Feasibility of concrete prestressed by shape memory alloy short fibers

Abstract

Mortar and concrete exhibit low tensile strengths. Hence, cracks develop easily due to shrinkage and extemal actions. They can be prevented by applying prestress, thus obtaining crack-free products. Such products exhibit a high bending and tensile strength, are leak proof and of high dmability. Presh•ess can be realized using extemal or internal wires or cables. In thin walled products, however, this is not feasible. For this purpose, short fibers of shape memory alloy (SMA) wires were embedded in m01iar. The wires had been shaped by inelastic elongation into loop-and star-shaped fibers. After hardening of the m01iar, the specin1ens were heated up in order to activate the tensile stress in the fibers, thereby causing a presh•ess of the surrounding m01iar. The effect was monitored by length measurements both on specimens with and without fibers. Compression sh•esses in the cement m01iar were estimated by multiplying the difference in strain between fiber-reinforced and reference prisms by the Yollilg's modulus. Thus, compression of some 7 MPa was reached in the experiments. For practical applications, alloys with suitable temperature domains of austenitic and maiiensitic trai1sfonnation, most likely Fe-based, and efficient methods for the production of such fiber mo1iars are to be developed.

Interaction Between Concrete Cylinders and Shape-Memory Wires in the Achievement of Active Confinement

“…When the shape memory effect was activated by the heating of the specimen, the prestressing effects were usually estimated by comparing strain measurements in the SMA/concrete specimen with strain measurements in a plain concrete companion specimen. By means of this method, compressive prestressing up to 6 MPa has been estimated in mortar samples reinforced with SMA short fibres [12].…”

“…Attempts were done of estimating the progressive stressing of small-scale SMA/concrete specimens caused by the shape recovery process in the SMA [11,12]. When the shape memory effect was activated by the heating of the specimen, the prestressing effects were usually estimated by comparing strain measurements in the SMA/concrete specimen with strain measurements in a plain concrete companion specimen.…”

New SMA Short Fibers for Cement Composites Manufactured by Cold Drawing

“…They used long NiTi SMA fibers, showing the self-stressing capacity of cement composites through experimental tests. Moser et al (2005) introduced loop and star shaped SMA fibers to provide a geometrical anchorage; they also used the shape memory effect of prestrained SMA wires to provide prestressing stress that prohibited tensile cracking in mortar. However, loop or star shaped SMA fibers are difficult to use for mass production and may induce a mixing problem that prevents uniform distribution of fibers in cement composites and that is observed in steel reinforcing fibers with end hooks; this problem is called "fiber balls".…”

Constitutive Modeling of Prestressed Shape Memory Fiber–matrix Compounds

“…Other authors use shape memory alloys for additional reinforcement in masonry structures (see Indirli et al [16], [17]) or self-healing applications [29]. A new proposal for the use of shape memory alloys was presented in Moser et al [24] where the material is introduced as fiber-reinforcement in concrete structures. The possibility of prestressing those structures subsequently is discussed.…”