Our Methods
CONCRETE PETROGRAPHY
Petrography is the 150-year-old geologic discipline of examining rocks and minerals to describe their texture and composition, macroscopically and microscopically. This geologic tool can be applied to concrete, essentially a manmade rock primarily made up of aggregates, cement, water, air, and at times with additives like supplementary cementitious materials. Characterization of individual components of concrete and their reactions with one another can be determined using this method. Concrete Petrography is one of the most important tools to determine concrete quality as microscopic features can shed light into issues of low strength or poor durability (Jana and Sarkar, 2015).
Concrete Petrography Basics
It is the application of geologic discipline of petrography--the study of rocks and tool such as the petrographic microscope to investigate the small-scale features in concrete that can lead to potential damage.
From concrete core to thin section: Sample preparation overview in 3 minutes!
Concrete samples are collected from buildings, submitted to the concrete petrography laboratory and treated with fluorescent dyed epoxy. Fluorescent epoxy highlights the presence of cracks and air voids in the concrete when exposed to UV light. The treated samples are then ground with abrasives until light can pass through to a thickness of 30 microns. That's thinner than a strand of hair!
our equipment
Grinding Wheel
This machine is used with grits or abrasive powders to grind and polish rock chips manually. It can make the sample rock chips flat or levelled and reduce the thickness of the sample. Here are the steps to use it:
Moisten the grinding wheel first. This will make the grit powder stick to the wheel and produce a slurry.
If the sample is hard and uneven, use a coarser grit (preferably 120 sized grit).
You can change grit size once the sample is even and flat.
When you reach the grit size of 600 and the sample is smooth you can now proceed to the next step.
Polish the sample in glass using 800 and 1000 sized grit. Keep polishing until the sample is smooth, even and shiny.
Thin Sectioning System
The Thin Sectioning System ⚙️
The thin sectioning machine is used to section rock and concrete rock chips in sample preparation.
The whole system is convenient and easy to use. It has its own grinder to achieve your target thickness and a vacuum chuck to help you hold and mount your sample during cutting. This provides a safer way to cut your samples. Water is applied during cutting and grinding to avoid damages to the sample and to make the process quicker.
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Petrographic Microscope
This is a type of optical microscope which uses visible light and an array of lenses to help the observer see tiny specimens of minerals and determine their properties using principles of optical mineralogy.
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NON-DESTRUCTIVE TESTING
Non-Destructive Testing methods are engineering tests done on concrete and other construction materials used to evaluate the strength and durability without causing damage. Compared to conventional strength tests, NDT is faster and usually less pervasive while providing reliable results.
Physical strength testing of concrete is primarily done with the use of destructive testing on concrete cores or sectioned beams.
Ultrasonic Pulse Velocity Test
Non-Destructive Testing methods are engineering tests done on concrete and other construction materials used to evaluate the strength and durability without causing damage. Compared to conventional strength tests, NDT is faster and usually less pervasive while providing reliable results.
One such method under NDT is the ultrasonic-pulse velocity test (UPV), UPV in principle is like getting an ultrasound exam, except done on concrete. A sound wave is sent across a set distance between two transducers. The time it takes for the pulse to travel that distance is used to calculate the velocity. This value can then be used to determine the quality of the concrete. As a general rule-of-thumb with more cracks the wave gets slower and indicates poor quality of concrete.
Of course, the best way to confirm this is to check with petrography!
References:
ASTM C597 - Standard Test Method for Pulse Velocity Through Concrete
https://civilblog.org/2015/03/27/what-is-non-destructive-testing-of-concrete-various-ndt-test-methods/
https://www.globalgilson.com/blog/non-destructive-testing-of-concrete-an-equipment-guide
Rebound Hammer Test
Rebound hammer tests are done to assess the strength of concrete in the field. A spring-loaded mass is driven in contact with the concrete surface being tested, after applying a set amount of force the hammer will rebound. Measuring the amount of distance that the hammer rebounded has a corresponding compressive strength equivalent. This makes it possible to measure the strength of concrete without coring. However, in order to have a reliable set of values the investigator must correlate these with actual uniaxial compressive strength tests.
References:
https://www.astm.org/Standards/C805.htm
CEMEX Technical Bulletin 2.1 - https://www.cemexusa.com/documents/27329108/45560536/proper-use-of-the-rebound-hammer.pdf/1417ecb8-2a04-1b8a-48aa-853149c76936
REBAR SCANNER
Rebar scanners are used to determine the location, depth, and thickness of concrete reinforcements such as steel bars. This is vital to avoid damaging the structures and the sampling instrument during coring or drilling.