Introduction to reinforced concrete degradation

As is now universally known, the material that was once thought of as being "eternal" is actually subject to such a multitude of degradation factors that listing all of them would be impossible: design causes, inadequate laying onsite or curing, atmospheric agents, chemical agents, acid rain, carbon dioxide, differential aeration, carbonatation, stray currents, high temperatures, frost/defrost cycles, wear, knocks, erosion, salt and chloride, abrasion, alkali-aggregate reaction, excessive loads and mechanical stress, polluting agents and ... in certain conditions, even water that is too pure!

All these phenomena, and certainly much more, have a degrading action which can weaken the manufactured piece, increasing its porosity, causing cracks and increasing the overall permeability of the matrix by carbon dioxide. This causes the pH to lower of the base solution that permeates the cement mix and, at the same time, weakens the ferrous hydroxide film coating the concrete reinforcement when this is healthy. This process generates a dangerous and vicious circle where the external causes already mentioned insinuate within the corroded reinforcement to create very serious destructive phenomena. Lastly, the depassivation of the iron and corrosion of the reinforcement leads to the creation of complex oxides which are more voluminous than the steel particles and lead to "spalling" (destructive expulsion of the concrete cover).

If the degradation of the manufactured concrete piece is not serious enough to require significant volumetric reconstruction to restore it (in which cause normal structural grout is used such as GROUT 6 or GROUT CR), reconstruction can normally be completed with the application of rheoplastic thixotropic mortar with compensated shrinkage.

Structural restoration technique

Restoring a degraded concrete structure can seem at first sight a rather banal task, but there are certain considerations which are often overlooked which instead make the difference between a temporary restoration and a stable restoration that lasts over time. Among the typical aspects to take into consideration in choosing the ideal intervention cycle, it is worth considering:

SUPPORT STRENGTH

The support, before applying the subsequent restoration mortar, should be adequately resistant and free of pulverisation. CONSILEX SAN, with a sodium silicate base, also works on this important modification, consolidating the existing, degraded concrete.

ALKALINITY

Good restoration should mainly be as compatible as possible with the rest of the structure to restore. You must work on the pre-existing conglomerate, with hardening, consolidating treatments, particularly restoring the original alkalinity. CONSILEX SAN is the specific product to restore alkalinity to the concrete portions to restore.

DIMENSIONAL STABILITY OF THE RECONSTRUCTION

During the reconstruction phase, the mortar with which volumetric repair is executed must perfectly adapt to the morphology of the volumes to reconstruction. The initial volume must remain stable during the maturation phase. REPAR TIX restoration mortar is combined with a special mix of additives that compensate its dimensional contraction during hardening.

ISOTROPY AND WATERPROOFING OF MORTAR

Isotropy, by definition, is the property of bodies to have the same physical characteristics in all directions. It is an important property in the context of mechanical strength. Adding fibre mixes considerably increases the isotropy of the matrix and its overall tenacity. Furthermore, the reconstruction of degraded and damaged surfaces and volumes should guarantee the protection conditions of the reinforcement irons, therefore preventing permeation of CO₂ and humidity (conditions necessary to trigger carbonatation!). REPAR TIX has polypropylene, multi-filament fibres added to combat cracks due to plastic shrinkage and to increase isotropy of the matrix, as well as being packaged with thickening micro-silicates to guarantee perfect waterproofing

BONDING

A fundamental condition to ensure perfect adhesion of the repair, mainly obtained by preparing the supports (cleaning, consolidation, achieving adequate surface roughness and the "saturated to dry surface" condition) and using specific bonding agents of which REPAR TIX repair mortar is full. If necessary, for even better bonding, you are advised to use the two-component mortar REPAR TIX BIC.

PROTECTION OVER TIME

Excellent structural restoration cannot be defined as such unless it protects the support and the relevant reconstruction over time from all causes of degradation. For this reason, you are advised to use an appropriate skimming coat (REPAR SM) on the repair (or the entire work) as a final structural coat with anti-carbonatation paint (PROTEC WAC).