64 | CONCRETO & Construções
Hammer. Today, the specification, C
1688, allows for either the use of the
Proctor Hammer or the Marshall Ham-
mer due to the low variability in results.
A method for hardened density
measurement was described by Mon-
tes [2005]. Another task group work-
ing under ASTM C09.49, led by Walter
Flood IV, refined this technique and for-
malized it as ASTM C 1754. This test
uses cores extracted from the pervious
concrete surface. Cores are weighed
submerged and after oven drying to
determine the density. Two drying
temperatures are allowed, depending
on how quickly the results are needed.
However, the density generated from
the higher drying temperature may not
be compared to the density generated
from the lower drying temperature, and
vice versa. The results are used as a
quality check on the contractor to prove
that the concrete placed is of sufficient
density to maintain durability through
the design life.
Obviously, one of the key attributes
of a pervious pavement system is how
quickly water passes through. Re-
searchers have described methods
for measuring the permeability (also
referred to as hydraulic conductivity or
infiltration rate) of pervious concrete,
both for cylindrical specimens [Neithal-
ath 2003] and full pavement systems,
including all layers from the surface to
the subgrade [Chopra 2011]. From a
practical perspective, the ASTM sub-
committee was interested in a test that
could measure surface infiltration over
the life of the pavement to determine
when maintenance might be neces-
sary. Based on a procedure described
by Montes [2006], Heather Brown’s
task group optimized this to work with
low-cost, easily obtainable materials in
ASTM C 1701.
The balance to permeability of a per-
vious concrete pavement is strength.
While with plain concrete, we are usu-
ally interested in flexural strength for
pavement design, the critical failure
mode of these pervious pavement sys-
tems is raveling – a failure where the
aggregate breaks loose at the surface
from the tire/pavement interaction. The
ASTM subcommittee fine-tuned a lab-
oratory-based procedure described by
Offenberg [2011] to measure the rav-
eling resistance potential of a pervious
concrete mixture. Today, the subcom-
mittee has a task group to standardize
a procedure for measurement of ravel-
ing resistance of hardened pavements.
With raveling being so critical, there
is little need to measure the strength
of the concrete in the pavement. Re-
sults to do so, either for compressive
or flexural strength, have failed to pro-
duce repeatable, reliable test meth-
ods. However, the subcommittee
sees a time in the future when raveling
is well understood and strength will
become a necessary design element
of heavier pavements. To this end,
the subcommittee is working on a test
method to measure flexural strength
of pervious concrete.
Now that the existing and develop-
ing test methods for pervious concrete
have been described, we can examine
how they impact pavements in practice.
3. RAW MATERIAL SELECTION
The challenge for any concrete pro-
ducer is selecting the best raw materials
and combinations to produce a high-
quality pervious concrete pavement.
In the early days of pervious concrete
(before 2011), producers had no guid-
ance on which raw materials helped
make good hardened concrete. They
could put up lab batches, and lay down
test panels, but they really had no easy
system for identifying which of their lo-
cally available raw materials might make
the best finished pavement. With the
introduction of ASTM C 1747 in 2011,
concrete producers were given a labo-
ratory test to compare raw materials
and combinations.
u
Figure 2
Pervious concrete pavement
