Koen Van Balen

Competition between Hydration and Carbonation in Hydraulic Lime and Lime-Pozzolana Mortars

A combined reaction of hydration and carbonation takes place in hydraulic lime and lime-pozzolana mortars. Hydration reactions are the first reaction and carbonation of lime is the complementary reaction in the strength gain. Competition between these two reactions can occur in lime-pozzolana mortars if the pozzolanic material has low reactivity with lime, leading to the consumption of lime by carbonation reaction. The degree and the order of these reactions are strongly influenced by the moisture content. Hydration reactions are enhanced under moist conditions while carbonation is delayed. Curing under dry conditions does not sufficiently increase their strength because the hydration reactions are slowed down or even terminated by the full carbonation of lime in lime-pozzolana mortars. The consequence of this on the mechanical properties of the mortars is remarkable while the same impact is not observed in their porosity. Such mortars require moist conditions to ensure sufficient strength development.

Cementitious binders from activated stainless steel refining slag and the effect of alkali solutions.

With an aim of producing high value cementitious binder, stainless steel refining slag containing a high amount of CaO in γ-dicalcium silicate form was activated with NaOH and Na-silicate as well as KOH and K-silicate solutions, followed by steam curing at 80 °C. Higher levels of alkali-silicate in the activating solution resulted in higher cumulative heat suggesting accelerated reaction kinetics. With respect to compressive strength, higher levels of alkali silicate resulted in higher strength and the mortars with Na activator were found to have higher early strength than the ones with K activator. The long term strength was found to be similar, regardless of the alkali metal. Thermogravimetric, QXRD and FTIR analyses showed an increase in the amount of reaction products (C-S-H type) over time, further confirming the reactivity of the crystalline slag. Batch leaching results showed lower leaching of heavy metals and metalloids with K activator compared to the Na activator. These results demonstrate that the alkali type and the ratio of hydroxide to silicates have a significant impact on the hydration and mechanical strength development of the stainless steel slag. The above findings can aid in the recycling and valorization of these type of slags which otherwise end up landfilled.

Effect of High Cooling Rates on the Mineralogy and Hydraulic Properties of Stainless Steel Slags

This article investigates the effect of chemical composition and cooling rate during solidification on the mineralogy and hydraulic properties of synthetic stainless steel slags. Three synthetic slags, covering the range of typical chemical composition in industrial practice, were subjected to high cooling rates, by melt spinning granulation or quenching in water, and to low cooling rates, by cooling inside the furnace. Both methods of rapid cooling led to volumetrically stable slags unlike the slow cooling which resulted in a powder-like material. Stabilized slags consisted predominantly of lamellar β-dicalcium silicate (β-C2S) and Mg, Ca-silicates (merwinite and bredigite); the latter form the matrix at low basicity and are segregated along the C2S grain boundaries at high basicities. Slowly cooled slags consist of the γ-C2S polymorph instead of the β-C2S and of less Mg, Ca-silicates. Isothermal conduction calorimetry and thermogravimetric analysis indicate the occurrence of hydration reactions in the stabilized slags after mixing with water, while calcium silicate hydrates (C-S-H) of typical acicular morphology are identified by SEM. The present results demonstrate that the application of high cooling rates can result in a stable, environmental-friendly, hydraulic binder from stainless steel slags, rich in β-C2S, without the necessity of introducing any additions to arrest the β polymorph.

Vision on Conservation: Virterf

Although more and more computer-aided technologies are utilised or demonstrated on well-known monuments or archaeological sites, there is - at least for the professionals working in the field - still some lack of clarity about their application. The main idea of our research project is to construct a prototype of a tool that tries to bring new technologies closer to the daily practice. It incorporates recent developments in computer vision and reverse engineering, while at the same time tries to answer the practical concerns from civil servants, architects, topographers, art-historians,… who are responsible for the conservation of monuments or archaeological sites. The proposed system covers automatic correspondence analysis and point cloud manipulation to build up a textured 3D model. This model then acts as the central core of a multimedia data structure for the annotation, geometric and thematic interrogation and visualisation of the building or site being studied.

Raw materials used in ancient mortars from the Cathedral of Notre-Dame in Tournai (Belgium)

Abstract: Mortar samples from the Notre-Dame Cathedral at Tournai in Belgium have been investigated as part of a broader studyconsidering the transition of ancient cities and their rural territories from Roman to late Roman society and the transformation to theearly Middle Ages. Masonry mortars and mortars used for flooring have been studied from the Imperial Roman period, theCarolingian style period and the Romanesque style period (4th–11th century AD).A selected set of samples has been characterised using a combination of mineralogical, chemical and microscopical techniques.This characterisation enabled us to refine our knowledge of the mortar composition, of the original materials and of their provenance.It appears that both chalk and ‘‘hard’’ Tournaisian limestone were used to produce the lime. Both locally available materials can yieldeither hydraulic or non-hydraulic lime. The aggregates have a local origin. Additionally, several microscopical techniques wereapplied to identify the nature of the overburnt particles. The low abundance of this type of Binder Related Particles in the Gallo-Roman and Palaeo-Christian mortars suggests that technological knowledge, be it empirical or theoretical, was available.Key-words: ancient mortars, raw materials, provenance, lime binder, lime burning, hydraulicity, archaeometry.

The Silk Roads Cultural Heritage Resource Information System: For World Heritage Monitoring and Preservation

Serial transnational World Heritage nominations are challenging the way cultural heritage has been managed and evaluated in the past. This type of nomination requires different methodologies and tools to improve the monitoring cycle from the beginning of the nomination towards the periodic reporting. The case study of the Silk Roads Cultural Heritage Resource Information System (CHRIS) illustrates the use of a Geospatial Content Management System (Geo-CMS) supporting the serial transnational World Heritage nominations and the future monitoring of the Silk Roads in Central Asia. The Silk Roads CHRIS is an initiative supported by UNESCO WHC and the Belgian Federal Science Policy Office (BELSPO), and developed by a consortium headed by the Raymond Lemaire International Centre for Conservation, KULeuven. The Silk Roads CHRIS has been successfully assisting in the preparation of the nomination dossiers of the Republics of Kazakhstan, Tajikistan and Uzbekistan and will be used as a monitoring tool in the Centra...

Assessment of the Compatibility of Repair Mortars in Restoration Projects

In restoration works compatibility requirements of repair mortars are defined based on the original mortar characteristics, but the efficiency and the performance of the repair mortars after application on masonry are not generally evaluated. From this perspective, original mortars and repair mortars from two historic masonry structures were analyzed for their characterization. Compatibility of the repair mortars with the historic mortars is investigated in terms of chemical, mineralogical, and physical point of view. The efficiency of the analytical techniques used for the mortar characterization is discussed. A methodology relying on a basic approach for a mortar analysis is adopted taking into account the added values and the basic requirements from both practical and scientific point of view. This study will contribute to the existing knowledge on mortar analysis and will provide new insights on the assessment of the compatibility of the repair mortars.

Experimental study of failure mechanisms in brittle construction materials by means of X-ray microfocus computed tomography

X-ray microfocus computed tomography (CT) is a powerful tool in the 3D visualization of fracture initiation and propagation in brittle materials, based on the attenuation of X-rays. Aim of this paper is to present the experience obtained at the Building Materials and Building Technology research group in using CT for the experimental study of failure mechanisms in brittle construction materials during three test programs, focusing on following issues: (i) triaxial behaviour of mortar joints, (ii) effect of pore saturation on micro fracture in sandstone and (iii) influence of flow distance on fibre distribution and orientation in fibre reinforced concrete. The resolution limit of the applied system is in the order of micro meters (microCT). Common goal of the presented experimental programs was to analyse the material’s inner structure and fracture propagation at microscale, in support of studying local failure mechanisms and developing numerical models. For each test program, setup optimization and resulting failure modes will be discussed. Several types of in-house-made loading stages were applied for observation of step-wise induced failure mechanisms. As a general conclusion, most test results supported the theoretical framework relevant to the effects of varying conditions (relative stiffness, pore saturation, viscosity) on the observed failure modes. However, sample size / image resolution balance remains an important focus point. Additionally, future research is briefly discussed, in relation to the experience gained in the described test programs.

Semi-automated Creation of Accurate FE Meshes of Heritage Masonry Walls from Point Cloud Data

The structural analysis of buildings requires accurate spatial models. Additionally, spatial information on pathologies such as settlement-induced damage is paramount in the assessment of heritage assets. This spatial information is used as a basis for Finite Element Methods (FEM) to evaluate the stability of the structure. Traditional data acquisition approaches rely on manual measurements which are labor intensive and error prone. Therefore, major simplifications are made to document structures efficiently. The goal of this research is to provide faster and more accurate procedures to capture the spatial information required by a Finite Element (FE) mesh. This paper presents a semi-automated approach to create accurate models of complex heritage buildings for the purpose of structural analysis. By employing remote sensing techniques such as terrestrial laser scanning and photogrammetry, a complex mesh of the structure is created. Also, a methodology is proposed to capture crack information. A stepwise approach is elaborated to illustrate how the spatial information is adapted towards a FE mesh. The results show a significant difference between the geometry of our model and a traditional wire-frame model. Not only does accurate modelling result in deviating loads, it also affects the behavior of the object. Through the proposed approach, experts can develop highly accurate FE meshes to assess the stability of the structure up to as-built conditions and taking into account existing damage patterns.

The Application of Sonic Testing on Double-Leaf Historical Portuguese Masonry to Obtain Morphology and Mechanical Properties

In order to perform a conservation or repair intervention of a historic building, knowledge of the mechanical properties of the historical materials and building components is essential. Obtaining these properties should be performed inflicting as little damage to the historical fabric as possible. Methods to do so are defined as non-destructive test methods (NDT). The paper investigates the use of sonic testing (NDT) on historical masonry. Nine double-leaf wallets were constructed according to a traditional Portuguese building method, using light ochre schist and mortar made of local soil and water. Three wall variations were present concerning plaster finishing and grouting strengthening. A testing procedure was developed for sonic testing to determine the morphology and mechanical properties. The wallets were also classified according to the Masonry Quality Index method (MQI), which can be used to identify strength and stiffness parameters of masonry by visual inspection without testing procedures. The method was used in conjunction with the sonic testing. In addition, compression tests with loading and reloading cycles were performed. Young’s moduli could be compared to those obtained by the MQI method and the sonic testing. The results revealed that the Young’s moduli of the sonic testing had a good agreement with those of the compression testing, although the former presented an overestimation due to testing on the outer leaves. The Poisson’s ratio presented inconsistent results due to a high scatter on experimental values. The sonic testing also showed a good indication of weak zones in the masonry. The MQI method produced less accurate results in terms of stiffness estimation but has potential and should be investigated further.