Method statement for site
handling of concrete made
with Ecocem GGBS cement
Introduction
Ecocem Ground Granulated Blastfurnace Slag (GGBS)
cement is a by-product of iron-making. It replaces up to
70% ordinary cement in concrete on a one for one basis,
giving superior concrete performance.
Health and safety (H & S)
Ecocem GGBS is a non-hazardous cementitious powder
certified to I.S. EN 15167-1 that has no classification
under the REACH directive. When used in concrete,
normal health and safety considerations for handling
fresh concrete apply. See Ecocem’s MSDS for full H&S
information.
Quality Assurance (QA)
Concrete with Ecocem GGBS shall be supplied by
independently certified concrete suppliers to I.S. EN 206
and sampling and testing shall be in strict accordance to
EN 12350-1&2 and EN 12390-2&3. Where higher than 50%
GGBS is specified, it is advisable to take extra cubes for
56-day strength testing.
Pre–ordering arrangements
1. Confirm the percentage of Ecocem GGBS required,
typically between 30-70%, most commonly at 50%.
2. Plan the pour to commence as
early as possible in the day
3.Confirm that the pour time
allows sufficient time for
finishing/power-floating and
optimal striking of concrete.
When Ecocem GGBS
percentages exceed 50%, or
in colder weather, concrete
setting times will be prolonged
by a number of hours.
TIP: Keep time
and date stamped
photos as a record
that good practice
is being followed
on site.
4.Arrange meeting on site with Ecocem, to discuss best
practice for working with concrete incorporating GGBS.
Taking delivery of concrete
with Ecocem GGBS
1. Check the mix design on the
delivery docket prior to discharge
to ensure the specified concrete
has been supplied.
TIP: Ecocem
GGBS cement is
white in colour,
and concrete with
Ecocem GGBS is
paler in colour than
ordinary concrete.
2. Water should not be added to
concrete as it will reduce the
strength and durability of the
concrete. Concrete made with
Ecocem GGBS has more fluidity
and stays workable for longer than
concrete without Ecocem GGBS.
Any addition of water on site is to be in accordance
with clause 7.5 of EN 206.
Placing and compacting
concrete with Ecocem GGBS
1. The usual methods of placing concrete (and selfcompacting concrete) apply for concrete with Ecocem
GGBS.
2.Do not drop concrete from more
than a height of 1m as the concrete
may segregate. For deep pours
use tremie pipes or pumps to
place the concrete.
3.Concrete with Ecocem GGBS
stays workable for longer, allowing
more time to place and compact,
and reduces the risk of cold joints
forming.
TIP: Concrete with
Ecocem GGBS is
easier to pump due
to its improved
workability.
4. Place poker to ensure vibrated areas overlap.
5.For subsequent layers the poker should be allowed
to sink under its own weight about 100mm into the
underlying layer, and the concrete vibrated from the
underlying layer upwards. Failure to do this can lead to
air bubbles being trapped, leaving blowholes.
6.Remove vibrator when air bubbles stop rising. Overvibration will lead to segregation.
7.Avoid poker burn by keeping the poker 75-100mm
away from the formwork. Avoid poker contact with the
reinforcing.
8. If plastic settlement occurs re-vibrate the top 75100mm of the concrete to ensure the concrete is
levelled.
ECOCEM Contact Details:
Tel: 00353 1 6781800 Fax: 00353 1 6781816 Email: technical@ecocem.ie Web: www.ecocem.ie
This is a guidance note and should be supplemented with the users requirements.
october 2012 - rev 1.0
Finishing and curing concrete
with Ecocem GGBS
1. The usual finishing techniques of using screeds, floats,
trowels, power floating, etc. apply to concrete with
Ecocem GGBS.
2.Flat surfaces of concrete with Ecocem GGBS are to be
finished only when bleed water has fully evaporated,
and not before.
3.For higher percentages of Ecocem GGBS (+ 50%)
and/or in cold weather,
setting times and duration
TIP: Longer setting
of bleed time may need
times allow concrete to
to be extended. Consult
be worked for longer
with Ecocem for further
periods so that time delays
guidance.
4.Concrete is to be cured in
accordance with EN13670.
5.Cure concrete for a
minimum of three days,
but ideally seven days.
between mixing and using
concrete are less critical.
This can also enable power
floating to be completed
on the morning after a
pour, rather than late at
night.
6.The two principle methods
of curing are:
a)Keep the surface of
the concrete wet by
ponding, mist spraying
or covering with damp
hessian.
b)Retain the moisture in
the concrete by using
polythene sheeting,
sprayed curing
compounds, leaving
formwork in place or
use of frost blankets.
(Curing compound
should be compatible
with end use of
concrete).
TIP: Finishing concrete
prior to evaporation of
bleed water can lead to
remixing of the surface
layer of concrete and
weakening of the concrete
surface. This can lead to
cracking, dusting,
delamination, abrasion,
frost or chemical
damage.
7.Failure to cure concrete adequately can result in loss of
up to 50% of the concrete design strength; increased
risk of cracking; dusty surfaces with low abrasion
resistance; reduced frost resistance and porous
concrete that will be susceptible to water ingress and
chemical attack.
8. In quick drying conditions or when concrete with > 50%
Ecocem GGBS is used, greater attention is required.
Striking formwork
1. Formwork shall not be removed
until the concrete has gained
sufficient strength.
2.Determine the required in-situ
concrete strength for striking
formwork from the Engineer’s
Specification or using guidance
from EN 13670 or The UK’s
Concrete Society publication
“Formwork – A guide to good
practice”.
TIP: Secure
polythene sheeting
to prevent wind
tunnel effect and
keep hessian damp
for the duration of
its use.
3.To optimize striking time, determine the insitu strength
of the concrete, rather than working to a fixed striking
time, as the early age strength gain of concrete with
Ecocem GGBS can vary according to variables such as
ambient temperature, mix design, the percentage of
Ecocem GGBS and the section size.
4. Standard 20oC cured cubes do not give an accurate
measure of early age in-situ strength.
5.To determine early-age in-situ strength of concrete
for optimum striking times use techniques such as
Temperature Matched Curing, Maturity Meters and
Maturity Functions, LOK Test or Capo Test.
6.Contact Ecocem to discuss formwork striking times and
to implement a site testing program to determine the
in-situ strength of concrete and determine the optimal
time to safely strike formwork.
7.After removing formwork, a blue/green colour
may temporarily appear on concrete with Ecocem
GGBS. This is due to iron and manganese sulphides.
However, these oxidise on exposure to air, returning
the colour to normal after several days. The desired
concrete properties such as strength, durability or final
appearance are not affected by this colouration.
Cold and Warm Weather concrete with Ecocem GGBS
1. Normal precautions are to be taken in cold and warm
weather, when concreting with Ecocem GGBS.
2.Cold weather will extend setting time which can lead
to increased formwork pressures and delays in striking
and finishing.
3. Warm weather can lead to excessive drying out or the
formation of cold joints. Consider modifications to
the concrete mix design, e.g. increase Ecocem GGBS
content and/or use chemical retarders.
ECOCEM Contact Details:
Tel: 00353 1 6781800 Fax: 00353 1 6781816 Email: technical@ecocem.ie Web: www.ecocem.ie
This is a guidance note and should be supplemented with the users requirements.
october 2012 - rev 1.0