The Devonian micritic limestones from the Prague Basin (Barrandian area, Bohemian Massif, Czech Republic), which were the primary raw material used for natural hydraulic lime burned in Prague, exhibit a feebly to eminently hydraulic character. Based on a laboratory experimental study, the burned product is composed of dominant free-lime (CaO) and/or portlandite (Ca(OH)2), larnite-belite (bicalcium silicate 2CaO.SiO2), and quartz (SiO2) - i.e. phases formed due to the decomposition of carbonate and quartz, present in the original limestones. Proportions of the newly formed phases depend on: the composition of the raw material, maximum burning temperature (the highest amount of larnite-belite appearing at a burning temperature of 1200 °C), and the granulometry of the experimental batches (a coarsely-ground batch exhibited a higher amount of larnite-belite compared to the finely-ground one). The presence of minor phyllosilicates in the raw material contributed to the formation of gehlenite, brownmillerite, wollastonite, calcium aluminate, and/or spurrite.
Despite the dominant use of Ordinary Portland Cement (OPC) as almost the exclusive hydraulic binder in the modern construction industry, the increased interest in the production and application of alternative hydraulic binders (natural hydraulic lime, natural cement) can be seen during the past decades (
The former lands of the Czech crown (specifically Bohemia, which makes up a major part of the current Czech Republic) are known to have produced diverse types of inorganic constructional binders over many centuries (
Despite detailed lithostratigraphical and/or palaeontological study of these limestones during the past decades (
The abandoned limestone quarries from where our samples were taken are situated in the Prague Basin, which represents the largest Neoproterozoic – Lower Palaeozoic sedimentary basin of the Bohemicum (Teplá-Barrandian) terrane in the centre of the Bohemian Massif (
Position of Palaeozoic sediments of Prague Basin within the Bohemian Massif (A) and a geological map of the central part of the Prague Basin (modified after (
The lithology of the Prague Basin is characterised by the presence of various sedimentary rocks (shales, siltstones, sandstones, limestones, silicites/cherts), locally accompanied with syngenetic volcanic rocks and volcanoclastics sediments. In contrast to dominant shale deposition in the Lower Silurian, eustatic movements caused basin shallowing during the Upper Silurian (
The sampling site is located in the southern part of Prague (Prague 4 district, a local area called Bráník, incorporated into Prague in 1949) where large outcrops (faces of a historic abandoned quarry) of the Lower Devonian (Pragian stage) rocks can be found. The area of the abandoned quarry, located on the right bank of the Vltava River, has been protected since 1986 as ‘Bráník Rocks Natural Monument’. The exposed quarry face (
General view of the southern part of the abandoned historic quarry in the Podolí district (southern part of Prague). Extensive exploitation of moderately to eminently hydraulic limestones from the 1860s until the 1920s destroyed all signs of earlier quarrying (14th–18th c.).
The beginnings of exploitation of limestones in this area is probably connected with the extensive construction activity of an expanding Prague in the mid 14th c. (during the reign of the Czech King and Emperor of the Holy Roman Empire, Charles IV Luxembourg). Exploitation and use of these limestones during the 14th c. cannot be proven from any written record but only through the material evidence, which is based on the analysis of mortars and ‘concretes’ from well-dated structures such as the Charles Bridge in Prague, for which the local NHL was used (
The experimental material was obtained from four levels of the Dvorce-Prokop Limestone unit (
Lower and Middle Devonian lithostratigraphy of the Prague Basin (modified by Chlupáč (
Macroscopic character of the experimental material employed in this study. From top left sample HPV/I/1, HPV/I/2, HPV/I/3, and HPV/1/4.
Following the macroscopically observable differences, 4 major types of limestones (
After a brief macroscopic description of the raw material (unburnt limestone) hand specimens, a major part of petrographic research was conducted on the micro-scale using thin section study using a conventional optical microscope (Leica DMLP), supplemented with a cathodoluminiscence (CL) study. Observations of thin sections with an optical microscope provided the possibility of an overall description of the rock microfabric (basic qualitative data on present phases, their sizes, shapes and mutual relationships, distinguishing of bioclasts); however, the extremely fine-grained character of the rocks studied prohibited any sound quantification of modal composition and/or characterisation of minor components by the use of optical microscopy. Also, the predominance of the fine-grained micritic carbonate component prevented the search for some specific features in the visible light mode. Some of the features were further studied by using a CL study employing ‘cold’ cathode type CCI 8200 Mk4 coupled with a Leica DMLP optical microscope. These observations were performed under the following conditions: beam current 300 μA, electron energy 15–18 kV. Microphotographs documenting typical CL colours and patterns were captured with a Canon digital camera coupled with the optical microscope.
The extremely fine-grained character of the studied rocks, and the inability to conduct any quantitative analysis within an ordinary optical microscope, lead to the adoption of scanning electron microscopy with energy dispersive spectrometry (SEM/EDS) of polished, carbon-coated thin sections. These measurements were performed using a Tescan Vega instrument, with an Oxford Instruments LINK ISIS 300 energy-dispersive analytical system under the following conditions: beam current 0.8 nA; 180 s counting time; and a 20–30 kV accelerating voltage. A 53 Minerals Standard Set #02753-AB (SPI Supplies) was used for the standard quantitative calibration. SEM/EDS was also employed to obtain X-ray scans of representative areas (each about 1 mm2) on which the quantitative analysis (specifically modal composition) was performed.
Based on the chemical analyses, as described below, a non-carbonate component makes up an important part of the studied limestones. Their extremely fine-grained nature and relatively homogeneous distribution within the micritic carbonate matrix make their microscopic examination impossible (especially in an optical microscope). For this reason, phase analysis of non-carbonate phase was primarily performed by powder X-ray diffraction (XRD) of the insoluble residue. This was obtained by leaching off the carbonates, using a 1 M solution of HCl and/or CH3COOH over a period of 12 hours. The samples were then centrifuged and washed in distilled water in order to remove water soluble salts (especially chlorides). After the settling of the insoluble residues, the excessive water was filtered through a filter paper on a laboratory suction device. The solid matter was then dried to a constant weight.
Dried insoluble residues were analysed by powder XRD using a PANalytical X'Pert Pro diffractometer equipped with a monochromator with X'Celerator multichannel detectors. The measurement conditions were as follows: Cu cathode α, 40 kV, 30 mA, measuring step 0.05°/200 seconds, angle 2.99–70° 2Θ. The resulting diffractograms were processed and evaluated using X'Pert High Score 1.0d software and the JCPDS PDF-2 database.
Prior to experimental burning, the studied limestones were also examined for their chemical composition. Major elements were determined by classical wet chemical analysis (
Data from the chemical analysis also served for the evaluation of the hydraulicity of the studied materials. This property can be computed by using so called hydraulic index (HI) as suggested by Spalding (
The resulting value is dimensionless and the scale for HI is: 0.1–0.2 (feebly hydraulic materials), 0.2–0.4 (moderate hydraulic materials) and 0.4–1 (for eminently hydraulic materials) (
Cementation index (CI) was proposed by Eckel (
The scale for CI is: 0.3–0.5 (feebly hydraulic materials), 0.5–0.7 (moderate hydraulic materials) and 0.7–1.1 (for eminently hydraulic materials) (
Experimental burning was performed in a laboratory furnace (type 0612 by Clasic Co.) by using two different experimental batches: (
The burned material was investigated for its phase composition by powder XRD. The measurement conditions were the same as for the XRD analysis of the insoluble residue.
The studied limestones can be classified as biomicrite limestone (
Results of qualitative and quantitative petrographic analyses of the studied limestones
HPV/I/1 | HPV/I/2 | HPV/I/3 | HPV/I/4 | |
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Carbonates | 90.13 | 90.36 | 82.75 | 80.03 |
Insoluble residue | 9.87 | 9.64 | 17.25 | 19.97 |
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Calcite | 88.97 | 87.17 | 80.18 | 79.73 |
Dolomite | 1.16 | 1.17 | 1.85 | 1.17 |
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Micrite | 55 | 55 | 60 | 60 |
Sparite | 10 | 15 | 15 | 15 |
Bioclasts | 35 | 30 | 25 | 25 |
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Tentaculites | 30 | 30 | 40 | 35 |
Cephalopods | 10 | 10 | 10 | 15 |
Ostracods | 20 | 10 | 10 | 15 |
Crinoids | 10 | 5 | 10 | 5 |
Brachiopods | – | 5 | – | 5 |
Trilobites | – | 5 | 5 | 5 |
Gastropods | 10 | 10 | 5 | 5 |
Non-identified | 20 | 25 | 20 | 15 |
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Quartz | 5.32 | 5.45 | 10.08 | 12.36 |
Illite | 3.29 | 3.53 | 3.22 | 3.55 |
Kaolinite | 1.09 | 1.23 | 1.09 | 1.12 |
Chlorite | 0.19 | 0.18 | 0.44 | 0.51 |
K-feldspar | 0.40 | 0.47 | 0.66 | 0.78 |
Plagioclase (albite) | 0.25 | 0.26 | 0.32 | 0.27 |
Rutile | 0.06 | 0.06 | 0.06 | 0.09 |
Fe-oxihydroxides | 0.15 | 0.14 | 0.15 | 0.23 |
Other minerals | 0.34 | 0.34 | 0.42 | 1.36 |
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Folk ( |
Biomicrite limestone | Biomicrite limestone | Biomicrite limestone | Biomicrite limestone |
Dunham ( |
Wackestone | Wackestone | Wackestone/packstone | Wackestone/packstone |
Konta ( |
Limestone | Limestone | Siliceous limestone | Siliceous limestone |
Carbonates are the most abundant rock-forming mineral (80–90 wt. %) in the studied rocks (
Characteristic microscopic features of the studied limestones as observed by optical microscopy of thin sections. Fine-grained micritic matrix rich in microfossils – cross-section of tentaculite
Bioclasts were derived from the most abundant and well-preserved shells of tentaculites (
Dolomite crystals were only commonly observed in one of the studied specimens (HPV/I/3), whilst remained rare in the others. The zonal fabric of these crystals (compare
Non-carbonate phases contribute to 10–20 wt. % of solid matter in the studied limestones (
According to the powder XRD study, the insoluble residue is composed of quartz (cryptocrystalline quartz – chalcedony), phyllosilicates (chlorite and clay minerals such as illite, kaolinite), and feldspars. Due to the dominance of quartz (chalcedony) and some clay minerals (illite and kaolinite), some minor and/or accessory phases were hardly detectable from the XRD data. The dominant forms of SiO2 were quartz grains (
According to the MINLITH algorithm, quartz makes up the most abundant non-carbonate phase in the studied rocks, ranging from 5 to 12 wt. % in the whole rock (
Microphotographs of the studied limestones as seen using CL. Cross-section through a couple of
Non-carbonate minerals are preferentially randomly distributed in the matrix (
SEM-BSE microphotographs of polished thin sections documenting the characteristic phenomena in the studied limestones. Dominant calcite (micritic matrix) with clay minerals (prevalent illite), a few larger domains of quartz grains, and very few larger (silt-size) clasts of K-feldspar, sample HPV/I/1 (A); Calcite (micritic matrix) forming clusters separated with quartz (cryptocrystalline quartz – chalcedony) rich rims, relatively abundant clay minerals are represented by both illite and kaolinite, sample HPV/I/2 (B); Coarser-grained microfabric with calcite (micritic matrix) and dolomite grains (probably sparitic), quartz (chalcedony) makes up the common filling of interparticle spaces, pyrite makes an accessory phase, sample HPV/I/3 (C); Detail showing character of zonal dolomite grains occurring in quartz (chalcedony) filling of microfossil, sample HPV/I/3 (D); Micritic calcite-dominated matrix with interstitial quartz (chalcedony) filling, and pressure solution seams, rich in clay minerals (illite and kaolinite), accompanied with some accessory pyrite, sample HPV/I/4 (E); Domain of sparitic dolomite-rich domain with frequent non-carbonate minerals (clay minerals, silt size feldspars and quartz). Note that pyrite again makes up a common accessory phase, sample HPV/I/3 (F).
Percentage of insoluble residue in the samples of the studied limestones prepared by leaching off carbonates using hydrochloric acid (HCl) and/or acetic acid (Aa); all data in wt. %.
Distribution of the principal elements (Ca, Mg, Si, Al, K) in the studied unburned limestones based on the XRD mapping performed by SEM/EDS. Based on these data, the spatial distribution of rock-forming minerals is highly homogeneous.
According to the results of wet-silicate analyses (
Chemistry of the studied limestone
HPV/I/1 | HPV/I/2 | HPV/I/3 | HPV/I/4 | |
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SiO2 | 6.70 | 6.48 | 13.94 | 15.76 |
TiO2 | 0.06 | 0.06 | 0.06 | 0.09 |
Al2O3 | 1.23 | 1.26 | 1.29 | 1.62 |
Fe2O3(tot) | 0.45 | 0.43 | 0.44 | 0.75 |
MnO | 0.05 | 0.06 | 0.03 | 0.03 |
MgO | 0.77 | 0.78 | 1.23 | 0.78 |
CaO | 50.01 | 49.76 | 44.84 | 43.97 |
Na2O | 0.03 | 0.03 | 0.07 | 0.02 |
K2O | 0.37 | 0.35 | 0.35 | 0.44 |
P2O5 | 0.05 | 0.08 | 0.06 | 0.05 |
H2O+ | 0.12 | 0.10 | 0.12 | 0.18 |
H2O– | 1.20 | 1.17 | 1.18 | 1.35 |
CO2 | 38.54 | 38.90 | 35.54 | 34.36 |
Σ | 99.79 | 99.60 | 99.55 | 99.57 |
The quality of a raw material for the production of NHL is primarily governed by the presence and amount of non-carbonate minerals, specifically of quartz and clay minerals that contribute SiO2 and/or Al2O3 (
Classification of hydraulicity of the studied limestones based on their chemistry. HI= hydraulic index, CI= cementation index
HPV/I/1 | HPV/I/2 | HPV/I/3 | HPV/I/4 | |
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HI (Spalding ( |
0.16 | 0.16 | 0.34 | 0.40 |
Feebly hydraulic | Feebly hydraulic | Eminently hydraulic | Eminently hydraulic | |
CI (Eckel ( |
0.40 | 0.39 | 0.87 | 1.03 |
Feebly hydraulic | Feebly hydraulic | Eminently hydraulic | Eminently hydraulic |
As expected from the study of the mineralogical and geochemical characteristics of the raw materials, the newly formed phases during burning are those typically found in the systems dominated by the presence of CaO-SiO2-Al2O3 (C-S-A).
The phase composition of burned Dvorce-Prokop Limestones is dominated by free-lime (CaO-C) and/or portlandite (Ca(OH)2-CH), larnite-belite (bicalcium silicate 2CaO.SiO2-C2S), as well as quartz and other forms of SiO2 (S) (
Complete XRD patterns (A, B) and XRD patterns in detail (C, D) of the samples burned at 1200 °C with the marked phases (HPV/I/1 - 1, HPV/I/2 - 2, HPV/I/3 - 3 and HPV/I/4 - 4). Both finely-ground batch (A, C) and coarsely-ground batch (B, D) are shown.
Along with these dominant phases, some less abundant, but still clearly detectable newly formed phases were detected by powder XRD: gehlenite (2CaO.Al2O3.SiO2-C2AS), brownmillerite (4CaO.Al2O3.Fe2O3-C4AF), wollastonite (CaO.SiO2-CS), calcium aluminate (CaO.Al2O3-CA), and spurrite (5CaO.2SiO2.CO2-C5S2).
The presence of the above mentioned phases and their mutual proportions vary depending on the composition of the raw material, maximum temperature reached during burning, and the granulometry of the experimental batch (
Relative (semi-quantitative) phase composition of products burned in the range of temperatures of 850–1200 °C. Both finely- and coarsely-ground batches are shown. Legend: L – larnite-belite, C – free-lime, Q – quartz and SiO2 phases, P – portlandite, B – brownmillerite, G – gehlenite, W – wollastonite, H – calcium aluminate CA, S – spurrite
HPV/I/1 finely-ground batch | ||||||||||
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Temperature | L | C | Q | P | B | G | W | A | H | S |
850 °C | 26 | 55 | 10 | 5 | – | – | – | 1 | 3 | – |
900 °C | 32 | 50 | 8 | 4 | – | – | – | 2 | 4 | – |
950 °C | 35 | 46 | 6 | 5 | – | 1 | – | 1 | 3 | 3 |
1000 °C | 37 | 41 | 2 | 3 | 3 | 3 | 4 | 1 | 2 | 4 |
1050 °C | 40 | 39 | 2 | 3 | 4 | 4 | 5 | – | – | 3 |
1100 °C | 42 | 36 | 2 | 4 | 4 | 5 | 5 | – | – | 2 |
1150 °C | 46 | 34 | 1 | 4 | 5 | 5 | 4 | – | – | 1 |
1200 °C | 49 | 33 | 1 | 4 | 4 | 4 | 5 | – | – | – |
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850 °C | 29 | 43 | 10 | 14 | – | – | – | 2 | 2 | – |
900 °C | 33 | 39 | 9 | 13 | – | – | – | 2 | 4 | – |
950 °C | 37 | 37 | 8 | 13 | – | 1 | – | 1 | 3 | – |
1000 °C | 39 | 35 | 4 | 11 | 2 | 4 | 3 | 1 | 1 | – |
1050 °C | 43 | 33 | 2 | 13 | 2 | 4 | 3 | – | – | – |
1100 °C | 44 | 31 | 2 | 11 | 4 | 5 | 3 | – | – | – |
1150 °C | 50 | 27 | 1 | 11 | 3 | 4 | 4 | – | – | – |
1200 °C | 53 | 25 | 1 | 10 | 3 | 4 | 4 | – | – | – |
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850 °C | 26 | 57 | 8 | 4 | – | – | – | 2 | 3 | – |
900 °C | 30 | 52 | 7 | 5 | – | – | – | 2 | 4 | – |
950 °C | 33 | 47 | 6 | 5 | – | 1 | 1 | 2 | 3 | 2 |
1000 °C | 35 | 43 | 3 | 4 | 3 | 4 | 3 | 1 | 1 | 3 |
1050 °C | 37 | 40 | 2 | 4 | 4 | 5 | 5 | – | – | 3 |
1100 °C | 43 | 37 | 1 | 4 | 5 | 5 | 4 | – | – | 1 |
1150 °C | 47 | 35 | 1 | 3 | 4 | 5 | 5 | – | – | – |
1200 °C | 49 | 32 | 1 | 4 | 5 | 4 | 5 | – | – | – |
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850 °C | 28 | 45 | 8 | 13 | – | – | – | 2 | 4 | – |
900 °C | 34 | 42 | 7 | 12 | – | – | – | 2 | 3 | – |
950 °C | 38 | 39 | 5 | 12 | – | 1 | 1 | 1 | 3 | – |
1000 °C | 40 | 37 | 4 | 9 | 3 | 2 | 3 | 1 | 1 | – |
1050 °C | 43 | 36 | 2 | 10 | 3 | 3 | 3 | – | – | – |
1100 °C | 45 | 30 | 1 | 13 | 4 | 4 | 3 | – | – | – |
1150 °C | 50 | 26 | 1 | 12 | 4 | 3 | 4 | – | – | – |
1200 °C | 51 | 24 | 1 | 10 | 5 | 4 | 5 | – | – | – |
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850 °C | 26 | 42 | 22 | 5 | – | – | – | 2 | 3 | – |
900 °C | 31 | 37 | 19 | 4 | – | – | – | 3 | 4 | 2 |
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950 °C | 34 | 35 | 16 | 4 | – | 1 | 1 | 2 | 3 | 4 |
1000 °C | 37 | 33 | 9 | 5 | 3 | 4 | 4 | 1 | 1 | 3 |
1050 °C | 46 | 30 | 5 | 5 | 4 | 4 | 5 | – | – | 1 |
1100 °C | 50 | 28 | 2 | 4 | 5 | 5 | 4 | – | – | 2 |
1150 °C | 55 | 25 | 1 | 5 | 4 | 4 | 5 | – | – | 1 |
1200 °C | 58 | 23 | 1 | 3 | 5 | 5 | 4 | – | – | 1 |
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850 °C | 28 | 31 | 22 | 13 | – | – | – | 3 | 3 | – |
900 °C | 34 | 27 | 20 | 14 | – | – | – | 2 | 2 | 1 |
950 °C | 38 | 26 | 16 | 12 | – | 1 | 1 | 2 | 1 | 3 |
1000 °C | 40 | 24 | 12 | 12 | 2 | 3 | 3 | 1 | 1 | 2 |
1050 °C | 44 | 22 | 9 | 10 | 4 | 5 | 4 | – | – | 2 |
1100 °C | 53 | 18 | 5 | 10 | 4 | 4 | 5 | – | – | 1 |
1150 °C | 57 | 17 | 2 | 11 | 4 | 5 | 4 | – | – | – |
1200 °C | 61 | 14 | 1 | 10 | 5 | 4 | 5 | – | – | – |
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850 °C | 28 | 40 | 22 | 4 | – | – | – | 3 | 3 | – |
900 °C | 31 | 36 | 19 | 5 | – | – | – | 3 | 4 | 2 |
950 °C | 36 | 34 | 15 | 5 | – | 1 | 1 | 2 | 3 | 3 |
1000 °C | 39 | 30 | 10 | 4 | 2 | 4 | 4 | 2 | 1 | 4 |
1050 °C | 44 | 28 | 7 | 4 | 2 | 5 | 4 | 1 | 1 | 4 |
1100 °C | 50 | 25 | 5 | 4 | 5 | 4 | 5 | – | – | 2 |
1150 °C | 56 | 24 | 2 | 3 | 4 | 5 | 4 | – | – | 2 |
1200 °C | 61 | 20 | 1 | 3 | 4 | 5 | 5 | – | – | 1 |
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850 °C | 29 | 28 | 25 | 11 | – | – | – | 3 | 4 | – |
900 °C | 33 | 25 | 22 | 11 | – | – | – | 3 | 4 | 2 |
950 °C | 37 | 24 | 18 | 12 | – | 1 | 1 | 2 | 3 | 2 |
1000 °C | 39 | 22 | 16 | 11 | 1 | 3 | 4 | 1 | 2 | 1 |
1050 °C | 44 | 19 | 10 | 12 | 3 | 4 | 4 | 1 | 1 | 2 |
1100 °C | 52 | 14 | 8 | 11 | 4 | 5 | 5 | – | – | 1 |
1150 °C | 61 | 12 | 3 | 10 | 4 | 4 | 5 | – | – | 1 |
1200 °C | 63 | 10 | 1 | 10 | 5 | 6 | 4 | – | – | 1 |
The most favourable conditions for the formation of larnite-belite, the principal phase of the burned material, together with gehlenite and/or brownmillerite took place when the burning temperature exceeded 1100 °C (
Calcium aluminate, and occasionally also the Al2O3-rich and Fe2O3-rich phases, are probably transitional phases that occur in the temperature range of 850–1000 °C, but disappear at higher temperatures, which are involved in the formation of other phases (
Along with the composition of the raw material, the burning temperature is the most important factor influencing the phase composition of the burned product (
Relative (semi-quantitative) percentages of: larnite-belite, free-lime, portlandite, quartz and SiO2 phases, and other phases formed during burning at 850 °C–1200 °C. Both finely-ground batch and coarsely-ground batch are shown.
The granulometry of the burned raw material seems to be another factor specifically influencing the amounts of newly-formed hydraulic phases. As can been seen from the percentage of larnite-belite formed in the finely-and coarsely-ground experimental batches (
On the contrary, the finely-ground experimental batch was probably ground to such a level that most of the present mineral grains (e.g., carbonates) were liberated, and thus it was more difficult to achieve the necessary reaction between the carbonate and non-carbonate phases. However, this observation is preliminary and requires further experimental evaluation, which is beyond the scope of current paper.
A set of limestones coming from one stratigraphic position (Dvorce-Prokop Limestone, Lower Devonian, Prague Basin, Bohemian Massif, Czech Republic) and exhibiting significant variation in composition (quantity of carbonates 80–90 vol. %, quartz 5–12 vol. %, phyllosilicates – clay minerals 4–5 vol. %) was burned under laboratory conditions at temperatures from 850 to 1200 °C.
Due to the mineralogical and chemical compositions of the raw materials, the burned product was dominated by free-lime (C) and/or portlandite (CH), larnite-belite (C2S), as well as quartz and other SiO2 phases (S). However, some minor admixtures of wollastonite (CS), gehlenite (C2AS), brownmillerite (C4AF), calcium aluminate (CA), and spurrite (C5S2) were detected as well. The presence of the hydraulic phases was not only affected by the composition of the raw materials and peak temperature reached during experimental burning, but also by the specific conditions during laboratory burning, as well as by the granulometry of the experimental batches. In this study, spurrite remained stable in specimens burned at temperatures of about 1200 °C, which is attributed to the specific conditions in the laboratory furnace where this phase remains stable due to a high concentration of CO2.
For raw materials exhibiting only 10 vol. % of non-carbonate phases (i.e., suitable for the production of feebly hydraulic lime), the peak burning temperature of about 1100 °C seems to be sufficient for the formation of all principal hydraulic phases. Raw materials with an eminently hydraulic character (i.e., containing about 20% of non-carbonate phases) require a burning temperature of about 1200 °C for the formation of the maximum amount of larnite-belite.
The amount of hydraulic phases formed during burning was also significantly affected by the granulometry of experimental batches. In the recent study, the amount of hydraulic phases was consistently higher in the coarsely-ground experimental batch (i.e., having grain size in the range of 1.25–3 mm) than in the finely-ground experimental batch (grain size up to 200 μm). It is assumed that for the coarsely-ground experimental batch, the mineral phases present in the studied limestones remain in mutual contact during burning, and thus have favourable conditions to react together to form larnite-belite and others hydraulic phases. On the contrary, the finely-ground experimental batch was ground to such a fine level that most of the mineral grains present (e.g., carbonates having a micritic character) were liberated, and thus it was more difficult to achieve the necessary reaction between the carbonate and non-carbonate phases.
This paper makes part of Petr Kozlovcev's Ph.D. study. Experimental part of the work has been financed by the research project No. 904314 “Influence of the mineralogical composition of raw material on phases formed during the burning of hydraulic lime and natural cement” from the Charles University Grant Agency.