Engineer Jagvir Goyal writes about the latest concrete testing equipment.
Concrete is one material that has allowed our wildest structural dreams to become reality. For instance, it has enabled the creation of iconic structures like Terminal 3 at Indira Gandhi International Airport, Burj Dubai, Bandra-Worli Sea Link, World One Towers and Taipei 101 to name just a few. However, this is one material that has been both used as well as abused by the construction industry. For years, scientists and engineers have kept themselves engaged in studying its behaviour and reaction with other materials to make it more economical, stronger, durable and compatible with other materials. At the same time, it has been played with, tampered with and downgraded in quality to satisfy the greed of those with vested interests. One major handicap has been the inability to test it to conform to specified parameters without destroying it. To overcome this, continuous efforts are on to develop increasingly precise concrete testing equipment.
Testing compressive strength
The most important parameter for concrete is its compressive strength. Therefore, compressive strength testing equipment is always made available at every site to fill cubes, compact and cure them, and then test them for compressive strength. This equipment includes a compression testing machine; cube moulds; vibrating table for compaction; a wheelbarrow to draw concrete; and accessories such as a tamping rod, scoops, trowels and spanners. This equipment is well known to most engineers. However, there have been new developments in this area.
Fully automatic compression testing machines
Manually operated compression testing machines are no longer in use. They have been replaced by better versions that give more accurate results, the latest among which are fully automatic compression testing machines. These machines are fully computer controlled. As computer configurations and versions of Microsoft Windows are revised year after year, these machines are also updated periodically to make them compatible with the latest versions and meet the needs of end users. The latest version of fully automatic compression testing machines is available in ranges of 50 to 5,000 kn. These switch off at predetermined conditions and have the capability of automatically turning the pump off and on and controlling the set pace rate. Data storage, data acquisition and analysis are fully automatic.
A fully automatic compression testing machine comprises:
Loading unit: This has a hydraulic jack fixed to the base. The upper plate is provided with self-aligning action. The plates are well ground and polished.
Hydraulic pump: The pump is driven by a 220-v AC motor of 0.5 hp with single phase supply.
Hardware: A PC with Microsoft Windows Operating System controls the machine. Measurement circuits indicate ambient temperature.
Software: This provides calibration files and the compression testing machine doesn鈥檛 start unless the proper file is loaded. The software enables the user to verify machine calibration. It allows automatic saving of data on the computer鈥檚 hard disk. The screen flashes the peak load when the test is over. The software makes the load release automatically on completion of the test.
Manual emergency button: As these machines are fully automatic, this button is provided to shut the machine off in an emergency.
Optional equipment: The machine provides the options of strain measurement and humidity measurement as optional items.
Flexural strength measurement: The latest compression testing machines allow even flexural strength measurement of concrete. A frame and required software are provided for testing flexural strength.
Split tensile strength measurement: The latest versions also provide the option of measuring split tensile strength of concrete samples in cube or cylinder shape. For this, optional attachments are made available that are mounted on the machine for measurement.
Report generation system: The latest machines enable analysis of the test and generate a report showing all required details. Graphical plots showing load vs time, stress vs time and load vs compression are generated. When strain measurement option is exercised, more graphs such as compression vs time and strain vs time are generated.
Concrete consistometer
Normally, we use a slump cone at site to check the workability of concrete and a compaction factor apparatus for checking the workability of concrete mixes with very low water cement ratio or slump. The concrete consistometers devised now check the consistency of concrete. The consistometer comprises a vibrating table, slump cone, specimen pot, graduated rod and an acrylic plate. The equipment is checked to conform to IS 10510 and IS 1199. It operates on 415-v, three-phase, 50 hz, AC supply.
Concrete consistometer has been invented by a mechanical variation of the simple slump test. The concrete is added to a slump cone positioned in a container and vibrated on a small table after removing the cone at a fixed amplitude and frequency. The equipment has a plastic spacer disc touching the upper surface of the concrete. It guides the operator with regard to the completion of compaction. The time taken to complete the vibrations gives an indication of the workability and consistency of concrete.
Spring-type concrete penetrometer
While laboratory tests on concrete are conducted to evolve concrete mix designs and check the suitability of materials, field tests are done to check whether the values pre-decided and fixed in the laboratory are actually being achieved. In addition, an engineer needs to make on-the-spot assessments through easy-to-use equipment. A spring-type concrete penetrometer is one such instrument. It consists of cylindrical spring housing with a plunger attached to the top of the spring. The plunger is graduated for a maximum capacity of 60 kg with a least count of 1 kg. A penetration needle is attached to the other end of the spring housing. The plunger reading can be taken with respect to the top end of the spring housing. Many needle points are provided with the equipment, each point with a different area.
IS 8142 is the guiding code for the penetrometer. It gives an idea of the initial and final setting times of concrete through an easy method of measuring concrete resistance. The penetrometer needle is pressed into the concrete layer to know the time by which it develops penetration resistances of 35 kg per sq cm and 280 kg per sq cm.
Air entrainment meter
After being able to achieve super high strength of concrete, engineers have focused on increasing its durability. One method of doing this is the right level of air entrainment. Air entrainment meters can measure the air entrained in concrete. A large percentage of air entrained has an adverse effect on concrete strength. Therefore, the air to be entrained needs to be accurately decided and maintained. A percentage of 3-6 per cent is specified when concrete has no admixtures and only 1-2 per cent when admixtures are used.
Air entrainment meters consist of a pressure tight flanged cylindrical measuring bowl, fitted with a removable flanged and conical cover assembly. The conical cover is provided with a valve and cock arrangement to bleed off water. On the conical assembly, a cylindrical stand pipe, graduated in percentage of air content, is fitted. Through a pressure bulb, pressure is applied on the concrete specimen. Pressure is measured by a pressure gauge. Air entrainment meters are produced for different capacities and aggregate sizes for concrete.
Beam moulds
The casting of cubes of concrete being poured at site to check its compressive strength is the most popular and prevalent method of testing concrete strength. If we also want to check the flexural strength of concrete, concrete beam specimens are required instead of cube specimens. For casting beam specimens, beam moulds are required. Beam specimens tested for flexural strength are either 150mm 脳 150mm 脳 700mm or 100mm 脳 100mm 脳 500mm in size. Like cube moulds, beam moulds to fill beam samples of these sizes are now produced in steel. They are provided with a base plate and can be easily assembled and dismantled.
Flexural strength testing equipment
Flexural strength testing equipment is designed to test beam specimens of concrete. Both electrically and hand-operated flexural strength testing machines are produced to conduct this test. The loading capacity of these machines is up to 100 kn. They have a double-action hydraulic pump, hydraulic jack with retraction spring and a self-aligning roller assembly and are operated on 220-v, single-phase AC supply in case of electric equipment. The supporting rollers have a centre-to-centre distance of 600 mm and 400 mm for 700 mm and 500 mm long beams respectively. Downward movement of piston applies the load on the beam specimens and the load gauge indicates the load applied.
Creep test equipment
Apart from compressive and flexural strength, engineers also need to ascertain the creep of the concrete 鈥� this requires creep test equipment. Cylindrical moulds are prepared and subjected to a sustained longitudinal compressive load by this equipment. It consists of a reaction frame with upper and lower jack plates, upper and lower bearing plates and load maintaining springs. There is an electrically operated pumping unit of about 1,000 kn capacity provided with a knob lever that can adjust the rate of loading. The knob fitted on the lever can be rotated to fine-adjust the loading rate. Another knob provided on the pump can be unscrewed to release the pressure whenever required.
The equipment has a hydraulic jack with a cylinder and piston and is sealed against any leakage. The piston has an air vent to bleed out air from the system before the jack is used to conduct the test. The hydraulic jack has a retraction spring to allow the piston to come back to its original position after the load is released. The hydraulic jack piston can travel for a maximum distance of 100 mm. A load gauge indicates the load applied. The equipment can be used to determine creep of concrete provided the maximum size of aggregate in concrete is below 50 mm.
Buoyancy balance
You can check the density of hardened concrete by checking its buoyancy with a buoyancy balance. This consists of a rigid support frame with a water tank mounted on a platform. The platform can be raised along with the water tank. The specimen to be tested is suspended above the water tank. As the water tank is raised, the sample suspended above is immersed and readings are noted to check buoyancy. The equipment is electrically operated on 220-v, single-phase AC supply.
Core cases
Often, we wish to draw concrete cores at site from finished structures when doubts arise about the quality, density and proper compaction of concrete. For this purpose, a core case is required. A core case can be used to cut concrete cores up to 100 mm in diameter provided reinforcement is not encountered during core cutting. Electrically run on 220-v, single-phase AC supply, core cases can be clamped to the surface of the concrete to be tested by core cutting. The cases include percussion hand drills operating at below 1 kw load. The bits for the drills can be 25 mm, 38 mm, 50 mm and 75 mm in diameter. When the structures to be tested have been built with very high strength concrete like M40, smaller diameter bits need to be used as large diameter bits often overload the machine motors. Core cases are important for a quality control and quality appraisal civil engineer.
Equipment companies
Many concrete testing equipment manufacturers are now marketing multiple concrete testing products in India and abroad. The buyer must ascertain the certified precision and accuracy of this equipment. AIMIL scores above all in achieving precision and accuracy. However, the cost of equipment produced by AIMIL is much higher than that of others and the company needs to rationalise prices to make its equipment more affordable and popular. Nevertheless, precision scores over the cost factor when it comes to testing important structures and evaluating their rating, strength and durability.
Quick bytes:
鈥� The latest compression testing machines enable analysis of the test and generate a report showing all required details.
鈥� Density of hardened concrete can be checked by checking its buoyancy with a buoyancy balance.
鈥� A core case can be used to cut concrete cores up to 100 mm in diameter.
Engineer Jagvir Goyal writes about the latest concrete testing equipment.
Concrete is one material that has allowed our wildest structural dreams to become reality. For instance, it has enabled the creation of iconic structures like Terminal 3 at Indira Gandhi International Airport, Burj Dubai, Bandra-Worli Sea Link, World One Towers and Taipei 101 to name just a few. However, this is one material that has been both used as well as abused by the construction industry. For years, scientists and engineers have kept themselves engaged in studying its behaviour and reaction with other materials to make it more economical, stronger, durable and compatible with other materials. At the same time, it has been played with, tampered with and downgraded in quality to satisfy the greed of those with vested interests. One major handicap has been the inability to test it to conform to specified parameters without destroying it. To overcome this, continuous efforts are on to develop increasingly precise concrete testing equipment.
Testing compressive strength
The most important parameter for concrete is its compressive strength. Therefore, compressive strength testing equipment is always made available at every site to fill cubes, compact and cure them, and then test them for compressive strength. This equipment includes a compression testing machine; cube moulds; vibrating table for compaction; a wheelbarrow to draw concrete; and accessories such as a tamping rod, scoops, trowels and spanners. This equipment is well known to most engineers. However, there have been new developments in this area.
Fully automatic compression testing machines
Manually operated compression testing machines are no longer in use. They have been replaced by better versions that give more accurate results, the latest among which are fully automatic compression testing machines. These machines are fully computer controlled. As computer configurations and versions of Microsoft Windows are revised year after year, these machines are also updated periodically to make them compatible with the latest versions and meet the needs of end users. The latest version of fully automatic compression testing machines is available in ranges of 50 to 5,000 kn. These switch off at predetermined conditions and have the capability of automatically turning the pump off and on and controlling the set pace rate. Data storage, data acquisition and analysis are fully automatic.
A fully automatic compression testing machine comprises:
Loading unit: This has a hydraulic jack fixed to the base. The upper plate is provided with self-aligning action. The plates are well ground and polished.Hydraulic pump: The pump is driven by a 220-v AC motor of 0.5 hp with single phase supply.Hardware: A PC with Microsoft Windows Operating System controls the machine. Measurement circuits indicate ambient temperature.Software: This provides calibration files and the compression testing machine doesn鈥檛 start unless the proper file is loaded. The software enables the user to verify machine calibration. It allows automatic saving of data on the computer鈥檚 hard disk. The screen flashes the peak load when the test is over. The software makes the load release automatically on completion of the test.Manual emergency button: As these machines are fully automatic, this button is provided to shut the machine off in an emergency.Optional equipment: The machine provides the options of strain measurement and humidity measurement as optional items.Flexural strength measurement: The latest compression testing machines allow even flexural strength measurement of concrete. A frame and required software are provided for testing flexural strength.
Split tensile strength measurement: The latest versions also provide the option of measuring split tensile strength of concrete samples in cube or cylinder shape. For this, optional attachments are made available that are mounted on the machine for measurement.Report generation system: The latest machines enable analysis of the test and generate a report showing all required details. Graphical plots showing load vs time, stress vs time and load vs compression are generated. When strain measurement option is exercised, more graphs such as compression vs time and strain vs time are generated.
Concrete consistometer
Normally, we use a slump cone at site to check the workability of concrete and a compaction factor apparatus for checking the workability of concrete mixes with very low water cement ratio or slump. The concrete consistometers devised now check the consistency of concrete. The consistometer comprises a vibrating table, slump cone, specimen pot, graduated rod and an acrylic plate. The equipment is checked to conform to IS 10510 and IS 1199. It operates on 415-v, three-phase, 50 hz, AC supply.
Concrete consistometer has been invented by a mechanical variation of the simple slump test. The concrete is added to a slump cone positioned in a container and vibrated on a small table after removing the cone at a fixed amplitude and frequency. The equipment has a plastic spacer disc touching the upper surface of the concrete. It guides the operator with regard to the completion of compaction. The time taken to complete the vibrations gives an indication of the workability and consistency of concrete.
Spring-type concrete penetrometer
While laboratory tests on concrete are conducted to evolve concrete mix designs and check the suitability of materials, field tests are done to check whether the values pre-decided and fixed in the laboratory are actually being achieved. In addition, an engineer needs to make on-the-spot assessments through easy-to-use equipment. A spring-type concrete penetrometer is one such instrument. It consists of cylindrical spring housing with a plunger attached to the top of the spring. The plunger is graduated for a maximum capacity of 60 kg with a least count of 1 kg. A penetration needle is attached to the other end of the spring housing. The plunger reading can be taken with respect to the top end of the spring housing. Many needle points are provided with the equipment, each point with a different area.
IS 8142 is the guiding code for the penetrometer. It gives an idea of the initial and final setting times of concrete through an easy method of measuring concrete resistance. The penetrometer needle is pressed into the concrete layer to know the time by which it develops penetration resistances of 35 kg per sq cm and 280 kg per sq cm.
Air entrainment meter
After being able to achieve super high strength of concrete, engineers have focused on increasing its durability. One method of doing this is the right level of air entrainment. Air entrainment meters can measure the air entrained in concrete. A large percentage of air entrained has an adverse effect on concrete strength. Therefore, the air to be entrained needs to be accurately decided and maintained. A percentage of 3-6 per cent is specified when concrete has no admixtures and only 1-2 per cent when admixtures are used.
Air entrainment meters consist of a pressure tight flanged cylindrical measuring bowl, fitted with a removable flanged and conical cover assembly. The conical cover is provided with a valve and cock arrangement to bleed off water. On the conical assembly, a cylindrical stand pipe, graduated in percentage of air content, is fitted. Through a pressure bulb, pressure is applied on the concrete specimen. Pressure is measured by a pressure gauge. Air entrainment meters are produced for different capacities and aggregate sizes for concrete.
Beam moulds
The casting of cubes of concrete being poured at site to check its compressive strength is the most popular and prevalent method of testing concrete strength. If we also want to check the flexural strength of concrete, concrete beam specimens are required instead of cube specimens. For casting beam specimens, beam moulds are required. Beam specimens tested for flexural strength are either 150mm 脳 150mm 脳 700mm or 100mm 脳 100mm 脳 500mm in size. Like cube moulds, beam moulds to fill beam samples of these sizes are now produced in steel. They are provided with a base plate and can be easily assembled and dismantled.
Flexural strength testing equipment
Flexural strength testing equipment is designed to test beam specimens of concrete. Both electrically and hand-operated flexural strength testing machines are produced to conduct this test. The loading capacity of these machines is up to 100 kn. They have a double-action hydraulic pump, hydraulic jack with retraction spring and a self-aligning roller assembly and are operated on 220-v, single-phase AC supply in case of electric equipment. The supporting rollers have a centre-to-centre distance of 600 mm and 400 mm for 700 mm and 500 mm long beams respectively. Downward movement of piston applies the load on the beam specimens and the load gauge indicates the load applied.
Creep test equipment
Apart from compressive and flexural strength, engineers also need to ascertain the creep of the concrete 鈥� this requires creep test equipment. Cylindrical moulds are prepared and subjected to a sustained longitudinal compressive load by this equipment. It consists of a reaction frame with upper and lower jack plates, upper and lower bearing plates and load maintaining springs. There is an electrically operated pumping unit of about 1,000 kn capacity provided with a knob lever that can adjust the rate of loading. The knob fitted on the lever can be rotated to fine-adjust the loading rate. Another knob provided on the pump can be unscrewed to release the pressure whenever required.
The equipment has a hydraulic jack with a cylinder and piston and is sealed against any leakage. The piston has an air vent to bleed out air from the system before the jack is used to conduct the test. The hydraulic jack has a retraction spring to allow the piston to come back to its original position after the load is released. The hydraulic jack piston can travel for a maximum distance of 100 mm. A load gauge indicates the load applied. The equipment can be used to determine creep of concrete provided the maximum size of aggregate in concrete is below 50 mm.
Buoyancy balance
You can check the density of hardened concrete by checking its buoyancy with a buoyancy balance. This consists of a rigid support frame with a water tank mounted on a platform. The platform can be raised along with the water tank. The specimen to be tested is suspended above the water tank. As the water tank is raised, the sample suspended above is immersed and readings are noted to check buoyancy. The equipment is electrically operated on 220-v, single-phase AC supply.
Core cases
Often, we wish to draw concrete cores at site from finished structures when doubts arise about the quality, density and proper compaction of concrete. For this purpose, a core case is required. A core case can be used to cut concrete cores up to 100 mm in diameter provided reinforcement is not encountered during core cutting. Electrically run on 220-v, single-phase AC supply, core cases can be clamped to the surface of the concrete to be tested by core cutting. The cases include percussion hand drills operating at below 1 kw load. The bits for the drills can be 25 mm, 38 mm, 50 mm and 75 mm in diameter. When the structures to be tested have been built with very high strength concrete like M40, smaller diameter bits need to be used as large diameter bits often overload the machine motors. Core cases are important for a quality control and quality appraisal civil engineer.
Equipment companies
Many concrete testing equipment manufacturers are now marketing multiple concrete testing products in India and abroad. The buyer must ascertain the certified precision and accuracy of this equipment. AIMIL scores above all in achieving precision and accuracy. However, the cost of equipment produced by AIMIL is much higher than that of others and the company needs to rationalise prices to make its equipment more affordable and popular. Nevertheless, precision scores over the cost factor when it comes to testing important structures and evaluating their rating, strength and durability.
Quick bytes:
鈥� The latest compression testing machines enable analysis of the test and generate a report showing all required details.鈥� Density of hardened concrete can be checked by checking its buoyancy with a buoyancy balance.鈥� A core case can be used to cut concrete cores up to 100 mm in diameter.
