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The Effects of Local Aggregates on the Mechanical Properties of Engineered Cementitious Composites (ECC)

Obied, Michel
A Master of Science thesis in Civil Engineering by Michel Obied entitled, "The Effects of Local Aggregates on the Mechanical Properties of Engineered Cementitious Composites (ECC)," submitted in June 2013. Thesis advisor is Dr. Adel K. Al-Tamimi. Available are both soft and hard copies of the thesis.
Engineered Cementitous Composites (ECC) are a class of ultra-ductile fiber reinforced cementitious composites characterized by a strain hardening behavior and a high strain capacity when subjected to tensile loading. ECC integrates micromechanical models and fracture mechanics principles in the design concept which makes it an engineered material. These features promote ECC as a promising material for a wide range of applications which include repair of structures, and resistance to seismic activity, impacts, and blasts. However the high initial cost of the material which is three times the cost of conventional concrete hinders the widespread use of ECC. Also, the high carbon footprint and the high cement volume can be a potential problem for the environment. Therefore this research sought to reduce the cement volume by producing ECC with aggregates and producing it at an Aggregate to Binder ratio of 0.8. This means the new non-standard ECC has twice as much aggregate as can be found in standard ECC. ECC with aggregates is expected to perform better than standard ECC in terms of drying shrinkage, creep, workability, strength, and cost, while still preserving all the good mechanical performance of standard ECC. There is however a decrease in strain capacity from 5% to 2%. Other researchers also faced this decrease in strain capacity when investigating ECC with aggregates. Yet, this research provides an even better version of ECC with aggregates which has a compressive strength of about 82 MPa and a tensile strength of 8 MPa on average. Furthermore, the fiber / matrix interfacial bond (τ) was estimated to be around 1.4 MPa. The high estimated bond value was a result of using a special technique to increase the strength and the particle packing of the ECC matrix. Moreover, by using local materials available in the UAE, this research proved that aggregates in the UAE are suitable for making ECC. Finally, this research attempted to use Ultra-fine fly ash in order to regain strain capacity and to enhance the greenness and the workability of the material. Results of the current research will open the door into a vast range of research regarding ECC with aggregates.
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