Page 5 - Open-Access-Jan-2022

TECHNICAL PAPER

drying shrinkage [14] , chloride transport [15] , effect on alkali-silica
reactions [16] , performance in self-compacting concrete [17] , the
fresh state performance [18] and general durability properties [19] .
The main difference between RCA and natural aggregates is
the adhered mortar on the RCA particles. Compared to natural
aggregates, this leads to increased porosity and therefore
higher water absorption (WA), lower bulk and particle density,
irregular geometry and weaker interfacial transition zone. It was
reported that the water absorbed to fine RCA during concrete
mixing was 49 to 89% of the full WA capacity [11] . Although the
water transport mechanisms (from cement paste to RCA) are
complex, it seems that full saturation of fine RCA is not achieved Figure 1: Demolished concrete used to produce fine RCA in the project
during mixing.
2. MATERIALS AND METHODS
Full-scale demonstration of RAC is obviously important to
promote the use of RCA, as it assesses the logistics, cost 2.1 C&D waste generation site – source material
viability and the technical suitability. The number of reported The concrete rubble used to produce fine RCA originated
full-scale demonstrations are seemingly low compared to the from Thane Metro rail project; Line 5 Thane-Bhiwandi-Kalyan
numerous desk and laboratory studies published for the past route. The concrete rubble (1000 t) was sourced from the site at
25 years. However, some important demonstrations are reported
Kausa, Mumbra, less than 5 km from the C&D recycling plant.
in recent years. 30% coarse RCA was used in laminated glued The demolished concrete was of grades M40 and M45 and
bamboo concrete composite beams [20] and the effect of both was reduced to 80 mm size with a jaw crusher before it was
fine and coarse RCA in concrete beams was assessed with transported to the recycling facility for processing, see Figure 1.
respect to time-dependent deflection [21] . In the latter study,
the deflection pattern was not influenced but the deflection
2.2 Description of the recycling process
increased with increasing RCA. Coarse RCA was applied in
concrete-steel tubular columns and improved bearing capacity The recycling operator was Metro Waste Handling Pvt Ltd
and energy dissipation for such application [22] . In another study, (Thane, Maharashtra, India) which has installed a wet recycling
both coarse and fine RCA from mixed C&D waste replaced the facility (CDE, ReUrban Mini) with an installed capacity of
primary aggregates in a full-scale concrete slab with satisfying recycling C&D waste of 30 t/h, see Figure 2. The plant applies
performance [23] . Furthermore, researchers applied RAC with the wet recycling technology (CDE Rotomax™ system) provided
10-30% coarse RCA in high-rise building [24] , whereas in situ tests by CDE Global (Northern Ireland). The process includes
were performed on four full-scale concrete structures [25] . The water washing steps, sieving, rinsing screens, flocculation and
latter study reported that RCA originated from precast elements settlement for the sludge content (< 75 µm). The process is
proved to be highly suitable for the use in concrete structural developed to recycle more than 90% of the water. In short, the
facility is installed with a hopper feed system for raw C&D waste.
elements. Full-scale demonstrations have also been performed Hopper is provided with a grizzly feeder with an 80 mm opening
in earlier years. Sørumsand High School in Norway was finalised grid to avoid any large oversize material to pass through. The
in 2003 and concrete with 37% coarse RCA was applied in all material is treated with intense wet scrubbing in the log-washer
foundations and in half of the basement walls and columns .
[4]
(Rotomax RX60). The scrubbed material falls onto wet screens
Although the number of successful demonstrations is increasing, for further washing and separation into different sizes.
there is still a need for projects that demonstrate the use of
The washed oversize materials from the upper and lower
RCA in concrete, in particular in India, where the availability of screens form the 20/80 mm, 8/20 mm, and 2/8 mm recycled
natural aggregates is decreasing rapidly. In the present paper, aggregates, respectively. The slurry and the 0/2 mm fraction are
the results from the full-scale demonstration of the use of fine transferred to the sand washing unit where it is washed in the
RCA for two different concrete qualities with high replacement first stage cyclone and where the fines (~ < 75 µm) are removed.
of natural aggregates. The RCA was used for the grade slab The underflow is treated in a second stage cyclone to form the
(M20) and in lean concrete (M10) in a newly constructed precast 0.075/2 mm fraction which will be referred to as RCA 0/2 mm in
concrete factory. The project was conducted to gain experience the following text. The overflow from the cyclones is fed into an
with properties of source concrete, recycling process, the integrated water management system for recycling 90% of the
performance of concrete with fine RCA and the costs. process water. The RCA 0/2 mm was used in the current project.

50 THE INDIAN CONCRETE JOURNAL | JANUARY 2022