Bond Strength and Flexural Capacity of Normal Concrete Beams Strengthened with No-Slump High-Strength, High-Ductility Concrete

Abstract

This study investigates the flexural behavior of normal-strength concrete (NSC) beams that were strengthened with no-slump, high-strength, high-ductility concrete (NSHSDC). A set of slant shear tests was performed to investigate the initial performance of the NSC substrate strengthened with NSHSDC. Slant shear tests considered two types of roughness of interface and five angles of the interface between NSC and NSHSDC. The test results showed that except for specimens with a 75° interface angle, the specimens with high roughness were conformed to the properties (14–21 MPa for 28 days) of the ACI Committee 546 recommendation. For flexural strength tests, NSC beams strengthened with an NSHSDC jacket on the top and bottom sides, three sides, and four sides resulted in strength increments of about 8%, 29%, and 40%, respectively, compared to the beams without NSHSDC jacket. Therefore, the use of NSHSDC is an effective method to improve the performance of NSC beams and is recommended for strengthening reinforced concrete members.

Effect of Strengthening Methods on Two-Way Slab under Low-Velocity Impact Loading

“…Despite the first blow, the NC-NF had a crack width in the center of the bottom side. The NSC-NF showed several bending cracks, most of which were identified near the central part of the it because of the bridging effect of the steel and PE fibers [ 36 , 37 ]. A lot of cracks were found on the back side, and the damaged area was the smallest.…”

“…The steel fiber (0.2 mm of diameter, 19.5 mm of length, and 7.8 g/cm 3 of density) and polyethylene (PE; 31 µm of diameter, 12 mm of length, and 0.97 g/cm 3 of density) fiber were mixed with volume fractions of 1.0% and 0.5%, respectively, and their physical properties correspond to those of existing studies [ 35 ]. Polycarboxylate high-performance reducer (liquid/brown, 1.07 g/cm 3 ) is adopted as superplasticizer (SP) at cement weight ratio of 3% [ 36 ] to facilitate the mixing of concrete. Table 3 presents the detailed mixture of the NSHSDC.…”

“…Furthermore, when mixing two types of fibers with different lengths, long fibers are considered to have an outstanding macro-crack control effect, whereas short fibers have excellent microcrack control effects [ 29 ]. In addition, NSHSDC confirmed the adhesion to the existing concrete made of high-strength concrete with a strength of 120 MPa [ 36 ].…”

“…This study evaluated the impact resistance properties for the following four strengthening methods: FRP, sprayed FRP, NSHSDC, and hybrid. Not only the bottom side, but also the top side were strengthened based on the existing research results [ 33 , 36 ]. The hybrid method strengthened the structure with NSHSDC on the top side and sprayed FRP on the bottom side, considering that the sprayed FRP and NSHSDC have excellent tensile and compression strengthening effects, respectively.…”

“…High-performance-fiber-reinforced-cement composites (HPFRCCs) exhibit high strength and are being studied and widely applied [33][34][35][36][37]. Among these HPFRCCs, no-slump high-strength and high-ductility concrete (NSHSDC) offers excellent adhesion with conventional concrete owing to its high viscosity, excellent load resistance, and ductility [35,36]. This is because a hybrid mix of two different fiber lengths is adopted to improve the mechanical properties during the NSHSDC manufacturing [35].…”