The Influence of Clay on Earth Mortar Behavior Determined by the Use of Rheometer

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1 The Influence of Clay on Earth Mortar Behavior Determined by the Use of Rheometer Givanildo Azeredo 1,a ; Aline F. N. de Azerêdo,2,b ; Jean-Claude Morel 3,b 1 Civil and Environmental Engineering, Federal University of Paraíba, Brazil. 2 Federal Institute of Education, Science and Technology of Paraíba, Brazil. 3 Ecole Nationale des Travaux Publics de l Etat. a givanildoazeredo@hotmail.com, b alinefnobrega@hotmail.com; c morel@entpe.fr Keywords: earth mortar, rheology, clay, workability Abstract. In earth mortars the binder is the clay. When cement or lime is used, its goal is to stabilize the mortar face water. When prevented from water, unstabilized earth mortars can be produced ans applied in building sites. Methods like Squeeze-flow, Abrams cone, Flow table, Cone impression or Penetrometer have been adopted in order to obtain rheological parameters of mortars. Except the rheometer, all other testing systems measure only one rheological parameter. This parameter measured is something related to both viscosity and yield shear stress. It can be slump, flow diameter, penetration, flow time. Each one measures the sensitivity of the influence of water in the consistency of the mortar but definitely does not allow the graphical description of the rheological law, giving precisely the viscosity and yield stress of the mortar, provided only by rheometers. Depending on the material and its application, only one measurement is enough to satisfy the requirements. But sometimes it is not. The goal of this paper is to present the influence of clay on the rheological law of earth mortars by the use of a rheometer. The results show that these unstabilized earth mortars are governed by a Bingham model. Introduction Nowadays, earthen masonry is managed by masons' empirism, without scientific direction. This is often true for baked brick cement-sand mortars masonries. Earth Masonry still remains dependent on the manual skill of the mason and especially on its knowledge. The mason accepts a mortar with his judged workability with the trowel. However this empirical know-how is often lost in Europe and in case of a new material, difficult to apply. On the other hand, the scientists must understand the behavior of the mortar with their own tools, in order to be able at least to justify the work of the mason, or to give him the means of better appreciating the mortars on building site. The purpose of this research is to obtain scientific parameters which can validate earth as a viable building material for masonries. These scientific parameters are useful for the redaction of standards which would allow governmental institutions to choose earth as a building material for public constructions. For masonry, it is important that the research assess the earth mortar workability and generally its behavior in the fresh state. This last can be obtained by the use of a rheometer [1](Aze2005) or by a combination of simple experimental devices, like Abrams cone, penetrometer and flowing table. In a previous article [1], the experimental test device, the rheometer RHEOMAT120 is described in details. The device is first applied on one type of earth, named Tassin 9% clay as a reference material. It was shown that the behavior of an earth mortar is close to Bingham fluid with however two Yield Points. So, it is necessary to determine 3 parameters (2 Yield Points (YP) and one Plastic Viscosity (PV)). Mortars Yield point and Plastic viscosities are directly related to its workability [3],[2]. Neither a dry mortar with high yield point and viscosity nor a fluid mortar presenting weak yield

2 point and viscosity are appropriate to the construction of masonries. One can then wonder why study the yield point and viscosity of a mortar if only its value of workability could be enough in practice. But, a workability test measures only a single parameter of the rheological law, or indicating YP or PV. And for each workability value, a mortar can present different rheological laws, i.e. for a same YP, one can have several PV or for a same PV, one can have several YP [4]. For the earth mortar, the importance is first of all to establish acceptable ranges of these rheologic parameters founded to precise scientific measures. Then, it is interesting to correlate scientific measurements of the rheometer with those obtained according to empirical tests which can be employed with more facility in building sites [5](pkla2003). The proposal as future research is thus to test in a building site the Abrams cone, the plunger and the flowing table, like apparatuses in potential to measure the earth mortars rheology. On the other hand, as these tests do not give a good precision in their results, they will have to be validated with other tests like the rheometer, much more precise and scientifically more valid, because founded on mathematical approaches of the continuum mechanics. Another very important point refers to the mortar content component. As the measurements given by the rheometer are accurate, the analysis concerning the clay content can be done. In other words, we will be able to know with more reliability which are the best contents for the mortars components. It is presented here a study about the influence of the clay being the earth mortar binder, on its rheology. It is first evaluated the influence of clay content, changing mortar constitution with sand addition. Then examined the behavior of an another type of earth, called Magagnosc, the goal is to observe the behavior of these mortars for three clay contents and two types of clay. For the earth mortar, it is interesting to find the optimal proportions of clay or sand, the influence of the clay minerals on these optimal proportions and also the water contents allowing correct use of the mortar. Outline about rheological characterization Yield point and plastic viscosity The rheometer offers as results the values of the yield point and plastic viscosity for a certain range of workability. This range depends on the rheometer s power. In Fig. 01, a review of the rheological curve determination is shown. The mortar is submitted to a shear loading, following the path programmed in Fig. 2.a). The paddle rotates and shear the mortar using a speed which varies from 0 up to certain value, remains constant and falls down from this constant value up to 0. Normally, the rheological measures are only obtained in the downward path, i.e. after the restructuration of the mortar. It means that the residual strains present in the mortar before shear loading were deleted. But, some mortars can be restructured yet in the ramp AB, and so the Bingham lines are yet reliable. Banfill [6] says that rheologic tests must be carried out in a small period of time due to the risk of mortar segregation. If Bingham line is formed yet during the ascending loading (AB path), which means that the mortar is restructured or reorganized early, it is possible that one minute later the results obtained will not be reliable anymore [6]. On the other hand, when the Bingham lines are formed only during the downward loading (CD path), we say that the mortar is restructured later. So, in order to get only reliable results, the following rules must be considered: a) if the ascending curve is yet a Bingham curve, it must be used to determine BYP and YP values; b) if not, the downward curve must be used to determine BYP and YP values.

3 Fig. 01- Charge history (a) and respective response (b) On the other hand, although it exists, it was not determined yet a correlation between the results given by the rheometer and mortars workability adopted in practice concerning their manufacture, what must be studied. In practice, simple and empirical tests are used and each one only measure one parameter, either the yield point or plastic viscosity, or rather an indirect parameter related to them. So, a combination of these simple tests would be necessary to determine both parameters. Two empirical tests from which one may estimate the yield point a) Abrams Cone [7] Hu1995 shows that in case of cement-sand mortar the slump test gives an indication reasonably correlated to the yield point, whereas the other tests like flow table DIN, maniabilimeter, according to [4], do not provide very useable results on the rheological level. The variability of the results of Abrams Cone test is due to especially to the technician who carries out it and also to variations in the mix design. In spite of this inaccuracy, this test is a very useful tool because it can help to detect errors of material content, in particular concerning water content. This test is standard in the United States [8], in France and also in other countries. b) Penetrometer or "Dropping ball" In these tests, the parameter which will have a relationship with the yield point is the penetration depth of an object on a fresh mixture (paste, mortar or concrete). According to [4], the mass or forces applied to the object which penetrates the mixture measures the yield stress of this one. In general, the force applied is constant and independent of the formulation of the mixture. One can obtain a value of penetration associated with water content or optimum workability obtained by empirism. We think in fact that any other test which can be sensitive to the variation of the water content of mixing and also measure this variation there, can be surely used to measure the workability of a mortar. According to the French standard [9], the penetrometer test can also be used to test the mortar workability, apart the flowing table. By using the penetrometer, we determine a value considered as reference for workability. If we decide to use the flowing table, it is enough to calibrate it compared to the penetrometer. The value of the spreading out must be equivalent to a penetration in the case of the penetrometer of 35 +\- 3 mm for the conventional mortar. Experimental device which may measure or estimate plastic viscosity By the flowing table, we cannot measure the stresses and strains associated with the flowing of the mortar. A priori, we cannot control the speed of mortar flowing. Therefore, one cannot define

4 by this test a real yield point value. Nevertheless, the final spreading out of the cone of deformed mortar, can indicate the evolution of the plastic viscosity of the mortar[4]. Equipments, materials and procedure The study on the mortars presented here refers to the quantification of the mechanical and physical parameters such as workability, plastic viscosity and yield point, which can be determined by rheometer RHEOMAT120 [10]. Two kinds of earth were tested, named Tassin and Magagnosc. These labels refer to the French regions where they came from. Their grading curves are shown in Fig. 02. Fig. 02- Granulometric curves of earths tested The water put in the mixture was controlled by weight, enabling to know, after mortar fabrication, its water content. Each mixture was tested several times, by adding water, up to an excessive fluidity. For each mixture and each water content, the rheological curve was recorded and Yield point, Bingham Yield Point and Plastic Viscosity were determined. At least the first three highest rheological measurements, for each formulation, presented an acceptable workability. In a previous paper [1], it is seen that there is a linear report between YP and BYP. So, in this paper, only YP are compared and analyzed. The other material used was Hostun sand [2] for varying the clay content of the mortars formulations. All the rheologic tests were made using only the Tattersall blade, defined in [1]. The penetrometer was used for testing mortars containing 9% and 12% for Tassin and Magagnosc earths. Finally, concerning workability measures and analysis, all manufactured mortars were observed by a mason to be sure if the workability was really adequate for masonry construction.

5 Results The influence of water/clay ratio on earth mortar rheology Case of yield point In Fig. 02, we observe that the yield points fall exponentially according to the water content for Tassin and Magagnosc formulations. The measurement error of the shear stress is 0.24 kpa, i.e. the maximum distance between the experimental value of the yield point and the exponential curve which fits all points. The exponential curve Tassin 6% clay does not shift towards the left as Tassin formulation 12% clay does towards the right compared to Tassin 9% clay. Indeed, the formulation Tassin 6% clay is very sandy and thus required a more important water content to present certain workability at sight, but there was no success. Fig Yield point (YP) as to the function of the water/clay ratio - Tassin and Magagnosc mortars YP of the Fig. 03 are analyzed now as to the function of water/clay ratio instead of water content, as shown in Fig. 04. It is seen that for Tassin containing 6% clay, the water/clay ratio is quite greater and unexpected since the mortar contains low content of clay. But, the mixture was very sandy, and more water was put just to verify if some workability appeared. The result was a very fluid mortar, so inadequate in practice.

6 Fig Exponential report between Plastic viscosity (PV) and kneading water/clay ratio (interval of acceptable workability for each mortar at least for the three highest PV) - Some Tassin and Magagnosc mortars For Magagnosc mortar, it was found by empirism that the clay content must be between 6% and 9%. This interval was determined because Magagnosc 6% clay is a little bit sandy and Magagnosc 9% clay is a little bit argillaceous, but both yet adequate for masonry construction. This means that for producing an earth mortar presenting a good workability for masonry construction it is necessary a water/clay ratio varying from 2 to 8. It is necessary to emphasize that although M12% is inside of the interval, it is not acceptable for construction due to its great cohesion. Case of Plastic Viscosity In Fig. 04, for the Tassin and Magagnosc 9% clay mortars, the increase of the water content makes the PV fall exponentially. On the other hand, for Tassin 12% clay, this report/ratio is not very well defined. In this case, to get an exponential report, it was necessary to take in account both ascending and downward parts of rheological curves in order to determine good PV values. A reason to explain this phenomenon was then searched by analyzing the restructuration or reorganization of the mortars. Observing then the rheological curves obtained for the earth mortar Tassin 12% clay, shown in Fig. 06, for the three lowest kneading water contents values, the ascending part of the rheological curve can be used to determine BYP and YP values. In fact, for a water content of 25.9%, both ascending and downward curves coincide. But, for 26.9%, BYP and YP values must be determined from the downward curve. So, the exponential report between plastic viscosity and water/clay ratio was only obtained when the rules cited before, concerning an early or later restructuration, were considered.

7 Fig. 05: (a) Variation of rotation speed for rheologic tests. (b) Aspect of rheologic curves obtained by our rheometer in case of a Bingham fluid - AB path corresponds to ascending curve and CD to downward curve - BC path has the goal to erase any initial stress or strain caused by filling of the rheometer s cup [1] Fig. 06 Rheological curve - Tassin 12% clay mortars For Magagnosc mortar 9% clay, its behaviour resembles that of the Tassin mortar 12% clay. The phase of reorganization varies according to the water content. For workability 25.6%, for

8 example, the reorganization is reached only during the application of a constant gradient speed (BC path). For other consistencies, the reorganization is reached earlier, which causes the ascending and downward curves to coincide. This means that the ascending curves can obviously also represent the lines of Bingham. For Magagnosc mortar 6% clay, it is restructured during the phase of constant gradient speed application. So, their BYP and YP must be determined by the downward parts of the rheological curves. In Fig. 07, the plastic viscosities as a function to the water content are shown for all the formulations here studied, by the Tattersall blade. We observe that the water/clay ratio has a very important influence on the variation of PV, in particular for the mortars containing 6% clay content. Fig. 07 Plastic viscosity (PV) according to the water/clay ratio (interval of acceptable workability at least for the first three measurements) - Tassin and Magagnosc mortars The very sandy T6% mortar needed a great amount of water content in order to present certain workability by empirism, but it was was not good. So, Fig. 07 shows that this increase of water content caused a very important increase in the water/clay ratio. Physically, it is impossible to have for the same water content, workable Magagnosc mortars for 6%, 9% and 12% clay. The increase of water for obtaining an acceptable workability at sight caused measurements of plastic viscosities in the same order of magnitude for the contents of clay 6%, 9% and 12%, sauf for T6%, which must be discarded. This result is very interesting and shows that, for these types of earth, with an acceptable workability by empirism, one obtains a single value of PV. One can notice that the water content of Magagnosc 12% is artificially increased so that the values of stress can be measured. But, it is very argillaceous. For the best water content of Magagnosc 12%, the value of stress could not be measured because exceeding 1.85 kpa, limit of the rheometer.

9 Tab Summary of optimum values de W, Bingham Yield Point (BYP), Yield Point (YP) and Plastic Viscosity (PV) Tested formulations for the rheologic study - Tatersall blade - n(max)=150 rpm Mortars Formulations Water content (%) Yield Point (Pa) Bingham Yield Point (Pa) Plastic Viscosity(10-3 Pa.s) Tassin 9% clay Tassin 12% clay Magagnosc 6% clay Magagnosc 9% clay Comparisons among Tassin and Magagnosc mortars In this section, the two kinds of earth are considered in terms of the influence of the clay content and its mineralogical nature and also in terms of the water content on the rheological behavior of the mortars. They are compared in terms of water contents which offered the best empirical workability. Indeed, this workability was estimated empirically with the trowel in order to have the smaller water content possible in order to limit shrinkage during drying. In Fig. 08, the lines of Bingham behavior for formulations presenting the best workabilities are compared. Fig. 08 Bingham lines - Non stabilised Tassin and Magagnosc formulations One can say that the mortars suitable YP for utilization in the building site range between 0.80 and 1.80 kpa. Obviously, that is valid only for the formulations here studied. This research makes evident that the presence of more fine materials in our mortars causes a more important Yield stress for constant water content. According to Banfill [6], that is coherent with the idea of the Yield stress as a result of the attraction forces between the particles. The more fine materials one has the more surfaces of contact and thus the more cohesive the resulting mixture will be.

10 In a general way, by Fig. 04 and 07, it can be concluded that the shear thresholds and plastic viscosities tend to behave similarly as to the function of the grain size of the particles (fines) and to the mixing water content. In other words, the augmentation of the water and the reduction in fines cause a drop in the shear threshold and also the PV. The influence of water content is clearer and more certain whereas that of the fines content is more complex, especially concerning PV. In Table 01, the optimum and limit values for YP, BYP and PV are presented for the formulation mortars evaluated in this rheological study which presented adequate workability for masonry construction. Tassin 6% clay is not adequate because it is very friable and does not provide sufficient strength to be used in masonry construction. On the other hand, Magagnosc 12% clay mortars, can be used to produce adobes or blocks by extrusion, for example. Rheological law measures obtained from the penetrometer - Influence of clay For the penetrometer, the results concerning an earth type only are shown in Fig. 09. The goal is to show the error of the test concerning its sensitivity about water content variation. The four lowest penetrometer values are considered inside the range of adequate workability for masonry construction. Fig. 09 Penetration as to the function of the water content for Tassin 9% clay mortar In Fig. 10, it is shown the penetrometer values for Tassin and Magagnosc earth mortars and an interval of measures is given for a good workability of the mortar for masonry construction. In a general way, for these two types of earth, we observe that a penetration value situated between 1.2 cm and 1.8 cm (1.5 cm +/- 0.3 cm) is adequate for an earth mortar to be used in earth masonry construction.

11 Fig Penetration as to the function of the water content for Tassin and Magagnosc earth mortars In Fig. 11, it is shown the relation between Yield and Bingham Yield Point values and Penetrometer values for T9% clay. This report was not constructed for the other mixtures, because the optimum kneading water contents obtained by the penetrometer could not be used to manufacture mortars to be tested by the rheometer, due to its weak capacity to shear them. Fig Relation among Yield and Bingham Yield Point values and Penetrometer values for T9% clay Conclusion This research is important in the sense of determining the range of clay content to be used in the manufacture of earth mortars. In a general analysis, for both Tassin and Magagnosc mortars, the clay content must be greater than 6% clay and lower than 12% clay, to present the adequate cohesion

12 needed by the mason. Analyzing separately, for Tassin mortars the clay content must be in the range > 6% and < = 12% and for Magagnosc mortars > = 6% and < 12%. Another interesting result concerns the influence of the restructuration on the Bingham rheological curve of the mortar. This shows the importance of using a rheometer to study mortars rheology. It shows when the mortar does not present anymore residual strains and can so be sheared in order to produce a reliable rheological law. It is also important to emphasize the tendency of obtaining a single value of plastic viscosity for mortars containing different clay contents, just manufacturing them with an acceptable workability with the hand. Finally, it was verified a linear correlation between YP and penetrometer values for an earth mortar. But, this analysis must be continued in future researches. References [1]Azeredo G.A. Morel J.C. Claude-Henri Lamarque, Applicability of rheometers to characterizing earth mortar behavior. Part I: experimental device and validation, Materials and Structures, 41: , [2] Azeredo G.A., Mise au point de procédures d essais mécaniques sur mortiers de terre: Application à l étude de leur rhéologie, Thèse de Doctorat - INSA - Lyon, [3]Bowler, G.K. Jackson, P.J. and Monk, M.G., The measurement of mortar workability, Masonry International, Vol. 10, No. 1, [4]Ferraris, C.F., Measurement of rheological properties of high-performance concrete: state of art report, National Institute of Standards and Technology, NISTIR 5869, 104(5): , Hu1995, Hu,C., Rhéologie des bétons fluides, études et recherches des LPC - OA 16, 203 pages, [5]Pkla, A. Mesbah, A. Rigassi, V. and Morel, J.C., Comparaison de méthodes d'essais de mesures des caractéristiques mécaniques des mortiers de terre, Material and Structures, 6(2): , [6]Banfill, P.F.G., Applications of Rheology in Mortar Production, Proceedings of the Fourth International Masonry Conference, 1:7-15, [7]Association Française de Normalisation (AFNOR), Norme française EN Essai au cône d'abrams - Norme européenne, P [8]ASTM C143 Standard test method for slump of hydraulic-cement concrete. [9]Norme européenne - Association Française de Normalisation (AFNOR), Norme française EN Methods of tests for mortars - Partie 4: Determination of consistence of fresh mortar by plunger penetration, [10]Analytical Proceedings, Equipment News, Vol. 26, 1989.