Jim Klinger, Concrete Construction Specialist The Voice Newsletter March 2023

Full Disclosure: To recap our column that appeared in last month's ASCC VOICE newsletter (Feb. 2023, "Guidance for Concrete Contractors, #14 in a Series"): we introduced and explained issues related to the performance of the "new" ASTM C595 Type 1L portland-limestone cement, hereinafter referred to as "PLC". Our reporting was sourced via jobsite accounts disclosed by concrete contractor members during ASCC Hotline phone calls, information presented in industry trade publications, and two educational seminars we attended at the 2023 World of Concrete designed to focus specifically on PLC industry impact. To gain a better understanding of how the new PLC is affecting ASCC members, we sent a survey to our contractor members in December 2022. Responses continue to come across the transom; in other words, the survey is still very much a work in progress. What follows is a status report that presents what we have learned. [N.B.: It is important to note there are several actual project case studies that were in the process of being reported to the ASCC Technical Division that were cut short by nondisclosure agreements (NDAs). Unfortunately, such gag orders are a recurring and quite damaging legal tool we described in our Feb. 2021 VOICE article regarding the so-called "Spearin Doctrine." It is a shame technical data, including mix designs, strength test reports, mill certs, and petrographic analyses that might help reveal the root causes of costly PLC failures must now remain under seal. Those examples, perhaps the most valuable of all are not included in the ASCC PLC survey (per se).]
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The ASCC PLC survey titled " ASCC Survey on Contractor Experience with Type 1L Cement" consisted of 17 questions asking members to report their experiences with Type 1L PLC. To date, we have received thirty-six responses. The respondents are structural concrete contractors located throughout the United States. Although company sizes varied--22 contractors reported annual sales volume more than $50M. The survey focused on three main potential PLC problem areas: compressive strength, fresh concrete set times, and water demand. Respondents were also given the opportunity to describe other issues, including potential problems with finishability, shrinkage cracks, effects of cold weather and so on. No respondents indicated PLC issues related to decorative or polished concrete. (Although not asked, no respondents indicated issues with PLC durability or problems related to PLC shotcrete applications). Note, that although there were 36 responses to the survey, not all respondents answered all questions.

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Question: We are seeing advertisements by one concrete management software developer who states, "Type 1L cement is more temperamental, requiring ready mix producers to have tighter control over the amount of water added to the concrete and the number and speed of drum revolutions in transit. Because it is sometimes ground finer, there can be an increase to the concrete's water demand as well as a decrease in strength and set times. A greater degree of control is required in order to sustain the desired performance of concrete containing 1L cement...achieving consistency across loads is particularly vexing with 1L cement, as minor changes in material properties, such as aggregate moistures, can have significantly more impact.” The solution, they then say is to install sensors inside the ready mix trucks and monitor concrete properties while the truck is on the way to the jobsite. Has this adjustment technique been used on any ASCC contractor members' projects?

Answer: This is a new one on us as are several of the PLC side effects reported from our members. In another industry advertisement, we found the following statement explains how to offset potential strength reduction caused by limestone use: "A more effective approach is to use a strength-enhancing cement additive, which can have a significant impact on strength. For a typical 5MPa (725 psi) gain, it would be possible to increase the limestone by 7% for the same mill output. Given that strength is substantially reduced in higher limestone levels (>5%), the selection of the appropriate quality-improving additive is important." Such examples indicate there is more going on with PLC behind the scenes than we are being led to believe in current industry promotional media. In Europe, for example, where "PLC has been used for more than 25 years," one major admixture producer addresses the issue of unintended consequences head-on : "The behavior of fresh concrete--expressed as slump flow or workability--is also a key factor, especially in terms of workability-enhancing concrete admixture costs. High limestone content and increased fineness lead (unavoidably) to higher water demand which generally increases the amount of superplasticizer needed to achieve targeted workability. Cement producers would like to avoid such discussions when introducing new and more environmentally-friendly cements to the concrete market." These examples all relate to cement and concrete property issues that come into play before the final PLC product reaches the end user--the concrete contractor--at the jobsite.

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Question: In addition to ASCC, where can concrete contractors go to find unbiased information about PLC? Almost all of what we find are industry promotional advertisements that state PLC is a "plug and play, 1-to-1 powder swap" proposition with zero side effects.

Answer: Despite the NDAs described above, side effects related to PLC continue to appear on concrete construction projects nationwide. The ASCC PLC survey is no doubt just a partial slice of what is happening. We must acknowledge not all concrete contractors or suppliers are members of ASCC, ACI, NRMCA, PCA and so on, where such information telling both sides of the story would likely be found.

ASCC has recently established a Sustainability Committee, where PLC will be one of the hot topics. We are also working collaboratively with the Portland Cement Association (PCA) and the National Ready Mixed Concrete Association (NRMCA) to assist contractors in understanding and managing all aspects of the construction industry efforts to reduce embodied carbon in the environment. One committee member, Dr. Heather Brown, PhD., has suggested a forum with admixture and cement suppliers is necessary to discuss compatibility, cement chemistry and further testing that will be required to address and solve the PLC issues. Dr. Brown has worked with ASCC on previous projects, and currently is the VP of Quality Control at Irving Materials, overseeing 180 concrete plants.

One of the seminars we attended at the World of Concrete 2023 was presented by Tim Cost, P.E., titled "What You Need to Know About the New Type 1L Portland-Limestone Cement." This common-sense, straightforward presentation described the PLC scenario from the grinding process at the mills to potential performance issues encountered in the field. Engineer Cost is the president of V.T. Cost Consulting, LLC and is an expert with over forty-one years of experience with cementitious materials, including twenty-one years at Holcim. Tim will be one of our featured speakers at this year's ASCC Concrete Executive Leadership Forum (CELF), covering PLC issues and how concrete contractors like us can successfully adjust to PLC use and what to look for in PLC mill certs and mix designs.

For printed material, we found one interesting article published by the Construction Specifications Institute (CSI) titled "Concrete's 'Cobra' Effect: The unintended consequences of 'simple solutions' in reducing embodied carbon in concrete.” This article appeared in the "Construction Specifier" magazine in January 2023, and describes many of the unsavory PLC side effects that ASCC members have reported. A link to the CSI article is https://www.constructionspecifier.com/concretes-cobra-effect-unintended-results-of-embodied-carbon-reduction/. There are industry advertisements aimed at specifiers that suggest all that is needed to make things right is for a specifier to merely open up their Division 3 specification template files and change "ASTM C150" to "ASTM C595" and then send the specification out for bid and then on to construction. It is hoped that LDPs and concrete specifiers read the CSI "Cobra" article and understand its implications.