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The Renascence of Lime Based Mortar Technology. An Appraisal of a Bibliographic Study.

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Database: GCIBibs - Lime Mortars & Plasters (GCIB_LMP). It is the author’s belief that only through scientific documentation of the advantages of lime can it regain its significance in building conservation and
  88  89 THE RENASCENCE OF LIME BASED MORTAR TECHNOLOGY AN APPRAISAL OF A BIBLIOGRAPHIC STUDY Georgia Zacharopoulou Member of the Hellenic Society for the Protection of the Environment and the Cultural Heritage  Summary It is the author‟s belief that onl y through scientific documentation of the advantages of lime can it regain its significance in building conservation and compete effectively with its basic rival viz portland cement. Although the study of the scientific papers that exist concerning the technology of historic lime based mortars and the manufacture of new repair mortars suitable for conservation work is an enormous - but essential - task, a synthesis  [ZACHAROPOULOU G.P. 1993] of the existing knowledge was attempted by examining the evolution of research studies; the tendencies, gaps and moreover the questions that recent studies have posed for future research. It is hoped that this literature survey will aid the future selection of appropriate mortars for historic buildings. The paper is divided into two parts. Part one introduces the present understanding of the subject of lime and proposes a convenient terminology for conservation purposes. Part two looks at how recent research has influenced this understanding. Finally, a brief conclusion summarises the results of this review. PART ONE   1. HIGHLIGHTS IN THE HISTORY OF LIME There are two periods that led towards the scientific understanding of limes as mortar binders in building construction:  90    From the Neolithic age to around the middle of the eighteenth century when the properties of limes and hydraulic limes began to be documented, and    From the middle of the eighteenth century to the present day. However, although hydraulic mortars were identified in constructions of Israel [COLLEPARDI 1990, MALINOWSKI 1979/81/91, STANLEY 1979] and ancient Greece [EFSTATHIADIS 1978], it was not until Roman times that their superior properties were fully appreciated. The Romans knew how to manufacture them (empirical knowledge) but several centuries were to pass  before a scientific understanding (scientific knowledge) of hydraulic mortars was achieved. For a whole century (1756-1856) scientists experimented with all kinds of limes trying to define scientifically “what produced a good, strong, durable mo rtar” [BURNELL 1892, COWPER 27, DAVEY 61, SICKELS 87, TAYLOR 57, VICAT 1818/1837]. These experiments tested the old treatises and laws and new theories and disputes arose until the advent of Roman (1796) and Portland cement (1824). Hence, new roads of investigation and discussions about Quality were opened to the present day (Table 1). 2. Classification of limestones and limes  The composition and diversity of limes depend, principally, on the choice of limestone used in their production. (The process of burning, slaking, maturing, storing and the working techniques during application also affect the quality of the limes produced). The scientific understanding of the chemistry of limes and the determination of hydraulicity began in the mid eighteenth century. Two parallel events accelerated research on this area [COLLEPARDI 1990]:    The beginning of modern chemistry with Lavoisier which gave rise to the chemical analysis of stones from which binders were produced by burning, and    The industrial revolution with its requirements for great engineering works which demanded strong and durable mortars. Limestones can be classified into various groups according to their srcin , their chemical composition , their crystal size  and the  porosity  of the calcium carbonates, and finally their texture  or the  geological formation  in which they occur. Bearing all these in mind, the following table gives the main types of limestone giving rise to building limes and these are proposed for use in  building conservation terminology (Table 1).  91 Table 1 TIME AREA MATERIALS, TECHNIQUES AND USE OF THE CONSTRUCTION  Neolithic Period 9000-8000 BC Jericho Messopotamia Mask: careful polishing of fresh lime mortar 7000 BC Jericho Messopotamia Wall of mud brick with a polished lime plaster floor 7000 BC Historic site at Yiftah El 180m 2  (1940 ft 2 ) polished lime plaster floor 5600 BC Stone Age River Danube, Lepenski Vir, Yugoslavia Floors of fishermens' huts: lime-concrete made from red lime, sand, gravel and water (thickness 250mm) 2500 BC Great Pyramid at Giza, Ancient Egypt Lime (& gypsum) mortars and plasterwork 1700 BC Minon Period Palace of Knossos, Crete, Greece Mural paintings on a two-coat pure lime plaster 1550 BC Phaestos, Malia, Crete, Greece High quality polished and painted wall plasters 1500 BC Vasiliki, Crete, Greece Coating for rubble masonry: 2 layers of rendering mortar used to cover sun-dried bricks and loose rubble 1400 BC Tel-el-Amarna Pavement, but it was apparently the floor of a part of the harem of King Amenhoted IV 1000 BC King Salomon Jerusalem Israel Drinking water reservoirs (aqueducts, ports, tanks): hydraulic mortars obtained by mixing lime and  pounded earthenware 500 BC Camiros, Rhodes, Greece Large underground water-tank: stones bonded with a  pozzolanic lime concrete made with a volcanic ash  possibly from the island of Santorini or Nisyros 500 BC Mycenae, Greece Temples: Fine lime stucco 500 BC Megara, Greece Cistern (hydraulic structure): single layer of a lime mortar rendering 450 BC Temple at Elis, Greece Polished lime stucco mixed with milk and saffron Classical Period Lavrion (near Athens), Greece Hundreds of cisterns of Lavrion metallurgical installations: stone masonry covered by 2 or 3 layers of lime mortar containing heavy elements 300 BC Works of Appius Claudious Caecus, Italy Appian aqueduct, Appian way: lime concrete manufactured by mixing lime, pozzolanic sand, water and hewn stones 117 BC Temple of Castor, Italy Lime concrete foundations 75 BC Pompei, Italy Theatre at Pompei constructed with pozzolanic lime concrete 27 BC Rome, Italy Pantheon: lightweight concrete made of lava-aggregate 98 BC - 117 AD Cologne, Germany Waterworks of Gaul: pozzolanic (truss) lime concrete 80 AD Rome, Italy Colosseum: lightweight concrete in some of its arches 0 - 100 AD Italy Basilica of Maxentious, Thermae of Caracalla and Diocletian 122 - 130 AD Britain Hadrian's wall: one of the largest Roman constructions where lime concrete was used 150 AD Nimes, France Aqueduct, Pont du Guard: both the core of some walls and the channel, along which the water was conveyed, are made of lime concrete C3 - C15 Thessaloniki, Greece Late Roman, early christian and byzantine churches  built with lime mortar in which finely ground burnt clay tiles had been added 700 AD St Albans, Britain Park street villa near St Albans: lime mortar 700 AD Northampton, Britain Three saxon lime mortar mixers were excavated 1130 AD Reading Abbey, Britain Lime concrete wall that will still remains while the stone faces have fallen 1220 - 1265 AD Wiltshire, Britain Salisbury Cathedral: the tallest spire in Britain is still standing on its srcinal lime concrete foundation 1753 AD Dublin, Ireland Foundations of the Essex Bridge over the River Liffey in Dublin 1756 AD Britain Eddystone lighthouse: hudraulic lime and pozzolana from Italy  92 Table 2 CLASSIFICATION OF LIMESTONES AND LIMES RAW MATERIALS PROPERTIES QUICKLIMES CHARACTERISTICS   High calcium white chalks CRETACIOUS SERIES  containing 98  99% CaCO 3  High calcium containing PURE LIMESTONES High calcium limestones CARBONIFEROUS SERIES  containing only 2  5% MgCO 3  quicklimes < 5% MgO Magnesian (Dolomitic) limestones PERMIAN SERIES 5  35 % of MgCO 3 (35  46 % of MgCO 3 ) *  Magnesian (Dolomitic) quicklimes containing >5% MgO Grey chalks or high calcium or magnesian (dolomitic) limestones with  clayey impurities (or marly limestones or limestones with chert) containing 5  12% of clay Slightly (feebly) hydraulic 0.1<I<0.2 setting in 15-21 days IMPURE   LIMESTONES containing 12  20% of clay Moderately hydraulic I>0.2 setting in 5-15 days containing 20  30% of clay Eminently hydraulic I>0.2 setting in 1-4 days * Higher levels of MgCO 3 indicate that the stone is not suitable for lime manufacture except for special purposes. 3. Manufacturing processes of air-hardening and hydraulic limes 3.1 The chemistry of limestone burning [BOYNTON 66/80, CAS 92, DAVEY 61, CZERNIN 80, LEA 80, GROOM 93, HOLMSTROM 93, MALINOWSKI 91, RAA 84/87, SPIROPOULOS 85, TORRACA 88, WILLIAMS 89, WINGATE 85/91] From the first neolithic achievements to the late C19 the heating and final burning of limestones was carried out in kilns that were almost similar. Since the beginning of this century, however, developments in modern kiln design have converted the traditional small scale lime production into the sophisticated and more energy-efficient modern lime industry. The history of lime-kiln design is, therefore, closely related to the development of alternative fuels. Most commercially available limes are not as good as those found in historic  buildings because lime is burnt today to meet requirements other than the building industry which is a minority market. One of the reasons that the high quality limes have disappeared from the market is because they cannot be produced by modern high temperature kilns (>1000 o  C) where lime is more likely to be over-burned and less reactive than traditional wood-burned stones (~900 o  C). The influence of the temperature and of the rate of heating to the ability of quicklime to react freely is essential, as the most reactive quicklimes are formed at the flame temperatures  produced historically by wood-firing and when the burning process is lengthy in consequence. This happens because wood burns with long, even flames of mild and moist heat, requires only natural draught and finally provides a uniform calcination. For this reason, efforts to regain the ancient technology through archaeological, scientific and technological historians‟ research should be  greatly encouraged so as limes of high reactivity can be produced economically, fulfiling both the special demands of building conservation and the concept of sustainable development. The hydraulic properties of the latter case can be attributed to the dicalcium silicate (belite) and in some degree  to the aluminates. The reactive ingredients of hydraulic limes and early portland cements were principally C 2 S and free lime (CaO). The amount of silicates and aluminates are related to the amount of silica and alumina included in the impure limestone. Table 3 demonstrates the chemical reactions of the calcination of high calcium chalks and limestones (case A:1),  of magnesian (dolomitic) limestones  (case B:1)  of natural argillaceous limestones (case D:1) [and of cements (case E:1) ].
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