Page 174 - Riem-Vol6_nº2

345 IBRACON Structures and Materials Journal • 2013 • vol. 6 • nº 2
E. POLESELLO | A. B. ROHDEN | D. C. C. DAL MOLIN | A. B. MASUERO
when kept in prolonged mixing for 4 hours. According to these re-
searchers strength at 28 days increased by 15% and 27%, respec-
tively. Alhozaimy (2007) investigated real- life conditions in the
delivery of ready-mixed concrete and also observed that the fall in
slump values observed between the arrival of the mixer truck at the
construction site and midway through the unloading operation was
accompanied by a small increase in strength when no retempering
was used. In the studies of Erdoğdu,(2005), there was an increase
in compressive strength of 15% at 28 days for concrete mixed for
150 minutes with no retempering. When a superplasticizer was
used to correct slump values, according to the methodology used
in the present study but for shorter intervals, of up to 150 minutes,
increases in compressive strength slightly greater than 10% at 90
minutes and approximately 8% at the end of 150 minutes were
A B
C
Figure 5 – Behavior of concrete produced with CPII on the compressive strength
at 28 days due: (a) w / c ratio, (b) production site, (c) mixing time
Table 4 – Slumps, environmental conditions and slump loss during 2h
Production
site
Relative
humidity (%) w/c Loss (mm) o Temp. ( C) Slump (mm)
Initial Final
Laboratory
Ready-mixed
concrete plant
89%
95%
73%
83%
81%
98%
w/c = 0,68
w/c = 0,52
w/c = 0,40
w/c = 0,68
w/c = 0,52
w/c = 0,40
50
50
60
40
45
35
120
140
130
120
125
120
70
90
70
80
80
85
18,0
18,3
17,9
13,7
15,8
14,6