design and application of hydraulic grouts of high ...design and application of hydraulic grouts of...

Design and application of hydraulic grouts of high injectability for the structural restoration of the column drums of the Parthenon Opisthodomos

A. Miltiadou-Fezans1, E. Papakonstantinou2, K. Zambas2, A. Panou2 & K. Frantzikinaki2 1Directorate for Technical Research on Restoration, Hellenic Ministry of Culture, Athens, Greece 2Service for the Conservation of Acropolis Monuments, Hellenic Ministry of Culture, Athens, Greece

Abstract The column drums of the Opisthodomos of the Parthenon featured a multitude of very fine cracks, due to the great fire of the 3rd century A.D. and the explosion of the building in 1687. Instead of dismantling the columns, the in situ structural restoration by hydraulic grouts injections was decided, as this would involve the least intervention to the monument. The objective of this intervention was to fill in the best possible way the very fine cracks, while maintaining the structural independence of the column drums, thus preserving the existing structural system of the columns. In this paper, the methodology of the design, the most important results of the comparative parametric studies for the selection of the optimum compositions, the basic principles of in situ production and application, the quality control of the injections and the extent of crack filling, will be presented and commented upon. Keywords: hydraulic grouts, injectability, structural restoration, architectural members, fine cracks, bonding, microstructure, durability, pozzolan, white cement.

© 2005 WIT Press WIT Transactions on The Built Environment, Vol 83, www.witpress.com, ISSN 1743-3509 (on-line)

Structural Studies, Repairs and Maintenance of Heritage Architecture IX 461

1 Introduction

The Parthenon Opisthodomos has suffered serious structural damage, mainly due to the big fire of the 3rd century A.D. and the explosion of the building in 1687, [1]. The column drums presented loss of their original mass, displacements and numerous cracks. The most significant cracks were almost vertical, fig. 1a and 1b, and they were often bisecting the drum and in some cases running in parallel levels. Apart from these main cracks, there were also numerous secondary ones reaching only to a certain depth, without intersecting the whole drum. Detailed measurements showed that the width of these cracks, in the drums’ mass, varied between a few tenths of a millimetre to a few millimetres, while on the external surface of the drum, it even reached up to one or two centimetres in some places, [1].

Figure 1a: View of the column drum

1.2. before intervention. Figure 1b: Survey drawings of the

cracks of column drum 4.4.

According to the study for the structural restoration of the Opisthodomos, [1], the in-situ structural restoration of the columns was decided, instead of dismantling them. In fact, dismantling would require the reworking of the top and bottom surfaces of the drums, during the reassembling, in order to assure a correct joint. The proposal for the structural restoration of the columns drums included the filling of the fine cracks with suitable hydraulic grouts in order to assure a degree of bonding, which with the help of the uneven internal surfaces of the fragments would further assure their contribution in case of shear loading. Thus, the objective of the intervention was the structural restoration of the columns by bonding together the various drum fragments, while retaining the structural independence of each column drum and the existing structural system of the columns. The accomplishment of this objective presented significant difficulty and particularity, because, in order to fill the fine cracks of each drum by injecting a grouting material, the whole procedure should be applied under low pressure and working from bottom to top. Hence, the injected grout had to penetrate through the base of each drum. Therefore, it was considered necessary to design and apply two different types of hydraulic grouts, providing different levels of structural strength: one for the drums, able to develop strength and adequate bonding with the ancient marble, so that the cooperation between their fractured pieces to be re-established, and one for the areas of the joints between the drums, of a lower strength to avoid bonding of the in between surfaces.


462 Structural Studies, Repairs and Maintenance of Heritage Architecture IX

On the other hand the design criteria for the hydraulic grout composition and the injections application had to take into account, not only the strength requirements, but also those relative to reversibility, compatibility with the marble, and durability, so that in no case would this intervention have any harmful action on the ancient architectural members. In addition to that, the grout, in its liquid state, should also have high injectability in order to be able to penetrate and fill these fine cracks under low pressure, without disturbing the sensitive balance of the fragmented drums. The simultaneous satisfaction of the above-mentioned requirements depends on mutually competing parameters. For this reason, in addition to the existing bibliography on the subject, [2, 3, 4, 5, 6, 7], various research projects and studies were accomplished for the design and application of the hydraulic grout injections, [8].

2 Design methodology

Based on the bibliography, it was decided that the hydraulic grouts should be composed of white cement and pozzolan, as the satisfactory behaviour of such a combination has already been well documented, regarding, both durability and strength requirements, [9, 10, 11, 12, 13]. After laboratory tests on the granularity and the physicochemical characteristics of different raw materials, the white Danish cement and five pozzolanic materials grounded so that max d<20µm [four natural pozzolans from Greece, Milos earth (ME), Santorin earth (SE), pozzolan of Milos (PM), and pumice (P) and an artificial pozzolan, a white silica fume from Norway (SF)], were chosen for the solid phase of the grout. Then, for various combinations of white Danish cement with each one of the pozzolanic materials, high injectability grouts were designed and their tensile strength was tested. This research led to the selection of two grout compositions per pozzolanic material, one for the strong and the other for the weak grout. The performance of these grouts was further studied, concerning the evolution of their strength and bonding to the marble, their microstructure, and their durability. The results were comparatively evaluated, and the pozzolanic material that had the optimum behaviour was selected for the two grouts to be applied in situ.

3 Injectability into fine cracks

The problem of injecting and filling fine cracks without the development of clogging, using hydraulic grouts (that is, with granular materials in the form of diluted suspensions) has been of great interest for the international scientific community for quite some time. Today, after extensive research and implementation, tested methods to conduct the design of hydraulic grouts and to realistically determine their injectability into fine cracks have been defined. In this project, the design of high injectability grouts was performed on the basis of specific criteria proposed in the literature concerning both the granularity of the materials, [2, 3] and the water ratio, [2], in order to ensure high



injectability of the grouts even in cracks of one or two tenths of millimetre width. To this purpose, the penetrability, fluidity and stability characteristics of the suspensions were fully examined. The standardized sand column test method (NF P 18-891, pr. EN 1771), [7], was used to check the penetrability and fluidity along with the standard apparatus for testing the fluidity (NF P 18-358) and stability (NF P 18-369) of the suspension. Concerning the mixing procedure, an ultrasound dispersion mixer was used assisted with a mechanical device of low turbulence, [2, 4]. For various ratios of white cement and pozzolanic material (90/10, 75/25, 60/40, 20/80) grouts were prepared in the laboratory with a gradual increase of the water percentage, and then tested as above mentioned. In order to determine the optimum percentage of water in each case, a time limit of 50 sec was set for the sand column penetrability test (T36), [4], as well as a maximum acceptable limit of 2% for the bleeding test. For each white cement-pozzolan ratio, all the results were reported into injectability diagrams in order to show comparatively both the time required to pass through the sand column and the bleeding percentage, as a function of the water ratio. Thus, the optimum water ratio was determined, according to the already set limits. Figure 2 shows the injectability diagram for a cement-pozzolan ratio of 75/25. In this case a water-to-solids ratio of 0.8 was selected. Furthermore, the apparent viscosity versus water percentage curve, also presented in Figure 2, proves that for the selected water to solids ratio, the fluidity has reached its highest limit and cannot be further increased. Moreover, the splitting tensile strength of the grouts was determined by testing the injected sand column cylindrical specimens (NF P18-892). Taking into account, both the injectability characteristics and the tensile strength, two grout compositions per pozzolanic material were chosen for additional comparative tests, one for the strong grout, containing 75% cement and 25% pozzolanic material and one for the weak grout, containing 20% cement and 80% pozzolanic material.

Figure 2: Injectability diagram for cement-pozzolan mixture at 75/25 ratio

versus the water-to-solids ratio.



Finally, to test the injectability under realistic on site conditions, pilot grout injections were applied on old fractured marble pieces, as well as on new ones, which were broken in two and were rebonded by injecting the grout. These applications confirmed the high injectability capacity of the grouts and allowed improvement of the preparation of the fractured columns for the injections, as well as the injection equipment.

4 Adhesion of grout and marble

The bonding strength of grouts to the marble was determined by direct tensile strength tests, carried out on specimens consisting of two marble pieces (each piece had: d=5cm, h=7,5cm) that were bonded together using the grout. Both the strong and weak grout compositions were tested for each one of the five pozzolanic materials, for joint widths of 1 and 3 mm, and for curing times of 60, 180 and 365 days. The specimens were kept in laboratory conditions of 80% RH and a temperature of 20o C. Some specimens underwent an accelerated curing process in a salt-spray (ASTM B-27) chamber and others in a sulphating chamber. The charts in figure 3 present the results for the strong grouts tested for curing time of 12 months, as well as those of the weak grouts tested for curing time of 6 months. In the case of the strong grout, the mixtures containing Milos earth, Santorin earth or pumice reached a strength ≤ 2 MPa, value that was set as an upper limit to avoid marble failure. The mixtures containing Pozzolan of Milos had tensile bond strength higher than this specific limit, while the mixtures containing silica fume had a very low one. Thus, only the mixtures containing Milos earth, Santorin earth or pumice satisfied the accepted bonding strength requirements (ftb≤2MPa). In the case of the weak grout, it was proven, fig. 3b, that all the compositions had developed low tensile bonding strength, as required for the grout to be used for filling the joints between the drums.

Figure 3a: Tensile bonding strength

of strong grout with marble at curing age of 12 months.

Figure 3b: Tensile bonding strength of weak grout with marble at curing age of 6 months.



5 Microstructure of grout marble interface

The marble and grout microstructure in samples taken from the joints of specimens of adhesion tests was examined by mercury porosimetry. The porosity of marble was found to be approximately equal to 1%. Figure 4a illustrates the pore size distribution of the strong grout at curing ages of 6 and 12 months, respectively. As it was expected, after twelve months curing time the paste proved to be more cohesive, the porosity had turned from approximately 40% to 30%, while the wide pores almost disappeared, mainly because of the products of hydration, which had been almost completed at this time. This was a positive outcome, since the deterioration processes of such materials is more likely to start through the wider pores. In the case of the weak grout, the porosity, as anticipated, was particularly high. Examination of the interface between the marble and the strong grout by electron scanning microscopy, showed very good adhesion, fig. 4b. The use of ultra fine pozzolans in the grout composition seems to enhance the adhesion by developing not only a chemical but also a mechanical bonding with the marble, already at an age of 6 months. After twelve months these conclusions were more prominent. The solidified grout was more uniform and cohesive and no signs of disjoining of the marble were visible.

Figure 4a: Pore size distributions of the strong grout at different curing times.

Figure 4b: Details at the interface between marble and strong grout by means of electron scanning microscopy at ages of 6 and 12 months, respectively.

6 months 12 months

x 630 x 1050



In the respective examination by means of electron scanning microscopy on specimens, which had undergone an accelerated curing process in a sulphating chamber, the elementary microanalysis on the grout, near the area of the interface, showed the existence of sulphates, something that was not noticed in the adjoining marble. Therefore, even in the exceptional case of attack by sulphates, it is likely that, while the grout may be attacked, the marble will not be affected.

6 Durability of grouts

In order to determine the durability of the various grouts, capillary absorption tests (RILEM II-6) were also carried out, under constant supply of water, sea water and sodium sulphate solution. Figures 5a, 5b present the respective diagrams for strong grouts. It is to be noted that the composition containing Santorin earth showed low absorption in all cases. Low rates of absorption were also noticed with the composition containing Milos pozzolan. Furthermore, all the specimens were left for five months under the influence of salts, and did not present any alteration. In the case of the weak grout the results were similar. Santorin earth as in the case of strong grout had the lowest rate of absorption. In the weak grout specimens, however, salt crystallization phenomena were detected after a period of five months. For this reason, it was decided, to use the strong grout for the base of the first drum of all the columns.

(a)

(b)

Figure 5: Absorption diagrams of the strong grouts in (a) sea water and (b)

sodium sulphate solution.



7 Selection of grout compositions for application

The comparative evaluation of all the results led to the conclusion that the high injectability grouts containing Santorin earth proved to have a very good adhesion to the marble and the best durability characteristics. Therefore the composition containing 75% white Danish cement and 25% ultra fine Santorin earth was chosen for the strong grout to be applied in situ, while the composition containing 20% white Danish cement and 80% ultra fine Santorin earth was chosen for the weak grout.

8 Application methodology

For the application of grouting a special preparation of the columns was necessary, which included thorough cleaning of the interior of the cracks, insertion of very fine plastic tubes (d: 0.8-2 mm) and sealing of cracks and joints with suitable mortar [14]. The grout was injected in different phases. Each phase started from bottom to top, initially with the strong grout. Five centimetres before the base of each drum, the strong grout was replaced with the weak one. The injection was continued until the grout reached five centimetres over the joint between drums. The next phase was initiated several days afterwards, fig. 6. The grout stability was checked for every batch of material prepared, by measuring the bleeding and density. The density was measured not only after mixing, but also on samples collected from various grout exit tubes. It was noticed that bleeding and density did not change significantly, fig. 7, [15], ensuring the quality of the grout and of its application process.

Figure 6: One column drum and two joints just after the grout injection The strong and weak injected materials can be distinguished by their light and dark colour, respectively.



Figure 7: Calendar notes of injected grout application (drum 2.5). Mapping of

damages on four quadrants, noted position of pipes, entry and exit inchronological order, evaluation of the cracks before and after theintervention, and bleeding and density test results of the injectedmaterial (initially and at various points of exit).

Figure 8: Drums 1.2 and 2.4 after their restoration.

After the completion of the injection all the plastic tubes were removed and the tube holes and cracks were sealed with an adequate mortar, fig. 8. The application project was carried out by the Conservation team of the Parthenon.

9 Conclusions

The design and application methodology of high injectability hydraulic grout injections presented above permitted the structural restoration of the Opisthodomos columns in situ, instead of their dismantling. All the conducted

2.4 1.2



studies for this project and the fully controlled implementation process allowed the filling of the very fine cracks of the fragmented drums, without bonding the adjoining bottom and top surfaces of the drums. The fragmented drums were structurally restored, while maintaining the structural independence of the column drums, thus preserving the existing structural system of the columns. Moreover, this original and specialized intervention contributed to the further investigation and development of the possibilities of the technique of high penetrability hydraulic grout injections. This knowledge will be very useful for further structural restoration interventions of monolithic architectural members of other monuments.

Acknowledgements

The constant support of the members of the Acropolis Monuments Conservation Committee and especially of its President Professor Ch. Bouras is gratefully acknowledged by the authors of this paper. Special compliments are addressed to Professor Th. P. Tassios for his essential contribution to the evaluation of the results for this project. The valuable collaboration of Dr A.M. Paillere and J.J. Serrano (LCPC, France), as well as of Professor Th. Skoulikides, Professor S. Kollias, Dr M. Katsakou (NTUA, Athens), Dr. Ch. Malami , Dr V. Kaloidas, Z. Tsimbouki (HCRC Ltd, Athens), Dr O. Chignon (Origny S. A. France), S. Economopoulos, G. Dogani and Cl. Papastamatiou and M. Naka (YSMA) is also acknowledged.

References

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[2] Miltiadou, A.E., Etude des coulis hydrauliques pour la réparation et le renforcement des structures et des monuments historiques en maçonnerie, PHD Thesis, Ecole Nationale des Ponts et Chaussées, Paris, 1990, published in the Collection "Études et recherches des Laboratoires des Ponts et Chaussées", série Ouvrages d'art OA8, ISSN 1161-028X, Paris, France, 1991.

[3] Paillere, A.M. & Guinez, R., Recherche d'une formulation de coulis a base de liants hydrauliques pour l'injection dans les fines fissures et les cavités, Buletin des Laboratoires des Ponts et Chaussées, 130, Paris, pp. 51-57, 1984.

[4] Paillere, A.M., Buil, M., Miltiadou, A.E., Guinez, R., & Serrano, J.J., Use of silica fume and superplasticizers in cement grouts for injection of fine cracks. Proc. of the 3rd Int. Conf. on Fly Ash, Silica Fume, Slag and Natural Pozzolans in Concrete, 2, Trondheim, pp.1131-1157, 1989.

[5] Miltiadou, A.E, Paillere, A.M., Serrano, J.J., Denis, A. & Musicas, N., Formulations de coulis hydrauliques pour l'injection des fissures et cavités des structures en maçonnerie dégradées, Proc. Conf. Int. Tech. Cons.



structurelle de la maçonnerie en pierre, Athènes, 31 oct.-3 nov., pp.299- 312, 1989.

[6] Paillere, A.M., Serrano, J.J. & Miltiadou, A.E, Formulations de coulis hydrauliques pour l'injection de fines fissures et cavités dans les structures dégradées en béton et maçonnerie, Bulletin des Laboratoires des Ponts et Chaussées, Ref. 3676, pp.61-78, 1993.

[7] Paillere, A.M. & Rizoulieres, Y., Réparation des structures en béton par injection de polymères, Bulletin des Laboratoires des Ponts et Chaussées, 96, pp.17- 23, 1978.

[8] Miltiadou-Fezans, A., Papakonstantinou, E., Zambas. K., Panou, A., & Frantzikinaki, K., Structural restoration of the column drums of the Opisthodomos of the Parthenon with hydraulic grouts of high penetrability: recherch, design and application, Proc. 5th Int. Meeting for the Restoration of the Acropolis Monuments, Athens, 4.-6 oct., pp.161- 178, 2002.

[9] Lea, F.M., Lea's chemistry of cement and concrete, 3rd ed., London, 1988. [10] Massazza, F., Pozzolanas and pozzolanic cements, Cement -Br. 1/1980-

81, March 13, Zagreb: pp.3-17, 1980. [11] Ftikos, Ch., Study of the activity of Santorin earth on cement hydration.

Thesis, Faculty of Chemists-Engineers, NTUA: Athens, 1977. [12] Kalogeras, A.N. & Tassios, Th. P., The fine Santorin earth as additive in

concrete, Technical Chronicles, 409-410, Athens, pp.327-344, 1958. [13] Mehta, P.K., Studies on blended Portland cements containing Santorin

earth, Cement and Concrete Research, 11, pp.507-518, 1981. [14] Dogani,G. & Papakonstantinou, E., The works performed at

Opisthodomos columns - 1996-1997, typed report, No 763, ESMA Archives: Athens, 1996.

[15] Panou, A., Papastamatiou, Cl. & Frantzikinaki, K., Filling the cracks of the Opisthodomos columns with hydraulic grouts, typed report, ESMA Archives, No 786, ESMA: Athens, 1998.



design and application of hydraulic grouts of high ...design and application of hydraulic grouts of...

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