Effect of utilizing geopolymer fly ash on potential and corrosion rate of reinforcement in high-strength concrete

With the increasing use of high-strength reinforced concretes as a structural element of construction, their resistance to corrosion in environmental conditions needs to be studied. It is well known that cement manufacturing at plants is un-environmental friendly due to plenty of fuel consumption and CO2 emission to the atmosphere leading to greenhouse effect. Therefore, substituting cement with environmentally friendly natural materials and natural wastes become a smart solution. This study aims to measure the potential level and corrosion rate of reinforcing steel in high-strength concrete with variations in cement replacement by geopolymer fly ash, environmental conditions, and concrete covering thickness. Corrosion potential measurement was carried out with the half-cell potential mapping method, while the corrosion rate used the linear polarization resistance method. Data collection was executed every two weeks during eight weeks of immersion. High-strength concrete beams with compressive strength target 70 MPa having dimension 15cm x 20cm x 80cm were substituted with 15% coal fly ash (CFA), 15% palm oil blast furnace slag fly ash (POSFA), and 10% pozzolanic fly ash (PFA) from cement weight. High-strength concrete specimens without fly ash substitution were made as a comparison (HSCWFA). It was installed 4 longitudinal reinforcement 010 mm and 7 stirrups 6 mm with a distance of 10 cm. The concrete covering thickness was 2 cm and 4 cm. Immersion medium uses artificial seawater (3.5% NaCl) and shallow well water. The results showed that specimens resulting in the lowest corrosion rate were PFA, CFA, POSFA, and HSCWFA respectively. Corrosion potential was obtained at low to medium levels, while corrosion rates were at low corrosion level criteria. It can be clearly concluded that the utilizing of a geopolymer fly ash could increase the permeability of high-strength concretes through their higher resistance to the penetration of chloride ions.