International Concrete Abstracts Portal

This CD contains 33 papers presented at the Tenth International Conference of Superplasticizers and Other Chemical Admixtures in Concrete held in Prague, Czech Republic, in October 2012. Topics include Synthesis, Characterization, and Dispersing Performance of a Novel Cycloaliphatic Superplasticizer; Compatibility between Polycarboxylate and Viscosity-Modifying Admixtures in Cement Pastes; Aspects of Gypsum-Free Portland Cement; A Novel Type of PCE Possessing Silyl Functionalities; and much more. Note: The individual papers are also available. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP-288

New automated slump control technology is available to manage the quality of concrete in a mixing truck. This technology measures the workability of concrete while in the mixing truck, and then adjusts the workability by adding water or superplasticizer during transit to the construction site. This paper describes this process control technology and the implications for polycarboxylate-based superplasticizer performance. Field data are presented showing the performance of superplasticizers when added in multiple doses during transit rather than all at once in the plant. The effect of varying superplasticizer dose on entrained air content is evaluated. The data confirm that the use of superplasticizer with process control technology can reduce variability in delivered slump. Recommendations are given for selecting admixtures and for programming process control systems to ensure optimal concrete performance.

Novel methods based on thermal desorption (TD) and pyrolysis gas chromatog¬raphy (pyr-GC-MS) have been developed for the determination of chemical additives that are either inter-ground with cement clinker during the manufacture of portland cement or admixed during the production of portland cement concrete. This technique has been found to be readily applicable for phenol, glycol, and alkanolamine-based cement grinding aids as well as a number of different chemical admixtures such as naphthalene sulfonate form¬aldehyde condensate (NSFC), and two durability enhancing admixtures, a calcium nitrite-based corrosion inhibitor and a shrinkage reducing agent (SRA) comprised of isomeric glycols and ethers (SRA). Overall, the pyrolysis gas chromatographic-mass spectrometric (pyr-GC/MS) analysis of cement and concrete has the potential to be far more specific and less tedious than the common extraction-spectroscopic based methods currently used. Front end in-situ derivatization can further expand the capability of pyr-GC/MS by volatil¬izing otherwise thermally unstable or strongly adsorbed additives in cement and concrete.

Hydration leads to hydrated phases precipitation which are more or less covered by the adsorbed admixture depending on the added amount and the nature of the surface. To predict the optimum dosage and to understand the fluidity evolution at the early age, it is interesting to study the specific surface area development of cement during this period. It was shown that the workability evolution is mainly due to the tricalcium aluminate (C3A) hydration. Here we choose a simplified system: C3A/CaSO4/calcite/superplasticizer. We measured the specific surface area by two techniques: the BET method using nitrogen as reference and the nuclear magnetic spin-spin relaxation of 1H water. We highlighted a good correlation between the surface measured by NMR relaxometry and by the BET method. Continuous NMR measurement confirms the point-by-point BET measurements that are often subject to question. Thanks to both methods, we studied the influence of the dosage in superplasticizer and of the structure in terms of anionic group density on the specific surface area. In the development of the surface area, we demonstrated that the step mainly impacted by superplasticizers is the nucleation and not the growth. When the dosage of superplasticizer increases, the nucleation is promoted and the growth of ettringite is limited. As consequence, the specific surface area of ettringite increases with both the number of charges added and the backbone charge density. The surface area goes up in presence of superplasticizer as consequence of a dispersing effect (hydrates are not attached to anhydrous phases) and of a reduction of hydrates size.

The viscosity-modifying admixtures (VMAs) contribute to the control of the rheology of grout and are used to enhance plastic viscosity, cohesion, stability, and resis¬tance to bleeding of cement-based systems. This paper reports the results of an investiga¬tion on the effect of VMAs, namely two types of diutan gums and a welan gum, on the rheology behavior of cement grouts. All mixtures were made with two types of superplas¬ticizers. The dosages VMAs were 0.05%, 0.10% and 0.15% with a fixed water-to-cement ratio of 0.40. The investigated fresh properties of the grouts included the mini-slump flow, Marsh cone flow time, plate cohesion, and rheology parameters: namely yield value and the plastic viscosity. Both rheological parameters were obtained using coaxial and vane viscometers. Two control grouts (with and without superplasticizer) were also tested and compared to mixtures containing VMAs. The results indicated that both types of diutan gums were better in controlling the grouts fresh properties and rheology compared to the welan gum.