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IBRACON Structures and Materials Journal • 2012 • vol. 5 • nº 5
Concrete properties produced with recycled coarse aggregates
mix. Therefore, the recycled aggregates (fine and coarse) were
pre-soaked in mixer for one minute before the preparation of the
concrete to avoid the absorption of part of the mixture water. The
quantity of this water was calculated with the difference between
the water required for the full saturation of the aggregates and the
water actually absorbed by the aggregates in one minute. The ab-
sorption of 70% of the total water absorbed by each aggregate had
already been observed in one minute.
The superplasticizer was used for a plastic consistence to
be reached.
The preparation of the concrete was: 1 - Reference concrete:
coarse and fine aggregates, and a little of water mixed for one
minute in a mixer. 2 - Recycled concrete: recycled coarse and
fine aggregates, and absorbed water from the recycled aggre-
gates (70%) mixed for one minutes in a mixer. Afterwards, the
cement and the water of the mix are placed in the mixer for two
minutes. At the end, the superplasticizer was mixed for one min-
ute and a half more.
After casting, the samples (cylinders with 10 cm in diameter and
15 cm in height) were led in molds for 24 hours, stripped and cured
in water for twenty-eight days. All concrete cylinders were capped
with a thin layer of sulfur with cement to ensure the smoothness of
the top surface.
2.4 Properties and test
The compressive strength, water absorption, air content and time
of air-permeability (Figg method) properties were obtained with
the intention of analyzing the possibility of producing concretes
with recycled aggregates. For each concrete, the tests were made
in cylinders of 100 mm in diameter and 200 mm in height; three
specimen for the compressive strength (NBR 5739 [22]), three
for the water absorption and air content (NBR 9778 [23]). For the
measurement of the air-permeability time (LNEC-E 413 [24]), a
prismatic mold of 15x15x30 cm was used with 5 holes of 6 mm in
diameter and 40 mm in height were made. The reference age for
the accomplishment of the tests was 28 days. The adopted cure
method for all the concretes was the total immersion of the speci-
mens in water.
3. Results and discussions
3.1 Aggregate Properties
The results obtained from the recycled aggregate properties: wa-
ter absorption and particles percentage with D < 0.075 mm, which
obeyed the minimum requirements defined by the NBR 15116
Ta�le 3 � �oncrete mixtures
(*) 67, 50 and 40 refer to effective w/c ratio; MR = recycled sand; MN = river sand; G1 and G2 = recycled coarse aggregates.
Mix(*)
Effective
w/c
ratio
3
Materials in volume (dm³)/m
3
Materials in mass (kg)/m
water
cement
Aggregate
water
cement
Aggregate
Fine
coarse
fine
coarse
67MRG1
0.67
200
99
301
400
200
300
752.5
832
67MRG2
0.67
200
99
301
400
200
300
752.5
900
67MNG1
0.67
200
99
301
400
200
300
806.7
832
67MNG2
0.67
200
99
301
400
200
300
806.7
900
50MRG1
0.50
200
132
268
400
200
400
670.0
832
50MRG2
0.50
200
132
268
400
200
400
670.0
900
50MNG1
0.50
200
132
268
400
200
400
718.2
832
50MNG2
0.50
200
132
268
400
200
400
718.2
900
40MRG1
0.40
200
165
235
400
200
500
587.5
832
40MRG2
0.40
200
165
235
400
200
500
587.5
900
40MNG1
0.40
200
165
235
400
200
500
629.8
832
40MNG2
0.40
200
165
235
400
200
500
629.8
900
Reference concrete (Ref)
Ref67
0.67
200
99
301
400
200
300
806.7
1048
Ref50
0.50
200
132
268
400
200
400
718.2
1048
Ref40
0.40
200
165
235
400
200
500
629.8
1048