The concrete layers of traditional sandwich elements were replaced by FRRPC in order to make the panel thinner and lighter. Standard reinforced concrete layers have a thickness of minimum 80 mm. This derives from protection requirements for the steel reinforcement. In our case we replaced the steel with an alternative non-corroding material, a carbon fiber textile grid in order to avoid steel corrosion. At the same time the strength of these layers were drastically increased.
RPC is a material with high cement clinker content. In order to reduce the absolute clinker content supplementary cementitious materials (SCM) were employed. In total three different mixes were developed. The next figure shows the binder composition and the respective amounts of cement clinker replacement and the achieved compressive strength.
For upscaling of the development to the panel stage the mix design RPC-CBI1 was chosen since it performed best in mechanical, and early age properties. A name for this mix, Sesbonite®, was protected by a trademark. The main results of RPC-CBI1 are summarised in the following:
– Clinker replacement 33 mass-%
– Compressive strength 142 MPa
– E-modulus 50 GPa
– Poison ratio 0.216
– Can be mixed in large scale mixer with low energy (e.g. force action mixer)
– With textile reinforcement a high peak deformation can be achieved. In 4-point bending tests of 25 mm panels midspan deflections between 40 and 50 mm could be achieved before failure.
– Material costs for the developed RPC mix excluding the reinforcement is more expensive as a standard concrete per cubic meter. Taking advantage of the higher strength and durability reduces the thickness of RPC panels. Material costs per square meter for carbon textile reinforced RPC panels are ca. double as expensive as standard steel reinforced concrete. However, production costs are lower since the total volume of mixed concrete is less and the carbon textile reinforcement is easier to install as steel reinforcement
– The material can be produced in different colors. For colored material Sesbonite® White is used, which has a white base color and can be pigmented with any color: