6.Conclusions
The following conclusions were drawn from this investigation.
(i) Water curing for a period of 28 days (at 23∘C) proved to be the best curing system (compared to air, cold, and heat curing) in terms of compressive strength, chloride permeability, and corrosion resistance. The 28-day water-cured samples (curing technique 2) had the longest times to show signs of corrosion initiation, cracking, and damage among all tested samples, under the curing conditions of the present tests.
(ii) Among all tested samples, the first samples that showed corrosion initiation, cracking, and damage were those cured in heated water for 7 days at 50∘C.
(iii) Increasing the water-curing period from 3 to 28 days (at 23∘C) in techniques 2, 3, and 4, regardless of the concrete cover thickness, decreased the chloride permeability, increased the 28-day compressive strength, and increased the corrosion initiation, cracking, and damage times by approximately 6%, 10%, and 3%, respectively.
(iv) The increase in the cold air-curing times (at 3–5∘C) from 21 to 28 days in techniques 5, 6, and 7 for all tested concrete covers maximized the chloride permeability, reduced the 28-day compressive strength, and yielded a reduction of the corrosion initiation, cracking, and damage times by about 9%, 6%, and 3%, respectively.
(v) Extending the heat-curing periods (at 50∘C) from1 to 7 days in techniques 8, 9, and 10 for all concrete cover samples was found to reduce the corrosion initiation, cracking, and damage times by almost 14%, 15%, and 3%, respectively.
(vi) The trend of the results of the corrosion initiation periods obtained from the accelerated corrosion test was similar to that obtained from Fick’s second law of diffusion for counterpart samples, under the same assumptions of the present study.
(vii) The results of the electrical current readings concur with those of the half-cell potential measurements in all tested samples. The corrosion initiation was
found to occur at the first jump of the current measurement and at half-cell potential reading values around −350mV, which indicate 90% probability of corrosion, as per ASTM C876.