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aggregate surface. Similarly, in the This emulsion seals the pores higher aggregate impact value,
ultrasonic treatment method, the of the RCA, enhancing the higher abrasion value, and lower
C&D waste is submerged in water, bond between the adhered specific gravity. To enhance the
and ultrasonic waves are applied, mortar and the aggregates, properties of RCA, researchers
which helps remove the adhered thereby addressing the issue of and practitioners have employed
mortar. In the acid soaking mortar detachment in the mix. various secondary modification
method, the C&D waste is soaked Additionally, the sealing of pores techniques, such as mechanical
in an acid solution, where the acid reduces water absorption, further treatment, thermal treatment,
reacts with the hydration products improving the RCA’s performance. acid soaking, pre-coating
in the mortar, effectively removing Researchers have also explored the with slag cement, calcium
it from the aggregate surface. use of liquid silicon resin for similar carbonate precipitation and
purposes, which helps to reinforce MCP, both individually and in
The second category of the bond between the adhered combination. These methods have
treatment processes focuses on mortar and the aggregate. generally resulted in significant
reinforcing the adhered mortar More recently, Microbial Calcite improvements, with many studies
in place. One such method is Precipitation(MCP) has been reporting increased specific
carbonation treatment, where CO investigated, where bacteria are gravity, reduced water absorption,
2
reacts with the adhered mortar to applied to the aggregate surface. and lower LA abrasion values.
form calcium carbonate (CaCO ), These bacteria produce calcium The use of RCA in asphalt mixtures
2
which densifies and strengthens carbonate crystals, which enhance has produced mixed results, largely
the mortar, securing it in place. the bond between the adhered due to the variable nature of RCA
Another approach involves mortar and the concrete. itself. The properties of RCA are
treating RCA with cementitious or closely tied to the history of the
pozzolanic materials, which help to Physical Properties original cement concrete. Some
stabilize the adhered mortar. When When comparing the physical studies have reported positive
using RCA for asphalt mixtures, the properties of RCA with natural effects of incorporating RCA into
aggregates can be coated with virgin aggregates, RCA typically asphalt concrete. Factors such as
bitumen emulsion. exhibits higher water absorption, the rearrangement of aggregate
gradation due to crushed adhered
mortar, residual cementing activity
from unhydrated cement particles,
and the rough surface texture of
RCA contribute to these beneficial
outcomes.
Researchers have further explored
various methods to enhance
the properties and performance
of RCA in bituminous mixtures.
These methods include calcination,
applying pre-coating pastes to RCA
surfaces, using organic silicon resin
to activate RCA, MCP, pre-coating
RCA with bitumen emulsion, and
incorporating lime, cement, and
other filler materials. Most of
these treatment approaches have
demonstrated significant positive
effects, indicating that RCA can
effectively replace a portion
of virgin aggregates without
compromising the quality or
performance of asphalt mixtures. TT

24 TRAFFICINFRATECH / August-September 2024 / www.trafficinfratech.com