Effect of CaO—Based Expansive Agent on Strength of ECC

Engineered Cementitious Composites (ECC) or Strain Hardening Cementitious Composites belong to the family of fibre reinforced concrete. They are known for their tensile strain capacity of 2–8% which is several hundred times that of normal concrete. This ductile nature of ECC makes them suitable for use in a wide range of applications, but they face the disadvantage of high shrinkage values (1200–1800 μℇ) which limits its applications. Normal shrinkage reducing agents work by reducing surface tension of pore solution. Shrinkage compensating agents on the other hand, allow for the growth of expansive crystals. Usual expansive agents (EA) also increase water requirement, which is unavailable in mixes with low water-cement ratios. This fact makes the selection and use of EA important. MgO—based expansive agents (EA) react in later stages whereas CaO based EAs react very fast and generate expansive effect in early stages when the composite has not achieved significant strength, and therefore won’t generate cracking stresses or durability problems. Even though the effect of expansive agents has been studied in the past, there is very little knowledge about their effect on strength. The aim of the study is to investigate the effect of CaO—based EA addition on compressive strength of ECC. The mix is incorporated with different dosages (2.5, 5, 7.5, 10%) of the agent, and compared to the reference mix. Compressive strength, and Ultra Pulse Velocity (UPV) tests were conducted to gain an understanding about the strength and homogeneity of the composite. The results were reflective of minor effect of CaO addition on strength (4–10%).