Abstract: The intensive use of natural aggregates, near cities and towns, associated to the increase of the global population, leads to its depletion and increases the transport distances. The uncontrolled deposition of construction and demolition waste in landfills and city outskirts, causes pollution and takes up space. The use of recycled aggregates in concrete preparation would contribute to mitigate the problem. However, it arises the problem that the high water absorption of recycled aggregate decreases the bleeding rate of concrete, and when this gets lower than the evaporation rate, plastic shrinkage cracking occurs. This phenomenon can be particularly problematic in hot and windy curing environments. Cracking facilitates the flow of liquid and gas into concrete which attacks the reinforcement and degrades the concrete. These factors reduce the durability of concrete structures and consequently the lifetime of buildings. A ring test was used, cured in a wind tunnel, to evaluate the plastic shrinkage cracking sensitivity of recycled aggregate concrete, in order to implement preventive means to control this phenomenon. The role of several aggregate properties on the concrete segregation and cracking mechanisms were also discussed.
Abstract: The development of new construction materials using
recycled plastic is important to both the construction and the plastic
recycling industries. Manufacturing of fibers from industrial or
postconsumer plastic waste is an attractive approach with such
benefits as concrete performance enhancement, and reduced needs
for land filling. The main objective of this study is to investigate the
effect of Plastic fibers obtained locally from recycled waste on plastic
shrinkage cracking of ordinary cement based mortar. Parameters
investigated include: fiber length ranging from 20 to 50mm, and fiber
volume fraction ranging from 0% to 1.5% by volume. The test results
showed significant improvement in crack arresting mechanism and
substantial reduction in the surface area of cracks for the mortar
reinforced with recycled plastic fibers compared to plain mortar.
Furthermore, test results indicated that there was a slight decrease in
compressive strength of mortar reinforced with different lengths and
contents of recycled fibers compared to plain mortar. This study
suggests that adding more than 1% of RP fibers to mortar, can be
used effectively for controlling plastic shrinkage cracking of cement
based mortar, and thus results in waste reduction and resources
conservation.