About Fosroc Conplast Blocksave

Fosroc Conplast Blocksave – re-branded by Fosroc International as Conplast SD110 – is a purpose-built admixture for the semi-dry concrete used in the block and paver industry, not for conventional wet ready-mix concrete. Semi-dry mixes are near zero-slump, very low in water and compacted by intense vibration and pressure on block-making machines. In these mixes the traditional water-reducing logic is reversed: the limit on strength is not slump but how effectively the small amount of mix water and cement can coat and bind the aggregate during compaction. Conplast Blocksave addresses exactly this. Supplied as a brown solution that disperses instantly in water, it spreads the fine particles and cement more uniformly through the mix, improving compaction and squeezing more strength out of every kilogram of cement. The practical payoff for a block manufacturer is direct: the same block strength, density and yield can be achieved at a reduced cement content, or higher strength can be obtained at the existing cement content – either way the cost per block falls. The product is chloride-free, so it carries no reinforcement-corrosion risk in reinforced precast units, and it incorporates a controlled degree of air entrainment that maintains mix yield, improves the surface finish of the demoulded unit and adds resistance to frost attack. It is compatible with all ordinary Portland cements and the common cement-replacement materials – PFA (fly ash), GGBFS (slag) and silica fume / microsilica – which makes it a natural fit for Indian block plants already blending fly ash to manage cost. Conplast Blocksave is one product in the broad Fosroc Conplast admixture family that Space Arc Engineering supplies across Delhi NCR and Pan-India; where a project actually needs a wet-concrete superplasticiser, an integral waterproofer or an accelerator, a different Conplast grade is the correct choice, and we help specifiers make that distinction up front.

The technical insight

The defining technical point is that Conplast Blocksave is engineered for semi-dry, vibration-compacted concrete rather than flowable concrete – a distinction that changes how it should be evaluated. In a slump-based wet mix, a water reducer is judged by how much it increases workability or cuts water at constant slump. In a near zero-slump block mix there is almost no free water to ‘reduce’, so the admixture works by improving particle dispersion and the efficiency of compaction, allowing the cement-water-aggregate system to reach a denser, higher-strength packed state under the machine’s vibration. This is why the headline benefit is expressed as a cement saving and a green-strength (freshly-demoulded) improvement, not as a slump or water-reduction percentage. Two consequences follow for the plant. First, the optimum dosage is genuinely process-specific and must be established by trial mixes on the actual machine, aggregates and moisture conditions – a starting band of 0.20-0.50 L per 100 kg of cementitious material is recommended, but the right figure depends on vibration intensity and sand grading. Second, the admixture can be ‘too effective’: on very high-intensity vibration equipment, or when aggregate stockpiles are wet, the improvement in water effectiveness can over-mobilise the mix and cause the freshly pressed block to slump or distort. Overdosing (roughly double the intended rate) pushes the mix into excessive workability with some set retardation and lower early strength. The chemistry is conventional and robust – specific gravity around 1.16 at 20 degrees C, nil chloride to BS 5075, alkali content typically under 5.0 g Na2O equivalent per litre – and it meets the BS 5075 Part 1 uniformity requirements, but the value is unlocked only through disciplined dispensing and trial calibration.

Where it is used

• Solid and hollow concrete masonry blocks produced on static or egg-laying (mobile) block machines
• Interlocking and pressed concrete paver blocks where green strength governs handling losses
• Concrete kerbstones, channels and edging units made by dry-cast / semi-dry methods
• Fly-ash, GGBFS or silica-fume blended block mixes seeking further cement-cost reduction
• Manufactured-sand or marginal-aggregate block mixes where improved cohesion is needed
• High-volume block plants targeting a lower cement factor at a fixed strength grade
• Cold-region precast where controlled air entrainment improves frost resistance of units

Key advantages

• Maintains block strength, density and yield at a reduced cement content, lowering raw-material cost per unit
• Can instead raise both early-age and later-age strengths without adding cement
• Improves green (freshly-demoulded) strength, cutting handling and stacking breakages
• Controlled air entrainment improves surface finish and frost-attack resistance
• Better mix cohesion allows economical use of a wider, lower-cost range of aggregates
• Chloride-free (nil to BS 5075) – safe for reinforced precast units
• Compatible with OPC and PFA / GGBFS / silica-fume cement-replacement systems
• Disperses instantly in water and is supplied ready-to-use; water-based and non-flammable
• Meets BS 5075 Part 1 uniformity requirements for batch-to-batch consistency

Limitations & considerations

• Designed for semi-dry / zero-slump block and paver concrete – not intended for wet ready-mix or flowing concrete (use a Conplast superplasticiser grade instead)
• Can be over-effective on very high-intensity vibration machinery, over-mobilising the mix
• Wet aggregate stockpiles can combine with the admixture’s water-efficiency gain to cause excessive workability and block slumping
• Overdosing (about twice the intended rate) causes excessive workability, set retardation and reduced early strength
• Optimum dosage is process-specific and must be confirmed by trial mixes on the actual plant – no single universal rate
• Normally only one admixture is used in a semi-dry mix; combining with others needs Fosroc technical clearance
• Liquid must be kept between 2 and 50 degrees C; outside this range Fosroc advice is required
• It improves cement efficiency, not cement quality – it cannot compensate for unsound cement or badly graded aggregate

Selection & best practice

Specifications

Industry use cases

How we position Fosroc Conplast Blocksave

Conplast Blocksave (now Conplast SD110) occupies a narrow but valuable niche: it is the Fosroc admixture purpose-built for semi-dry block, paver and masonry concrete, where the goal is cement cost reduction and green strength rather than slump. It should not be confused with Fosroc’s wet-concrete admixtures – Conplast SP430 and the SP430/SP431R superplasticiser range for high-workability and high-early-strength structural concrete, Conplast WL / WL Xtra for integral waterproofing, Conplast X400 as a waterproofing additive, or Conplast NC where an accelerator is needed – and Space Arc routinely steers specifiers to the correct grade. For dry-cast block production specifically, the comparable competitor offerings include Sika’s block and paver admixtures (the SikaPaver / Sika cement-saver family), Master Builders Solutions (MBS, formerly BASF) MasterPave / block-machine admixtures, and locally Dr. Fixit (Pidilite) and STP Limited supply block-industry water reducers; for wet structural concrete, Sika ViscoCrete, MasterGlenium and Fosroc Auracast/Structuro polycarboxylate ranges are the relevant alternatives. As an authorised Fosroc distributor and applicator, Space Arc Engineering supplies Conplast Blocksave/SD110 across Delhi NCR and Pan-India and, importantly, runs the trial-mix and dosage calibration support that this product genuinely requires – which is where most of its real-world cost saving is won or lost.

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