Rebound Hammer test is a Non-destructive testing method of concrete which provide a convenient and rapid indication of the compressive strength of the concrete. The method, thus, also be used to assess the uniformity and quality of concrete. It is based on the principle that the rebound of an elastic mass depends on the hardness of the concrete surface against which the mass strikes.
Rebound Hammer test assess the likely compressive strength of concrete with the help of suitable correlations between rebound index and compressive strength. When the plunger of rebound hammer is pressed against the surface of the concrete, the spring- controlled mass rebounds and the extent of such rebound depends upon the surface hardness of concrete. The surface hardness and therefore the rebound is taken to be related to the compressive strength of the concrete.A concrete with low strength and low stiffness will absorb more energy to yield in a lower rebound value.
CIMEC is equipped with rebound hammers from Controls(Italy) & Proceq(Switzerland).
Ultrasonic testing of concrete or ultrasonic pulse velocity test (UPV Test) on concrete is a non-destructive test to assess the homogeneity and integrity of concrete. With UPV test, concrete can be assessed for quality in terms of density, uniformity and homogeneity, its gradation in different locations of structural members and any discontinuity like cracks, cover concrete delamination etc.
UPV test consists of measuring travel time of ultrasonic pulse produced by an electro-acoustical transducer, held in contact with one surface of the concrete member under test and receiving the same by a similar transducer in contact with the surface at the other end. With the path length (i.e. the distance between the two probes) and time of travel the pulse velocity is calculated. The ultrasonic pulse velocity depends on the density and elastic properties of the material being tested.
CIMEC is equipped with UPV testers (PROCEQ PUNDIT LAB+)
When compressive strength tests of laboratory-cured specimens fail to meet the specified acceptance criteria, core tests are commonly used to verify the strength and to obtain acceptance of the in-place concrete.
When the concrete is doubted or the structure is intended to be used for higher stress conditions, in-situ strength of concrete is determined to assess the current strength of a structure and to determine whether the strength and durability are adequate for its future use. From general perspective, the core test is required when the result of concrete cubes are not giving satisfactory result. In addition, concrete core test is also used for safety assessment of the existing concrete structure.
Concrete in the member represented by a core test is considered acceptable, if the average equivalent cube strength of the cores is equal to at least 85 percent of the cube strength of the grade of concrete specified for the corresponding age and no individual core has a strength less than 75 percent.
This test determines of the pull-out strength of hardened concrete by measuring the force required to pull an embedded metal insert and the attached concrete fragment from a concrete test specimen or structure. The insert is either cast into fresh concrete (LOK-Test) or installed in hardened concrete (CAPO-Test).
LOK-TEST is used to estimate the in-place strength of concrete in newly cast structures. A 25mm diameter steel disc is embedded in the fresh concrete at a depth of 25 mm from the testing surface. The disc is pulled against a counterpressure, 55 mm inner diameter, placed concentric with the disc on the surface, until rupture of the concrete occurs.
The CAPO-TEST is used to perform pull-out tests on existing structures without the need of preinstalled inserts.A 25 mm diameter ring, inserted and expanded into a recessed groove at a depth of 25 mm and pulled against a counterpressure same as with Lok-Test.
The concrete in the strut between the disc and the counter pressure ring is subjected to a compressive load. Therefore, the pull-out force is correlated directly to the compressive strength of concrete. The test is of great importance whenever verification or quality assurance of in-situ concrete is required.
UPV method is an effective way for estimating the depth of surface cracks. The methodology involves detecting the travel time of stress waves of ultrasonic energy transmitted through concrete sections. Longer travel times through the same cross-sectional areas indicate discontinuities and potential cracking. Crack depth is estimated by varying the transducer spacing. The difference in travel time with varying distance between transducers is used to calculate crack depth.
CIMEC is equipped with PROCEQ PUNDIT LAB+for crack depth measurements in concrete. Longitudinal stress wave pulses are generated by an electro-acoustical transducer that is held in contact with one surface of the concrete under test. After traversing through the concrete, the pulses are received and converted into electrical energy by a second transducer located at a distance from the transmitting transducer. The transit time is measured electronically. The pulse velocity and crack depthare calculated automatically by instrument.
Ensuring sufficient concrete cover is critical for the durability of concrete structures subject to poor environment during their service life. The identification of embedded steel rebar, cover depth and size are the important parameters in the inspection of reinforced concrete structures. Usually, the information of interest includes the location of steel reinforcement, the concrete cover depth, the bar size/diameter, and the likelihood/extent of rebar corrosion. The Profometer test is a perfect on-site solution where the location, depth and size of rebar needs to be known. This may include Corrosion investigation, Quality Control and Assurance of new concrete structures, Location of rebar for penetrations or coring.
CIMEC is equipped with Proceq Profometer650 AI (Profometer analyser and rebar scanner) for concrete cover measurements and rebar scanning. This is an advanced cover meter that enable the precise and non-destructive measurement of concrete cover, estimation of rebar diameter and the detection of rebar locations using eddy current pulse induction as the measuring method. Multiple coil arrangements in the probe are periodically charged by current pulses and thus generate a magnetic field. When a reinforcing bar lies within this field, the lines of force become distorted. The disturbance caused by the presence of the metal in turn produces a local change in field strength as detected and indicated by the instrument. The resulting change in voltage can be utilized for the measurement. Advanced signal processing allows localization of a rebar, determination of the cover and estimation of the rebar diameter.
Corrosion of reinforcing steel is an electro-chemical process, and the behaviour of the steel can be characterised by measuring its half-cell potential. The greater the potential the higher the risk that corrosion is taking place. This technique is used for assessment of the durability of reinforced concrete members where reinforcement corrosion is suspected, and to evaluate the corrosion state of the rebars after repair work and thus evaluate the efficiency and durability of repair work. The measurement can be applied regardless of the depth of concrete cover and the rebar size. Half-cell potential measurements indicates corroding rebars not only in the most external layers of reinforcement facing the reference electrode but also in greater depth.
CIMEC is equipped with Proceq Profometer 650 AI (Corrosion meter) for half-cell potential measurements. The methodology involves measuring the potential of an embedded reinforcing bar relative to a reference half-cell placed on the concrete surface. The concrete functions as an electrolyte and the risk of corrosion of the reinforcement in the immediate region of the test location can be related empirically to the measured potential difference. The procedure is firstly to locate the steel and determine the bar spacing using a cover meter. The concrete cover is removed locally over a suitable bar and an electrical connection is made to the steel for half-cell potential measurements.
