Abstract:
Engineered Cementitious Composites (ECC) are known as “bendable concrete” for their high ductility and strain-hardening behavior. ECC can also address durability and sustainability issues in modern infrastructure. For this reason, this material has gained attention as advanced construction material worldwide. However, ECC usually requires high-quality materials such as manufactured silica sand which is not available in the local market of Bangladesh. This type of high purity sands needs to be imported which is associated with high cost. To address this issue, utilization of locally available resources offers a cost-effective solution for wider use of ECC in construction sector. This study investigates the potential use of locally available Sylhet Sand and PVA fiber to produce ECC mixes. The objective of this study is to develop ECC mix using Sylhet sand and PVA fiber with optimal mechanical properties.
In this study, 14 different ECC blends and one cement composite blend without any fiber were analyzed. The aim was to investigate how variations in fly ash-to-cement ratio, fiber volume, fiber length, sand-to-binder ratio, and water-to-binder ratio affect the mechanical properties of ECC. Mechanical tests, including compressive strength, splitting tensile strength, and flexural strength test were conducted on a total of 405 hardened specimen. These tests were performed at curing periods of 7, 28, and 90 days. The compressive strength, compressive stress-strain behavior, flexural strength and toughness, deflection under bending, and splitting tensile strength of each mix at each curing period were analyzed in this study.
Key findings reveal that most of the studied blends with Sylhet sand exhibit required ductility and flexural toughness. Most of the blends can undergo large curvature development under bending as load increases with deflection in the post-cracking region before reaching strain-softening period. Also, ECC mix with fiber volume of 2.5% shows strain-hardening behavior with prolonged curing time which is highly desirable for ECC material. However, the ECC blend with 1% fiber showed maximum compressive strength (15% increment than that of ECC with 2.5% fiber). With extended curing up to 90 days, a fly ash-to-cement ratio of 0.25 improves flexural, tensile, and compressive performance. Similarly, ECC blends with fiber lengths of 12 mm exhibit optimum strength throughout compressive, splitting tensile, and flexural testing, whereas 18 mm fibers marginally increase the flexural toughness. Considering, both the workability and mechanical strength, a water-to-binder ratio of 0.30 shows ideal performances. A sand-to-binder ratio of 0.36-0.50 provides comparable compressive, tensile, and flexural strengths. On the other hand, the sand-to-binder ratio of 0.42 exhibits a slightly greater value of flexural toughness. Also, all the ECC blends show a lower modulus of elasticity and higher Poisson’s ratio than conventional concrete.
The fresh property, measured by the flow spread diameter and mechanical properties such as compressive strength, flexural strength, splitting tensile strength, modulus of elasticity, and Poisson’s ratio of studied blends meet the recommended range of mechanical properties of ECC. Also, ECC blends with fiber show improved flexural toughness property. So, a cost-effective ECC blend can be developed using local Sylhet sand and PVA fiber without compromising the characteristics of ECC material.