Maintaining concrete cohesion during underwater placement reduces the risk of segregation and paste washout. Sika® UCS Pak is a powdered anti-washout admixture supplied in water-soluble bags for carefully designed underwater concrete mixes. It is intended for use alongside a compatible high-range water reducer or superplasticiser.
Marine concrete and piling in porous ground
UCS Pak is used in underwater civil and marine works and in suitable piling concrete where segregation or moisture loss is a concern. It improves cohesion and helps reduce bleed while the companion water reducer maintains the high workability required for placement by pump or tremie.
Dosage by placement conditions
- Static segregation control: 1–2 bags per m³.
- Moderate underwater exposure: 2–3 bags per m³.
- Severe flowing-water exposure: 4–5 bags per m³.
These supplier guidelines require confirmation in project mix trials. Add bags with cement or aggregate at batching, not into the gauging water. Sika recommends at least 120 seconds of wet mixing under suitable conditions. Addition can extend set time, and overdosing may increase entrained air and reduce strength or workability.
Pack contents
One sealed tub contains 24 × 0.4 kg water-soluble bags (9.6 kg total). This is a concrete mix admixture, not a standalone waterproofing system.
Sika® UCS Pak Physical Properties
| Property | Value |
|---|---|
| Product type | Underwater anti-washout concrete admixture |
| Composition | Powder blend of plasticisers and viscosity modifiers |
| Appearance | Pale buff powder |
| Unit | 0.4 kg water-soluble bag |
| Sealed tub | 24 bags (9.6 kg total) |
| Indicative dosage—static segregation control | 1–2 bags/m³ |
| Indicative dosage—moderate underwater conditions | 2–3 bags/m³ |
| Indicative dosage—severe flowing water | 4–5 bags/m³ |
| Recommended wet mixing time | At least 120 seconds under suitable mixer conditions |
| Indicative minimum cementitious content | 400 kg/m³ |
| Indicative maximum water/cement ratio | 0.45 |
| Technical conformity | BS 8443 requirements |
| Shelf life | 12 months unopened |
| Storage | Dry, 5°C to 35°C; protect from sun and frost |