Integral Water-Resisting Concrete System

In an integral approach the below-ground structure is itself designed and built to resist the passage of water. Nothing separate is applied to it. The resistance comes from the concrete element, from the way cracking is controlled within it, and from the treatment given to every place where the pour was interrupted or where something has to pass through.

The difference from a barrier-waterproofing-system can be seen on site before backfilling. A barrier approach shows a distinct applied layer between ground and structure that can be pointed at; an integral structure shows the excavation face meeting bare concrete, and what is relied on is that concrete together with the waterstops, seals and injection provision built into its joints. This entry describes resistance rather than a performance outcome, because how such a construction behaves depends on the design, on the workmanship and on the conditions it meets.

That puts the whole subject at the discontinuities. A pour has to stop somewhere. A structure has to accommodate shrinkage while something restrains it. Formwork has to be tied through. Services have to enter. Each of those introduces a purpose-made role - a waterstop cast into a joint, a hydrophilic strip, a sealed tie, provision for later injection - and none of them makes sense except in relation to how, and in what order, the concrete was placed.

Cracking is not a property of the concrete on its own; it is what happens when shrinkage meets restraint. A wall cast against an already hardened base is restrained along its foot, so the pour arrangement, the size of the bays and the distribution of reinforcement are settled together as a single decision. Casting longer lengths to suit the programme transfers demand onto the crack-control provisions and onto the joints, and that transfer is rarely visible on a drawing.

A waterstop performs only if the concrete closes fully around it, and it sits exactly where the reinforcement is densest and the pour hardest to compact. The component meant to seal the joint is therefore placed in the least favourable position in the whole element. That is why joint behaviour is discussed alongside reinforcement congestion, access for compaction and the order of placing, rather than as the selection of a product.

Penetrations couple the structure to work that happens much later. A drainage connection, an incoming service or a fixing drilled for a lining all pass through the resistance, and each is sealed by a different means from the joints around it. Once backfill is placed none of them can be reached from the ground side, so the sealing strategy has to be settled while the fit-out is still only a proposal.

Because there is no applied layer and no drained void, the internal finish becomes part of the moisture story rather than a decoration applied to it. Concrete goes on releasing moisture long after casting, and a lining fixed tight against it holds that release where nothing can remove it. Lining arrangement, ventilation of the space and the condition of the structure therefore have to be considered as one subject.