Cement Render and Mortar and Their Damages Due to Salt Crystallization in the Holy Trinity Church, Dominicans Monastery in Cracow, Poland

minerals

Article Cement Render and Mortar and Their Damages Due to Salt Crystallization in the Holy Trinity Church, Dominicans Monastery in Cracow, Poland

Mariola Marszałek * , Krzysztof Dudek and Adam Gaweł

Department of Mineralogy, Petrography and Geochemistry, AGH University of Science and Technology, al. Mickiewicza 30, 30-059 Kraków, Poland; [email protected] (K.D.); [email protected] (A.G.) * Correspondence: [email protected]

Received: 22 June 2020; Accepted: 17 July 2020; Published: 20 July 2020

Abstract: The investigations focused on the façade of the 17th-century Myszkowskis chapel at the 13th-century Church of the Holy Trinity in Cracow, Poland. Most of the chapel’s façade is made of rusticated limestone blocks, but its lower part is covered with cement render, and the basement consists of irregular pieces of limestone and sandstone, bound and partly replaced with cement mortar. The façade exhibited clearly visible damages: gray soiling of the surface, cracks, scaling, and efflorescence. The study presents characteristics of the cement render and mortar used for stone repair and/or substitution, as well as efflorescence from the lower part of the Myszkowskis chapel façade. The materials were analyzed with optical microscopy, scanning electron microscopy (SEM-EDS), Raman microspectroscopy, X-ray diffractometry (XRPD), and mercury intrusion porosimetry. The analyses demonstrated that the render covering some of the decayed limestone blocks was prepared using Portland cement (residual clinker grains represent alite and belite) as a binding agent, mixed with crushed stone as an aggregate. The cement mortar consisted of rounded quartz grains, rock fragments, and feldspars in very fine-grained masses of calcite and gypsum, also containing relics of cement clinker (alite, belite, ferrite, and aluminate). All these components point out the use of the ordinary Portland cement. Analyses of the efflorescence allowed us to distinguish several secondary salts, among others, thenardite, aphthitalite, and darapskite. The appearance of these phases is related to the composition and physicochemical properties of the building materials, atmospheric alteration agents, air pollution, and some other anthropogenic factors.

Keywords: cement render; cement mortar; Portland cement; deterioration; secondary salts

1. Introduction Construction mortars consist of various inorganic or organic binding materials and natural or artificial aggregates with or without pigments. Inorganic binders may be lime, cement, silica gel, or gypsum, and organic ones can be animal glue, polyester, acrylic or epoxy resins, whereas aggregates are most often sand or gravel. The kind of binder depends on the application area, climatic conditions and, in particular, on the moisture transport and mechanical properties of stones. Inorganic or organic additives are often used to adapt the mortar properties to the stone and to improve its durability. Repair and joint mortars have been used to fill open masonry joints or to repair and replace smaller missing parts of dimension stones, ornaments, and sculptures since antiquity [1]. Natural cement, called Roman cement (RC), was invented at the end of the 18th century and played an important role until the 1860s, when the artificial Portland cements (PC) gained broader usage. RC is still in use in conservation because the restoration of historic masonry requires materials with physico-chemical and mechanical properties similar to the original ones [2–6].

Minerals 2020, 10, 641; doi:10.3390/min10070641 www.mdpi.com/journal/minerals Minerals 2020, 10, 641 2 of 19

Roman cements are produced by firing marls (limestone containing a significant amount of clay) between 800 and 1200 ◦C (i.e., below their sintering temperatures). Ordinary Portland cement is usually produced by firing a ground mixture of limestone and clay in a temperature range of 1440 to 1480 ◦C (vitrification) [4,7–9]. The natural mixture of lime and clay (source of silica, alumina, and iron oxide) in the marl allows for RC synthesis at low temperatures, which could not be attained in any man-made mixture [2,4]. The main characteristics of RC were a short setting time (of around 15 min), warm (yellow-to-brown) color, little shrinkage on setting and good durability to atmospheric conditions and salt crystallization [2,4]. This made Roman cement a favored material for the easy manufacture of ornaments and renders for the exterior of buildings in the 19th/early 20th century (European Historicism and Art Nouveau period) [4]. Different calcination temperatures of Roman and Portland cements cause differences in their phase compositions [4,9]. While belite—C S (dicalcium silicate, 2CaO SiO )—is the major hydraulic 2 · 2 phase in Roman cements, alite—C S (tricalcium silicate, 3CaO SiO )—is the major phase in ordinary 3 · 2 Portland cement. Next to belite (as a mixture of two structural modifications β and α0, with the latter being predominant), the following compounds eventually form in an RC: wollastonite (monocalcium silicate, CaO SiO , CS); gehlenite (dicalcium aluminosilicate, 2CaO Al O SiO ,C AS); · 2 · 2 3· 2 2 aluminate (tricalcium aluminate, 3CaO Al O ,C A); ferrite, also called brownmillerite (tetracalcium · 2 3 3 aluminoferrite, 4CaO Al O Fe O ,C AF) [2,4,7,9]. The major compounds present in PC clinkers, · 2 3· 2 3 4 next to alite (predominant component, making up 50–70%), are belite (which makes up 15–30%), aluminate (C3A), and ferrite (C4AF) [9]. In contrast to PC, alite cannot form in RC because of low calcination temperatures. After hydration, both belite (β- and α0-belite) and alite form hydrated calcium silicates (CSH phases), being the main components of the cements, next to portlandite Ca(OH)2. Unreacted and unhydrated components of Roman cements (in good quality cements present only in very small quantities)—calcium silicates: β-belite (as less reactive then α0-belite), gehlenite (C2AS), and wollastonite (CS)—can be labelled as Roman cement fingerprint phases [2,4], like relics of alite (C3S), which are characteristic of ordinary PC and are absent in RC [5,9]. As most calcareous materials exposed in urban environment, RC and PC undergo atmospheric sulphation, resulting in their alteration. Soluble sulphates can react with the cement components to form various salts, such as ettringite Ca Al (SO ) (OH) 26H O and gypsum CaSO 2H O [2,10–12]. 6 2 4 3 12· 2 4· 2 Crystallization of secondary salts, being the most efficient deterioration process in porous materials, may substantially contribute to the damaging of building materials. The most important damaging factor is crystallization pressure during salt precipitation, resulting in the formation of cracks and loss of cohesion between the material components [13]. The crystallization can occur at the surface (efflorescence) or within the porous structure of the building materials, in confined spaces (subflorescence). Mineralogical and chemical changes in cement, due to water penetration through and dissolution of the material components, can lead to structural changes by favoring cracks and material disintegration. Rainwater infiltration, bringing about both the crystallization and dissolving of salts over an extended period of time, can contribute to the disintegration of building materials. The investigations presented are focused on the southern wall façade of the 17th-century Myszkowskis Chapel, a part of the 13th-century Church of the Holy Trinity at the Dominicans monastery in Cracow, Poland. The chapel, founded by Zygmunt Myszkowski and his brother Alexander as the family mausoleum [14], was most likely designed by Santi Gucci from Florence (Italy) and built by masters from his workshop. The substantial part of the façade is covered with a Mannerist rustication [15,16] made of regular blocks of the Middle Miocene (Early Badenian), lithothamnium limestone, so-called Pińczów limestone, quarried in and near Pińczów (Carpathian Foredeep, South-Central Poland) [17,18]. Rusticated blocks are underlain by a small, horizontal element in the shape of a shaft, and a belt consisting of two rows of rectangular, plain limestone blocks, without rustication. The next lowest part of the façade wall, close to the pavement level, consists of rectangular bright blocks of various dimensions, as shown in Figure1. Available sources [ 17–19] and unpublished conservatory documentations yielded some information about the rusticated Pińczów Minerals 2020,, 10,, 641x FOR PEER REVIEW 3 of 19 rusticated Pińczów limestone, but any detailed information about the other elevation materials was limestone,not encountered. but any In detailedthe course information of our previous about theresearch other [ elevation20], we observed materials that was the not stony encountered. elements Inbelow the coursethe rusticated of our previous blocks researchof the Pińczó [20], wew limestone observed thatwere the also stony covered elements with below a thin the layer rusticated of a blocksbeige-brown, of the Pińcz highlyów exfoliated limestone cement were also render. covered However, with a thin some layer of ofthe a limestone beige-brown, blocks highly in the exfoliated row of cementthe façade render. below However, the small some shaft of thecontain limestoneed replacements blocks in the and row thick, of the bright façade render below theof smalla different shaft containednature than replacements the previous. and thick, bright render of a different nature than the previous.

Figure 1. MyszkowskisMyszkowskis Chapel Chapel of of the the Holy Holy Trinity Trinity Church Church in in Cracow ( aa)) and and sites of sampling: rusticated wall and elements beneath ( b));; exposed part of the foundations ( (cc)) (after (after [20], [20], modified) modiﬁed).. The samples represent: KD-M-4-2—bright,KD-M-4-2—bright, c cementement rendered part of the elevation;elevation; KD-M-3—cementKD-M-3—cement mortar from the subwall, in places covered with salt efflorescence. eﬄorescence. (1) (1)—sampling—sampling area in detail in (b); area presented in (c) is located beneath the pavement level, below the area marked as (1). Photos (b (b)) and (c) by K. Bałaga.

The exposedexposed foundations foundations of theof the chapel chapel (subwall) (subwall) are made are ofmade irregular of irregular pieces of brightpieces limestonesof bright andlimestones gray sandstones, and gray sandstones, bound with bound and partlywith and replaced partly byreplaced a cement by a mortar. cement Themortar. Upper The Jurassic Upper limestonesJurassic limestones most likely most came likely from came quarries from quarries in close vicinity,in close northvicinity, or north northwest or northwest from the from Old Townthe Old of CracowTown of [21Cracow]. The [2 sandstones1]. The sandstones proved to proved represent to represent the Upper the Cretaceous Upper Cretaceous Istebna sandstones Istebna sandstones and were probablyand were quarriedprobably a quarried few tens ofa few kilometers tens of kilometers south of Cracow south inof theCracow Flysch in Carpathians. the Flysch Carpathians. The mortar wasThe appliedmortar was unevenly; applied in un someevenly places; in some covers places the stony covers elements, the stony and elements, in others and forms in others convex forms welds. convex welds.The façade exhibits clear signs of damage that include dark gray soiling of the surface, black crusts,The surface façade exfoliations, exhibits clear cracks signs and of damage fine-crystalline that include salt e ffldarkorescence. gray soiling The lastof the three surface, are mainly black associatedcrusts, surface with exfoliations, the elements cracks covered and with fine render,-crystalline however, salt e fflefflorescence.orescence occurs The onlylast three on the are lower mainly part ofassociated the subwall, with chiefly the elements on the bordercovered between with render, the limestone however, blocks efflorescence and the cement occurs mortar. only on The thepart lower of thepart façade of the withsubwall, rectangular chiefly on bright the blocksborder doesbetween not revealthe limestone clear signs blocks of damage. and the cement mortar. The part ofNo the detailed façade information with rectangu onlar conservation bright blocks work does on not the reveal chapel’s clear façade signs was of encountered;damage. however, it canNo be detailed suspected information that many on conservation conservation interventions work on the were chapel's carried façade out duringwas encountered its history.; Nonetheless,however, it can it is be known suspected that following that many the damagesconservation brought interventions about by the were fire ofcarried 1850, theout chapelduring was its renovatedhistory. Nonetheles under directions, it is known of Z. Hendel that following in the years the 1900–1910 damages brought [22]. In 1959, about a by thorough the fire conservation of 1850, the waschapel carried was renovated out by the Historicalunder direction Monuments of Z. Hendel Conservation in the years Labs. 1900 Bright–19 replacements10 [22]. In 1959, ofthe a thorough material belowconservation the shaft was could carried have out been by applied the Historical both by HendelMonuments during Conservation the works of Labs. 1900–1910 Bright (the replacements drain ditch, unveilingof the material the subwall, below wasthe probablyshaft could made have by been Hendel) applied and byboth Historical by Hendel Monuments during Conservationthe works of Labs1900– (R.1910 Rolewicz, (the drain a stoneditch, conservator, unveiling the personal subwall, communication). was probably made by Hendel) and by Historical Monuments Conservation Labs (R. Rolewicz, a stone conservator, personal communication). Minerals 2020, 10, 641 4 of 19

The presented study began during conservatory works in 2017, thanks to the courtesy of the Monastery authorities and Mr Bartłomiej Polczy´nski.Some of the results were published in 2019 [20]. Current research was focused on a bright render, in places covering the limestone blocks and ﬁlling the material losses (lower part of the façade wall, just above the bright blocks, close to the pavement level) and mortar that bound and partly replaced the stones in the chapel subwall, below the pavement line. The study was also aimed at characteristics and the determination of the render and mortar cement(s), as well as signs of their deterioration.

2. Materials and Methods Samples selected for the studies represent two types of the building materials taken from the Myszkowskis Chapel façade and subwall, as shown in Figure1: a piece of the wall in places covered and/or filled with bright cement render, above the pavement level (samples labelled KD-M-4-2), and the cement mortar between stony blocks in the subwall below the pavement level (samples labelled KD-M-3). Salt efflorescences from the contacts between the limestone surface and the cement mortar, observed in the lower part of the subwall, were analyzed as well. Laboratory tests included mineralogical, chemical, and petrophysical analyses. Optical microscopy, scanning electron microscopy (SEM-EDS), Raman microspectroscopy, and X-ray diffractometry (XRPD) were used for analyzing the materials and deterioration products of the cement render and mortar. The petrophysical properties of the materials were determined using mercury intrusion porosimetry. The petrographic characteristics of the materials were based on analysis of thin sections cut perpendicularly to the outer layers of the samples (optical microscopy in the transmitted polarized light, TPL), using an Olympus BX-51 instrument coupled with an Olympus DP-12 digital camera (Olympus Corporation, Tokyo, Japan). The porosity and pore size distributions were analyzed with a mercury intrusive porosimeter AutoPore IV 9520 (Micromeritics Instrument Corporation, Norcross, GA, USA), operating within the 0.1–413 MPa pressure interval and allowing us to determine pores within the 0.003–1000 µm range. The morphology of the cement components and microstructure of the materials were studied using a FEI 200 Quanta FEG scanning electron microscope with an EDS/EDAX spectrometer (FEI Company, Fremont, CA, USA). A large number of standardized analysis points were used to characterize residual cement grains and other binder-related phases. The maximum excitation voltage was 20 kV and a low vacuum mode (the pressure 60 Pa) was used. The samples analyzed included polished thin sections, broken, and sharp surfaces of weathered materials, and the efflorescence itself. Phase compositions of the samples, both of cements and efflorescence, were determined using the X-ray powder diffraction method (XRPD) with a Rigaku MiniFlex 600 instrument (RIGAKU Corporation, Tokyo, Japan). The measurement conditions were as follows: CuKα anode; generator settings 40 kV and 15 mA; recording range 3–70◦ 2θ; step size 0.05◦; counting time 1 sec/step. The results were processed with XRAYAN software using a diffraction X-ray pattern database of the International Centre for Diffraction Data (the Powder Diffraction File PDF-4, 2013). Some phases, mainly secondary minerals, were also determined using Raman microspectroscopy. The spectra were recorded with a Thermo Scientific DXR Raman microscope (Thermo Scientific, Waltham, MA, USA) with a 900 grooves/mm grating and a CCD detector. The Olympus 10x (NA 0.25) and 50x (NA 0.50) objectives (theoretical spot sizes 2.1 µm and 1.1 µm, respectively) were used. Excitation was activated with a 532 nm diode laser with maximum power of 10 mW. The laser power varied in the 3–10 mW range and the measurement time from 30 to 300 s, selected appropriately to avoid a possible thermal decomposition of the samples and to obtain the best quality of spectra. The phase identification was performed using an in-house and the RRUFF Raman Minerals spectral libraries, as well as the literature data [23–28]. The cement notation used through the paper is as follows: A = Al2O3;C = CaO; F = Fe2O3;H = H2O; S = SiO2. Minerals 2020, 10, 641 5 of 19

3. Results and Discussion

3.1. Bright Cement Render at Limestone Blocks above the Pavement Level Microscopic analysis (TPL) demonstrated that the cement render, covering some of the Pińczów limestone blocks (samples KD-M-4-2), is of a dozen or so millimeters thick, as shown in Figure2. This outer layer proved to contain fragments of carbonate bioclasts, sharp-edged quartz grains, opaque components, as well as aggregates of high relief that were colorless or colored, mostly isotropic or very slightly anisotropic (very low birefringence) that were difficult to unequivocally identify. Conservation putty, filling the material losses of the limestone blocks, exhibited similar composition. SEM-EDS elemental maps allowed us to identify the presence of Ca, Si, Mg, Al, S, and O, and sometimes Fe as well, as shown in Figure3. They represent residual cement grains—clinker, that have been identified as alite (C S: tricalcium aluminate, 3CaO Al O ) and belite (C S: dicalcium silicate, 2CaO SiO ), with the 3 · 2 3 2 · 2 latter predominating, as shown in Table1 and Figure4. Although after hydration both alite and belite form hydrated calcium silicates (CSH phases), being the main components of the cements (next to portlandite), these phases can survive in unreacted grains of cements or encapsulated in mortars because of their low hydration rates [5,29]. C3S exhibits mainly subhedral, rounded, or distorted crystals and often coalescent grains, up to 100 µm in size, as shown in Figure4a,b. Most of the C 3S grains are corroded and surrounded by partly Mineralscarbonated 2020, hydration10, x FOR PEER rims, REVIEW as shown in Figure4a,b. The presence of the silica gel at the boundary5 canof 19 be considered as a weathering product of the cement exposed to atmospheric carbonation. The reaction 3.1.between Bright C 3CementS and CO Render2, led at to Limestone the decalcification Blocks above of Cthe3S Pavement and precipitation Level of silica gel, which is a residual product of Ca depletion. Belite reveals a diversity of crystal forms and textures. Besides typical, Microscopic analysis (TPL) demonstrated that the cement render, covering some of the Pińczów rounded crystals, frequently forming large clusters, atypical, elongated, or wedge-like [30,31] shapes limestone blocks (samples KD-M-4-2), is of a dozen or so millimeters thick, as shown in Figure 2. could be observed as well. Rounded crystals, usually of a dozen or so µm in size, or their clusters, up to This outer layer proved to contain fragments of carbonate bioclasts, sharp-edged quartz grains, 100 µm, show polysynthetic twinning, exhibiting one set of parallel lamellae, typical for the type II C S opaque components, as well as aggregates of high relief that were colorless or colored, mostly2 (β C S) [32], as shown in Figure4c,d. Belite with two sets of intersecting lamellae (type I, α’C S, [32]) isotropic2 or very slightly anisotropic (very low birefringence) that were difficult to unequivocal2 ly and C S not showing any clear lamellae (type III, [33]) were observed only in a few crystals, as shown identif2y. Conservation putty, filling the material losses of the limestone blocks, exhibited similar in Figure4d. The dominance of β C S probably results from the fact that α -belite is more reactive composition. SEM-EDS elemental maps2 allowed us to identify the presence of0 Ca, Si, Mg, Al, S, and β O,than and the sometimes-belite [5 Fe,29 as]. Severalwell, as crystals shown ofin beliteFigure also 3. They demonstrate represent finger-like residual cement patterns grains within— theclinker, flux phases, as shown in Figure4a. Although C 2S is generally more stable than C3S, upon slow cooling, that have been identified as alite (C3S: tricalcium aluminate, 3CaO·Al2O3) and belite (C2S: dicalcium it can reveal reabsorbed finger-like patterns within the interstitial phases [33]. Within the clusters with silicate, 2CaO·SiO2), with the latter predominating, as shown in Table 1 and Figure 4. Although after alite and belite phases, interstitial groundmass composed of hydrated calcium silicate (CSH) occurs. hydration both alite and belite form hydrated calcium silicates (CSH phases), being the main Thecomponents components of the are cements cemented (nex witht to very portlandite), fine-crystalline these mass, phases presumably can survive carbonate in unreacted micrite, grains which of is cementsalso indicated or encapsulated by the elemental in mortars composition because obtainedof their low with hydration the SEM-EDS rates [5,2 method.9].

Figure 2. Microphotographs of the sample KD KD-M-4-2-M-4-2 taken from the wall in places covered and/or and/or filledﬁlled with bright cement render, above the pavement level; cement clinker clusters are marked with the arrow (one polar ((a) andand crossedcrossed polarspolars ((bb)).)). Minerals 2020, 10, 641 6 of 19 Minerals 2020, 10, x FOR PEER REVIEW 6 of 19

FigureFigure 3. 3.SEMSEM elemental mapsmaps and and backscattered backscattered (BSE) (BSE) electron electron image showingimage showing the qualitative the qualitative chemical chemicalcomposition composition of the cement of the rendercement with render residual with cement residual grains cement from grains sample from KD-M-4-2. sample KD-M-4-2.

TableTable 1. 1.ChemicalChemical composition, composition, inin atomic atomic percentage, percentage, of characteristicof characteristic residual residual cement cement grains. grains. For exact For position of the analyzed points, see Figure4 for the sample KD-M-4-2 and Figure 10 for the sample exact position of the analyzed points, see Figures 4 for the sample KD-M-4-2 and Figure 10 for the KD-M-3, discussed in the paragraph 3.2. sample KD-M-3, discussed in the paragraph 3.2. Element AnalyzedAnalyzed Element SampleSamplePhase Phase PointPoint O Na Na Mg Mg Al AlSi SiCa CaFe FeP P KD-M-4-2KD-M-4-2 C3S +1 55.52 0.00 0.47 1.80 10.87 31.34 C3S +1 55.52 0.00 0.47 1.80 10.87 31.34 C2S +2 56.64 0.00 0.00 0.83 14.33 28.19 C2S +2 56.64 0.00 0.00 0.83 14.33 28.19 C3S +3 55.86 0.00 0.00 2.14 10.71 31.29 C3S +3 55.86 0.00 0.00 2.14 10.71 31.29 C2S +4 54.39 0.00 0.00 0.69 14.37 29.95 0.25 C2S +4 54.39 0.00 0.00 0.69 14.37 29.95 0.25 C2S +5 56.42 0.00 0.00 0.90 14.04 28.64 C2S +5 56.42 0.00 0.00 0.90 14.04 28.64 KD-M-3KD-M-3 C3S +6 56.98 0.00 0.98 1.88 12.40 27.76 C3S +6 56.98 0.00 0.98 1.88 12.40 27.76 C3A +7 54.12 1.07 0.00 14.33 5.73 23.29 1.46 C3A +7 54.12 1.07 0.00 14.33 5.73 23.29 1.46 C4AF +8 54.99 0.00 1.30 11.06 5.76 20.67 6.23 C4AF +8 54.99 0.00 1.30 11.06 5.76 20.67 6.23 C2S +9 57.88 0.00 0.00 1.62 16.12 24.38 C2S +9 57.88 0.00 0.00 1.62 16.12 24.38 C2S +10 58.14 0.00 0.00 0.70 13.36 27.79 C2S +10 58.14 0.00 0.00 0.70 13.36 27.79 Minerals 2020, 10, 641 7 of 19 Minerals 2020, 10, x FOR PEER REVIEW 7 of 19

FigureFigure 4. 4.BackscatteredBackscattered (BSE) (BSE) electron electron image image of ofresidual residual cement cement grains grains from from sample sample KD KD-M-4-2:-M-4-2: (a)

Grain(a) Grain with withcoalescent coalescent C3S Calite3S alite (+1) (+ and1) and belite belite C C2S,2S, revealing revealing finger ﬁnger-like-like patternpattern ( +(+2)2).. The The grains grains are are surroundedsurrounded by by rim rim of of inner inner hydration hydration product; product; (b) ClusterCluster ofof typicaltypical alite alite crystals crystals (+ (+3)3) surrounded surrounded by by silicasilica gel gel (carbonation (carbonation product product of of C 3S); ( c) Small,Small, roundedrounded belite belite crystals crystals with with parallel parallel lamellae lamellae (+4) (+4) in a in a hydratedhydrated matrix; ((dd)) Subhedral Subhedral belite belite crystals crystals type type II with II with lamellae lamellae (+5). (+5). For qualitativeFor qualitative analyses analyses of the of thephases, phases, see see Table Table1. 1.

X-ray powder diffractometry (XRPD) allowed us to determine: calcite; portlandite Ca(OH)2; C3S exhibits mainly subhedral, rounded, or distorted crystals and often coalescent grains, up to ettringite Ca6Al2(SO4)3(OH)12 26H2O; quartz; dolomite CaMg(CO3)2; monosulphite Ca4Al2O6SO3 11H2O, 100 μm in size, as shown in ·Figure 4a,b. Most of the C3S grains are corroded and surrounded· by as shown in Figure5. No phases being relics of the original cement, alite and belite, identiﬁed through partly carbonated hydration rims, as shown in Figure 4a,b. The presence of the silica gel at the scanning electron microscopy in the binder related grains, were detected using this method. boundary can be considered as a weathering product of the cement exposed to atmospheric All these components point out and conﬁrm the use of the Portland cement (PC). Calcium carbonation.carbonates (calciteThe reaction as well between vaterite) C are3S productsand CO2, of le thed to carbonation the decalcification of calcium of hydroxide C3S and precipitation (a product of of silica gel, which is a residual product of Ca depletion. Belite reveals a diversity of crystal forms and hydration both of C2S, C3S, and of lime—CaO, formed after the calcination of raw material, which reacts textures. Besides typical, rounded crystals, frequently forming large clusters, atypical, elongated, or with CO2 during the hardening of cement, forming CaCO3). Ettringite is a primary hydration product wedge-like [30,31] shapes could be observed as well. Rounded crystals, usually of a dozen or so μm in ordinary Portland cement (reaction between the calcium aluminate C3A and the sulphate from added in gypsum),size, or their but rapidlyclusters, dissolves up to 100 after μm, the show sulphate polysynthetic depletion. However,twinning this, exhibiting phase can one also set precipitate of parallel lamellae,when internal typical (e.g., for pyrite)the type or externalII C2S (β sources C2S) [3 of2 sulphate], as shown areavailable in Figure (e.g., 4c,d atmospheric. Belite with SO 2two[34 –sets36]). of intersectingThe presence lamellae of sulphate (type I, dioxide α’ C2S, in[32 urban]) andand C2S industrialnot showing sites any mainly clear promoteslamellae (type the formation III, [33]) were of observedgypsum only and ettringitein a few in crystals the pores, as and shown the matrix in Figu of cementitiousre 4d. The dominance materials. Ettringite of β C2S is probably thus a product results fromof reaction the fact between that α′ gypsum-belite is and, more still reactive present inth thean cement, the β-belite anhydrous [5,29]. grains Several of calcium crystals aluminates of belite[ 3also]. demonstrateDepending onfinger the- concentrationlike patterns ofwithin available the sulphatesflux phases and, calciumas shown aluminates in Figure (C 34a.A and Although tetracalcium C2S is generallyaluminoferrite, more stable ferrite Cthan4AF), C crystalizing3S, upon slow ettringite cooling generates, it can internal reveal mechanical reabsorbed strength; finger in-like particular patterns within the interstitial phases [33]. Within the clusters with alite and belite phases, interstitial groundmass composed of hydrated calcium silicate (CSH) occurs. The components are cemented with very fine-crystalline mass, presumably carbonate micrite, which is also indicated by the elemental composition obtained with the SEM-EDS method. Minerals 2020, 10, x FOR PEER REVIEW 8 of 19

X-rayMinerals powder2020, 10 ,diffractometry 641 (XRPD) allowed us to determine: calcite; portlandite8 of 19Ca(OH)2; ettringite Ca6Al2(SO4)3(OH)12·26H2O; quartz; dolomite CaMg(CO3)2; monosulphite Ca4Al2O6conditionsSO3·11H2 (locationO, as shown of ettringite in Figure growth, 5. space No availability)phases being the highrelics pressure of the of original its crystallization cement can, alite and belite, identifiedlead to the through damage ofscanning the cement electron matrix. microscopy Monosulphite in is alsothe abinder product re oflated the cement grains, hydration were detected using this(sulphite method. ions are often observed when sulphuric sources are available; [37,38]).

Figure 5.Figure Characterist 5. Characteristicic X‐ray X-ray patterns patterns of ofthe the cement cement renderrender of of sample sample KD-M-4-2. KD-M Abbreviations:-4-2. Abbreviations: Cal—calcite,Cal—calcite, Dol—dolomite, Dol—dolomite, Et— Et—ettringite,ettringite, Ms Ms—monosulphite,—monosulphite, Prt—portlandite, Prt—portlandite, Qz—quartz. Qz—quartz. The results suggest that the cement render analyzed was based on Portland cement as a binding All agent,these mixedcomponents with crushed point stone out as and an aggregate. confirm In the this use case itof was the an Portland organogenic, cement most probably(PC). Calcium carbonatesPincz (calciteów-type as limestone well vaterite) with characteristic are products bioclasts: of the red algaecarbonation of the genus of Lithothamnium,calcium hydroxide bryozoans, (a product foraminifers, including genus Amphistegina, and also fragments of bivalve shells. of hydration both of C2S, C3S, and of lime—CaO, formed after the calcination of raw material, which Based on mercury intrusion porosimetry measurements, the sample reveals a high open porosity reacts with CO2 during the hardening of cement, forming CaCO3). Ettringite is a primary hydration of 31.54% and a bulk density of 1.77 g/cm3. Its pore size distribution reveals a domination of the pores product in twoordinary ranges: Portland 1.0–0.1 µm, cement that makes (reaction 45.25%, andbetween 0.1–0.003 theµ mcalcium (46.33%). aluminate Larger pores C of3A 10.0–1.0 and theµm sulphate from addedmake gypsum), 4.9%, and thebut poresrapidly of 70–10 dissolvesµm make after 3.46%, the assulphate shown in depletion. Figure6. The However, total pore this area phase is can also precipitate20.31 m2/ g,when and the inte averagernal pore (e.g., diameter pyrite) is 0.03 orµ mexternal (calculated sources as a weighted of sulphate average, with are the available weight (e.g., determining the number of pores, and not the percentage of the pore space). The internal movement of atmospheric SO2 [34–36]). The presence of sulphate dioxide in urban and industrial sites mainly solutions through the stone is very difficult and inferior (quite high hysteresis effect—45%, and very promotes the formation of gypsum and ettringite in the pores and the matrix of cementitious low threshold diameter—0.5 µm), the permeability is very low 0.075 mD. The pore distribution is materials.unimodal Ettringite and is heterogeneous thus a product with theof poresreaction in the between range 1.0–0.003 gypsumµm. and, still present in the cement, anhydrous grainsEven thoughof calcium the microscopic aluminates analysis [3]. Depending (TPL) did not on reveal the concentration surface coatings of with available secondary sulphates and calciumminerals, aluminates gypsum on(C the3A surfaceand tetracalcium could be observed alumino withferrite, the scanning ferrite electron C4AF), microscope. crystalizing Small, ettringite generatesplate-like internal crystals mechanical of this mineral, strength; up to in several particular tens µm conditions in length, were (location also detected of ettringite inside the samplesgrowth, space analyzed, in pores and cracks, as shown in Figure7a,b. The formation of gypsum, CaSO 2H O, exerts availability) the high pressure of its crystallization can lead to the damage of 4the· 2cement matrix. mechanical stress on the stone because of its much higher molecular volume than calcite, CaCO3. MonosulphitePresence is ofalso gypsum a product was confirmed of the bycement Raman hydration microspectroscopy. (sulphite Its spectraions are show often strong observed Raman when 1 1 1 sulphuricbands sources at 1010 are cm available;− (ν1), minor [37,38]). bands at 416 and 492 cm− , as well as the 621 and 672 cm− (ν2 and ν4) 1 2 The andresults 1136 suggest cm− (ν3) that vibrations the cement of SO4 −render[24,27]. analyzed was based on Portland cement as a binding agent, mixed with crushed stone as an aggregate. In this case it was an organogenic, most probably Pinczów-type limestone with characteristic bioclasts: red algae of the genus Lithothamnium, bryozoans, foraminifers, including genus Amphistegina, and also fragments of bivalve shells. Based on mercury intrusion porosimetry measurements, the sample reveals a high open porosity of 31.54% and a bulk density of 1.77 g/cm3. Its pore size distribution reveals a domination of the pores in two ranges: 1.0–0.1 μm, that makes 45.25%, and 0.1–0.003 μm (46.33%). Larger pores of 10.0–1.0 μm make 4.9%, and the pores of 70–10 μm make 3.46%, as shown in Figure 6. The total pore area is 20.31 m2/g, and the average pore diameter is 0.03 μm (calculated as a weighted average, with the weight determining the number of pores, and not the percentage of the pore space). The internal Minerals 2020, 10, x FOR PEER REVIEW 9 of 19

movement of solutions through the stone is very difficult and inferior (quite high hysteresis effect—45%, and very low threshold diameter—0.5 μm), the permeability is very low 0.075 mD. The pore distribution is unimodal and heterogeneous with the pores in the range 1.0–0.003 μm.

Minerals 2020, 10, 641 9 of 19

Minerals 2020, 10, xTiny, FOR needle-shaped PEER REVIEW ettringite crystals were probably dispersed in the matrix, as shown in Figure3 9 of 19 (distribution of S). Despite the registration of ettringite in the XRPD analyses, no Raman spectra of movement this of mineral solutions have throughbeen recognized. the stone It is possible is very that verydifficult ﬁne and and disseminated inferior crystals (quite within high hysteresis the matrix were simply not found. Microchemical methods used (e.g., SEM-EDS), do not allow for effect—45%,any and unequivocal very low identiﬁcation threshold of diameter monosulphite,—0.5 whose μm), elemental the permeability composition isis the very same low as that0.075 mD. The pore distributionof ettringite.Figure is 6. unimodal The pore size and distribution heterogeneous of the cement with basedthe pores materials in the(sampl rangees KD 1.0-M-–4-0.0032 and μm. KD-M-3)—for position of the samples, see Figure 1—with regard to certain processes: a—vapor absorption and capillary condensation; b—salt and ice crystallization; c—capillary imbibition; d—mechanical strength in the material pore space. Intensities and ranges of the processes after Benavente [39].

Even though the microscopic analysis (TPL) did not reveal surface coatings with secondary minerals, gypsum on the surface could be observed with the scanning electron microscope. Small, plate-like crystals of this mineral, up to several tens μm in length, were also detected inside the samples analyzed, in pores and cracks, as shown in Figure 7a,b. The formation of gypsum, CaSO4·2H2O, exerts mechanical stress on the stone because of its much higher molecular volume than calcite, CaCO3. Presence of gypsum was confirmed by Raman microspectroscopy. Its spectra show strong Raman bands at 1010 cm−1 (ν1), minor bands at 416 and 492 cm−1, as well as the 621 and 672 cm−1 (ν2 and ν4) and 1136 cm−1 (ν3) vibrations of SO42− [24,27]. Tiny, needle-shaped ettringite crystals were probably dispersed in the matrix, as shown in Figure 3 (distribution of S). Despite the registration of ettringite in the XRPD analyses, no Raman Figure 6. The pore size distribution of the cement based materials (samples KD-M-4-2 and KD-M-3)— Figurespectra 6. The of this pore mineral size have distribution been recogniz of ed. the It is cement possible based that very materials fine and (sampldisseminatedes KD crystals-M-4-2 and for position of the samples, see Figure1—with regard to certain processes: a—vapor absorption and KD-Mwithin-3)— forthe positionmatrix were of thesimply samples not found., see Microchemical Figure 1—with methods regard used to certain(e.g., SEM processes:-EDS), do anot—vapor capillary condensation; b—salt and ice crystallization; c—capillary imbibition; d—mechanical strength absorptionallow for in and theany material capillaryunequivocal pore space. condensation identification Intensities and; ofb ranges—monosulphite,salt of and the processes ice whose crystallization after elemental Benavente composition [;39 c].—capillary is the imbibitionsame ; d—mechanicalas that of ettringite. strength in the material pore space. Intensities and ranges of the processes after Benavente [39].

Even though the microscopic analysis (TPL) did not reveal surface coatings with secondary minerals, gypsum on the surface could be observed with the scanning electron microscope. Small, plate-like crystals of this mineral, up to several tens μm in length, were also detected inside the samples analyzed, in pores and cracks, as shown in Figure 7a,b. The formation of gypsum, CaSO4·2H2O, exerts mechanical stress on the stone because of its much higher molecular volume than calcite, CaCO3. Presence of gypsum was confirmed by Raman microspectroscopy. Its spectra show strong Raman bands at 1010 cm−1 (ν1), minor bands at 416 and 492 cm−1, as well as the 621 and 672 cm−1 (ν2 and ν4) and 1136 cm−1 (ν3) vibrations of SO42− [24,27]. Tiny, needle-shaped ettringite crystals were probably dispersed in the matrix, as shown in Figure 3 (distributionFigureFigure 7.7. BackscatteredBackscattered of S). Despite (BSE) electronelectron the registration image image of theof the secondary secondary of ettringite gypsum gypsum on thein on surface the the XRPDsurface (a) and in( aanalyses,) cracks and in no Raman spectra of thiscracks (mineralb) of (b the) of sample the have sample KD-M-4-2. been KD- Mrecogn-4-2. ized. It is possible that very fine and disseminated crystals within the3.2. 3.2. matrix Cement Cement Mortarwere Mortar between simply between Stony Stony not Blocks Blocks found. of of the the Microchemical Subwall Subwall below thethe PavementPavement methods Level Level used (e.g., SEM-EDS), do not allow for any unequivocalIn the microscopic identification image (TPL) of cement monosulphite, mortar samples whose (KD-M-3) elemental display thecomposition presence of is the same as that of ettringite.well-rounded quartz grains, rock fragments, and feldspars (both potassic and plagioclases). These grains are cemented with very ﬁne-grained mass, mainly of Ca, Si, S, and O in composition (SEM-EDS), in which larger yellowish aggregates with high relief, as shown in Figure8a,b, and low interference colors or even optically isotropic could be observed as well. They represent residual, unhydrated clinker grains of ordinary Portland cement.

Figure 7. Backscattered (BSE) electron image of the secondary gypsum on the surface (a) and in cracks (b) of the sample KD-M-4-2.

3.2. Cement Mortar between Stony Blocks of the Subwall below the Pavement Level Minerals 2020, 10, x FOR PEER REVIEW 10 of 19

In the microscopic image (TPL) cement mortar samples (KD-M-3) display the presence of well-rounded quartz grains, rock fragments, and feldspars (both potassic and plagioclases). These grains are cemented with very fine-grained mass, mainly of Ca, Si, S, and O in composition (SEM-EDS), in which larger yellowish aggregates with high relief, as shown in Figure 8a,b, and low interferenceMinerals 2020 ,colors10, 641 or even optically isotropic could be observed as well. They represent residual,10 of 19 unhydrated clinker grains of ordinary Portland cement.

FigureFigure 8. 8. MicrophotographsMicrophotographs of of the the cement cement mortar, mortar, sample sample KD-M–3 takenKD-M from–3 taken the exposed from foundations:the exposed foundations:(a) gypsum (a crust) gypsum on the crust surface on andthe surface cement clinkerand cement clusters clinker (marked clusters with (marked the arrow); with (b )the relics arrow) of ; (b)charcoal relics of used charcoal as a fuel used for as the a cement fuel for burning the cement and residual burning cement and residual grains (arrow) cement (plane grains polarized (arrow light).) (plane polarized light). Their chemical composition is variable; except, aggregates mostly composed of Si, Ca and O, particles,Their chemical also containing composition Ca, Al is and variable Fe, could; except be noted, aggregates as well, mostly as shown composed in Table1 of and Si, FigureCa and9. O, particlesThe analyses, also containing allow us to distinguishCa, Al and among Fe, could them be clusters noted withas well alite, as C3 Sshown and belite in Table C2S, the 1 and latter Figure being 9. more abundant than C S. Alite crystals are angular, subhedral in shapes, and 10–50 µm in size, as shown The analyses allow us 3to distinguish among them clusters with alite C3S and belite C2S, the latter in Figure 10a. Typical belite crystals are rounded, a dozen or so micrometers in size, most of them being more abundant than C3S. Alite crystals are angular, subhedral in shapes, and 10–50 μm in size, β α as exhibitshown onein Figure set of parallel 10a. Typical (type II,beliteC2 crystalsS) or two are sets rounded (type I, , a’C dozen2S) of intersectingor so micrometers lamellae, in as size, shown most in Figure 10a,b. Some of the crystals show finger-like shapes, as shown in Figure 10c. Together with of them exhibit one set of parallel (type II, β C2S) or two sets (type I, α’ C2S) of intersecting lamellae, alite and belite, interstitial phases, composed of aluminate (C A: tricalcium aluminate, 3CaO Al O ) as shown in Figure 10a,b. Some of the crystals show finger3-like shapes, as shown in Figure· 2 10c.3 and ferrite (C4AF: tetracalcium aluminoferrite, 4CaO Al2O3 Fe2O3), occur within the clusters, as shown Together with alite and belite, interstitial phases, composed· · of aluminate (C3A: tricalcium aluminate, in Figure 10a,c and also in Figure9. Most of the clusters are around 100 µm in size and surrounded by 3CaO·Al2O3) and ferrite (C4AF: tetracalcium aluminoferrite, 4CaO·Al2O3·Fe2O3), occur within the hydration rims, as shown in Figure 10a,b. The reaction between clinker grains and CO2 leads to the clusters, as shown in Figure 10a,c and also in Figure 9. Most of the clusters are around 100 μm in size decalcification of cement relics. The reduction in the Fe content in C4AF, as shown in Table1 can be and surrounded by hydration rims, as shown in Figure 10a,b. The reaction between clinker grains related to weathering processes and/or the substitution of Mg for Fe. The enrichment in Si both C3A and CO2 leads to the decalcification of cement relics. The reduction in the Fe content in C4AF, as and C4AF, as shown in Table1, may result from the isomorphic substitution of Si for Al. These phases shownare characterized in Table 1 can by thebe morerelated frequent to weather occurrenceing processes of substitutions and/or than the alite substitution and belite. of However, Mg for inFe the. The enrichmentcase of ferrite, in Si this both problem C3A mayand be C more4AF, complexas shown and in related Table to 1, the may specific result distribution from the of Feisomorphic and Al substitutionatoms in the of Ca Si2FeAlO for Al.5 structure, These phases as they couldare characterized be located in octahedralby the more or tetrahedral frequent layersoccurrence (about of substitutions75% of octahedral than alite and tetrahedraland belite. sites However, are occupied in the by Fecase and of Al, ferrite, respectively). this problem This implies may abe mixed more complexsubstitution and related of Mg for to both the Fespecific and Al distribution and similarly of of Fe Si and for Al Al and atoms Fe, but in withthe Ca a preference2FeAlO5 structu accordingre, as theyto thecould order be givelocate (i.e.,d in Mg octahedral for Fe and or Si fortetrahedral Al; [40,41 layers]). (about 75% of octahedral and tetrahedral sites areRelics occupied of charcoal by Fe used and asAl, a fuelrespectively). for the cement This burningimplies werea mixed also found,substitution as shown of Mg in Figurefor both8b. Fe and Al Theand XRPDsimilarly analysis of Si for of theAl and cement Fe, but mortar with samples a preference revealed according only quartz, to the order calcite, give feldspars, (i.e., Mg forand Fe and gypsum. Si for Neither Al; [40,4 C13S,]). C2S, C4AF, nor C3A were detected with this method. The sample displays an open porosity of 18.33% and a bulk density of 2.08 g/cm3. Its pore size distribution indicates the pores in the ranges: 350–10 µm that makes 44.8%, 1.0–0.1 µm that makes 22.9%, and the pores of 0.1–0.003 µm (21.5%). The pores of 10.0–1.0 µm make 10.8%, as shown in Figure6. The average pore diameter (calculated as a weighted average, with the weight determining the number of pores and not the percentage of the pore space) is of 0.06 µm, and the total pore area is 5.69 m2/g. The quite low hysteresis effect (28%) and threshold diameter (50 µm) indicate that the internal movement of solutions through the material is easy and the permeability is 8.96 mD. In places, the surface of the cement mortar samples is coated with a discontinuous layer with tiny, plate-shaped almost isotropic components, opaque grains, and sharp-edged iron oxides, as shown in Figure8a, apparently formed due to exposition in the polluted atmosphere. Main components of that crust are calcium sulphates (mostly gypsum), also found deeper in the sample. The pore Minerals 2020, 10, 641 11 of 19 size distribution distinctly points out susceptibility to salt crystallization in the pores of the material investigated, as shown in Figure6. Gypsum occurs as small plate-like crystals, mostly up to several tens µm in length, sometimes accumulating on the surface in the form of rosettes, as shown in Figure 11a. The presence of gypsum was verified by Raman microspectroscopy, based on the bands: strong band 1 1 1 at 1010 cm− (ν1), minor bands at 416 and 492 cm− and also at 621 and 672 cm− (ν2 and ν4), 1 2 and 1136 cm− (ν3) vibrations of SO4 −, as shown in Figure 12a [24,27]. Efflorescences could be observed on the border between the limestone blocks and the cement mortar. The XRPD analyses allowed us to identify sulphates—thenardite Na2SO4, aphthitalite (glaserite) (K,Na) Na(SO ) —and sulphate–nitrate salt—darapskite Na (SO )(NO ) H O. The remaining 3 4 2 3 4 3 · 2 components—calcite and quartz, are mostly related to the underlying material, as shown in Figure 13. Thenardite reveals characteristic euhedral (bipyramidal) crystals composed of Na, S, and O with sizes not exceeding 20 µm in length, as shown in Figure 11b. The identification of this mineral has 1 2 been based on its Raman spectrum, as shown in Figure 12b: main band at 990 cm− (ν1 SO4 −), 1 2 1 2 set of bands at 449, 460 cm− (ν2 SO4 −), and 617, 629, 643 cm− (ν4 SO4 −), and also other bands 1 2 at 1099, 1128 and 1149 cm− (ν3 SO4 −)[28]. Nevertheless, the presence of decahydrous mirabilite Na SO 10H O is also possible. At RH > 76,4% mirabilite predominates, but with an increase in the 2 4· 2 temperature and a decrease in the humidity, it turns to thenardite [25,42]. However, distinguishing mirabilite from thenardite in Raman spectroscopy could be ambiguous because of the close positions of their main Raman bands [25,28]. Salts, which can crystallize as various hydrates are particularly damaging. For the volumometric changes in reversible, dissolving/recrystallizing processes in the case of anhydrous thenardite, decahydrous mirabilite even reaches 314%, and a stone damage results just from the crystallization pressure generated in their course [43]. Minerals 2020, 10, x FOR PEER REVIEW 11 of 19

FigureFigure 9.9.SEM SEM elemental elemental maps maps and and backscattered backscattered (BSE) (BSE) electron electron image showingimage showing the qualitative the qualitative chemical compositionchemical composition of the cement of the mortar cement with mortar residual with cement residual grains cement for grains sample for KD-M-3. sample KD-M-3.

Relics of charcoal used as a fuel for the cement burning were also found, as shown in Figure 8b. The XRPD analysis of the cement mortar samples revealed only quartz, calcite, feldspars, and gypsum. Neither C3S, C2S, C4AF, nor C3A were detected with this method. The sample displays an open porosity of 18.33% and a bulk density of 2.08 g/cm3. Its pore size distribution indicates the pores in the ranges: 350–10 μm that makes 44.8%, 1.0–0.1 μm that makes 22.9%, and the pores of 0.1–0.003 μm (21.5%). The pores of 10.0–1.0 μm make 10.8%, as shown in Figure 6. The average pore diameter (calculated as a weighted average, with the weight determining the number of pores and not the percentage of the pore space) is of 0.06 μm, and the total pore area is 5.69 m2/g. The quite low hysteresis effect (28%) and threshold diameter (50 μm) indicate that the internal movement of solutions through the material is easy and the permeability is 8.96 mD. In places, the surface of the cement mortar samples is coated with a discontinuous layer with tiny, plate-shaped almost isotropic components, opaque grains, and sharp-edged iron oxides, as shown in Figure 8a, apparently formed due to exposition in the polluted atmosphere. Main components of that crust are calcium sulphates (mostly gypsum), also found deeper in the sample. The pore size distribution distinctly points out susceptibility to salt crystallization in the pores of the material investigated, as shown in Figure 6. Gypsum occurs as small plate-like crystals, mostly up to several tens μm in length, sometimes accumulating on the surface in the form of rosettes, as shown in Figure 11a. The presence of gypsum was verified by Raman microspectroscopy, based on the bands: strong band at 1010 cm−1 (ν1), minor bands at 416 and 492 cm−1 and also at 621 and 672 cm−1 (ν2 and ν4), and 1136 cm−1 (ν3) vibrations of SO42−, as shown in Figure 12a [24,27]. Minerals 2020, 10, 641 12 of 19 Minerals 2020, 10, x FOR PEER REVIEW 12 of 19

Figure 10. BackscatteredBackscattered (BS (BSE)E) electron electron image image of ofresidual residual cement cement grains grains from from sample sample KD- KD-M-3:M-3: (a)

(elongated,a) elongated, angular angular crystals crystals of alite of alite C3S C (+6)3S(+ in6) a inn aluminate an aluminate C3A C 3(+7)A( +and7) and ferrite ferrite C4AF C4 AF(+8) ( +matrix;8) matrix; (b) (clusterb) cluster of belite of belite C2S C type2S type I with I with two two sets sets of intersecting of intersecting lamellae lamellae (+9) (+ in9) ferrite in ferrite matrix, matrix, surrounded surrounded by byhydrated hydrated rim; rim; (c) (cfinger) ﬁnger-shaped-shaped belite belite crystals crystals (+10) (+10) in in ferrite ferrite matrix. matrix. For For qualitative qualitative analy analysesses of the phases, see Table1 1..

BothEfflorescences double salts—aphthitalite could be observed (K,Na) on 3theNa(SO border4)2 andbetween darapskite the limestone Na3(SO4 )(NOblocks3) Hand2O—display the cement a · complexmortar. The crystallization XRPD analyses behavior allowed and may us be to highly identify damaging sulphates for building—thenardite materials Na2SO [444,45 aphthitalite]. They are incongruently(glaserite) (K,Na) soluble;3Na(SO that4) is,2— underand equilibriumsulphate–nitrate conditions, salt— thesedarapskite compounds Na3(SO do not4)(NO crystallize3)·H2O. fromThe aremaining solution ofcomponents their own stoichiometric—calcite and quartz, compositions are mostly [44, 45related]. to the underlying material, as shown in FigureAphthitalite 13. (K,Na)3Na(SO4)2, in EDS analyses revealing the presence of Na, K, S and O, occurs in theThenardite form of anhedral, reveals characteristic often isometric euhedral crystals (bipyramidal) and irregular crystals aggregates, composed as shown of Na, in Figure S, and 11 Oc. 1 Itswith Raman sizes spectranot exceed exhibiteding 20 aμm strong in length band, atas 986shown cm− in, assignedFigure 11b. to theTheν 1identificationsymmetric stretching of this mineral mode 1 ofhas the been sulphate based on group, its Raman and the spectrum bands at, as 449 shown (ν2), in 1082 Figure (ν3), 12b: and main 1203 band cm− ,at as 990 shown cm−1 in(ν1 Figure SO42−), 12 setc. 1 1 Theof bands presence at 449, of a 460 band cm at−1 ~1202 (ν2 SO cm42−−), andand 617, the lack 629, of 643 band cm at−1 465(ν4 SO cm4−2−),allows and also us toother distinguish bands at sodium 1099, and1128 potassiumand 1149 sulphate—aphthitalite cm−1 (ν3 SO42−) [28]. and Nevertheless, anhydrous sodiumthe presence sulphate—thenardite of decahydrous that havemirabilite very similarNa2SO4·10H Raman2O spectra,is also possible. and both At of RH them > 76,4% appear mirabilite in the eﬄ predominates,orescence analyzed but with [23,28 an]. increase in the temperatureEuhedral, and platy a decrease crystals ofin variousthe humidity length,, upit turns to several to thenardite tens µm, [2 sometimes5,42]. However, fan-shaped, distinguishing consisting ofmirabilite Na, S, and from O, thenardite are most likely in Raman darapskite spectroscopy Na (SO could)(NO be) H ambiguousO, as shown because in Figure of the 11 closed. The positions Raman 3 4 3 · 2 spectraof their conﬁrmmain Raman the presence bands [2 of5,2 this8]. mineralSalts, which without can anycrystallize doubt. as The various spectra hydrates exhibit strongare particularl bands aty 1 1 2 1060damaging. cm− and For 992–989 the volumometric cm− of ν1 NO changes3− and inν1 reversible,SO4 −, respectively, dissolving/recrystalli as shown in Figurezing processes 12d. The in bands the 2 1 2 atcase 452 of can anhydrous be assigned thenardite to ν2 SO,4 decahydrous−; 728 and 706 mirabilite cm− to ν 4evenSO4 reach− andesν 4314%,NO3− ,and accordingly; a stone damage 640 and 1 2 1 2 617results cm −justto fromν4 SO the4 − crystallization. Weak signals pressure at 1123 and generated 1083 cm in− theirareconnected course [43 with]. ν3 SO4 −, and those at 1 1353Both cm− doublewith ν 3saltsNO—3−aphthitalite[26]. (K,Na)3Na(SO4)2 and darapskite Na3(SO4)(NO3)·H2O—display a complex crystallization behavior and may be highly damaging for building materials [44,45]. They are incongruently soluble; that is, under equilibrium conditions, these compounds do not crystallize from a solution of their own stoichiometric compositions [44,45]. Minerals 2020, 10, 641 13 of 19

Aphthitalite can crystallize from mixtures containing solutions of sodium sulphate—Na2SO4 and potassium sulphate—K2SO4. Darapskite is a mineral of the system Na2SO4–NaNO3–H2O. Founded in the efflorescence analyzed, both aphthitalite and darapskite suggest a more complex system of solutions; that is, containing K2SO4–Na2SO4–NaNO3–H2O. According to the solubility data, aphthitalite should precipitate as the first upon evaporation of an equimolar mixed solution of sodium sulphate—Na2SO4 and potassium sulphate—K2SO4 [46]. Darapskite is stable between 13.5 and 74 ◦C and can never occur together with nitratine NaNO3 and thenardite/mirabilite, because the stability fields of the latter two are separated by the darapskite field [47,48]. However, in the efflorescence analyzed, thenardite and darapskite occur together. According to the solubility diagram of the Na2SO4–NaNO3–H2O system at 20 ◦C[44], as water evaporates, the concentration of these two salts increases, first reaching saturation with mirabilite. The remaining solution becomes enriched in nitrate, and then also gets saturated with darapskite. In the equilibrium conditions mirabilite will re-dissolve and darapskite will crystallize instead. However, in porous materials, the re-dissolution of mirabilite may not occur, as the evaporation front moves inside, and the precipitated mirabilite will be separated from the solution. The latter will then first precipitate darapskite and, in the end, nitratine. Nitrate salts—nitratine NaNO3 and nitre KNO3—have been detected on the surface of the Jurassic limestone in the vicinity of the

Mineralseﬄorescence 2020, 10 [, 20x FOR]. PEER REVIEW 13 of 19

Figure 11. BackscatteredBackscattered (BSE) (BSE) electron electron image image of of the the secondary salts salts from the crust of the sample KDKD-M-3-M-3 ((aa)) andand from from the the eﬄ efflorescenceorescence at theat borderthe border between between the subwall the subwall limestone limestone blocks andblocks cement and cementmortar (mortarb–d). (b–d).

Aphthitalite (K,Na)3Na(SO4)2, in EDS analyses revealing the presence of Na, K, S and O, occurs in the form of anhedral, often isometric crystals and irregular aggregates, as shown in Figure 11c. Its Raman spectra exhibited a strong band at 986 cm−1, assigned to the ν1 symmetric stretching mode of the sulphate group, and the bands at 449 (ν2), 1082 (ν3), and 1203 cm−1, as shown in Figure 12c. The presence of a band at ~1202 cm−1 and the lack of band at 465 cm−1 allows us to distinguish sodium and potassium sulphate—aphthitalite and anhydrous sodium sulphate—thenardite that have very similar Raman spectra, and both of them appear in the efflorescence analyzed [23,28]. Euhedral, platy crystals of various length, up to several tens µm, sometimes fan-shaped, consisting of Na, S, and O, are most likely darapskite Na3(SO4)(NO3)·H2O, as shown in Figure 11d. The Raman spectra confirm the presence of this mineral without any doubt. The spectra exhibit strong bands at 1060 cm−1 and 992–989 cm−1 of ν1 NO3- and ν1 SO42−, respectively, as shown in Figure 12d. The bands at 452 can be assigned to ν2 SO42−; 728 and 706 cm−1 to ν4 SO42− and ν4 NO3−, accordingly; 640 and 617 cm−1 to ν4 SO42−. Weak signals at 1123 and 1083 cm-1 are connected with ν3 SO42-, and those at 1353 cm−1 with ν3 NO3− [26]. Aphthitalite can crystallize from mixtures containing solutions of sodium sulphate—Na2SO4 and potassium sulphate—K2SO4. Darapskite is a mineral of the system Na2SO4–NaNO3–H2O. Founded in the efflorescence analyzed, both aphthitalite and darapskite suggest a more complex system of solutions; that is, containing K2SO4–Na2SO4–NaNO3–H2O. According to the solubility data, aphthitalite should precipitate as the first upon evaporation of an equimolar mixed solution of sodium sulphate—Na2SO4 and potassium sulphate—K2SO4 [46]. Darapskite is stable between 13.5 and 74°C and can never occur together with nitratine NaNO3 and thenardite/mirabilite, because the stability fields of the latter two are separated by the darapskite field [47,48]. However, in the efflorescence analyzed, thenardite and darapskite occur together. According to the solubility Minerals 2020, 10, x FOR PEER REVIEW 14 of 19 diagram of the Na2SO4–NaNO3–H2O system at 20 °C [44], as water evaporates, the concentration of these two salts increases, first reaching saturation with mirabilite. The remaining solution becomes enriched in nitrate, and then also gets saturated with darapskite. In the equilibrium conditions mirabilite will re-dissolve and darapskite will crystallize instead. However, in porous materials, the re-dissolution of mirabilite may not occur, as the evaporation front moves inside, and the precipitated mirabilite will be separated from the solution. The latter will then first precipitate darapskite and, in the end, nitratine. Nitrate salts—nitratine NaNO3 and nitre KNO3—have been Minerals 2020, 10, 641 14 of 19 detected on the surface of the Jurassic limestone in the vicinity of the efflorescence [20].

FigureFigure 12. 12.Representative,Representative, characteristic characteristic Raman spectraspectra of of the the secondary secondary salts: salts: gypsum gypsum from from the the cemencementt mortar mortar crust crust (a ()a )and and efflorescence efflorescence atat thethe border border between between the the subwall subwall limestone limestone blocks blocks and and cementcement mortar: mortar: thenardite thenardite (b (b);); aphthitalite aphthitalite ((cc);); darapskitedarapskite (d ().d). The ions of crystallized sodium, potassium, calcium sulphate, and sulphate–nitrate salts may The ions of crystallized sodium, potassium, calcium sulphate, and sulphate–nitrate salts may come from both internal and external sources—natural and anthropogenic ones. The internal sources of comethe f ionsrom are both mainly internal weathering and andexternal leaching sources cement— components,natural and but anthropogenic also in the adjacent ones. stone The blocks internal sources(sandstones of the ions and limestones)are mainly ofweathering the foundations and leaching exposed. cement The domination components, of sodium but also and potassiumin the adjacent stonesalts blocks in the (sandstones efflorescence (thenarditeand limestones)/mirabilite, of the darapskite, foundations and aphthitalite) exposed. impliesThe domination that these cations of sodium andcould potassium migrate salts from in both the cementefflorescence mortar (thenardite/mirabilite, and sandstone blocks (Na darapskite and K released, and fromaphthitalite) weathering implies thatfeldspars, these cations micas, could and clay migrate minerals). from Although both cement the information mortar and on previoussandstone conservation blocks (Na works and cannot K released frombe weathering verified, their contributionfeldspars, micas seems, toa bend very clay likely. minerals). Materials Although used at the the conservation, information such ason water previous conservationglass, could works yield Nacannot and Cabe (Caverified, regarding their gypsum) contribution ions [49 seems,50]. to be very likely. Materials used at the conservation,The analysis such of as the water external glass, anthropogenic could yield sources Na and should Ca (Ca start regarding from the gypsum) air pollution—wet ions [49,50]. and dry airborne deposition supplying mainly sulphate and nitrate anions. The road de-icing salts The analysis of the external anthropogenic sources should start from the air pollution—wet and (NaCl and CaCl ) and detergent solutions used for cleaning (e.g., streets) could be sources of both dry airborne deposition2 supplying mainly sulphate and nitrate anions. The road de-icing salts (NaCl Na and Ca cations and also chloride ions. Halite was observed at various elements of the chapel andfaçade CaCl2 and) and foundations detergent [ 20solutions]. The position used for of the cleaning foundations (e.g., belowstreets) the could pavement be sources level, adjacently of both Na to and Ca cationsthe drying and ditch, also exposingchloride subwall,ions. Halite promotes was observed the movement at various of these elements substances of tothe the chapel foundations. façade and foundationsOther extrinsic [20]. The sources position of ions of for the precipitated foundations salts below could bethe animal pavement (e.g., droppingslevel, adjacently of birds, to such the asdrying ditch,pigeons exposing in Cracow) subwall, and microbiologicalpromotes the activities,movement as wellof these as capillary substances rises in to ground the foundations. and soil waters. Other extrinsic sources of ions for precipitated salts could be animal (e.g., droppings of birds, such as Minerals 2020, 10, x FOR PEER REVIEW 15 of 19 pigeonsMinerals 2020 in , Cracow)10, 641 and microbiological activities, as well as capillary rises in ground and15 soil of 19 waters.

FigureFigure 13. 13. CharacteristCharacteristicic X‐ X-rayray patterns patterns of ofthethe efflorescence eﬄorescence sampled sampled from from the theborder border between between the subwallthe subwall limestone limestone blocks blocks and and cement cement mortar. mortar. Abbr Abbreviations:eviations: Aph Aph—aphthitalite,—aphthitalite, Cal Cal—calcite,—calcite, DrDr—darapskite,—darapskite, Th Th—thenardite,—thenardite, Qz Qz—quartz.—quartz.

AlthoughAlthough since thethe 1990s1990s thethe concentration concentration of of pollution pollution in Cracowin Cracow has has been been decreasing, decreasing, the levelthe levelof gaseous of gaseous and particulate and particulate pollution pollution is still signiﬁcant is still significant [51,52]. This [51,52 is a]. consequenceThis is a consequence of the unfavorable of the unfavorableatmospheric atmospheric conditions of theconditions town, which of the include town, weak which winds, include temperature weak winds, inversions, temperature fogs [53], inversions,as well as the fogs presence [53], as of w largeell as industrial the presence centers of and large fossil industrial fuel burning. centers Additionally, and fossil roadfuel transportburning. Acontributesdditionally, its road share, transport notably contributes in the dense its structural share, notably layout in of the the dense Cracow structural Old Town. layout Industrial of the Cracowemissions, Old carried Town. byIndustrial prevailing emissions, western carried winds fromby prevailing neighbouring western regions, winds further from neigh increasesbouring the regions,pollution further level inincrease the city.s the pollution level in the city.

44.. Conclusions Conclusions TheThe study study presents presents characteristics characteristics of the of thecement cement render render and mortar and mortar used for used stone for repair stone and/or repair substitutionand/or substitution at the atMyszkowskis the Myszkowskis chapel chapel of the of Holy the Holy Trinity Trinity Church Church in inCracow. Cracow. The The a analysesnalyses demonstrateddemonstrated that that the the render render covering covering some some of of the the decayed decayed Pińczów Pi´nczów limestone limestone blocks blocks of of the the chapel chapel façadefaçade was was prepared prepared using using Portland Portland cement cement as as a a binding binding agent, agent, mixed mixed with with crushed crushed stone stone as as an an aggregate.aggregate. Characteristic Characteristic bioclasts bioclasts—red—red algae algae of of the the genus genus Lithothamnium, Lithothamnium, bryozoans, bryozoans, foraminifers, foraminifers, brokenbroken pieces pieces of bivalve shells—pointshells—point outout anan organogenicorganogenic limestone limestone of of the the Pi´ncz Pińczówów type. type. The The relics relics of the PC clinker detected include unhydrated alite C S and belite C S crystals of various morphology and of the PC clinker detected include unhydrated3 alite C3S and2 belite C2S crystals of various morphologytexture in the and form texture of clusters, in the often form with of rimsclusters, of inner often hydration with rims products. of inner The hydration main components products. of The the cement, in addition to portlandite Ca(OH) , are ettringite Ca Al (SO ) (OH) 26H O, monosulphite main components of the cement, in2 addition to 6portlandite2 4 3 Ca(OH)12· 2,2 are ettringite Ca Al O SO 11H O, and gypsum. Although ettringite is a primary hydration product in ordinary Ca64Al2(SO2 64)3(OH)3· 12·26H2 2O, monosulphite Ca4Al2O6SO3·11H2O, and gypsum. Although ettringite is a primaryPortland hydration cement, it rapidlyproduct dissolves in ordinary when Portland the sulphate, cement, generally it rapidly gypsum dissolves added to when the PC, the is exhausted.sulphate, generallyThis phase, gypsum however, added precipitates to the PC, again is exhausted. with the availability This phase, of anhowever, external precipitate source of sulphates again with (e.g., the air availabilitypollution sulfur of an dioxide,external stillsource abundant of sulphate in Cracow). (e.g., air In pollution the case sul studied,fur dioxide, the secondary still abundant gypsum, in Cracowobserved). In on the the case surface studied, and the in thesecondary cracks ofgypsum, the render, observed presents on the such surface a sulphate and in source,the cracks allowing of the render,ettringite presents and monosulphite such a sulphate to precipitate. source, Moreover,allowing ettringite the C3A and and C 4monosulphiteAF substrates neededto precipitate. to form these sulphates have not been observed, either within the clusters of C S and C S, or in the cement Moreover, the C3A and C4AF substrates needed to form these sulphates2 have not3 been observed, matrix. This may suggest their exhaustion due to the sulphate crystallization and seems to support either within the clusters of C2S and C3S, or in the cement matrix. This may suggest their exhaustion duethis supposition.to the sulphate The crystallization crystallization and of ettringite, seems to monosulphite, support this andsupposition. gypsum undoubtedlyThe crystallizat damagedion of the render used for the stone repair and/or substitution. Minerals 2020, 10, 641 16 of 19

The cement mortar between stony blocks of the subwall below the pavement level was based on the Portland cement mixed with aggregate containing quartz, feldspars, and rock fragments. The relics of unhydrated PC clinker include alite C3S and belite C2S clusters with aluminate C3A and ferrite C4AF as interstitial phases within the clusters. The main components of the cement mortar analyzed are calcite, quartz, feldspars, and gypsum. The following hydrated secondary salts have been detected: simple salts—except gypsum CaSO 2H O thenardite/mirabilite Na SO /Na SO 10H O; a double 4· 2 2 4 2 4· 2 sodium/potassium salt—aphthitalite (K,Na)3Na(SO4)2; a double sulphate/nitrate salt—darapskite Na (SO )(NO ) H O. Gypsum, in the form of crusts, was observed on the mortar surface. 3 4 3 · 2 The sulphate and sulphate/nitrate salts of sodium and potassium—thenardite/mirabilite, aphthitalite and darapskite—are present in the form of efflorescence (in some parts of the foundations). The high porosity and capillary of the cement matrix promote the salt migration and allow the salt crystallization at the interface cement/stone. The compositions of the salts are mostly related to the components of the cement mortar in replacements and joints, but it may be affected by the sandstone blocks and possible past conservation materials as well. The secondary sulphate and sulphate/nitrate salts reported are related to the air pollution in Cracow as well. More accurate characteristics of different sources of sulphates would require sulfur and oxygen stable isotope analyses.

Author Contributions: M.M. conceived the idea, performed most of the measurements and interpreted the result, wrote the manuscript, and prepared most of the figures; K.D. assisted with the OM analyses and helped to improve the English version of the manuscript; A.G. performed XRPD analyses and prepared some of the figures. All authors have read and agreed to the published version of the manuscript. Funding: The studies were supported by the AGH University of Science and Technology, Kraków, grant 16.16.140.315. Acknowledgments: The authors acknowledge the help of B. Polczyńskiand K. Bałaga in sampling the historic monument and G. Machowski, E. Pstrucha and A. Pstrucha from the Mercury Porosimetry Laboratory, AGH-UST, for performing mercury porosimetry measurements. We would like to thank both anonymous reviewers for their comments, which were helpful in improving the manuscript. Conflicts of Interest: The authors declare no conflict of interest.

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