عنوان مقاله [English]
A number of experimental tests were conducted to better understand of the mechanical performance of a special class of high performance fiber reinforced cementitious composites, namely engineered cementitious composites (ECC) which is reinforced with high modulus polymeric fibers. The design approach of the ECC materials is based on fracture mechanics principles, which will be described in the first part of the paper. Unlike concrete or regular fiber reinforced concrete (FRC), ECC materials are characterized by their ability to sustain higher level of loading after first cracking undergoing additional straining. This strain hardening gives ECCs a significant advantage under flexural loading. The application of ECC materials and other strain hardening
cementitious composites require adequate information on their basic material properties for structural purpose. The ECC examined in this investigation is a Portland-cement based mortar matrix with a low volume fraction (typically 2%) of high modulus PVA fibers. The ECC properties measured by use of accurate experimental test setups include uniaxial tensile, compressive, and flexural behaviors as well as multiple cracking development. The experimental results showed that the ECC material exhibits a unique strain hardening behavior with high tensile strain capacity due to multiple cracking. The results of uniaxial tensile tests presented in terms of first crack strength, ultimate strength and ultimate strain at the peak stress. The average first crack strength was found
to be 3.25 MPa and all ECC dogbone specimens showed strain hardening behavior with strain capacity from 3 to nearly 3.7%. The compressive behavior of ECC cylinders exhibited an average of ECC beams compressive strength of 47 MPa at a strain level of 0.55%. The flexural characteristics tested under four-point bending revealed high deformability and strain hardening behavior in comparison to low deformation capacity and strain softening behavior of steel fiber reinforced concrete beams. The significant enhancement of energy absorption
capacity and tight crack width control in ECC beams under bending indicate that ECCs can serve as a basic structural material or use in repair works.