Essay: Identify information of an existing concrete structure

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ABSTRACT

Which methods can be used to determine the capacity of an existing concrete structure?

1 INTRODUCTION

Planet earth struggles with different kind of environmental issues. Global warming is one of the most important environmental issues. The increasing concentration of greenhouse gas emissions resulted in the goal of the EU countries for 2020 to cut the emissions to 20% below 1990 levels. The Netherlands proposed that the goal for 2030 should be a reduction of 40% below 1990 levels (Hof Andries, 2012).

Besides global warming another important issue is the scarcity of raw materials. The earth population is growing fast and in 2050 it is estimated to be 40% more than the population of 1950. This increase will lead to a larger consumption of raw materials (Wouters Huib, 2009). Measures must be taken in order to minimize the damage caused by the extraction of raw materials from various places on the earth. The reduction of the use of raw materials will also results to the reduction of CO2 emissions (Coolrec, 2015)

It is estimated that the building industry is responsible for 38% of the global greenhouse gas emissions while it uses 40% of the global energy. The wastes form the construction, renovation and demolition of buildings are estimated to be 40% of the solid waste streams in developed countries. At the same time the building sector is responsible for the consumption of approximately 3 billion tons of raw materials annually (Comstock, Garrigan, & Pouffary, 2012).

One major problem that the Dutch building industry faces nowadays is the increase of empty office buildings. Due to the economic crisis and the short functional life time of buildings there is a high vacancy rate (14,7% at the mid of 2013, according to DTZ Zadelhof).

Figure 1 Lifecycle of building elements
During the manufacturing and transportation to the site, a high level of CO2 is produced. By re-cycling building elements the transportation is still a CO2 producing matter. Reusing buildings do not increase the CO2 concentration, see Figure 2. Reuse of these buildings can be a good solution for the global warming, scarcity of raw materials and the empty building issues. In order to reuse buildings, knowledge of the structure is needed to provide and assure the safety of the buildings and its structural possibilities.

The following research question is composed:

“How is it possible to identify information of an existing concrete structure in order to analyze the structural possibilities?”

There are different methods to gather information of an existing concrete. To answer the research question, the different techniques and methods are explained and divided in three main parts, namely;
– The historic analysis
– The visual analysis
– The technical analysis

2 THE HISTORIC ANALYSIS
By starting analyzing an existing building it is needed to gather sufficient amount of information to prevent unexpected situations in the construction during execution phase. The first step is the historic research by collecting the original documentation (architectural drawings, structural drawings, reinforcement drawings etc.) to visualize the load bearing system. This kind of information is mostly found at the government database where these documents are submitted in order to give the planning permission. The engineer should be aware that this information always brings a certain level of inaccuracy and uncertainty. This also informs the structural engineer about the material and structural characteristics of historic concrete. (Florisson, 2013)

3 THE VISUAL ANALYSIS

Figure 2 Building stripped (Source: www.ggardner.myzen.co.uk/wordpressblog/?p=2250)

Inspecting a concrete building starts with visual analysis. Therefore the building has to be stripped, as showed in Figure 2. This is the starting point for further research. Visual analysis is the often used non- destructive testing method (NDT). NDT are techniques for inspecting structures without demolishing or damaging construction parts of the building. Visual analysis gives information about the geometry and deterioration of the structure see Figure 3. (Gijsbers, 7-2012)

4 THE TECHNICAL ANALYSIS
Mostly, historic and visual analysis are not enough to ensure the structure capacity and its quality. The information produced by visual analysis and the information of the original documentation do not match or are incomplete. Therefore local technical analysis is needed. This part can be done by destructive or non- destructive testing methods.

4.1 NON- DESTRUCTIVE TESTING METHOD
There are several NDT methods for analyzing existing concrete structures. Depending on which information is needed a testing method is selected to use.
In Figure 4 an overview of the most common NDT methods and the field of use for concrete structures. The reliability and precision of these different NDT methods differ in uncertainty. The covermeter and Ground Penetrating Radar have a high precision by detecting the amount of rebar’s in existing concrete structures up to a depth of 100mm. Information about rebar’s located deeper than 100mm are still uncertain. Partly destructive testing is needed to confirm and assure the needed information. (Selek, 2015).

Figure 4 Overview of the most common NDT methods (Selek, 2015)

4.2 DESTRUCTIVE TESTING METHODE
Determining the compression strength of an existing building is mostly done by core drilling see Figure 3 . By producing small test specimen a lot of information can be gathered. The carbonation, elasticity modulus, the bending strength, and the tensile strength can be found. This test method is accurate but in order to identify the other properties, several test specimen are needed.

Figure 5 Core drilling concrete

Identifying information of an existing concrete structure can be obtain differently.

Reuse of these buildings can be a good solution for the global warming, scarcity of raw materials and the empty building issues. In order to reuse buildings, knowledge of the structure is needed to provide and assure the safety of the buildings and its structural possibilities.

The following research question is composed:

5 CONCLUSION

The conclusion is presented as answer to the research question;

“How is it possible to identify information of an existing concrete structure in order to analyze the structural possibilities?”

It can be concluded that reuse of buildings gives a good solution for the global warming, scarity of raw materials and the empty building issues.

Gathering information to identify information of an existing concrete structure can be done by 3 phases.
Historic analysis

Historic analysis
Visual analysis
Technical analysis

conclusie
This concept is introduced to bridge the knowledge gap between past and present and eliminate possible risks occurring from this gap by visualizing the differences in material durability, and provide structural information to clarify the original documentation or when no original information is available to substantiate the making of assessment assumptions. The quality assessment of materials and structures is time consuming, expensive and difficult when performed into detail. The structural engineer is therefore challenged to formulate a targeted and efficient approach without compromising the desired information. To stimulate this process the protocol introduces at the end of the historic assessment a general strategy which helps to formulate the desired and required input and output regarding the visual and technical assessment. The visual assessment stimulates the engineer to visualize the structural and material quality in-situ, by proposing a visual inspection towards deterioration and the optical verification of the original drawings. The assessment V step also provides a description of the non-destructive measuring techniques which can either be used to verify certain forms of deterioration or to verify the test results found with the technical assessment. At the end of the visual assessment the engineer is granted the possibility to take concrete and steel samples for additional research to be performed in the laboratory to indicate, the mechanical properties, the cause of deterioration or to estimate future deterioration. The protocol provides an estimate of the required research pool, and the considerations which have to be taken into account when estimating the sample location. The technical assessment step provides the structural engineer with a general introduction on the different laboratory tests, and their specifications. The quality assessment is completed by introducing the evaluation step, which provides the structural engineer with the general methodology for reinforced concrete repair and protection. This methodology points out the importance for conservation, and a durable and compatible approach. The assessment step also provides a list with the general methods that can be used for repair and protection.

Innovaties

Enige vernieuwingen in deze methodiek is het vroegtijdig kunnen signaleren van corrosie verschijnselen van het wapeningsstaal. Door middel van een echo scan wordt gekeken naar de molecuul samenstelling van het staal en aan de hand hiervan kan gekeken worden waar en wanneer er corrosie zal optreden. Dergelijke onderzoeken worden nullastpotentiale onderzoeken (OCP) genoemd.

Conclusie inventarisatie onderzoeksmethodieken

De onderzoeken die zojuist besproken zijn, zijn de klassiekers onder niet destructief en destructief onderzoek. Bij het beoordelen van bestaande constructies kunnen de wapeningconfiguratie, de afmetingen en het eigen gewicht van het constructie element bepaald worden. De diameter van het betonstaal kan op niet-destructieve wijze slechts indicatief worden vastgesteld. De vloeigrens van het betonstaal, de kans op putcorrosie en de aanwezigheid van putcorrosie kunnen alleen op destructieve wijze worden gemeten.

Onduidelijkheid resultaat

Dergelijke onderzoeken worden door de praktijk gezien als onderzoeken waar gegarandeerd resultaat uit voort komt. Men verwacht dat door het gebruiken van dit soort technieken hij/zij een volledig inzicht krijgt van de wapening en betonkwaliteit. Dit is echter niet zo. Niet destructief onderzoek geeft puur een beeld van de positionering, en dus de hart op hart afstand van de wapeningsstaven. De dekking kan middels dit onderzoek ook prima bepaald worden. NDO verleend informatie over de staafdiameter bij eenvoudige constructies. bij ingewikkelde wapeningsknopen is NDO niet geschikt. Dit komt omdat de stralingen worden weerkaatst door de eerste en tweede laag wapening en dus de achterliggende staven moeilijk te definiëren zijn. Destructief onderzoek biedt hier wel mogelijkheden voor. Hiervoor moet voorafgaand in nauw overleg besproken worden waar destructief onderzoek kan plaats nemen zonder schade aan de constructie te brengen. Dit laatste is van essentieel belang bij het onderzoek doen naar bestaande contructies. De laatste stap wordt door de praktijk vaak overwogen omdat men de veiligheid in risico brengt.

Gebrek aan deskundigheid

Deskundigheid op het gebied van de meettechniek en kennis van constructies en materialen zijn onmisbaar voor goede interpretaties van de meetgegevens. Meetapparaten hebben de laatste jaren een vergaand ontwikkeling bereikt. Dergelijke ontwikkelingen vraagt om ervaren, gespecialiseerde deskundige. Deze deskundige zijn schaars waardoor meetgegevens slecht geïnterpreteerd worden. dit is de voornaamste reden dat dergelijke technieken duur zijn.

Cement and Concrete Research, Detection of the corrosion damage of rebar in concrete using impact-echo method, Ming-TeLiang,Po-Jen Su, Elsevier October 2001

The impact-echo method by N.J. Carino, Building and Fire Research Laboratory, National Institue of Standards and Technology, Gaithersburg USA

Meten is weten, of toch niet?, Theodoor Gijsbers, SGS INTRON, Cement nr. 7-2012

Renoveren is analyseren, ir. Theo van Wageningen, Ingenieursbureau Dijkhuis bv, Cement nr. 7-2012

Betonpetrografie- microscopisch onderzoek van beton, dr.E.Soers, en licM.Meyskens, GEOS Onderzoeks- en Controlelaboratorium, Wellen (Beligë)

Betononderzoek & de praktijk (IV), ir.G.M.Wolsink, Bouwdienst Rijkswaterstaat

CUR Bouw en Infra, platform constructieve veiligheid, Onderzoek naar en beoordeling van de constructieve veiligheid van uitkragende betonnen vloeren van galerijflats, publicatie 248-2012

6 REFERENCES

Comstock, M., Garrigan, C., & Pouffary, S. (2012). Building Design and Construction – Forging Resources Efficiency and Sustainable Development. UNEP – Sustainable Buildings and Climate Initiative.
Coolrec. (2015, November 21). Scarity of raw materials. Opgehaald van http://www.coolrec.eu/duurzaamheid/grondstoffenschaarste.aspx
Florisson, S. (2013). Master Thesis; Assessing existing structures 1910- 1950. Delft: Delft University of Technology.
Gijsbers, T. (7-2012). Meten is weten, of toch niet? Cement, pp. 54-58.
Glias, A. (2013). MAster Thesis; The Donor Skelet – Designing with reused structural concrete elements. Delft: Delft University of Technology.
Hof Andries, B. C. (2012). Greenhouse Gas Emission Reduction Targets for 2030 – Conditions for a EU target of 40%. The Hague: PBL Netherlands Environmental Assessment Agency.
Selek, I. (2015). Master Thesis; Relability of non-destructive testing methods for detecting steel rebar in existing concrete structures. Eindhoven: Einhoven University of Technology.
Wouters Huib, B. D. (2009). Material Scarcity. Delft: Materials Innovation Institute.

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