As a follow up to Eight Things Learned at the ACI Spring 2016 Conference, featured in our blog back in May, Adam Boswell, P.E. and Chad Boyea, P.E traveled to The City of Brotherly Love for The ACI Convention and Exhibition: Revolutionary Concrete Conference, held October 23-27 in Philadelphia.
While in the city that is home to the Liberty Bell and the famous Rocky statue, our guys gleaned some insights at the conference that we think might be worth sharing.
- The Pier Luigi Nervi exhibit was a beautiful reminder of what is possible when there is close collaboration between art and science.
- Two items to discuss right away when it comes to exposed, cast-in-place concrete elements are:
- How to address “bug holes” (small openings in the concrete face that form on the surface of the form), and
- What level of color variation is acceptable. These vary depending on budget and the architectural vision for the space.
- For concrete elements that are to be exposed to view in the final condition, good communication, mockups, and realistic expectations are the keys to producing the desired aesthetic.
- Thickness tolerances for slabs-on-ground – ACI 117 – Specifications for Tolerances for Concrete Construction and Materials provides standard tolerances for concrete construction. The current tolerance for the thickness of slabs-on-ground is -3/4 inch for an individual sample and -3/8 inch for the average of all samples. Coring existing slabs and measuring the thickness reveals that this tolerance is almost impossible to achieve with modern construction techniques. The members of ACI 302 – Guide to Concrete Floor and Slab Construction agreed that if you measure the thickness of any constructed slab it won’t meet the specified tolerances. Furthermore, most concrete subcontractors placing and finishing the slabs are not responsible for the fine grading of the subbase material which has the biggest impact on the slab thickness. The ACI 117 committee is working on the next edition of the document and has requested input from the ACI 302 committee regarding what a realistic tolerance should be. In the next edition, the tolerance will be based on statistics using standard deviation.
- Super Air Meter –Air entrainment is used to provide freeze-thaw durability in concrete by allowing water to expand into the voids when it freezes. Smaller air bubbles in the concrete are more effective in providing freeze-thaw resistance and have less of an impact on concrete strength than larger air bubbles. The current test method for measuring air content (ASTM C231) will tell you the air volume in the fresh concrete but does not tell you the size and distribution of those bubbles. Tyler Ley, Ph.D., P.E., of Oklahoma State University, discussed a new test apparatus called the Super Air Meter (SAM) that is used to measure the air volume and air void spacing in fresh concrete. The SAM is currently being used by many state DOTs and is expected to become increasingly popular in other market sectors.
- Tilt-Up Concrete Panel Bracing – The Tilt-Up Concrete Association (TCA) publishes the TCA Guideline for Temporary Wind Bracing of Tilt-Up Concrete Panels During Construction. The document provides a standardized method for the design and erection of a temporary bracing system for tilt-up concrete panels. The current edition of the document includes the following statement for the assessment of the floor slab capacity to resist the bracing forces, an important and currently under-addressed area of the bracing design: “The Owner’s designated representative for construction shall be responsible for assigning a qualified firm to review the floor slab capacity for the bracing of the tilt-up panels in accordance with the latest edition of the TCA bracing guidelines.” The lifting and bracing designer determines the sizing, locations and connections of the bracing. They do not typically check the capacity of the slab-on-ground to resist the brace forces. The project specifications should clearly identify who is responsible for checking the slab so that it is properly addressed.
Finally, “The Great Cheesesteak Debate” was a great failure. Adam and Chad had been asked by our Business Development Manager to compare the structural integrity of Geno’s Cheesesteak’s to Pat’s and rate the sandwiches based on which performed better. Unfortunately, they didn’t coordinate their efforts and they both ended up with only Pat’s sandwiches. Without having Geno’s as a comparison, it would be inaccurate to deem one more structurally sound than the other. But they did provide us with this advise: know what you want when you get in line at Pat’s as the staff doesn’t take kindly to slow poke customers and bring cash as Geno’s doesn’t accept debit or credit cards.
PES is looking forward to Spring 2017 — Driving Concrete Technology, slated for March 26-30 at the Renaissance Center in Detroit, MI. And if you will be there too, be sure to shoot Adam and Chad an email so they know to look for you in March.
|Author: Adam Boswell, PEAdam earned his BCE from Auburn University and his MSE from the University of Texas. As a Project Manager, Adam manages a variety of projects from senior living facilities to municipal courthouses to office buildings, from the early stages through construction. Adam brings over 10 years of experience to PES, with a love for the creative process of growing a building from concept to a useful part of the community.
Adam can be reached at
|Author: Chad Boyea, PEChad initially pursued architecture but then decided structural engineering was a better fit. As a Project Manager, Chad works on a host of project types ranging from hotels, manufacturing and distribution facilities, office buildings, retail developments, educational facilities, to healthcare facilities and historic preservation projects. He’s well versed working with structural systems involving concrete, masonry and steel design.
Chad can be reached at firstname.lastname@example.org