To assess the concrete strength in the control of existing buildings, taking cores is often necessary. Cores are used for conducting some indirect methods.

In addition to the compressive strength of concrete by taking cores, we can still examine:

The method of Schmidt Hammer, is a non-destructive method for estimating the strength of concrete, which is based on measuring the surface hardness of the components tested.

By using the method of Schmidt Hammer, we examine the quality of concrete of the outer surface of the existing constructions, and up to a depth of 30mm.

The method of Schmidt Hammer, refers to the measurement of a rebound value of a steel hammer on hardened concrete.

Our company performs the Schmidt Hammer testing by following the ASTM C805-02 regulations.

The measurement of the speed of ultrasound pulses of the longitudinal waves that run in the concrete, can be used in the following applications:

The differences identified in an ultrasonic speed measuring kit along different paths inside the concrete structure reflect the change of the concrete situation.

RESTAT S.A. performs the speed test to measure ultrasonic based on the recommendations of the standard BS 1881: Part 203: 1986.

Nail pull out test is an indirect method for determining the compressive strength of the concrete. The nail is inserted in the concrete, after its ejection from a special gun. The nail has a length of 1-4cm and a diameter of 4mm. The nail is extruded from the concrete by using a specific extruder which carries a dynamometer. The force recorded by the dynamometer is associated with the compressive strength of the concrete.

The pull-off test is designed to assess the force necessary to detach the coating rigid surfaces such as metal, concrete or wood.

This test determines the maximum vertical force that a surface can sustain before the detachment of the coated material, or if the surface remains intact to imposing more power.

The failure will occur at the weakest area of the interface consisting of the test piece, the adhesive, the surface coating and the substrate and will be revealed by the fracture surface.

RESTAT S.A. carries out the above test based on the standard ASTM D 4541-02.

With this method the reinforcement of concrete can be detected, by using a magnetometer, and it is estimated, to quite an extent, the coating thickness as well as the diameter of the rod.

The magnetometers are based on the interaction of the reinforcement bars and a low-frequency electromagnetic field.

Our company carries out the detection of reinforcement based on the standard BS 1881: 204: 1988.

The process of the carbonation depth measurement is based on the change of pH of the concrete of a structural element by the presence of carbon dioxide (CO2).

The measurement is carried out by spraying on freshly concrete core, made of phenolphthalein solution which colors the non-carbonated concrete red, and remains colorless in the carbonated area.

Our company carries out the determination of the carbonization depth based on standards:

The purpose of crack measuring gauges placement is to monitor the evolution of the crack and its characterization as active or inactive. Depending on the scope and speed of drilling we recommend any intervention.

Composite materials are placed on the surfaces of the components and constitute a sort of permanent external reinforcement. The connection and cooperation of different materials is achieved by epoxy resins. Their use is now one popular strengthening technique because it is easy to implement.

The fiber reinforced polymers are divided into::

The choice of one of these categories depends on the type of support we want to achieve, but also by the environmental conditions during the application.

Uses of composite materials

In cases of reinforcement in flexion or shear rods of reinforced concrete, laminated thick steel sheets from 1mm to 5mm are placed at the bottom pad or at the sidewall of the bar respectively. The sheets shall cooperate with the existing rod with bolts, screws, chemical anchors, epoxy resin or a combination of them by creating a new stronger and stiffer composite section.

In the columns, respectively, with the method of the laminated sheets, we can achieve increase of resistance in flexion and shear, flexural resistance and reinforce with active or passive confinement. Different column reinforcement methods are pasting the entire steel sheet and the method of the metal cage.

Adding new steel members is an economic and highly efficient method for strengthening reinforced concrete beams and slabs. The obvious advantage is the reduction of the openings, creating new composite sections with greater resistance from the existing ones and the support of active or passive approach.

The shotcrete (sprayed concrete or shotcrete or gunite) that is used in reinforcement projects is concrete of fine aggregate gradation which is concreted with blasting. The application requires special equipment and trained staff. In the following four characteristics is due the widespread use in intervention projects:

Conventional production methods are the dry and wet method. In reinforcement interventions is mainly applied the dry method since it has an advantage over the wet indoors.

Gunite is used primarily to:

The grouting is used to fill cracks in buildings of masonry and stonework or to improve the mechanical characteristics and sealing of a soil or a rocky formation.

For sealing the cracks, a strong cement mortar is used and then the cementitious grout is injected through plastic pipe pieces fitted to holes, that are opened in advance, in cases of masonry or through steel nozzles (packers) in cases of soil formation improvement.

The ratio of of blend composition starts from a 1: 1 by weight of water and cement. Where applicable and depending on circumstances and the structural design added additives are such as pumice, lime solution, retarding or accelerating coagulation, etc.

The method of grouting can be applied to the following project categories:

The use of epoxy resins is highly increased in operations primarily to repair cracks but also other applications. The technique of resin injections is found mainly in bearing construction body made of concrete and masonry. It aims to recover the original bearing capacity of cracked structures as well as their rigidity. Recommended for protection against reinforcement corrosion, the creation of robust connection between concrete parts and for sealing.

The main advantages of the technique of the epoxy resins injection are:

It should be mentioned that for the proper selection of epoxy resin, we should assess the properties, depending on the application to the intended use such as viscosity, elasticity modulus and the clotting time.

Bolts and Anchors

As bolts are characterized the metal links when they are stressed with shear load, and as anchors when the external load is axial. Obviously when a metal link is stressed axially and in shear then acts as anchor and bolt simultaneously.

Types of bolts and anchors

a) Vertical Bolts

b) Horizontal Bolts

c) Roof Vertical Bolts

Factors that affect strength of a bolt are:

The repair process of a component is designed to restore its initial mechanical characteristics it had before the undergone damages. The proceedings carried out, realize a full restoration of the element section, but also reset its rigidity.

The choice of the repair method depends on the degree of the injury, that the structural element has suffered.

In case of minor damages, the repair is made by welding cracks by injecting suitable epoxy-resin compatible with electrochemical and mechanical characteristics to the current member. If in addition to the cracking, a surface erosion or even delamination of the concrete, without disrupting the core member, is observed, the damage is restored by using repair mortar and using a corrosion inhibitor. In any case, he state of reinforcement of the item should be tested as well as to take the necessary measures to inhibit the corrosion phenomenon.

Our company has in its property the following equipment in order to implement undisturbed cuts in reinforced concrete elements and roadworks.

• Diamond discs (different diameters)
• Concrete Cutter
• Carrottery (Full cutting range)
• Diamond Hand disc
• Handheld Chainsaw