Integrated Life Cycle Assessment of Concrete Structures
Concrete is the most used man-made material. The production of concrete in the industrialized world annually amounts to 1.5-3 tons per capita. Concrete is used in the construction of buildings, bridges, dams, roads, tunnels; basically, every contemporary construction contains concrete. Due to its mechanical properties, durability, variability, and availability of resources, concrete represents the most widespread structural material for building construction.
Cement production is associated with large energy consumption and consequently with high CO2 emissions. World cement production has increased 12 times in the second half of the last century; the cement industry produces at present about 5-7% of global man-made CO2 emissions. Moreover, high concrete use is associated with high transport needs and demands on production and demolition processes within the entire life cycle. This all has significant impacts on the environment.
Current concrete developments, production technology, and the development of concrete constructions during the last twenty years have led to a quality shift of technical parameters and related environmental impacts. Due to mix optimization, new types of concrete have significantly better characteristics from the perspective of strength, mechanical resistance, durability, and resistance to extreme loads. Concrete is gradually becoming a building material with a high potential for environmental impact reduction. Better knowledge is still needed about the technological processes and their impacts with respect to a wide variety of sustainability aspects within the entire life cycle, from the acquisition of materials, through the production of concrete and concrete components, construction, use, up to the demolition of the concrete structure and recycling.
The technical and technological qualities of concrete have a significant impact on many aspects of structure sustainability within the whole life cycle. The evaluation of complex quality considering all important and relevant aspects of sustainability (environmental and economic) requires a holistic approach. This could be achieved by applying an integrated life cycle assessment – ILCA.
In the frame of the SPHERE Project, the Master Builders Solutions Concrete Eco-Efficiency Analysis is developed to comprehensively define the environmental estimates of potential impacts for concrete products from a cradle-to-gate perspective. The results are an accurate comparison of impacts between the alternatives evaluated, and they include a wide range of environmental impact metrics.
The system boundaries for the Master Builders Solutions concrete analysis are determined prior to the initiation of a specific study. Many times, the boundaries will be cradle-to-gate based on the similarity in the additional stages of the life cycle and therefore will have no impact on the overall results. The model is flexible for a full cradle-to-grave or cradle-to-cradle analysis, see Fig. 1 and Fig. 2.
Integrated Design of a Building
Integrated design is a complex approach implementing all relevant and significant requirements into one single design process. Several different sources for the definition of integrated design exist so that no single definition prevails. Commonly defined characteristics of integrated design are a holistic mindset and the goal of improving the performance of the resulting building structure by including long-term performance as a criterion from the earliest parts of the design process.
This approach integrates material, component, and structure design, and considers selected relevant criteria from a wide range of sustainability criteria, subjected to technical, functional, and sustainability requirements. So, in order to overcome the information overload issue, the SPHERE platform may link directly to an innovative specification tool designed to support construction professionals to find the right solutions for their projects in a safe, fast and efficient way, and download the relevant BIM objects directly without the need to surf through several databases.
The tool also adjusts to changing project requirements and provides crucial information along each step of the project planning process, offering additional details about the products selected. With a single click, the user can request also product and application pricing information, and the project report is compiled and immediately made available for download, see Fig. 3.
Life-Cycle Cost Assessment (LCCA)
Building Life Cycle Costing is the analysis of the costs of your building over the whole life cycle, and it can help to assess long-term savings and costs. Often, it is calculated along Building Life Cycle Assessment, and LCC is also a credit in many Green Building certification credits. As with Building LCA, the earliest in the design process you calculate Building Life Cycle Costing analysis, the most savings you can achieve. Moreover, in both cases, you can compare design alternatives to find out which is better over the whole life cycle of the building. For example, if you perform LCC calculations you might find out that a product that has a cheaper initial cost might end up being much more expansive in the long run because it will need to be replaced more times during the building use phase, which is usually around 60 years. In short, the business case for Building Life Cycle Costing is a strong one. What Building LCC does is to provide reliable metrics on costs and savings over the whole lifetime of the building, and when paired with LCA, it can help design buildings that are more sustainable both from an environmental and financial perspective.
The basis for the cost impact evaluation should be a condition assessment of the entire structure or structural elements, where the performance of the structure, deterioration mechanism, extent, and future degradation rate are estimated. Fig. 4 shows two performance strategies, A and B, considering estimated development of cost or environmental impacts within the life cycle of a concrete structure, including all consequent technical provisions like formwork, temporary structures, access roads, etc. It is evident that higher initial cost and higher environmental impact (leading to higher performance quality) can, at the end of the entire life of the structure, result in lower total life cycle cost and total life cycle environmental impact. Appropriate settings of repair periods, keeping or improving performance quality, are essential for the extended life of the structure.
Technically feasible repair methods shall be set forward and priced both in relation to actual costs but also in relation to indirect costs, where the user inconvenience due to lower performance quality is priced depending on the duration of the repair works. The degradation rate is important, as an owner often has to prioritize between different repair works. Therefore, the consequences of postponing a repair project have to be evaluated, see Fig. 4.
An important aspect in relation to LCC calculations is the consideration of interest rates. For LCC calculations, national applied interest rates can be used allowing for a calculation of net present value for a structure.
With regards to cost evaluation, the model calculates the Life Cycle Costs of each solution. This is a measure of the total costs incurred during the lifetime of the structure, expressed as the Net Present Costs (NPC). The solution with the lowest NPC should be selected from an economic point of view (see calculation method in Fig. 5 below).
Case Studies – Concrete Structures
In order to demonstrate how the above methodological framework for the assessment of cost impacts can be applied to various types of protection, repair, and maintenance systems for concrete structures, two examples of commonly used systems are the subject for analysis, the results of which are briefly outlined in the following.
The first comparison has been made between three different waterproofing membranes
1.a. Cement waterproofing (MasterSeal 531)
1.b. Polyurea waterproofing (MasterSeal M 689)
1.c. Polyurethane waterproofing (MasterSeal M 808)
The second scenario compares the concrete protection using two different systems:
2.a. Anticarbonation coating based on acrylic polymers (MasterProtect 330 EL)
MasterProtect 330 EL is a single component, ready to use, water-based coating formulated from a blend of high-performance acrylic polymer emulsion with pigments and fine fillers. The coating provides a protective and decorative finish for exterior and interior use on concrete and other substrates. It has very good adhesion onto the concrete substrate and is very elastic – even in temperatures below zero and provides excellent protection against carbonation and remains water steam permeable, see Fig. 6.
2.b. Advanced organofunctional corrosion inhibitor for concrete protection (MasterProtect 8000 CI)
MasterProtect 8000 CI is an advanced organofunctional silane-based corrosion inhibitor, which combines the proven effectiveness of penetrative silane treatments for the control of moisture and Chloride ion ingress with advanced organofunctional corrosion inhibition, see Fig. 7.
This model is used to compare MasterBuilders Solutions for repair and coating on the basis of Life Cycle Costs (LCC).
The model can be tailored to a user specific situation. As a result, the total Life Cycle Costs are presented for each solution. This provides a solid economic foundation to select the best repair/coating solution for your specific situation.
The results are shown as the calculated Life Cycle Costs of each solution, see Fig. 8 and 9. This is a measure of the total costs incurred during the lifetime of the structure.
The tools help to comprehensively define the environmental estimates of potential impacts for concrete products from a cradle-to-gate perspective, and smart selection of materials for building retrofitting purposes. It achieves the objective of an accurate comparison of impacts between the alternatives evaluated, and it includes a wide range of environmental impact metrics and construction materials comparison criteria.