We have a wide range of concrete add-ons to suit your project’s needs.
Set accelerators work by accelerating cement hydration, which results in shortened setting times and increased early age strengths, particularly in cooler temperatures. They increase the rate of early strength development and reduce time required for curing and protection.
At one time, calcium chloride was the predominant accelerating admixture. Chloride is considered to contribute to corrosion of reinforcement or embedded metal in concrete. In turn this corrosion has been associated with spalling, cracking, loss of bond and if left uncorrected can cause eventual failure of the element involved. Now, chloride-free set accelerators are available based upon other chemicals.
Stevenson Concrete only uses non chloride accelerators.
Set retarders are used where delay in setting time is required to ensure sufficient placement, vibration or compaction time.
• Long hauls
• Trucks waiting a long time – even for a small pour
• Undermanned placement crew
• Slow pour rate
• Hot temperatures that may accelerate set time and concrete setting.
Things to consider:
Project location – long or short haul
• Size of pour
• Rate of pour
• Placement method
Environment exterior, interior
Thick sections – (if dry windy conditions, early surface drying while the underlying concrete is still soft can make finishing difficult and result in a wavy or cracked surface).
Superplasticizers (High-Range Water Reducers) can make a low-to-normal slump concrete into a high-slump flowing concrete which can be placed with little or no vibration. However, the change in slump usually lasts only about 30 to 60 minutes depending upon the brand and dosage rate.
Other applications and benefits of high-range water reducers include:
• difficult wall placements
• narrow forms
• sections with blockouts, penetrations, or embedded items
• pumping high vertical distances
• fast placement of concrete
Superplasticiser can be added either during batching or at the job site. At the jobsite the admixture will cause the concrete to be flowable for a longer period of time. This can delay the finishing process. Redosing is possible to regain the plasticity of the mix and manufacturer’s recommendations should be followed closely.
Addition of water to concrete can be detrimental to its performance.
Overdosing may cause segregation.
Priced / Litre
Polypropylene and Cellulose fibre
Stevenson currently use Ultrafibre 500 –
Cellulose fibres are used as an aid to reduce plastic shrinkage cracking. They are not a replacement for steel or steel fibre.
The fibre increases the early age tensile strength.
The dose rate is usually 2 bags of Ultra fibre/m3. Priced $/bag.
Ultra Fibre suppliers claim that their fibre is able to be used in place of steel, however we do not promote it for steel or mesh replacement. If used as a replacement it is the responsibility of the supplier to guarantee the performance.
Ultra fibre is good in exposed concrete as it is virtually invisible.
Steel Fibres are added to the concrete to improve engineering performance it can replace reinforcing steel and mesh.
The dose rate is specific to the mix design and must be designed by an engineer.
There are a range of sizes of steel fibres with varying properties.
Steel fibre can be added to most types of concrete.
We commonly use the Dramix range.
Combinations of synthetic and steel fibres are available.
Generally priced /kg.
A liquid or powder added to fresh concrete to change the colour of the concrete.
Oxide is added at the concrete plant.
Black oxide is carried at all plants. Other oxides need to be ordered in and are job specific.
Added as a % (typically 5%) of the cement content.
Priced by the kg and wash out charges may apply.
Oxides are supplied by Peter Fell (see links) or Oxide Distributors (see links).
Minimum recommended dose rate of black oxide is 6kg/m3.
If in doubt call Peter Fell 828-6460
A chemical added to fresh concrete to increase its ability to pump. It is a polymer that locks the water phase and reduces the ability to pressure bleed.
Pump aid is generally recommended for pumping long distances and through marginal pumps.
There are a large range of pumps with varying technical specs and in various ststes of repair.
Slight variations in grading can have serious effect on pumpability of concrete.
Pump aid is added at a rate of 1 litre /m3 and priced / litre.
Shrinkage Reducing Admixture
Shrinkage Reducing Admixture is aa chemical added to fresh concrete to decrease the long term drying shrinkage.
A reduction in shrinkage will allow greater joint spacing, or a reduction in crack size.
Often specifications limit the amount of shrinkage allowed in concrete. Shrinkage in concrete is measured in microstrain.
The admixture dose rate depends on cement content and type of mix and the shrinkage reduction required.
Priced as part of the mix design or as an extra to the mix.
Shrinkage compensating Cement
Shrinkage compensating” is defined in ACI 116R as “a characteristic of grout, mortar, or concrete made using an expansive cement in which volume increases after setting to approximately offset the tendency of drying shrinkage. In these materials, a chemical agent added to the cement reacts during curing to produce an expansive compound, resulting in a net volume increase of the material.
A chemical applied to the fresh finished concrete to slow the evaporation rate of water from the concrete surface.
Commonly recommended on days when plastic cracking may happen.
The film is sprayed across the surface prior to finishing and must be reapplied after each finishing process.
Several applications may be required while finishing the concrete.
It can also be used as an aid to stop cold joints in concrete.
Sold by the pail.
A chemical sprayed on the finished concrete surface to retard the setting of the surface concrete.
Sprayed onto the concrete before it sets and after bleed has finished.
The surface slurry is washed off that day or in some cases the following morning.
Performance is dependant on temperature, cement content, application rate and timing.
Sold by the pail
A chemical sprayed on the finished concrete surface to slow the movement of water from the hardened concrete.
Usually wax or petroleum based.
Often floor coverings will not stick well to these surfaces.
These products need to comply to the specification which limits the volume of water moving through the membrane.
A major disadvantage is that they have to be mechanically removed although they can break down over time. Alternative curing methods include the use of polythene sheet or a special curing sheet designed to retain the water on the surface to facilitate curing.