ABSTRACT

Modem development around the globe led the construction industry to build new and innovative high-rise buildings. The vertical expansion of the structural development has become unavoidable due to increasing demand of living space and associated facilities particularly in the city centers of the world. The phenomenon consumes concrete aggregates in huge quantum. on the other hand, the space problem in city center of the world requires demolishing of old structures to build new structures with more capacity. It generates demolishing waste in large quantities. Demolishing waste generally goes in landfills, which on other hand poses serious social and environmental issues. Particularly in under developing countries like Pakistan with agriculture as main source of GDP; dumping of the aggregates creates serious issues to the agricultural land. Therefore, since past few-decades utilization of this waste in new concrete has remained active area of research among the scholar and researchers. The idea not only reduces waste management issues and environmental problems but also helps in preserving the natural sources of the aggregates. This research work presents the experimental study on the flexural behavior of reinforced concrete beams made with partial replacement of 50% of natural coarse aggregates with recyclable aggregates from old demolished concrete. 18 reinforced concrete beams of size 75" x 6" x 12 were east and used I :2:4 mix and 0.5 water/cement ratio in three groups. In each group fifty percent beams were cast with all-natural coarse aggregates and remaining fifty percent with 50% replacement of natural coarse aggregates with aggregates from old demolished concrete. To reinforce the beams #4 deformed bars were used as main reinforcement and #3 bars were used in rings. The curing of the beams was done by fully immersing in water for 28 days. Three beams were tested for maximum load, 50% of which is used as the long-term sustained load. All the beams were mounted on purpose made frames for age of 6, 9 and 12 months. The sustained load was applied with the help of screw jacks and load cells. The deflection, strain and cracking were observed in the beams on daily basis. Comparison of the results of proposed beams with control specimens shows that under sustained load both deflection and strain increase due to introduction of recycled aggregates. It was observed due to duration of the sustained load. Maximum deflection and strain after six-month sustained loading were recorded equal to 2.22 mm and 0.00252 respectively. The same after nine and twelve-month sustained loading is equal to 2.34 mm and 0.00261 and 2.58 mm and 0.00278. The maximum increase in eflection and strain is observed with twelve-month sustained loading. Dominant cracking in the beams is flexural cracks. However in few beams minor diagonal cracks were also observed. The maximum crack width in all proposed beams is recorded equal to 0.55. The widest crack was even less than I mm. The beams, after elapse of successive sustained loading duration, are tested in universal testing machine till failure. Ultimate load, deflection, cracking and failure mode are observed. Maximum reduction in ultimate load and maximum increase in deflection in proposed beams are recorded equal to 3.04% and 19.5%. The failure mode in almost all the beams was observed as flexural failure. Regression analysis of experimental observation for deflection and strain was also done to develop numerical equation to estimate the deflection and strain under sustained loading. The counter check of the developed equations shows good agreement between predicted and experimental observations. Results show that the behavior of proposed beams under sustained loading for proposed duration of time is in good agreement with control specimens. Therefore, the use of the material in new reinforced concrete beams is a viable solution to reduce waste management and environmental issues and may be used as substitute of coarse aggregates to produce green concrete. The outcome is particularly good for Pakistan to save agricultural land from dumping of the demolishing waste. It also sets landmark for future research in the field and guidelines for industry personals.
Keywords: Recyclable aggregates, demolishing waste, green concrete,
reinforced concrete beams, long-term loading, sustained loading.