Frequently Asked Questions

How is the dosage of Conplast SP430SRV calibrated for SCC production and what tests are used to verify SCC performance?

The dosage of Conplast SP430SRV for SCC production must be established by trial mix testing — there is no fixed single dosage that applies across all mix designs, cement types, aggregate gradings, and ambient temperatures. The SCC mix design process for SP430SRV involves: selecting the mix proportions (paste volume, aggregate volume, water-cement ratio) appropriate for the required SCC class; determining the base dosage of SP430SRV from the Fosroc technical data sheet recommendation for the target slump flow class; producing a trial batch and measuring the SCC fresh properties using the standardised SCC test methods; and adjusting the SP430SRV dosage in subsequent trial batches to achieve the target fresh properties. The three key SCC fresh property tests are: slump flow (EN 12350-8 or IS equivalent — measuring the spread diameter and T500 time); J-ring (EN 12350-12 — measuring the passing ability through reinforcement bars); and V-funnel (EN 12350-9 — measuring plastic viscosity and segregation resistance). For production SCC, the slump flow test on every truck or batch is the primary quality control check. The T500 time (time for the concrete to spread to 500 mm diameter) is an indicator of plastic viscosity — too fast (below 2 seconds) indicates risk of segregation, too slow (above 5 seconds) indicates over-viscous mix.

Can Conplast SP430SRV be used for underwater concrete in bored piles without a separate anti-washout admixture?

Conplast SP430SRV provides good cohesion and segregation resistance through the VMA component, which improves the concrete resistance to water infiltration and washout compared to a plain superplasticiser-dosed mix. However, the VMA component in SP430SRV is calibrated for the anti-segregation requirements of standard in-air SCC production — the cohesion level provided may not be sufficient for truly underwater concrete applications (tremie concrete, direct underwater placement) where the concrete is actively in contact with standing or flowing water during placement. For piles placed using the wet process tremie method (where fresh concrete flows down through a tremie pipe and displaces drilling fluid or water as it fills the pile bore from the bottom up), the anti-washout requirement is more about containing the concrete within the tremie flow column rather than water contact after placement — and SP430SRV dosed SCC with its high cohesion and VMA component is generally well-suited for this application. For situations where concrete is directly placed into flowing water or is at risk of water washout during placement, a dedicated anti-washout admixture (such as Fosroc Conplast UW-L) should be used in combination with the superplasticiser.

What is the temperature sensitivity of Conplast SP430SRV SCC performance and how should dosage be adjusted in Indian summer?

Self-compacting concrete produced with Conplast SP430SRV is significantly more sensitive to ambient and concrete temperature than conventional vibrated concrete — the same SP430SRV dosage that provides target slump flow at 25 degrees Celsius concrete temperature may give substantially reduced slump flow (100 to 150 mm less spread) at 35 degrees Celsius concrete temperature in Indian summer conditions. This temperature sensitivity arises because the cement hydration rate and the rate of superplasticiser consumption increase with temperature, meaning the high-flow window of the SP430SRV-dosed SCC narrows significantly in hot weather. For SCC production in Indian summer (April to June in Delhi NCR), three adjustments are typically needed compared to the cooler season mix design: the SP430SRV dosage may need to be increased by 10 to 20 per cent to compensate for the higher consumption rate at elevated temperature; the concrete temperature at batching should be reduced by using chilled water and pre-cooled aggregates to the extent possible; and the target T500 time should be monitored more closely, as hot weather SCC can transition from well-performing to segregating quickly if the mix temperature exceeds 35 degrees Celsius. Trial mixes at the expected peak summer concrete temperature should be completed before the summer construction season to recalibrate the SP430SRV dosage for SCC production at elevated temperature.