Schmidt Rebound Hammer Testing

EL.Y.KAT. OE uses the Proceq Silverschmidt ST/PC. The Proceq rebound hammer is a device to measure the elastic properties or strength of concrete or rock. The SilverSchmidt ST/PC is the first integrated rebound hammer featuring true rebound value and unmatched repeatability. The rebound hammer meets the customers' needs for in-situ measurement of concrete quality and compressive strength. Two factors contribute to the improved performance of this concrete test hammer over its predecessors:

• Velocity based detection of the rebound quotient
• The lightweight hybrid design of the impact plunger is made from aerospace alloy, matched to the elastic properties of the concrete and equipped with a hardness steel cap
• Independent validation testing by BAM (Federal Institute for Materials Research and Testing, Germany) has shown the SilverSchmidt ST/PC to have less dispersion than the classical concrete test hammer over the entire range.
• The unique design and high quality construction of the concrete test hammer SilverSchmidt ST/PC makes rebound hammer testing quicker and more accurate than ever before

Ultrasonic Pulse Velocity

Ultrasonic testing uses the same principle as is used in naval SONAR and fish finders.  Ultra-high frequency sound is introduced into the part being inspected and if the sound hits a material with different acoustic impedance (density and acoustic velocity), some of the sound will reflect back to the sending unit and can be presented on a visual display.  By knowing the speed of the sound through the part (the acoustic velocity) and the time required for the sound to return to the sending unit, the distance to the reflector (the indication with the different acoustic impedance) can be determined.  The most common sound frequencies used in UT are between 1.0 and 10.0 MHz, which are too high to be heard and do not travel through air.  The lower frequencies have greater penetrating power but less sensitivity (the ability to "see" small indications), while the higher frequencies don't penetrate as deeply but can detect smaller indications.

The Pundit Lab+ is an ultrasonic pulse velocity (UPV) test instrument which is used to examine the quality of concrete. It comes with an extended feature set, making it particularly suitable for on-site measurements. Naturally it contains all of the features of the Pundit Lab. The new functions include, an integrated gain stage making an external amplifier unnecessary when using long cables or exponential transducers, a real time stamp for recording the time of measurement, a data review list that allows previous measurements to be viewed on site, and a correlation to compressive strength either directly from pulse velocity or in combination with a rebound value (SONREB method).

 

Electromagnetic Testing (Profometer 5+, Proceq) 

Electromagnetic testing is a general test category that includes Eddy Current testing, Alternating Current Field Measurement (ACFM) and Remote Field testing. While magnetic particle testing is also an electromagnetic test, due to its widespread use it is considered a stand-alone test method rather as than an electromagnetic testing technique.  All of these techniques use the induction of an electric current or magnetic field into a conductive part, then the resulting effects are recorded and evaluated.

Eddy Current Testing uses the fact that when a an alternating current coil induces an electromagnetic field into a conductive test piece, a small current is created around the magnetic flux field, much like a magnetic field is generated around an electric current.  The flow pattern of this secondary current, called an "eddy" current, will be affected when it encounters a discontinuity in the test piece, and the change in the eddy current density can be detected and used to characterize the discontinuity causing that change.  A simplified schematic of eddy currents generated by an alternating current coil ("probe") is shown in Figure 14-a.  By varying the type of coil, this test method can be applied to flat surfaces or tubular products.  This technique works best on smooth surfaces and has limited penetration, usually less than ¼".

Encircling coils (Figure 14-b) are used to test tubular and bar-shaped products. The tube or bar can be fed through the coil at a relatively high speed, allowing the full cross-section of the test object to be interrogated.  However, due to the direction of the flux lines, circumferentially oriented discontinuities may not be detected with this application.

EL.Y.KAT. OE uses the Profometer 5⁺ cover meter. It is a sophisticated device for the non destructive location of rebars and for the measurement of concrete cover and bar diameters, using the eddy current principle with pulse induction as the measuring method. As well as detecting the rebar diameter accurately to the millimeter by only one measuring procedure, the cover meter Profometer 5⁺ offers the transmission of the measured data to a PC. This supersedes the time consuming business of note taking, allowing the user to focus on the essential. Proceq offers two different models of the Profometer 5⁺ cover meter, each designed to meet the individual needs of the customer:

• Profometer 5⁺ cover meter Model S (Basic Unit) performs the following functions:
• The Profometer 5⁺ cover meter Model Scanlog has all the function of the model S but offers additionally the following features:

• Locating rebar
• Concrete cover meter
• Storing individual cover values and statistical evaluation
• Determining the bar diameters

• 2-dimensional display of rebar layout
• 2-dimensional display and mapping of concrete cover values

The cover meter meets the customers' needs for digital rebar location.

Steel Hardness Test Method

Hardness is not an intrinsic material property dictated by precise definitions in terms of fundamental units of mass, length and time. A hardness property value is the result of a defined measurement procedure.

Hardness of materials has probably long been assessed by resistance to scratching or cutting. An example would be material B scratches material C, but not material A. Alternatively, material A scratches material B slightly and scratches material C heavily. Relative hardness of minerals can be assessed by reference to the Moh's Scale that ranks the ability of materials to resist scratching by another material. Similar methods of relative hardness assessment are still commonly used today. An example is the file test where a file tempered to a desired hardness is rubbed on the test material surface. If the file slides without biting or marking the surface, the test material would be considered harder than the file. If the file bites or marks the surface, the test material would be considered softer than the file.

The above relative hardness tests are limited in practical use and do not provide accurate numeric data or scales particularly for modern day metals and materials. The usual method to achieve a hardness value is to measure the depth or area of an indentation left by an indenter of a specific shape, with a specific force applied for a specific time.

There are three types of tests used with accuracy by the metals industry; they are the Brinell hardness test, the Rockwell hardness test, and the Vickers hardness test. Since the definitions of metallurgic ultimate strength and hardness are rather similar, it can generally be assumed that a strong metal is also a hard metal. The way the three of these hardness tests measure a metal's hardness is to determine the metal's resistance to the penetration of a non-deformable ball or cone. The tests determine the depth which such a ball or cone will sink into the metal, under a given load, within a specific period of time. The followings are the most common hardness test methods used in today`s technology:

1. Rockwell hardness test
2. Brinell hardness
3. Vickers
4. Knoop hardness
5. Shore

Corrosion Rate Measurements

The rate of corrosion is the speed at which a metal deteriorates in a specific environment. The rate, or speed, is dependent upon environmental conditions as well as the type, and condition, of the metal. Corrosion rates are normally calculated using mpy (Mils per year). In order to calculate the rate of corrosion, the following information must be collected:

· Weight loss (the decrease in metal weight during the reference time period)

· Density (density of the metal)

· Area (total initial surface area of the metal piece)

· Time (the length of the reference time period)

EL.Y.KAT. OE uses the MS1500E Handled ER Corrosion Data Logger. It is a battery-powered, hand-held corrosion meter that enables you to directly take measurements from an electrical resistance probe, store the data, and upload directly to a computer. The unit features an easy-to-use Main Menu that will permit even an operator who is unfamiliar with the unit to take readings with ease. Corrosion rate measurements are made using the electrical resistance method. The electrical resistance method has a wide range of applications since it can be used in conductive or nonconductive environments including oil and gas. The unit measures the change in resistance of the probe element as metal loss occurs. The rate of change is directly proportional to the corrosion rate.

 

Concrete Core Testing

Cores are usually cut by means of a rotary cutting tool with diamond bits. In this manner, a cylindrical specimen is obtained usually with its ends being uneven, parallel and square and sometimes with embedded pieces of reinforcement. The cores are visually described and photographed, giving specific attention to compaction, distribution of aggregates, presence of steel etc. the core should then be soaked in water, capped with molten sulpher to make its ends plane, parallel, at right angle and then tested in compression in a moist condition as per BS 1881: Part 4: 1970 or ASTM C 42-77. The core samples can also be used for the following:

• Strength and density determination
• Depth of carbonation of concrete
• Chemical analysis
• Water/gas permeability
• Petrographic analysis
• ASHTO Chloride permeability test

The strength of a test specimen depends on its shape, proportions and size. The influence of height/diameter (H/D) ratio on the recorded strength of cylinder is an established fact. Strength of core has to be related to the standard cylinder strengths, i.e. for H/D ratio of 2. Thus core should be preferably having this ration near to 2. For values of H/D less than 1, between 1 and 2, a correction factor has to be applied. Cores with H/D ratio less than 1 yield unreliable results and BS 1881: Part-4:1970 prescribes a minimum value as 0.95. The same standard specifies the use of 150mm or 100mm cores. However cores as small as 50mm are also permitted in the standards. Very small diameter cores exhibit more variability in results than larger dia cores, hence their use is generally not recommended. The general rule adopted for fixing the core size, besides the H/D ratio, is the nominal size of stone aggregate and the dia should be not less than 3 times the maximum size of stone aggregate. For diameter of core less than 3 times the size of the stone aggregate, an increased number of cores have to be tested.

 

Steel Tension Testing

Tension tests provide information on the strength and ductility of materials under uniaxial tensile stresses. This information may be useful in comparisons of materials, alloy development, quality control, and design under certain circumstances.

The results of tension tests of specimens machined to standardized dimensions from selected portions of a part or material may not totally represent the strength and ductility properties of the entire end product or its in-service behavior in different environments. However, these test methods are considered satisfactory for acceptance testing of commercial shipments. The test methods have been used extensively in the trade for this purpose.

 

 

 

 

Carbonation Depth Measurement Tests

Carbonation of concrete occurs when the carbon dioxide, in the atmosphere in the presence of moisture, reacts with hydrated cement minerals to produce carbonates, e.g. calcium carbonate. The carbonation process is also called depassivation. Carbonation penetrates below the exposed surface of concrete extremely slowly.

The significance of carbonation is that the usual protection of the reinforcing steel generally present in concrete due to the alkaline conditions caused by hydrated cement paste is neutralized by carbonation. Thus, if the entire concrete cover over the reinforcing steel is carbonated, corrosion of the steel would occur if moisture and oxygen could reach the steel.

If there is a need to physically measure the extent of carbonation it can be determined easily by spraying a freshly exposed surface of the concrete with a 1% phenolphthalein solution. The calcium hydroxide is coloured pink while the carbonated portion is uncoloured.

 

Visual Testing

Visual testing is the most commonly used test method in industry. Because most test methods require that the operator look at the surface of the part being inspected, visual inspection is inherent in most of the other test methods. As the name implies, VT involves the visual observation of the surface of a test object to evaluate the presence of surface discontinuities. VT inspections may be by Direct Viewing, using line-of sight vision, or may be enhanced with the use of optical instruments such as magnifying glasses, mirrors, boroscopes, charge-coupled devices (CCDs) and computer-assisted viewing systems (Remote Viewing). Corrosion, misalignment of parts, physical damage and cracks are just some of the discontinuities that may be detected by visual examinations.