Roman Cement Research Articles

Preparation of Alternative Hydraulic Binder Based on Secondary Raw Materials

Reusing and recycling of secondary raw materials from high-volume industrial productions (especially form construction materials and binders fabrications) is very important way of conserving environment and it is also interesting from the economical point of view. The production of common hydraulic binders, especially Portland cement, burdens the environment with considerable amount of combustion gases and consumes energy in massive scale. Alternative (low – energy) binder can be used as Portland cement substitution in applications with lower mechanical properties requirements. Mined limestone wash sediments contain large amount of clay components, but there is also indispensable share of fine calcite. This composition makes these sediments a promising material for the preparation of hydraulic binders as Roman cement or hydraulic lime.

Characterization and Degradation of Masonry Mortar in Historic Brick Structures

This study characterized mortars from a masonry fortification in Charleston, South Carolina (USA), harbor where construction was during the period 1839–1860. This location for analysis was interesting because of the sea water impingement on the structure. The study was included as part of an overall structural assessment with restoration as an objective. The mortars were found to be cement, lime, and sand mixtures in proportions similar to ones expected from the historic literature, that is, one part binder to two parts of sand. The binder was found to be American natural cement, a substance analogous to the European Roman cement. The results suggest that the thermal history of the cement during manufacturing affected setting rate explaining why the cements were considered as variable during the mid-to-late 1800s. Fine pores were found in mortars exposed to sea water resulting from corrosion. Contemporary natural cement was shown to release calcium in aqueous solution. While this release of calcium is necessary for setting in natural and Portland cements, excessive calcium solution, as exacerbated by sea water contact and repointing with Portland cement mortars, was shown to result in brick scaling or decay through cryptoflorescence.

Modified Plasters for Restoration and Finishing Works

The paper is devoted to the research and development of modified plasters for restoration and finishing works based on decorative multicomponent cements containing white Portland cement and supplementary cementitious materials (silica fume, metakaolin and fine ground limestone). This cements are similar to Roman cement by their chemical composition. The use of optimal granulometry of decorative multicomponent cements provide directed formation of microstructure of the cement matrix with the formation of stable hydration products. Compositions of modified plasters by the criterions of workability and compressive strength were designed. Physico-chemical modification of plaster by complex air-entraining admixture allows to obtain high-quality modified plasters with improved quality parameters.

Decorative Multi-Component Alkali Activated Cements for Restoration and Finishing Works

The paper is devoted to development and research of decorative multi-component alkali activated cements with enhanced quality characteristics. The use of finely dispersed mineral additives and alkali metal salts allows to obtain multi-component cements with the lower content of OPC clinker. In chemical composition these decorative multi-component cements are similar to Roman cement. The developed multi-component cements have comparable or better performance properties compared to Roman cement and allow for to use them successfully in making plasters, mortars, etc. for restoration, finishing works and decoration of facades.

Problems of protection and restoration of historical monuments of L’viv built using Roman cement

In article are shown examples allow confirming that Roman cement was widely used in Lviv in the second part of the 19th century while erecting the public and residential buildings. The creating and develop a program on research, preservation and restoration of historical and architectural monuments, on which the architectural and ornamental finishing of facades was carried out with application of Roman cement is proposed.

Low-temperature Hydraulic Binders for Restoration Needs

The late 19th/ early 20th century was a period of active usage of low-temperature hydraulic binders, e.g., Roman cement, for the construction of buildings. Dolomitic Roman cement was characteristic of Latvia in contrast to the rest of Europe, where calcitic Roman cement was applied. The research has been conducted with the aim to synthesize a binder from local clay and dolomite compatible with historical dolomitic Roman cement. The results of chemical and XRD phase analyses have approved that Devonian as well as Quaternary clay mixed with dolomite can form a binder that closely conforms with historical ones. The obtained compositions can be considered perspective for restoration needs.

Non‐metallurgical Slags in the Masonry of Obřany Castle in the Czech Republic: Evidence for the Local Production of Hydraulic Lime in the 14th Century?

Two types of compositionally heterogeneous slags have been found in the wall masonry of the Gothic Castle ruin Obřany. The bright phase is composed of quartz, tridymite, cristobalite, and porous glass, while the dark one also contains feldspars, hercynite, magnetite, clinopyroxenes, and a suite of accessory phases. The bright slags have a similar chemical composition as the mortar from the castle masonry or local sandstones, based on rare earth elements (REE) and other trace element abundances. In contrast, the dark slags are characterized by elevated contents of Al2O3 (15.4–18.6 wt.%) and Fe2O3tot (4.1–10.0 wt.%), and consequently resemble the local clay. The investigated slags are not related to iron metallurgy in terms of their composition and texture. They probably originated in a medieval lime kiln through heat sintering of the inner lining during the burning process under relatively high temperatures (1080–1500°C). Simultaneously, the finding of relics of clinker‐like material together with products of its hydration in the hydraulic mortar from the wall masonry infers the production of hydraulic lime or Roman cement during the construction of the castle in the 14th century. The Obřany Castle appears to represent one of the first applications of hydraulic binders in Moravia.

Shrinkage cracking in Roman cement pastes and mortars

Roman cements were key materials used in the architecture of the nineteenth and early twentieth centuries. Fine cracks, caused by restrained shrinkage during drying, are a distinct characteristic of all Roman cement stuccoes. Today, cracking has become an important barrier preventing broader acceptance of Roman cement as a material by the restoration and construction sector. Drying shrinkage and tensile properties of Roman cement pastes and mortars submitted to various curing and drying regimes were determined as key parameters controlling cracking. A higher volume of aggregate in the mortar mix and a moderate curing time produce optimum Roman cement mortars from the standpoint of reducing the risk of cracking. Fast drying produced significant microcracking due to moisture gradients and differential shrinkage across the specimens. Stress relaxation observed during the long-time loading of the materials reduced their vulnerability to cracking.

The decorative in urban Vienna: Its preservation

The Vienna cityscape has retained its nucleus of the Roman fort through Medieval times to the present. Since the thirteenth century it has been enlarged, and its outlines changed again with the building of new fortifications in the sixteenth and seventeenth centuries. Gardens spread around the perimeter during the eighteenth century until the building of the new Ringstraße after 1857 replaced the dismantled bastions. Vienna's cathedral, the Court, palaces, public and private houses with characteristic built features including details such as pavings, lighting or railings, symbolic ornaments on buildings or in public spaces, all illustrate aspects of the decorative. In 1864–1874 the first museum and school for applied arts in mainland Europe set new standards for techniques and design of decoration. In 1889 Camillo Sitte in his book on urban architecture promulgated the idea of retaining historic details in growing cities, and regarding them as artistic creations. In 1895–1905 plans to adapt the narrow city streets for modern traffic following the example of Paris would have destroyed large areas, but the plans were cancelled in time. Adolf Loos rejected superficial ornamentation in 1908 and placed bare white plaster or coloured marble or precious metal on his façades. Around 1900 Otto Wagner had even more influence on the townscape through his own immense oeuvre and the works of his many disciples. Decorations on Viennese façades were made from a variety of stone, lime plaster, lime stucco and since 1847 Roman cement, bare brickwork and glazed tiles, which will be briefly discussed in their historic context, along with aspects of their conservation. Colouring, mainly in ‘stone colours’, has been examined and can be compared to paintings of the city from the fifteenth century onwards. There is less direct evidence for painted façades from the fifteenth and sixteenth centuries, and only small traces still survive. From the time of the Ringstraße frescoes and sgraffiti have undergone conservation, in recent decades combined with increasingly scientific examination and precise documentation. Major issues in urban conservation within Vienna include the disruption of its skyline by the construction of speculative tall commercial buildings close to protected areas (which include the World Heritage Sites of Schönbrunn designated in 1996, and the city with the Ringstraße and Belvedere, designated in 2001), reduced context for historic façades due to the preservation of the façade but not the interior construction (façadism), expanding the elevation with additional storeys, and aggressive confrontation from new façades made from steel and glass.

Mineralogical and microstructural characteristics of historic Roman cement renders from Budapest, Hungary

Abstract Roman cements, one of the most extensively produced types of hydraulic binders of the second half of the 19th century, played an important role in the architecture of many European countries. This paper deals with the chemical-mineralogical and microstructural characterisation of historic Roman cement renders from Budapest, Hungary. Different microscopic techniques were used on polished thin sections and fracture surfaces in order to understand the method of producing these renders and the effect of urban pollution on them. The renders exhibited characteristics typical to a Roman cement mortar, such as high binder to aggregate ratios (b/a), mostly fine-grained aggregates and high capillary porosity, but without the shrinkage cracks that are also normally present. This research suggests that coarse residual cement grains may have acted in a manner similar to aggregates by absorbing stress and thereby reducing the formation of shrinkage cracks. Based on the mineral characteristics of residual cement grains, the samples could be divided into two groups, which correspond to either a higher or lower temperature of calcination of the original source material of the cement. Chemical characteristics of the binders suggest the presence of intermixed CaCO 3 originating from the carbonation of hydration products and partly from residual calcium carbonate of the raw material. Despite dense and often impermeable coats applied in later renovations and exposure to a polluted urban environment, which resulted in formation of gypsum on the surface of the renders, the samples show good to excellent state of preservation after more than a century. The strong “house of cards”-like arrangement of the complex C-(A)-S-H-type phases is responsible for both the high capillary porosity and the good resistance of Roman cement renders to atmospheric pollution and potentially damaging salts such as Na- and K-chlorides which are found near the base of the building due to sidewalk de-icing. These results help to better understand the behaviour of historic Roman cement renders, which in turn assists in making good decisions in choosing a repair material to future restorations of 19th century facades built with this material.

Determination and imaging of binder remnants and aggregates in historic cement stone by Raman microscopy

We present to our knowledge the first application of Raman microscopic imaging to cementitious materials. This technique yielded the composition and phase distribution (spatial resolution ≈ 500 nm) in samples of cement stone taken from façade elements of four Swiss buildings covering the period of 1892–1924. Raman maps of Roman cement, a predecessor of modern Portland cement, reveal the chemical heterogeneity of clinker remnants consisting of various crystalline, polymorphic, and amorphous phases and visualize different crystal orientations. Our findings include the observation of the γ‐polymorph of Ca2SiO4 – previously, only detected in Portland cement – and Raman spectra of calcium aluminate (ferrite) interstitial phases in Roman cement showing significant differences to the corresponding phases in Portland cement clinker. Furthermore, calcite, vaterite, gypsum, and ettringite were identified in the rim of a nonhydrated residual nodule. Beyond binder remnants, aggregates in the form of spherical (≤500 µm diameter) slag and irregularly shaped pigment particles were analyzed. Here, we focused on the unambiguous identification of compounds in complex matrices by comparing sample spectra with database and own reference spectra. A Raman map collected on blast furnace slag in cement stone shows the spatial distribution of calcite, quartz glass and pyrite. Furthermore, several Fe‐containing, Si‐containing, and Pb‐containing phases were identified. The analysis of pigments partly confirmed and partly contradicted the bequeathed historic recipe of a cement stone façade. These results have direct implications in the field of conservation and restoration and generally demonstrate the potential of Raman imaging to provide deeper understanding of (historic) building materials. Copyright © 2013 John Wiley & Sons, Ltd.

Influence of the combination of Roman cement and lime as the binder phase in render mortars for restoration

It is known that lime was added to historic Roman cement render mortars. The focus of this work is the influence of the combination of NHL5 and CL90 with Roman cement in mortars for restoration; however, the results indicate a wider potential for render applications in general. It is shown that simply adding lime to Roman cement does not retard its hydration and yields mortars where the binding action of the cement is compromised by the mixing process. If the cement is retarded by means of a pre-hydration process, hybrid mortars can be produced with improved workability and workable life as well as permitting the fine control of strength and moisture transport.

Pre-hydration as a technique for the retardation of Roman cement mortars

The setting of Roman cement is so rapid as to make the use of retardation essential in most practical mortars. This work reports an approach to retardation of Roman cement mortars by means of a pre-hydration process in which pre-determined amounts of water (de-activation water) are added to the cement prior to subsequent mortar formation. It is shown that this process yields both monocarboaluminate and a carbonated AFm phase, the balance of which is modified by storage time; the belite phases are not affected. Increases in both de-activation water and pre-hydrated mix storage time yield a longer workable life and slightly lower strength of the mortar. An increase in de-activation water also yields an increase in shrinkage whilst an increase in storage time results in a reduction in shrinkage. Other parameters such as mixing protocol and re-mixing affect workable life without compromising the strength.

The Effect of Composition of Roman Cement Repair Mortars on Their Salt Crystallization Resistance and Adhesion

Crystallization of soluble salts in porous networks is a major source of decay for mortars used in historical buildings. The optimum formulation and application of Roman cement mortars which could produce compatible and durable repairs of the original substrates was studied. Measurements were performed with the aim of determining the pore size distribution, the hydric parameters as well as the salt crystallization resistance of the mortars. The adhesive strength of the repair materials laid on historic substrates was also determined. The results of the crystallization tests show that repair Roman cement mortars with hydric parameters close to those of the historic substrates, though different pore size distributions, have related salt crystallization resistance.

Effect of hydrophobization treatment on the hydration of repair Roman cement mortars

Hydrophobization agents are commonly used in conservation practice to enhance the water-repellent properties of stone and masonry structures such as bricks and restoration mortars. In this project, we have tested and analyzed the effects of various commercially-used water repellents on the hydration process of Roman cement mortars. The necessity to investigate the progress of hydration of these materials in the presence of water-proofing agents arises from the well known fact that Roman cement mortars require adequate times and conditions for curing, which gives the restoration material compatibility with the original substrates. The effects of hydrophobic treatment on the pore size distribution and some physical features, such as water absorption and capillary rise, were investigated on Roman cement mortars treated with polymer-based coatings and inner waterproofing agents. The behavior of mortars in terms of their freeze resistance was also evaluated. The surface treatment using a hydrophobization agent completely prevented water absorption and thereby interrupted the hydration process. In the case of inner water-repellent admixtures, the hydration process progressed in spite of the decrease in water capillary transportation. In such circumstances, unimodal distribution of pore sizes was observed along with a decrease in threshold pore width with increased curing time.

Pore structure of historic and repair Roman cement mortars to establish their compatibility

Mercury porosimetry was applied to the study of pore structure of the historic Roman cement mortars representative of different locations in Europe and time periods as well as different application techniques from architectural castings to in situ formed renders and profiles. Three categories of pores were found to coexist in the mortars. The finest pores, with diameters below 0.1 μm, are present within the hardened aged Roman cement matrix. The larger ‘air’ pores, with diameters between 0.2–2 μm, are due to the evaporation of the excess unbound water and restricted hydration. Pores larger than 2 μm are rare and, in general, can be related to microcracking induced by shrinkage drying and mortar weathering. The mortars have rarely been found to develop a dense fine-porous microstructure characteristic of the ideal conditions of moist-curing; massive architectural castings being the only exception identified. The presence of larger ‘air’ pores was, in turn, almost universally observed. The investigations of the freshly prepared Roman cement mortars have revealed that the restricted hydration could be due to the exposure of the freshly laid surface to dry real-world external environments, a high water-to-cement ratio in the original mortars, or the drawing of water from the stucco mass due to insufficient pre-wetting of the porous masonry. The insufficient reactivity of historic cements, resulting from a high content of over-burned, non-reactive cement components or coarseness of the cement grains, could be another reason for yielding poorly hydrated mortars in the past. In general, Roman cement stuccoes are in an excellent state of preservation in spite of their usual exposure to polluted urban environments for more than a century. Therefore, the coexistence of Roman cement mortars of widely different pore structures has not brought about any problems of incompatibility which field observations could reveal. The Roman cement repair materials have been found to develop pore structures similar to those of historic mortars. Therefore, they are in broad terms compatible with historic masonry or stuccoes. However, the porosity and strength of the repair materials can be controlled by a careful manipulation of the water-to-cement ratio of the mix to adapt them better to the properties of the host material.

Porosity and specific surface area of Roman cement pastes

Mercury porosimetry, water vapour and nitrogen adsorption were used to follow the hydration of Roman cements — belite cements calcined at low temperature. Generally, unimodal distribution of pore sizes was observed, with the threshold pore width decreasing considerably with increasing curing time. An open porous structure with the threshold pore diameter between 0.2 and 0.8 μm and the specific surface area not exceeding 20 m 2/g was produced at early ages when quick growth of the C–A–H phases is observed. The surface area reached up to 120 m 2/g and the threshold pore width shifted to around 0.02 μm when the subsequent formation of C–S–H gel filled the larger pores. Both mercury porosimetry and water vapour adsorption were found to be capable of following the progress of hydration of the Roman cements with high reliability at least for a comparative evaluation of historic Roman cement mortars and repair materials used in restoration projects.

Roman cements — Belite cements calcined at low temperature

Roman cement was a major material used in the architecture of the nineteenth and early twentieth century across Europe, until it was displaced by Portland cement, and is absent from the palette of materials from which conservationists may now select. Calcination of cement-stones and marls from six sites in Poland, Austria and the UK has been conducted. The resulting mineralogy is dependant upon the characteristics of the original feedstock and the calcination temperatures. The principal hydraulic components are belites and amorphous aluminates. The stable belites in cements calcined at lower temperatures are largely α / C 2S while β C 2S is stabilised as the calcination temperature is increased. Other components include uncalcined remnants, lime, brownmillerite and gehlenite. Optimum cements, assessed by compressive strength, were produced at relatively low temperatures, typically in the region of 750 °C. Two strength development profiles have been observed.

Natural cement and stone restoration of Bourges Cathedral (France)

Natural also called Roman cement, was invented at the end of the 18th Century and played an important role in the development of civil engineering works until the 1860s. More surprisingly, it was also used to restore historic buildings, such as gothic cathedrals. This paper deals with the mineralogy and the durability of natural in the particular case of the Bourges Cathedral in France. This study illustrates the interest of this material particularly adapted in stone repair or substitution. Contrary to traditional mortars, the present samples are made of neat cement paste, revealed by the absence of mineral additions as quartz or carbonate sand. Several combined techniques (SEM-EDS, TGA, XRD) were carried out to determine the composition of the hydraulic binder rich in calcium aluminate hydrates. The raw marl at the origin of the cement production contains oxidized pyrites which consist in a potential source of sulphate pollution of the surrounding limestone. The exposition of the cement in urban environment leads to some weathering features as atmospheric sulphation. Finally a petrophysical approach, based on water porosity, capillary sorption and compressive strength, has been performed to demonstrate the durability and the compatibility of roman cement applied as a restoration mortar of historical building.

Roman Cement Mortars in Europe’s Architectural Heritage of the 19th Century

Abstract Natural cements calcined at low temperatures, so-called Roman cements, formed an important binder material in 19th century construction and facade decoration of many European cities and towns. As a rule, Roman cement mortars appear well preserved. In order to understand their range of composition and properties, a number of samples from historic buildings were collected and analyzed. Microscopic techniques including scanning electron microscopy were employed along with the assessment of physico-mechanical properties. The study shows that the most significant feature of Roman cement mortars is a wide range of differently calcined clinker relicts within each mortar. These unreactive particles, classified as being either overfired or underfired, obviously play an important role for the mortar properties. The binder relicts are composed of a number of phases in the system Ca-Si-Al-Fe. C2S and C2AS (gehlenite) are among the most frequent compounds, their grain size and microstructure depending on calcination temperatures. In particular, the clinkers produced at lower temperatures show nonequilibrium features such as solid solution systems and zoning by partial diffusion. The aggregates found in the mortars cover a wide range of mineralogical compositions reflecting local geological conditions. Cast and in situ applied mortars differ in the amount of aggregate, which is generally lower for cast elements. There is no correlation between the amount of inert material and the state of preservation indicated, e.g., by the occurrence of shrinkage cracks. Historic cast mortars show high compressive strengths at comparably low moduli of elasticity. The total porosity is frequently high. This contribution presents the above-mentioned properties and discusses them in terms of the excellent aging performance of the historic Roman cement mortars.