Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - ClimatCon (Climate-resilient pathways for the development of concrete infrastructure: adaptation, mitigation and sustainability)

Teaser

Climate change is one of the key challenges facing the human race in the 21st century. This phenomenon is primarily attributed to global anthropogenic CO2 emissions, 5% of which come from Portland cement production that is an integral part of the concrete industry. To respond...

Summary

Climate change is one of the key challenges facing the human race in the 21st century. This phenomenon is primarily attributed to global anthropogenic CO2 emissions, 5% of which come from Portland cement production that is an integral part of the concrete industry. To respond to this challenge new approaches to sustainable development of concrete infrastructure combining both mitigation and adaptation measures are needed. The project contributes to the formulation of such approaches.
The project aims to develop a method for the evaluation of the whole life performance of RC structures subjected to carbonation in conditions of climate change, which takes into account both mitigation and adaptation measures. The method is based on the integration of two techniques: Life Cycle Assessment (LCA), which places emphasis on environmental issues, and Life-Cycle Cost Analysis (LCCA), which concentrates on economics. Since there are numerous uncertainties associated with associated with environmental and mechanical loads, material properties, models, etc. the method uses a probabilistic approach. To achieve this aim the following objectives have been planned:
• Experimentally determine the carbonation rate in traditional and ‘green’ (i.e. with fly ash and blast furnace slag) concretes in unloaded and loaded states;
• Develop a numerical model for predicting carbonation and CO2 uptake of concrete, which accounts for the influence of loads (including caused by them cracks), time-variant ambient CO2 concentration, temperature and relative humidity;
• Develop an integrated probabilistic LCA-LCCA method for evaluating the whole life performance of RC elements subjected to carbonation with particular emphasis on their deterioration and subsequent repairs and associated CO2 emissions;
• Prepare case studies illustrating application of the method.
Results obtained during the project demonstrate a clear influence of loading conditions on the carbonation rate of concretes, especially of ‘green’ concretes. Thus, it has been essential to account for that in the numerical model of concrete carbonation that has been developed. The LCA-LCCA analysis of a case study has shown that the use of ‘green’ concretes in RC structural elements leads to a reduction in carbon dioxide emissions, while the life-cycle cost of the elements remains similar to that of the elements made from Portland cement concrete. However, the use of ‘green’ concretes increases the probability of carbonation-induced corrosion, in particular in conditions of climate change.

Work performed

Major experimental studies of carbonation of traditional and ‘green’ concretes in unloaded and loaded states have been completed. Six different concrete mixes with two different water/binder ratios and different proportions of Portland cement, fly ash and blast-furnace slag were prepared. The mixes were used to cast 24 reinforced concrete (RC) beams (100×120×900-mm) and 54 100-mm concrete cubes. The beam specimens were loaded in four-point bending and placed into a carbonation chamber. The specimens were subject to accelerated carbonation (CO2 concentration of 4%) for 120 days (first group) and 240 (second group), then extracted from the chamber and the carbonation depths were measured. Photographs of the tests are attached.
The results of the experiments showed that the loading state and concrete cracking had a major influence on concrete carbonation. To improve the accuracy of the carbonation prediction a numerical model of carbonation was been developed. The model takes into account the transport of CO2, water and calcium ions, changes in the concrete porosity due to carbonation and applied loading, and the presence of cracks. These phenomena are described by a system of nonlinear partial differential equations, which is solved by a finite difference method. The model has been formulated for one- and two-dimensional problems. The solution procedure for one-dimensional problems has been implemented in MATLAB.
A probabilistic method integrating LCA and LCCA techniques has been developed for evaluating the whole life performance of RC elements subjected to carbonation. The environmental impact is evaluated by LCA in terms of the emitted mass of CO2 and takes into account CO2 uptake. Deterioration of RC structures during their service life due to carbonation-induced corrosion is considered, including the effect of climate change, that allows to address adaptation measures. It is assumed that a RC element needs to be repaired when either corrosion starts or cracking of the concrete cover caused by corrosion becomes excessive. The environmental impact of repairs and the repair costs are taken into account. To fully evaluate the effect of the CO2 uptake the end-of-life stage is considered. Probabilistic analysis is performed using Monte Carlo simulation and yields distributions of CO2 emissions and life-cycle cost of RC elements. Using the developed method a case study of a RC element of a multi-storey car park in London has been carried out. The use of different concrete types, traditional and ‘greens’, for the element has been compared.

Final results

The experimental study carried out in the project is the first one in which carbonation of ‘green’ concretes in a loaded state has been investigated. Results of the study have clearly shown a major influence of loading on the carbonation resistance of concrete. Loading (especially tension) had a much larger effect on the carbonation resistance of ‘green’ concretes than on that of Portland cement concrete. The results have also indicated that structural cracks (i.e. ones caused by loading) more affect the carbonation propagation than drying shrinkage cracks.
The experimental results show the importance of taking into account the loading state of concrete when predicting its carbonation. However, prior to this project, there was no physically-based carbonation model that would do this. The numerical model developed in the project addresses this important issue. The model simulates essential processes affecting the concrete carbonation and, in addition, is capable to account for the effect of load-induced deformations. It also allows taking into account the presence of macro cracks.
The development of the probabilistic method, which integrates LCA and LCCA techniques, is a major step in achieving a more realistic and reliable evaluation of the sustainable performance of concrete infrastructure. It is the first method that enables to simultaneously consider the effects of mitigation and adaptation measures. The method takes into account both CO2 emissions and uptake during the whole life of RC concrete elements. The method also explicitly accounts for numerous uncertainties associated with such an evaluation. This enables to estimate not only expected CO2 emissions and life-cycle costs for RC elements but also distributions of these parameters that provides more complete and realistic information for decision making.
The area of the project – sustainable development, which is a key objective of the EU, while concrete is the most common construction material. The methods, models and data produced by the project are very useful for the development of strategies for sustainable management of concrete infrastructure in conditions of climate change. Europe is currently a world leader in sustainability research and the project outcomes contribute to its excellence and competitiveness in this field.

Website & more info

More info: https://www.egis.hw.ac.uk/climatecon/.