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).

Adsorption characteristics of polycarboxylate-based superplasticizers (PCE) on tricalcium silicate (C₃S) and its effect on the hydration of C₃S were investigated. In addition, the morphology change of Ca(OH)_{2 in the presence of PCE was also examined. The results showed that the saturated adsorption amount of PCE on C3S is about 6~7 mg/g. Adsorption occurred on C3S surface as well as its hydrates and played an important role on hydration of C3S. Before the induction period, adsorption of PCE promote the hydration of C3S, while during induction period and reduction period, PCE retarded the C3S hydration. The morphology and size of Ca(OH)2 are found to be changed with the adsorption of PCE. The size of Ca(OH)2 crystals is about 0.5~1 μm, while it decreased to 0.2~0.5 μm after PCE modification. This study provides direct evidence for applying PCE to improve the mechanical and durability of concrete.}

Admixtures for concrete offer a wide range of water reducers that are mostly based on polycarboxylate polymers (PCE) bearing polyethylene oxide nonionic side chains. It is possible to increase PCE effectiveness mixing them with a special workability retention agent (WRA). We focused on ester-based PCE, synthesized from methoxypolyethylene glycol (Mpeg) and acrylic or methacrylic acid, and allylic-type PCE, synthesized from TPeg (polyethyleneglycol isopentenyl ether) or Ipeg (polyethylenglycol methallyl ether) and acrylic or methacrylic acid. By modifyng the composition of the backbone, the kind of repeating units and the molecular weight of polyethylene oxide side chains of PCE it is possible to optimize the properties of the mixture of PCE and WRA. The structures of the most interesting polymers we prepared are described in terms of their conformations (worms or stars). WRA is a particular acrylic polymer that can hydrolyze in alkaline environment; to work properly it must have a certain molecular weight and a low polydispersibility index. If it is used alone it is an ineffective water reducer. To investigate the reason behind this behavior slump test and rheological measured were carried out on mortar.

The water-reducing typed PCE (KZJ-1) has a short branched chain and a long main chain structure, while the structure of early strength typed PCE (KZJ-2 and KZJ-3) with a long branched chain and a short main chain. A detailed investigation on the chemical structure of different typed PCEs was characterized by GPC and particle charge density test. The effects of superplasticizer on dispersion, retarding stability and strength development are studied at the same time by paste and concrete. The superplasticizer was placed into different concentration to test the surface tension. The amount of adsorption and hydration heat were carried by TOC and TAM AIR. The molecular chain of KZJ-2 and KZJ-3 stretches more than KZJ-1 in the alkaline environment of concrete. The KZJ-2 and KZJ-3 can accelerate cement early hydration, shorten the induction period significantly, promote the hydration of C3A, and accelerate the formation of AFt.

In cement paste with low water-powder ratio, non-adsorbed superplasticizer molecules increase the fluidity of paste, but their function is not investigated in detail. This study investigates the influence of non-adsorbed superplasticizer on the fluidity of cement paste using several superplasticizers having different molecular structures. The paste consisted of belite-rich low-heat Portland cement, ultra-fine silica particle, and polycarboxylate-based superplasticizer solution. First, a superplasticizer having moderate amount of functional groups was added to the paste, and adsorption was saturated. Subsequently, another superplasticizer was added. The influence of subsequent addition was related to the molecular structure of another superplasticizer. Another superplasticizer having few functional groups decreased adsorption of the first superplasticizer but the fluidity did not change. Another superplasticizer having moderate functional groups did not change adsorption but increased the fluidity. Another superplasticizer having many functional groups increased adsorption but decreased the fluidity.