Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences Kraków, 2008 Hydration of natural cements Hydratace naturálních cement Renata Tišlová A PhD thesis prepared under supervision of: Roman Kozowski PhD, DSc Acknowledgements Many people and institutions helped me to complete this research. I would like to thank them all. I am especially grateful to my supervisor Roman Kozowski PhD, DSc for his professional support, sharing knowledge and setting an excellent example of enthusiasm for the research. I owe also thanks to my colleagues at the Instittute of Catalysis and Surface Chemistry, Polish Academy of Sciences in Krakow, Anna Klisiska-Kopacz, Antonina Kozowska, Grzegorz Adamski, ukasz Bratasz, Dariusz Mucha for their unfailing support as well as to the Faculty of Restoration, the University of Pardubice, for making my work on the thesis possible. The work described in this thesis has been in part carried out within the EU research project: ROCEM – Roman Cement to restore built heritage effectively (Contract No. EVK4-CT-2002-00084) within the 5th Framework Programme, Thematic Priority: Environment and Sustainable Development, Key Action 4: City of Tomorrow and Cultural Heritage and the national research project „Wdroenie technologii cementu romaLskiego do praktycznej konserwacji zabytków“, project of the Sectorial Operational Programme – Growth of the Competitiveness of Enterprises, No WKP_1/1.4.1/1/2005/8/8/222/2005/U. Thanks are due to all colleagues working in the ROCEM project particularly from the ICSC PAS, Krakow and the University of Bradford, UK for supplying samples of Roman cements and data on their composition and properties. Thanks are also due to the University of Applied Arts, Vienna, Austria for cooperation on the SEM analysis, as well as to Wolfgang Schwarz for his valuable contribution to the X-ray diffraction analysis. I´m also grateful to Edison Coatings Inc., USA and Vicat, France, for supplying samples of natural cements they produce for this study. 2 Finally, it would have been not possible accomplishing this research without support of my family, especially my husband Petr. 3 Table of Contents Acknowledgements 2 Table of Contents 4 Abbreviations 7 1. Roman cements key materials of the built heritage of the nineteenth/early twentieth centuries 8 1.1 History 9 1.2 Definition 10 1.3 Raw materials and production 13 1.4 Historic Roman cement mortars 18 1.5 Conservation problems 27 2. Calcination of marls to produce Roman cements 30 3. Hydration of Portland cement 30 3.1 Early hydration of OPC 32 3.2 The late period of OPC hydration 36 3.2.1 Composition and structure of C-S-H 37 3.2.2 Morphology of C-S-H 38 3.3 Microstructure of the OPC pastes and mortars 39 4. Study Aims 41 5. Materials investigated 43 5.1 Cements 43 5.2 Cement pastes - design, setting and strength development 48 5.2.1 Setting 49 5.2.2 Compressive strength 50 5.3 Mortars – design and curing conditions 53 5.4 Historic Roman cement mortars 55 6. Experimental methods used 57 6.1 X-ray diffraction of cement materials 57 6.1.1 X-Ray diffraction of cement powders 57 6.1.2 In-situ X-ray diffraction of pastes 58 4 6.2 Mercury intrusion porosimetry 59 6.2.1 Physical basis of the method, its strength and limitations 59 6.2.2 Cement paste drying 60 6.3 Specific surface area 61 6.3.1 The BET equation 62 6.3.2 The t-method 63 6.3.3 The water vapour surface area 64 6.4 Thermal analysis 64 6.5 Scanning electron microscopy (SEM) 64 6.6 Adhesion 66 7. Results and discussion 67 7.1 Hydration during wet-air curing 67 7.1.1 Growth of crystalline hydrates and consumption of the components of original cements in the hydration process as measured by the in-situ XRD 67 7.1.1.1 Initial stage of hydration 67 7.1.1.2 Late stage of hydration 81 7.1.1.3 Hydration of Roman cement mortars 87 7.1.2 The development of specific surface area in Roman cement pastes 90 7.1.2.1 Experimental approach 90 7.1.2.2 Interpretation of the measurement data 93 7.1.2.3 Specific surface area of Roman cement pastes and mortars 95 7.1.3 Thermal analysis 101 7.1.3.1 Identification of hydrated products in Roman cement pastes 101 7.1.3.2 Quantification of the hydrated product content 106 7.1.3.3 The degree of hydration 109 7.1.4 The microstructure of Roman cement pastes by means of SEM-EDX analysis 116 7.1.5 Pore structure of hydrated Roman cements as measured by mercury intrusion porosimetry (MIP) 121 7.1.5.1 Pore structure of Roman cement pastes 121 7.1.5.2 The influence of water content on the pore structure of the pastes 126 7.1.5.3 Porosity structure of Roman cement mortars 128 7.2 Hydration on exposure to real-world environments 129 7.2.1 Hydration of mortars in different curing conditions 129 7.2.2 Porosity of historic mortars 132 7.2.3 The influence of different porous substrates on the hydration of mortars 137 5 7.2.4 The influence of water repellent treatment on hydration 138 7.3 The influence of hydration on the adhesion of Roman cement repair mortars 140 7.3.1 The adhesion of Roman cement repairs and the effect of curing conditions 141 7.3.2 The influence of mortar composition on the adhesion 142 7.3.3 Adhesion of subsequent layers of fresh mortar 143 Conclusions 146 List of Figures 150 List of Tables 156 List of Equations 158 References 159 6 Abbreviations Cement Chemical Nomenclature: S = SiO2 A = Al2O3 F = Fe2O3 S = SO3 C = CaO M = MgO H = H2O C = CO2 K = K2O N = Na20 C2S dicalcium silicate (belite) C3S tricalcium silicate (alite) C4AF tetracalciumferroaluminate (ferrite, also denoted as brownmillerite) C3A tricalciumaluminate (aluminate) AFm hexagonal calcium ferro-aluminate-hydrates, written in chemical - - nomenclature [Ca2(Al,Fe)(OH)6]·X·xH2O, where x=(0; 1), X= OH or Cl , ½ 2- 2- SO4 or CO3 AFt trigonal calcium ferro-aluminate-hydrates, most commonly ettringite Ca6Al2(SO4)3(OH)12.26H2O CH calcium hydroxide (portlandite) A1 calcium aluminum oxide carbonate hydroxide hydrate 2[Ca2Al(OH)6]·1/2CO3·OH·5.5H2O (C4A C 0.5H12) A2 calcium aluminum hydroxide hydrate 2[Ca2(Al,Fe)(OH)6]·OH·H2O (C4AH13) A3 calcium aluminum oxide carbonate hydrate 2[Ca2 (Al,Fe)(OH)6]· CO3 .5 H2O (C4A C H11) 7 Chapter 1: Roman cements key materials of the built heritage of the nineteenth/early twentieth centuries The nineteenth and early twentieth centuries were an era of rapid urban expansion and extraordinary building activity in all European cities. The wealth and power of the new social elites were expressed in sumptuous building façades, decorated with rich architectural and ornamental forms imitating the grand styles of past epochs (Figure 1). While the stylistic costume of the buildings drew upon the past, the technology used in manufacturing the decorative elements was entirely contemporary. The key material was a natural, highly hydraulic binder, known as Roman cement, which was an alternative to the traditional decorative materials such as stone, brick or terracotta. Its main advantages were that it was fast-setting, and featured high early strength, excellent durability, and a beautiful warm yellow-to-brown colour. The above features combined with low cost of production enabled the easy and economic manufacturing of renders and decorative elements on the external facades of buildings. Roman cement was often referred to as the exterior equivalent of gypsum plaster as it offered the same speed of setting and manipulation yet could withstand exterior conditions very effectively. Its unique properties enabled craftsmen to develop a stylistic language of architectural decoration which has determined the aesthetic appearance of central areas in most European cities today. The advent of functionalism in the twentieth century, favouring the architectural language of simplicity and absence of any decorations, brought a quick decline in the production and use of Roman cement with newer Portland cement dominating the construction market. The renaissance of interest in Roman cement and its use spans the last 8 twenty years, and is a result of the growing interest in European art of the late 19th/early 20th centuries. Attempts have been undertaken to investigate historic Roman cement stuccoes and develop strategies and adequate measures for their conservation. The use of inadequate restoration materials that do not fit the original, and the lack of knowledge on Roman cement technology were recognized as key conservation problems, which, in turn, have led to extensive research aimed at re-establishing this historic material and technology to conservation practice. Figure 1: Example of a façade decorated with Roman cement stucco, Trade Academy in Krakow, Poland, 1904-1905, Jan Zawiejski. The present thesis is an element of this research effort. In its introductory part, information is provided about the historic cements and stuccoes based on historic literature but also on the outcome of the recent plethora of research work on this subject. 1.1 History The birthplace of Roman cement production was England. The advent of Roman cement era dates back to 1796 when James Parker patented a novel binder which became 9 known as Parker’s or Roman cement (Parker, 1796). In early production, Parker used Septarian nodules of clayey limestone from costal clay beds in Sheppey and Harwich in the south of England. In mainland Europe, the manufacture of Roman cement was developed after 1840.