The Recovery of the Walls of the Moorish Castle

Transcription

1 The Recovery of the Walls of the Moorish Castle Abstract: The objective of this dissertation for the master degree in Civil Engineering, was to assess the conservation condition of part of the walls of the Moorish Castle in Sintra, and to contribute to its recovery. The interventions occurred in these walls during their lifetime were analyzed following a methodology not very much utilized in Portugal but common in several cases abroad: Archaeology of Architecture. The application of this method, in a simplified version, helped in the determination of the different construction phases and the identification of the necessary methods and materials for the wall recovery. For the study a representative section of the walls was chosen. This choice was justified not only in terms of dimensions but also because the section presents the various interventions and the detectable pathologies that occur in the rest of the wall. The pathologies were analyzed and it was possible to find the locations where interventions are necessary. Several studies and proposals for intervention are made. The analysis of the mortars enabled their characterization and confirmed the existence of different construction phases. For the wall recovery the use of a suitable trace mortar, compatible and aesthetically acceptable, is proposed. Key-words: castle walls, recovery, construction phases, mortars Introduction Today, the walls of the Moorish Castle present several pathologies, from the biological colonization or even partial destruction. The paper proposes the identification of these pathologies, the source of their causes and a proposal to consolidate the walls in future recovery works. From the historic research carried out in this study, the Moorish Castle had several interventions in the course of its existence. Nevertheless, only four of these interventions are considered as construction phases: Moorish (VIII Century), D. Fernando II (XVIII Century), DGEMN (1939) and a recent limited intervention (1986) (Morgado, 1998). Methodology and yours application Archaeology of Architecture Overlaps, adjustments, replacements or demolitions usually occur in the architectural heritage. In this sense, a construction stage is the result of a long sequence of additions and subtractions on the initial construction (Ramalho, 2002). The historic importance of this heritage building is too important to be forgotten. Archaeology of Architecture is a new specific discipline of registration and interpretation of the built heritage that also facilitates its description. With the method it is possible to identify historical pathologies, to date some structural defects and to analyse how the construction has reacted to different past interventions. This archaeologyical field can also help interventions, simplifying the prescription of necessary and appropriate solutions. i

2 Archaeology of Architecture, based on a deep and credible historical research, has a methodology that can be described in the following steps (Caballero Zoreda, 2006): identification of stratigraphic units. These units consist in the separation of zones that were added or removed; Study of stratigraphic relationships between units. This study can be called stratigraphic analysis and is based on stratification principles, an Archaeology field. Creation of a diagram of stratigraphic relationships. This diagram presents all stratigraphic units in a chronological matrix form, ordered from the oldest to the most modern, from the bottom to top. It represents precedence shares and correlations between units. Archaeology of Architecture applied to the case study In this case study, a representative section of the Walls of the Moorish Castle was chosen. The next figure shows all its stratigraphic units. It is important to enhance that this interconnected step with the Moorish Castle history, permits to distinguish different castle construction phases. Some mortar samples were taken in the stone masonry joints in order to analyse the relationship between the stratigraphic units and the construction phases (results from the historical research) and the relations between units. Figure 1 - Stratigraphic units (black and white) and sample labels (blue) ii

3 Characterization of the mortars Five mortar samples were taken. They are represented in table 1. In the supposed Moorish construction phase three samples were colleted (1A1, 1A2 and 2A). The length of this long period does not permit an easy distinction of the mortars collected. Therefore it was considered as part of original construction phase all constructions also made at the time of the D. Afonso Henriques and D. Sancho I. Table 1 - Sample zone and its construction phase Sample Sample zone Construction phase 1A 1 U1 Moorish 1A 2 U1 Moorish 2A U1 Moorish 3A Similar to U2 D. Fernando II 4A U5 DGEMN - century XX The bad condition of sample 1A 1, justified the necessity of collecting a second sample, 1A 2, also representative of this construction phase. Sample 3A belongs to the D. Fernando II construction phase (XIXth Century). Sample 4A, corresponds to the XXth century construction phase. Objectives and conclusions of the analysis of mortars The main objective of these analyses was to determine the components and proportions of the materials of the mortars. From this analysis, it is possible to conclude (Velosa, 2010): The main constituents of the mortars are lime and silica sand, respectively as a binder and aggregate The mortars belonging to the studied wall section (1A 1, 1A 2, 2A, 3A and 4A) may contain loamy sand, given the presence of clay minerals Mortars 1A 1, 1A 2 and 2A contain soluble salts, like sulphates, in the form of bassanite and/or plaster. The presence of bassanite is probably caused by the process of analysis of the mortars, which indicates the presence of plaster The more common traces are 3:7 in mass (about 1:1 in volume) and 1:9 (between 1:3 to 1:4 in volume). These results shall be useful to formulate a mortar traces that can be used in the recovery of the walls of the Moorish Castle. iii

4 Proposed recovery In this intervention some requirements must be taken into account: The use of traditional building techniques; The maintenance of the formal features of the building, with no addition or subtraction of the discharacterize constructive elements; Traditional and modern materials must be compatible; The reuse of original elements, like the stone blocks fallen from part of the wall, always if possible. Classification of Pathologies and intervention decisions The decision criteria defined by Veiga (2007) were: Take into account the value of the building and, in particular, its constructive elements; Assess the building conservation, in terms of the severity of each pathology and its reparability condition; Assess the availability of different technologies, and of human, opportunity and fund resources. As for the building conservation status, the same document was used, which helped on the classification of the severity of pathologies (Table 2): Degree of degradation caused by the pathology: High Medium Reduced Each type of pathology has a minimum recommended intervention: Maintenance Located superficial repair Located repair Consolidation Partial replacement Total replacement The high cultural value of the Moorish Castle justifies, in most cases, the minimum recommended intervention. Dirt was detected in small scale and therefore attributed the degree of reduced degradation. This pathology needs maintenance and was classified of severity 1 The important extension of the area covered by biological colonization, justifies the attribution of high degree to this pathology. It was classified as severity 3, and the option between minimum intervention or located repair was chosen. iv

5 The most important pathology is the loss of cohesion due to the missing mortar in stone masonry joints. It was attributed a high degree of degradation and severity 5, requiring partial replacement of the mortar joint. The partial destruction detected is the result of the collapse of wall panels. It was classified as severity 4, with a medium degree of degradation, advising minimal intervention as the consolidation of the wall. Finally, analyzing the latest pathology, the presence of weed vegetation was found in the zone of partial destruction as described above. It was considered a pathology with medium degree of degradation, classified as severity 3, and the partial substitution, corresponding to the minimum intervention, was advised. Table 2 - Criteria of Intervention Choice Type of Minimum Value of Choice of Degree Classification pathology intervention building intervention Dirt Reduced Maintenance Severity 1 Maintenance Biological colonization High Located repair Severity 3 Located repair Loss of Partial Partial High Severity 5 cohesion replacement High replacement Partial destruction Medium Consolidation Severity 4 Consolidation Weed vegetation Medium Located repair Severity 3 Located repair Studies of mortars in similar cases It is important to ensure mechanical, water and climate characteristics in selecting mortars for the recovery of the Castle walls (Veiga, 2002). Veiga (2003) studied the use of possible mortars for interventions in old buildings. From that study it can be concluded that: The cement mortars are too rigid. This characteristic confers a resistance higher than recommend. They transmit excessive forces to the support, causing a too fragile rupture. These mortars are not recommended for the present walls. Artificial hydraulic lime mortars are also too "strong" and sensitive to cracking. On other hand, natural hydraulic lime appears too weak". The lime mortars have acceptable mechanical properties. However, the introduction of pozzolan and hydraulic binders in lime mortars tends to improve their mechanical and behaviour to water characteristics. Mortars have, generally, a good water behaviour. v

6 To obtain better mechanical resistances it is advised to use a combination of river and clay sands instead of river sand only. For the recovery of the Moorish Castle walls, mortars with a trace of lime and hydraulic lime were chosen. Choice of Mortar Some of the more modern mortars analyzed have traces with 3:7 in mass (1:1 in volume), with high binder concentration while the older ones showed much lower levels of binder with a trace 1:9 in mass (1:4 in volume). Therefore, it seams preferable to select an intermediate trace instead of one as rich as 3:7 or one as poor 1:9 A 1:3 in volume trace was thus selected, with a binder composed of hydrated lime and free salts hydraulic lime (NHL 3.5) and river sand and Sintra s grit as aggregate. In this formulation, the amount of the hydraulic component in the binder was taken in account. The trace in volume was formulated as 1:2 (hydrated lime:hydraulic lime) and the proportion grit:river sand as 6:3 in volume. In conclusion, a trace of 1:2:6:3 (lime, hydraulic lime, grit, river sand) was recommended. The Sintra s summer season conditions are favourable to the mortar (lime carbonation process), due to the daily humidity cycle. In addition, hydraulic lime free of salts was added to the formulation to accelerate the initial mortar harden. It is proposed to mix local grit to river sand in the aggregate composition. Although the chemical characteristics of the grits are unknown, it is clayey, siliceous and derives from granite. This is a guarantee that its application in the granite masonry of the walls is compatible In the second aggregate, is advisable to use a siliceous river sand with a granulometric curve similar to that of the mortar samples analyzed. Conclusions The historical and cultural importance of the Moorish Castle, located in an extraordinary environment, listed as World Heritage, lead to a recovery proposal, of an exemplary intervention in order to preserve its values. The discipline of Archaeology of Architecture was applied and proved essential to assess the conservation condition of the Moorish Castle walls. Each construction phase was individually studied for an integrated intervention proposal, compatible with the historic memory, materials and constructive methods present in the castle As an important limitation, the lack of knowledge in disciplines like Archaeology, Architecture, and Chemistry has not permitted, as desired, a full application of the method of the Archaeology of Architecture. vi

7 Bibliography Caballero Zoreda, L. (2006). Arqueología de la Arquitectura. Conocimiento e intervención. In Património estudos nº9. Lisboa: IPPAR. Morgado, F., & Magalhães, F. (1998). Sintra. In À Descoberta das Sentinelas - Roteiro de Castelos e Fortalezas da Região de Lisboa e Vale do Tejo (pp ). Lisboa: Comissão de Coordenação da Região de Lisboa e Vale do Tejo. Ramalho, M. d. (2002). Arqueologia da Arquitectura. O método arqueológico aplicado ao estudo e intervenção em património arquitectónico. In Património estudos nº 3. Lisboa: IPPAR. Veiga, M. d. (2003). Argamassas para revestimento de paredes de edifícios antigos. Características e campo de aplicação de algumas formulações correntes. Encontro sobre Conservação e Reabilitação de Edifícios. Lisboa: LNEC. Veiga, M. d. (2007). Materiais e técnicas construtivas tradicionais. Revestimentos de paredes antigas: Argamassas, Rebocos, Estuques e Pinturas. LNEC Veiga, M. d., & Tavares, M. (2002). Características das Paredes Antigas.Requisitos dos Revestimentos por Pintura. A indústria das tintas no início do século XXI (pp. 1-5). Lisboa: APTETI. Velosa, A. L. (2010). Análise da Composição e do Estado de Patologia de Argamassas do Castelo dos Mouros - Sintra. Universidade de Aveiro, Departamento de engenharia Civil, Aveiro. vii