Coating protection of loaded RC columns to resist elevated temperature

The objective of the present research work is to determine the effect of different coating types with different thicknesses on the residual load capacities of reinforced concrete loaded column models when subjected to symmetrical temperature rise up to 650 °C for 30 min. Seventeen RC column specimens with concrete cover 1.0 cm and a specimen dimensions 10×15×70 cm3 were cast and reinforced with 4∅6 mm longitudinal reinforcement and 7∅3.5 mm stirrups equally distributed along the height. The concrete mix is designed to give characteristic strength, fcu, of 25 MPa. Siliceous gravel aggregate has been used in preparing the concrete mix. Among the 17 column models, there are two uncoated specimens. One of them was tested directly in ambient temperature and the other was exposed to elevated temperature up to 650 °C for 30 min. The remaining 15 specimens are divided into five groups. Each group is used to investigate certain type of coating. Five different types of coating have been used in this study namely traditional-cement plaster, perlite-cement, vermiculite-cement, LECA-cement and perlite–gypsum. Three different thicknesses of each type of coating have been used in this study 1.5, 2.5 and 3.5 cm. Every column specimen was equipped with eight thermocouples to measure the temperature distributions inside the specimen at mid height. An electric furnace has been used in this work. Every specimen was exposed to the simultaneous effect of the axial service load and temperature of 650 °C for 30-min period. The readings of applied loads and thermocouples were recorded at 5-min interval. Testing the columns after cooling to obtain their residual axial load capacity showed that, perlite proves to be the most effective plaster in increasing the loaded column's resistance to elevated temperature. Specimens coated with vermiculite cement came in the second place. Specimens coated with LECA-cement came in the third place. Finally, specimens coated with traditional-cement came in the last place.