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Various roadmaps have been developed by the cement and concrete industry that highlight the need for a significant reduction of carbon dioxide (CO2) emissions associated with concrete production. One strategy to reduce emissions is to reduce the clinker content in concrete. This can be accomplished by optimizing aggregate gradations or chemical admixtures to reduce total cement content used or use cementitious materials that have a low percent of clinker in them. However, low-clinker (content) concretes may, or may be perceived to, suffer from lower early-age strengths, which have limited their application in practice. This TechNote discusses low-clinker concrete, primarily obtained through the use of supplementary cementitious materials (SCMs), and provides practical advice concerning the strength of these mixtures at early ages (from setting to 7 days).

In May 1978, the first 3-day conference on the use of superplasticizers in concrete was sponsored by the Canada Centre for Mineral and Energy Technology (CANMET) and the American Concrete Institute (ACI) in Ottawa, ON, Canada, with selected papers from the gathering published as ACI Special Publication SP-62. The Second International Conference on the Use of Superplasticizers in Concrete took place in 1981 in Ottawa, ON, Canada, again under the joint sponsorship of CANMET and ACI, with the resulting technical proceedings published as ACI SP-68. The Third International Conference hosted by CANMET and ACI was held in Ottawa, ON, Canada, in 1989 with the primary purpose of reviewing the technical progress achieved since the initial meetings in 1978 and 1981. This event marked a significant turning point for the series, as its scope was formally expanded beyond superplasticizers to include all other types of chemical admixtures. Furthermore, the conference successfully brought together representatives from the chemical admixtures, cement, and concrete industries to exchange information and delineate new areas of needed research. The comprehensive findings and technical contributions from this expanded dialogue were formally published by ACI as ACI SP-119. The Fourth International Conference was held in Montreal, QC, Canada, in October 1994, sponsored by CANMET in association with ACI and other organizations, with proceedings published as ACI SP-148. In October 1997, the Committee for the Organization of CANMET/ACI International Conference (ACI Council), in association with ACI and various Italian cement and concrete organizations, sponsored the Fifth conference in Rome, Italy, publishing the results as ACI SP-173. The Sixth conference was hosted in Nice, France, in October 2000, where the ACI Council and partners from Canada and France accepted 37 papers for publication in ACI SP-195. In October 2003, the ACI Council and organizations from Canada and Germany sponsored the Seventh conference in Berlin, Germany, featuring 39 papers published as ACI SP-217. The Eighth conference was held in Sorrento, Italy, in October 2006, sponsored by the ACI Council, with 36 papers accepted and published as ACI SP-239. In October 2009, the Committee for the Organization of International Conferences (COIC) sponsored the Ninth ACI International Conference in Seville, Spain, where 35 papers were accepted and published as ACI SP-262. The Tenth International Conference on Superplasticizers and Other Chemical Admixtures in Concrete took place in Prague, Czech Republic, in October 2012, sponsored by COIC, resulting in 33 accepted papers published as ACI SP-288. In July 2015, COIC and ACI sponsored the Eleventh International Conference on Superplasticizers and Other Chemical Admixtures in Concrete in Ottawa, ON, Canada, where more than 36 refereed papers were accepted and published as ACI SP-302. The Twelfth International Conference on Superplasticizers and Other Chemical Admixtures in Concrete was hosted in Beijing, China, in October 2018, sponsored by the Chinese Ceramic Society (CCS) and the China Academy of Building Research (CABR) in association with ACI, with 36 refereed papers published as ACI SP-329. Fifty-four additional papers were presented and were published in the Supplementary Papers volume. In July 2022, following a postponement due to the pandemic, the ACI Italy Chapter and the University of Bergamo sponsored the Thirteenth International Conference on Superplasticizers and Other Chemical Admixtures in Concrete in Milan, Italy, featuring 35 refereed papers published as ACI SP-354 and approximately 20 supplementary papers. The Fourteenth International Conference on Superplasticizers and Other Chemical Admixtures in Concrete is being held in Munich, Germany, from 6-8 July 2026. Hosted by the Technical University of Munich (TUM) with the support of ACI, this event continues a nearly 50-year tradition of fostering global dialogue on chemical innovations that enhance the performance and sustainability of concrete. Thirteen refereed papers for this conference are published herein as an ACI Special Publication, along with more than 60 presentations, most of them available in a Supplementary Papers volume, explore a wide range of topics, including superplasticizers, rheology-modifying agents, shrinkage-reducing agents, superabsorbent polymers, and self-healing admixtures. These studies examine the influence of admixtures on the properties of concrete in both fresh and hardened states, specifically addressing workability, slump retention, heat of hydration, strength, and durability. The organizing committee expresses its profound gratitude to the authors, reviewers, and partner organizations whose dedication continues to drive the evolution of concrete technology toward a more sustainable future. The support of the American Concrete Institute for the publication of the proceedings is gratefully acknowledged. The Editor Prof. Dr. Johann Plank

The effort of increasing the sustainability of concrete led to the development of a new class of admixtures specifically designed to reduce the carbon footprint of this material, hence called “Low Carbon Concrete Admixtures (LCCAs).” They act as hydration promoters for binders, increasing the degree of hydration and improving the compressive strength of the concrete. Consequently, the dosage of cement in a concrete can be reduced without affecting the mechanical properties of the resulting product. In the present work, a reference concrete mix was compared with concretes containing two different LCCAs, at different dosages of cement and water-to-cement ratios. Results confirmed the positive effect of LCCAs on strength development, water permeability, and water penetration, suggesting an improvement of the microstructure of concrete; this was confirmed by pore size distribution measurements. On the other hand, coulomb metric tests, like surface resistivity and rapid chloride penetration tests, did not confirm such effects. In an effort to further understand this apparent contradiction, rapid chloride penetration tests were repeated, and the chloride concentration of the cathodic half-cell was measured, revealing that many different ionic species, and not just Cl- ions, contribute to the total passing charge measured during the experiment.

PCEs have become essential ingredients in concrete technology, because they allow the production of modern concrete, characterized by ease of placement, low water-to-cement ratio and high durability. The possibility of modifying the chemical structure of PCEs over a wide range of properties allowed the development of plenty formulations engineered for different applications (ready-mixed, precast concrete industry), types of cement and climate conditions. In PCEs’ technology, the side chain length is a fundamental parameter not only in determining the dispersibility but also the cement hydration kinetic. Longer side chains are used for PCEs with high water reduction capability and low retarding effect, while shorter chains offer more a robust behavior in different application conditions. In the present work three different PCEs were synthesized, characterized by same backbone length, same carboxylic acid to side chain ratio and different side chain length. Several measurements and tests were performed, both in cement paste and mortar. Results confirmed the importance of the side chain length of PCEs in determining the plasticizing effect while the retardation of hydration mainly depends on backbone charge density and distribution. This contributes to clarify the correlation existing among the different parameters determining the functionalities of this fundamental class of admixtures.

Ultra-High-Performance Concrete (UHPC) provides excellent mechanical properties and durability but often relies on high cement content, raising sustainability concerns. To enhance environmental performance, supplementary cementitious materials (SCMs), such as recycled glass powder (RGP), are increasingly used as partial cement replacements. The efficiency of RGP as a reactive SCM is strongly influenced by its dispersion behavior, which depends on the chemical composition of the cement pore solution, including its pH and ionic concentration. In this study, pore solutions were extracted using vacuum filtration and pressure squeezing at varying water-to-cementitious ratios (w/cm) and pressures. Results showed that higher w/cm increased calcium concentrations and decreased alkali and sulfur content, whereas pressure squeezing yielded solutions that closely resembled those in UHPC. Sedimentation tests were performed in RGP suspensions prepared in deionized (DI) water, untreated pore solution, and polycarboxylate ether (PCE) based high-range water-reducing admixture (HRWRA) treated pore solution. Results indicated that untreated pore solutions caused rapid agglomeration and settling of RGP, whereas PCE addition stabilized suspensions and improved dispersion. The study advances understanding of RGP dispersion behavior and supports the more efficient utilization of SCMs, enabling reduced cement demand and more sustainable UHPC production.