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concrete mix issuesWhen concrete mix issues arise onsite, it has the potential to delay or halt construction and can quickly turn an otherwise amicable project team into a finger-pointing, litigious environment. Figuring out how the issues arose or who might be liable is a complex process given all the parties involved in concrete construction from designer to supplier to contractor. VERTEX has a unique perspective in dealing with construction and design related issues such as concrete construction because we have seen the issues first hand in the role of insurance professionals (property, liability, and surety), contractors, designers, and attorneys. It is common for all these professionals (“Invested Parties”) to be left trying to evaluate the cause and liability of alleged concrete issues. 

Some of the most common concrete issues onsite are alleged deficiencies/issues in the design and/or execution of the concrete mix. Evaluating the role of the design and execution of the concrete mix can be a difficult task given the countless variables involved such as performance properties, weather conditions, regional variability in materials, etc. The evaluation process can be fraught with misconceptions, misleading information, and an abundance of documents, leaving the Invested Party unsure where to turn. 

This article aims to provide guidance to insurance professionals, contractors, designers, and attorneys about the first steps to troubleshooting alleged concrete mix issues and the misconceptions associated with this evaluation. The information can also be used by Invested Parties in concrete construction to, hopefully, prevent issues from occurring in the first place and/or mitigate their impact.

Evaluating Concrete Mix Issues

Concrete mix issues can arise from alleged issues with the design or approval of the concrete mix, or from execution of that mix design during production by the supplier or placement by the contractor. Based on industry guidelines as well as our own design and contractor experience, the following key items are provided as first steps to consider when evaluating an alleged mix issue.

  • Regardless of the role of the Invested Party, it’s important to remember that there are industry accepted publications, resources, and guidelines such as ACI 211.8 [1] and ACI 211.1 [2]; and technical resources available from the Portland Cement Association (PCA) at cement.org or the National Ready Mix Concrete Association (NRMCA) at nrmca.org. Given the ever-increasing complexity of concrete mix designs that include material, environmental, geologic, and location variables, an evaluation must include solid, well-researched resources to develop a sound technical evaluation of potential concrete mix issues. Are your designated experts utilizing industry accepted resources founded on proven research? 
     
  • Check the mix design specifications. Do they provide clear, measurable, and achievable requirements? For example, “Concrete from delivery truck shall have entrained air of 4% (+/- 1.5%) when tested in accordance with ASTM C231”. If the mix design specifications don’t provide clear, quantifiable requirements, it becomes difficult for the contractor to execute the intended design and for designers to properly evaluate if the intended design has been achieved. 
     
  • Typically, concrete specifications for a project are adapted from ACI 301: Specifications for Structural Concrete. If this standard is cited and/or adapted and modified by the Project Specifications, evaluation of ACI 301, section 4 is critical and may be the best place to start when evaluating mix issues onsite. 
     
  • Do the mix design specifications require compliance with industry guidelines that are written in non-mandatory language? There are many “guideline” documents out there written for designers or contractors but not all of them are mandatory building code requirements which can cause ambiguities on project requirements for the concrete producer and contractor. Designers should beware of referring to guidelines written in non-mandatory language within their design documents. 
     
  • Are there inherent conflicts in proportioning and/or performance requirements in the mix design specification? For example, specifying a certain minimum cement content and a certain water/cement ratio can result in problematic conflicts in the proportioning or unintended performance depending on the values specified. Designers should carefully review and avoid conflicting requirements within their mix design specification.  
     
  • As typically is the case, the designer should avoid outlining contractor means and methods within the design documents.
     
  • Documentation is key: Has the proper submittal information been submitted, reviewed and approved? Does the information include a mix proportion breakdown, applicable batch or plant testing data, and the applicable prescriptive and performance criteria?
     
  • Communication is key: Have the intended performance characteristics of the concrete been properly communicated and understood by the contractor and supplier (i.e. is durability, workability, or strength the primary concern driving the mix proportions)? If the supplier knows this information, they can often provide recommendations to mitigate potential issues before they arise – utilize their expertise! 
     
  • Field techniques and conditions need to be properly documented and evaluated. In order to rule out placement or finishing operations as a potential cause of the alleged concrete issues, it is critical to have information on the actual techniques and conditions in the field at the time of placement and finishing. Most concrete issues never come up until the concrete has been placed and at least partially finished. Therefore, it is critical for designers and contractors to document field conditions at the time of the work, so that these records can be reviewed later if needed. This information should include weather reports/conditions, daily reports, testing data, batch tickets and truck numbers, and lots of photographs. The best defense to mitigate liability claims is a good offense which includes careful, proactive documentation of field conditions during each and every concrete pour. On that note, Invested Parties should be leery of wide-sweeping opinions from experts that have not included an evaluation of the accurate field conditions as part of their review.

The Role of Placement and Finishing Operations

The role of placement and finishing operations on alleged concrete issues goes hand and hand with evaluating alleged concrete mix issues. The topic of placement and finishing operations deserves its own separate discussion, but it is worth mentioning here since the majority of concrete issues, in our experience, come from placement and finishing operations. 

Was the concrete properly cured following placement? Did the placement follow necessary cold- or hot-weather requirements? Was the concrete properly jointed at the correct spacing, location, and at the right time? Was the concrete surface overly worked during finishing operations? These are just some of the questions that come into play when evaluating the role of placement and finishing operations. In order to properly pin-point a concrete mix issue, there has to be a conclusive consideration of the placement and finishing operations as well.

Managing Expectations

Concrete is unique in that it is a structural and finished component. Architects and owners increasingly want smooth, crack-free, concrete components to complement the building’s aesthetic. However, it is our experience that the expectations of design professionals and/or owners may not be in-line with concrete industry expectations, actual job-site conditions, or intended structural behavior of the concrete.

Across their publications, ACI indicates cracking and surface defects can be expected on every project.  For example, in relation to slabs on ground, ACI 360: Design of Slabs on Grade states:

“Even with the best slab designers and proper construction, it is unrealistic to expect crack-free and curl-free floors. Every owner should be advised by the designer and contractor that it is normal to expect some cracking and curling on every project. This does not necessarily reflect adversely on the adequacy of the floor’s design or quality of construction”.

Accordingly, it is critical to manage the expectations of owners, occupants, and designers prior to construction. Structural engineers should be on the look out for conflicts in aesthetic and structural requirements because sometimes the aesthetic requirements may actually govern the design. Architects should be on the look out for determining the feasibility of a certain finished look by engaging the structural engineer, concrete supplier, and finishing contractor in the decision making process.

Takeaways of Troubleshooting Concrete Mix Issues

Determining the cause and potential liability of alleged deficiencies in the design and/or execution of concrete mixes on construction projects can be a complex, daunting task for insurance professionals, contractors, designers, and attorneys. In this article, we have presented several critical items and common issues to consider as first steps in the evaluation process. It is important to utilize industry-accepted resources that are based on well-researched data to evaluate alleged concrete mix issues and ensure designated experts do the same. 

Often times, a more likely cause of the alleged issues may be attributable to placement or finishing operations rather than the mix itself. Evaluating actual field conditions and techniques used during placement and finishing is critical to be able to rule-out these potential contributors. Concrete is unique in that it is a structural and finished product, so it is important to manage the expectations of the architect/designer about the feasibility of intended design aesthetics of the concrete. In some cases, the alleged defects may not be the result of any designer, supplier, or contractor error; rather, it may be the result of an unrealistic expectation of the concrete itself. 

[1] ACI 211.8: Guide to Troubleshooting Concrete Mixture Issues as influenced by Constitutive Materials, Jobsite Conditions, or Testing Practices;

[2] ACI 211.1: Standard Practice for Selecting Proportions for Normal, Heavyweight, and Mass Concrete

Learn more about VERTEX’s Forensic Engineering and Structural Design Engineering Services.

Author

Eric Ryan, PE, SE, LEED AP

Structural Engineer and Division Manager