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TECHNICAL PAPER

Table 3: Technical properties obtained for RCA 0/2 mm.

PARAMETER UNIT CSS 0/4 mm RCA 0/2 mm IS 383 LIMITS
Specific gravity - 2.64 2.52 2.1-3.2
Bulk density kg/dm 3 - 1.53 -
Water absorption % 4.1 a 4.6 ≤ 10
Particles < 75 µm % 10 a 2.9 ≤ 10
Coal and lignite % < 0.1 0.9 ≤ 1
Clay lumps % < 0.1 0.2 ≤ 1
Reduction in alkalinity mmol/L 127 333 -
Dissolved silica mmol/L 23 7.3 -
Soundness (Na 2 SO 4 ) % 4.3 4.0 ≤ 10
Acid soluble sulphate % - 0.05 ≤ 0.5

Acid soluble chloride % - 0.004 ≤ 0.04
pH (5% solution) - log [H ] - 10.2 -
+
A Monthly average
the RCA contained a residual moisture content from the wet WA only by increasing the mixing water for relatively dry RCA,
recycling process. Hence, compensation of the full WA in the increases the risk for slump losses. On the other hand, over-
mixing water was avoided. wetted RCA increases the bleeding of the concrete and should
therefore be avoided .
[28]
4.3 Concrete properties
In the current project, 0.80% of superplasticizer was used.
The consistency of fresh concrete was controlled by slump and The WA for CSS and fine RCA was not too different (varied
slump retention (loss over time) measurements and is shown
in Table 4. The casting area was adjacent to the concrete in the range of ~ 3-5%) due to the wet recycling process of
the latter, which most likely made it easier to maintain stable
mixing plant and the concrete was poured from the trucks to
the formwork with a chute. The slump loss obtained in the fresh concrete properties. Hence, no bleeding was observed,
current study was evaluated to be acceptable. Earlier studies and the concrete was cohesive. The obtained compressive
have shown that concrete with RCA may increase the initial strength data at 7 days and 28 days curing are shown in Table 4.
slump and the slump loss, compared to the reference concrete Sufficient strength was achieved for both M10 and M20 and
[4, 27] . The mechanisms were explained that the initial slump was comparable with the reference strength, i.e., concrete with
was dependent on the available initial free water, whereas the CSS 0/4 mm. It proved the viability of RCA at high replacement
slump loss was dependent on the initial moisture condition of levels. The current project applied 50% of fine RCA, which was
the recycled aggregates. Thus, pre-wetted aggregates tend to significantly above the 20% limit specified in IS: 383 (2016). It
increase the initial slump, as the added water is only absorbed can be mentioned that the fines content (< 75 µm) was around
by RCA over some time. Furthermore, compensating for the 3% and originated from the cement paste of the RCA particles.

Table 4: Fresh and hardened concrete properties
PARAMETER UNIT M10 M10-Ref M20 M-20 Ref

Slump factory production control mm 160-185 75-125 1 150-185 100-150 1
Slump retention: 0 min mm 210 Collapse 190 Collapse
Slump retention: 60 min mm 160 150 150 170
Slump retention: 120 min mm 120 100 120 110
Compressive strength 7 days 2 MPa 7.0-9.0 7.5 13-19 20
Compressive strength 28 days 2 MPa 13-14 13 24-27 28
1 Target slump
2 Mean strength of 3 numbers of 150 mm cube

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