Frequently Asked Questions

What dosage of Sika Plastiment is needed to maintain 120 mm slump for 75 minutes in an RMC plant delivery during Delhi summer (42 degrees C ambient) and what are the strength implications of over-dosing?

At 42 degrees C ambient temperature in Delhi summer, a concrete mix using OPC without any retarder may lose 50 to 80 mm slump within 30 to 45 minutes of mixing — arriving at a congested Delhi construction site (45 to 75 minutes from plant) with slump below 60 mm, inadequate for pump delivery and compaction. To maintain 120 mm slump for 75 minutes at 42 degrees C, the required Sika Plastiment dosage in a trial mix at plant conditions is typically 0.25 to 0.35 per cent by cement weight — 0.60 to 0.85 kg per 100 kg OPC in the mix, or approximately 2.0 to 2.8 litres of Sika Plastiment per m3 for a 450 kg/m3 cementitious content mix. The required dosage must always be established by a trial mix at the actual plant mix design and ambient temperature — dosage calculations from standard conditions cannot be simply transferred to hot weather without verification. Regarding over-dosing: if Sika Plastiment dosage exceeds approximately 0.5 per cent by cement weight, the risks include: severe set retardation (initial set after 8 to 12 hours or more), potential surface dusting due to excessive retardation of surface mortar, and delayed strength gain (24-hour and 3-day strengths significantly below design, though 28-day strength typically recovers). Over-dosing Sika Plastiment does NOT produce a permanently weak concrete but can cause serious construction schedule delays. Always dose at the minimum effective rate established by trial mix.

Can Sika Plastiment be combined with Sika ViscoCrete (PCE superplasticizer) in the same concrete mix for a high-strength M60 pour in summer?

Yes — Sika Plastiment and Sika ViscoCrete can be used in combination in the same concrete mix, and this combination is standard practice for high-strength concrete production in hot Indian summer conditions. The two admixtures serve complementary functions: Sika ViscoCrete (PCE superplasticizer) provides the high water reduction (25 to 35 per cent) necessary to achieve the low w/c ratio (0.30 to 0.35) required for M60 strength, while Sika Plastiment provides the set retardation and workability retention extension needed to maintain the design slump through long transit times and placement in hot weather. Dosed together, Sika ViscoCrete provides dispersion efficiency (low w/c) and Sika Plastiment provides workability duration (extended set time). The combined dosage for a typical M60 summer pour might be: Sika ViscoCrete at 0.5 to 0.7 per cent by cement weight for high water reduction, plus Sika Plastiment at 0.15 to 0.25 per cent by cement weight for 60 to 90 minute additional set retardation. Important compatibility note: when combining PCE and lignosulphonate admixtures, always add them sequentially during plant batching (water first, then admixtures through separate inlet points) and verify by trial mix that the combined dosage provides the target slump, slump retention, and set time without incompatibility effects. Contact Space Arc Engineering for Sika technical support on multi-admixture mix design for summer RMC production.

Does Sika Plastiment affect the 28-day compressive strength of concrete and can it be safely used in M40 bridge pier concrete?

At correct dosages (0.1 to 0.4 per cent by cement weight), Sika Plastiment does not reduce 28-day compressive strength of concrete below the design value — the lignosulphonate provides 5 to 8 per cent water reduction that partially offsets any slight hydration retardation effect at 28 days, so cube strength at 28 days is typically within the normal statistical variation of the untreated concrete. The early strength at 1 to 3 days will be lower than untreated concrete at equivalent ambient temperature — 24-hour cube strength may be 15 to 25 per cent lower due to the set retardation effect — but this is the intended behaviour for managing early hydration in hot weather. For M40 bridge pier concrete, Sika Plastiment is suitable and commonly used on bridge projects in North India where large continuous pours are required and 24-hour form-stripping is not a project constraint. Bridge specifications (IRC codes) typically require 28-day cube strength compliance, which Sika Plastiment does not compromise at recommended dosages. If the bridge specification requires a specific minimum 3-day or 7-day cube strength (for form-stripping or prestressing operations), verify at the specific Sika Plastiment dosage that the early strength requirement is still met before approving for production. At higher retarder dosages (above 0.4 per cent), early strength development is significantly impacted and may not meet 3-day minimum values specified for form stripping.