Monitoring strain in engineered cementitious composites using wireless sensors

The emergence of new structural materials opens exciting venues for improving the strength and durability of civil structures. Engineered Cementitious Composites (ECC) are a special class of fiber reinforced cementitious composite (FRCC) that combine short polymer fibers with a cement matrix to produce a material, which undergoes strain-induced hardening and is ultra-ductile when loaded in tension. The unique electrical properties of FRCC materials render them a smart material capable of measuring strain and the evolution of structural damage. In particular, the material is piezoresistive with changes in electrical resistance correlated with mechanical strain. In this study, the piezoresistive property of ECC structural specimens are exploited to directly measure levels of tensile strain. To enhance the resistivity properties of the material without disrupting mechanical strength, small volume fractions of short steel or carbon fibers are included within the ECC matrix. Changes in ECC electrical resistance are measured using a two-probe direct-current (DC) resistance test as specimens are monotonically loaded in tension. To collect the resistance measurements of ECC specimens during testing, a low-cost wireless sensing unit is employed.