24-07-2014, 12:54 PM
Application of recycled waste aggregate to lean concrete subbase in highway vement
Application of recycled.docx (Size: 16.94 KB / Downloads: 10)
Abstract
As aggregates recycled from various types of construction waste are continuously being produced, interest
has focused on how to apply them for use in highway pavement. This paper considers the application of waste aggregates
to lean concrete, based on basic mechanical property tests and environmental toxicity. Compared with natural aggregates,
waste aggregates derived mainly from recycled concrete have low specific gravity and high water absorption
characteristics. After testing their environmental toxicity, it was found that waste aggregates do not release any metallic
ions when introduced to alkaline conditions but do release a small but seemingly harmless amount of metallic ions
when introduced to acidic solutions. Concrete made with waste aggregates has significant limitations in strength, particularly
flexural strength, which is the main parameter of quality control and design for concrete pavement. It is therefore
not practical to use waste aggregates for the surface layer of concrete without using additives or special
treatments.
Introduction
As the expected life of a building in Korea functionally
and (or) structurally approaches its end, it is common to
build a replacement. Building a replacement is one solution
to addressing land shortages and developing new infrastructure,
but it naturally introduces the problem of treating waste
materials. Concrete waste accounts for 60%–70% of total
waste production in Korea. According to data from the Department
of Environment (2000) for 1999, the amount of
concrete waste produced annually is approximately 25 million
tonnesGiven the tonnage, recycling this type of waste
by using it in highway construction should be considered.
Manufacturing processes in Korea for recycled aggregates
Treatment of construction waste in Korea lacks a uniform
separation process. Almost all construction waste is gathered
from different resources such as buildings, highways, dams,
and even sludge from sewers. When construction waste arrives
at the recycling plant, magnets and pools of water separate
steel and wood, respectively, before and after the
crushing system. Figure 1 is an outline of a recycling-based
aggregate production plant. Here, separation of metals and
wood is possible, and the cone crusher improves the size and
shape of the recycled aggregates. In most developed countries,
waste that cannot be reclaimed is first sorted and then
buried, or is burned in the recycling process, and only reclaimable
waste is processed for production of recycled aggregates
(Toshion 1997). Because this is not done in Korea,
the quality of waste aggregates is relatively low, and using
them in new infrastructures like buildings or bridges is almost
impossible due to the higher risk incurred
Conclusions
Most waste aggregates produced in Korea contain large
amounts of impurities because of inefficiencies in the collection
process of construction waste and inferior production
techniques. Little is known about their composition, use, and
limitations in domestically produced waste, however. Detailed
research is therefore needed on the application of
waste aggregates in concrete structures.
The following conclusions are made based on our research
using typical waste aggregates:
(1) Compared with natural aggregates, waste aggregates
have a lower specific gravity and higher water absorption.
In addition, due to high creep and drying shrinkage,
it is impractical to use waste aggregates in general
concrete structures for civil engineering purposes.
(2) When testing for toxicity to the environment, and when
introduced to alkaline conditions, waste aggregates do
not release metallic ions. When introduced to acidic solutions,
however, they release small but apparently
harmless amounts of metallic ions