Construction and Demolition Waste (C&D Waste or CDW) includes all the waste from the construction of new buildings, demolition of old ones and small refurbishment works. The generation and management of CDW is a serious environmental problem. Neglect or mismanagement produce negative impacts and can cause water, ground and air pollution, contributing to climate change and affecting ecosystems and human health.
Current regulations on CDW management determines the need for an ex-ante estimation of the debris type and volume a project will generate. The level of detail and accuracy should be adequate to allow an effective planning to carry out the management of this waste.
Concern about the amount of CDW generated and its environmental impact is growing. For this reason, governments and public authorities are reviewing their policies on how these wastes should be managed. In order to improve this management, it is necessary to know the composition and magnitude that should be dealt with, as well as some estimating method of waste generated in a project, in a region or a country.
Despite all the problems that CDW may cause, and difficulties on their treatment, when waste is properly managed become resources, or products that contribute to saving raw materials, conservation of natural resources, avoid climate change and thus to sustainable development, in accordance with the principles of the circular economy.
How to estimate the waste generated by construction and demolition activities varies significantly from place to place, as explained below.
America In the United States, USEPA (US Environmental Protection Agency) estimates the amount of CDW generated in a specific region only from the built-up area, but regardless of whether the building is residential or not, or whether the works are new construction, refurbishment or demolition, which influences the type and amount of produced waste.
Another interesting case is Brazil, because it is an emerging country but CDW legislation is very similar to the European one, particularly the Portuguese. In this country, the civil construction sector is an important waste generator and national laws require manufacturers to take responsibility for the waste generated in their work and planning their management. A very important part of this effort is waste estimate to be generated, differentiating by waste type (brick, wood, glass, etc.) as each need a suitable deposit space and will be treated differently.
Asia The situation in Asia varies greatly from one country to another. Except for Korea and Japan, lack of knowledge and awareness of efficient building practices results in natural resources overuse and generation of large amounts of CDW that is rarely recycled. Approximately 40% of the total generated waste comes from construction and demolition activities. This waste is difficult to manage because it is heavy and bulky and can not be incinerated or used for composting.
Europe The European Union, in the EWC (European Waste Catalogue) provides a classification of the CDW by category. According to statistics, there are huge differences in recycling and recovery rates between EU countries, between less than 10% and over 90%. In Spain, recycling rate is around 65% of generated CDW. Construction companies benefit from the reduced amount of generated waste by reducing landfilling associated costs and reducing raw materials purchasing budget.
CDW Management in Spain Most of not recycled waste, at best, goes to landfills, taking up large discharge spaces and causing faster filling. In Spain, CDW estimation is usually done based on the floor area. To estimate each type of waste amount, a widespread criterion is 20 cm tall mixed waste per m2 built, according to use, with a standard density from 0.50 t/m3 to 1.50 t/m3. In order to obtain the weight by waste type, data based on studies about the composition of the CDW going to landfill could be used.
Summarizing, research in this field has focused in two ways: “hard” methods, measuring waste produced directly on site or through the weight of the trucks leaving the work, and “soft” methods, through questionnaires, interviews and surveys of experts and workers. When dealing with waste generation rates forecast, two approaches have been found. First is sorting waste into different categories, e.g. those established by the EWC. The second is managing waste as a whole and estimating the total volume.
A realistic approach to the problem undertakes to manage the project as a large number of interrelated and different task types (project units), in which each of these works affects differently in waste generation. Similarly, if forecasting models are developed based only on available historical data, without the necessary preliminary analysis and processing, a significant error could be introduced, as this information can come from heterogeneous and unevaluated sources.
Have you ever wondered how it is decided when a road or a tunnel should be repaired? The most common is that an operator notes damages down in his notebook while he goes walking, and then, these annotations are used to determine the state of the infrastructure. Operators often walk on the hard shoulder, while traffic circulates normally around them, with the corresponding threat to themselves and to users of the road. This task is really monotonous and repetitive, resulting in eyestrain that difficult to obtain an acceptable degree of reliability in the inspection. Furthermore, although the visual inspection adapts well to new situations when it is performed by human operators, it has a high degree of subjectivity, which causes that two different operators, or the same operator on different times, could provide different results.
The implementation of new technologies to perform these inspections can reduce the risks described, get objective results, increase the speed of inspection and make these data digitally available. In brief, working conditions of operators and the quality of the results are improved.
Among the different variables that are required to be measured in road infrastructure it can be found surface deterioration. To measure this deterioration is necessary to analyse the visual appearance of the surface. The technology that allows us to obtain this information, as you can imagine, are the cameras. But we must keep in mind that these surfaces have some quirks that do not allow us to obtain the desired results using conventional cameras.
Such surfaces are defined by having a limited width and indeterminate length but much greater than its width, so they could be considered continuous surfaces. The images of these surfaces should be taken in motion and as fast as possible in order to make the acquisition efficiently. To do this, although it would be possible to use area-scan cameras, it is much better to use linear camera. A linear camera builds the images capturing them line by line, and therefore a continuous image in the forward direction is constructed. The camera consists of a linear sensor, which is usually between 512 and 12,000 pixels. For capturing the object, it has to move relative to the camera, or the camera must move relative to the object.
The main advantage of using linear cameras is that it is only necessary to illuminate a thin line of the object to be inspected. As a result, the amount of energy required is reduced drastically and it is easier to illuminate homogeneously the area to be inspected. The lighting of a line is done primarily through LED light sources that focus light through optical in a desired line width. To achieve this, the lighting system must be at the proper distance from the object to be inspected and must be aligned with the camera sensor accurately. Laser illumination sources are also very effective, with the advantage that concentrate the light at any distance. Finally, incremental encoders are used to synchronize the acquisition of each image with the displacement of the surface to be inspected relative to the camera. Incremental encoders generate a pulse each time the inspection vehicle moves forward a certain distance, indicating the camera the exact moment for acquiring the line image.
Having the images of the surface to be inspected available is itself extremely useful for the infrastructure manager. However, what really gives added value to the inspection system is the automatic interpretation of images. You must remember that the ultimate goal is to detect damages on the surface and classify them by its type. Often, it is difficult to automatically differentiate defects from areas without deterioration and, moreover, defects of the same type have a very uneven visual appearance.
In order to process the images successfully, complex image processing techniques have been developed characterizing anomalies in the space-frequency domain.
CARTIF has collaborated with companies from the construction industry to address the inspection of this type of surfaces in several research projects. In one of them, it has been developed an inspection vehicle for detecting road surface deterioration. Furthermore, it has also been developed a platform for inspecting the surface of tunnels. Similar techniques also have been applied to the inspection of industrial products that fall within the definition of continuous surfaces, such as coils of cold rolled steel.
In all cases, the results of the inspection are displayed to the end user, so that appropriate decisions can be taken and, most importantly, it can be determined when the infrastructure has to be repaired.
3D printing is here to stay. When a new technology is so widespread that no longer catches the attention it is that its implementation is complete. More and more people have a plastic 3D printer at home and many of us know someone who has bought one or it has been built by pieces. It was only a matter of time before this technology would give the jump to other sectors. Although the construction sector usually adopts this type of technological developments rather late, in this case there are already several projects trying to bring the additive manufacturing (as is also known 3D printing) to construction.
What is wanted, among other things, it is to face the new architectural designs that are increasingly complex, industrialize certain construction processes which, today, are almost artisanal and improve sustainability using recycled materials for printing.
Such systems pose major challenges such as the development of new building materials that allow their proper implementation. Usually, the addition of other materials or compounds that improve the properties (or achieve the desired properties) in setting times, strength and insulation is used.
One of the first projects in relation to additive manufacturing in construction is called “Contour Crafting“, led by Dr. Behrokh Khoshnevis of the University of Southern California. And now there are many research centresand universities focused on these issues as AMRG University of Loughborough considered a world reference or IAAC in Spain.
They have also appeared commercial developments such as the case of a Chinese company that manufactured homes, offices and entire buildings using these techniques. The specific case of this company seems to respond to marketing strategies (which seems to be taking effect) because a good position in these technologies can open important markets.
In any case, there are many interesting initiatives such as WASP, an Italian project for sustainable buildings in disadvantaged areas, the construction of a steel bridge in Amsterdam, or NASA contest for construction of buildings on the moon or Mars using these techniques, the winner of which proposed the use of ice as raw material.
In the light of these developments it is easy to see that the additive manufacturing construction offers some advantages hard to match with other methods such as complexity in designs that can be obtained, the accuracy and repeatability of certain construction procedures. It is undeniable that industrialization is increasingly integrated into many building processes and 3D printing sure to have your niche in the construction sector.
As always with new technologies, certain optimistic sectors are saying that the additive manufacturing will be the majority system used in all industries but certainly there are currently no universal manufacturing technologies (beyond certain methods such as mass production). The current manufacturing processesare highly specialized and uses the most appropriate technologies in each case it seems complicated than a single technology is able to replace almost all existing. Therefore, and being realistic, we must find the most suitable application field for 3D printing in construction.
In this regard, CARTIF participates in a major national research project related to 3D printing in construction. This project focuses on the application of 3D printing technologies in construction in those areas where it is considered that can be especially useful: the manufacture of prefabricated modules and rehabilitation of facades. It does not seek a universal technology to serve in all areas of construction, but to reach the market with a product that offers a viable alternative to other existing technologies (i.e. realistic and sustainable applications). And without forgetting that all progress made in this field (whether by R & D or marketing strategies) will impact in the future, for the benefit of the whole society because what it is pursued, is to build better, faster, cheaper and in a more sustainable way.
Have you ever thought on the importance of the monuments close to you?. Do you happen to know they really are a source of employment and local development?. Here you are a few lines to explain it, and also to make you understand how the applied RTD is effectively contributing to the study, protection, conservation, refurbishment and reuse of cultural heritage.
Since 1999, with the Florence Conference, and later with the World Bank and the UNESCO reports, cultural heritage is considered a rightful source of socio-economic development for the countries. It is really a form of capital that the economist David Throsby noted as ‘cultural capital’, i.e. an asset with specific key features (the economic value is added to the cultural value -primordial, symbolic, intangible-).
Europe is the region that counts with the most important and the richest cultural heritage all over the world. This contributes to attract millions of tourists every year. Obviously it helps to create jobs and enhances the quality of life of European citizens while reinforcing a common shared identity.
The European Union Treaty (Article 167) specifies that safeguarding cultural heritage (moveable and immoveable) must be treated as a priority for the EU and is the legal basis for protection initiatives including research on cultural heritage. Besides, UNESCO expressly states that “the protection of cultural heritage, as an expression of living culture, contributes to the development of societies and the building of peace”.
The protection and preservation of important monuments and sites is more pressing than ever as cultural heritage is exposed to pollution, climate change and socio-economic pressures. According to specialists in the field, the activities oriented to ensure the sustainability of heritage are proving to have a major impact boosting the local economy and attracting foreign capital (because of related cultural tourism).
The following figures emerging from the EVoCH Platform within CARTIF is a founding member, will take you on the way of we are talking about:
The recognition of the importance of the mentioned aspects leads cultural heritage to be considered into specific RTD proposals in the current EU Research and Innovation programme (Horizon 2020). In fact, since 1986 the EU has been supporting research for the preservation of tangible cultural heritage to develop ‘state of the art’ methodologies, tools and products.
During the last years, a few successful results of technology transfer are giving evidence that the most effective and practical way of supporting and developing innovative services, is a collaboration between applied research organizations and enterprises to make these fit ICT tools into their daily work. In CARTIF, we have been working in this field more than 15 years. Some of our projects, INCEPTION, COST Action i2MHB, SHBUILDINGS, RENERPATH or 3D Virtual Restoration of Historical Paintings, have developed the most innovative technologies.
A researcher installs a sensor in Palencia´s cathedral
This means that new technological solutions are really the basis to meet actual demands on the five internationally recognised levels of intervention on cultural heritage: study, protection, conservation, restoration and dissemination. Only in this way, reliable, fast, easy-to-use and affordable tools will be available to shift the very traditional procedures of those levels to the 21st century we are living in.
Consequently stable and high-quality associated skilled jobs will be created, directly related to an intrinsic and non-transferable resource such cultural heritage is by itself.
It is usual, during our work as researchers at CARTIF, we have to model and solve (with the help of advanced software) complex mechanical systems. Their behaviour is affected by the interaction effects, with different levels of coupling, among several physical phenomena of differing nature (structural deformation, heat transfer, electromagnetic fields, etc). These cases are known as multiphysics problems and are solved using computational multiphysics, a new discipline which sets out theoretical and numerical challenges. Mathematically, multiphysics problems are defined by a set of strongly coupled partial differential equations that require the development of strong algorithms to be solved in an efficient way.
In the past, because of the lack of computing power, the effects of the connection between the different physical fields could only be considered in a rough way or be completely ignored. Nowadays, the improvement of software and hardware makes possible to solve most of this problems using multipurpose calculus commercial codes, e.g., ANSYS or ABAQUS. The possibility of including connection effects leads to a better understanding of the causes and the consequences of the involved natural phenomena. From an engineering perspective, it is possible to approach problems from a more general perspective, making feasible to obtain a closer estimation of the actual performance of each of the different proposals for any prototype. Products obtained by this method are safer and more cost-effective, meeting customer’s needs in a better way.
“Elephant´s foot” buckling localized at the tank base
The most important multiphysic simulation method in structural engineering is the Fluid-Structure Interaction (FSI), this method is the one with more practical uses at industrial level and the most developed of all. It consists on analysing the interaction produced between a deformable solid and the fluid (liquid or gas) surrounding it or circulating inside of it. This interaction happens when the pressure applied by the fluid over the solid produces a deformation of the structure that modifies the boundary conditions of the fluid flux. This modification changes the pressure applied over the solid and so on, when this happens it is said that the structure and the fluid are coupled and therefore they cannot be analysed separately (with the exception of weak-coupled systems). FSI method is widely used at many industries, such as automotive (airbag deployment), aerospace (sustentation surfaces fluttering), biomechanics (aneurysms), energy (combustion at boilers), etc.
The figure shows the multiphysic simulation of the dimpling produced at the bottom of an open tank when is under seismic action, phenomena known as “elephant’s foot”.
In recent years, being the instrumental techniques cheaper and cheaper and the computational algorithms more accesible (even open source) several researchers and consultancy companies are developing new 3D abilities. Laser scanning or photogrammetry techniques are applied to mechanical or structural systems in order to collect some geometric specifications, which may be not available for different reasons.
Although direct engineering process will usually have the technical reports and drawings of the product prior to its building or manufacturing, it is usual that the old factories or buildings are not documented or, if they are, it is quite common that the drawings do not match to project. And even so, the time may have caused differences in the material behavior (chemical attacks, damage, settlements of supports or other common structural pathologies).
Footbridge stadium Balearic (Mallorca, Spain)
Often the collected data are focused on geometric dimensions and surface characteristics such as roughness and color. One of the most obvious applications is the three-dimensional reconstruction of architectonic buildings, either for rehabilitation or development of augmented drawings (BIM) or for historical or industrial heritage.
Being very useful the geometric data collected, in structural engineering it is necessary to add more information about the characteristics of different building materials, the joints between them and their possible interaction with the supports and the ground.
Fortunately, other enabling technologies to extract some additional information are also becoming more widely available. In this post we will see how using simple acceleration records and identification algorithms together with computational model updating techniques can complete the geometric information so that all technical specifications, necessary to estimate the dynamic behavior of the structure under study, can be obtained. These procedures do not require destructive testing and, even though these tests were viable, they did not provide the required information despite their higher cost.
First it should be noted that the geometric data collectedusing 3D techniques, irrespective of dimensional accuracy, refer to a particular state of load on the structure (at least due to the gravitational action) and corresponds to a particular ambient temperature. Both conditions can affect in a significant way when dealing with slender structures such as bridges and pylons. Furthermore these constructs generally experience unavoidable deformations due to environmental actions that can also affect dimensional accuracy of the 3D model.
Second it is interesting to note that in structural engineering and building is usual to use commercial components (proper cross-sections, formworks, pipes, lamps, …) of known discrete dimensions. This enables the possibility of carrying out adaptive scaling for improving the dimensional accuracy or for local refinement. So, it is not necessary comprehensive dimensional records and low cost systems (both instrumental as compact cameras and computer software) can be good enougth.
Considering the above and assuming certain skills for computational modeling, it is posible to create a preliminary model of the structure. On this model, using the finite element method, it is easy to estimate the incremental deformation due to certain loads or thermal actions and through appropriate correlations begin to estimate certain internal parameters (effective density, stiffness, damage, etc.). However, the methodology is especially important when the above information is combined with modal data.
To do this, first thing is to have the experimental eigenmodes (identified through operational modal analysis by post-processing acceleration records under environmental loading) and then select certain parameters of the computational model to be modified. Now it is the turn to adjust the value of these parameters (through optimization routines and depending on the sensitivity of each parameter and its range of reasonable values) to match with the experimental modes to the numerical ones (calculated via FEM). This process should take into account not only the most representative mode shapes but also their modal frequencies and damping.
Once proper values for these parameters are determined, the computer model can be used not only to generate the corresponding technical documentation of the as-built structure but also to estimate their vulnerability to accidental loads, or to evaluate the life-span or to estimate the performance of conservation jobs, among other applications. Those tasks are known as “structural re-engineering”, whose advantages can be matter for other post.
