Innovative use of recycled materials in reinforced concrete beams

  • Robert Ataria

Student thesis: Phd

Abstract

Despite extensive research studies, construction demolition waste (CDW) and worn-out tyres of motor vehicles are still not fully reused and are hence disposed of in ways that are damaging to the environment. . There have been a number of investigations into manufacturing concrete using recycled aggregates from CDW and crumb rubber. However, it has not been possible to make recycled aggregate concrete with the-same performance as standard natural aggregate concrete (NAC) without incurring extra costs. Production of natural coarse aggregates is environmentally damaging and also costly. With surging demand for concrete worldwide, and to respond to the call of sustainable development, it is vital that the enormous quantities of CDW and tyres with high embodied carbon content are used in structural applications without compromising cost and performance. This thesis focuses on two ways of doing so: by finding alternative ways of improving the mechanical properties of recycled aggregate concrete to achieve those of concrete using natural aggregates, and to find new ways of using recycled aggregate concrete where the demand on the mechanical properties of concrete can be easily met by recycled aggregate concrete. Regarding the former, the research investigates the feasibility of adding a tiny amount of graphene (109g) to a cubic metre of recycled aggregate concrete. The 109g of graphene is equivalent to 0.01% (optimized concentration) of the combined weight of cement and sand of the design concrete mix. Regarding the latter, this research considers using recycled aggregate concrete in the tension zone of reinforced concrete beams. Mechanical property tests have been carried out on recycled aggregate and crumb rubber concrete, with or without graphene. In the first part of this research, comparisons were made between concrete using 10mm size uncrushed quartzite stones (NAC mix, C40), recycled aggregate concrete (RAC) and rubber recycled aggregate concrete mix (RRAC). The slump test results show RAC suffered a 73% reduction in slump value compared to the NAC mix. However, the slump value of RAC was increased by 72% by introducing an additional amount of water (4.21% of recycled aggregate weight measured from a water absorption test) or by 75% using DARACEM 215 superplasticizers (1% of cement weight). As expected, the compressive and tensile strengths, elastic modulus and ultrasonic pulse velocity of the recycled aggregate concrete were lower than those of the NAC mix, by 14.9%, 14.8% , 4.3% and 7.4% respectively. Introducing crumb rubber (by 5%, 10%, 15% and 20% of recycled aggregate weight) into the recycled aggregate concrete further decreased its workability and mechanical properties with or without superplasticizers. In the interest of workability, this research recommends limiting the weight of rubber to not more than 10% of the recycled aggregate weight. With 5% and 10% rubber, the compressive strengths of RRAC were 32.8% and 47.1% of the NAC mix using uncrushed 10mm quartzite aggregates. Inclusion of rubber crumb seemed to help the ductility of RRAC as observed by the slower rate of stress reduction in the descending branch of the measured stress strain curve. The second part of the mechanical property investigation explores the feasibility of using graphene to improve the mechanical properties of recycled aggregate concrete and rubber recycled aggregate concrete with 10% of crumb rubber content. Graphene concentrations of 0.01%, 0.02%, 0.05% and 0.1% of the combined weight of cement and sand and of different sizes (5um, 10um and 20um) were incorporated into recycled aggregate concrete and natural aggregate concrete. Except where G5 0.02% was used (graphene size 5µm, 0.02% by weight) which resulted in a modest 12.2% increase in compressive strength compared to the recycled aggregate concrete with rubber, including graphene decreased the compressive strength of rubber recycled aggregate concrete. This was attributed to the inabil
Date of Award1 Aug 2020
Original languageEnglish
Awarding Institution
  • The University of Manchester
SupervisorPaul Nedwell (Supervisor) & Yong Wang (Supervisor)

Keywords

  • Bending resistance
  • Shear resistance
  • Graphene concrete
  • Recycled aggregates
  • Rubber recycled aggregate concrete
  • Crumb rubber
  • Two layer concrete beams

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