To enhance the durability of reinforced concrete structures, high performance concrete with low water/binder ratio is often employed. However, the opening of cracks in the concrete cover due to mechanical loading or shrinkage can accelerate the penetration of water and chloride to induce steel corrosion. The present study focuses on an alternative approach for the construction of durable concrete members with the use of permanent formwork.

To make the formwork, pseudo-ductile cementitious composites (PDCC) are employed. With the addition of fibers, the PDCC exhibits multiple cracking up to strain level of several percent. With crack openings controlled to very small values, the transport properties stay similar to those of the un-cracked material. In addition to PDCC, glass fi...[ Read more ]

To enhance the durability of reinforced concrete structures, high performance concrete with low water/binder ratio is often employed. However, the opening of cracks in the concrete cover due to mechanical loading or shrinkage can accelerate the penetration of water and chloride to induce steel corrosion. The present study focuses on an alternative approach for the construction of durable concrete members with the use of permanent formwork.

To make the formwork, pseudo-ductile cementitious composites (PDCC) are employed. With the addition of fibers, the PDCC exhibits multiple cracking up to strain level of several percent. With crack openings controlled to very small values, the transport properties stay similar to those of the un-cracked material. In addition to PDCC, glass fiber reinforced polymer (GFRP) can be incorporated into the formwork to provide flexural resistance. In some applications, the member can be made by casting concrete directly on the formwork. In others, a reduced amount of steel reinforcement can be added. With steel protected by the GFRP/PDCC formwork (which acts as part of the cover), high durability can be ensured.

In the thesis, we will first describe the material employed for making the permanent formwork and the method to fabricate U-shape formwork for slabs and beams. Test results on components made with both flat and U-shape permanent formwork will then be presented. Failure behavior will be discussed and failure load compared to analytical values. Special attention will be paid to the effect of debonding between cast concrete and formwork, and how debonding may be controlled. A design envelope is raised based on the experimental results for a safe design avoiding debonding failure in flexure.

To replace the stirrups inside the structures in order to further extend the service life, studies on the feasibility of employing CFRP/GFRP textile embedded in the formwork as shear reinforcement is also studied. The simple joining method for formworks when a longer span is needed is also tested and the results will be discussed in the thesis. An example will be provided to illustrate the use of GFRP/PDCC formwork in practice.