Flexural Performance of Reinforced Concrete Beams Incorporating Cement-Bonded Fly Ash Aggregates as Partial Replacement of Natural Coarse Aggregate: Experimental Investigation, ANN Modelling, and Durability Assessment

Abstract

The rising demand for natural coarse aggregate and its consequences have necessitated investigations into alternative aggregates from industrial sources. The structural performance and durability of reinforced concrete beams with cement-bonded Fly Ash Aggregate (FAA) at 25%, 50%, 75%, and 100% of the volume of natural coarse aggregate has been investigated. FAA was prepared by pelletisation of fly ash and cement at a 95:05, 90:10, and 85:15 mass ratio. The beams were of 100 mm × 150 mm cross-section and 1350 mm span, reinforced with 8 mm and 10 mm deformed bars and subjected to four-point bending test. The tests determined the Cracking Load (Pcr), Service Load (Psl), Ultimate Load (Pu), mid-span deflection, crack width, ductility index and energy absorption of FAA RC beams. The durability characteristics of FAA RC beams were also tested for Rapid Chloride Penetration (RCPT), water absorption, sorptivity and carbonation. The experimental results indicated that FAA3 (85:15) at 25% of natural aggregate replacement achieved a higher compressive strength (40.91 MPa) at 28 days than conventional M25 concrete (37.43 MPa). Furthermore, beams made with 25% FAA3 (85:15) sustained an ultimate load equal to that of the control beams for 8 mm tension reinforcement (42.11 kN in both cases) and 4.0% lower for 10 mm reinforcement (50.11 kN against 52.21 kN). At service load, the 8 mm FAA3 beams deflected 9.3% more than the corresponding control beam (4.48 mm against 4.10 mm), whereas the 10 mm FAA3 beams deflected 23.2% less (3.15 mm against 4.10 mm); the maximum crack width at service load was reduced by 9.9% in the 8 mm series and by 39.8% in the 10 mm series. The 25% FAA3 beams with 8 mm reinforcement also showed a 30.8% higher ductility index and 31.5% higher energy absorption than the control. The chloride penetration of all the mixes falls within the ASTM C1202 category for moderate chloride penetration of concrete. A feedforward artificial neural network of 5-6-4-1 topology, trained on the experimental data together with data drawn from the literature, predicted the ultimate load with R2 = 0.9921 and RMSE = 0.72 kN on an independent test set, outperforming a linear regression model (R2 = 0.934). The results indicated that 25% replacement level of natural aggregate with cold-bonded FAA3 (85:15) is a viable and eco-friendly alternative to natural aggregate in RC beams.