Croatian Railway Tunnel Rejuvenated with Crystalline Admixture-Treated Shotcrete

The rehabilitation of the Dujmovača Tunnel in Split, Croatia, strengthened the railway tunnel lining with upgraded waterproofing designed to prevent water seepage and support long-term structural stability. PENETRON ADMIX, a crystalline waterproofing admixture, was incorporated into the tunnel's shotcrete layers in late 2025 to meet durability requirements and help keep the project on schedule.

ORLANDO, Fla., Oct. 16, 2026 /PRNewswire/ -- Part of the Split suburban railway line, the Dujmovača Tunnel (M604) is one of two railway tunnels running beneath the city center of Split, Croatia. Split is now the country's second-largest city and a key economic, cultural, and transportation hub for the region.

The tunnel lining rehabilitation focused on upgrading waterproofing and drainage to control water ingress and improve long-term structural performance. The original design called for a dimpled membrane system to direct water inflows to through drains and half-pipes into a drainage channel and covered

"Several challenges emerged during implementation. The specified composite drainage material was no longer available and shotcrete adhesion tests produced values below the required threshold," notes Theodor Mentzikofakis, Managing Director and Partner of Penetron Hellas. "These issues highlighted the need for improved mechanical resistance and enhanced waterproofing performance, which led to a redesign of the system."

The revised technical approach addressed the limitations of the original design through several alternative solutions. Two options required an increased number of implementation steps and increased total construction costs. The third proposal introduced a new technical solution that combined reinforcement mesh with two additional waterproofing shotcrete layers (8 cm on the base layer and new 10 cm on untreated surfaces). This strategy would create a static arch effect to enhance mechanical resistance.

As part of the waterproofing and repair process, PENETRON ADMIX, a crystalline admixture for concrete, was proposed as an optimal waterproofing enhancement for the shotcrete layers. PENETRON, a topical crystalline waterproofing material and PENEPLUG, a rapid-setting crystalline compound, were also specified to stop active leaks and repair surface cracking in the tunnel walls.

PENETRON ADMIX offered several engineering advantages. The admixture delivers waterproofing performance comparable to two layers of a sprayed waterproofing membrane system and reacts with water and moisture to self-seal cracks. Installation was also simplified because the shotcrete could be applied in thicker layers, such as a 3+8 cm configuration instead of the original 3+3+4-cm sequence. This approach generated significant time savings by eliminating approximately 60 days originally allocated for waterproofing works and enabled faster rehabilitation even when limited to a 6½-hour daily work window.

"Testing and validation showed water penetration depth was reduced by 83% after ten cycles. This showed how PENETRON ADMIX SB significantly improved the water resistance of the shotcrete layers," concludes Theodor Mentzikofakis. "The admixture was a cost-effective and time-efficient alternative to traditional PVC sheet membranes as well as sprayed waterproofing systems. It also improved mechanical resistance through the combined use of reinforcement mesh and crystalline-enhanced shotcrete."

The Penetron Group is a leading manufacturer of specialty construction products for concrete waterproofing, concrete repairs, and floor preparation systems. The Group operates through a global network, offering support to the design and construction community through its regional offices, representatives, and distribution channels.

For more information on Penetron waterproofing solutions, please visit penetron(dot)com or Facebook(dot)com/ThePenetronGroup, 

SOURCE The Penetron Group