Behavior of functionally graded concrete beams made of eco-friendly engineered cementitious composites

Functionally graded concrete (FGC) is a construction technique that helps the structures to adapt to varying structural and functional requirements. In this study, eco-friendly engineered cementitious composites (ECC) mixes made of stone processing waste (SPW), crumb rubber (CR), and hybrid basalt fibers (BF), were developed and employed in FGC beams to improve their flexural performance. In the proposed eco-friendly ECC mixes, SPW, and CR were used as partial substitutions of the conventional ECC fine aggregate volume by 20%. Several types of SPW were used including basalt waste (BW), dolomite waste (DW), and marble waste (MW). The slump, slump-flow, compressive strength, and uniaxial tensile strength were measured for the eco-friendly ECC mixes. In addition, eight reinforced FGC beams (130 x 230 x 1000 mm) were prepared and tested. The beams included different configurations in which the proposed ECC mixes were employed in the beam tension zone (bottom one-third). The structural performance of the proposed FGC beams was assessed through testing them under a 4-point bending loading. The results indicated that the utilized SPW and CR decreased the ECC by 15.0-33.3%. CR reduced the ECC's compressive and tensile strengths by 28.1% and 11.2%, respectively. The BW improved the compressive and tensile strengths of ECC by 7.14% and 14.3%, respectively as opposed to the reference ECC. The use of BW consequently enhanced the flexural performance of the FGC beams. The FGC beams showed an enhanced ductility with using eco-friendly ECC. The FGC beams made with CR-ECC and BW-ECC achieved the highest deflections of 16.46 mm and 15.35 mm (73.9% and 62.2% higher than that of beam made with control ECC), despite slight reductions in their peak loads making them suitable for applications requiring high ductility.