Micro-cements
Micro-cements for Injection Grouting
Superfine cements ground to defined particle sizes for grouting fine to medium sands and for tunnel pre- and post-grouting.
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Introduction
Micro-cements are superfine cements, ground in special mills to defined particle sizes. Their use has become widespread in Japan and North America for grouting fine to medium grade sands that are not groutable with ordinary cement grouts.
In Scandinavia, ultrafine and microfine cements are used extensively in pre-grouting (and post-grouting) of rock tunnels for consolidation and water tightening of the rock. Rapid hardening cement or OPC may be used in cases of larger fissures.
Micro-cement grout has become an accepted means of overcoming problems of toxicity, low strength and uncertain permeability associated with chemical grouts used for fine granular soils.
Advantages (as stated)
- Able to replace chemical fluids and gels.
- No toxicity or environmental problems.
- Higher strengths and durability than chemical gels.
- More economical compared to chemical injection.
- Better permeation and tightness characteristics than normal cements.
Cement range in the MultiGrout® System
- Ultrafine cements: two grades, max. particle size < 16 µm and max. particle size < 12 µm, for fine penetration injection grouting.
- Microfine cement: max. particle size < 20 µm and max. particle size < 30 µm sulphate resistant cement, for less demanding penetration injection grouting.
Applications
As part of the MultiGrout® System, the micro-cements are stated to be suitable for underground and civil engineering applications including:
- Rock injection: pre-injection, post-injection, rock stabilisation, curtain grouting.
- Soil injection: stabilisation, water tightening, control of ground water.
- Grouting of anchors in rock and soil.
- Injection of cracks in concrete.
Particle size (as provided)
Particle size distributions are referenced in the source material (Figure 2). Surface area is stated to be measured by the BET (nitrogen absorption) method.
| Cement | d95 | d50 | Surface area (m²/kg, BET) |
|---|---|---|---|
| Ultrafin 12 | 10 µm | 3 µm | 2200 |
| Ultrafin 16 | 14 µm | 5 µm | 1600 |
| Microfine 20 | 19 µm | 6 µm | 2600 |
| Injektering 30 | 22 µm | 7 µm | 1250 |
Stability
Micro-cements are stated to improve grout stability compared to OPC. To penetrate the finest fissures it is desirable to inject high water/cement-ratio grouts; the use of GroutAid® (a microsilica-based additive developed for use with injection cements) is stated as always recommended. Extremely ‘thin’ grouts can be injected without problems with bleeding and fluid loss.
Setting
Setting time is described as important because tunnelling often has to stop during grouting. The use of the Blocker Cement System in combination with injection cements is stated to ensure control and flexibility during the grouting operation.
Nominal setting times are stated as 80 minutes (ultrafine) and 140 minutes (microfine).
Manufacture (as stated)
Micro-cements are stated to be manufactured in Sweden from selected clinker and ground in a specially designed and patented mill. The cements are stated to be chromate-reduced, complying with European Directive 2003/53/EG.
The microfine cement is stated to comply with Swedish Standard 134201 and CEM I 52.5 LA/SR, and ultrafine cements with Swedish Standard 134201 and CEM I 52.5 R/LA/SR.
Packaging
Standard packaging is stated as 20 kg multi-layer paper bags, with forty or twenty bags per pallet, shrink-wrapped.
Storage & shelf life
Being finely ground, micro-cements may become more sensitive than ordinary cement to storage conditions. Storage in damp air, or direct exposure to moisture, is stated to quickly damage the cement.
The cement is stated not to be stored for more than six months, since chromate reduction gradually loses its effect.
Mixing & use
When mixing injection cements, it is stated as essential to use a high-speed colloidal mixer (1,500+ rpm) that recirculates grout through a centrifugal pump. Colloidal mixing is stated as something that should always be specified in contract documentation.
Handling
The micro-cements, like any cementitious product, should be handled using appropriate precautions and safety equipment. Please consult the Material Safety Data Sheet.
The MultiGrout Team
The MultiGrout activities extend well beyond materials supply and involve a core group of technical specialists providing four key service elements:
- Materials supply
- Application methodology
- Education / on-the-job training
- Engineering / design support
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