A SYNERGIST FOR CHLORIDE-BASED ACCELERATORS
- Chlorides have been used as concrete setting aids for a long
time. In spite of many undesirable, sometimes even disastrous side-effects such
as corrosion, efflorescence and reduced final strength, chlorides are still the
most effective and economical accelerators and are widely used at dosage ratios
of + -1% of the cement weight. Guidance figures have been adopted in overseas
and local standards (Appendix A), limiting the dosage according to the type of
concrete desired. However, in reality the dosage figures recommended in these
standards have virtually no effect in practice. For satisfactory acceleration
the dosage rate of calcium chloride is well above 1%.Therefore the application
of chloride has been restricted to use in non-pigmented bricks, blocks, or
similar products where efflorescence and corrosion is not a problem.
- The chemical action of the chloride in the fresh concrete is not yet fully
understood. Present knowledge indicates that most of the chloride ions can move
freely in the cement gel and can be washed out after hydration has taken place.
This explains the corrosion and efflorescence problems. It is generally assumed
therefore, that some kind of catalytic action takes place, but catalytic action
does not require high dosage, so if the dosage rate were to be drastically
reduced, the undesirable side-effects could be eliminated. We have developed a
product - POWERCHLOR - which has the effect of a catalyst but which, unlike a
catalyst, is consumed in the reaction. POWERCHLOR is therefore a synergist.
DESCRIPTION OF PRODUCT
- POWERCHLOR is an accelerator for Portland cement,
containing synergistic activated chloride. It is used at one-twentieth of the
usual dosage of calcium chloride. To a much lower degree it also activates
fly-ash and finely ground blast furnace slag. Unlike calcium chloride, instead
of decreasing the final strength of the concrete, POWERCHLOR increases it by up
to +-15%. The drastic reduction of the chloride addition rate from 2,5 to 0,05%
renders POWERCHLOR acceptable for South African specifications (Appendix A).
According to Fulton Concrete Technology 1994, the product would even be
acceptable for pre-stressed concrete, although at this stage we do not advocate
- For ease of application the optimum dosage of 0,1% was bulked up to 0,5% by
the addition of inert fillers or water. Doubling or trebling the correct dosage
will not change the performance of the product. POWERCHLOR is a free-flowing,
non-toxic powder containing 9% chlorides. A concrete made with the recommended
0,5% addition of POWERCHLOR containing 300kg cement/cbm therefore will contain
15 parts chloride, which equals 60 ppm. For comparison, tap water contains 25-50
ppm. These minute quantities of chloride are fixed in the molecular structure,
insoluble in water and can only be determined by acid treatment of the concrete.
Figures obtained with this method gave results from 70 ppm to 410 ppm, showing
no relation to whether the cement was treated or not. It can be assumed that
more accurate analytical method- probably nephelometric methods - have to be
- As is known from conventional chloride applications, the performance varies
with cement type. This also applies to South African cements. Cape cements give
similar results to European cements, showing an increase of 50% or less in
one-day strength. All other cements show an 80 to 150% increase, especially in
fly-ash and slagment blends.
- Thereafter, all South African cements behave similarly, showing an increase
at all times of +-15 %. POWERCHLOR is supplied in 25kg bags as a concentrate -
ready for dilution - in KwaZulu-Natal.
- POWERCHLOR is recommended for all types of concrete where
Chloride content of 60ppm is acceptable. In fly-ash blends the ash content can
be increased to half the total cement. Three-way mixes containing fly-ash,
ground slag and cement are highly recommended. Generally, POWERCHLOR is
extremely suitable for upgrading of slow-setting cement or cement mixtures,
particularly in concrete works. POWERCHLOR is non-corrosive.
- POWERCHLOR is added into the cement mixer at the earliest
possible moment - with other aggregates. POWERCHLOR liquid should be added
simultaneously with the mixing water.
- It is believed that the unique properties of POWERCHLOR may help
in reconsidering the present attitude towards chloride in general and may
indicate a method of how the chloride problems caused by over-dosage can be
- At the recommended dosage rate, each 25kg pocket of POWERCHLOR will, when
mixed, treat 500 x 50kg pockets of cement.
D.G.N. Manufacturing warrants that their products are of the quality
represented in their product literature and are suitable for use in accordance
with their recommendations. Since the products are used entirely under
conditions beyond the control of D.G.N. Manufacturing, this Warranty is limited
solely to the quality of their products. D.G.N. Manufacturing cannot be held
responsible for consequential loss or damage. The onus is on the user to
determine the suitability of the product by conducting his own trials.