infrastructures Article
Experimental Study of the Mechanical Behaviour of Bricks from 19th and 20th Century Buildings in the Province of Zamora (Spain) Ana Belén Ramos Gavilán 1, * , María Ascensión Rodríguez Esteban 2 , María Natividad Antón Iglesias 2 , María Paz Sáez Perez 3 , María Soledad Camino Olea 4 and Julen Caballero Valdizán 2 1 2 3 4
*
Mechanical Engineering Department, University of Salamanca, 49022 Zamora, Spain Construction and Agronomy Department, University of Salamanca, 49022 Zamora, Spain;
[email protected] (M.A.R.E.);
[email protected] (M.N.A.I);
[email protected] (J.C.V.) Architectural Construction Department, University of Granada, 18071 Granada, Spain;
[email protected] Architectural Construction IT MMCC TE Department, University of Valladolid, 47014 Valladolid, Spain;
[email protected] Correspondence:
[email protected]; Tel.: +34-980545000-3728
Received: 31 July 2018; Accepted: 11 September 2018; Published: 16 September 2018
Abstract: Interventions in historic brick buildings require an exhaustive analysis of the current characteristics of bricks in order to establish the role performed by these elements in the buildings. This study presents the results of an experimental analysis of the compressive strength of brick specimens extracted from different buildings built in the 19th and 20th centuries in the province of Zamora (Spain). The study analyses specimens with very different characteristics to compare results from different masonry units and manufacturing processes. Specimens are classified into four groups according to their macroscopic and microscopic analyses. Compressive strength results are correlated to the above classification and to the results of density, absorption and open porosity of the samples. The compressive strength results present high variation between clay bricks (9.2–64.4 N/mm2 ) and between samples extracted from the same brick due to the heterogeneity of the material. Correlations between compressive strength and open porosity, absorption and dry density values are observed, with less dispersion in the case of high sintering level, up to 1000 ◦ C. Finally, the compliance with the current Spanish Technical Building Code with respect to their compressive strength is checked. Keywords: compressive strength; historic bricks; restoration and rehabilitation
1. Introduction Many studies on interventions in historical masonry buildings, such as those conducted by Binda et al. [1], Papayianni and Stefanidou [2], Lourenço and Fernandes [3], Brandonisio et al. [4] and Vintzileou [5], point to the importance of knowing the manufacturing conditions and the compressive strength, as well as the compatibility with other materials. The mechanical analysis of bricks is common in many of them, including the works of Fernandes and Lourenço [6], Singha, et al. [7], Matysek et al. [8], Balasubramanian et al. [9], Azeez et al. [10], Pérez-Gálvez et al. [11], Brozovsky et al. [12] and Bajare et al. [13]. Because of the difficulty of extracting samples, estimates of the bearing capacity of brick walls based on empirical formulas and analytical models that use the bricks and mortar strength are very useful. European Standard EN 1996-1-1 [14] and different research works, such as Sahlin [15] and Kaushik et al. [16], collect some of the most significant methods. Numerical models based on mechanical properties of the constituents reduce the difficulties associated with masonry laboratory tests. Computer
Infrastructures 2018, 3, 38; doi:10.3390/infrastructures3030038
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compressive strength of masonry buildings, as reported by Lemos [17], Barbosa et al. [18], Uday et al. [19] and Sousa [20]. the mechanical behaviour and compressive strength of masonry buildings, as simulations can predict Thisby paper analyses the results compressive strength tests carried reported Lemos [17], Barbosa et al. of [18], Uday et al. [19] and Sousa [20]. out on ancient clay brick samples extracted from facades of different buildings built in the 19th and centuries the This paper analyses the results of compressive strength tests carried out 20th on ancient clayinbrick province of Zamora during their intervention workinincludes the samples extracted from(Spain) facades of different buildings built in or the demolition. 19th and 20thThe centuries the province experimental analysis of the porosity, absorption and density, wellincludes as the macroscopic and of Zamora (Spain) during their intervention or demolition. The as work the experimental microscopic study of theabsorption material. The strength clay bricks isand related to their physical analysis of the porosity, andcompression density, as well as theofmacroscopic microscopic study of properties, and manufacturing the material.origin The compression strengthprocess. of clay bricks is related to their physical properties, origin and Lastly, theprocess. study checks on compliance with the requirements of BD SE-F of the Spanish manufacturing Technical [21], which facilitates therequirements evaluation of state of ofthe conservation of the Lastly,Building the studyCode checks on compliance with the of the BD SE-F Spanish Technical building, required Lawfacilitates 8/2013 LRRRU [22]. Building Code [21],by which the evaluation of the state of conservation of the building, required by Law 8/2013 LRRRU [22]. 2. Brick Specimens 2. Brick Specimens This study was carried out on 15 ancient clay bricks from buildings located in different This study carried out on 15 ancient clay buildings bricks from buildings located different municipalities of was the province of Zamora. The selected were built between theinend of the municipalities of the the beginning province of The selected were built between the end of 19th century and of Zamora. the 20th century. Most buildings of them originate from Toro, where brick the 19th century and the beginning of theat20th Most of century, them originate from Toro, whereinbrick building construction greatly increased the century. end of the 19th or were manufactured the building construction greatlyin increased at the end 19th century, or were the San Antonio Factory, located the municipality ofof Elthe Perdigón. The study also manufactured includes a clayin brick San Antonio Factory, located in the municipality Elthe Perdigón. The study also includes a clay brick from the municipality of Otero de Bodas, locatedofin Sanabria-La Carballeda Area, and another fromfrom the municipality of Otero Bodas, located in thewere Sanabria-La Carballeda Area, by andaanother one one Entrala. Most of thedeclay bricks analysed traditionally produced handmade from Entrala. of manufactured the clay bricks in analysed were traditionally producedorbymoulded a handmade process, process, exceptMost those San Antonio Factory by extruded process. The exceptused thosecome manufactured in San Antonio Factory extruded moulded process. The clays used clays from different facies, mainly frombyEntrala andorTierra de Campos. Therefore, the come from different facies, mainly from Entrala and Tierra de Campos. Therefore, the study analyses study analyses samples with different origins, manufacturing processes, surface finishes and physical samples with different origins, manufacturing processes, surface finishes and physical properties. properties.
Macroscopic and Macroscopic and Microscopic Microscopic Study Study Prior to to the the mechanical mechanical analysis analysis of of bricks, bricks, an an initial initial visual visual inspection inspection and and an an optical optical microscopy microscopy Prior analysis were were carried carried out. out. This This initial initial study study facilitates facilitates the the specimen specimen description description based based on onpeculiarities: peculiarities: analysis inclusions, phases, textures, flow lines caused by the manufacturing process, interaction inclusions, phases, textures, flow lines caused by the manufacturing process, interaction between between minerals, sintering sintering and minerals, and firing firing processes, processes, reactions reactions between between particles, particles, etc. etc. The analysed analysed bricks bricks are are classified classified into into four to the and their their The four groups groups according according to the visual visual inspection inspection and behaviour during the cutting process. Group number one (G1) is made up of bricks 1, 6 and 8. behaviour during the cutting process. Group number one (G1) is made up of bricks 1, 6 and 8. These These specimens softdetected zones detected visual inspection andprocess, cuttingwhich process, which have specimens presentpresent soft zones by visualby inspection and cutting have yellowish yellowish colour because of the low content in iron oxides [23–30], and cracks between macro phases. colour because of the low content in iron oxides [23–30], and cracks between macro phases. A detail A of oneclassified sample classified as G1 isinshown Figure 1a. of detail one sample as G1 is shown Figurein1a.
(a)
(b)
(c)
(d)
Figure 1. Brick classification based on macroscopic analysis: (a) G1; (b) G2; (c) G3; (d) G4.
Bricks 2, 5, 7 and 9 form group number two (G2). The visual inspection of these bricks identify identify granular texture because of the sand particle content, as as can can be be seen seen in in Figure Figure 1b. 1b. These specimens specimens present present vitreous vitreous zones, zones, Clay bricks 3, 4 and 10 form the third third group group (G3). (G3). These identified by optical microscopy, and large visible purple and dark red areas identified by optical microscopy and visual inspection. Clay bricks of this group present hardness when cut, and their
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microscopy and visual inspection. Clay bricks of this group present hardness when cut, and their optical microscopy analysis reveals a solid cohesion, since there are no necks between particles, the initial stage of sintering [31]. Figure 1c shows a brick sample classified as G3. Finally, the fourth group (G4) is made up of moulded and extruded bricks manufactured in San Antonio Factory, which correspond to specimens 11 to 15. These bricks show flow lines due to the shaping process, as shown in Figure 1d, which could weaken some load directions. Table 1 summarizes the main results obtained in the visual inspection and optical microscopy study of each specimen, with T representing the estimated firing temperature, D the disintegration or detachment of particles during the handling of the pieces, R the reaction between mineralogical components during firing, Df the silica diffusion and breakage after firing, I the final interaction between the clay minerals, and C the red colour due to the higher content of iron oxides. D and C are visually assessed, R, Df and I are identified by optical microscopy, and T is estimated through visual inspection and optical microscopy. Since the range of temperatures from 900 to 1000 ◦ C is suitable for the firing/sintering of bricks, the presence of necks between particles reveals a low sintering level, under 900 ◦ C, and the presence of visible dark-coloured areas reveals a sintering temperature over 1000 ◦ C [23–25,28,29]. Table 1. Description of the specimens analysed in the study. Clay Brick
Test Specimens
Origin
Production
Microscopic Analysis 1
Group T
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
8 15 4 3 2 8 1 2 11 4 12 11 8 6 4
Toro Toro Toro Toro Toro Toro Toro Toro Entrala Otero Bodas El Perdigón El Perdigón El Perdigón El Perdigón El Perdigón
handmade handmade handmade handmade handmade handmade handmade handmade handmade moulded moulded moulded extruded extruded moulded 1
G1 G2 G3 G3 G2 G1 G2 G1 G2 G3 G4 G4 G4 G4 G4
◦C
1000 ◦ C
