Unidirectional Fiber Composite Profiles

Unidirectional fiber-composite rods used for reinforcing concrete in buiiding construction are often exposed to long-term loads and various ambient media. Prediction of their creep behavior is typicaiiy based on laboratory experiments that rareiy extent to more than one year. For time scaiing, increased temperatures and stresses are used, as well as direct exposure to chemicais [1017]. 

The difficulty lies in the complexity of the mechanisms governing the effective action of these special ambient conditions. Intensified exposure does not necessarily lead to linear dependence on particular influencing factors. 

Increased mechanical loads mean deformation in both resin and fibers. Here, the fibers, which provide the actual strength, exhibit iess differing behavior than the viscoelastic matrix. The matrix exhibits increased diffusion tendency when the volume is increased, in particular to fluid media. 

Creep-tensile test results for aramid fiber rods in various ambient media [1011] 

Water-saturated rods made from aramid or glass fiber reinforced plastics exhibit a reduction of 8 to 10% in short-term strength compared to dry rods (which is largely reversible). At elevated temperatures, permanent hydrolytic damage may occur [1011]. Therefore, short-term tests are often performed applying loads far above actual operating loads and under time-dependent physico-chemical ambient conditions that in service may cause very different softening effects at much lower mechanical loads. 

---