Structural repair and reinforcement
Since the builder William Wilkinson applied for the first patent for reinforced concrete in 1854, this material, like no other, has developed to become the icon of 20th century construction, thanks to its excellent mechanical and chemical properties that make it almost indestructible over time.
The reality of the last 30 years shows us that, like many other construction materials, concrete suffers significant degradation processes that make maintenance and repair work necessary.
Repair and reinforcement
Reinforced concrete undergoes important degradation processes that considerably modify its mechanical characteristics.
This reduction in its structural properties may be caused by a deficient quality of the materials of which it is composed, which gives rise to pathologies such as aluminosis, or it may be caused by the attack of external chemical agents, which give rise to increasingly common pathologies such as carbonation or chloride attack.
When degradation is detected, it is essential to carry out structural rehabilitation on reinforced concrete.
The reinforcement of concrete structures by bonding inorganic matrix composite materials based on carbon fibre filaments began in the 1980s in the USA and Japan as a more viable system for adapting existing structures to the new structural safety coefficients established in recent earthquake-resistant construction regulations.
FRP laminates are one of the possibilities that the market offers for flexural reinforcement, thanks to their excellent tensile properties, whose values are around 3.100 Mpa, while the modulus of elasticity can vary between 170 and 210 GPa.
Reinforcement with screeds
The use of high-performance mortars with compensated shrinkage is a common practice in the reinforcement of building structures. In these cases, they are usually installed using the wet spraying technique.
The execution of structural reinforcements by means of shotcrete spraying requires a construction site to ensure the mechanical characteristics of the concrete once it has been installed.
It has some disadvantages, such as the increase in the structure’s own weight and reductions in gauge; on the other hand, it has some advantages, such as attaching a material with similar characteristics to the existing one, thus achieving a more homogeneous structure.
Metal reinforcement is the most widely used historically. It is used by means of adhesion or by simple collaboration of the new metal profiles on the structure to be reinforced.
This type of reinforcement can be carried out by replacing the structure to be reinforced with a new one, parallel to it, which is capable of receiving both the loads of use and the permanent loads of the structure itself.
Metal reinforcement is also carried out by bonding new profiles with epoxy resins that collaborate with the old structure, helping it to obtain the expected safety coefficients (L’Hermite method).
An important phase in the repair of a structure is the injection of passive cracks.
This is intended to restore the lost monolithism of the structure between the two sides of the crack so that the mechanical continuity and impermeability of the cracked element is restored.
This procedure can be applied to beams, pillars or other structural elements made of reinforced or mass concrete.
This type of injection is carried out by introducing two-component epoxy resins into the crack at pressures of less than 20 kg/cm2.
For this purpose, pressure pots or double piston machines with tip mixing are used.
The work process begins with the preparation of the substrate, removing paint, dirt, dust, etc., and leaving the crack visible.
The crack is then sealed with epoxy resin and injectors are installed along the crack, spaced between 20 and 35 cm apart, depending on the width of the crack to be injected.