Use of eco-concrete containing limestone fines as cementitious paste replacement in circular concrete-filled steel tube columns

One effective way of reducing the cementitious content and carbon footprint so as to produce eco-concrete is to add limestone fines (LF) to replace an equal volume of cementitious paste. Herein, such eco-concrete was used as the concrete infill of circular concrete-filled steel tube (CFST), and a number of circular CFST specimens infilled with conventional concrete or eco-concrete had been tested under axial compression. The steel tubes were of grade S355 and had diameters ranging from 88.9 to 168.3 mm, whereas the concrete infills had water/cement ratios of 0.40 and 0.60, and LF contents (by volume of concrete) of 0%, 4%, 8% and 12%. The test results revealed that the eco-concrete had lower cementitious content but higher compressive strength, and the CFSTs infilled with the eco-concrete had similar axial load-strain behaviour but higher axial strength. Moreover, the eco-concrete offered similar steel-concrete composite action but larger increase in axial strength due to concrete infill. Comparing the measured axial strengths to the predicted values, it was found that the existing design equations are also applicable to CFSTs infilled with eco-concrete. Lastly, a new and more accurate design equation is developed for applications to CFSTs infilled with conventional concrete or eco-concrete.