For concrete structures the use of structurally curved elements provides a better design. Curved elements, designed to experience mainly membrane action, are stronger, stiffer and more efficient than straight lined elements in bending. Hence, slender shell structures with efficient material use can be designed.

However, the construction of concrete shells remains currently a challenge in Western regions. Current formwork systems for concrete shells are very labour intensive or wasted after use. Furthermore the placement of traditional steel reinforcement is difficult to integrate in these flexible formwork systems.

This research examines a new formwork method using textile reinforced cement composites.Textile reinforced cement composites (TRC) consist of continuous fibre systems, textiles, which are impregnated with a cement or fine grained mortar. They harden at ambient temperatures. TRC composites are flexible in the wet phase; hence curved shapes can easily be obtained. In hardened phase, they are stiff and strong in both tension and compression.

To obtain a curved TRC surface, the TRC formwork can be shaped onto any (reusable) mould such as foam moulds, flexible formwork moulds, pneumatic formwork and prestressed membranes. The low weight of the TRC layer compared with concrete, which is normally poured on these moulds, is a great advantage. The TRC formwork can also repeatedly be prefabricated on the same mould and transported to site to act as permanent formwork for the concrete shell thanks to its good mechanical properties.

Finally, after hardening of the concrete, a mixed TRC-concrete section is obtained. Thanks to the relatively high tensile capacities of TRC and the good bonding between the two materials a reinforcing function is expected.

During the research the TRC layer is extensively examined in its functions as formwork and tensile reinforcement. On the one hand numerical (material) models are developed, which describe the behaviour of the shells, and on the other hand experiments are performed to evaluate these models.

The formwork market for columns is open for new technologies and materials, provided that the alternative offers a better or cheaper solution. For this reason, a resarch on stay-in-place formwork in textile reinforced cement composites (TRC) for circular columns is done. This formwork also replaces the steel reinforcement which is always present in traditonal concrete columns.

Firstly the effect of the structural formwork in the load capacity of concrete is examined. Theoretical predictions are compared with experiments (100 mm high specimens, with 50 mm concrete core and different thicknesses of the TRC formwork). The TRC formwork is executed in different ways to examine the effect of the interface and fixation between concrete and TRC. As seen in the results, the formwork gives a little increase in load capacity and especially has a great impact on the ductility of concrete. The thicker the formwork and the rougher the interface surface, the greater the impact on the ductility.

Secondly, slender columns of 1m height and 50 mm concrete core are examined. A formwork of 2-3 mm  has little or no impact on the critical buckling load, while starting from 5 mm thickness, there is a serious increase in the buckling load and this load even exceeds the predicte values. 

Finally, a case study is made in which these columns are used as the supporting structure of a building. Using established formulas, the columns are dimenioned in the whole building.