98 people died when severely deteriorated concrete led to the collapse of the Champlain Tower condominiums in Surfside, Florida in 2021. The sudden loss of life was so jarring that it led the state of Florida to overhaul its concrete structural standards for high rise condos.
This tragedy, and others like it, could have been avoided if the concrete had been properly maintained through routine evaluation and analysis.
Concrete can be tested to assess the quality, strength, and durability of the material, regardless of its age. The American Concrete Institute defines concrete testing as “a trial, examination, observation, or evaluation used as a means of measuring either a physical or a chemical characteristic of a material, or a physical characteristic of either a structural element or a structure.”
There are various tests and evaluations that can be undertaken to ensure that a concrete slab or structure meets desired specifications and standards. Some of these tests occur on sample specimens of the same concrete mix that will be used for the slab, while others require actual sampling from the finished slab itself. Most concrete testing methods are destructive in nature, meaning they must take a sample or core of the concrete to assess its strength, but there are also a number of non-destructive testing methods (NDT) available as well.
Compression Test:
The compression test measures the compressive strength of hardened concrete, giving you the best possible strength that it can achieve in perfect conditions. Concrete cubes or cylinders are subjected to increasing compressive loads until failure occurs. The maximum load is recorded, and the strength is calculated based on the cross-sectional area. The results of a compression test can be affected by factors such as the size and shape of the specimen being tested. The amount of friction at either end of the specimen during compression can also affect the results of this test.
Flexural Strength Test:
The flexural test indirectly evaluates the tensile strength of an unreinforced concrete beam or slab. In other words, it tests a slab’s ability to resist bending or flexure. A sample beam of concrete is subjected to either a two-point or three-point loading system, and the deflection, applied load, and crack patterns are measured.
Flexural tests are extremely sensitive to specimen preparation, handling, and curing procedures. The National Ready Mixed Concrete Association (NRMCA) and American Concrete Pavement Association (ACPA) both have policies stating that compressive strength testing is the preferred method of concrete testing compared to flexural strength testing.
Water Absorption Test:
To determine the susceptibility of a concrete slab to water penetration, a concrete specimen is either taken from drilled cores or molded in cylinders. The samples should be saturated and weighted before the test. The absorption can be estimated at different distances from the exposed surface.
Flexural tests are extremely sensitive to specimen preparation, handling, and curing procedures. The National Ready Mixed Concrete Association (NRMCA) and American Concrete Pavement Association (ACPA) both have policies stating that compressive strength testing is the preferred method of concrete testing compared to flexural strength testing.
Moisture Content Test:
Moisture content tests measure the moisture present in hardened concrete. Excessive moisture content can weaken the concrete, affect its strength, and lead to other problems like mold growth.
A calcium chloride kit or a relative humidity meter is required for a definitive moisture content test. Testing with either tool will give you the precise amount of moisture present in a concrete slab.
Chloride Ion Penetration Test:
Also known as the Rapid Chloride Permeability (RCP) test, this process assesses the resistance of concrete to chloride ion penetration, which can cause corrosion of steel reinforcement. Samples are exposed to a chloride solution, and the depth of chloride penetration is measured.
This test is time-consuming, laborious, has rather high variability, and, is to a degree, user sensitive, making it problematic for inclusion in a performance-based specification.
The GPRS Difference
Concrete testing is typically conducted by trained professionals in laboratories or on-site using specialized equipment. The test results are used to verify compliance with industry standards, guide construction decisions, and ensure the quality and longevity of concrete structures.
GPRS offers certain types of testing*, including Ultrasonic Pulse Velocity (UPV) and Tomography, in a limited geographic region. And our non-destructive technology services like ground penetrating radar (GPR) and 3D laser scanning are non-invasive alternatives to destructive concrete testing such as core sampling or load testing.
GPRS offers GPR and 3D laser scanning services to Intelligently Visualize The Built World™ of concrete structures. Unlike destructive concrete testing, GPR and 3D laser scanning allow for the assessment of concrete without physically removing or damaging parts of a slab or other structure.
*GPRS does not offer destructive concrete testing services
Ground Penetrating Radar (GPR)
Using GPR scanning technology, it is possible to scan 18”-24” deep into a concrete slab or structure. This tool allows the construction, engineering, and maintenance industries to assess concrete and avoid damaging important elements during drilling, cutting, or coring. Precision concrete scanning ensures the safety of workers and prevents accidents by identifying potential hazards before any work occurs.
GPRS uses GPR in tandem with Electromagnetic (EM) locating, as well as 3D laser scanning, UPV testing and imaging, tomography, drone photogrammetry, and 3D laser scanning services to completely assess concrete structures without the need to core or cut at all.
Thanks to GPR and these complimentary technologies, it is possible to “see” inside a post tension slab and assess it without drilling, cutting, or sounding.
3D Laser Scanning
3D laser scanning allows contractors, inspectors, and designers to easily identify issues and reduce errors with millimeter-accurate data. Dimensional and tolerance assessments can be completed quickly to prevent costly project rework.
The current method for assessing concrete requires manual inspection and contact-type measurement devices, which are time consuming. The process for gathering information is prone to human error, documentation is tedious, and communicate of that documentation is often informal.
3D laser (LiDAR) scan technology is transforming the way contractors document and assess concrete projects. It can measure floor flatness and levelness, scan wet concrete, scan pre-pour and post-pour, check tolerances and deflection, perform MEP and construction verification, assess structural concrete, allow for prefabrication of stairs and railings, inspect for ADA compliance, measure parking garages, assess concrete stairs, and more.
GPRS’ cutting-edge 3D laser scanning services can help eliminate the headaches associated with the old ways of performing all these tasks.
Ultrasonic Pulse Velocity (UPV) Test:
This non-destructive test measures the travel time of ultrasonic waves through concrete. It helps assess the homogeneity, quality, and integrity of concrete.
This is the simplest non-destructive concrete testing option for slabs. UPV measures the distance or velocity of a sound wave through a structure. To use UPV on a slab, a GPRS Project Manager places a transmitter on one side of the slab and a receiver on the other. The transmitter sends a series of ultrasonic pulses, known as “taps,” through the concrete, where the receiver picks up the taps to measure the amount of time it took for the pulse to travel through the slab. The denser the concrete, the longer it takes for the pulse to travel, making it a simple job to find the interruptions occurring within.
It takes a trained and experienced technician to ensure the precise data collection required to accurately calculate the UPV measurements and findings. The standards for how to nondestructively test and determine pulse velocity readings through concrete are provided by ASTM C597, 180/902-7, and EN 124504-4 and EN 13791.
The ultrasonic wave forms and data points can be integrated to create maps that show the variations in pulse velocity that may point to potential structural issues.
UPV can determine the location and approximate size of:
- Honeycombing
- Inclusions
- Cracks
- Cold Joints
- Overall Uniformity
- Correlated Strength of the Slab
- Changes over Time
UPV is a cost-effective solution for non-invasive concrete imaging that can provide specific strength and structural integrity data. There are, however, additional tools available to provide a more comprehensive picture of what is happening underneath the surface of a concrete slab that can confirm the UPV findings quickly.
Tomography:
Tomography, also known as Ultrasonic Tomography, can be used to both confirm UPV results, and to provide clear 3D tomographic imaging of the interior of the slab. Tomography is potentially more informative than a UPV test result because it maps the interior and provides a color-coded three-dimensional map – much like a heat map – that shows in detail any insertions, cavities, cracks, holes, honeycombing, foreign inclusions, and other flaws. The warmer the color (red, orange, etc.), the more serious the structural defect.
Unlike UPV, which needs a transmitter and receiver, each placed on opposing sides of the slab to determine the speed of pulse dispersion, Tomography allows for complete imaging from only one exposed surface because each of the tomograph’s multiple transducers both transmit and receive. Further, because tomography utilizes shear wave reflections instead of taps, its data processing provides more informative imaging that is instantly readable: solid concrete shows up as blue with 0% void, and damaged concrete with a 100% void like a hole, shows as red. Color variances between the red and blue extremes are interpolations of the data and shear wave reflections and provide an accurate assessment of the strength, depth of any defect detected, and structural integrity of the slab.
It is important to note that Ultrasonic Tomography requires more specialized training than UPV, and while UPV is less costly, Tomographic imagery provides the most precise internal strength and structural integrity measurements.
You are never left wondering what got missed due to human error because the entire interior of the slab is visualized in three dimensions and color, so you can immediately locate defects and deterioration, and their severity. This allows everyone from the architect to the HOA President to an individual condo owner to understand the condition of the structure easily, and it can pinpoint areas of concern before they become significant.
The Right Hands
No matter what kind of concrete testing or analysis you require, it’s imperative that you hire the right company for the job.
GPRS Project Managers utilize the Subsurface Investigation Methodology (SIM) to ensure our 99.8%+ accuracy rate on concrete scanning and utility locating jobs. This months-long training regimen includes 320 hours of field training and 80 hours of classroom training ,where Project Managers tackle real-world scenarios in a safe and structured environment.
SIM-certification ensures that our team members can accurately interpret the readings provided by our state-of-the-art technology, and that the Project Manager has the expertise to apply a variety of data capturing tools to complete the job.
GPRS Intelligently Visualizes The Built World™ through our concrete scanning, utility locating, 3D laser scanning, Video Pipe Inspection (VPI), leak detection, and mapping & modeling services.
What can we help you visualize?