How To Build A Spray-In-Place Concrete Fence - Monolithic

tor’s experience.
Concrete Strengths
Normally shotcrete is much
stronger than conventional concrete
because of several factors. First more
cement is used in the mix. Also the
impaction created by the air tends to
drive out the larger air spaces thus
providing a somewhat denser product.
Usually shotcrete will have a compressive
strength of more than 4,000 psi.
The concrete strength depends
greatly on the aggregate, the amount
of cement and the amount of water.
The concrete is being poured over the front
of the Monolithic Integrator SL30 Concrete
Mixer into the MudSlinger EHP 1500 concrete
pump (above). The mixer also has a
side gate for letting smaller amounts out
(below), such as would be needed for filling
post holes. The side dump is demonstrated
below.
Aggregate
The best aggregate for shotcrete
is a very even gradation from 3/8 to
nearly nothing. If any of the sizes are
left out that size must be replaced by
the cement creating a much harder
mixture to pump and work with.
Rarely in the United States do we find
nice, even graded aggregate. Aggregate
that has been crushed is also
much harder to work with than river or
natural aggregates. The jagged edges
of the crushed aggregate tend to hang
up in the pumping process. Rarely do
we find an even graded aggregate. So
generally we have to make the best
with what we can find in the locality.
Mix Water
Wherever possible the water/
cement ratio needs to be held at .4 to
.45. This creates an extremely strong,
workable concrete. Sometimes additional
water must be used to create
a pumpable mix. This is done most
often when some of the aggregate is
off-size or cracked. Theoretically the
slump test will give you an indication
of the water cement ratio. However,
with 3/8 minus aggregate slump tests
are very unreliable.
Slump Test
The slump test is performed by
filling an inverted cone with concrete,
then removing the cone and measuring
the distance the concrete slumps from
the original height. A slump test is an
17