66 | CONCRETO & Construções
surface was sealed in construction),
the permeability of the subgrade usu-
ally has the largest impact on the
drainage rate of the system. For the
engineer or the regulator, it is impor-
tant to know the drainage rate of the
pervious concrete system to know
that it is functioning as designed. For
the concrete contractor, it is important
to know the infiltration rate of storm-
water at the pavement surface, imme-
diately after curing, to know that the
pavement was installed correctly.
When considering just the con-
crete layer in the system, the rate of
surface infiltration will be impacted
by the gradation of the coarse aggre-
gate, the maximum aggregate size,
the design density of the pavement,
the relative density achieved during
construction, the vertical porosity dis-
tribution [Haselbach 2006], and the
amount of clogging by foreign materi-
al. Of these, the first three factors are
impacted by raw material selection by
the concrete producer. Whereas, we
have C 1747 to test the raveling po-
tential of a pervious concrete mixture
prior to construction, we don’t have
an equivalent, standardized, labora-
tory test to quantify the drainage po-
tential at the same point in the project.
ASTM C 1701 was designed to
measure the drainage rate (permea-
bility) of the concrete layer. However,
even this has limitations. If the system
is saturated, stormwater can back up
into the pervious concrete layer. When
testing, this mound of stormwater can
produce artificially low drainage rates
through the pavement. This is why C
1701 includes the text, “Do not repeat
this test more than twice at the same
location on a given day.”
When this test was developed, the
ASTM group thought it was best to be
used only to measure reductions in
surface infiltration to help owners de-
cide on proper maintenance. As the
industry has evolved, contractors have
begun to use it to protect their inter-
ests and prove the pavement surface
drained well immediately after cur-
ing. This would protect them from a
claim if the pavement were to become
clogged either by other trades, during
construction, or by outside influences
after construction. The ASTM sub-
committee expects to change the sig-
nificance and use of this test to allow it
to be used to prove that the contractor
installed the material properly.
5. STRUCTURAL ISSUES
Vertical and horizontal applications
need to be considered separately
when considering structural issues
with pervious concrete. While the
history and oldest applications of the
material were in structural walls, the
body of work today is primarily in non-
structural applications.
The biggest difference in perfor-
mance between pervious concrete
and plain concrete comes from con-
solidation. Both types of concrete
require densification to develop their
maximum strength. However, in nor-
mal concrete, aggregates are well
graded and there is paste between
the aggregates, which allows the
concrete to flow when vibratory en-
ergy is applied in the form of rodding
or mechanical vibration. This flowing
property is what allows plain concrete
to be consolidated to a consistent,
repeatable density. With pervious
concrete, however, there are no fine
aggregates and only a thin coating of
paste exists between the coarse ag-
gregate particles, so this flow does
not occur when the concrete is vibrat-
ed. The only way to get repeatable
and predictable density is to apply a
repeatable amount of compactive en-
ergy [Offenberg 2008].
For vertical applications, typically
walls, pervious concrete is not used
in the US, today. In the future, pervi-
ous concrete may return to vertical
u
Figure 3
Structural cracking in a pervious concrete pavement without raveling
