PVAC-modified

SBR-MOOFIED BVE-MOOIFIED PWC-MOOIFIED SBR-MODIRED l%E-MODIFIED PVAC-MODIFIED... 

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.

The effect of plasticizer (i.e., dibutyl phthalate) content in PVAC latexes on the strengths of PVAC-modified mortars is represented in Fig. 4.12.i i Like SBR-modified mortars, the strengths are governed by the nature of polyvinyl acetate (with variation of the plasticizer content), and is reduced with an increase in the plasticizer content. 

Figure 4,12 Effect of plasticizer content in PVAC latexes on flexural and compressive strengths of PVAC-modified mortars.

Figure 4.20 Relation between void-binder ratio and compressive strength of latex-modified mortars (expect PVAC-modified mortar) with sand-cement ratio of 3.

The modulus of elasticity in compression and Poisson s ratio of latex-modified concretes are listed in Table 4.5. [ 1 The modulus of elasticity generally tends to decrease with a rise in the polymer-cement ratio. The Poisson s ratio of PAE- and SBR-modified concretes is nearly equal to that of unmodified concrete regardless of the polymer-cement ratio, but that of PVAC-modified concretes increases with rising polymer-cement ratio. 

Figure 4.41 illustrates the water immersion period and polymer-cement ratio vs. water absorption of latex-modified mortars. The water absorption increases with additional water immersion period, and at lower polymer-cement ratios becomes nearly constant at 48 hours regardless of polymer type. Figures 4.42l l shows the 48-hour water absorption and the amount of water permeation (under a water pressure of 1 kgf/cm ) of the latex-modified mortars. Generally, the water absorption and the amount of water permeation are considerably reduced with an increase in polymer-cement ratio. In all cases, except PVAC-modified mortar, as the resistance to water absorption increases, the resistance to water permeation also increases. The waterproofness of PVAC-modified mortar is low. Polyvinyl acetate swells due to water absorption, and is partially hydrolyzed under alkaline conditions as expressed by the following equation t l i J... 

Tables 4.9 1 and 4.10l l give the chemical resistance data of mortars using elastomeric and thermoplastic latexes respectively at a polymer-cement ratio of 20%. In particular, NBR-modified mortar shows excellent resistance to organic solvents and oils, but NR-modifled mortar does not resist these agents. Although ordinary cement mortar completely fails on contact with rapeseed oil, most elastomeric and thermoplastic latex-modified mortars are hardly attacked. In general, PVAC-modified mortar hardly resists acids and alkalis, but is stable to a great extent toward organic solvents such as mineral oils.i i...

Under long-term outdoor exposure, involving frost action and car-bonation, latex-modified mortar shows increased resistance to weathering in comparison with conventional mortar and concrete. The weatherability of the latex-modified mortars is shown in Fig. 4.69The exposure test was done at the Building Research Institute Outdoor Exposure Site in Ibaraki Prefecture, Japan. Except for PVAC-modified mortars, the flexural and compressive strengths of most latex-modified mortars under outdoor exposure conditions tend to become nearly constant at one year or more, and a weatherability factor is greater or similar to that of unmodified mortar. 

Fig. 2. Typical properties of PVAc-modified UP resins as a function of the PVAc amount. At the critical concentration the morphology evolves from one containing PVAc in dispersed domains to a bicontinuous structure...

Uses Plasticizer for cellulosics, PS, PVAc modifier for lacquers, hot-melt coating formulations, extrudable plastics film-former, pigment dispersant in cosmetics emulsifier, stabilizer in foods emulsion stabilizer for flavoring oils in nonalcoholic beverages emulsion stabilizer, clouding agent, modifying extender for film-former biopolymers in food-pkg. adhesives... 

Crotonlc acid Dimethyl maleate PVAc modifier... 

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