Investigation on the flexural behaviour of reinforced concrete beams using phyllite aggregates from mining waste

Highlights: → Most parts of the world's geology is underlain by phyllite rocks. → Crack widths not well predicted so may not be used in water retaining structures. → Shear failure mode and low displacement ductility often observed in beams. → Concrete shear capacity observed lower than code values. -- Abstract: This paper investigated the flexural behaviour of 12 reinforced concrete (RC) beams made of phyllite coarse aggregates produced as by-product of underground gold mining activity. The beams were tested to failure under four point test. Collapse of the beams which were adequately designed against shear failure occurred mostly through either flexural-shear failure and/or diagonal tension failure. The experimental failure loads averaged approximately 115% of the theoretical failure loads. It was observed that the beams developed early shear cracks and higher flexural crack widths than allowable at service loads. Deflections compared reasonably well with the design code requirement but displacement ductility was low. It is recommended that British Standard (BS) 8110 design concrete shear stress values be multiplied by 0.8 to assure that the predicted shear capacity of phyllite concrete would be low and reasonable as compared to flexural capacity. In that case, BS 8110 can be used to provide adequate load factor against flexural failure for under-reinforced RC beams made of phyllite coarse aggregates.