Sponsors: American Concrete Institute, RILEM, Université de Sherbrooke, CRIB, Université Toulouse III, Lmdc Toulouse, Kruger Biomaterials, Euclid Chemical, Prodexim International inc., BASF Master Builders, ACAA Editor: Arezki Tagnit-Hamou In July 1983, the Canada Centre for Mineral and Energy Technology (CANMET) of Natural Resources Canada, in association with the American Concrete Institute (ACI) and the U.S. Army Corps of Engineers, sponsored a five-day international conference at Montebello, Quebec, Canada, on the use of fly ash, silica fume, slag and other mineral by-products in concrete. The conference brought together representatives from industry, academia, and government agencies to present the latest information on these materials and to explore new areas of needed research. Since then, eight other such conferences have taken place around the world (Madrid, Trondheim, Istanbul, Milwaukee, Bangkok, Madras, Las Vegas, and Warsaw). The 2007 Warsaw conference was the last in this series. In 2017, due to renewed interest in alternative and sustainable binders and supplementary cementitious materials, a new series was launched by Sherbrooke University (UdeS); ACI; and the International Union of Laboratories and Experts in Construction materials, Systems, and Structures (RILEM). They, in association with a number of other organizations in Canada, the United States, and the Caribbean, sponsored the 10th ACI/RILEM International Conference on Cementitious Materials and Alternative Binders for Sustainable Concrete (ICCM2017). The conference was held in Montréal, QB, Canada, from October 2 to 4, 2017. The conference proceedings, containing 50 refereed papers from more than 33 countries, were published as ACI SP-320. In 2021, UdeS, ACI, and RILEM, in association with Université de Toulouse and a number of other organizations in Canada, the United States, and Europe, sponsored the 11th ACI/RILEM International Conference on Cementitious Materials and Alternative Binders for Sustainable Concrete (ICCM2021). The conference was held online from June 7 to 10, 2021. The conference proceedings, containing 53 peer reviewed papers from more than 14 countries, were published as ACI SP-349. The purpose of this international conference was to present the latest scientific and technical information in the field of supplementary cementitious materials and novel binders for use in concrete. The new aspect of this conference was to highlight advances in the field of alternative and sustainable binders and supplementary cementitious materials, which are receiving increasing attention from the research community. To all those whose submissions could not be included in the conference proceedings, the Institute and the Conference Organizing Committee extend their appreciation for their interest and hard work. Thanks are extended to the members of the international scientific committee to review the papers. Without their dedicated effort, the proceedings could not have been published for distribution at the conference. The cooperation of the authors in accepting reviewers’ suggestions and revising their manuscripts accordingly is greatly appreciated. The assistance of Chantal Brien at the Université de Sherbrooke is gratefully acknowledged for the administrative work associated with the conference and for processing the manuscripts, both for the ACI proceedings and the supplementary volume. Arezki Tagnit Hamou, Editor Chairman, eleventh ACI/RILEM International Conference on Cementitious Materials and Alternative Binders for Sustainable Concrete (ICCM2021). Sherbrooke, Canada 2021

This paper focuses on developing ambient-cured alkali-activated concrete incorporating recycled concrete aggregates (RA). The binder was either slag or a blend of slag and fly ash (3:1, by mass). Hook-ended steel fibers were added, in 2% volumetric fraction, to improve the properties of concrete made with RA. The alkaline activator solution was a blend of sodium silicate and sodium hydroxide. Concrete mixtures were proportioned to achieve three target compressive strengths, namely 30, 45, and 60 MPa. The performance of concrete mixtures was assessed based on 1, 7, and 28-day compressive strengths. Experimental results showed that full replacement of natural aggregates by RA caused up to 28% reduction in compressive strength of plain alkali-activated slag concretes, with greater reductions being reported in mixtures with higher target strength and tested at 28 days. The incorporation of 2% steel fibers enhanced the strength and caused limited strength reductions of up to 7%. Compared to alkali-activated slag RA concretes, mixtures with 25% fly ash replacement exhibited lower strengths at 1 and 7 days, but their 28-day strength was superior. Analytical multi-linear regression models were developed to identify statistical significance of concrete components and examine their impact on the compressive strength.

The occurrence of CAH10 in a calcium sulfoaluminate (CSA) clinker and in the CSA clinker blended with anhydrite was assessed by experimental data and thermodynamic modelling. For the CSA clinker it was found that CAH10 forms as an intermediate phase directly from the hydration of ye’elimite together with ettringite and aluminium hydroxide, which is an alternative reaction path to the formation of monosulfate and aluminium hydroxide. The occurrence of CAH10 is linked to the solubility of the aluminum hydroxide formed, which decreases with time due to an increase of its crystallinity. In case of a highly soluble aluminum hydroxide, which occurs at early hydration times, the formation of CAH10 and ettringite is thermodynamically more favoured than the formation of monosulfate. At later ages, when the solubility of aluminum hydroxide decreases, CAH10 and a part of the ettringite convert to monosulfate. This conversion is associated with an increase of porosity, which leads to a significant loss of compressive strength beyond a sample age of 28 days. In the CSA clinker blended with anhydrite the formation of CAH10 could not be evidenced. No loss of compressive strength was observed for this sample.

Recent studies focused on the quality of the interfacial transition zone (ITZ) of ordinary concretes made from recycled aggregates (RA), without however focusing on High Performance Concretes (HPC).

This paper aims to formulate HPC from RA that are exclusively derived from concrete, whose composition is controlled. These concretes are made in a ready-mixed concrete plant and then undergo a crushing and riddling process to produce RA. Partially saturated gravels are substituted up to 100% in the HPC composition in order to accentuate internal cure phenomenon. This phenomenon was observed and demonstrated using a scanning electron microscope (SEM) in the low Water/Cement (W/C) paste up to a distance of 150 μm from the RA and compared by image processing, to a reference concrete made from natural aggregates (NA).

The comparison of the mechanical performances and the microscopic analysis of HPC show that the characteristics transfer of the RA seem to favor a hydration of the paste by a mechanism of desorption of their absorbed water, in a process of “internal cure”. The internal cure appears optimal for concrete C60. In addition to this observation, there was an increase in the strength of the recycled HPCs compared to control natural-aggregate HPCs.

A layer of 2-4 mm (0.08-0.16 in) protective render coat (PRC) has proven to be an effective anticarbonation barrier at two bridges protecting the underlying concrete against carbonation for 100 years. The carbonation of concrete under the PRC with low permeability was found to be less than 2 mm (0.08 in). It is assumed that the PRC was placed for aesthetic purposes. Taking into account the considered XC3 exposure class according to EN 206, to which concrete structures were subjected and compressive strengths of the underlying concrete between 20 - 25 MPa (2900 - 3625 psi), low carbonation depth can be explained by the presence of the PRC applied on concrete surface. The main scientific goal of this article is to explain the cause of extremely low carbonation depth of concrete under the PRC. Its composition has been unknown until now but the present research reveals the secret of this substance. Investigations of the aspects of low carbonation depth thoroughly focused on the PRC role covering concrete beneath as well as material development of new current PRC based on the present cement and sand, without the use of chemical admixtures, are also the subject of ongoing research.