Concrete structure repair is one of the most demanded interventions in the construction and civil engineering sector. The aging of Spain’s building stock, together with increasingly strict requirements in terms of structural safety, has turned the rehabilitation of concrete structures into a first-order technical discipline. Columns, beams, slabs, walls and foundations eventually deteriorate due to multiple causes: the action of time, environmental aggressiveness, design or execution errors, and the simple increase in use loads over the years.
This article offers a complete technical vision of the structural repair process: from the identification of damage and its diagnosis to the most advanced solutions available today in the market, through the most suitable materials and the regulations governing these interventions in Spain.
Why do reinforced concrete structures deteriorate?
To address any reinforced concrete structure repair process with guarantees, it is essential to first understand why deterioration occurs. Reinforced concrete is a composite material of extraordinary durability when well designed and executed, but it is neither eternal nor immune to degradation. The mechanisms that trigger its deterioration are varied and often act simultaneously, accelerating the loss of resistance and the appearance of visible damage.
Rebar corrosion is, by far, the most frequent and costly pathology in concrete structures. It originates mainly through two processes: carbonation of the concrete, which reduces the pH of the mass and destroys the protective passive layer of the steel, and the penetration of chloride ions from the marine environment, de-icing salts or the construction materials themselves. Once steel oxidation begins, the generated rust occupies a volume up to four times greater than the original metal, causing internal stresses that crack and spall the concrete cover.
Other common deterioration agents are freeze-thaw cycles, the action of sulfates present in the ground or water, alkali-silica reactions between cement components and certain reactive aggregates, and damage caused by accidental overloads or seismic phenomena. Understanding which mechanism is acting in each case is the first step to designing an effective and durable structure repair strategy. For a broader vision of the most common pathologies in construction, you can consult our article on most common construction pathologies.
Prior diagnosis: the starting point of all structural repair
No reinforced concrete structure repair intervention should begin without a rigorous prior diagnosis. The evaluation phase determines the real extent of the damage, identifies its causes and completely conditions the choice of materials and repair techniques. A deficient diagnosis inevitably leads to repairs that fail in the short term or that are disproportionate to the real problem.
Visual inspection and data collection
Detailed visual inspection is always the first step. The specialist technician surveys all structural elements, identifying cracks, fissures, spalling, rust stains, efflorescence and visible deformations. The geometry of the cracks is recorded—their width, length, orientation and whether they are active or passive—because this data is decisive for selecting the most appropriate repair system. Active cracks, which continue opening or closing, require elastic solutions that accompany the movement, while stabilized cracks admit rigid products such as epoxy resin injections or repair mortars.
Laboratory tests and trials
Beyond what can be seen with the naked eye, the technical evaluation of concrete requires specific tests that provide quantitative data on the state of the material. The most common are the carbonation test using phenolphthalein, which stains non-carbonated areas pink and allows measuring the advancement front; the measurement of corrosion potentials in rebars with reference electrodes; electrical resistivity tests of the concrete; and the extraction of cylindrical cores to determine the real compressive strength of the element. In more complex cases, non-destructive techniques such as ground-penetrating radar, infrared thermography or ultrasound are used, which allow detecting voids, delaminations and internal discontinuities without damaging the structure.
Structural settlement determination
When structural damage is related to foundation movements, the diagnosis must also include the study of structural settlement. Differential settlements—those in which different points of the building sink at different rates—are especially damaging, as they introduce stresses into the structure for which it was not calculated, generating characteristic diagonal or stair-step cracking. In these cases, the repair of visible damage in columns or walls must necessarily be accompanied by an intervention on the foundation, since treating only the symptoms without eliminating the cause condemns any solution to failure. To expand information on foundation types and their behavior, consult our article on foundations: types, materials and applications.
Materials for concrete structure repair
The market for structural repair materials has experienced enormous evolution in recent decades. Today there is a wide range of products specially formulated for each type of damage and working condition. The correct selection of the material is as important as the execution: using the wrong product, even if it is high quality, can lead to repair failure.
Structural repair mortars
Structural repair mortars are the most widely used family of products in rehabilitation interventions. Unlike conventional mortars, they are formulated with special additives—silica fume, polymers, microsilica, fibers—that give them specific properties: high adhesion to existing concrete, low or compensated shrinkage, high mechanical strengths and compatibility with the elastic modulus of the substrate. This compatibility is fundamental: if the mortar is more rigid than the base concrete, any differential deformation will generate stresses that will end up detaching the repair.
Repair mortars are classified according to their base into cementitious mortars, which are the most common and economical, and resin mortars, of higher cost but with superior performance in aggressive environments or when very rapid commissioning is required. Within cementitious mortars there are one-component formulations—only water needs to be added—and two-component formulations, where the addition of a polymer emulsion notably improves the adhesion and flexibility of the final product.
Structural repair cement
The term structural repair cement refers to the special hydraulic binders with which high-performance repair mortars are manufactured. The most used are Portland cements with pozzolanic additions—which reduce permeability and improve chemical resistance—and calcium aluminate cements, widely used when rapid mechanical strength is needed or in sulfate exposure. The UNE-EN 1504 standard establishes the requirements that products and systems for concrete protection and repair must meet, being the mandatory technical reference in any structural rehabilitation project in Spain and Europe.
Epoxy resins and injections
Epoxy resins are two-component products that, once mixed, polymerize and develop mechanical properties far superior to those of concrete: high tensile and bending strengths, excellent adhesion on clean surfaces and high surface hardness. They are mainly used for structural crack and fissure injection, sealing them and restoring the continuity and monolithic nature of the element. They are also used as adhesion bridges—applied in a thin layer on the substrate before placing the mortar—and as chemical anchors for reinforcing bars. Resin injection is a very effective technique but requires meticulous preparation of the cracks and strict control of the mixing ratio and application temperature.
Structural repair and reinforcement techniques
Once the diagnosis is completed and the materials selected, the execution of structure repair requires following specific procedures that guarantee the durability of the intervention. Available techniques range from the most traditional, such as mortar overlays, to the most advanced, such as carbon fiber reinforcement or external post-tensioning.
Substrate cleaning and preparation
Substrate preparation is probably the most critical step of any repair. All deteriorated, carbonated, chloride-contaminated or low-strength concrete must be completely removed before applying any repair material. If degraded concrete is left under the new mortar, the repair will detach or corrosion will continue advancing under the repaired layer.
Cleaning is usually performed by hydrodemolition—water jets at very high pressure—or with electric hammers and disc grinders, always seeking sound edges perpendicular to the repair plane. The roughness of the substrate must be sufficient to guarantee adhesion, with a minimum surface profile of CSP 3-4 according to the ICRI standard classification.
Treatment of corroded rebars
When rebars are corroded, the preparation process must also include their treatment. In mild corrosion, it is sufficient to mechanically clean the steel to grade Sa 2½ to remove the rust and apply a corrosion-inhibiting primer. In more serious cases, with cross-sectional area reduced by more than 20%, it is necessary to add additional reinforcement welded or tied to the existing one before filling with mortar. The protection of treated rebars with zinc-rich passivators or with high-alkalinity mortars is essential to guarantee that corrosion does not reactivate once the repair is finished.
Carbon fiber reinforcement (FRP)
Carbon fiber reinforcement, also known as FRP (Fiber Reinforced Polymer), is one of the most innovative and efficient techniques in concrete structure rehabilitation. It consists of adhering carbon fiber sheets or fabrics impregnated in epoxy resin to the surface of the structural element to be reinforced. The result is a composite material of extraordinary strength and stiffness, but very light, that collaborates with the existing structure and significantly increases its load-bearing capacity without increasing the self-weight or the dimensions of the element.
This technique is especially valued in situations where available space is limited, where added weight would be problematic—such as in slabs with maximum load or in bridge structures—or where very rapid execution with minimal disturbance to building activity is required. Carbon fiber sheets can be applied on beams to increase bending strength, on columns to improve axial strength and ductility in seismic zones, and on walls to increase their shear resistance.
Overlays and jacketing
Structural jacketing is a classic reinforcement technique that consists of wrapping the existing element—generally a column or beam—with a new layer of reinforced concrete. Jacketing increases the resistant section and, with it, the load-bearing capacity of the element, and also improves its ductility and fire resistance. For the jacketing to work together with the existing core, it is essential to guarantee the transfer of forces between both, which is achieved through adequate preparation of the contact surface and, in many cases, with steel connectors chemically anchored.
Mortar overlays have a similar function, but are applied on flat surfaces such as slabs, beams on their underside or walls. The main difference with jacketing is that the overlay usually has a smaller thickness and does not completely wrap the element. The key to success in both cases is compatibility between the new and existing material: excessive differences in the elastic modulus or in the coefficient of thermal expansion can generate delaminations with thermal cycles.
Cement grout injection
Cementitious grout injection is a technique used both for filling cracks and cavities inside massive concrete elements and for consolidation and reinforcement of existing foundations. Through holes drilled in the concrete or in the ground, a fluid mixture of cement and water—with or without additives—is injected under pressure that penetrates the voids and cracks, filling them and restoring material continuity. This technique is especially useful in dams, bridges and retaining walls where access to the interior of the section is otherwise impossible.
Applicable regulations for structural repair in Spain
Any concrete structure repair intervention in Spain must be framed within a specific regulatory framework that guarantees the technical and legal safety of the action. Knowing this regulation is fundamental both for design technicians and for structure repair companies that execute the works.
EHE-08: Structural Concrete Code
EHE-08 is the reference technical standard in Spain for the design and execution of concrete structures. Its annex 9 specifically develops recommendations for the durability of structures and the design of repair interventions. EHE-08 establishes the minimum requirements for rebar cover according to the environmental exposure class, the criteria for selecting repair materials and the principles that should guide rehabilitation interventions. Although work is currently underway on its revision and update, it remains the mandatory reference standard in any structural concrete rehabilitation project in Spain.
UNE-EN 1504 standard: Products and systems for concrete repair
The European standard UNE-EN 1504, transposed in Spain as a UNE standard, is the reference standard for products and systems intended for concrete protection and repair. It consists of ten parts that cover from the general principles of interventions to the specific requirements of each product family: structural mortars, bonding agents, rebar protectors, injections, etc. This standard also establishes the intervention principles that should guide the repair strategy—from cover restoration to corrosion control or structure strengthening—which requires the design technician to make reasoned and documented decisions about the intervention approach.
CTE DB-SE: Technical Building Code
The Technical Building Code, in its Basic Document on Structural Safety, establishes the safety requirements that building structures must verify both in their original state and after repair or reinforcement interventions. When the intervention modifies the resistant capacity of the structure or alters the building’s use conditions, the competent technician must verify that the resulting structure continues to comply with the ultimate and serviceability limit states required by the CTE.
Aid for structure repair: subsidies and financing
The cost of a structural repair intervention can be high, especially in buildings of certain size or age. Therefore, it is essential to know the aid for structure repair available at state, regional and local level, which in many cases can significantly reduce the economic outlay of owners and homeowners’ associations.
The Recovery, Transformation and Resilience Plan (PRTR), financed with European Next Generation EU funds, has provided important resources to the Residential Rehabilitation Program and the Urban Rehabilitation and Regeneration Plan in Spain. Through calls managed by the Autonomous Communities, individual owners and homeowners’ associations can access subsidies that partially cover the costs of structural interventions provided they are accompanied by energy efficiency improvements. In addition to these state aids, many municipalities have their own urban rehabilitation programs that include subsidies or low-interest loans for interventions in buildings located in urban regeneration areas. Checking with the corresponding municipality’s urban planning department is the first step to explore these possibilities.
How to choose a concrete structure repair company
The choice of the executing company is decisive for the success of any structural repair intervention. Not all concrete structure repair companies have the same technical qualification, material resources or experience in different repair systems. A poorly executed structural intervention is not only ineffective: it can aggravate the original problem and seriously compromise the structure’s safety.
When selecting among different structure repair companies, it is advisable to evaluate demonstrable experience in similar works—requesting references and visiting other completed interventions is always a recommended practice—, the technical team’s qualification, the availability of own resources for executing the works and knowledge of the most appropriate materials and systems for each case. A solvent company should be capable of actively participating in the diagnosis phase, providing its own technical criteria on the most appropriate repair strategy and offering documented guarantees on the executed works.
At Site and Field we have a team of engineers and technicians specialized in repair and rehabilitation of reinforced concrete structures, with extensive experience in interventions in both building and civil works. From the initial diagnosis to the final delivery of the work, we accompany our clients at each stage of the process, guaranteeing rigorous, durable technical solutions adapted to each specific case.
Concrete structure repair is a complex technical discipline that requires deep knowledge of structural pathologies, available materials and the most appropriate execution techniques in each situation. Addressing a repair without a rigorous prior diagnosis or with inadequate materials is equivalent to condemning the intervention to short or medium-term failure, multiplying costs and risks for occupants.
Investing in a complete diagnosis process, in quality materials certified according to the UNE-EN 1504 standard and in specialized companies with proven experience is the only way to guarantee that the intervention is truly effective and durable. Current techniques—from high-performance structural repair mortars to carbon fiber reinforcement or concrete jacketing—offer solutions for practically any type of damage, provided they are applied with adequate technical criteria and respecting the principles established by current regulations.
Frequently Asked Questions
What are the main causes of reinforced concrete structure deterioration?
The main causes of deterioration are rebar corrosion due to concrete carbonation or chloride penetration, freeze-thaw cycles, sulfate action, alkali-silica reactions between cement components and reactive aggregates, and damage from overloads or seismic phenomena. Corrosion is the most frequent and costly pathology, as rust can occupy up to four times more volume than the original steel, causing cracks and spalling.
What diagnostic techniques are used in concrete structure evaluation?
The main techniques include detailed visual inspection to identify cracks and visible damage, carbonation tests with phenolphthalein, corrosion potential measurements on rebars, electrical resistivity tests and extraction of cylindrical cores. In complex cases, non-destructive techniques such as ground-penetrating radar, infrared thermography and ultrasound are used to detect voids and internal discontinuities without damaging the structure.
What materials are used in concrete structure repair?
The main materials are structural repair mortars formulated with special additives (silica fume, polymers, microsilica, fibers), structural repair cements such as Portland cements with pozzolanic additions or calcium aluminate cements, and epoxy resins for crack injection and as adhesion bridges. All must comply with the UNE-EN 1504 standard that establishes requirements for concrete protection and repair products.
What is carbon fiber reinforcement for concrete structures?
Carbon fiber reinforcement or FRP consists of adhering carbon fiber sheets or fabrics impregnated in epoxy resin to the structural element surface. This technique creates a composite material of extraordinary strength and stiffness but very light, significantly increasing load-bearing capacity without increasing weight or dimensions. It is especially useful in limited spaces, slabs with maximum load or when rapid execution with minimal disturbance is required.
What regulations govern concrete structure repair in Spain?
The main regulations include EHE-08 (Structural Concrete Code) which is the reference technical standard in Spain with specific recommendations in its annex 9 on durability and repair, the European standard UNE-EN 1504 that establishes requirements for concrete repair products and systems, and the CTE DB-SE (Technical Building Code) that defines structural safety requirements that must be verified after interventions.
