About Sika Sigunit L-93 AF (I)

Sika Sigunit L-93 AF (I) is the accelerator that goes into the spray line when a contractor needs freshly placed shotcrete to stiffen almost instantly. It is a liquid, alkali-free formulation built on a mixture of special organic substances, and it is metered into the concrete right at the nozzle rather than pre-batched. The moment it mixes with the cement, hydration is pushed forward hard, so the layer sets in seconds instead of minutes. That is what allows a crew to build meaningful thickness on a vertical rock face or hold material against an overhead tunnel crown without it sloughing off. Being alkali-free is the whole point of the product: earlier generations of shotcrete accelerators were strongly caustic, which was rough on the nozzleman’s skin and eyes and tended to hurt the long-term strength of the hardened concrete. This one sidesteps both problems.

For engineers and consultants, the appeal is that speed does not come at the cost of the finished job. Because there is no alkali and no added chloride, the sprayed concrete keeps its long-term strength and durability, and the embedded rock bolts and mesh are not exposed to a corrosive additive. It suits both the wet-spray process, where the concrete is pumped already mixed, and the dry-spray process, where water meets the dry mix at the gun. It works across all common cements and pairs cleanly with much of the wider Sika admixture range, so it slots into an existing mix design rather than forcing a redesign. For Space Arc’s tunnelling, mining and slope-stabilisation clients across Delhi NCR and the rest of India, it is a dependable workhorse where output and safety both matter.

The technical insight

Ordinary Portland cement is deliberately formulated to set slowly, which is exactly wrong for shotcrete that has to hang on a wall the instant it leaves the nozzle. An alkali-free accelerator like Sigunit L-93 AF (I) works chiefly on the aluminate phase of the cement: it drives the very rapid formation of ettringite and related hydrates, which flash-builds an early crystalline skeleton and stiffens the paste within seconds. The older, highly alkaline accelerators achieved this by dumping soluble alkali into the system, which triggered fast set but left a residue that raised porosity, encouraged later strength loss and pushed the concrete toward alkali-silica issues. By carrying no alkali, this product forces the early set through controlled hydrate growth rather than a caustic shock, so the matrix that forms is denser and the 28-day and long-term strengths are preserved. The trade-off is sensitivity: because the reaction is a fast hydration effect, its behaviour genuinely shifts with cement chemistry, cement content, ambient and substrate temperature, and the water content of the mix, which is why a site trial to pin down the right dosage is not optional but part of the method.

Where it is used

• Securing freshly exposed rock in drill-and-blast and TBM tunnel construction
• First-pass and permanent sprayed-concrete linings in tunnels and underground works
• Rock-face and slope stabilisation on hillsides, cuttings and highway embankments
• Overhead crown and vertical-face shotcrete where material must hold without sagging
• High-quality structural shotcrete for general construction and repair
• Sprayed linings in mining galleries and underground excavations
• Wet-process sprayed concrete pumped and accelerated at the nozzle
• Dry-process gunite where dosage is added at the spray gun

Key advantages

• Alkali-free and non-caustic, so it is far safer for the nozzleman and the working environment
• No added chloride, so embedded rock bolts, mesh and reinforcement are not attacked
• Preserves good long-term strength and durability of the hardened shotcrete
• Sharply reduces rebound, saving material and cutting site clean-up
• Noticeably lowers dust for a cleaner, healthier spray environment
• Improved adhesion on rock, concrete and in the overhead crown position
• Suits both wet-spray and dry-spray processes from one product
• Compatible with all cement types and with much of the Sika admixture range

Limitations & considerations

• Performance genuinely varies with cement type, content and age, so a site trial is essential to fix dosage
• Results shift with shotcrete and substrate temperature, so cold or hot conditions need re-checking
• In wet spray the w/c ratio, and in dry spray the water added at the gun, strongly affect the result
• Any metal in contact with the product must be stainless steel; brass parts must not be used
• Being acidic (pH 1.5-3.5) it needs proper PPE and stainless dispensing equipment
• Shelf life is only 6 months, and the suspension must be stirred well before every use

Selection & best practice

Specifications

Industry use cases

How we position Sika Sigunit L-93 AF (I)

Sigunit L-93 AF (I) sits in Sika’s shotcrete-admixture line and is best specified alongside the products that complete a sprayed-concrete system. Pair it with a Sika ViscoCrete superplasticiser to control the base mix workability in wet-spray work, and with Sika steel or macro-synthetic fibres where the lining needs fibre reinforcement instead of mesh. For curing the finished shotcrete, a Sika Antisol or Sikafloor curing solution helps lock in strength. Where a client works to a single-brand tender, Space Arc also carries the equivalent alkali-free liquid accelerators from other principals we distribute, including MC-Bauchemie and Master Builders Solutions (MasterRoc) lines, so the specification can be matched to the approved vendor list without compromising performance.

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