Jim Klinger, concrete construction specialist The Voice Newsletter February 2022
Full disclosure: The human central nervous system is a totally natural product that looks like it could be peeled right out of one’s dearly departed corpse and laminated onto a great big sheet of plywood (just run an image search for “real nervous system” and see what appears). The system is designed to transmit information related to certain loads and stresses. Any learned discussion of this system typically involves use of these terms: tension, compression and even depression. The nervous system obviously works, but the medical profession cannot say they know exactly how. Just when they think they’re getting close, technical advances cause another new feature to appear. It is sometimes possible to control the behavior of the nervous system with chemicals, but it cannot always be guaranteed when the effects might kick in; perhaps within 60 minutes, but anything more than 90 minutes would probably be unacceptable. Some might say any effort to influence or predict the behavior of the nervous system would be a purely trial-and-error proposition.
And for years they’ve been telling us that concrete’s the thing that moves in mysterious ways.
Despite advances in its component technology, concrete remains a mostly natural product. Potential compressive strength uncertainties might exist at any time during construction; from the first introduction of mix water to long after supporting formwork has been removed. According to ACI 318-19 Commentary recommendations referenced in Chapter 26, engineering judgement should be applied to help evaluate and determine significance and structural implications once apparent low compressive strength has been suspected.
You aren’t likely to find the term “engineering judgement” defined explicitly anywhere in civil engineering textbooks or construction industry literature. Roughly speaking, the term might commonly be used to describe a developmental process that combines classroom education and a healthy dose of field experience to further one’s understanding of the unpredictable behavior of a naturally moving target.
Ideally, the field portion of the process that is supposed to refine an engineer’s sense of concrete situational awareness evolves over the course of one’s career. After all, how many engineering textbooks could possibly cover practical, potential concrete strength issues commonly detectable only in the field; often subtle conditions that involve materials, forming, placing, finishing, inspecting and testing?
Many veteran engineers and ASCC members will tell you straightaway that impressions of their own jobsite experiences concluded with an understanding that no matter what the textbooks and computer programs say, concrete seems to move in unpredictable--and often mysterious--ways.
In a recent “President’s Memo” column, (Concrete International, January 2022) ACI president Cary Kopczynski introduced a Constructability Certification program aimed at design engineers and currently being developed to “include training modules that will provide designers with a working knowledge of formwork, reinforcing bar detailing, specifying concrete, differences in the way designs should be approached as a function of project delivery type, and many more subjects”. In addition to describing the rationale driving the constructability training modules, Kopczynski reminds us of the importance of collaboration between designers and builders. Collaboration is the key to most successful projects and a fantastic way to help encourage the development of engineering judgement.
Unfortunately, some industry legal/contract language can make collaboration either impossible or very cumbersome. In a design-build project, for example, there is a fairly decent chance that an ASCC concrete contractor might actually have a seat at the bar next to the engineer when the Owner pulls the pen out to sketch schematic details on the proverbial cocktail napkin.
On the other hand, if a project is set up to be the standard design-bid-build, AIA contract language will probably limit direct communication between the concrete contractor and the engineer, which means communications could be tied up with RFIs and red tape. After all, how many are there among us who have been told by a GC that we are not allowed to collaborate with the engineer directly, that we have to involve the GC first? And how long did that take...and was it ever productive and beneficial to the Owner?
To make matters worse, our colleagues at the American Society of Civil Engineers (ASCE) tell us that it is okay for a contractor to collaborate with the engineer during the design phase of a project, just as long as that same contractor is not allowed to bid and build the job:
Periodic constructability reviews conducted by the design professional during the project design phase may reduce problems during construction and help control costs. Often, constructors can be solicited during project design to assist with constructability reviews.
When soliciting contractors to participate in constructability reviews, it is critical that the contractor not be placed in a position where a conflict of interest could occur. Contractors conducting constructability reviews must not be allowed to bid on the construction project being reviewed.
Despite these industry obstacles, however; once a project is awarded, the ASCC concrete contractor should make every effort to follow Kopczynski’s advice. Approach the engineer ...and collaborate. At a minimum, ACI documents provide two possible opportunities to make this happen.
ACI 117-10, Section 1.1.3 states that a meeting among the contractors to discuss the work and tolerances is mandatory; the owner and the design team, however, do not have to attend. Invite the structural engineer (and the owner) anyway. If they choose not to attend, insist that both are copied on the meeting minutes.
ACI 301-20, section 1.6.1 states that, if specified, the concrete contractor must attend a preconstruction conference with the engineer to discuss project requirements, acceptance criteria, and responsibilities. So meet with the engineer. Come to the meeting prepared. Tell the engineer you are an ASCC concrete contractor and you want to collaborate on a successful project.
The key here is that the concept of collaboration between the structural engineer and the concrete contractor is way too understated in many ACI documents. It can be sensed in so many places, just below the surface. Thanks to Cary Kopczynski for helping to bring this to light.
Speaking of unpredictable behavior and judgement, two members of the ASCC Technical Division assisted in publishing “Expect Compressive Strength Test Results Less Than Specified Strength on Every Project” in a recent industry magazine (Concrete International, February 2022). Additional technical writing assistance was provided by Colin Lobo (NRMCA) and Eamonn Connolly (McHugh). In this article, strength testing of concrete cylinders is explored, along with reserve cylinders, core testing and engineering judgement. It’s not what you think.