Abstract:
This disclosure is directed to an improved ballistic concrete barrier and methods of using the barrier for training with weapons using live ammunition or grenades or other fragmentation devices.

Description:
FIELD OF THE DISCLOSURE 
     This disclosure relates to an improved ballistic concrete barrier and methods of using the barrier for training with weapons firing live ammunition. Training facilities need backstops or other components which can safely absorb live ammunition. 
     BACKGROUND OF THE DISCLOSURE 
     Shock Absorbing Concrete (SACON®) 
     Training is essential for both the military and civilian police forces. However, designing adequate backstops for military training, police, or civilian target practice, has been difficult. There are many difficulties associated with preparing such backstops. For example, a material must be strong enough to stop bullets, yet also must not cause ricochets because of risk to a shooter or bystander and must minimize the creation of lead dust from bullets spalling or fragmenting on impact. Wood backstops are problematic because insect or vermin infestation may lead to degradation and breakdown. Chemical treatment of wood creates additional environmental hazards associated with biocides or other toxins. Earthen barriers are difficult to move and stage in different settings, such as different lighting conditions. Over time earthen barriers may erode or wash away. Historically, fiber reinforced foamed concrete provided some benefits for training structures as a material that (1) resisted breakdown, (2) stopped bullets, and (3) prevented ricochets. 
     Lead from bullets is another fundamental problem. Lead is a heavy metal neurotoxin that accumulates over time in soft tissues, blood and bone. Exposures to extremely low concentrations of lead have been documented to cause learning disabilities and other neurological damage. Thus, lead is hazard with a potential for long-term harm. Lead from bullets may enter the environment as either elemental lead dust generated from the impact of bullets with the backstop or lead salts which may leach from the backstop into water supplies. 
     To address many of these concerns, researchers at the U.S. Army Engineer Research and Development Center (ERDC) invented SACON® ballistic concrete, a low-leaching, foamed concrete. SACON® ballistic concrete is effective absorbing low power projectiles and eliminating ricochets. As currently formulated it is a fiber-reinforced concrete with high concentrations of calcium phosphate and aluminum hydroxide to prevent leaching of lead fragments. U.S. Pat. No. 6,264,735 (Bean et al., “the &#39;735 patent”) describes SACON® and the reduced lead-leaching from the SACON® ballistic concrete blocks. U.S. Pat. No. 6,620,236 (Huntsman et al., “the &#39;236 patent”) describes an improvement of the &#39;735 patent formulation that includes an aluminum hydroxide additive to reduce or eliminate the erosion of heavy metals such as lead from the foamed concrete. The contents of both the &#39;735 and the &#39;236 patents are hereby incorporated by reference in its entirety. 
     SACON® ballistic concrete is prepared using an air compressor by adding a wet foam that contains a foaming agent and a foam stabilizing agent such as hydroxypropyl methyl cellulose. The wet foam is added to the concrete mixture to achieve the appropriate density required by the military specifications. SACON® ballistic concrete has been widely used by the military on bases in the U.S. and abroad. It has been used by other government agencies, e.g., police forces or the Drug Enforcement Agency. It is effective in stopping bullets from conventional small arms such as rifles (0.22 caliber, M16 (5.56 mm)) or pistols (0.38 caliber, 0.45 caliber, and 9 mm) The reported penetration depths range from 1 inch (25 mm) for a 0.38 caliber pistol to 2.55 inches (63 mm) for 5.56 mm (M16 rifle), see Hudson et al., Final Report Demonstration of Shock-Absorbing Concrete (SACON) Bullet Trap Technology, August 1999. 
     Training facilities use a number of barriers made from precast panels or other shapes to form backstops, simulated buildings, villages, or other structures such as a tank. When combining precast panels together to make a barrier such as a wall or other structure, the precast panel will include features to allow the precast panels to be connected to one another. However, the majority of the precast panel will be bullet absorbing structural components which are intended to capture live fire bullets or projectiles from other munitions such as grenades. 
     Process for Making Traditional SACON® Ballistic Concrete 
     Traditional SACON® ballistic concrete is prepared following ERDC specifications. By ERDC specifications it is meant the “Technical Specification for Shock Absorbing Concrete (SACON®)—Shock Absorbing Concrete for Constructing Live-Fire Training Facilities. This 25 page specification with reference to 35 other detailed specifications sets forth in great detail a process for creating a ballistic concrete and using the ballistic concrete to create panels and other structures using the ballistic concrete. The precision of this specification and the requirement for testing involving shooting live ammunition and measuring the depth of penetration of the bullet is a recognition of those in skill in the art of the great difficulties in creating a ballistic concrete that is capable of stopping penetration of a bullet within an acceptable depth without allowing the bullet to ricochet off the surface of the panel. 
     ERDC Specifications require the following ingredients: 
     
       
         
               
               
               
             
               
               
               
               
               
             
           
               
                   
               
               
                 Ingredient 
                 Cubic Meter 
                 Cubic Yard 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Portland Cement 
                 577  
                 kg (1272 lbs.) 
                 972  
                 lbs. (441 kg) 
               
               
                 Fine Aggregate (SSD) 
                 577 
                 kg (1272 lbs.) 
                 972 
                 lbs. (441 kg) 
               
               
                 Water 
                 277  
                 kg (611 lbs.) 
                 466  
                 lbs. (211 kg) 
               
               
                 Calcium Phosphate 
                 5.78 
                 kg (12.7 lbs.) 
                 9.72 
                 lbs. (4.4 kg) 
               
               
                 Aluminum Hydroxide 
                 5.78 
                 kg (12.7 lbs.) 
                 9.72  
                 lbs. (4.4 kg) 
               
               
                 Foam Stabilizer 
                 0.15  
                 kg (0.33 lbs.) 
                 0.25  
                 lbs. (0.11 kg) 
               
               
                 Foam (Void System) 
                 0.33  
                 m 3  (11.7 cu ft.) 
                 9.0  
                 cu ft. (0.25 m 3 ) 
               
               
                 Fiber (choice of) 
                   
                   
                   
                   
               
               
                 Polypropylene 
                 8.8  
                 kg (19.4 lbs.) 
                 14.8 
                 lbs. (6.7 kg) 
               
               
                 Steel 
                 115  
                 kg (254 lbs.) 
                 193 
                 lbs. (88 kg) 
               
               
                   
               
             
          
         
       
     
     ERDC requires the use of a foaming agent and foam stabilizing agents. Specifically they require:
         Section 2.4.1 Foaming Agents: Foaming agent shall comply with ASTM C 869, tested in accordance with ASTM 796; and   Section 2.4.2 Foam Stabilizing Agents: The stabilizing agent shall contain hydroxypropyl methylcellulose powder limited to 19.0 to 24.0% methoxy and 7.0 to 12.0% hydroxypropoxyl, similar to Dow Chemical Co. K100M.       

     Traditional SACON® ballistic concrete uses an air compressor and water to generate pre-formed foam. 
     Traditional SACON® ballistic concrete specifications require meeting the following density standards: 
     Density 
     
         
         
           
             (Without fibers) 1442 kg/m 3  (90-pcf) 
             (With polypropylene fibers) 1458 kg/m 3  (91-pcf) 
             (With steel fibers) 1554 kg/m 3  (97-pcf) 
           
         
       
    
     The foam is added to the mix, as follows using the ERDC specifications. The void material, pre-formed foam shall be added to the cement slurry to obtain the required density. The material shall be added in increments to reduce the possibility of moving outside the SACON® ballistic concrete density tolerances. The recommended procedure is to add the foam in half increments, i.e., add half of the foam initially by time of insertion and calculate the density. If the density remains above the upper tolerance, add half of the remaining foam and re-calculate the density. If the density continues to remain above the upper tolerance, then add half of remaining foam until the density tolerance of +48 kg/m 3  (3-pcf) relative to the target density (based on fiber use) has been achieved. 
     SACON® ballistic concrete is traditionally installed in modular panels that are typically 24″ to 30″ thick. Panels may be considered compromised when they have been penetrated by greater than 50% of the thickness of the panel, both because of the danger of collapse of the panel and because of the danger of shoot through if the panel is hit at the same point a second time. The panel may be repaired with ballistic concrete or replaced. 
       FIG. 1  sets forth the prior art process  1000  for making SACON® ballistic concrete. 
     Step  1004 —Create mix without foam. 
     Step  1008 —Create foam (this step could be completed before creating the mix). 
     Step  1012 —Add half the foam to the mix. 
     Step  1016 —Check density of mix plus added foam to see if the density is in range. Note that the target range for density is a pre-fiber target. Anecdotal reports indicate that frequently it is difficult to get the mix into the pre-fiber density range. 
     Step  1020 —Add half of remaining foam if needed to reduce density. 
     Step  1024 —Check density of mix plus added foam to see the density is in desired pre-fiber density range. 
     Step  1028 —If density is too high, go to  1020 . If density is now in range, go to  1032 . 
     Step  1032 —Add the prescribed fiber and mix. 
     Step  1036 —Test final density. Adding fiber increases the density of the ballistic concrete. Thus, a pre-fiber density of 90 pounds per cubic foot may be increased to a target of 91 pounds per cubic foot when using polypropylene fibers or 97 pounds per cubic foot when using steel fibers. 
     Step  1040 —Branch based on whether the final density has reached the density for the particular fiber. If not, go to  1036 . If the density has been reached then proceed to step  1044 . 
     Step  1044 —Pour the ballistic concrete into the mold. 
     Note—Due to the fragility of the foam bubbles within the prior art ballistic concrete mix, the Technical Specifications for Shock Absorbing Concrete (SACON®)-Shock Absorbing Concrete for Constructing Live-Fire Training Facilities has a number of limitations on how the mixed ballistic concrete material is handled. For example, in section 3.6.1 Placement Operations—there is a prohibition against any vertical drops of 2 feet or more absent special authorization and special equipment. The concern from a drop is that a drop larger than 2 feet may destroy a large percentage of the foamed bubbles. 
     Likewise a horizontal layer shall not exceed more than 2 feet. Here the concern is that the weight of the ballistic concrete on the lower portions of a deep pour would destroy an unacceptable percentage of the foam bubbles. This depth of pour limitation means that wall panels that will be more than two feet tall need to be poured with the height of the final wall in a horizontal plane. This limitation combined with the depth of drop limit precludes pouring a wall in place as the wall cannot be oriented with the height dimension arranged in a vertical orientation. To pour a panel with a thickness of more than two feet, the panel is poured on its side with a trough to lower the ballistic concrete into the form. 
     Yet another limitation on the treatment of the prior art ballistic concrete material is a requirement that poured SACON® panels are not to be moved for a period of 14 days. The sides of forms may be removed after 3 days. There is a fear of internal cracking in the poured panels if the forms are removed early. Given that wall panels will need to be poured with the long dimensions (wall height and width) placed in a horizontal plane, so that the short dimension (wall thickness) is in the vertical orientation—the large panel sized bottom portions of the mold are tied up for 14 days at a time. 
     Penetration Test. 
     The Technical Specification For Shock Absorbing Concrete (SACON®)—Shock Absorbing Concrete For Constructing Live-Fire Training Facilities has a penetration test for ballistic structures. Section 3.3.4.1 Penetration Test reads:
         All SACON® wall panels and other cast objects shall be individually tested with a live-fire test of an M855 round fired from an M16A2 rifle at a distance of 25-m (82-ft) and measured for penetration depth to the back of the bullet. Any penetration depth less than 25-mm (1-in.) or greater than 125-mm (5-in.) shall constitute a failure. Those objects failing to meet the penetration depth requirement shall be discarded without further testing or modifications.   For SACON® wall panels and other cast objects that are intended for close quarter usage (distances less than 25-m (82-ft)), the live-fire test shall be conducted with an M855 round fired from a remotely fired M16A2 rifle from the usage distance. Any penetration depth less than 25-mm (1-in.) or greater than 125-mm (5-in.) shall constitute a failure. Those objects failing to meet the penetration depth requirement shall be discarded without further testing or modifications.       

     Those of skill in the art will recognize that the term M855 round is the United States military name for the cartridge called the 5.56 NATO round or more specifically, the 5.56 NATO, 62 grain, green tip round. Those of skill in the art will recognize that a bullet is a projectile that is fired from a round (sometimes cartridge) that includes the bullet, casing, propellant, and primer. 
     SUMMARY OF THE DISCLOSURE 
     In particular non-limiting embodiments, the present disclosure provides a method for creating a bullet absorbing structural component made with ballistic concrete. The bullet absorbing structural component made with ballistic concrete comprising: 
     (a) about 1 part by mass Portland cement; 
     (b) about 0.5 to 1.5 part by mass fine aggregate; 
     (c) about 0.005 to 0.15 part by mass fiber; 
     (d) about 0.005 to 0.05 part by mass calcium phosphate; 
     (e) about 0.005 to 0.05 part by mass aluminum hydroxide; and 
     (f) about 0.0005 to 0.05 part by mass air entrainment additive, such that the bullet absorbing component is capable of passing the penetration test described above. 
     In one non-limiting embodiment, the bullet absorbing component comprises 
     (a) about 0.8 to 1.2 part by mass fine aggregate; 
     (b) about 0.008 to 0.012 part by mass fiber; 
     (c) about 0.008 to 0.012 part by mass calcium phosphate; 
     (d) about 0.008 to 0.012 part by mass aluminum hydroxide; and 
     (e) about 0.0008 to 0.002 part by mass air entrainment additive. 
     In another non-limiting embodiment, the bullet absorbing component comprises 
     (a) about 0.9 to 1.1 part by mass fine aggregate; 
     (b) about 0.009 to 0.011 part by mass fiber; 
     (c) about 0.009 to 0.011 part by mass calcium phosphate; 
     (d) about 0.009 to 0.011 part by mass aluminum hydroxide; and 
     (e) about 0.0009 to 0.0015 part by mass air entrainment additive. 
     The mixture comprising the Portland cement, the fine aggregate, the fiber; the calcium phosphate, the aluminum hydroxide, and the air entrainment additive may be mixed until the mixture has a density within a range of 88 to 94 pounds per cubic foot. The teachings of the present disclosure may be used to create a ballistic concrete without the use of the calcium phosphate and aluminum hydroxide if lead-leaching control is not an objective. 
     In one non-limiting embodiment, the fiber may be a polyolefin fiber, which may or may not be fibrillated. In another embodiment the air entrainment additive is DaraFill® Dry. 
     The bullet absorbing component may have air bubbles resulting from the air entrainment additive that are less than about 0.04 inches (1 mm) in diameter. Alternatively, the bullet absorbing component may have air bubbles resulting from the air entrainment additive that are greater than 0.0004 inches (10 μm) in diameter. In another non-limiting embodiment, the bullet absorbing component has air bubbles resulting from the air entrainment additive that are less than about 0.04 inches (1 mm) in diameter and greater than 0.0004 inches (10 μm) in diameter. 
     The training with the live ammunition may be performed with at least one of the following types of weapons: 
     0.22 caliber weapon, 
     0.38 caliber weapon, 
     0.40 caliber weapon, 
     0.45 caliber weapon, 
     5.56 mm weapon, 
     6.8 mm weapon, 
     7.62 mm weapon, 
     9 mm weapon or a 
     grenade or other fragmentation device. 
     The facility may be a training village, an assault house, a shoot house, a mock cave, or a live-fire practice range. The bullet absorbing component may be a backstop. Moreover, the bullet absorbing components may be made on site or at facility and brought to the location for use. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       The disclosure can be better understood with reference to the following figures. 
         FIG. 1  sets forth the prior art process  1000  for making SACON® ballistic concrete as done in the prior art using a foam made with water, foaming agent, and at least one foam stabilizing agent. 
         FIG. 2  summarizes the process  2000  for making bullet absorbing components using ballistic concrete made with chemical air entrainment additive rather than foam. 
     
    
    
     DETAILED DESCRIPTION 
     Definitions 
     The term “fine aggregate” means natural sand (including quartz, chert, igneous rock and shell fragments), limestone (calcium carbonate), manufactured sand (crushed stone, recycled concrete, slag) ranging from mesh size #8 to #200 (2.4 mm to 0.07 mm) In preferred, non-limiting embodiments the fine aggregate is masonry sand (ASTM C 144) or general concrete sand (ASTM C 33) meeting the size criteria. In one non-limiting embodiment the fine aggregate is saturated surface dry (SSD) material, see ASTM C 128. 
     The term “fiber” means concrete additives to reinforce the concrete with may be steel, alkali-resistant glass strands, or synthetic polymers. In preferred, non-limiting embodiments the fiber is a polyolefin, a polyester, a polyamide, (e.g., Kevlar®, nylon, polyester, polyethylene, polypropylene) or a mixture thereof, which may be a monofilament, fibrillated, or structured fibers (macrofibers). In one embodiment, the fibers meet ASTM C 1116 standards, such as ASTM C 1116 Type III requirements for polypropylene or ASTM C 1116 Type I for steel. Non-limiting examples include Grace Fibers™ (W.R. Grace &amp; Co., Cambridge, Mass.); Nylon—N6600, Polyester—PE7, Polypropylene—CFP 1000, Polypropylene—PP7 (Concrete Fibers Inc., Dallas, Tex.); Nycon-MM, NYCON-PVA, Nycon-RECS100, Nycon-RF4000, Nycon-RSC15, Nycon-XL (Nycon Corp., Fairless Hills, Pa.); ENDURO® 600, Fibercast® 500 for Precast, Fibercast® 510, Fibermesh® 150, Fibermesh® 300, Fibermesh® 650, Novocon® 1050, Novocon® XR, Novomesh® 850, Novomesh® 950 (Propex Concrete Systems Corp., Chattanooga, Tenn.); PSI Fibers™ (PSI Packaging, LaFayette, Ga.). Additional examples of suitable fibers include fibers described in U.S. Pat. No. 5,456,752 (Hogan); U.S. Pat. No. 6,423,134 (Trottier et al.); U.S. Pat. No. 6,582,511 (Velpari); or U.S. Pat. No. 6,758,897 (Rieder et al.), the contents of which are hereby incorporated by reference in their entirety. 
     The term “air entrainment additive” means admixtures that are part of the ballistic concrete mix to incorporate air bubbles of controlled sizes in the ballistic concrete matrix. These admixtures stabilize the air bubbles entrained during the mechanical mixing of ballistic concrete by the mixer blades. Examples of air entrainment additives include, but are not limited to, DaraFill® Dry or wet DaraFill formulations (W.R. Grace &amp; Co.), Rheocell® Rheofill™ (BASF Construction Chemicals, Cleveland, Ohio), Micro Air® (BASF Construction Chemicals), EUCON EASY FILL (Euclid Chemical Co., Cleveland, Ohio), Fritz-Pak Fill Flow (Fritz-Pak, Dallas, Tex.). Additional examples of air entrainment additives may be found in U.S. Pat. No. 4,488,910 (Nicholson et al.); U.S. Pat. No. 4,737,193 (Gutmann et al.); U.S. Pat. No. 4,249,948 (Okada et al.); U.S. Pat. No. 4,046,582 (Kawamura et al.); or the Portland Cement Association publication entitled “Manual on Control of Air Content in Concrete” (PCA EB 116), the contents of which are hereby incorporated by reference in their entirety. 
     The term “depth of penetration” with respect to a bullet penetration into a barrier is measured by inserting a measuring implement into the hole formed by the bullet and measuring from the point of entry to the trailing end of the bullet. Thus, the maximum penetration is actually a bit deeper than the measured penetration as the bullet, while altered in shape from the impact has a non-zero length. The depth of penetration of bullets into the absorbing material may be measured using alternative methods known to those skilled in the art. Laser based tools such as a laser range finder may also be used. 
     Preparations of Bullet Absorbing Component 
     In a non-limiting formulation, the bullet absorbing components are prepared by mixing cement, fine aggregate, and water to form a grout. The grout may be obtained from a ready mix concrete supplier. 
     Next an air entrainment additive is mixed into the grout. Then calcium phosphate, aluminum hydroxide and fiber are added. After mixing for a number of minutes the density is checked. As noted below, the addition of the calcium phosphate and aluminum hydroxide may be omitted if preventing lead leaching is not a concern. 
     If the mixture is above the target density range, additional mixing adds additional entrained air bubbles to reduce the density. The process of measuring density and providing additional mixing is repeated until the measured density is within a target range of the optimal density. 
     When the density is deemed appropriate, the ballistic concrete is poured into molds to form the component. Typically, the ballistic concrete is allowed to harden and cure for at least 4 weeks. Batching, mixing, transporting, testing, curing and placing the ballistic concrete would preferably meet the standards described in the Army Corp. of Engineers guidelines “Technical Specification for Shock Absorbing Concrete (SACON®)”: 
     American Concrete Institute (ACI) Standards 
     ACI 117 (1990) Standard Specifications for Tolerances for Concrete Construction and Materials 
     ACI 301 (1999) Standard Specification for Structural Concrete 
     ACI 304R (2000) Guide for Measuring, Mixing, Transporting, and Placing Concrete 
     ACI 305R (1999) Hot Weather Concreting 
     ACI 306R (1997) Cold Weather Concreting 
     ACI 544.1R (1996) State-of-the-Art Report in Fiber Reinforced Concrete 
     ACI 544.2R (1999) Measurement of Properties of Fiber Reinforced Concrete 
     American Society for Testing and Materials 
     ASTM C 33 (2001) Standard Specification for Concrete Aggregate 
     ASTM C 39 (2001) Standard Test Method for Compressive Strength of Cylindrical Concrete Specimens 
     ASTM C 94 (2000) Standard Specifications for Ready-Mixed Concrete 
     ASTM C 138 (2001) Standard Test Method for Density (Unit Weight), Yield, and Air Content (Gravimetric) of Concrete 
     ASTM C 144 (2002) Standard Specification for Aggregate for Masonry Mortar 
     ASTM C 150 (2002) Standard Specification for Portland Cement 
     ASTM C 171 (1997) Standard Specification for Sheet Materials for Curing Concrete 
     ASTM C 172 (1999) Standard Practice for Sampling Freshly Mixed Concrete 
     ASTM C 567 (2000) Standard Test Method for Unit Weight of Structural Lightweight Concrete 
     ASTM C 1116 (2002) Standard Specification for Fiber-reinforced Concrete and Shotcrete 
     Us Army Corps of Engineers Handbook for Concrete and Cement (CRD) 
     CRD-C 400 (1963) Requirements for Water for Use in Mixing or Curing Concrete 
     National Ready-Mixed Concrete Association (NRMCA) 
     NRMCA QC 3 (January 1990; 9th Rev) Quality Control Manual: Section 3, Plant Certifications Checklist: Certification of Ready-Mixed Concrete Production Facilities 
     NRMCA CPMB 100 (January 1990; 9th Rev) Concrete Plant Standards 
     NRMCA TMMB 1 (1989; 13th Rev) Truck Mixer and Agitator Standards 
     The Portland cement used would preferably be ASTM C 150 Type I-II. The fine aggregate may be masonry sand (ASTM C 144), or general concrete sand (ASTM C 33). 
     The calcium phosphate may be granulated bone meal, bone ash, or precipitated calcium phosphate. In one non-limiting embodiment, it is technical grade or higher. The aluminum phosphate may be metakaolinite or precipitated aluminum hydroxide. In one non-limiting embodiment, it is technical grade or higher. Color pigments may be optionally added to create the appearance rocks, trees, buildings, etc. Suppliers of concrete pigments include Scofield Co. (Douglasville, Ga.) or Lambert Corp. (Orlando, Fla.). Thus, the present disclosure teaches the option of pigmented bullet absorbing components. 
     The present disclosure teaches the creation of components made from wet ballistic concrete prepared without an addition of preformed foam. 
     One of skill in the art of ballistic concrete manufacturing would recognize that these materials are prepared on industrial scale and accordingly quantities and proportions may vary in accordance with industry norms. In addition, one skilled in ballistic concrete manufacturing would recognize that materials may be measured by volume or by timed delivery from a storage container. 
     The following examples further illustrate the various teachings of the disclosure and are not intended to limit the scope of the claimed invention. 
     Preparation of Components for Use Live Fire Ammunition 
     The ingredients for making the ballistic concrete components are as follows: 
     
       
         
               
               
             
               
               
               
             
               
               
               
               
               
             
           
               
                   
               
               
                   
                 Amount per unit ballistic concrete in 
               
             
          
           
               
                 Ingredient 
                 English System 
                 Metric System 
               
               
                   
               
             
          
           
               
                 Portland Cement 
                 972  
                 pounds 
                 441  
                 kilograms 
               
               
                 Fine Aggregate (SSD) 
                 972  
                 pounds 
                 441  
                 kilograms 
               
               
                 Water 
                 466  
                 pounds 
                 211  
                 kilograms 
               
               
                 Calcium Phosphate 
                 9.72  
                 pounds 
                 4.41  
                 kilograms 
               
               
                 Aluminum Hydroxide 
                 9.72  
                 pounds 
                 4.41  
                 kilograms 
               
               
                 DaraFill ® Dry 
                 11.4  
                 ounces 
                 323  
                 grams 
               
               
                 Grace Fibers ™ 
                 14.8  
                 pounds 
                 6.71  
                 kilograms 
               
               
                   
               
             
          
         
       
     
       FIG. 2  summarizes a process  2000  for making bullet absorbing components. As noted below, some of the steps may be performed in slightly different orders but for sake of clarity, it is useful to introduce one sequence of steps for discussion rather than muddy the water with premature digressions on alternatives. The steps may be summarized as follows: 
     Step  2004 —Obtain a grout of Portland cement, fine aggregate, and water in a mixer in accordance with ACI standard 304R and/or ASTM standard C 94. The act of obtaining includes creating the grout or obtaining the grout from some third party. 
     Step  2008 —Add a chemical air entrainment additive (DaraFill® Dry, W. R. Grace &amp; Co.). 
     Step  2012 —Following the addition of the additive, mix the grout for five minutes. Mixing may be achieved by rotating the drum on a cement mixer truck. 
     Step  2016 —Add Calcium Phosphate, Aluminum Hydroxide, and fiber. One suitable fiber is Grace Fibers™. Mix for an additional ten minutes. 
     Step  2020 —Check density such as by weighing using a ¼ cubic foot testing pot. Target weight is 22.7 pounds (approximately 91 pounds per cubic foot) as the actual target is 91 pounds per cubic foot±3 pounds per cubic foot. 
     Step  2024 —Continue to mix if needed to reduce density to desired range. Additional mixing lowers the density. Continue to mix, checking frequently, until target density is achieved. The target wet density material when poured into components is 1458 kg/m 3  (91-pounds per cubic foot+3 pounds per cubic foot). 
     Step  2028 —Pour ballistic concrete material into molds. As with traditional SACON® type ballistic concrete, vibration such as may be used with standard structural concrete is to be avoided to minimize destruction of air bubbles. 
     Changes in Order and Additives. 
     Note that the step of adding the calcium phosphate and aluminum hydroxide could be done at the same time as adding the chemical air entrainment additive. 
     Note further, that as the calcium phosphate and aluminum hydroxide are added to reduce lead-leaching from ballistic concrete blocks which have absorbed ammunition with lead components; these chemicals are not central to the ballistic properties of the ballistic concrete. Thus, in applications where the need to reduce lead-leaching is not important (whether because of local rules, post use disposal plans, or a movement to ammunition with minimal or no lead), one can make ballistic concrete in accordance with the teachings of the present disclosure without addition of calcium phosphate or aluminum hydroxide. 
     The fiber may be added at the same time as the chemical air entrainment additive (and possibly the calcium phosphate and aluminum hydroxide) as this process does not require achieving a pre-fiber density before adding the fiber. When the process is modified so that there is not a need to add material after five minutes of mixing, simply mix for fifteen minutes before checking density. Additional mixing may be required to reduce density. 
     After filling the molds, the material may be optionally tapped down with a rod to eliminate voids around embedments in the casting forms. Not all components will be poured into molds with embedments. Molds without embedments may not need a rod to eliminate any voids, but a form with an embedment such as a window cutout may need a treatment with a rod to eliminate voids. 
     Less Restrictions on Pouring. 
     Unlike traditional SACON® type ballistic material with fragile foam bubbles, ballistic material made in accordance with the teachings of the present disclosure is not limited to a 2 foot maximum drop during pouring or a 2 foot maximum depth of a pour. Thus, unlike traditional SACON® type ballistic material, ballistic material made in accordance with the teachings of the present disclosure may be poured into wall panels oriented in their final vertical orientation. Optionally, ballistic material made in accordance with the teachings of the present disclosure may be poured into molds with pour heights well in excess of 2 feet tall. Pours of greater than 3 feet in height are obtainable. Pours of greater than 6 feet in height are obtainable. Pours of greater than eight feet in height from bottom to top of mold are obtainable. Pour structures of full height walls of eight feet or more may be done. 
     Quicker Turn-Around on Use of Mold Components. 
     While traditionally, SACON® ballistic concrete components have been left in the molds for fourteen days with the sides only removed after three days, an alternative process viable with the improved ballistic concrete is to remove the sides of the forms within 24 hours and remove the bottom of the form after at least three days. 
     Those of skill in the art will recognize that the ability to remove the mold components significantly faster results in an overall throughput of molded panels of more than 300% for a given investment in molds. Thus, less money needs to be tied up in molds, transportation and storage of molds. T 
     The component is wrapped in plastic to assure adequate hydration during curing. One of skill in the art will recognize that the timing of these steps may be adjusted based on weather conditions, particularly temperature but also factoring humidity. The components are allowed to harden and dry and are ready for use and/or testing after 28 days. 
     One of skill in the art will recognize that the fibers enhance the strength and resilience of the components and ability of the molded components to withstand a bullet entry without spalling. Spalls are flakes of material that are broken off a larger solid body such as the result of projectile impact, weathering, or other causes. It is desired that the molded components retain their structural integrity with the exception of the trail formed by the bullet entry. Thus while the fibers are important, one of skill in the art can identify and substitute other fibers that are suitable for the task, see e.g., paragraph defining term fiber in definitions section above. The choice of fibers will impact the overall density of the wet material as the weight of the fibers impact the density calculation. 
     Benefits of the Improved Bullet Absorbing Components 
     To date, the improved bullet absorbing components have consistently performed well in ballistic testing. Anecdotal evidence suggests significantly higher failure rates for traditional SACON® ballistic concrete than with the improved production process. These failure rates may be due to a lack of consistency of the product using traditional SACON® ballistic concrete. The improved production process produces a very consistent material with an extremely low (much less than 1%) failure rate of the penetration test listed above. 
     Other benefits for the improved ballistic concrete are the predictable and uniform results in ballistic performance when the mix falls within the target density range. By uniform results, it is meant that penetration tests on different parts of a panel made with the improved ballistic panel will all pass the penetration test. 
     The process is sufficiently predictable that when a sample falls outside of the target range for density after the prescribed mixing period, this aberrant result is a strong indicator that the sand used in the mix is out of specifications, perhaps because of inclusion of clay or another contaminant. 
     Modification for Slower Projectiles 
     Those of skill in the art, recognize that the muzzle velocities for different types of ammunition differs a considerable amount. For example, within pistols, the muzzle velocity of a 9 mm handgun is significantly higher than the muzzle velocity of a 45 caliber pistol. The muzzle velocity for a given type of ammunition will actually depend on part on the length of the barrel of the gun. 
     In order to design a ballistic barrier for a lower velocity projectile than used in the standard penetration test described above, the ballistic barrier must be made easier to penetrate so that the back end of the projectile penetrates more than one inch into the ballistic barrier. Increasing the amount of chemical air entrainment additive and or increasing the mix time to downwardly adjust the density target for the ballistic material will enable the ballistic panel to be tuned for use with a particular lower velocity projectile. Density of the ballistic concrete may be dropped by simply mixing longer without changing the amount of air entrainment additive. May need to augment with additional air entrainment additive for a severe change in density. 
     Modifications for Other Bullet Depth Ranges. 
     One of skill in the art could modify the teachings of the present disclosure to tune the ballistic concrete to capture a bullet from a prescribed round, firearm, and firing distance within a depth range that is different from the 1 to 5 inch range referenced above. Thus, a ballistic concrete component could be tuned to capture bullets in a depth range of 2 to 6 inches of depth as measured to the part of the bullet closest to the entry point, or 0.5 inches to 3 inches of depth as measure to the part of the bullet closest to the entry point. 
     It is to be understood that, while the teachings of the disclosure have been described in conjunction with the detailed description, thereof, the foregoing description is intended to illustrate and not limit the scope of the claimed invention. Other aspects, advantages, and modifications of the teachings of the disclosure are within the scope of the claims set forth below. All publications, patents, and patent applications cited in this specification are herein incorporated by reference as if each individual publication or patent application was specifically and individually indicated to be incorporated by reference. 
     One of skill in the art will recognize that some of the alternative implementations set forth above are not universally mutually exclusive and that in some cases additional implementations can be created that employ aspects of two or more of the variations described above. The legal limitations of the scope of the claimed invention are set forth in the claims that follow and extend to cover their legal equivalents. Those unfamiliar with the legal tests for equivalency should consult a person registered to practice before the patent authority which granted this patent such as the United States Patent and Trademark Office or its counterpart.