Civil Engineering Reference
In-Depth Information
Fig. 5.79 Oxygen permeability index of concrete versus replacement ratio of coarse NA by RCA
(Olorunsogo and Padayachee
2002
)
Table 5.25 Carbonation depth (in mm) of conventional concrete and RCAC's
References Type of aggregate Concrete type Carbonation depth/substitution
level (%, volume)
Limbachiya
2010
RCA/coarse C30 21/0; 21/30; 20/50; 18.5/100
C35 18/0; 18/30; 17.5/50; 16.5/100
Gomes and de Brito
2009
RCA/coarse Conventional 5.13/0
RCAC1 5.63/50
RCAC2 5.56/25
RCAC3 6.57/37.5
C30, C35 Concrete with design strength of 30 and 35 MPa; RCAC1, RCAC2, RCAC3: concrete
prepared by replacing coarse NA by RCA, CBMRA and a 2:1 mixture of RCA and CBMRA,
respectively
resistance of reinforced structures goes down. The presence of micro cracks and
pores in concrete generally enhances the rate of carbonation. Several reports are
available on the evaluation of carbonation resistance of concrete. Normally RCAC
has higher rate of carbonation than conventional concrete. Hansen (
1992
), after
analysing various studies, concluded that RCAC had 4 times faster carbonation
rate than that of conventional concrete. Two typical examples of the effect of RCA
on the carbonation depth of concrete are presented in Table
5.25
.
Limbachiya (
2010
) observed similar carbonation depth of two classes of air-
entrained conventional concrete and concrete with a 30 % replacement of coarse
NA by RCA. However, the carbonation depth of concrete decreased when the
replacement level of coarse NA increased to 50 and 100 %. The author gave two
reasons for resistance against carbonation to improve due to the incorporation of
coarse RCA: increase in calcium hydroxide content with more attached cement
paste content and increase in alkalinity due to increased cement content in RCAC
to reach equal strength of concrete as well as to reduce the w/c ratio. These results
are presented in Table
5.24
. In this study, the concrete samples were exposed for
