BEHAVIOR OF SCC BEAMS STRENGTHENED WITH CFRP UNDER SHEAR

ABSTRACT This paper presents an experimental study of structural behavior of self compacting reinforced concrete beams strengthened in shear by vertical CFRP strips. The experimental work consists of casting and testing of eleven simply supported reinforced concrete beams. One of the tested beam was un-strengthened to be considered as beams, while the remaining beams were tested after being strengthened using vertical CFRP strips. In this study, three parameters were considered, the configuration of CFRP sheets wrapping system, i.e. two sides, U-shape and full wrapped, effect of horizontal strap of CFRP strips to enhance the vertical CFRP strips and CFRP amount. The results showed that the presence of horizontal strap of CFRP strips on the vertical strips increases the shear capacity of the beams ranged between (3-27)% for beams with the same properties, while the increase in the ultimate loads ranged between (20-26)% and (39.5-46)% by comparison of wrapping system (two side with U-shape) and (two side with full wrapped) of CFRP strips, respectively.


Self-Compacting Concrete (SCC) is an important development in concrete technology. It is a
new type of high performance concrete with the ability to flow under its weight and without the need for vibrations. Recently, a large local interest towards self-compact concrete has been derived (Al- Mishhadani and Al-Rubaie, 2009). SCC is a relatively new type of concrete that is highly flowable and non-segregating. It does not require vibration when it is cast; it is capable of flowing through narrow opening or extremely congested reinforcement, and it provides a void-free surface. It is known as self-consolidating concrete, self-leveling concrete, and high fluidity concrete (Horta, 2005). SCC flows like ''honey'' and has nearly a horizontal concrete level after placing. When SCC is placed in a form, its motion may be a creeping movement or a rapid flow. Because of this style of flow, the surface finish between the form and the concrete can be exceptionally smooth, creating a much-improved from finish over conventional concrete (Dehn et al., 2000).
The three main types of FRP used in the construction industry are: aramid (AFRP), carbon (CFRP), and glass (GFRP) (Dolan et al., 2001). The advantages of CFRP application includes a high strength to weight ratio, flexibility and available in long lengths, rapid execution on site, high elastic modulus, high dynamic strength, and no need for special equipment (Dolan et al., 2001;Athawale, 2012). As stated in the ACI Committee 440.2R-08 (ACI Committee, 2008), there are three types of wrapping patterns are used to increase the shear strength of beams or columns as shown in Fig.1. Completely wrapping system of FRP around the structural member on all sides is the most efficient and most common wrapping scheme for columns. However, the overall wrapping is not practical from the construction point of view in the case of beam applications where the integrated slab makes it impractical to completely wrap the member; the shear strength can be improved by wrapping the FRP system around three sides of the member (U-wrap) or bonding to two opposite sides of the member (ACI Committee, 2008;Khalifa, 1999).
In all wrapping schemes, the FRP installation can be used continuously along the length of the member or spaced strips Fig.2. The second alternative could be effective in improving the quantity of materials used. In particular, the shear resistance of reinforced concrete beams can be enhanced by bonding FRP shear reinforcement in the form of complete wraps, U-jackets and two side strips (Chen et al., 2013). Engineering, Vol. 10, No. 1, January 2019113 Meshfeq, 2012 Test program consists of ten RC continuous (two-span) beams; the investigation includes parametric studies for CFRP sheet strengthening, such as their location (two, three and four sides), orientation, and keeping the amount of CFRP sheet for all strengthened beams constant.

EXPERIMENTAL PROGRAM
The experimental program consists of testing eleven simply supported beams molded by using SCC with two point loads. All beams have the same dimensions, flexural reinforcement, and shear reinforcements. These beams were designed to avoid the flexural failure, so that the failure is governed by shear. The variables investigated in this work included CFRP strips amount and distribution.
The specimens were divided into three groups (A, B and C). All Groups with (a/d) equals to 2.37. Ten SCC beams strengthened by CFRP, and the eleven beam were not strengthened by CFRP strips and selected as reference beam. All eleven beams were casted using SCC with compressive strength (f ʹc) equals to 36.5 MPa.

Details of Test Beams
The overall length of beams is 1500 mm with a clear span of 1400 mm, whilst the width and height are 150 mm and 250 mm, respectively, as shown in Fig. 3. All beams were longitudinally reinforced with two bars of 16 mm diameter and one bar of 12 mm diameter placed at the tension side with a clear cover of 25 mm. At the top face, two bars of 6 mm diameter were provided. For vertical shear reinforcement, deformed bars of 6 mm diameter were provided at a spacing of 250 mm center to center.

Specimen Identification and Strengthening schemes
Strengthened beams schemes by one layer of CFRP strips with constant width (40 mm). The thickness of this strip was (0.166 mm) as provided by the manufacturers, it was chosen carefully based on the field conditions and the practical needs, mainly, economic and crack pattern. In this study, where the letter B indicates beam specimen, C indicates control specimen, the letter V indicates vertical strengthening, letter H indicates horizontal strengthening, the letter U Indicates U-shape strengthened, and the letter F indicates full warp strengthened. While the numbers (1, 2, 4, and 5) represent the number of strips. The first beam control (BC) has not strengthened by CFRP. The following strengthening layouts by CFRP were applied: 1. Group (A): contains four beams as following: i. Beam (BV4 and BV5) were provided with four and five vertical strips at each side, respectively; it was installed at angle of 90˚ along shear span, as shown in Figs. 4 and 5. ii. Beam (BV4H2 and BV5H2) were provided with four and five vertical strips at each side, in addition to two horizontal strip placed at the end of the upper and lower along shear span, as shown in Figs. 6 and 7.
2. Group (B): contains four beams as following: i. Beam (BV4U and BV5U) were provided with four and five vertical U-shape strips at each side; it was installed at angle of 90˚ along shear span, as shown in Figs. 4 and 5. Kufa Journal of Engineering, Vol. 10, No. 1, January 2019 115 ii. Beam (BV4UH1 and BV5UH1) were provided with four and five vertical U-shape strips at each side, in addition to one horizontal strip placed at the end of the upper along shear span, as shown in Figs. 8 and 9. 3. Group (C): contains two beams, (BV4F and BV5F), is provided with four vertical and five full wrapping strips each side; it was installed at angle 90˚ along shear span, as shown in Figs. 4 and 5.

Materials
The properties of cement, aggregate, admixture, carbon fiber reinforced polymer CFRP, and epoxy used in this investigation are presented in this section.

Sarmad S. Abdulqader et al.
Ordinary Portland Cement OPC (Crista) was used in this study. It complies with the Iraqi specification (IQS) No. 5/1984(Iraqi Specification, No.5, 1984. The laboratory test results of this type of cement illustrate its physical properties as: The compressive strength at 3 days and 7 days were equal to 19 and 28 MPa, respectively.

Fine Aggregate (Sand)
Natural sand from (Al-Akaidur) region was used for concrete mixes in this study. The fine aggregate was passing from the sieve (4.75 mm) maximum size and remaining on sieve (0.15 mm). The obtained results indicated that the fine aggregate grading was within the requirements of the Iraqi specification No. 45/1984(Iraqi Specification, No.45, 1984. The main properties of the fine sand used are: The sulfate content equals to 0.08%, Absorption equals to 0.75%, and Specific gravity equals to 2.6.

Coarse Aggregate
The rounded coarse aggregate from Al-Niba'ee quarry is used with a maximum aggregate size of (14 mm). The results obtained indicate that the classification of coarse aggregates was within the requirements of the Iraqi Standards No. 45/1984(Iraqi Specification, No.45, 1984. The main properties of the fine sand used are: The sulfate content equals to 0.03%, Absorption equals to 0.5%, and the Specific gravity equals to 2.65.

Limestone Powder (LSP (
This substance is locally called as "Al-Ghubra", which was brought from the Darbindkhan plant area and has been used as a filler for concrete production for many years. It has been used to increase the concrete workability and early strength. The particle size of LSP less than 0.125 mm (sieve No.200) was used in the current research work.

Steel Reinforcing Bars
Deformed steel bars ( Table 1.

Carbon Fiber Reinforced Polymers (CFRP)
When CFRP is loaded in tension, it doesn't show any plastic behavior (yield) before rupture.
Sika Wrap®300 C/60 was used to enhance external testing SCC beams. The mechanical properties of CFRP sheet are tabulated in Table 2.

Bonding Materials
The most suitable adhesives with CFRP sheets are Sikadur®330. The adhesive type consists of two compounds, compound A (white) and compound B (gray). The mix ratio is 4: 1 as A: B.
Its main characteristics as provided by the manufacturer are shown in Table 3.

SCC Mix Design
To meet the self-compacting requirements and the designed compressive strength, many trial mixes were conducted. The SCC mix is designed according to EFNARC (EFNARC, 2005). In the present work, the cement content was 350 kg/m3, fine aggregate content was 797 kg/m3, coarse aggregate content was 767 kg/m3, limestone powder content was 170 kg/m3, water content was 150 l/m3, the superplasticizer content was 4.2 l/m3 (1.2 liter per 100 kg of cement), and the w/c ratio was 0.43.

Mixing and curing of Concrete Batches
Mixing procedure is important to obtain the required workability and homogeneity of SCC.
The method used to mix the materials was summarized as follows:  The fine aggregate was added to the mixer with a quantity of one third from the (water and dosage of superplasticizer well as mixed together) and mixed for one minute.
 The powder (Cement and LSP) were added with one third amount from (water and dosage of super plasticizer which were mixed together). The mixture is then mixed for one minute.
 The coarse aggregate was added with the last one third amount of (water and dosage of super plasticizer which were mixed together), and mixing extends for one and half minute.
After the mixing process is completed, the main specimens are casted into molds without the need for vibration where the concrete molds are easily filled and interspersed between reinforcement bars without any segregation. The hardened specimens were demolded after 48 hours; burlap sacks were monitored and kept wet until twenty-eight full days passed.

Strengthening with CFRP
The strengthening system used in this work comprised of fiber strips, epoxy. All the strengthening processes were done after 28 days of moist curing for the beam specimens. Only the first specimen (BC) was kept without strengthening as control specimen, whereas the other ten beam specimens were strengthened with externally applied CFRP strips. The following different schemes illustrate the technique of this strengthening as shown in Figs. [4][5][6][7][8][9]Vol. 10,No.

RESULTS AND DISCUSSION
The eleven beams were tested in this study, including one reference beam. While ten SCC beams strengthened by CFRP were divided into three groups. The cracking load, ultimate load, and mid span deflections at first cracking and ultimate stages are listed in Table 4. All beams were tested for shear failure. Table 4. Experimental results of the tested beams.
*Refer to load at initiation of first flexural crack.
** Refer to load at initiation of first shear crack.

General Behavior and Crack Patterns
In general, all the tested beams exhibited almost the same behavior from the initial loading up to the load causing failure. Cracking of each specimen was generally progressed as follows: With the increase of loading a small flexure crack appeared at or near the mid-span of the beam, then it extended upward. With further loading, an inclined crack appears at shear zone approximately at the mid-length of load path.
It can be observed that the beams without strengthening showed almost the same crack pattern and failure mechanism as strengthened beams, but differ in the ultimate loads. It was observed that the increase in cracking and final load was affected by the amount and shape of the strips. It was found that when using strengthened full wrapped of CFRP strips, the failure pattern was transformed from shear failure to flexural failure; this failure occurred ingroup C. ......

First Cracking and Ultimate Loads
The first cracking load increases with increase in the amount and shape of CFRP sheets as shown in Table 4. The diagonal crack that caused failure initiated suddenly from the last shear crack that became inclined and crossed mid depth, and then such a crack propagated simultaneously towards the load-point and towards the support along the tensile reinforcement (due to dowel action) causing a loss of bond and failure of the beam. External strengthening of SCC beams by CFRP sheets showed an improvement in the first cracking loads when compared with the control beam as shown in Table 4 with the same loading level.
From comparison of the four specimens in group A, it can be seen that the ultimate load carrying capacity increases with increasing of the vertical CFRP strips distributed between the support and the point of concentrated load. On the other hand, when the two horizontal CFRP strips were connected to the vertical CFRP strips to prevent the failure of the latter by de-bonding, an increase was made in the ultimate load comparing to the beams without horizontal CFRP strips.
The specimens in this group failed suddenly by de-bonding and rupture of CFRP strips, while by comparison of the four specimens in group B, it can be seen that the ultimate load capacity is increased with the increasing of vertical U-shape CFRP strips distributed between the support and the point of concentrated load. On the other hand, when one horizontal CFRP strip was connected to the vertical U-shape CFRP strips to prevent the failure of the latter by de-bonding, an increase was made in the ultimate load compared to the beams without horizontal CFRP strip. The specimens in this group failed suddenly by de-bonding and rupture of CFRP strips.
On the other hand, group C gave a better improvement in strength than previous groups. This

Load deflection Behavior
Experimental load versus mid-span deflection curves for these SCC beams are presented in this section as shown in Figs

Shear Crack Width
Shear cracking load is defined as the load at which the first major inclined diagonal tension crack appears in the shear span. The crack is sudden and is usually originated at the middle of the shear span and propagates toward the support and loading point during subsequent increase in the applied load. Maximum crack widths along the major inclined crack in the shear span occurred almost at mid depth of the beam. Beams without CFRP strips exhibited considerably larger crack width at failure.
For each load increment, crack width of the major inclined crack at mid-depth of the beam was measured by means of crack detection pocket microscope. Figs. 21-24 show the behavior of the total applied load versus the maximum crack for control beam BC and beams for groups (A, B, and C).

CONCLUSIONS
The following points have been reached in this research: 1. The experimental test results confirmed that the strengthening technique of CFRP system is applicable and can increase the shear capacity for strengthened SCC of RC beams. In this study, the ultimate load capacity of the strengthened beams ranged between (15 % to 74%) over the ultimate load capacity of the reference beam (BC), while increase in ultimate loads