Precast Panel Blast Testing Summary

Two blast tests were performed on monolithic precast panels of the ProtectiFlex technology at the Stone-OBL blast testing site located in Deschutes County, Oregon near Bend, Oregon.  An existing reinforced concrete reaction structure was supplemented with a rigid steel frame and plate system to accommodate the test panel, as shown in Figure 1.

 
 
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Figure 1- Stone-OBL Test Fixture with Steel Frame and Plate System

 
 

Specifications

The blast-tested monolithic precast panels were nominally 8-ft (2440-mm) tall by 4-ft (1220-mm) wide by 8-inch (203-mm) thick. They were each reinforced with double mats of #3 (9.5-mm) fiber-reinforced polymer (FRP) rebar. Bolted panel connections to be made between the test specimen and the test fixture.

The U.S. Army Corps of Engineers Protective Design Center Technical Report PDC-TR 06-08 (Revision 1 dated 7 January 2008 – APPROVED FOR PUBLIC RELEASE) describes damage levels and levels of protections (LOPs) and was used to classify the responses for each test. Table 1 provides descriptions for each component damage level and the corresponding building LOP considering the component as a façade or secondary (i.e., non-load bearing) structural element. For a primary (i.e., load bearing) structural element, each damage level would correspond with the building LOP in the row immediately above it.

 
 

Table 1.  Component Damage Level Descriptions per PDC-TR 06-08

Component Damage Level Description Building Level of Protection*
Blowout Component is overwhelmed by the blast load causing debris with significant velocities. Below Antiterroism Standards
Hazardous Failure Component has failed, and debris velocities range from insignificant to very significant. Very Low (VLLOP)
Heavy Damage Component has not failed, but it has significant permanent deflections causing it to be unrepairable. Low (LLOP)
Moderate Damage Component has some permanent deflection. It is generally repairable, if necessary, although replacement may be more economic and aesthetic. Medium (MLOP)
Superficial Damage Component has no visible permanent damage. High (HLOP)
 
 

Unified Facilities Criteria (UFC) 4-010-01 (dated 9 February 2012 with Change 1 from 1 October 2013 – APPROVED FOR PUBLIC RELEASE) provides minimum antiterrorism standards for U.S. Department of Defense buildings. Within that document, conventional construction types and acceptable standoffs for each type to meet a Low Level of Protection (LLOP) per PDC-TR 06-08 to two explosive weights (W I and W II) are tabulated. However, the conventional construction standoff distances (CCSDs) within UFC 4-010-01 apply only for certain ranges of wall spans and thicknesses. Similar required standoffs for specific wall spans and thicknesses can be generated using a single-degree-of-freedom (SDOF) methodology. It can be shown via SDOF analysis that reinforced concrete and fully grouted masonry walls spanning 8 feet (2440 mm) with a thickness of 8 inches (203 mm) and #3 conventional vertical reinforcement at 12 inches (305 mm) on center on each face are expected to achieve Moderate Damage (i.e., maximum deflection of 1.7 inches or 43 mm) for Explosive Weight WI, similar to the explosive weight used in each test, at a standoff as close as 40 to 50 feet (12.2 to 15.2 m). A significantly larger standoff would be required to achieve Superficial Damage for these construction types, a consequence of the stiff walls having a very low elastic deflection limit (i.e., less than 0.2 inch or 5 mm).

An 8-inch (203-mm) thick normal weight reinforced concrete wall weighs 100 psf (490 kg/m2), while an 8-inch (203-mm) thick, fully grouted medium weight reinforced masonry wall weighs 80 psf (390 kg/m2). This blast testing program compared the standoffs and wall weights used in the test program to the required standoffs and wall weights noted above.

The explosive charges used in the testing program were equivalent to car and truck bomb threats with different standoff distances for each test. The performance of the monolithic precast panels during these tests were recorded using sensors and normal and high-speed cameras. The ranges of gauge readings recorded for positive phase pressure and impulse are presented in Table 2, along with summary of the blast performance. Figure 2 and Figure 3 show photographs of the ProtectiFlex monolithic precast panel following Test 1 and Test 2, respectively.

 
 

Results

 

Table 2. Blast Test Results Summary

 

Test Specimen Charge Standoff Peak Pressure Positive Phase Impulse Post Test Notes
1 1 50ft
(15.2m)
45-48psi
(310-330 kPa)
117-237 psi-ms
(810-940 kPa-ms)
Minor horizontal hairline flexural cracks in inbound and rebound. No observable permanent deflection. No spall or debris. Response categorized as Superficial Damage/HLOP for secondary element.
2 2 40ft
(12.2m)
77-102psi
(530-700 kPa)
164-204 psi-ms
(1130-1400 kPa-ms)
More Prominent horizontal hairline flexural cracks in inbound and rebound than in Text 1. Minor permanent deflection observered. No spall or debris. Response categorized as Moderate Damage/MLOP for secondary element.
*-Level of protection corresponding to given damage level for a secondary structural component.

 
 
 
Figure 2. Post-Test Photos of Test 1
 

Figure 2. Post-Test Photos of Test 1

 
Figure 3. Post‐Test Photos of Test 2
 

Figure 3. Post‐Test Photos of Test 2

 
 
 

ProtectiFlex Precast Panel Blast Test - External View

 
 
 

ProtectiFlex Precast Panel Blast Test - Internal View

 
 

As a basis of comparison, reinforced concrete and fully grouted masonry walls spanning 8 feet (2440 mm) with a thickness of 8 inches (203 mm) and #3 conventional vertical reinforcement at 12 inches (305 mm) on center on each face are expected to achieve Moderate Damage for Explosive Weight WI from UFC 4-010-01 at the tested standoffs listed in Table 1.

It can be observed that the standoff at which the tested 8-inch (203-mm) thick ProtectiFlex monolithic precast wall panel system achieved a Moderate Damage is similar to that of these two typical construction types.  The weight of the ProtectiFlex wall in these cases (78 psf or 380 kg/m2) approaches reinforced masonry (80 psf or 390 kg/m2), but is significantly less than reinforced concrete (100 psf or 490 kg/m2).  Moreover, per the results of the 50-ft (15.2-m) standoff case, it appears that the ProtectiFlex is noticeably more flexible than either reinforced concrete or masonry, allowing it to deflect more than these wall types without sustaining permanent deflections.

 
 

Precast Panel Ballistic Testing Summary

A ballistic resistance testing evaluation of the ProtectiFlex precast panel technology was conducted within an indoor range at Oregon Ballistic Laboratories in Salem, Oregon for various thicknesses of the ProtectiFlex precast panel technology in accordance with UL 752 and NIJ-STD-0108.01 testing standards. The muzzle of the test barrel was mounted at selected distances from the target and positioned to produce 0-degree obliquity impacts.

 
 
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Figure 4. Ballistic Test Set-Up

 

All panels tested for both ballistic testing standards had overall dimensions of 3 feet (910 mm) wide by 3 feet (910 mm) tall with thicknesses ranging from 3 inches (76 mm) to 10 inches (254 mm). Figure 5 shows a representative ballistic test specimen. Two developed proprietary mix designs for the ProtectiFlex precast system were evaluated. The mixes are designated as Ballistic Mix Design and Ballistic-Blast Mix Design. Further details of the ballistics testing results and associated ballistic ratings for the various thicknesses evaluated can be requested and released to authorized organizations.

 
Figure 5. Ballistic Test Specimen

Ballistic Test Specimen

Results

 

Overall, the ballistic testing results and assessment show that a thinner and lighter ProtectiFlex layer than concrete or masonry is needed to protect against higher ballistic ratings such as the UL 752 Level 10 threat, as well as to NIJ-STD-0108.01 Levels III and IV.  Overall, the biggest advantage of the ProtectiFlex precast wall panel system is seen in its mass-efficient protection against the larger ballistic threats (e.g., .50 caliber) and minimizing any potential spalling and debris.

 
 

Flame Testing

 

4” thick slabs of ProtectiFlex with FireCap coating were subjected to a constant 2000 °F, simulating UL 1709 conditions as an upper-bound for the fire load. After 60 minutes of direct fire impingement, the backside remained cool to the touch

 
 
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Close-In Blast Testing

 

Multiple Target Close-In Blast Demonstration

During a Stone-OBL demonstration course, a multiple target hand carried bomb scenario was performed comparing the effects of close range blasts on ProtectiFlex panels and reinforced concrete panels. The reinforced concrete panels were badly damaged or destroyed, becoming a flying debris hazard; And while the ProtectiFlex panels showed effects of the blast the coating layers and panel itself remained more structurally intact, minimizing the effects of fragmentation, spalling and risk of collapse or secondary entry.

 
 

Panels Pre-Blast

 
 
 

High Speed Video

 
 

Drone Video

 
 

Real Time Video

 
 

Panels Post-Blast

 
 

Contact Charge Testing of ProtectiFlex Solid Panel

3 tests were performed on ProtectiFlex panels of various thicknesse2s reinforced with composite rebar, placing charges in contact or near-contact. Though the charges were able to make a hole in the panel it remained largely intact, demonstrating the materials ability to remain structurally sound after an event and deny subsequent forced entry attempts.

 
 
 

Test 1 - 8” Panel

 
 

Test 2 - 10” Panel

 
 

Test 3 - Damaged 10” Panel 1 Foot Standoff

 
 

Repeated Person-Borne IED (PBIED) Threat Tests on ProtectiFlex Panel at Close Ranges With No Damage

During a Stone-OBL blast & ballistics testing demonstration event, a 12” thick ProtectiFlex panel was subjected to repeated close range blasts at progressively smaller standoffs, simulating the size and effects of a PBIED. After 3 charges, the panel remained undamaged.

 
 
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Panel Pre-Test

Panel After 3 Close-In Blasts