The construction industry contributes up to 60 % of global resource consumption, with growing demand fuelled by the world's growing population. The production of cement and concrete consumes about 10 % of the world's energy and is a major source of global greenhouse gas emissions. Reinforcing concrete with glass, basalt or carbon fiber reinforced plastics can significantly reduce material consumption, construction material costs, time, weight, wall thicknesses as well as greenhouse gas emissions and waste generation. Due to the corrosion resistance of the composites, considerably less concrete cover can be used. Compared to reinforcement with steel, this results in an up to 80 % reduction in concrete consumption with a corresponding reduction in the weight of the concrete structures.
The possible applications of fiber-reinforced composites as concrete reinforcements and generally for the construction of buildings and bridges have so far been limited mainly by the relatively low working temperature of the organic matrices (< 200 °C) and their flammability or fire behavior. Often, they do not meet the high fire safety requirements in construction. One way of utilizing the aforementioned advantages of textile composites in construction and meeting the fire safety requirements is to use Fine-grained concrete or inorganic chemically bonded ceramics (CBC) matrices such as water glass systems or phosphate ceramics. Water glass matrices and concretes are strongly alkaline in nature and aggressive for E-glass or basalt fibers. For this reason, only expensive AR-glass or carbon fibers are usually used.
The AiF project NiBreMa addresses these challenges through the development of phosphate ceramic matrix that is in the acidic pH range in its initial state and thus does not harm E-glass or basalt fibers. For this approach, the DITF together with the DLR ( German Aerospace Center) investigated both the matrix and the process development. Various parameters play a decisive role in the development of the phosphate ceramic slurry:
> the choice of raw materials; they must contain the required amount of aluminum and silicate with suitable physical properties
> the pH of the slurry; it determines the pot life of the matrix and the reaction kinetics of the alumino-silicate salts with the acid solution
> the viscosity and wettability of the slurry; they influence the processability with basalt fibers in the pultrusion and winding process
In the project, different slurries with various additives and fillers were developed and tested to maximize the mechanical properties and compatibility of the matrix for concrete. With regard to the processability, curing behavior and mechanical properties of the basalt fiber-reinforced phosphate ceramic composite, the fiber volume content, pultrusion temperature, pulling speed and post-curing temperatures were investigated in the pultrusion process. The cold-cured basalt fiber-reinforced composites exhibit good mechanical properties and good compatibility with Portland cement concrete.
The developed ceramic composites maximize the use of E-glass and basalt fibers for construction applications, especially where fire safety requirements are critical.