1.5 in. A partial depth flexural crack was observed in this photo at the barrier bottom edge. This crack d~ffersfrom that observed in the umeinforced preliminary test barrier in that it is only partial (approximately one-half to two-thirds depth) thickness. The reinforcement included in the modified or reinforced design most likely precluded !his crack from propagating to full depth. The crack width on the rear face was approximately 0.5 m. Figure 4 shows the local material scabbing that occurred behind the near char e (the charge was oriented horizontally with res ect to this photo). The SIFCON appears t have\egun to s all The depth of t i e and scab as indicated by the petalEd appearance over an area of about 1.0!tf scabbing observed was 2.0 in., or about 40% of the panel depth. The flexural crack mentioned above is visible at the right side of the barrier. The scabbed sections rotated from 30 to 45 degrees off of the plane of the panel, although no large pieces were found to have separated from the panel. The cementlfiber matrix obviously held together well to prevent the escape of large pieces of hazardous secondary debris or fragments.

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JOURNAL DE PHYSIQUE

Figure 4. Photograph of Rear Face Local Damage to Reinforced SIFCON Panel After Combined Loading Test.

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5 Closure

Analysis and tests have shown that a fibrous reinforced composite, such as the reinforced SIFCON evaluated in this study, exhibits superior characteristics during structural response in severe blast and impact environments. Further development of this composite should be pursued to optimize its performance and geometry. REFERENCES / I / Mondragon, R., "Development of Material Properties for Slurry Infiltrated Fiber Concrete (SIFC0N)--Compressive Strength, NMERI-WA8-18 (8.03) New Mexico Engineering Research Institute, Albuquerque, NM, Dec 1985. /2/ Cheney, S. M., "SIFCON Information and Material Properties", T N 86-04 Air Force Weapons Lab. Kirtland AFB, Albuquerque, NM, Feb 1985. /3/ Malvern. L. E. and Ross, C. A., "Dynamic Response of Concrete and Concrete Structures," AFOSR Contract F49620-83-K007, Air Force Office of Scientific Research Bolling AFB, DC Annual Report AFOSR-TR 84-0165, Annual Report Jan 1984., Annual Report, Feb 1985; Final Feport, May 1986. /4/ "ASTM Test Designation C190-82," 1987 Annual Book of ASTM Standards, Vol, 14. / 5 / Jones, N., "Plastic Failure of Ductile Beams Loaded Dynamically," T - Feb 1976 pp 131-136. / 6 / Ross, C. A., Sierakowski, R. L. and Schauble, C. C., L "Concrete Breching Analysis" AFATL-TR-81-105, Air Force Armament Lab, Eglin AFB, FL, December 1981. /7/ Mayrhofer, C. and Heinz, J. T., "Experimental Investigation of Fibre and Steel Reinforced Concrete Plates Under Simulated Blast-Load," Proceedings of 2nd Symposium on the Interaction of Non-Nuclear Munitions With Structures, Panama City Beach, FL, April 1985.