Conservation Of Heritage Structures Research Articles

Carbonation of air lime mortars under natural and accelerated conditions – A systematic review

Lime was a prominent building material in ancient times that was replaced by cement by virtue of its fast application properties. The use of lime as a construction and repair material is gaining significance recently as the conservation of heritage structures has become a concern. Moreover, the CO2 associated with the production of cement is proliferating. The use of cement mortars in repairing heritage structures did not prove to be a good choice as the composition, characteristic properties and strength were very different to that of lime binders and therefore reduced the breathability of the existing structures. Lime mortars generally react with the CO2 present in the atmosphere to gain strength and this property of lime can be employed to use it as a CO2 sink. However, the time associated with the reaction is quite high and the present systematic review focuses on the methods by which the CO2 absorption process can be accelerated. The influence of various organic and inorganic additives in accelerating the reaction in natural and high CO2 environments is critically compared. The influence of carbon curing the lime-based mortars on mechanical and microstructural properties is studied. The current review critically compares the behaviour of lime mortars in the mentioned conditions and gives an insight into the amount of future work to be done to promote lime-based binders commercially.

Sustainable production of nanolime using plant extracts by fermentation: A traditional approach towards conservation of heritage structures

Nanolimes have emerged as efficient consolidants for the conservation of historic and heritage structures. This research investigates an effective, economical, and sustainable way of synthesizing nanolimes using hydraulic lime and natural plant extracts. The lime is fermented with aqueous organic extract for 14 days to produce nanolimes. The fermented compounds in liquid phases and the organic extract were identified using high-performance liquid chromatography (HPLC) and gas chromatography with mass spectrometry (GC-MS). Alcohols, which are substantial fermentation byproducts, were found to aid the nanoscale dispersion of portlandite particles. The narrow size distribution and mean particle size of 130–290 nm in seven-day fermented samples were able to penetrate deeper into treated surface strata for better conservation of structures. The presence of portlandite and calcite nanoparticles observed by X-ray diffraction in nanolime assisted to fill the pores that are too big for nano-portlandite alone and intensifies its ability to hold the grains of the treated surface. The biomineralization process resulted in the development of carbonate compounds ranging in size from 0.4 to 50 nm, thus rendering nanolime as more effective and facilitating the filling of nanopores smaller than 100 nm, which eventually signifies the durability of structure. Ultimately, this research emphasizes importance of nanotechnology in resurrecting tangible heritage.

Isotropic modelling and blast analysis of heritage structure

The protection and conservation of heritage structures are of foremost importance. Hence, the present study focuses on the isotropic modelling of a heritage school building, to determine its response to the action of various blast scenarios. The impact due to blast explosion may result in severe damage to any structure especially those made of brick masonry. The heritage building under study is an unreinforced masonry structure that by its inherent nature is extremely weak in out-of-plane loading such as; blast. The considered building has been modelled in STAAD Pro using finite element macro-modelling approach. The idealised blast pressure–time histories have been developed using IS: 4991-1968 (Reaffirmed 2018). Nodal Force application method has been implied to apply corresponding blast load on the structure at varying standoff distances.

Seismic Vulnerability Assessment and Strengthening of Heritage Timber Buildings: A Review

Recent studies highlight the potential impact of earthquakes on cultural heritage sites and monuments, which in turn yield significant adverse impacts on economies, politics, and societies. Several aspects such as building materials, structural responses, and restoration strategies must be considered in the conservation of heritage structures. Timber is an old organic construction material. Most of the historic timber structures were not designed to withstand seismic forces; therefore, the seismic vulnerability assessment of heritage timber structures in areas with high seismic hazard is essential for their conservation. For this purpose, different strategies for the numerical modeling of heritage timber buildings have been developed and validated against tests results. After performing seismic analysis using detailed analytical methods and predicting the susceptible structural components, strengthening techniques should be utilized to mitigate the risk level. To this aim, various methods using wooden components, composite material, steel components, SMA etc., have been utilized and tested and are reviewed in this study. There are still some gaps, such as full-scale numerical modeling of strengthened buildings and investigating the soil–structure interaction effects on the seismic behavior of buildings that should be investigated.

Structural Vulnerability Assessment of Heritage Timber Buildings: A Methodological Proposal

The conservation of heritage structures is pivotal not only due to their cultural or historical importance for nations, but also for understanding their construction techniques as a lesson that can be applied to contemporary structures. Timber is considered to be the oldest organic construction material and is more vulnerable to environmental threats than nonorganic materials such as masonry bricks. In order to assess the structural vulnerability of heritage timber structures subjected to different types of risk, knowledge about their structural systems and configurations, the nature and properties of the materials, and the behavior of the structure when subjected to different risks, is essential for analysts. In order to facilitate the procedure, different assessment methods have been divided into the categories in situ and ex situ, which are applicable for vulnerability assessments at the element and full-scale level of a case study. An existing methodology for structural vulnerability assessments and conservation of heritage timber buildings is reviewed and a new methodology is proposed.

Influence of organic additive on carbonation of air lime mortar – changes in mechanical and mineralogical characteristics

This research work aims at studying the influence of fermented organic additive on strength and carbonation of air lime mortar for the conservation of heritage structures. Binder to aggregate ratio of 1:3 by weight and water to binder ratio of 0.7 were considered. Red grape (Vitis vinifera) as an organic additive with 2, 4, 6, 8 and 10 percentages were accounted for fermentation of 0, 1, 2 and 3 days and were added with lime mortar. Experimental investigations were conducted on mechanical and mineralogical properties. 6% of organic addition with 3 days of fermentation resulted in a 49% increase in the mechanical resistance compared to the reference mortar on 90th-day test. XRD records an increased calcite formation due to accelerated carbonation. FTIR indicates the presence of polysaccharides that have helped in accelerating carbonation. TGA-DTA supports XRD and FTIR results in confirming the strength gain through the formation of calcium carbonate. Hence, the results are explicit, revealing that the fermented organic addition in air lime mortar has increased the carbonation rate, as the polysaccharides present in organic played a crucial role in accelerating the transformation of calcium hydroxide to forms of calcium carbonate and thereby enhancing the strength significantly.

An Innovative Methodology for Online Surrogate-Based Model Updating of Historic Buildings Using Monitoring Data

ABSTRACT Structural Health Monitoring (SHM) based on Automated Operational Modal Analysis (A-OMA) has gained increasing importance in the conservation of heritage structures over recent decades. In this context, finite element model updating techniques using modal data constitute a commonly used approach for damage identification. Nevertheless, the large number of simulations usually involved in the associated minimization problem hinders the application to real-time condition assessment. This is especially critical for historic buildings, where the modelling of complex geometries involves large computational burdens. Alternatively, surrogate models offer an efficient solution to replace computationally demanding numerical models and so perform continuous model updating. In this light, this paper presents a surrogate-based model updating approach for online assessment of historic buildings and its application to a medieval masonry tower, the Sciri Tower in Perugia (Italy). Using modal properties identified by A-OMA, the proposed approach allows the continuous fitting of certain damage-sensitive parameters of the structure. To do so, three different surrogate models are considered, including the quadratic response surface method, Kriging, and Random Sampling High-Dimensional Model Representation, and their effectiveness is compared from an SHM perspective. The reported results demonstrate the suitability of the proposed methodology for tracking the temperature-dependent intrinsic properties of the tower.

Optimum water content tests for earthen construction materials

There is considerable interest in earthen construction materials, owing to their inherent sustainability, and also in the conservation of heritage structures. For new-build in situ construction a key aspect of quality control is the achievement of full compaction to maximum dry density. At present the guidance available in this area to those using these materials varies from British Standard tests to heuristic-based methods developed by practitioners. In this paper, the various tests are compared for different soil mixes and also to judge the influence of the test operator. The study demonstrates shortcomings in the heuristic methods and indicates that, for modern standards of quality control to be achieved, alternative tests should be used.

Conservation of Heritage Structures in Turkey: Practice and Difficulties

Conservation studies in developing countries might have additional problems to those that are being experienced by leading developed countries. The problems and difficulties mentioned here do not reflect the common practice in Turkey and mostly list rare cases for information purposes. Countries located in Asia and Middle East have rich structural heritage, in number and significance, which are sometimes even a few millenniums old. On the other hand, often times financial or bureaucratic constraints make the conservation studies more difficult, while technical problems remain to be an issue. It is quite interesting that sometimes having available financial support for conservation studies turns out to be the main source of problem, since quick and not well thought interventions end up damaging hundreds of years old surviving structures, rather than conserving them. Other most common application problems include use of Portland cement in humid environments causing salt contamination (which is now widely being avoided), infilling and freezing cracks that used to work as seasonal water table movement based motion or thermal expansion joints that are cyclic in nature, covering the structure to protect but forming unintentional green house effect – micro climates forming fungus, improper drainage to cause support settlements, removing earth fill or structural members to cause structural movements and cracks, strengthening parts of a flexible structure only to make it more rigid and cause to attract more earthquake forces, disable its energy dissipating mechanisms, applying improper chemicals, using incompatible material or irreversible techniques etc. are just a few to mention. The problem solution strategies in conservation studies should include internationally accepted conservation rules. Multi disciplinary teams are always recommended since combination of various expertise areas are mutually needed in conservation studies; architects, geotechnical and structural engineers, geology and material science specialists, archeologists, art historians are among the most important team members. Analytical modeling and simulations, on-field non destructive testing, instrumented monitoring (SHM), and small scale field treatment tests are recommended to be merged and used in conservation studies, because conventional methods or commercial repair/treatment materials available over-the-counter may not always suitable for a given specific case. Reversibility, minimum intervention, and respect to authenticity should be among the main principles to avoid serious conservation problems.

Lost Heritage: a survey of historicbuilding demolitions in Ontario, Canada

There has been legislation in place since the 1970s in Canada's largest province, Ontario,that encourages the identification of significant heritage buildings and is supposed to providethem with at least a degree of protection. Both heritage recognition and most other land usedecisions, however, are exercised at the local government level. W'hile conservation ofheritage structures has been successful in some places, an alarming number of significanthistoric buildings in the province continue to be lost. Relying on dozens of volunteers, thisstudy examined thousands of buildings in over twenty Ontario communities and sought toestablish how many heritage buildings had been demolished and to determine why theselosses were occurring. It was discovered that in the municipalities surveyed over 400historically recognised buildings had been lost in the last sixteen years. Recommendations forhow to deal with this problem are included in the study.