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Ischler hydraulic lime

Historical development of cement:

Even the Romans knew how to use the fact that a hydraulic binder, “pozzolanic lime”, was created from a mixture of slaked quicklime and natural or artificial pozzolana (volcanic ash, trass, crushed brick). Mixed with water and sand, the pozzolanic lime resulted in a water-resistant (“hydraulic”) product that hardened slowly, but to great strength and was therefore ideal for sea water construction (port facilities). Even the famous Pantheon in Rome, which still has the largest non-reinforced concrete dome in the world today, was built a good 2nd century ago  000 years built from this binder. The Roman Heidentor in Carnuntum is the oldest concrete structure in Austria.

Heidentor Carnuntum, Wikipedia

But like so many technical cultural assets, the knowledge of the production of this concrete and the binding agent that went with it was probably lost in the turmoil of the migration of peoples.

It was not until the middle of the 18th century in England, whose maritime location caused numerous hydraulic structures, that hydraulic lime and cements began to be produced by burning natural limestone. In 1759, the English engineer John Smeaton discovered that limestone types that left a clayey residue when dissolved in nitric acid were particularly suitable.

Consequently, John Smeaton used such clay-contaminated limestone (“marl”) for the hydraulic binders, which he now began to burn on a large scale himself. The lighthouse at Eddystone , England, was the first modern concrete structure to be built from Smeaton's hydraulic limes in 1774.

John Smeaton, um 1770, Internet
Leuchtturm von Eddystone, England, Internet

before it was replaced in 1850 by Portland cement , which was also invented in England. Portland cement is burned above the sintering temperature of 1475°C and thus results in a hydraulic binder with significantly higher strength than Roman cement. Based on this discovery, the Englishman James Parker invented a hydraulically hardening product in 1796, which he had fired from lime marl with a high clay content mined near London. Parker patented his binder as "Roman Cement". The lime marl was heated to around 1200°C just before sintering (caking together without melting).

Cement, initially referred to as "Roman cement" in memory of Roman concrete, was reinvented.

Since hydraulic building materials could now be produced without imported volcanic components or expensive powdered bricks, natural clayey limestones with good "hydraulicity" were sought out in many places. "Hydraulicity" means the property of a binding agent, e.g. As cement, hydraulically, ie dressed with water to harden both in air and under water.

It was not until 1818 that the French chemist Louis Vicart found out that limestone with a clay content of 27 – 30% is required to produce ideal building lime. From this point on, the manufacture of Roman cement spread rapidly from England and France to all other European countries.

Roman cement was the preferred binder used in Europe from 1800 to 1850

Hydraulic Lime:

There are two large groups of limestone from which burnt lime is extracted.

On the one hand there is the air lime, which, after being prepared into mortar with water and additives, absorbs the “carbonic acid” (CO2) expelled during firing, mainly from the air (“carbonate hardening”) for hardening. These limestones mainly include the white limestones and dolomite limestones.

Then there are the hydraulic limes. These are limestones that are referred to as marl due to ingredients such as clay. These limestones form a compound with the silicic acid when they are fired, but when processed with water and additives to form mortar, they no longer need the air to harden, but also bind under water.

Kalkmergelschichten, Internet
Romanzementofen - Gesamtansicht, Versuchsanlage Leube, Hallein, 2011, Archiv IGM

This hydraulic lime was already burned in shaft kilns, often with continuous firing. Limestone marl was alternately filled with fuel from above into the shaft in layers. Firing took place below the sintering limit, i.e. up to a maximum of 1,200 °C. The fuel was wood, peat or coal.

Romanzementofen - Brenngut, Versuchsanlage Leube, Hallein, 2011, Archiv IGM

In addition to hardening itself, this hydraulic lime also had the advantage that it hardened more quickly and achieved a significantly higher strength, which it retained even in the absence of air in the water. The greatest advantage of hydraulic lime, which sets itself, may well be that it could also be used to produce cast masonry, i.e. walls that were poured between two formwork with mortar mixture that was prepared too viscous.

Romanzement: ungebrannter Kalkmergelstein, gebrannter Stein, gemahlener Romanzement, Internet

A disadvantage was that this hydraulic lime could no longer be extinguished after burning, but had to be ground into powder in mills. This additional effort made the hydraulic lime more expensive. Milling began with stamp mills, then mills followed. Due to the powdery state after grinding the hydraulic lime, the packaging had to be adapted for transport. The hydraulic lime powder was packed in wooden barrels and later in paper bags. These limes were also sold under the name "Roman cement".

The hydraulic lime described, burned from marl limestone below the sinter limit, is referred to as natural hydraulic lime. The hydraulic lime, which is burned from air lime (quicklime) and only binds after it has been slaked with admixtures, is referred to as artificial hydraulic lime. Burnt air lime gets its hydraulic properties by adding trass or pozzolan earth. You could also add crushed bricks or powdered bricks. It has been proven that the Romans already used hydraulic lime for their buildings.

The properties and quality of these mortar mixtures made from hydraulic lime, which is described as artificial, were similar to the natural hydraulic lime burned from marl limestone if the dosage and preparation were correct.

Founding of the Ischl cement works:

The production of Ischler Romanzement began as early as 1845. In that year, at the instigation of the Verwesamt, an extensive deposit of marl layers suitable for burning hydraulic lime was discovered on the Ischler Salzberg. The court chamber quickly approved the funds for the construction of a kiln and a crushing plant below the Ludovika tunnel. Since the hydraulic lime, which was otherwise not available in the Salzkammergut, soon attracted private buyers and the salt works did not want to miss out on this business, they expanded the original plant for an annual production of 3000 to 6000 hundredweight.

As early as 1846, 2 kilns, a larger squeezing and stamping mill and a mill for finely grinding the hydraulic lime were built near the Josef tunnel. With a cord of wood, 30 centners of hydraulic lime could be burned. In 1847 the saltworks sold 120 hundredweights of burnt hydraulic lime per week. The lively business interest led the hydraulic lime from Ischl to make it known in the provinces, even to Linz, where the administration presented it in various samples at an industrial exhibition.

August Aigner, kk Ober-Bergverwalter am Ischler Salzberg, describes the "cement manufacture at kk Salzberge Ischl" in an 1880 article published in the Berg- und Hüttenmännisches Jahrbuch.

Manufacturing only had to cover its own needs. It was limited to the constant amounts of rain during the summer months, since the pounding and grinding aggregates had to be operated with a water wheel.

Situationsplan hydraulisches Kalkwerk beim Josef Stollen, um 1860, Archiv Salinen Austria

Production process in the Ischler cement works:


The roughly 100-million-year-old marl layers from the lower Cretaceous period opposite the confluence of the Gaisbach and Radgrabenbach served as the raw material. These rocks are now counted among the geological formations of the "Lower Roßfeld Layers". These are well stratified, dark grey, sandy marl slate and limestone marl.

The layers of marl were mined in the quarry directly on the Radgrabenbach and transported over a bridge on a small, about 50 m long railway to the two kilns on the Gaisbach.


The marl rocks were burned in two small shaft furnaces. The kiln room, which is elliptical in plan and elevation, was 2.20 m long and 2.00 m wide. The height of the furnace chamber was 2.60 m. The furnace chamber (b) and the ash channel below (a) were located on the floor of the furnace. Next to it was the attachment wall (c) on which the stone vault was built.

When filling the furnace with marl stones, a pointed arch-like vault was first built from larger stones, which served as a firebox. The remaining limestone was placed on top of this vault through the gout until the furnace shaft was completely filled. The vault built in this way was connected to a closable opening in the front wall of the stove, through which the fuel wood was poured. There was only an ash channel under the furnace. A separate grate was not required for wood firing.

Schema eines Ofens im Brennbetrieb, Feichtinger, 1885
Pernecker Brennofen, Aigner, 1880

After inserting the stones, an easily combustible fuel, such as brushwood, was brought through the heating opening and ignited. This gradually warmed the kiln to avoid cracking the stones that made up the vault. Gradually, more and more heat was added by adding more wood, until the stones were completely burned. At the beginning of heating, when the furnace temperatures were still low, the stones became wet with condensation and soot also settled on the stones. Water vapor first escaped from the gout, forming heavy white mists, then thick black smoke, the so-called "powder". Then, as the temperature of the kiln rose, the smoke became bluish and diminished, the soot on the stones burned and they became light-colored. The flames appearing at the gout, initially dark and sooty, became increasingly lighter and freer of soot as the firing progressed. When the lime marl stone appeared from the gout as a white-hot, loose mass, the lime marl was completely burned. The furnace was then allowed to cool and emptied.

The work of inserting the bricks to be fired was particularly tedious for the worker when the kiln was to be reloaded before it had completely cooled down. Complete cooling, however, causes considerable time losses and greater fuel consumption.

After firing, the underfired stones and the vitrified, overfired stones were selected.

6.5 m³ of stones were required to fill a Pernecker oven. Burning lasted 48 to 60 hours. During this period, an average of 15 cubic meters of soft wood was burned. A fire delivered fired bricks for an average of 5,200 kg of powdered lime.

Ofenziegel des Pernecker Brennofens, links aufgeschmolzene Feuerseite 2016, Archiv IGM

stamp mill:

The fired bricks coming from the kilns were first pounded in a stamp mill and then ground in a mill. The stamp mill and the mill were driven by a 6.2 m high, 65 cm wide and 25 cm deep overshot water wheel. The water was supplied from the Radgrabenbach via a 58 m long, 31 cm wide and 25 cm deep wooden drainage system. The amount of water fed in in this way resulted in a raw power of 2.7 hp. If there was enough water, the stamp mill and the mill could be operated together. When the water supply decreased, it was only possible to operate the stamp mill or mill alternately.

Pochwerk mit Wellbaum und Stempeln, Kefer, 1836, Archiv Salinen Austria

The Perneck stamp mill consisted of 8 stamps (b) fitted with iron shoes, which were lifted 30 cm by the 24 wooden lifting thumbs (a) fitted in the long waterwheel shaft (z) and fitted with sheet iron. The stamps then fell onto the 2 wrought-iron tamping plates (c) lying on 2 hard trees in the stamp mill niche and thus crushed the fired stones.

In the stamp mill, an average of 350 kg of coarse, burnt limestone could be crushed in an eight-hour shift.

: Pernecker Pochwerk, Wellbaum mit Hebedaumen und Stempeln, Aigner, 1880

cement mill:

The cement grinding took place on a grinding course which essentially did not differ from a grain mill. The upper stone (l) turned on a fixed lower stone (k). The material to be ground was placed in the center of the grinding stones from a flour box (m), drawn in by the rotary movement of the upper rotor stone and ground between the two stones. The rotary movement of the head stone was transmitted via a transmission to the pulley (i), which was attached to the mill rod. The grinding gap between the two runner stones could be adjusted with the adjusting screw (p). The flour was discharged via a flour hose (n) into the flour box (o).

: Pernecker Zementmühle, Aigner, 1880

The bevel gear (d) mounted on the water wheel shaft meshed with the vertical gear € located above, on whose shaft the first belt pulley (f) was mounted. This drove the second pulley (g), which was attached to a vertical transmission shaft (h – g). The third pulley (h) was attached to the lower end of this transmission shaft. This finally moved the fourth pulley (i), which was located on the mill rod and thus drove the upper running stone (l).

Pernecker Zementmühle, Antriebssystem, Aufriss, Aigner, 1880
Pernecker Pochwerk und Zementmühle, Antriebssystem mit Wasserrad, Grundriss, Aigner, 1880

The mill produced 260 kg of finely ground hydraulic lime in an eight-hour shift.                                                                                                                                   

On average, 36,000 kg/a of ground, hydraulic lime could be produced in this way in the 1870s.

At the Ischler Salzberg, hydraulic lime was used primarily for lining tunnels in damp, brittle stretches and for the production of concrete pipes for introducing the freshwater required for brine production into the pit and for discharging the brine produced in the pit.

Betonausmauerung, Matthias Stollen, 2010, Archiv IGM
Betonausmauerung und Betonrohrleitungen, Leopold Stollen, 2018, Archiv IGM

Development of cement production in Austria:

The "cement works" at Ischler Salzberg, which went into operation as early as 1845, is by far the oldest cement production site in Upper Austria. The other Upper Austrian cement works were founded much later, namely in 1888 the Hoffmann cement works in Kirchdorf and in 1908 the Hatschek cement works in Gmunden. Even the nearby Salzburg cement works are younger. The Leube cement works in Gartenau started in 1852 and the Perlmoos cement works in Hallein Gamp in 1859.

Zementwerk Leube, Hallein, um 1855, Internet

The oldest cement production sites in Austria and Hungary were in Tyrol, from 1838 in Bad Häring and from 1842 in Endach near Kufstein. In 1842, Franz Kink was already able to produce 700 tons of hydraulic lime. Most of his production was packed in barrels and shipped to Vienna via the Inn and Danube. Without Tyrolean cement, the later construction of the Ringstrasse would not have been possible. All decorative ornaments were manufactured as prefabricated parts from hydraulic lime mortar

Kink’sches Zementwerk in Endach bei Kufstein, um 1845, Internet
Zementabfüllung in Fässer, Zementwerk Endach, um 1890, Internet

Production of cement pipes at the Ischler Salzberg:

Pipes made of hydraulic cement have been used on the Ischler Salzberg since around 1875. For the production, a separate concrete factory was built on the Sulzbach opposite the Leopold tunnel, in which the own cement fired at the Josef tunnel was used.

Lageplan Zementröhrenfabrik, 1893, Archiv Salinen Austria
Umbau Zementröhrenfabrik, 1911, Archiv Salinen Austria

A mixture of equal parts of washed sand and hydraulic cement served as material for the production of the cement pipes, which was mixed in a stirrer with the addition of the required amount of water and poured into pipe moulds.

The sand required for the concrete production was won in the sand pit above the pipe works. Since this sand also contained clay, it had to be washed. A separate washing machine was used to wash the sand. It consisted of a water trough in which the lower part of the octagonal drum with a cast-iron axle was immersed. On the sides of this drum were iron grates made of wire rods, through which the fine sand and the unclean, earthy parts were separated. The sand washer was set in motion by a small overshot water wheel installed on the Sulzbach.

The agitator for the tube mass consisted of a wooden floor and a wooden cylindrical wall. Wall and floor were lined with sheet metal on the inside. The stirrer consisted of a cross stirrer to which 14 skewed blades were attached. The agitator was also powered by a small water wheel.

Sandwaschapparat, Aigner, 1875
Rührapparat, Aigner, 1875g

The hydraulic lime and sand were first dry blended and the water added as needed. The whole mixing lasted 8 minutes, after which the whole mass was pulled through a snout with a crutch into the actual mold, the filled mold was lifted out of the pit and taken by truck to the temporary drying place. The flasks, cast-iron cores which filled the cavity of the tube, had to be rotated every half hour for a period of 8 hours, then the flasks were pulled out by a pulley.

Gussform mit Kolben, Aigner, 1875
Gussform, Querschnitt, Aigner, 1875

The molds were then left to stand for 24 hours, then the two mold parts were removed and the exposed tubes left to dry free standing on the floorboards for a further 48-60 hours. After this time, the tubes were transportable, they had to be brought from the vertical to the horizontal position.

To do this, the cement tubes together with the floor boards were lifted by 2 workers and placed on a shackle. The tubes were then lifted into the drying room using a lifting machine. Here the tubes were pre-dried on the floor boards for a period of 8 days, after which they could be lowered again with the lifting machine and carried to the actual drying area. The action of the air (carbonic acid) and the rain were beneficial to the tubes and gradually made them stronger. Only at the beginning of winter did the tube layers have to be protected from the weather with movable roofs.

The tubular form consisted of a floor board and iron side walls. The floor pan was shod with sheet iron to provide a firm base for the cast-iron piston. After the piston was cleaned, the inner surfaces of the walls were lubricated with machine oil, a bead of batten was laid down on the bottom board and the side walls of the mold were inserted into this bead. The side walls formed an octagonal prism, the two halves of which overlapped at the point of contact and were held together by 2 to 3 hooks. The slightly conical piston was made of cast iron. It consisted of a tube 6.6 mm thick. The butt was also oiled and slid into the model, its vertical position being held by an iron guide. In this position you could fill in the mortar.

The strength of the tubes was enormous. A 1-year-old pipe withstood a pressure of at least 3 atmospheres. Higher pressures could not be tested on the pipes due to a lack of testing equipment.

The dimensions of the cement pipe were 3.66 feet (1.16 m) long, 2½ inches (6.66 cm) wall thickness and 5 inches (13.15 cm) inside diameter. The weight of a cement pipe was around 83 kg.

The cement pipes were connected with a putty made of quicklime and coal tar. For this purpose, the tubes were first lined up horizontally in the 0.6 m deep trench and fixed. Then a spatula lubricated with the above viscous mass was wound into the wedge-shaped space of the tubes and successively wound with thicker and thicker knitted parts, finally with hemp strands, and putty was continuously applied. An iron ring was tightened with a screw over the bulge on the circumference and a sheet metal strip was inserted for better distribution.

Röhrenverlegung, Längsschnitt, Aigner, 1875
Röhrenverlegung, eiserner Ring, Aigner, 1875

The cement pipes could be kept almost indefinitely in those places where there was no movement, i.e. on solid ground. Another advantage of cement pipes was their cost. They cost only 1/3 of the cast iron pipes that were common at the time.

The wall thickness of the tubes, initially 6.6 cm with an inner diameter of 13.5 cm, was very thick for safety reasons. This resulted in a weight of 83 kg for a 1.16 m long pipe. After the tubes began to be used in the pit, the heavy weight was a major problem when handling. In addition, the small lug cross-sections have been further narrowed.

In 1877, Carl Balzberg developed his own testing device to determine the compressive strength of concrete pipes. The tests showed that the tubes with a wall thickness of 6 cm withstood a pressure of 2 bar (20 m water column) with five times the safety. The wall thickness was far too large for its usual use as a channel for draining the service water from the Leopold tunnel. Carl Balzberg calculated that a wall thickness of 3 cm should be completely sufficient. With this wall thickness, a pipe would have weighed only 30 kg.

: Prüfmaschine für Röhren, Balzberg, 1877

The tubes that can still be found today have a wall thickness of 5 cm. This slightly reduced wall thickness is likely to be the compromise result of Balzberg's tests.

Tube production was very successful. In 1911 the tube factory buildings were even expanded. When the production was finally stopped, could not be determined. This probably happened after the end of World War I.

Betonrohr mit Eisenring, Matthias Stollen, 2010, Archiv IGM

Sources used:

August Aigner "Cement production at the kk Salzberge Ischl", Bhmjb., 28. Jg., Leoben 1880

August Aigner "The manufacture of cement and its application for brine lines in Ischl", Bhmjb., 23 Jg., Leoben 1875

August Aigner "On the manufacture of cement pipes on the kk Salzberg Ischl", Bhmjb., 24 Jg., Leoben 1876

Carl Balzberg "Samples of the strength of the Ischler Cement - Rohren", Bhmjb., 25. Jg., Leoben 1877

G. Feichtinger "The chemical technology of mortar materials", Braunschweig 1885

Carl Schraml "The Upper Austrian Salt Works from 1818 to the end of the Salt Office in 1850", Vienna 1936

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