POLYMER CONCRETE REINFORCEMENT

Polymer concrete has traditionally been reinforced with steel rebar, but WEAV3D composite lattice technology has emerged as a superior reinforcement system that offers corrosion resistance and design freedom not possible with rebar cages. Unlike steel, our patented and patent-pending thermoplastic composite lattice forms an adhesive bond with the polymer concrete, enhancing the impact strength and other mechanical properties of the finished concrete part.

To demonstrate the adhesion of our lattice reinforcements with open- and closed-mold polymer concrete, we engaged a local university to conduct lap shear tests on several sets of plastic-embedded polymer concrete specimens. Six thermoplastic materials were tested to evaluate interfacial adhesion between the plastic and the polymer concrete:

• Polypropylene (PP)
• Polyester terephthalate (PET)
• Polyester terephthalate glycol (PETG)
• Polyamide 6 (nylon 6)
• Polyamide 6,6 (nylon 6,6)
• Polycarbonate (PC)

For each material, four plastic strips were incorporated into an unsaturated polyester polymer concrete slab as part of a regular pour cycle and cured per standard processes, either open molding or closed molding.

Test specimens were prepared by cutting the as-cast polymer concrete parts into strips approximately 0.75-inch wide using a waterjet. Two notches were cut into the specimens — the first notch through the polymer concrete and the second notch through the plastic strip — to create a lap shear region approximately 1-inch long and 0.75-inch wide. In order to fit the grip width of 1-inch on the universal testing machine, the polymer concrete on each end of the open mold specimens was notched to reduce the thickness from 1.5 inches down to 0.75 inch.

Specimens were loaded into a 5-kN universal testing machine and a tensile displacement was applied at a crosshead rate of 1.5 millimeters per minute. Recording the force and displacement allowed calculations of max shear stress and total shear toughness.

Of the six materials tested, PETG emerged as the best tape material considering its high adhesion and its low cost relative to PC which also exhibited good adhesion. All PETG samples failed in tension, either due to PETG rupture or polymer concrete rupture, rather than shear failure. Polypropylene and both nylon grades exhibited such low adhesion that many disbonded from the polymer concrete during the waterjet cutting process.

While PETG is a copolymer in the same family as PET, PET specimens failed via lap shear disbond instead of tensile rupture. The average force required to induce tensile failure in the PETG-Open specimens was three times that of the average force to induce shear disbond in the PET-Open samples, indicating that PETG possesses unique chemical properties that enhance adhesion with the unsaturated polyester resin used in polymer concrete.

Closed Mold. While PETG exhibited some softening-compressive flow caused by the elevated curing temperature of the closed-mold process, this behavior does not appear to have weakened the material. In fact, it may have actually improved the interface with the polymer concrete as it provided a compliant surface to accommodate the aggregate and increase contact area. In both of the closed-mold specimens tested, the polymer concrete fractured under tension before the lap shear region failed. The difference in failure mode between the closed-mold and open samples is largely attributable to the fact that the closed-mold samples are thinner in the test region, only 0.75-inch thick compared to the 1.5-inch thick open-mold samples. This, combined with the higher aggregate fraction of the closed-mold mix, leads to greater stress concentrated in the polymer concrete. Due to the observed tensile ruptures, we were not able to precisely determine the lap shear strength of the interface, though we can conclude that it exceeds the tensile strength of the constituent materials of this cross-sectional area.

Open Mold. In all four of the PETG-Open samples, the PETG itself failed in tension before any disbond occurred in the lap region. The fracture consistently originated in or adjacent to the polymer concrete notch and then propagated through the thickness of the plastic strip, leaving a hinge contact on the exposed face of the plastic strip. Similar to the PETG-Closed, we cannot definitively state the adhesion strength, only that the adhesion strength of the PETG-polymer concrete interface is higher than the tensile strength of the PETG, adjusting for tensile cross-section.

Conclusions. PETG withstood the high cure temperature of the closed-mold process and also exhibited very high interfacial bond strength with the polymer concrete in both molding processes. Glass-reinforced PETG exhibits 15 to 20 times the tensile modulus and 10 times the tensile strength of unreinforced PETG, while carbon-reinforced PETG exhibits 50 times the tensile modulus and 15 times the tensile strength of PETG. As a result, the overall load capacity of a lattice-reinforced polymer concrete structure will be substantially higher than what was observed in these shear specimens. Lattice-reinforced polymer concrete can be used to replace steel rebar in a variety of polymer concrete applications. Beyond polymer concrete, these results also indicate the potential for strong adhesive interaction between PETG lattices and any product made from unsaturated polyester resins, including sheet molding compound, bulk molding compound and composite spray molding.