Setting Behavior

In general, the setting of latex-modified mortar and concrete is delayed to some extent in comparison with ordinary cement mortar and concrete, and this trend is dependent on the polymer type and polymer-cement ratio. 

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Wilson, A. D., Crisp, S. Ferner, A. J. (1976). Reactions in glass ionomer cements IV. Effect of chelating comonomers on setting behavior. Journal of Dental Research, 55, 489-95. 

Fig. 6.5 Setting behavior of washout-resistant concrete (Rakitsky [41])...

Governments assist in the acquisition of information by funding and conducting basic research. Under command-and-control regulation, however, government agencies also use information to set behavior standards. 

Properties of CBCs lie between ceramics and cements. These materials are formed at room temperature like cements, or may be synthesized at slightly elevated temperatures, but their structure is highly crystalline or glass-crystalline composite. The particles in CBCs are bonded by a paste formed by chemical reaction, as in cements, but the particles themselves are mostly crystalline. Their strengths are higher than those of cements but fall short of sintered ceramics. Their corrosion resistance is close to ceramics, but at the same time, they may be vulnerable to erosion like cements. The ease of formation of these ceramics, their rapid setting behavior and low cost make them very attractive for the various applications discussed in this book. 

S.H. Oh et al., Preparation of calcium aluminate cement for hard tissue repair Effects of lithium fluoride and maleic acid on setting behavior, compressive strength, and biocompatibility. J. Biomed. Mater. Res. 62(4), 593-599 (2002). 

Figures 4.8l °l and 4.91 show the setting behavior of the latex-modified mortars and concretes respectively. The setting is delayed with an increase in the polymer-cement ratio. The slower setting does not cause inconvenience in practical applications. NR-modified mortar causes the most delay in setting. Usually, the reasons for the setting delay are that the surfactants such as alkylbenzene sulfonates and caseinates contained in latexes inhibit the hydration of cement.I J Rheological studies on PVAC-modified concrete by Zivical l revealed that the hydration of cement is inhibited by the adsorption of the surfactants on the binder surface.

Table 4.1 Effects of Surfactants and Antifoamer on Setting Behavior of Cement...

In handling mixes made with low-porosity cement, their particular rheology and setting behavior must be taken into consideration. So far, low-porosity cements have been produced and applied on an industrial scale only in the former Czechoslovakia (Skvara et al, 1981). 

Phosphate-bonded lefractory concretes are combinations of a phosphate binder and a refractoiy aggregate. The hardening of the system takes place as the result of a cherrrical reaction between these two corrstituents. To control the setting behavior small amorurts of a setter (such as nragnesium chronrate) nray also be added to the nrix. 

Yilgor, 1. Eynur, T. Bdgin, S. Yilgor, E. Wilkes, G. L., Influence of Soft Segment Molecular Weight on the Mechanical Hysteresis and Set Behavior of Silicone-Urea Copolymers with Low Hard Segment Contents. Polymer 2011, 52,266-274. 

O Observe the target behaviors during a preintervention baseline period to set behavior-change goals. 

Yilgor I, et al. Influence of soft segment molecular weight on the mechanical hysteresis and set behavior of sihcone-urea copolymers with low hard segment contents. Polymer... 

Structural characterization of the polymers was obtained by FT-IR and NMR spectroscopy using a Nicolet MX-1 and Varian EM-390 spectrometer. The IR spectra for the oligomers and the copolymers were obtained from solution cast films on KBr discs. Dog-bone specimens were cut from the films for mechanical testing of the segmented copolymers. Mechanical measurements included stress-strain, stress relaxation, tensile hysteresis and permanent set behavior. All these tests were performed on an Instron. Model 1122 at room temperature. All stress-strain and hysteresis measurements were carried out at a strain rate of 200 per minute based on the initial sample length. 

Interestingly, interactions between chiral amines and acid components can be transformed into macroscopic properties. For example, chiral amine 39a (Figs. 2.10 and 2.11) upon interaction with L- or D-tartaric acid self-assembles into nanofibers leading to gel formation [11]. Fibrous assemblies of 39a-D-tartaric acid are less stable than 39a-L-tartaric acid due to the unmatched interaction between the chiral centers. To minimize unfavorable interactions they form nano-vesicles. The macroscopic result of this phenomenon was the difference in sol-gel behavior of two diastereomeric salts. This unusual heat-set behavior of 39a-D-tartaric acid system was explained by lowering unfavorable interactions as the temperature increases that allowed for formation of the nanofibers. 

Ramachandran, V. S., and Beaudoin, J. J., Handbook of Analytical Techniques in Concrete Science and Technology, William Andrew Publishing, Norwich, New York, p. 964 (2001) Michaux, M., and Nelson, E. B., Flash Set Behavior of Oil Well Cement Slurries Containing Lignosulfonates, 9th Int. Congr. Cements, New Delhi, India, 4 584-590 (1992)... 

Electrochemical methods appear to have distinct advantages in the study of cement hydration. Methods involving potential measurement (including pH, zeta potential, and selected ion potential), conductivity measurement, and a.c. impedance measurement provide useful information related to both ion concentration of pore solution and microstructural change in hydrating cement paste. The early hydration and setting behavior of OPC-CAC and OPC-Hydrated-CAC paste systems can be determined using these techniques. 

The exact mechanism by which gypsum addition to portland cement controls setting behavior is not known although much work has been reported in this field. It is clear, however, that interactions between C3A and gypsum are integral to the stiffening and hardening processes. 

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