Page 9 - Open-Access-Jan-2022

TECHNICAL PAPER

Furthermore, the pH was 10.2, which indicated that the parent the cost of CSS was Rs 650/ton. The final price of the fine RCA
concrete was carbonated. Hence, the carbonated fines in RCA was Rs 600/ton including the transportation of 30 km to the
0/2 mm contained fine precipitated CaCO 3 and reactive silica- construction site. Thus, the savings for using RCA in M20 and
alumina gel. This may indicate that the fines in the recycled M10 were Rs 20/m and Rs 46/m , respectively. It showed that
3
3
aggregates contributed both as a filler and as a supplementary RCA was competitive, even with a transport distance of 30 km
cementitious material (SCM), which have recently been compared to the CSS. Moreover, the general price of CSS in
reported [29] . Mumbai is around Rs 950/ton. The saving in concrete cost/m
3
using fine RCA for M20 and M10 may have been Rs 138 and Rs
5. FINAL STRUCTURE AND EXPERIENCE
320, respectively, if the construction site had been located in the
GAINED Mumbai Metropolitan Region considering the prevailing market
rates.
The precast concrete factory for the CIDCO project was
constructed using almost 500 m of concrete with high quantities
3
of fine RCA. The RCA concrete was used in the grade slab 6. CONCLUSION
(Figure 4) and in miscellaneous structures. RCA demonstrated
consistent properties, especially with respect to its gradation A full-scale project has been conducted to demonstrate the
and good control on the fine particles (< 75 µm). In crushed use of fine recycled concrete aggregates (RCA) for two different
stone sand normally available for construction, the fine particle concrete qualities with high replacement of natural aggregates.
contents are high with significant variation, which is a constant The fine RCA replaced the crushed stone sand fraction in the
source of concern for the concrete producers. Hence, sufficient grade slab (M20) and in the lean concrete (M10) at replacement
control of the crushed stone sand production is decisive to avoid levels of 50% and 100%, respectively. The recycled aggregate
variation in the concrete water demand. The washing process concrete was used in the newly constructed precast concrete
applied for RCA ensures good control of the fine particles. element factory for the CIDCO project. The demonstration
project also aimed to gain experience regarding the quality of
L&T site managers expressed great satisfaction over their C&D waste recycled with the wet process.
experience of using fine RCA as a partial replacement of fine
aggregates for M20 and complete replacement of CSS for lean The fine RCA produced for this project complied with
concrete. They also expressed their desire to continue exploring IS: 383 (2016) and achieved Zone II grading, i.e., suitable for
future opportunities for use of RCA in concrete and plan to concrete production. Foreign material fractions like clay lumps,
engage their client CIDCO to encourage it’s use for future wood pieces etc. were absent. Hence, by having good control
projects. of the incoming feedstock material and running the production
process according to the specifications, good quality recycled
Owing to a combination of factors, the price difference between aggregates were produced.
fine RCA and the price of Crushed Stone Sand (CSS) produced
from natural source was small. The site was close to the quarries The properties of recycled aggregate concrete obtained were
that supply natural aggregates to Mumbai region and therefore of the same quality as the concrete without fine RCA. The

(a) (b)
Figure 4: Overview of the newly constructed precast concrete factory (a) and the grade slab with 50 % RCA fine aggregates (b)

54 THE INDIAN CONCRETE JOURNAL | JANUARY 2022