Thixotropic mortars for restoring reinforced concrete

11/01/2021 – Reinforced concrete structures (reinforced concrete), especially those in contact with the outside, are subject to possible deterioration processes due to the action of atmospheric agents, pollution and salt, if are located near the sea.

May they be finished O face on sight, the alteration of the concrete structures can affect the most superficial part up to reaching depth, causing for example:
1) the posting of concrete cover;
2) the detachment of greater thicknesses of the concrete cover and which partly affect the original core of the structure;
3) the substantial loss of the original section, in the most critical cases.

Situations of this kind require a prompt reconstruction intervention.

In the first case will be needed in cortical reconstruction surgery: a thickness of a few centimeters is reconstructed (generally equal to the concrete cover), this type of intervention is non-structural as the portion of the reconstructed section does not participate in the static.

In the second case reconstruction will be required partial or total of the original section: the reconstruction involves higher thicknesses, therefore, it is structural interventions. The portion of the reconstructed section will contribute, together with the original non-degraded one, to the statics of the structural element.

In the third case you will need a structural or anti-seismic adjustment intervention with an increase in the original section, the ringrosso. This intervention is of a structural type because it increases the bearing capacity of a structural element or modifies its stiffness.

Photo: Malta REPAR TIX HG SB © Azichem

In all cases exposed, it is possible to intervene using the restoration mortar but following the prescriptions of the UNI EN 1504-3. The standard defines four classes of repair mortars, dividing them into mortars for structural and non-structural repairs. In particular, the mortars for non-structural use they are identified by the abbreviations R1 e R2, while the acronyms R3 and R4 indicate mortars for structural use.

Restoration mortars include Tissotropiche malt (thixotropic). These mortars, a fine-grained, are so called by virtue of thixotropy, that is the ability of the material to behave like a “gel”. Under mechanical action, the thixotropic mortars thin out more quickly and, once the stress is over, they return to their original state. A thixotropic mortar does not run during application, it remains firm on the point where it was laid.

The performance characteristics of a thixotropic repair mortar are:
– excellent compressive strength;
– excellent elasticity;
– strong bond of adhesion;
– very low shrinkage / expansion;
– resistance to carbonation;
– thermal compatibility with freeze and thaw cycles;
– excellent workability.

The thixotropic mortar is a premixed based on cement to which aggregates and special additives are added. By adding water to the mixture, a compound is obtained with high adhesive power to the original structure in reinforced concrete e durable. Thixotropic mortars are not subjected to traction, due to the very low hygrometric shrinkage. This does not involve the formation of shrinkage cracks and further displacements or detachments later on.

Compared to traditional cement-only mortars, a thixotropic mortar has much faster setting and hardening times.

Photo: Thixotropic premixed cement mortar MasterEmaco S 950 © BASF Construction Chemicals

Thixotropic mortars are available in three versions:
Ultra fast, with setting times between about 10 and 15 minutes (generally used for restoration work involving small surfaces);
fast, with setting times between about 20 and 50 minutes (generally used for the restoration of surfaces of a few square meters in extension);
– a normal socket, with setting times between about 60 and 120 minutes (generally used for large surface extensions, but small maintenance works are not excluded).

The thixotropic mortars, being fine-grained, in addition to being used to carry out reconstruction interventions, are also used for final smoothing shave, with the advantage of using a single product for multiple processes.

Once the reconstruction and restoration phase is over and the shaving is complete, you can proceed quickly (1/3 hours of waiting) to drafting of protective e decorative acrylic based finishes. This is because thixotropic mortars have a modest content of calcium hydroxide and have a considerable resistance to carbonation, therefore there is no risk that the lime, present on the surface, reacts in contact with the air, due to carbonation, and form unsightly spots.

In accordance with EN 1504-2, i surface protectors for concrete they are distinguished in:
film-forming coatings;
hydrophobic and impregnating treatments in acrylic dispersion.

The interventions of restoration / reconstruction of the reinforced concrete structures are among the tax deductible works. Depending on the type of intervention, structural or non-structural, of the intended use of the building, it will be possible to access the bonus facades o al renovation bonus o al sismabonus o al super bonus.

Source: by

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