Assessment of flexural response of RC beams and unrestrained shrinkage of fiber-reinforced high-volume fly ash-based no-aggregate concrete and self-compacting concrete

Abstract

The use of industrial byproducts as a substitute for cement in concrete production to improve its properties is becoming a widespread practice in producing sustainable concrete. Although research around the world emphasizes higher substitution levels of fly ash (FA) to accrue the benefits from the microstructure refinement, no attempt has been made to study the deflection behavior and drying shrinkage of concrete that is devoid of aggregates while supplementing 80% of cement with class F fly ash (F-FA). Two types of concrete are used to cast full-scale reinforced concrete (RC) beams of size 150×300×2200 mm. The first type is a novel no aggregate concrete (NAC) made up of 80% F-FA and 20% ordinary Portland cement (OPC). The second type is high-volume fly ash self-compacting concrete (HVFASCC), which has 60% F-FA as a cement supplement and is equivalent in compressive strength to NAC. The NAC is reinforced with polypropylene fibers (PF) in three varying volume fractions: 0.6%, 0.8%, and 1.0%. All the beams are tested under a simply supported four-point loading condition. The drying shrinkage strain and mass loss are measured for prisms of size 75×75×300 mm up to 220 days exposed at 20% relative humidity (RH) and 50 ºC temperature in a humidity oven for all the mixes. The mechanical properties are also assessed along with the water absorption (sorptivity). The results indicate that adding PF to the beams with NAC delays the formation of the first crack and improves the peak load, the ultimate load, and the ductility of the NAC beam. Additionally, the beams with PF exhibit lower mid-span deflection and ductile failure mode, improving the overall structural performance. Regarding drying shrinkage, the HVFASCC prisms record the lowest shrinkage strains of all mixes. Adding PF to NAC increases the initial and ultimate drying shrinkage strains. However, adding PF to NAC inhibits the rate of shrinkage strain over the test duration. This research enhances understanding of how PF affects no-aggregate concrete behavior, paving the way for more comprehensive construction materials.