Turning The Construction Waste Powder(CWP) Into Artificial Aggregates

The demolition of concrete structures generates a large amount of construction wastes which rises a serious problem in today's world.Reusing construction waste is therefore a good way to deal with this problem while reducing the construction costs.Several studies are focusing on the possibility of recycling c onstruction waste as aggregates or powder in concrete.However,the direct use of concrete waste,in particular construction waste powder?CWP?negatively affects the overall performance of concrete products?mechanical properties,dry shrinkage performance,etc.?which is limiting its partial replacement content to 30%.Using this low amount o f waste materials in concrete wouldn't solve the rapid increase of waste concrete and would probably slow the transition to a more sustainable environment.Therefore,waste reduction efforts need to maximize the volume of waste in concrete while effectivel y controlling its impact on concrete performances.The production of artificial aggregates using CWP can be then considered as one of the most efficient solution to achieve this aim.Therefore,this paper focuses on turning CWP into sustainable artificial aggregates using cold bonding pelletization process.Because of the environmental cost of cement,cement-free binding aggregates are gaining recently an increased interest from researchers,therefore,GGBS and calcium hydroxide?Ca?OH?₂?is considered in this study in order to improve the strength of the developed aggregates and reduce the cement content.The produced aggregates were then cured using two different regimes:air and CO ₂ curing.Different trial mixes were first conducted in order to optimiz e the tilt angle,the mixing speed of the pelletizer machine as well as the mix design.It was noticed that the tilt angle and rotation speed have a huge impact on the size of artificial aggregates.In fact,in a certain angle and speed range the diameter,the size of artificial aggregate increases when the tilt angle and the rotation speed increase.In consideration of production efficiency,a tilt angle of 45°and the speed of about 25 r/min were selected to produce aggregates with uniform shape and size?around 10 mm?.On the other hand,the optimum Ca?OH?₂ content resulting in the maximum 28 days strength of the aggregates was about 3%.Moreover,the increase of GGBS content resulted in the gradual increase of the aggregate's strength and the gradual decrease of their water absorption.Compared to nature air curing,CO₂ curing contributed significantly in improving the aggregates properties by increasing the crushing strength and reducing the water absorption of artificial aggregates.Finally,the effect of different type of aggregates?natural,artificial and ceramsite?on the mechanical and drying shrinkage performance as well as the interface transition zone?ITZ?was investigated.The results showed that the compressive strength of artificial aggregate concrete was 20%lower than that of natural aggregate concrete while it was 2-3 times higher than that of the ceramsite concrete.Furthermore,artificial aggregates had a negligible effect on the drying shrinkage and ITZ as compared to natural aggregates.The result of this work can provide some theoretical and practical bases for the effective application of concrete waste powder into sustainable artificial aggregates.