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

Concrete shrinkage cracking is a common problem in all types of concrete struc¬tures, especially at environments where cracks are prevalent and the repercussions are most severe. Hence, several mitigation strategies have been proposed, including the addition of shrinkage-reducing admixtures (SRAs) and/or using superabsorbent polymers (SAPs) particles. While substantial research has focused on predicting the shrinkage behavior and evaluating the efficiency of such shrinkage mitigation admixtures under laboratory condi¬tions, very limited research has explored that behavior under field-like conditions. These conditions include drying/wetting cycles and submerged condition, which simulate outdoor environmental exposure in marine and offshore structures and structures subjected to mois¬ture cycles (i.e. rain/dry). The results of the present study highlight the substantial influence of environmental conditions on the evaluated shrinkage behavior. It was discovered that exposure to simulated field conditions dismisses the effectiveness of using SRA through a washing out mechanism. It is concluded that adequately considering in-situ conditions in testing protocols should allow gaining a better understanding of shrinkage mitigation mechanisms and developing suitable admixture performance specifications.

Evidence that materials used by the building industry are not damageable for their environment has become a major issue. In particular, the question of organic admix¬tures released from cement based materials by leaching has to be addressed. This paper presents the results of the work carried out with a leaching test derived from the Soxhlet extractor allowing to accelerate the leaching process of organic admixtures. Studied compound is a Polycarboxylate-co-polyethylene glycol based superplasticizer. Numerous analytical methods have been used in the past to detect traces of this chemical. However, mass spectrometry has not yet been applied for this purpose. The last method has enabled us to demonstrate that during the leaching of concrete samples admixed with usual dosages; organic compounds are not released in the leachates. Additionally, in case of cement pastes with high admixtures dosages, we have shown that the leaching process can be assimilated to surface washing.

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.

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.