Interlaboratory Study on Precision Statement of Using Terrestrial Laser Scanner (TLS) to Verify Concrete Tolerance
Study Information:
- Location – San Francisco Bay Area Conco construction job site
- Date – July 27 – 28, 2024
- Objective – To provide a precision statement of using a terrestrial laser scanner (TLS) as a test method to verify concrete tolerance following ASTM E-691-23, and to estimate the bias of the TLS test method with the accepted reference values from a total station following ASTM E177-20.
- Publication – Concrete International magazine article in 2024 (September, or October issue to be
decided), an article in xyHt magazine, and a research paper to be decided
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Photos from the event: July 27 & 28, 2024
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- Objective
• Previous Study: In 2018, there was a laser scan study to determine target coordinates from scanner
organized by the American Society of Concrete Contractors (ASCC). Eight parties participated in that study
at a job site in Walnut Creek, CA, USA. One of the conclusions based on all the data collected from that
study was that it is appropriate to use a laser scanner for specification compliance when measuring a
vertical tolerance of 5/8 in. or more and a horizontal tolerance of 1 in. or more. With the 3 best participants’
data, the vertical tolerance to be verified with the scanner can be as low as about ¼ in., and horizontal
tolerance can be as low as 1/2 in. following best practices.
• Objective 1: Revisit a similar procedure after six years with the hardware advancing and collect data for a
precision statement following ASTM E691-23
• Objective 2: Data from this study will be applied to a few selected ACI 117-10 tolerances (listed below) with
the consideration of the human interpretation of the data (i.e. when an operator checks a slab edge with a
½ in. chamfer from the point cloud, he or she might not be able to extract the actual edge of the slab when
there is not a set-up position close to the edge, thus the result will lead to a false reading. Another example
is that some operators use sophisticated software to generate “best fit” linework to idealize the edge that
does not reflect the true edge, etc.)
Participants
10 qualified candidates (single or multiple individuals from each party) from diCerent geographic regions
Location
A job site in the San Francisco Bay Area, CA, USA with recently poured elevated slab and vertical concrete
elements.
Time
Two days on a weekend (Saturday and Sunday) in July, 2024
Selected applicable ACI 117-10 (reapproved 2015) tolerances
4.1 Deviation from Plumb
4.2 Deviation from location
4.4 Deviation from elevation
ASTM standard
ASTM E691-23 Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a
Test Method
Study Outline (test day)
Step 1: Mark the test areas (10 points on slab edges, bottom of columns/walls, top of columns/walls, openings,
example as shown on the photo below);
Step 2: Provide four survey controls (grid intersection points and elevations) surveyed from a total station;
Step 3: A total station will be used as baseline measurements on these 10 spots;
Step 4: A CAD file will be provided as the design location and elevation (shared the same coordinate as the survey
controls provided on-site) for participants to decide the concrete element deviation from the design (plumb,
location, or elevation) on the 10 test spots;
Step 5: All 10 participants will be given 1-2 hours to capture the required testing areas and controls (reproducibility
requirement);
Step 6: Each participant will perform scans twice on the same testing areas (time slot will be Saturday morning,
Saturday afternoon, Sunday morning, and Sunday afternoon) (repeatability minimum requirement);
Step 7: All participants are required to report results on an Excel data sheet template (to be developed) within 10
days after the study.