International Concrete Abstracts Portal

On October 28-31, 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 the ACI as SP 329. Also, 54 additional papers were presented at the conference, and were published in the Supplementary Papers Volume. The organizers of the conference were the Chinese Ceramic Society, Beijing and the Committee for the Organization of International Conferences (formerly CANMET/ACI Conferences).

The production of sustainable building materials, such as concrete, has drawn increasing attention in the last decade. Breakthroughs in the development of new admixtures, optimized mix designs, innovative concrete management systems, together with a deeper understanding of the best-mode usage of admixtures with different cementitious materials have resulted in the production of sustainable concrete with better performance at a lower cost. This paper presents three approaches for producing sustainable concrete: (1) introduction of a new class of admixture systems that produce control flow concrete or concrete with flow characteristics of self-consolidating concrete (SCC) without using high cement content, (2) minimization of polycarboxylate ether/ester (PCE) and cement usage through better understanding of the interaction between PCEs and sulfates and (3) use of in-transit concrete management systems (iCMS) to consistently deliver concrete that will meet desired specifications with minimal over-design.

The addition of carbon dioxide into fresh ready mixed concrete has been observed to produce a measurable increase in hydration and a significant compressive strength increase. An optimal dose introduced during batching and mixing of ready mixed concrete imparts physiochemical changes to the early hydration. The mechanistic basis for macroscopic performance changes was investigated through the study of a model tricalcium silicate system.

A C₃S paste was treated with carbon dioxide immediately after hydration started. The carbon dioxide reaction products, and the attendant effects, were examined through isothermal calorimetry, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atom probe tomography (APT). Carbonate reaction products around 80 nm formed within 60 seconds of the CO₂ gas injection. The carbonates were intermixed with silicate reaction products

The article deals with the evaluation of the effect of a tartaric acid-based set retarding admixture on the properties of environmentally friendly mortars manufactured with CSA, anhydrite, hydrated lime and supplementary cementitious materials (fly ash, metakaolin and slag cement). Results indicated that the tartaric acid, acts as superplasticizer and it is effective to extend the pot-life of mortars up to about 2 hours. On the other hand, the set-retarding admixture determines a strong retardation of binder hydration and, consequently, a reduction of compressive strength at early ages. Mortars without tartaric acid showed an initial expansion during the first 5-7 days as a consequence of ettringite formation than mixtures shrink. When set-retarding admixture is used, the initial free-expansion totally disappears and shrinkage begins immediately after final set has occurred. However, after 270 days shrinkage is substantially the same for mortars with and without tartaric acid.

The shrinkage of concrete can adversely affect not only its fitness for use, but also the durability of concrete structural elements. Compared with traditional PCEs, shrinkage-reducing polycarboxylate superplasticizer (SR-PCE) can decrease the concrete shrinkage. Therefore, it’s a new way to increase the durability of concrete in recent years. In this paper, three novel SR-PCEs were designed and synthesized by the free radical copolymerization of acrylic acid and the macromonomers with hydrophobic poly(ethylene oxide and/orpropylene oxide)-based side chains.The effect of the side chain hydrophobicity on drying shrinkage and dispersion performance for concrete was investigated, and the relationship between side chainhydrophobicity, drying shrinkage and pore solution properties (surface tension and alkali ions concentration)was also studied. Based on these investigations, a new kind of SR-PCE was developed (SR-PCE3). Upon the addition of 0.4% SR-PCE3, the water-reducing rate was about 21.4% and the drying shrinkage of concrete was decreased by 24.0% at 60 days. Introducing hydrophobic group as the side chain into the polymer may be an effective way to change the properties of pore solution significantly with low concentration of SR-PCE and thus solve the contradiction between adsorption dispersing and shrinkage reducing.