The presence of chloride ions is one of the most widespread causes of corrosion initiation in reinforcing steel in concrete. Trace chlorides present in cementitious materials or admixtures typically result in very low fresh chloride contents in normal-strength concrete that do not present a danger of corrosion. UHPC mixture designs, however, use much higher dosages of cementitious materials and admixtures that can result in non-negligible total fresh chloride contents. These high chloride values are likely to occur more frequently in the future as more UHPC mixtures are made with locally available materials and alternative cementitious materials and may result in concrete mixtures failing to meet specifications for fresh chloride content limits that are based on mixture proportions used in normal-strength concrete mixtures. UHPC and normal concrete samples were made without fibers and with increasing levels of internally admixed chlorides for four different levels of strength to determine chloride thresholds for internally added chlorides. The chloride threshold for fresh concrete was measured using a slightly modified version of the accelerated test EN 480-14. The water-soluble and acid-soluble chloride ion content of UHPC mixtures tested were measured according to ASTM C1218 and Florida Method FM 5-516 to determine the bound chlorides and fresh chloride limits for corrosion. The results demonstrate that the UHPC had ~ 25% higher chloride threshold than the control mixture when measured as an absolute content per unit volume of concrete. When the UHPC chloride content is normalized by mass of cementitious material, it was found that the amount needed to initiate corrosion may be lower than fresh chloride limits given in ACI-318 and ACI 222. Therefore, the ACI-318 water-soluble chloride limits as a % by mass of cementitious materials were found to be non-conservative for the two of the UHPC mixtures tested and should be re-examined for UHPC.

Maintaining workability can be a challenge when the total cement content of a concrete mixture is minimized in order to lower the carbon footprint. This is especially the case in everyday concrete where Portland cement content is mostly optimized for a targeted strength. Unlike high-performance or self-consolidating concretes (SCC) which commonly have high cement or cementitious materials contents, a minimum paste volume is generally required in normal strength concrete (NSC) mixtures to ensure adequate workability for the application and to be acceptable in the field. In this study, a new generation of rheology-modifying water-reducing admixture that improves concrete rheology is used to further reduce cement content and provide favorable workability for concrete applications. Comparisons to reference concrete are presented for their fresh and hardened properties, including plastic viscosity, dynamic yield stress, finishability, pumpability, and targeted strength. By combining concrete technology and this new rheology modifying water-reducing admixture, an economical, workable low-carbon concrete can be achieved.

Concrete has played a pivotal role in shaping the modern world’s infrastructure and the built environment. Its unparalleled versatility, durability, and structural integrity have made it indispensable in the construction industry. From skyscrapers to long-span bridges, water reservoirs, dams, and highways, the ubiquitous presence of concrete in modern society underscores its significance in global development. As we stand at the crossroads of environmental awareness and the imperative to advance our societies, the sustainability of concrete production and utilization is becoming a new engineering paradigm. The immense demand for concrete, driven by urbanization and infrastructure development, has prompted a critical examination of its environmental impact. One of the most pressing concerns is the substantial carbon footprint associated with traditional concrete production. The production of cement, a key ingredient in concrete, is a notably energy-intensive process that releases a significant amount of carbon dioxide (CO2) into the atmosphere. As concrete remains unparalleled in its ability to provide structural functionality, disaster resilience, and containment of hazardous materials, the demand for concrete production is increasing, while at the same time, the industry is facing the urgency to mitigate its ecological consequences. This special publication investigates the multi-faceted realm of concrete sustainability, exploring the interplay between its engineering properties, environmental implications, and novel solutions, striving to provide an innovative and holistic perspective. In recent years, the concrete industry has witnessed a surge of innovation and research aimed at revolutionizing its sustainability. An array of cutting-edge technologies and methodologies has emerged, each offering promise in mitigating the environmental footprint of concrete. Notably, the integration of supplementary cementitious materials, such as calcined clays and other industrial byproducts, has gained traction to reduce cement content while enhancing concrete performance. Mix design optimization, coupled with advanced admixtures, further elevates the potential for creating durable, strong, and eco-friendly concrete mixtures. Concrete practitioners will gain an advanced understanding of a wide variety of strategies that are readily implementable and oftentimes associated with economic savings and durability enhancement from reading these manuscripts. The incorporation of recycled materials, such as crushed concrete and reclaimed aggregates, not only reduces waste but also lessens the demand for virgin resources. Furthermore, the adoption of efficient production techniques, along with the exploration of carbon capture and utilization technologies, presents an optimistic path forward for the industry. This special publication aspires to contribute to the ongoing discourse on concrete sustainability, offering insights, perspectives, and actionable pathways toward a more environmentally conscious future.

In May 1978, the Canada Centre for Mineral and Energy Technology (CANMET), in association with the American Concrete Institute (ACI) sponsored a 3-day conference in Ottawa, ON, Canada, on the use of superplasticizers in concrete. Selected papers from the conference were published as ACI SP-62. In 1981, CANMET, again in association with ACI, sponsored a second 3-day international conference in Ottawa on the use of the superplasticizers in concrete. Proceedings of the conference were published as ACI SP-68. The purpose of the third international conference in Ottawa in 1989 was to review the progress made since the meetings in 1978 and 1981, and to bring together representatives of the chemical admixtures, cement, and concrete industries to exchange information and delineate new areas of needed research. The scope of this conference was expanded to include chemical admixtures other than superplasticizers. Proceedings of the conference were published as ACI SP-119. In October 1994, CANMET in association with ACI and several other organizations sponsored the fourth conference in Montreal, QC, Canada. The objective of this conference was to bring attention to new developments in chemical admixture since the last conference in 1989. The proceedings of the conference were 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 several cement and concrete organizations in Italy, sponsored the fifth conference in Rome, Italy. The conference was aimed at transferring technology in the fast-moving field of chemical admixtures. The proceedings of the conference were published as ACI SP-173. In October 2000, Committee for the Organization of CANMET/ACI International Conferences, (ACI Council), in association with several organizations in Canada and France, sponsored the sixth conference in Nice, France. More than 50 papers from more than 20 countries were received and reviewed by an ACI review panel, and 37 were accepted for publication in the proceedings of the conference. The proceedings were published as ACI SP-195. In October 2003, the Committee for the Organization of CANMET/ACI International Conferences (ACI Council) in association with several organizations in Canada and Germany, sponsored the seventh conference in Berlin, Germany. The conference attracted more than 275 delegates and proceedings of the conference consisting of 39 papers, were published as ACI SP-217. In October 2006, the Committee for the Organization of CANMET/ACI International Conferences, (ACI Council), sponsored the eighth conference in Sorrento, Italy. More than 60 papers from more than 25 countries were received, and peer reviewed by the CANMET/ACI review panel in Budapest, and 36 were accepted for publication as ACI SP-239. In October 2009, the Committee for the Organization of International Conferences (COIC) (formerly CANMET/ACI International Conferences) sponsored the ninth ACI International Conference in Seville, Spain. More than 50 papers from more than 20 countries were received and peer reviewed, and 35 were accepted for publication in the proceedings of the conference. The proceedings were published as ACI SP-262. In October 2012, COIC sponsored the Tenth International Conference on Superplasticizers and Other Chemical Admixtures in Concrete in Prague, Czech Republic. More than 70 papers from all over the world were peer reviewed, and 33 were accepted for publication in the proceedings of the conference. The proceedings were published as ACI SP-288. In July, 2015, the COIC in association with ACI sponsored the Eleventh International Conference on Superplasticizers and Other Chemical Admixtures in concrete in Ottawa, ON, Canada. More than 60 papers from the world over were peer reviewed, and 28 were accepted for publication in the proceedings of the conference. Also, additional papers were presented at the conference that were published in the Supplementary Papers Volume. In October 2018, the Chinese Ceramic Society and the China Academy of Building Research (CABR), Beijing China, in association with ACI, sponsored the Twelfth International Conference on Superplasticizers and other Chemical Admixtures in Concrete in Beijing China. More than 80 papers from all over the world were received and peer reviewed. A total of 36 refereed papers were accepted for publication in the proceedings of the conference. The proceedings were published by as ACI SP-329. The proceedings were published as ACI SP-302. Also, 54 additional papers were presented at the conference, and were published in the Supplementary Papers Volume. In July, 2022, after a postponement for the COVID-19 pandemic, the ACI Italy Chapter and the University of Bergamo, Italy, sponsored the Thirteenth International Conference on Superplasticizers and Other Chemical Admixtures in Concrete in Milan, Italy. The proceedings of the conference consisting of 35 refereed papers were published by ACI as SP-354. In addition to the refereed papers, about 20 other papers were presented at the conference, and were published in a supplementary papers volume. The main topics of the papers presented at the conference are related to superplasticizers, accelerating admixtures, retarding admixtures, air-entraining agents, shrinkage-reducing agents, superabsorbent polymers, and self-healing admixtures, and their influence on the properties of the concrete in fresh and hardened state. These properties include: workability, slump-loss, time of setting, heat of hydration, strength, durability, shrinkage, and creep of the concrete mixtures. Thanks are extended to the reviewers for the valuable efforts in reviewing all the manuscripts published in the conference proceedings and in the supplementary volume. The guidance from Dr. V. M. Malhotra and Prof. M. Collepardi, the Honorary Chairpersons of the conference, is sincerely appreciated. Also, acknowledged is the support of ACI International for the publication of the proceedings (ACI SP-354). The Editors Dr. Denny Coffetti Prof. Luigi Coppola Dr. Terence Holland

Entraining tiny and stable bubbles into cementations mixtures and concrete is becoming more and more important with the complex composition of cement and concrete. Surfactants as air-entraining agents are important concrete admixtures that intentionally create a number of functional air voids in concrete. In this study, nonionic surfactants appear to be a stabilizing agent for ionic surfactants to improve the bubble stability in fresh concrete. The surface tensions and foam properties of their solutions, and the air contents and bubble size distribution of the fresh cement mortars were determined. The results show that nonionic surfactants are introduced into the interface for co-assembly, the electrostatic repulsion between ionic surfactant molecules is effectively diminished and making the arrangement on the interface more stable. The blend of nonionic and ionic surfactants induced smaller bubble formation in aqueous solutions, which also have increased bubble stability in cement mortars. So, it is of great practical significance to blend nonionic and ionic surfactants to improve the air-void stability in concrete.