Self-healing on natural hydraulic lime mortars

Project Information

HeaLime

Grant agreement ID: 101003395

DOI

10.3030/101003395

Project terminated on 6 August 2021

EC signature date 15 April 2020

Start date 1 January 2021

End date 31 December 2022

Funded under

• SPREADING EXCELLENCE AND WIDENING PARTICIPATION

Total cost

€ 147 815,04

EU contribution

€ 147 815,04

Coordinated by

UNIVERSIDADE DO MINHO
Portugal

Periodic Reporting for period 1 - HeaLime (Self-healing on natural hydraulic lime mortars)

Reporting period: 2021-01-01 to 2022-12-31

Summary of the context and overall objectives of the project

Most of the civil and architectural heritage of nowadays is built with masonry structures. However, historic masonry structures, being submitted to high loads for long periods of time, end up cracking. Cracks in such structures affect both the serviceability and ultimate limit states. The interventions on such structures require the usage of compatible materials and in this sense natural hydraulic lime (NHL) mortars offer a promising solution due to their large compatibility in terms of physical, chemical and mechanical performance with original masonry materials. At the same time, it is well known that the interventions on historical masonry structures demand great economical and technical efforts so it results of paramount importance that such interventions are as much durable as possible.

One obvious solution to enlarge the durability of the interventions on masonry structures is to use more durable materials or in other words to study the properties of NHL mortars so that to make them more durable. In this sense, the self-healing capacity of such materials results of paramount importance and of potential value. If active research was performed to improve the already known self-healing capacity of NHL mortars, then durability of masonry structures would be improved, which would imply significant savings in the long run on money and efforts.

Another important issue is the way self-healing is measured in NHL mortars. For concrete, the common practice consists in damaging the specimen in three-point bending test, leaving it to cure and to self-heal and, after a certain period of time, breaking it to evaluate the flexural strength recovery. For NHL mortars it is not recommended to perform three-point bending tests as the specimen is weak and could be broken just in the damage stage. Then, it is common to perform compression tests and evaluate the strength recovery after a curing period. The main drawback of this approach is that the interpretation of the results becomes much harder as significant damage is inflicted to the specimen (not just cracking), which makes more difficult the interpretation of the results. At the same time, the currently existing methodologies to study self-healing are somewhat qualitative in nature in regard to actual service life behaviour; they normally are centred in ultimate limit capacity, which is clearly not the performance requirement that the self-healing capacity aims to fulfil. Therefore, a research gap is identified in this context.

The main objective of HeaLime is to close the above identified research gaps, both in regard to the need for better identification of the performance of materials upon self-healing (in a quantitative manner in service), as well as for the systematic characterization of the combination of several variables in the context of the performance of the healing capacity. The ultimate goal is therefore to be capable of proposing optimized mix proportioning and blend components that behave adequately for ordinary requirements, while having a quantified confirmation of much improved self-healing abilities. This will invariably contribute to global sustainability increases in NHL mortars in masonry structures, with expectable benefits of reduced CO2 emissions, gladly accompanied by no relevant aggravation of the initial costs of the material.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The project started the 1st January with a deep review of the state of the art. Different scientific papers on self-healing of cementitious materials were read and analysed. Furthermore, it was improved the researcher’s background on structural dynamics by reading several scientific books on the topic, such as, “Dynamic of Structures” by Ray W. Clough and Joseph Penzien, or “Structural Dynamics” by Mario Paz and William Leigh. Furthermore, it was made an online course entitled “Fundamentals of Engineering Structural Dynamics with Python” instructed by Dr. Seán Carroll. The course extended for 7 hours and it was finished the 19th January, 2021.

Following this, the focus was a virtual meeting with the researcher’s supervisors, Prof. Paulo Lourenço and Prof. Miguel Azenha, together with the supervisor at the first secondment, Prof. Nele de Belie, from the University of Ghent. For the purpose, it was made a thorough summary of the state of the art on self-healing of cementitious materials and a detail planning of the project for the first year and the first secondment. The meeting took place the 9th February through the Teams platform. Fruitful discussion was derived from it that encouraged the researcher to continue her work with some numerical simulation.

The numerical simulations focused on modelling the healing effect of a simple supported beam of natural hydraulic lime mortar. First, she validated the model by comparing the resulting modes of vibration to the analytical results after application of formulas of structural dynamics. Then, she modelled different configurations: a beam without notch, another one with a centred notch and, finally, others with two notches at different positions. The objective was to study the expected natural frequency of vibration of the specimen to be tested under the new EMM-ARM method to be developed during the project. The range of first natural frequencies obtained varied from 93.373 Hz to 142.76 Hz, depending on the beam configuration.

Once the numerical part of the project was finished, the experimental one was started. Six wooden molds were fabricated with the dimensions obtained from the numerical simulations to test various beams with the new experimental method.

Unfortunately, due to unexpected circumstances a suspension of the project had to be applied the 24th June, 2021. However, the methodology applied in the numerical models as well as the molds fabricated could be used to study the self-healing capacity of similar materials at the University of Minho. More especifically, two master students are working on the self-healing of stabilized soils and mortars. It is likely that a publication with the procedure and the main results is prepared soon.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

After making a deep review of the state of the art, it was made a numerical simulation to represent a simple supported beam of natural hydraulic lime mortar. First, the model was validated by comparing the resulting modes of vibration to the analytical results after application of formulas of structural dynamics. Then, different configurations were modelled: a beam without notch, another one with a centred notch and, finally, others with two notches at different positions. The objective was to study the expected natural frequency of vibration of the specimen to be tested under the new EMM-ARM method to be developed during the project. Furthermore, it was fabricated six wooden molds, with the dimensions obtained from the numerical simulations, to test various beams with the new experimental method.

Due to unexpected circumstances, a suspension of the project had to be applied. However, the numerical models performed and the wooden molds fabricated were useful for other students to study the self-healing capacity of stabilized soils and mortars. The study of the self-healing of said materials are likely to bring a lot of economic saving as well as better environmental behaviour of materials in the short and long term.

Analysis and comparison on different beams configurations

Scheme of the new experimental method proposed

Validation of the numerical model on slender specimens