A Corrosion Model for prediction of Service Life of Reinforced Concrete water structures.

Abstract

As the world economies endeavor to support the United Nations sustainable development goals, new technologies are evolving for efficient design and manufacture of civil engineering products. Researchers have up scaled their effort to develop techniques to monitor the performance of civil engineering structures within their service life for optimum return from investment. The aim of this research was to develop a service life model to for prediction of the service life of reinforced concrete water conveyancing structures. To achieve the desired objective, steel samples were cast in concrete of characteristic strength of 25N/mm2, 9 cylinders each of 150mm diameter x 300mm long, 130mm diameter x 300mm long and 100mm diameter x 300mm long respectively in concrete characteristic strength 25/mm2,30N/mm2 and 35N/mm2 for accelerated corrosion test were cast. After 24 hours the cast specimens were demolded and immersed in curing tanks for 27 days and then immersed in a 3.5% industrial sodium chloride solution under 6V. The accelerated corrosion specimens were monitored for onset of cracks and stopped when the cracks were 0.2mm in width. The physical and chemical properties of the materials were investigated for compliance to relevant applicable British and Kenyan standards for conformity to acceptable criteria. The concrete materials were batched by weight and mixed by a lab electric pan concrete mixer in batches of 0.009 m3. The concrete batches were tested for consistency by the slump and compaction factor tests. From the results a model that takes account of the cover to the rebar, the rebar size and the compressive strength properties of concrete and steel/concrete interface was developed. The model developed here is for water structures and shows that the time to corrosion cracking of the cover concrete in a chloride contaminated concrete structure is a function of reinforcement cover, corrosion rate and critical mass of the corrosion products. The times to cracking predicted by the model are in good agreement with the observed times to cracking based on this research