MDOT has been working with Lawrence Technological University [in Michigan] for many years to develop carbon fiber reinforced polymer (CFRP) prestressed concrete beams. Recent research developments on demonstration projects have shown that 0.6 inch diameter CFRP strands have smaller nominal area and lower allowable capacity than steel 0.6 inch diameter steel strands; thus requiring more strands for a given design. This makes it difficult for bridge designers to find projects where we can fit enough CFRP strands in a beam to meet load carrying requirements.

1. To evaluate material properties, details, and design criteria to use 0.7 inch diameter CFRP strands for pretensioning of prestressed AASHTO I girders, bulb-t, and box beams. 2. To evaluate performance of 0.7 inch diameter CFRP strands for environmental conditions and extreme events. 3. To prepare design procedures and examples. 4. To prepare construction specifications for 0.7 inch CFRP strands and identify fabrication concerns with the larger diameter strands.

Currently, 0.7 inch diameter CFRP strands are available; thus, making the use of CFRP pre-tensioning in pre-stressed beams more viable. The proposed research is necessary in order to evaluate the safe use of 0.7 inch diameter CFRP strands in a beam to meet load carrying requirements. The following research tasks are recommended: Task 1: Evaluate and report on the material properties of larger diameter (0.7 inch) CFRP strands including confirmation of ultimate strength and manufacturer guaranteed tensile/strain capacity at ambient as well as elevated temperatures. Compare and report on the difference in material properties and performance between 0.7 inch CFRP strands and strands with a smaller strands diameter (0.6 inch) CFRP strands under various harsh conditions such as ASTM 666. Prepare and evaluate the effectiveness of various anchorage systems for prestressing applications. Evaluate creep rupture stress, relaxation loss, and overall long-term losses using available test standards and verify the results through extended monitoring period subjected to harsh environmental conditions that highway bridges are exposed to. Task 2: Evaluate and report on the interaction between 0.7 inch CFRP strands and structural concrete in pre-tensioning applications. Evaluate design criteria such as guaranteed ultimate tensile strength, transfer length, development length, bond strength, proper concrete cover, strands spacing, and effect of difference in coefficient of thermal expansion between concrete and CFRP on the bond strength under loads and severe weather conditions. Task 3: Evaluate and report on the performance of 0.7 inch CFRP strands under extreme events such as fire/loading events following ASTM E-119 and under multiple cycles of freezing and thawing on large-scale prestressed beams following appropriate test standards. Task 4: Evaluate and report on unique changes to CFRP prestressed beam design procedures when 0.7 inch CFRP strands are used for longitudinal pre-tensioning. Task 5: Test and evaluate the performance of full-scale precast prestressed beams prestressed with 0.7 inch strands and compare the performance with similar beams prestressed with 0.6 inch steel and CFRP strands. Task 6: Prepare design procedure/examples and construction specifications for 0.7-inch CFRP prestressed concrete highway bridge beams and identify fabrication concerns and potential solutions to the larger diameter strands in relation to the current stressing bed layouts.

Contract Extension Authorization Z3/R2. Revised completion date 12/31/2021.