ملخص البحث :

Repairing of reinforced concrete structures is currently a major challenge in the construction industry and is being put back into operation with a slight loss in load carrying capacity. Damage occurs due to many factors that reduce the strength of concrete structures and their durability. The aim of this paper is study the compatibility between three types of reactive powder concrete with (steel fibre, glass fibre and polypropylene fibre) as a repair materials and normal strength concrete as a substrate concrete. Compatibility was investigated in three steps. First: individual properties for substrate concrete were studied, these are (slump test, compressive strength, splitting strength, and flexural strength) also, for repair material these are (compressive strength and flexural strength) were determined by using standard ASTM test methods. Second: bond strength of composite cylinder for substrate concrete with different repair materials were evaluated by using slant shear test. Third: compatibility was investigated by using composite prisms of substrate concrete with different repair materials under two-point loading (flexural strength test). From the experimental results concluded, bond strength between reactive powder concrete with glass fibre as a repair material and normal strength concrete as a substrate layer is higher (17.38 Mpa) compared with RPC with steel fibre (13.13 Mpa) and polypropylene fibre (14.31 MPa). Also, it is more compatible due to flexural strength for composite prisms (having higher flexural strength (8.13 MPa). Compared with steel fibre (7.44 MPa) and polypropylene fibre (6.47 MPa). These results due to RPC with glass fibre have good workability with suitable flowability and glass fibre have higher tensile strength compare with other fibre.

ملخص البحث :

Reactive Powder Concrete (RPC) is a cement-based substance that's considered as one of the ultrahigh performance concrete types. In fact, it is an ultrahigh strength concrete with excellent toughness. It can somewhat be referred to as a mortar than a real concrete mix due to the substitution of fine and coarse aggregate in conventional concrete by extremely fine sand having a particle size within the range (150-400 µm). In this investigational work, the compressive as well as the flexural strength of control mixture ((RPC) and (RPC) with three different nano alumina contents (1.5, 3 and 5%) replaced from the weight of silica fume was obtained, and the outcomes were compared. Anexperimental work was conducted on these four groups of mixtures, consisting of 12 cubes of (50 × 50 × 50) mm and 12 prisms of (50 × 50 × 300) mm. The microstructural analysis was performed using Scanning Electron Microscopy (SEM)and X-Ray Diffraction (XRD). The results manifested that the ultimate compressive strength is 140.32 MPa, and the maximum flexural strength is 30 MPa in mixes with 3% nano alumina. Mixes with 1.5% and 5% nano alumina also enhanced the compressive and flexural strength compared with the plain concrete mix. The XRD and SEM results elucidated that the nano alumina addition enhanced the microstructural bonding and augmented the hydration of the cement, which led to improving RPC mechanical properties.

ملخص البحث :

: Concrete is considered one of the greatest innovations in the construction industry since it has significant applications in the construction field. The main limitation of concrete is the low flexural and tensile strength, especially for concrete tiles used for floors and roofs. Therefore, this study aims to enhance the behavior of concrete tiles by using both nano-papyrus (NP) and carbon fibers (CF). Eleven different concrete mixtures with different content of NP and CF were prepared using various models, and the percentage of NP content ranged from 1.5 to 7.5%, while the percentage of CF content ranged from 0.2 to 1%; flexural strength and water absorption tests were also conducted. It was found that employing NP enhanced the flexural strength of concrete tile by up to 48%, whereas using both NP and CF optimized the flexural strength by up to 57%. Also, the surface and total absorption rates decreased by up to 47.1 and 52.6%, respectively.