Pull-off test and the determinations of the adhesive parameters

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Constitutive equations of rheological models

Rheological properties of fresh cement pastes were calculated from the resulting flow curves, using various rheological models. In this section, the mathematical equations of these models will be presented.
The rheological behavior of fluids flow can be classified into Newtonian and non-Newtonian fluids based on the relationship between the shear stress and shear rate. If this relationship is linear, the fluid is Newtonian. Otherwise, it is non-Newtonian. Typical flow curves of shear stress versus shear rate for different rheological behavior models are shown in figure 1.21. At the fresh state, mortars (complex fluid) can be characterized by its rheological parameters at the stationary state like yield stress, plastic viscosity, etc. We assume that there is no time- dependent behavior (thixotropy, creep, etc.). The Bingham fluids, which exhibit a linear behavior of shear stress against shear rate and has a yield stress value, is given by the following formula: 􀁗 􀁗 􀁐 􀁊􀀆 0 0 􀀠 􀀎.

Rheological measurements

The aim of rheological tests is to select the correct type and dosage rate of constituents in order to improve placement (or processing) characteristics of the materials. A mortar can be considered to be a fresh concrete without the coarse aggregate and its testing has attractions for the study of the effects of ingredients at small scale [59]. Banfill has described the use of the Viskomat as a small calibrated mixer for mortar testing [Banfill 1994]. More recently, E.Bauer 2007 used a rheometer equipped with Vane-cylinder geometry to investigate the rheological properties, including yield stress, of non-Newtonian fluids (figure 1.22). It was concluded that the Vane system is an efficient method to measure the yield tress of non-Newtonian fluids [Bauer 2007].

Sodium bentonite

We consider the formulation given in table 2.7 and we set a cellulose-ether content equal to 0.05 %. We will focus on their rheological and adhesive effects when added to mortars. The bentonite content has been varied in the following range: [0.05; 0.2; 0.5; 0.8; 1; 2] % by weight, while the percentages of the other constituents remained unchanged (table 2.7). The results, which concern the influence of cellulose Methocel and of bentonite clay, are discussed in chapter 4.

Vinnapas 5010n

The combination of inorganic and polymer binders in dry-mix mortars is essential to modern construction techniques. In this part of study, we will see the influence of the combination of organic additives (cellulose-ether) and a dispersible polymer powder, Vinnapas 5010n, in fresh state. The formulation of test mortar is shown in table 2.8, in which the cellulose-ether content was set equal to 0.22 %. We have varied the content of Vinnapas 5010n, which is supplied by Parex Lanko Company. The typical general characteristic and specification data of Vinnapas 5010N are shown in table 2.4 and 2.5. The dosage was varied in the following range: [1; 2; 3; 4; 5] % by weight. The water content remained unchanged at 21 %. The content of other constituents such as cement, lime and sand are shown in table 2.8.

Vane-cylinder test

As introduced in the previous chapter, for characterizing the rheological properties of the mortars by minimizing slippage, the rheometer is equipped with 4-blade vane geometry (figure 1.23). Yet, with this geometry the tested material is not subjected to a uniform shear rate. This condition is usually required in rheological measurements in order to measure actual material properties, and to have an analytical relationship between the measured torque/rotational velocities and shear rate/shear stress. Nevertheless, vane geometry has been retained since it is appropriate for high yield stress fluids such as dense granular suspensions, including mortars [Kaci 2010], as slippage can be avoided and the material can be sheared in volume.
The yield stress is measured with the vane-cylinder geometry in stress controlled mode in which a « ramp » of steps of increasing stress levels is applied to the vane immersed in the material, and the resulting shear rate is measured as a function of applied stress. The yield value is determined from the critical stress at which the material starts to flow. Between two successive steps there is no pre-shear or rest. The measurement point duration is set and assumed that equilibrium reached at each stress condition to obtain a flow curve. In the present study, the point duration is set 1-2 minute depending on the mortar formulation.
Depending on each specific experiment, we have to perform the test at least three times to determine the best possible procedure. In the first run, the interval between two successive steps must be chosen large enough to reduce the duration of the test. The yield stress is determined, but with a low precision. And then, for the latter runs, the measuring points must be increased around the determined yield point. That would help to determine a high accuracy yield stress of the test sample.

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Adhesive failure energy

As it has been discussed in the previous section, the adhesion energy is calculated by the equation 1.12. From the experimental data, we can calculate the adhesive failure energy by integrating the normal force versus time data. The calculated adhesion energy is then plotted as a function of fiber dosage rate (figure 3.9) and separation velocity (figure 3.8). Figure 3.8shows that the adhesion energy decreases with the applied pulling velocity in the separation process. It can be explained that when a high pulling velocity is applied, the layer of mortar between two plates are broken immediately so that there is no time for the particles to re- arrange. Inversely, at low pulling velocity, i.e. 10 , the particles have enough time to re- arrange their structure against the separation process. Thus it takes more energy to finish the tack. A.Zosel found similar results in his research in 1985 that the adhesive failure energy is dependence on the rate of separation in the case of elastomeric adhesives [Zosel 1985].

Table of contents :

List of Figures
List of Tables
1.1. Industrial mortars
1.1.1. Composition
1.1.2. Mortar types
1.1.3. Method of test for fresh mortar
1.2. Adhesive properties
1.2.1. Basic notions of adhesives of fresh materials
1.2.2. Mechanism of adhesion
1.2.4. Pull-off test and the determinations of the adhesive parameters
1.3. Rheology of pastes and granular materials
1.3.1. Basic notions of Rheology
1.3.2. Constitutive equations of rheological models
1.3.3 Rheological measurements
2.1. Apparatus and Materials
2.1.1. Apparatus
2.1.2. Material used
2.1.3. Mortar formulations
2.2. Experimental procedures
2.2.1. Probe Tack test
2.2.2. Vane-cylinder test
3.1. Effect of fiber on the adhesive properties
3.1.1. Tack test results
3.1.2. Adhesive strength
3.1.3. Cohesion force
3.1.4. Adherence force
3.1.5. Adhesive failure energy
3.2. Effect of fiber on rheological properties
3.2.1. Flow curves
3.2.2. Rheological parameters
3.3. Compare the adhesive properties to the rheological behavior
3.4. Conclusion
4.1 Effect of organic additives, case of Methocel
4.1.1 Effect of Methocel on the adhesive properties
4.1.2. Effect of Methocel on the rheological behavior
4.1.3. Compare the adhesive properties to the rheological behavior
4.2 Effect of mineral additives, case of bentonite
4.2.1 Effect of bentonite on the adhesive properties
4.2.2 Effect of bentonite on the rheological behavior
4.2.3 Compare the adhesive properties to the rheological behavior
4.3 Comparison between organic and mineral thickeners
4.3.1. Adhesive properties
4.3.2. Rheological properties
4.4 Conclusion
5.1. Effect of HEMCs type A
5.1.1. Effect of A on the adhesive properties
5.1.2. Effect of A on the rheological behaviors
5.1.3. Compare the adhesive properties to the rheological behavior
5.2. Effect of HEMCs type B
5.2.1. Effect of B on the adhesive properties
5.2.2. Effect of B on the rheological behaviors
5.2.3. Compare the adhesive properties to the rheological behavior
5.3. Effect of HEMCs type C
5.3.1. Effect of C on the adhesive properties
5.3.2. Effect of C on the rheological behaviors
5.3.3. Compare the adhesive properties to the rheological behavior
5.4. Comparison the effects of three types of HEMCs
5.5. Conclusion
6.1. Effect of Vinnapas on the adhesive properties
6.1.1. Tack test results
6.1.2. Adhesive strength
6.1.3. Cohesion force
6.1.4. Adherence force
6.1.5. Adhesive failure energy
6.2. Effect of Vinnapas on the rheological behavior
6.3. Compare the adhesive properties to the rheological behavior
6.4. Conclusion


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