The lineal range of water-to-cement (w/c) ratios to be used for general construction works is 0.38 to 0.55, considering ‘mild’ to ‘extreme’ environments as per IS:456 specifications. Irregardless using such w/c ranges, certain factors such as poor quality materials, improper aggregate gradation, inadequate compaction and curing periods, poor workmanship and quality control practices, etc., can yield poor quality concretes or concretes that are permeable. In addition, specific applications involve concrete to be used for underwater construction, lean construction and others. Although conventional or lower w/c ratios are used in underwater construction, the placed concrete under water may have very high w/c as against the originally designed concrete. In the current study, efforts are taken to study the behavior of high w/c concrete containing limestone powder. While provisions are available to use limestone powder as a partial replacement material for cement as per ASTM, the same is experimented at dosages of 10%, 20% and 40% by mass of cement. The objective of the study is to investigate the ability of limestone powder to serve as a pore filling material for concretes having high w/c ratio. Eight tests were conducted and attempts were taken to inter relate pore properties of these concretes to their corrosion mitigating ability in microcell and macro-cell corrosion tests using cylinder and prism specimens, respectively. While limestone powder addition was observed to be beneficial at 10% and 20% dosage levels, their addition beyond 20% provided poorer properties in most tests.