It was also observed that as the concrete strength increases, the gain in flexural capacity of RC slabs from CFRP reinforcement decreases. Based on the results of this pilot study, the authors will expand the test matrix in a future study to examine the effect of several parameters including concrete compressive strength, reinforcement ratio, and number of CFRP layers on the performance of thin RC slabs.
Introduction In the modern days, the construction materials field had grown in complexity and applications, so there are materials invented for almost all modern uses.
One of the most critical technologies developed in the construction materials field is fiber-reinforced polymer FRP composite materials that are used to repair, strengthen and rehabilitate structures. There are many materials that could be used for these purposes and they vary with the type and extend of damage to the structural member.
Each type of damage should be analyzed and studied to assess the repairing material and strengthening method. One of the most common and widely used methods nowadays in strengthening reinforced concrete RC structural members such as slabs, beams, columns, and walls in shear and flexure, is by externally bonding FRP composite sheets and plates to concrete surfaces Niu et al.
The old method of strengthening RC slabs and beams in flexure was by attaching steel plates to concrete surfaces Borgerson, et al. Since the invention of the FRP strengthening systems, it had proven to have enormous potential and advantages over the steel alternative Borgerson, et al. These advantages can be summarized in the ease of FRP installation and insulation, high resistance to corrosion, strong structural bonding, high strength-to-weight ratio, and less labour intensive.
As the range of applicability of this system started to widen, engineers and researchers have conducted various research studies on developing the optimum techniques of using this technology Rezazadeh et al. It was found from these studies that bonding FRP sheets and plates to surfaces of RC members will increase their flexural and shear strengths significantly.
There are many types of FRP composite materials in the construction materials market. On the structural engineering side, flexural members slabs and beams can use the extra capacity provided by the external FRP reinforcement to reduce their cross-section depth.
One important structural element that this research deals with is slabs. Slabs are flexural members that are used for flooring and roofing purposes. They act like beams in transferring and reacting to loads and are the largest elements in any structure. Accordingly, slabs add significant dead load to buildings compared to other structural members. Thus, reducing the slab thickness can drastically reduce the dead weight of buildings. In addition, when slabs are designed with high strength concrete, the Whitney block depth a will decrease, leading to an increase in the couple lever moment arm.
Thus, the flexural capacity of RC slabs increases with the increase in the concrete compressive strength. The aim of this paper is to study the flexural performance of thin RC slabs cast with high strength concrete when externally strengthened with CFRP laminates at their soffit. This study can be applied to newly built slabs to reduce their thickness, or to the existing slabs to enhance their load carrying capacity if the intended use of the structure is changed.
The general trend of strengthening such elements is attaching the FRP system to the soffit of the slab with epoxy resin adhesives. In this case, the FRP system will act as secondary flexural reinforcement to help the main longitudinal steel reinforcement in increasing the flexural capacity.
The parameters varied and studied in this experimental investigation are the concrete compressive strength and the number of CFRP layers. Experimental Program 2. Specimen Detail The experimental program consisted of two groups of specimens cast with highconcrete compressive strengths of 50 C50 and MPa C , respectively. The CFRP sheets were attached to the soffit of the slab specimens with epoxy adhesives. The length, span length, width, and height of the cast specimens are , , ,and 75 mm, respectively.
The slabs were reinforced with two 12 mm diameter steel bars located at a depth of 50 mm from the top compression fibre. Figure 1 shows details of the control and strengthened slab specimens. The thickness of each CFRP ply of the cured laminate is 0. Material Properties Coupon tests were carried out to examine the mechanical properties of the steel reinforcement. The averages of the experimentally measured modulus of elasticity, yield strength, and tensile strength were found to be GPa, MPa and MPa, respectively.
In addition, standard concrete cylinders were tested after 28 days to obtain the concrete compressive strength concrete. The averages of the measured concrete strength for the two groups of specimens were found to be 52 and MPa, respectively.
Testing and Loading A four-point bending test arrangement was used to test all specimens as shown in Fig. This testing arrangement was chosen to simulate the common loading case on slabs, which is uniformly distributed loading. Results and Discussion 3. Load versus midspan deflection response curves Figures 3 and 4 show the load versus midspan deflection response curves of the C50 and C specimens, respectively.
It is clearly indicated from Figs. However, the ductility of the beam specimens decreases with the increase in the number of CFRP layers. The ultimate load-carrying capacity Pu of the tested specimens are shown in Table1.
Table 1 also shows the percent increase in the load-carrying capacity of the strengthened specimens over that of the control slab specimens. Lost your password? Please enter your email address. You will receive a link and will create a new password via email. Sorry, you do not have permission to ask a question, You must log in to ask a question. Join now! Do you need to remove the ads?
The concrete is a versatile construction material used all over the world for all types of construction applications. Concrete in its green form can be molded into any shape, size, and finish with the help of different finishing techniques and equipment to give a beautiful and long-lasting surface with a high aesthetic value. The most basic type of concrete finish is a smooth surface created through the use of screeds and trowels.
Trowel finish is the most common and popular finish of concrete used for major types of applications. After the concrete is laid in the formwork and leveled, the trowel is used to smooth and fine-level the surface of concrete.
Trowels are available in both manual and mechanical types. A manual trowel consists of a flat steel blade with an attached handle that is pushed and pulled across the concrete surface. A mechanized trowel is used for large commercial projects which resemble large fans with the blades sitting directly against the concrete. The broom finish of the concrete is rough textured finished obtained by dragging a broom on the trowelled surface of the concrete while the concrete is still fresh.
Dragging of broom on the fresh concrete surfaces creates small ridges that provide for traction control and slip-resistant. The stamped concrete finish is obtained by pressing the required patterns on the freshly levelled concrete. This type of concrete finish after completion of their construction looks similar to stones such as slates or flagstones, brick, tile or with proper skill they can look similar to wood.
Stamped concrete finish is a very intelligent and innovative innovation in concrete widely applied for floor in patios, car porch, driveways and sidewalks. Features, Methods, and Procedures of Stamping Concrete. The salt finish concrete surface is obtained by inserting coarse rock salt crystals using rollers on the freshly placed concrete surface and washing it off with streams of water after the concrete is set. This finish gives a decorative, rough subtle texture and skid resistance to plain or colored concrete.
It is mainly used for swimming pools or other wet areas. The construction of exposed concrete finish is to have leveled concrete floor surface, distribute aggregate evenly, and keep air voids to as minimum as possible. Power Floater or Diamond Polisher is used to polish the top surface of the partially cured concrete. The equipment removes a concrete layer whose thickness does not exceed a few millimeters at the top of the concrete. A fine grade protection layer is applied to provide the favored polished finish.
Swirl finish is one of the most exceptional types of concrete finish that is generated by smearing the concrete surface in a uniformly overlapping circular pattern.
It provides an aesthetically pleasing appearance to the concrete surface which is favored for outdoor applications because not only does it add beauty to the surface, but it also provides a safer walk and stand in comparison with smooth surface finish, specifically during the wet season. The polished finish on a concrete surface is achieved by a mechanical process of grinding and polishing with the help of a penetrant chemical to provide different texture with the help of specialized tools and equipment.
The colored finish of the concrete is accomplished through mix-added pigments or post-cure staining to provide a pleasing look to match the surrounding environment. The colored finish on a concrete surface can be carried out by either pigment or strains. The pigmented colored concrete can be accomplished by adding the pigments directly to the concrete mix prior to pouring. The strained colored concrete can be obtained by applying stains to concrete of any age to obtain a more vibrant colored finish.
The application of stain is typically followed up with the installation of a seal over the concrete to protect the surface. The concrete is a versatile material in its fresh state and can be finished in many types as per the desired appearance such as Trowel finish, Broom finish, Salt finish, Exposed aggregate finish, Polished finish, and Colored finish. Generally, the preferred finish for the roof slab concrete is Trowel finished.
However, the fineness of the concrete surface is kept rough to have a better bond with the upcoming layers, such as flooring or waterproofing.
Roof Slab - Trowel Finish 2. Swimming pools - Salt Finish 3. Commercial and Industrial flooring - Trowel Finish 4.
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