In my long professional career of almost 45 years, in addition to underground structures, I also had to deal with the structural rehabilitation of bridges, viaducts, embankments, earth and concrete dams. Therefore, through this new post, I would like to begin to address the problems inherent in the degradation of the concrete of our above-ground infrastructures, using particular resinous and cementitious formulations for the construction, repair and restoration of bridges.

1. AUTHOR: Lamanna Luigi Franco [*]
TITLE: Illustration of the various materials for the construction and repair of bridges
SUBTITLE: The most frequent aggressions, the use of cementitious mortars and resinous formulations and
related repair techniques for the restoration of concrete on bridges and viaducts
PREMISE
In my long professional career of almost 45 years, in addition to underground structures, I also had to deal
with the structural rehabilitation of bridges, viaducts, embankments, earth and concrete dams.
Therefore, through this new post, I would like to begin to address the problems inherent in the degradation of
the concrete of our above-ground infrastructures, using particular resinous and cementitious formulations for
the construction, repair and restoration of bridges.
By restoration works we mean all those interventions necessary to restore functionality, continuity and greater
resistance to the chemical-physical aggressions of the environment in which they are located.
The rehabilitation and / or restoration must always be preceded by the demolition of the surface layer of
deteriorated cement conglomerate and / or by any other processes that have occurred over time, in order to
make the surface sufficiently rough and free of friable parts, dust and encrustations.
The surfaces, obtained with the demolition of the degraded parts, before their restoration in which "resinous"
formulations or "cement mortars" will be used, must be treated by removing the degraded concrete and
subsequently treated with an energetic dry sandblasting or hydro-sandblasting [no simple brushing as
generally some inexperienced technicians suggest] or with a jet of water vapor at 100° C at a pressure of 7 - 8
atm.
It is necessary to carry out this treatment in order to obtain a healthy, clean and compact concrete, removing
the small residual parts in the detachment phase, the oxide that may be present on the reinforcing rods and
removing dust, small impurities, traces from the surface of aggressive fats, oils and salts.
The cleaning system of the substrate must be chosen according to how the substrate looks and / or its location
in the environmental environment where the structure is located.
The reinforcing rods, laid bare, during the removal of the deteriorated concrete and cleaned to an almost white
metal by sandblasting, must be treated with a suitable corrosion inhibitor with the specific function of
preventing a new formation of "oxide"; the inhibitor to be used must be able not to alter the adhesion between
the application of the subsequent "repair mortar" and the "treated iron".
1) CHEMICAL - PHYSICAL FACTORS THAT DETERMINE THE DEGRADATION OF CONCRETE

2. a) aggressiveness of the environment;
b) durability of the concrete;
c) errors or deficiencies dating back to the design and / or during the construction phase;
in particular:
a) atmosphere (marine, industrial), waters (rain, waterways), climate and microenvironment with which the
structure lives, and which can contribute to:
- vibrations;
- the mechanical disintegration action, caused by freezing and thawing;
- chemical aggressions, due to sulphates, chlorides, magnesium salts, oils, etc.
b) technological deficiencies, such as:
- incorrect proportioning in the choice of materials making up the concrete (mix-design: cement, additives,
water);
- diffuse or concentrated macro and micro porosity (a compact, homogeneous and waterproof concrete will
offer greater resistance to the penetration of water and gas than a poor quality concrete, inhomogeneous,
cracked and porous).
c) execution errors, such as:
- the incorrect combination of concrete-steel materials and insufficient attention to the crack pattern caused
and accelerated by mechanical phenomena, such as shocks and vibrations;
- an exasperated tendency towards the complete exploitation of the structure for architectural, economic and
transportability reasons.
2) AGGRESSION OF CONCRETE
The environmental factor is the primary cause of initiation and propagation of the corrosion phenomenon of
the reinforcement, in particular:
- the penetration of carbon dioxide present in the atmosphere dissolved in water when it comes into contact
with the concrete reacts with its alkaline components to generate calcium "carbonates" resulting in
"carbonation":
Ca(OH)2 + CO2 = CaCO3 + H2O
- the penetration of "chlorides" dissolved in the water (antifreeze salts).
3) FUMES
3.1) action on concrete
they are particularly rich in sulfur compounds. They form sulfuric acid with oxygen dissolved in water and the
components of the cement stone. They extract the cement stone for the formation of calcium sulphide.
3.2) action on the armor
the sulfuric acid formed strongly attacks the iron it reacts with the lime depriving the reinforcing iron of its
basic protection. It acts as an electrolyte and forms a sort of"pile" between Fe covered with calamine (cathode)

3. with corrosion of the anode. Brittle steel that is strongly stretched due to the absorption of H+ ions resulting
in intercrystalline corrosion.
3.3) treatment of reinforcing bars
The reinforcing rods laid bare during the removal of the deteriorated concrete and cleaned to an almost white
metal by sandblasting, must be treated with a suitable corrosion inhibitor having the specific function of
preventing a new formation of oxide.
Normally, a brushable thixotropic grout is used as an inhibitor, obtained by mixing two components (A + B) at
the time of application:
- a liquid (A) which must be composed of a formulation of an aqueous dispersion based on polymers;
- and a powder (B) which must consist of a mixture formed by hydraulic binders.
The silica powders and the specific corrosion inhibitors must form an absolutely waterproof, highly adhesive
layer around the treated rods to prevent the penetration of carbon dioxide chlorides, significantly slowing down
any carbonation and corrosion process.
The formulation must also possess an alkaline action which constitutes an effective "passivation of the
reinforcements", on which it is necessary to apply it with a brush in two layers, at a distance of 2 - 3 hours, with
a thickness of 1 mm. per layer.
4) SEA SALTS
4.1) action on concrete
they exert a breakthrough action due to the presence of magnesium chloride in high concentration.
These chlorides recalcify the cement forming gypsum and candlot salt through a particularly vigorous reaction.
4.2) action on the armor
magnesium and sodium chloride act as soluble salts causing electrolytic corrosion.
5) EXAMPLES OF RESTORATION AND TYPE OF MATERIAL TO BE USED
5.1) Example of rehabilitation of the lower bulb (localized "crawl spaces") of a beam by injection of rheoplastic
cement mortar.
Characteristics of a rheoplastic mortar
This is a ready-to-use cement mortar, with the addition of water only, used to create low thickness cladding
up to 3 - 4 cm, for massive structures and mainly subject to compression (about 2,000 kg / m³).
An electro-welded mesh can be used (to compensate for expansions in the plastic phase according to UNI
8996).
The mortar can also be used with spray pumps (such as plastering machines) or with injection pumps.
The mortar has a high adhesive power to iron and concrete.
5.2) Example of structural rehabilitation of the lower bulb of a beam
Description of the execution mode:

4. 5.2.1) removal of the damaged concrete cover exposing the iron attacked by corrosion;
5.2.2) sandblasting until the "slow armatures" and any stripped prestressing cables are cleaned;
5.2.3) replacement of broken and corroded "slow reinforcement" with new steel bars welded to existing ones;
5.2.4) restoration of the concrete cover with a “rheoplastic” type mortar.
5.3) Example of structural rehabilitation of the lower bulb of a beam with an increase in the resistant section.
Description of the execution mode:
5.3.1) partial demolition of the lower bulb of the beam;
5.3.2) cutting of broken or corroded bars;
5.3.3) cutting of the "slow armor", broken or corroded;
5.3.4) sandblasting until cleanliness of the “slow armatures” and of the stripped “prestressing cables”;
5.3.5) replacement of broken and corroded “slow reinforcements” with new bars welded to existing ones;
5.3.6) positioning of a disposable metal formwork and subsequent casting of "grout" made with "rheoplastic"
type mortar (max diameter of the aggregates 5 mm).
6) CHARACTERISTICS OF THE MATERIALS
6.1) Formulations of epoxy-type resins
In common use, we erroneously speak of "epoxy resins" meaning such thermosetting resins in the form of
more or less viscous liquids also used as building materials.
The formulations based on epoxy resins are obtained by mixing three elements: the pure resin, the hardener
and filler materials (composed of fillers, sand, gravel, quartz).
A formulation of epoxy resin confers high values of elastic modulus, a shrinkage and a zero aging as well as
exhibiting a behavior under dynamic loads and fatigue better than that of reinforced concrete structures (about
1,800 - 2000 kg / m³).
Example of external added prestress with slub section of the beam.

5. 6.1.1) Use and characteristics of a mortar or a conglomerate based on epoxy resins
An epoxy resin mortar, this too is a formulation, is used when the intervention project requires high strengths
and in a very short time.
To prepare the "epoxy resin mortar" it is necessary to mix the two components of the resin using equipment
[concrete mixers] at slow rotation speed in order to avoid inclusion of air.
Subsequently, a formulation of "resins" and "aggregates" will be introduced into the mixer which will blend
until a homogeneous mixture is obtained.
Products already formulated from premixes in Mix-Design, for example "resins" and "inerts", to which it is
sufficient to add only the hardener [this is also a particular resin studied ad hoc], may be accepted.
It is necessary to avoid that small quantities of pure resin remain in the packages and consequently the use of
common concrete mixers is recommended; indicatively, a mixer with a movable bowl rotating in the opposite
direction to that of the blades should allow a more intimate adhesion between the resin and the aggregates.
The latter will consist of "calcareous sand" with a continuous grain size, dry and stored away from water;
calcareous sand is preferable to silica sand for these works as it is able to give the mortar a "thermal expansion
coefficient" closer to that of the traditional concrete of the structure to be repaired.
The maximum granulometry of the aggregates must be proportional to the size of the old structure to be
restored, in any case it must not exceed 5 mm.
The installation will take place with spatulas and / or casting and care must be taken to avoid any vibration of
the material once installed.
Strength values that an epoxy resin mortar must possess:
- compression resistance 100-170 Mpa
- flexural strength 35-100 Mpa
- tensile strength 40-75 Mpa
- elastic modulus 3000-25000 Mpa
- elongation at break 0,8 - 4,5 %
6.2) Rheoplastic / expansive cementitious mortars
The combined addition of special additives to be added to the concrete mix of any type and for any use, in
order to compensate for shrinkage, increase impermeability, avoid cracking or cracking is very advantageous
for the production of mortars / concrete in all those cases where the strong reduction of the Water / Cement
ratio, allowing to obtain high mechanical strengths, are considered "special concretes" or even "rheoplastic

6. concretes" that is those concretes that are able to control the "shrinkage" that I remember the latter [il
shrinkage] occurs to a greater or lesser extent depending on the type of seasoning.
The percentage of this particular additive to be used compared to an ordinary cement varies from 5 ± 20%
according to the type of concrete or mortar to be obtained and the percentage / arrangement of metal
reinforcement present in the product.
Other parameters that can affect the speed of the expansive phenomenon are the granulometry and porosity
of the expansive agent of the compound 3CaO.Al2O3.3CaSO4.32H2O consisting in the production of ettringite,
which is usually indicated with the symbol C4A3S where C = CaO, A = Al2O3, S = SO3, and the accompanying
reaction makes a sharp increase in volume:
4CaO.3Al2O3 + 6CaO + 8CaSO4 + 96H2O ➔ 3 [3CaO. Al2O3.3CaSO4.32H2O].
I would like to point out that an expansive agent quantity between 40-55 kg / m3 (about 10-15% on concrete)
is able to produce a free expansion between 0.05-0.3% while contained above 70 kg / m3 (about 20% on
cement) is able to reach values higher than 1%.
Therefore, I want to bring to your attention that when the degree of free expansion reaches values of one
percent, the phenomenon becomes destructive and the mechanical strength of themixture is completely poor.
Therefore, for each application it is important to study the optimal quantity of expansion according to the type
and quantity of reinforcement, to define the optimal ratio between longitudinal and lateral reinforcement so
that the concrete reaches the desired pre-stress and at the same time its physical qualities. and mechanics are
equally of an adequate level in every direction.
The curing methods must also be carefully examined, above all to prevent the development of resistance and
expansion from proceeding in a differential way.
6.2.1) properties of rheoplastic cementitious mortars:
- compressive strength after 1 day 30-90 Mpa
- 1 day flexural strength 5-8 Mpa
- elastic module:
at 1 day 30,000 Mpa
at 7 days 20,000 Mpa
at 28 days 40,000 Mpa
- contrasted expansion (ASTM-C-878) 0.10 %
- adhesion to concrete after 28 days 6 Mpa
- adhesion to steel:
at 7 days 20 Mpa
at 28 days 30 Mpa
6.2.2) properties of rheoplastic cementitious grouts
- compressive strength after 3 days 30-55 Mpa
- compressive strength after 28 days 50-80 Mpa
- 3-day flexural strength 5-8 Mpa
- flexural strength after 28 days 12 Mpa
- elastic module:
at 28 days 20,000-40,000 Mpa
- adhesion to concrete after 28 days 6-10 Mpa
Other characteristics of cementitious mortars or rheoplastic grouts are those of:

7. - be durable in aggressive environments with the presence of carbon dioxide, sulphates, sulphides, chlorides,
etc;
- they can be cast or injected into formworks;
- absence of withdrawal;
- absolute impermeability.
7) FINAL PROTECTION OF CONCRETE SURFACES AND METALLIC STRUCTURES
The subsequent painting of the concrete surfaces is necessary to protect the rest of the concrete from the
harmful effects of carbonation, preventing the penetration of CO2 and other aggressive gases, through the
porosity and micro-cracks of the old cement paste.
7.1) Painting of concrete surfaces
Painting of concrete surfaces with a "resin" formula to be sprayed in two successive coats in the final
thickness of 200 - 600 microns, after applying a first "coat [called primer]" at a thickness of 200 microns.
The type of resinous formulations can be:
• aliphatic polyurethane, for a minimum thickness of 400 microns;
• polyethylene-chlorosulfonated, for a minimum thickness of 250 microns;
• epoxy-bituminous, for a minimum thickness of 200 microns;
• acrylic, for a minimum thickness of 120 microns;
• polyester, with a minimum thickness of 600 microns.
7.2) Painting of the metal sheet (cast formwork around the pillars or used for restoring beams)
The external corrosion protection of the sheet metal formwork (disposable formwork of the piles / pillars or to
create the still valid concrete-plaque type coating, today erroneously replaced by many technicians with very
valid carbon fiber fabrics, widely used, for the seismic adaptation or improvement of reinforced concrete
structures and old masonry, which we will discuss in detail in a future article), once fixed to the concrete
substrate, will be treated with a formulation of resins, of the type indicated below, by apply by spray in two
successive layers with a final thickness of 200 - 600 microns [the thickness depends on the environment the
structure has to live with], after dry sandblasting to SA2 grade of all the surfaces involved in the subsequent
treatments, with the application of a first coat of galvanizing base in the ratio of 50 microns of thickness.

8. Type of protective coating resin formulation:
• aliphatic polyurethane, for a minimum thickness of 400 microns;
• polyethylene-chlorosulfonated, for a minimum thickness of 200 microns;
• epoxy-bituminous, for a minimum thickness of 200 microns.
8) CONCLUSIONS
I remember that the new technical standards for construction, at international level, require the designer to
establish durability criteria based also on the place where the structure must live and on the particular
conditions of use.
However, alongside these obligations, the standards leave open the choice on how to do and what to use (use
of innovative materials), the important thing is not to compromise its durability and functionality even in
relation to the service life for which it was designed.
[*] Luigi Franco, LAMANNA
- Independent Technical Consultant in the sector of Tunnelling, Mining and Underground Technology
- President of the Fondazione Internazionale di Centro Studi e Ricerche, ONG
132, via dei Serpenti, 00184 ROMA, Italy, U.E.
Email: lamannaluigifranco1@gmail.com