Home' MHD Supply Chain Solutions : MHD Nov-Dec 2015 Contents Consistency of the material properties and
delivery to site are the keys to a well-finished
It is worth noting that high-strength concrete
such as 40mpa does not guarantee better
abrasion resistance. 32mpa concrete will be
provide just as good abrasion resistance as
40mpa, without the risk of additional shrinkage.
Countless studies conducted over recent years
have proven that high-strength concrete does
not improve abrasion resistance, in fact, it can
be potentially detrimental to it.
Although reinforcement will give some enhance-
ment to the structural load capacity of the
floor slab, the primary function is to restrain
the opening of sawn induced joints, and to
maintain good load transfer properties - or if
cracks occur, it is there to strain the opening of
The traditional method of reinforcement in
jointed ground-supported slabs is with steel
mesh. Although in Australia the position of the
mesh is traditionally specified at 50mm from
the top of the slab, this is now considered an
outdated practice, and it is recommended that
it is placed 50mm from the bottom of the slab.
Alternatively, floors can be reinforced with steel
fibre, or post-tensioned.
Caution must be taken with nominally rein-
forced steel fibre slabs (less than 30kg per
cubic metre) with saw-cut joints. The joints can
become wider than predicted, and load transfer
between sections of floor can be lost. This
can result in floor movement at the joints, and
breakdown of the joint itself.
Jointless slabs with no saw cuts joints can offer
the warehouse user a floor with reduced mainte-
nance, but this method comes with some words
of caution. The quantity of steel fibres should
always be equal to or greater than 35kg/m3.
Steel fibre suppliers will often quote a lower
dosage than 35kg/m3 if you use their particular
fibre type, claiming all sorts of performance
characteristics. In addition, they may also claim
the floor can also be thinner, but be warned,
and approach steel fibre floors with caution.
Some steel fibres are better than others, but a
minimum dose is essential for long-term perfor-
mance regardless what the supplier will state
- and for a jointless floor, this is a minimum
Detail design in detail
Joints are the most critical element in a floor.
Most maintenance requirements are related to
the breakdown of joints in some form. Joints
create unavoidable discontinuities in a floor,
which can be damaged by mechanical handling
equipment when trafficked.
Joints are provided for two purposes:
1. To form the boundaries of each
day's concrete pour
2. To reduce the risk of cracking as the
floor shrinks (contraction joints and isola-
Construction joints must incorporate dowels
to provide a load transfer mechanism between
the sections of floor.
Contraction joints are most commonly created
by saw cutting. Sections of cast floor are usually
cut into panels of 6m x 6m. The intention is
that a crack will then form beneath the saw cut,
relieving drying shrinkage stresses. A typical
detail is shown in Figure 2. The reinforcement
must be continuous across the sawn joint to
restrain the opening of the engineered crack
and maintain adequate load transfer.
Floors must be isolated from fixed elements of
the building to allow the floor to contract without
cracking. This is achieved by surrounding
columns with compressible materials. These are
known as the isolation details.
Ground supported slabs can be jointed or joint-
less. Jointed floors have construction joints at
the edges of each day's concrete pour, and they
typically have sawn joints at 6m intervals.
The term jointless is something of a misnomer
as all slabs have construction joints at the edges
of areas of floor that are poured in any one day.
On a jointless floor, these are the only joints.
Joints are provided to permit breaks in
construction and to allow for shrinkage as
the concrete dries out over a period of up to
Some floors are built without sawn joints. These
are usually fibre reinforced. The principle is that
the steel fibres limit the crack widths of shrink-
age cracking. Care must be taken to ensure
that all possible steps are taken to minimise
the restraint to shrinkage, including mix design,
correct curing, and limiting pour sizes.
Flatness and levelness requirements
There are essentially two methods for defining
floor flatness requirements. Floors are divided
into free movement areas (FM) and defined
movement areas (DM).
The FM criteria is where trucks operate at low
level when moving, such as marshalling areas,
block stacking areas, and aisles greater than
Cracking in concrete
Cracking in concrete can happen for many
reasons, but ultimately concrete should not
crack and it should certainly not be the norm.
A floor that is well designed, with a good quality
mix design and high attention to detail when
constructing the slab, should produce a crack
Glenn Powell is the principal of Face
Consultants, specialists in floor design,
testing and surveying. For advice, or to speak
to them about a floor design or survey, call
(02) 9316 8808 or 1300 802 558, email
Typical contraction joint detail.
MHD SUPPLY CHAIN SOLUTIONS --- NOVEMBER / DECEMBER 2015
WAREHOUSE OPTIMISATION 19
Typical armoured construction joint detail.
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