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Creep is a complex behavior of concrete since it induces different stages of response under loading and unloading with time. It represents the time-dependent strain as a result of a constant sustained load applied with time. In cementitious materials such as engineered cementitious composite concrete, ECC, the loaded cement paste is the principal source of creep strain. Therefore, investigating the overall creep behavior, under the loading and unloading stages, will be beneficial in providing data for the performance of ECC concrete. The test for compressional creep strain is done according to the ASTM C- 512 under controlled temperature (21 oC) and relative humidity (40%). In this research, the loading stage lasted for 9 months, and the unloading stage lasted 3 months. The total creep strain, creep coefficient, and specific creep were recorded for six ECC concrete mixes. The mixes have two strength levels, 30 and 60 MPa at 28 days, and contain polypropylene and polyvinyl alcohol fibers. Results revealed significant enhancement, and lower creep behavior, in mixes including fibers compared to plain mixes. The best promising results for the creep coefficient and specific creep were recorded when using mixes of 60 MPa containing polyvinyl alcohol fibers compared to plain mixes.

Engineered Cementitious Composites (ECC) are ultra-ductile materials, and the fibers used provide superior flexibility and strain capacity. This study investigates the use of two different types of polymeric fibers, Polypropylene (PP) and Polyvinyl Alcohol (PVA), with volume fractions of 1 and 2%, and studies their effect on stress-strain relationships, load-displacement behavior, toughness, and elasticity of ECC mixes produced with two strength levels, 30 and 60 MPa. The results showed that mixtures with PVA fiber ionic coating had a better performance than those with PP fibers due to the chemical reaction between the PVA fibers and the ECC matrix. This performance was confirmed by Scanning Electronic Microscopy (SEM). For normal-strength concrete (30 MPa), the modulus of elasticity increased by 7.8 and 9.6% for mixes with PP and PVA fibers, respectively, while in high-strength mixes (60 MPa), it increased by 9.4 and 10.85%, respectively. Toughness increases with increasing matrix strength, which is associated with an increase in cement content and fiber fraction. This study also investigates the effect of incorporating a PVA solution in ECC mixes, which leads to an increase in yield stress. This behavior was observed in the stressstrain behavior of 60 MPa mixes with 2% fibers which were compared to 30 MPa mixes with 1% fibers. [ABSTRACT FROM AUTHOR]