3. 4. 1 Introduction
Guadalajara, Mexico is located at 20°40'N and 103°19'W with an altitude of 1589 m above sea lev-el. It is the capital of the state of Jalisco and is the second largest city in Mexico today. Guadalajara was founded in 1532 under the name of Espiritu Santo by the Spaniards and was built as a grid of streets. Throughout the 17th and 18th centuries, Guadalajara increased its wealth and influence by importing goods from the Pacific coast and distributing them to the rest of Mexico. The region also achieved a greater stability by negotiating peaceful settlements with the indigenous tribes.
During the war for independence, the people of Guadalajara freed themselves by defeating the loy-alist militia at Zacoalco on the 4th of November 1910, which opened the way for Hidalgo’s new army to take the city of Guadalajara a few weeks later. Moreover, during the Mexican Revolution of 1910 the state of Jalisco and Guadalajara became a battleground again. Shooting-marks can be also found at some walls of the church.
The church of Santa Mónica is located in the historical centre of Guadalajara and is one of the old-est churches in the city. This building was once part of a monastery and was erected in the first half of the 17th century. The church is an outstanding representation of Mexican Baroque because of the richly decorated facades (Fig. 75) and has a dimension of 12 x 64 meters in size and 14 meters in height (Fig. 74). Two portals with Solomonic twisted columns decorate the baroque facade, where they are covered with rich and intricately carved ornamentations, including grapes, cobs of maize, angels, double eagles and symbols of religious orders. As a model for the different decorations, the cathedral of Cajamarca in Peru (built from 1682-1762) was possibly used as an example. On one corner of the church an early and impressive statue of St. Christopher looks down upon the passing traffic (Fig. 75 a & c). Furthermore, a large dimensioned cross is carved into the northern facade.
Figure 74: Architectural drawing of the Santa Mónica Church in the historical center of Guadalajara with different arichtectural areas. Mangenta - lower ground floor, brown - walls and architectural decoration, orange - cornices.
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The metropolitan zone of Guadalajara has a high seismic potential. Over the last several centuries large destructive earthquakes have occurred in the region (Chavez 2000). One large event is histori-cally documented before the erection of the church in December of 1568 with an estimated magni-tude of 7 after the Modified Mercalli Intensity scale (MMI), (Suarez et al., 1994). Another earth-quake took place in 1845 with a similar magnitude of 7. Thirty years later in 1875 another event occurred with an estimated magnitude of 7 MMI, depth 10 to 15 Km, and an epicenter distance of about 30 km northwest of Guadalajara. This event produced a maximum MMI of 9-10 in the center of the town and caused further destruction (Figueroa 1987).
Figure 75: a) Church before restoration. b) Area where architectural elements were discovered (arrow) that include three niches for the placement of religious sculptures. c) Church after restoration.
3. 4. 1 a) Climatic and environmental conditions
The climate in Guadalajara is humid and subtropical featuring dry, mild winters and hot humid summers with a very strong seasonal variation in precipitation (Fig. 76). Climatic classification is Cwa after the Köppen-Geiger system (Tab. 1). The northward movement of the Inter-Tropical Con-vergence Zone, especially from June to September, brings a great deal of rain, whereas for the rest of the year, the climate is very arid.
The annual average temperature is 19 °C (Fig. 76). Average monthly temperatures vary by 8 °C. In the spring, the hottest time of the year, temperatures climb reaching 30 °C, generally in the after-noon with overnight lows of 11.3 °C. During the summer average high temperatures are 27 °C and average low temperatures are 15.7 °C. Come autumn temperatures decrease achieving average highs of 25.3 °C during the day and lows of 12 °C generally shortly after sunrise. Total annual pre-cipitation averages 914 mm.
According to the Holdridge life zones system of bioclimatic classification, Guadalajara is situated in or near the subtropical dry forest biome (Tab. 1). The city of Guadalajara is similar to many other metropolitan areas in Latin America and has grown considerably in the period from 1970 to 2000, more than at any other time in its history.
Figure 76: Guadalajara Climate Graph.
This growth took place without control, clear regulations and often outside the law (Cruz et al., 2005). According to Cruz et al., (2005), the surrounding municipalities have shown signs of an ex-tremely high rate of growth between 1970 and 1990. In contrast, the central municipality and the historical center of Guadalajara have shown a lower rate of growth since the 1980’s, and in the 1990’s it even achieved a negative rate of growth.
Government officials were following the concept of a car-friendly city. The streets were widened and green areas were paved. The historical center and many historical buildings were neglected. For the last several decades individual traffic and smog has been and still is a serious problem. Howev-er, today city planners are following a new ambitious plan for the revitalization of the historical center. Just one block away from the Santa Mónica Church pedestrian precincts are being created and trees are being planted.
3. 4. 1 b) Main weathering forms
In the foundation area of the Santa Mónica Church as well as other historical buildings extensive back-weathering due to disaggregation and distinct fragmentation is observable (Fig. 77 c). Map-ping results indicate a yearly back-weathering rate of 1.7 % in the foundation area (Fig. 80 e, f and g). Most of the stones concerned were installed like plates, which mean perpendicular to the bed-ding. Salt efflorescence is recognizable on many building stones.
Cantilevering and overhanging building components such as the numerous gargoyles, mouldings
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and ornamental elements especially at the eaves areas often contain many fractures (Fig. 77 b).
Crack formation in these areas can be traced back to thermal and hygric fluctuations, dilatation and material fatigue. Temperature measurements show a heating up of the surface to 65 °C, whereas af-ter sunset and with a periodically rising cool wind, the surface temperature can be reduced by 15-20
°C.
Figure 77: Typical weathering forms of the Cantera Amarilla Tuff, a) shows structural flaking and disaggregation, b) broken areas and crack formation, c) massive back-weathering at the foundation (Santa Mónica Church) and d) material
loss due to crust formation and weathering (Museo Regional).
3. 4. 1 c) Quantified mapping
Quantified mapping of the main pillar at the edge of the building clearly shows that back-weathe-ring phenomena occupy a surface area of 6.8 % (Fig. 78 a). Disaggregation is 1.7 %, whereas the weathering out of clastic material is only 0.09 %. Weathering in the form of flaking is concentrated at the podium zone, where it amounts to 67 % of this area. Also disaggregation is concentrated in the podium zone with nearly 75 %. Cracks are found at the eave area while salt-efflorescence is
only found in the podium zone. Dark deposits are evenly distributed but concentrated at exposed building parts as well as at the eave and podium zone. These deposits are related to microbiological growth, and therefore, an indicator for the accumulation of moisture.
Results of the quantified mapping underline the assumption that salt weathering is the main reason for disaggregation as well as flaking. Formation of cracks seems to be related to the interplay of wetting due to rain and the drying out to sunshine and wind.
Figure 78: a) Mapping of the main pillar of the Santa Mónica Church. b) The pillar before and c) after restoration.
d) Podium zone of the statue of St. Christopher before and e) after restoration.
3. 4. 1 d) Observations, further investigations and weathering model
During the rainy season parts of the streets are flooded and the drainage systems are often not able to drain the water away in a proper fashion. The problem is furthermore reinforced by the damaged drainage and water supply systems.
Under these circumstances evaporation often takes place through the porous building materials such as volcanic tuffs, bricks or adobe constructions, which are mostly used in historical buildings.
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ting and drying produces a cyclical softening of the materials and damages by salt-weathering. Dur-ing the rainy season uprisDur-ing capillary water up to two meters in the stone occurs in numerous his-torical buildings as well as in the Santa Mónica Church (Fig. 77 c and d). These have been mea-sured with a portable hygrometer.
Most of the back-weathering observed occurs in this area, when considering the total surface area of the monuments (Fig. 79 a-c and e-g). The moisture content in this area as measured by drilling powder analysis is 8-15 M% in the beginning of the dry season at the end of September. Back-weathering in the pedestal area of the Santa Mónica Church is recognizable all around the building and also leads to structural problems.
Figure 79: Weathering and weathering model of the Santa Mónica Church. a-c) The weathering situation at the edge of the building (lower part) from 1995 until 2007 before the restoration began. d) Weathering model of the building as defined by water infiltration coming from the damaged drainage system during the rainy season and direct sunshine. e -
g) Depiction of the ongoing surface loss (red), lost joints (green) or damaged joints (blue).
3. 4. 2 The salts of Guadalajara, their sources and damage potential
The main salt found is sodium nitrate (NaNO3) and gypsum analyzed by X-ray diffraction (XRD) measurements. The highest concentration of contamination occurs near the surface and in the first
two centimeters of the stone material as evaluated by the drilling powder analysis method (Fig. 80 b and c).
The danger from NaNO3 results in its hygroscopic potential. Experimental laboratory studies show a rise of the moisture uptake of NaNO3 contaminated stone blocks in relation to the temperature and humidity (Goudi, Viles 1997). The critical conditions for a significant hygroscopic behavior start with a relative humidity of 80 % and 35 °C, which are the climatic conditions very common in Guadalajara. Salt crystallization may enforce the flaking effect often found at areas confronted by water infiltration (Fig. 80 a and b).
A possible source of the salt can be derived from the stone material itself (e.g. plagioclase), whereas the source of the nitrates occur in high concentrations in many examples of environmental pollu-tion.
Figure 80: Close-ups of the typical weathering forms of the Cantera Amarilla Tuff show a) internal crack formation and crumbling, b) alveolar weathering clearly related to salt, c) flaking also related to salt accumulation as well as
d) structural flaking.
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3. 4. 3 Rock material
The Cantera Amarilla Tuff (CA) belongs to the Quaternary volcanics in the Guadalajara area and occurs one to two meters beneath the soil. Today most of the deposits are covered by the present urban area. Only a small outcrop is still available for mining the stones for restoration purposes.
The Cantera Amarilla Tuff is a yellowish to orange-brownish porphyritic tuff (hypercrystalline to aphanitic texture) containing clasts of very different sizes. The macroclasts are mainly pumice, but other lithic clasts such as basalt and other pre-existing volcanic fragments occur (Fig. 81 a, d and e).
Grain sizes vary from a few mm (fine-grained sand) up to 10 cm and sometimes even coarser (Fig.
81 c). The Cantera Amarilla Tuff is rich in K-feldspar and plagioclase (Fig. 81 b). Crystobalite and tridymite also occur along with accompanying clay minerals. Smectite, kaolinite and halloysite were identified in separated clay fractions. Most of the pumice inclusions are not well cemented to the matrix (Fig. 81 e).
Figure 81: a) The Cantera Amarilla Tuff shows a secondary iron-rich cementation with a vertical orientation and brown iron-rich pumice inclusions (arrows). b) Thin section showing the glassy to microcrystalline matrix. C) Overview of the matrix by SEM. d) The grey variety of the Cantera Amarilla with dark colored inclusions, rock fragments and pumice (arrows). e) In the center a fragment of feldspar and pumice occurs that only shows a poor cementation within the
ma-trix. f) Single sharp egded crystals within the microcrystallin poorly welded matrix shown by SEM.
The thin section in Fig. 81 b shows a hypocrystalline to aphanitic texture. The matrix is reddish to yellowish, glassy to microcrystalline and poorly welded (Fig. 81 f). Crystals are essentially platy and tabular and subhedral to euhedral (Fig. 81 b and e). They consist of well-twinned alkali-feldspar phenocrysts, subrounded to angular reworked quartz and unidentified opaque crystals (Fig. 81 c and f).
The XRD analysis shows that the Cantera Amarilla Tuff is rich in clay minerals, principally kaolin-ite, but smectite and altered illite-montmorillonite also occurs. Halloyskaolin-ite, crystobalite/tridymite and larger amounts of K-feldspar and plagioclase have also been determined. The cation exchange ca-pacity (CEC) of 4.2 attains a moderate value (Wedekind et al., 2013).
The chemical analyses (wt.-%) show that the rock mainly consists of 71.4 % quartz components (SiO2) and 14.4 % alumina (Al2O3). It also contains relevant amounts of potassium oxide (4.8 % K2O), sodium oxide (4.6 % Na2O) and traces of phosphorus pentoxide, calcium oxide, magnesium oxide and sulfur trioxide (Wedekind et al., 2012).
3. 4. 3 a) Petrophysical experiments
To evaluate the affect of clasts within the bedding in regards to tension and dilatation, experimental measurements were undertaken on a 10 x 10 cm cube of Cantera Amarilla. The dilatation was mea-sured in a 1.5 cm grid in the Z-direction (Fig. 82 b). The stone block was totally immersed in water until the entire block was completely saturated.
3. 4. 3 b) Petrophysics
The porosity of the samples ranges between 42 % (CA) to 51 % (CA gray), with a particle density of around 2.5 g/cm3 and a bulk density of 1.48 g/cm3. The microporosity reaches 18 % for the yel-low variety and 22 % for the gray variety. Pore radii distribution is characterized by a bimodal sys-tem consisting of a high amount of macropores, where capillary moisture transport takes place and a significant amount of mircropores probably responsible for hygric and hydric dilatation. The cal-culated water absorption coefficients (w value) show a more or less similar value of around 3.5 kg/
m2 √h for the X and Y direction, while the Z direction only has a value of 0.5 kg/m2 √ (Tab. 15).
The avarage µ value with 75.2 is high (Tab. 15).
In the hydric expansion measurements the values for the X and Y direction are around 0.13 mm/m, while the expansion perpendicular to the bedding is 0.9 mm/m with an anisotropy of 82 % (Tab.
15). Expansion with a 95 % RH is reached at a value of 0.17 mm/m and a low anisotropy of only 11
%. Swelling pressure attains a moderate value of 0.011 MPa.
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Sorption reached a value of 0.036 g/cm3 at a relative humidity of 95 %, is mostly linear and attains a point of significant decrease at around 80 % RH. During the process of desorption, the water output is slightly reduced when compared to the sorption, especially when the relative humidity ranges between 20-80 %.
Measurements by the surface hardness tester after water saturation show an average reduction of surface hardness of 21 %. The results also show that there is no significant influence of long-term water storage to the reduction of surface hardness. Following the saturation and measurement the values remained constant every 12 h for a period of two days. The hardness of the pumice inclusi-ons is 34 % less than the matrix of the tuff, and is further reduced by 20 % in water-saturated condi-tions.
With an average value of 9.12 N/mm2 the Cantera Amarilla Tuff has a low compressive strength;
however, under water-saturated conditions its internal stability decreases down to only 5.81 N/mm2, a reduction of more than 37 %. The anisotropy of the specimens measured under water-saturated conditions is double when compared to the dry tested samples (Tab. 16).
By comparing the results of the dry to the water-saturated specimens a reduction of the splitting tensile strength of nearly 50 % could be determined. The anisotropy increase of more than three ti-mes the amount shows a clear weakening of the binding forces parallel to the bedding due to water saturation (Tab. 16). The breakage parallel to the bedding often took place at the material boundary between pumice and matrix.
Table 15: Water transport properties and hygric and hydric dilatation of the Cantera Amarilla Tuff used for the Santa Mónica Church
Directions (X, Y, Z) / Anisotropy (A) X Y Z A % Average ∅
w value [kg/m2 √h] 3.34 3.78 0.51 85 2.54
µ value 72.7 75.8 77.2 6 75.2
Hydric dilatation [mm/m] 0.16 0.11 0.90 82 25
Hygric dilatation 95% RH [mm/m] 1.8 1.6 1.7 11 17
Thermal expansion [mm/m, 60 °C] 0.68 0.66 0.62 9 0.65
Tabel 16: Petro-mechanical properties of the Cantera Amarilla Tuff, Santa Mónica Church.
Directions (X, Y, Z) / Anisotropy (A) X Y Z A [%] reduction [%]
Compressive strength dry [N/mm2] 9.45 8.21 9.72 16
Compressive strength water-saturated [N/mm2] 5.06 5.33 7.06 28 37 Splitting tensile strength dry ßSZ [MPa] 0.99 -- 1.05 6 Splitting tensile strength water-saturated ßSZ [MPa] 0.49 -- 0.56 13 49
Surface hardness dry [HLD] 332 20
Surface hardness wet [HLD] 266
The results of the dilatation experiment on the stone block emphasize the influence of the bedding towards moisture expansion. What becomes clear is that the periphery of the stone shows a higher moisture expansion than the center of the block (Fig. 82 a). Furthermore, the large pumice inclusi-ons seem to play a role in keeping the moisture values low. Above the large inclusion there is also a tendency to lower dilatation values, probably due to the lower amounts of matrix. In the sample cube where the concentration of clasts is lower, the dilatation is higher (Fig. 82 a).
Figure 82: a) Stone block and results of the dilatation experiment. b) The measuring equipment.
3. 4. 3 c) Salt resistance test
Salt resistance tests were done on both varieties of the Cantera Amarilla Tuff (Fig. 83).
Table 17: Ultrasonic velocity of the Cantera Amarilla Tuff varieties under dry and water saturated conditi-ons (ws)
Ultrasonic velocity
[km/s] Amarilla (dry) Gray (dry) Amarilla (ws) Gray (ws)
X 2.649 2.047 1.97 1.31
Y 2.461 2.022 1.914 1.438
Z 2.158 1.807 1.688 1.173
Average 2.423 1.959 1.857 1.307
Anisotropy [%] 17 24 14.7 9
Reduction Ø [%] 0 0 - 23.6 - 33.6
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Figure 83: Salt weathering test of the Cantera Amarilla Tuff varieties.
- CA, Cantera Amarilla Tuff
The loss of material starts within the yellow pumice inclusions. They weather out after the second cycle. A tendency towards rounding also takes place. After total saturation by salt within the highly porous structure the stone starts to break after the 20th cycle, which leads to total destruction at the 27th cycle.
- CA, Cantera Amarilla Tuff/gray variety
The loss of material starts with a rounding at the edges. Continuous breakdown takes place after the 16th cycle with a material loss of 30 %. Total destruction occurs after the 17th cycle.
3. 4. 4 Discussion
The situation at the Santa Mónica Church is like that of many other historical buildings and structu-res in the urban areas of Mexico and is characterized by its problematical hydraulic situation. Since the roads are paved, moisture infiltration during the rainy season leads to an accumulation of huge amounts of aggressive salts within the pedestal area of the monuments.
Rising water infiltration is also influenced by the bedding of the stone material due to its high aniso-tropy of more than 80 % of the w-value and the high hydric dilatation with a remarkable anisoaniso-tropy of up to 25 %. This becomes relevant because most of the ashlars are used as panel-like cladding, which means perpendicular to the bedding plane (Fig 79 d). Surface loss at singular ashlars are
found preferentially at those which are built perpendicular to the stones´ bedding plane (Fig. 79 a, b, c, e f, and g).
The different weathering resistance of the investigated rocks is possibly attributed to their varying content of secondary imbedded iron oxides. Compressive strength of the yellow CA is low and around 20 % higher than for the gray CA variety. Also the porosity of both varieties is in general very high, but the gray CA is even 18 % higher than the yellow CA. However, especially the yellow CA variety shows a comparably good salt resistance related to its low compressive and splitting ten-sile strength, propably due to secondary embedded iron compounds.
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