Superplasticisers

Superplasticizers, also known as plasticisers or high-range water reducers (HRWR), reduce water content by between 12 and 40% and can be added to concrete with a low-to-normal slump and water-cement ratio to make high slump slowing concrete.

Superplasticizers are linear polymers containing sulphonic acid groups attached to the polymer backbone at regular intervals. Most of the commercial formulations belong to one of four families with polycarboxylates being the latest in polymer technology:

• Sulphonated melamine-formaldehyde condensates (SMF)
• Sulphonated napthalene-formaldehyde condensates (SNF)
• Modified lignosulphates (MLS)
• Polycarboxylate derivatives

The sulphonic acid groups are responsible for neutralizing the surface charges on the cement particles and causing dispersion, thus releasing the water tied up in the cement particle agglomerations and thereafter reducing the viscocity of the paste and concrete.

RheoActiv SP is our latest range of polycarboxylate based products which offers superior performance over traditional superplasticisers.

Technical benefits:

• Increased 'early strength' development
• 'Ultimate strength' & durability is increased through reduced permeability
• Superior 'slump retention' affords longer workability if required
• Improved appearance due to minimal 'air entrapment'
• Reduced 'shrinkage' and reduced 'water bleed'
• Superior flow characteristics in self-levelling screed
• Environmental benefits, i.e. better biodegradability
• Formaldehyde-free

Commercial/Practical Benefits:

• Our new polycarboxylate production technology allows excellent cost savings
• Cement economies i.e. the same strength can be achieved with less cement
• No need for compacting machinery i.e. less noise & labour at job-site
• Reduced health & safety risks

Typical Applications:

• Cementitious Grouts
• Cementitious Screeds
• Repair Mortars
• Shotcrete and Gunite Repair Mortars
• Smoothing Coats
• Damp Proofing Renders
• Underwater Concrete
  

The Slump Test:

The fresh concrete is placed in a hollow cone-shaped form and compacted. When the form is raised, the slump gives a measure of the concrete consistence. The slump is the difference in mm between the height of the form and the height of the fresh concrete cone out of the form. Standard EN 12350-2 states that the whole process from the start of pouring to raising of the form must be completed within 150 seconds. The test is only valid if it gives a residual slump in which the concrete remains largely intact and symmetrical after removal of the form, i.e. the concrete remains standing in the form of a cone. If the concrete collapses another sample must be taken. If the specimens collapse in two consecutive tests, the concrete does not have the plasticity and cohesion required for the slump test.

Flowing concrete is a highly fluid but workable concrete that can be placed with little or no vibration or compaction. The effect of superplasticizers lasts only 30-60 minutes, depending on dosage rates etc, and is followed by a rapid loss in workability. As a result of the slump loss, superplasticizers are usually added to the concrete at the jobsite.