FOR REPAIR AND STRENGTHENING OF STRUCTURAL ELEMENTS

Field of the Invention

The invention falls in the field of structural and mechanical departments of civil engineering and relates to a confinement element produced as a result of the carbonization of waste denims and the production method thereof for use in repairing and strengthening processes of structural elements such as columns , beams , slabs or partition walls .

Background of the Invention

Today, by imparting fiber form using various methods , carbon or glass-based fiber reinforcements are utilized to improve the capacities of damaged or insufficient structural elements such as concrete columns , beams , shear walls and slabs . In the method used, the surface is made smooth by applying epoxy primer to the reinforced concrete element surface first . In the next stage , fabrics in the form of carbon, glass or special fiber impregnated with epoxy-based resin are wrapped in a sufficient number of layers . In addition, the fibers can be wrapped with repair mortar, or the cracked or shattered parts in the concrete may need to be filled with repair mortar .

The specially processed carbon or glass fibers used are very costly materials . Since the primers and resins used in the application process are offered by the manufacturer companies specifically for fiber, these chemicals are also supplied at high prices . Out of plane behaviour that occur during or after the application, especially in the longitudinal fiber directions , reduce the capacities of the confinement elements .

In order to reduce the cost of production in the art , there are developments regarding the use of waste products in confinement elements . As an example of the current state of the art , the document titled 'Development of novel carbon fiber produced from waste fiber by carbonization' ( Kawasaki , N . , Tominaga , H . , Ogata , F . et al . Journal of Oleo Science 61 , ( 10 ) 593- 600 ( 2012 ) ) may be referred . The aforementioned document describes obtaining carbon fiber by subj ecting waste fibers to a carbonization process . In the study of the document , wool , polyester and cotton fibers are used as waste fibers and the products obtained by applying the carbonization process to the said fibers under different conditions are examined . In the production method of said carbon-derived materials /carbon fibers , the wool , polyester and cotton samples are first put in the oven under 1 L/min nitrogen gas and their temperature is increased to a temperature of 400 ° C-1000 ° C for 3 hours . At the highest determined temperature , the samples are kept in the range of 0-2 hours and then the obtained materials are allowed to cool . The mentioned study states that the form obtained by carbonization of cotton fiber has a fibrous and porous structure despite the melting of wool and polyester in the carbonization process . It is thought that the products obtained in the temperature range in the said document have a limited surface area and elemental carbon content .

Another example of the current state of the art is the patent document No . CN105793374A. The said document relates to an adhesive layer that exhibits high support/repair performance when applied to building materials . The adhesive layer of the present document comprises a substrate impregnated with acidic resin, comprising reinforcing fibers , and an adhesive layer positioned on the substrate . For example , the document describes that the sample is wrapped with fiber reinforced plastics ( FRP ) for reinforcing concrete columns , and for this process , epoxy resin is applied to columns primarily to remove the roughness on the surface . An embodiment of the invention of the said document describes that denim fabric can be used as reinforcing fiber and that the reinforcing fiber can be guided and woven in certain orientations . It is thought that the original tissue form of the waste denim cannot be preserved due to the fact that the carbonization process is not applied in the production method of the document . Therefore , the weaving process is necessary .

Another example of the current state of the art may be referred to as 'Mesoporous activated carbon fibers synthesized from denim fabric waste : efficient adsorbents for removal of textile dye from aqueous solutions ' ( Silva , T . , Cazetta , A. , Souza , P . et al . Journal of Cleaner Production 10826 ( 2017 ) ) . The document relates to the production of mesoporous-activated carbon fiber from waste denim fabrics . The method of the document comprises the following process steps : collecting waste denim fabrics to obtain carbon fibers , drying, cutting into certain size pieces , placing waste denim fabric in the stainless steel reactor, adding H3PO4 to the reactor to provide activation and obtaining acid-impregnated material , the material is then pyrolyzed under nitrogen gas at temperatures of 300 ° C- 500 ° C- 1000 ° C, respectively, to be exposed to each temperature for 1 hour and the oven is allowed to cool . The use of carbon fibers obtained in the document as an adsorbent in removing textile dyes from aqueous solutions is emphasized, and it is not mentioned that it is suitable for use as a confinement material for reinforcing building materials . In addition, the product is subj ected to a chemical processing during the carbonization process of the product of the document .

Therefore , to address the disadvantages of the existing documents in the art , a low-cost , easy-to-applicable confinement element production method that does not require chemical processing in the carbonization process has been developed for use in reinforcement and repair processes of structural elements .

Detailed Description of the Invention

The invention falls in the field of structural and mechanical departments of civil engineering and relates to a confinement element production method comprising the carbonization of waste denim for use in the repairing and strengthening processes of structural elements such as columns , beams , slabs or shear walls . The confinement element obtained by the method in question is also within the scope of the invention .

The invention aims to provide a safe design against dynamic effects by increasing the resistance against axial load, shear and flexural capacities as a result of the confinement effect .

The confinement element of the invention falls into structural engineering, a sub-sector of civil engineering and is used in the processes of repairing and strengthening the structural elements damaged after an earthquake or those deemed to be incompetent to withstand an earthquake .

In addition to its use in reinforcing structural elements such as concrete columns , beams , shear walls and slabs , the confinement element of the invention is also used in partition walls built with materials such as brick and aerated concrete . The confinement element of the invention also provides an advantage against fire and corrosion by wrapping the steel elements from the outside .

Because the carbon fabric confinement element of the invention is produced from waste denim fabrics , it contributes to waste recycling and produces a very low-cost reinforcing fabric compared to its counterparts .

The waste denim fabric used in the content of the invention is 5 -10 times cost-effective than carbon fiber ( carbon fiber reinforced polymer, CFRP ) and glass fiber ( glass fiber reinforced polymer, GFRP ) fabrics . Although CFRP and GFRP applications reach better capacities , the same performance levels may be attained by wrapping the invention ' s confinement element produced from waste fabrics on the structural element surface in large numbers . Even in this case , the cost remains within the appropriate limits .

Since the confinement element of the invention is produced from waste denim fabrics , the carbonization process preserves the original texture form of the denim . Therefore , as with other confinement fabrics known in the art , there is no need for a weaving process . The 45 ° weaving form in the elevations allows the fibers to work more effectively against both shear forces and bending moments .

The confinement element of the invention has potential use as an alternative adsorbent in filtering processes thanks to its fibrous and porous structure . The invention aims to provide efficient solutions in low and medium-damaged structures due to cost , labor and ease of application .

The invention is a method of manufacturing a confinement element for repairing and strengthening structural elements , comprising the following steps : a . washing and sizing of waste cotton denim fabric , b . applying a carbonization process to the said waste cotton denim fabric by heating in a reactor in the nitrogen gas environment in the temperature range of 500-800 ° C, c . comprising obtaining all fiber-structured carbon fabric that has been preserved after the room conditions are met as a result of the carbonization process .

In one embodiment of the invention, the reactor is a stainless-steel fixed bed reactor .

In one embodiment of the invention, the heating rate is applied in the range of 2 -10 ° C/min . Preferably the heating rate is 10 " C/min .

In an embodiment of the invention, the carbonization process is applied in the temperature range of 500-800 ° C at the final temperature for 60- 90 minutes . Preferably, 600 ° C is applied at the final temperature for 60 minutes .

In one embodiment of the invention, waste cotton denim fabric is fixed on a sieve during or after the carbonization process . Preferably the sieve is steel . This provides an increase in the ease of use . It can be packaged in the form of a roll after production . After the confinement element of the invention is brought to the area where the application is desired, the roll is opened and cut into the appropriate dimensions and applied to the surface of the structural element with the help of resin without deteriorating the form.

The temperature range applied in the method of the invention ensures that the obtained carbon f abric/conf inement element has a high surface area and elemental carbon content . In one embodiment of the invention, the carbonization process is applied at a heating speed in the range of 2 -10 ° C/min, at a temperature in the range of 500-800 ° C, at the final temperature for a period of 60- 90 minutes . In this way, the carbon f abric/conf inement element obtained shows high performance for the repair and reinforcement of building elements .

The confinement element obtained from the waste denims of the invention includes application steps similar to the repair and reinforcing steps using fibrous polymer in the process of reinforcing structural elements with insufficient capacity in post-earthquake damaged structures or in disaster ris k areas according to the regulations . The parts to be wrapped with the confinement element (wrapping fabric ) of the invention are ground and the sharp corners are rounded with a certain radius . This ensures that sharp edges do not harm the wrapping fabric when subj ected to dynamic stresses . The lining material is applied with a roller brush on the surfaces to be covered with the wrapping fabric . Epoxy-based repair mortar can be used to increase the adherence between the concrete surface and the wrapping fabric . Before the repair mortar is cured, the wrapping fabric strips cut in the specified sizes and numbers are applied together with the epoxy material that allows the strips to harden and gain their strength . The wrapping direction is irrelevant since the wrapping fabric has fibers in both directions . The number of layers of wrapping fabric can be increased to reach the desired target strength for repair and reinforcement . Sufficient overlapping can be done to increase the operational efficiency .

In a detailed embodiment of the invention, the confinement element production method includes the following process steps . No chemical treatment is applied for the carbonization process of previously washed and properly sized waste cotton denim fabrics . In the stainless-steel fixed bed reactor , carbonization process is applied to the denim fabric in a 100 cm ³ /minute nitrogen gas environment , at 10 ’ C/minute heating rate and 600 ° C final temperature for 60 minutes . As a result of the carbonization process , the reactor is allowed to cool and the whole fiber-structured carbon fabric that has been preserved when the room conditions are met for the reactor is obtained . During or after the carbonization process , the ease of use can be increased by fixing the waste denim fabrics on the steel sieve . In this way, it can be packaged in roll form after production . Having been brought to the desired area , the roll is opened, and the fabric is cut into appropriate sizes , then they can be applied to the reinforced concrete or steel element surface with the help of resin without deteriorating its form.

As a result of the experimental studies , an increase of approximately 36 . 00% was noted when the low strength cylindrical concrete samples with an average 28-day axial compressive strength of 11 . 83 MPa were wrapped in a single layer with the confinement element of the invention . The unit strain values observed at the final compressive strength levels are in the order of 0 . 70% in both cases . Therefore , the confinement element of the invention increases its compressive strength by 36 . 00% even if it is wrapped in a single layer on the concrete surface while keeping the ductility levels constant .

Considering that the existing reinforcement elements used in the market applications significantly change the stiffness or ductility levels in the structural elements , thereby offering an alternative solution in this respect . Considering the production, application and test results ; the best way to obtain the confinement element of the invention is the recommended production method in terms of cost , time , labor and efficiency .