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

Polycarboxylate superplasticizers have revolutionized concrete technology in the past years. Their Comb-like structure consisting of a polyelectrolyte backbone and nonionic poly (ethylene oxide)-based “teeth”side chains offers a huge opportunity to polymer design. However, to our knowledge, almost all polycarboxylate belong to anionic copolymers. In this study, amphoteric comb-like copolymers (PAMP) with different molar ratio of anionic to cationic group in main chain were synthesized and characterized. The effects of molar ratio of anionic to cationic group in main chain on dispersion, dispers¬ibility retention, adsorption behavior and early hydration behavior in fresh cement suspen¬sions were investigated systematically to elucidate their mechanisms. The moderate incor¬poration of cationic group into comb-like copolymers improved the dispersion ability. However, when the content of cationic group was further increased, as the adsorbed amount of PAMP was increased, the dispersibility became worse. The fluidity retention for PAMP was enhanced with increasing cationic content in main chain. Besides, there is a negative correlation between the dispersibility retention ratio and copolymer concentration in solu¬tion. The adsorption sites, adsorption conformation and early hydration behavior should be together considered to explain its dispersion and the dispersibility retention of cement pastes with amphoteric copolymers. Besides, there exists an optimal balance between the molar ratios of anionic to cationic groups in backbone of comb-like copolymers.

This report presents the results of experiments conducted in a study of concretes for shotcrete reinforced with synthetic structural macrofibers. There are a number of benefits to be gained by building tunnels out of concrete reinforced with synthetic structural macrofibers rather than the traditional electro-welded mesh or metal fibers. A number of problems in construction are thus eliminated, such as the need for a second layer of concrete without fibers to prevent the ends of the metal fibers from perforating the waterproofing layer. The most important problem with mixtures containing fibers was homogeneous distribution of the fibers according to superplasticizer employed. To assess the dispersion of fibers in the different mixtures, a mechanical test was used involving loading on a plate in accordance with European standard EN 14488-5. The energy absorbed during the loading test was therefore correlated with the homogeneity of the mixes, which proved to be dependent on the chemical structure of the superplasticizer employed.

This paper presents the results of an investigation carried out to develop colored self-compacting concretes (SCCs), especially devoted to architectural structures. Two different inorganic pigments were tested, both at a dosage of 20 kg [44.09 lb] per cubic meter of concrete, replacing limestone filler. The first is cobalt-salt based (for blue-colored SCC), the other iron-oxide based (for red colored SCC). SCC mixtures were characterized in the fresh state by means of slump flow and V-funnel tests as well as after hardening by means of compression tests and free dying shrinkage measurements. The influence of the inorganic pigments as well as of fly ash addition on the rheological behavior of the SCCs was also previously studied by means of rheological tests on cement pastes. Low water/binder ratio (0.45) was always adopted for durability reason. Moreover, shrinkage-free SCC was studied due to the combined use of a CaO-based expansive agent and a shrinkage reducing admixture.

Depending upon the chemical source and the polymeric structure, stabilizing agents affect cementitious systems differently with effect on rheology and early age prop¬erties. They can also modify the effects produced by superplasticizers. Additionally, envi¬ronmental temperatures can change their effectiveness significantly, yielding adverse work¬ability properties or modified early hydration. This study presents the effects of different stabilizing agents on cementitious binder pastes exposed to varied climatic conditions during casting and early hydration. Rheological measurements show in which ways envi¬ronmental conditions affect the flow properties and the resistance to segregation. Further¬more it is demonstrated that due to interactions, the typically observed retarding effect of stabilizing agents on the setting of cementitious systems does not necessarily occur when superplasticizers based on polycarboxylate ether are present.