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 influence of slag or limestone as a cement main constituent on the perfor¬mance of superplasticizers based on polycarboxylate ether (PCE) was investigated on cements made of identical clinker and sulfate components. Investigations were done by means of pore solution analyses, zeta potential measurements and consistence tests. Depending on the proportion of clinker in the cement the composition of the pore solution, the zeta potential of cement paste and the effective charge of PCE varied significantly. This led to a modified adsorption behavior and plasticizing effect of PCE. Consequently, the specific plasticizing effect of PCE can be diminished with decreasing proportion of clinker in cement.

Superabsorbent polymers (SAP) made of acrylic acid and acrylamide were studied as chemical admixtures for mitigating autogenous shrinkage of high-performance concrete or mortar, respectively. The absorptivity of the particles in saline solutions and in cement pore solution was investigated. Ca2+ in the alkaline solution modified the absorp¬tivity essentially, which closely depended on the polymer structure. Furthermore, the release of internal curing water from SAP particles into the hardening cement-based matrix was monitored by neutron radiography. The kinetics of uptake and release of cement pore solution by SAP and hence, their molecular structure, could be linked with their efficiency in mitigating autogenous shrinkage of a high-strength mortar. Finally, the compressive strength of these mortars was determined. The addition of SAP had no negative effect, but could even lead to an increase in the compressive strength.

Polycarboxylate ether (PCE) admixtures are generally used in concrete at rela¬tively low concentrations, enabling the reduction of mixture cost and enhanced flow prop¬erties due to reduction of cement content and significant enhancement of rheology, respec¬tively. However, typical PCE polymer structures that are used in Portland cement have little or no effect on alkali activated slag (AAS) binder rheology due to ineffective consump¬tion of polymer by a number of mechanisms, including degradation of the polymer chains within the high alkaline environments present in AAS systems. In this study, a range of PCEs with long and moderate PolyEthyleneGlycol (PEG) side chain lengths, and with high and low molecular weights (Mn), are examined. Co-polymers containing a higher density of backbone charges, as is typical for a Portland cement superplasticiser, increase the yield stress of alkali-activated slag. A co-polymer with longer side chains and lower Mn show a yield stress reduction, indicating a mild increase in workability compared to an unmodified AAS paste. It is suggested that in the high ionic strength environment of an AAS binder, a more charged polymer is consumed through interactions with other ions and charged particles, which can bring an increase in yield stress and plastic viscosity of AAS.

Over recent years, polycarboxylate superplasticizers have found their way into grinding aids used in cement production to reduce the electrical energy consumption. The effectiveness of these large molecules challenges the pre-existing theories concerning the factors that govern the performance of grinding aids. This paper reports on molecular dynamics simulations to examine a physical property believed to control the effective¬ness of grinding aids, namely their adsorption energy. The molecules selected are TIPA (Triisopropanol amine), TEA (Triethanol amine) and glycerine. The surfaces examined are dry and hydroxylated C3S surfaces, which are believed to be more representative of reality, since some humidity is always present during the grinding. Detailed results of this part of the work show that glycerine interacts relatively more with dry as well as hydroxylated surfaces of C3S both at 25°C, ambient temperature and 110°C, grinding temperature with respect to TIPA and TEA. These result help to better understand the specific interaction of these molecules with cement surfaces. In the second part of this work oligomers of some PCE superplasticizers are examined with similar numerical tools on dry and hydroxylated surfaces of C3S. Results for different types of these oligomers, together with the previous results, shed light onto the reasons why polycarboxylate superplasticizers have found to also be effective grinding aids in cement production.