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

The fundamental interactions between polycarboxylate superplasticizers (PCEs), multi-walled carbon nanotubes (MWCNTs), Ca2+ ions and cement were investigated. Two commercial samples of MWCNTs were characterized by SEM and TEM imaging. It was found that only one sample contained mostly individual, non-agglomerated CNTs which were used in further tests. The MWCNT sample reduced cement paste flowability, but increased 28 day compressive strength by ~ 20% and tensile strength by 26%. The rela¬tively modest increase can be attributed to agglomeration of individual CNTs into large bundles (Ø ~ 900 nm, 3.51 × 10–5 in.). Agglomeration is caused by adsorption of Ca2+ ions onto the initially negatively charged surfaces of CNTs. This way, Ca2+ ions present in every cement pore solution impede maximal dispersion of CNTs in the cementitious matrix, thus limiting their potential application as nano reinforcement for concrete.

To reduce CO2 emission, portland clinker in industrial cement is substituted by reactive and nonreactive mineral additions. This research examines the effect of the structure of selected polymers on their dispersing activity on three different matrixes: portland cement (CEM I 52.5R), portland slag cement (CEM II/B-S 42.5N) and pozzolanic cement (CEM IV/A-P 42.5R). The role of the length of the main parts of a typical comb-polymer on its adsorption behavior and deflocculating capability has been evaluated. For the purpose different poly¬mers having Mw of polyacrylic backbone equal to 2000 and 5000Da and methoxy-PEO dispersing side chains equal to 1000 and 3000 Da were synthesized. Esterification ratio was fixed at 30%. Adsorption isotherms were evaluated by TOC technique while dispersing behavior by mini-slump test. It results that dimension of superplasticizer has a remarkable role on dispersing ability particularly in the case of pozzolanic cement.

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.