Mechanical properties of old concrete—UHPFC interface

The uniqueness of Ultra-High Performance Fiber Concrete (UHPFC) is its extremely low porosity gives its low permeability and high durability, making it potentially suitable for rehabilitation and retrofitting reinforced concrete structures or for use as a new construction material. This experimental study was performed to assess the bond strength between UHPFC as a repair material and Normal Concrete (NC) substrate as an old material; split tensile strength and slant shear tests were performed to quantify the bond strength in indirect tension and shear respectively, also the correlation between split tensile strength and slant shear were studied. The result showed that UHPFC has been cured by steam, gives high bond strength at the early age of the repair process, and interacts well with the surface of NC, as a result the failure occurred mostly in the NC substrate. A good correlation between the slant shear test results and the split tensile test results has been observed

Effect of different curing conditions on the mechanical properties of UHPFC

(Received: Match 20, 2013; Accepted in Revised Form: June 22, 2013) Abstract: Ultra-High Performance Fiber Concrete (UHPFC) is a new class of concrete. Because of its distinguished mechanical properties, UHPFC is considered as an ideal alternative material for use in developing new structural solutions. This paper discusses on influence of different curing conditions on mechanical properties of UHPFC. An experimental program was performed to study the mechanical properties of UHPFC which were cured under six different curing conditions. Test results indicated that steam and boil curing methods showed a promising performance particularly at early age of curing compared to other type of curing

Compressive Stress-Strain Behavior of Composite Ordinary and Reactive Powder Concrete

The deterioration of reinforced concrete structures is a major social problem. To minimize this problem and ensure effective structural management, the number and extent of repair interventions must be kept at the lowest probable level. Good bond is one of the main requirements for successful repair. The main aim of this study was to investigate the compressive stress-strain behaviour of the composite specimens consist of ordinary concrete (OC) substrate as old concrete and reactive powder concrete (RPC) as a retrofitting material, by using different types of OC substrate surface preparation methods. The results showed that the composite OC/RPC specimens were able to behave closely to individual OC, in the case of using OC substrate with surface prepared by sand blasted

Utilization of ultra-high performance fibre concrete (UHPFC) for rehabilitation–a review

Under normal circumstances, reinforced concrete structures (RCS) show excellent performance in terms of durability and structural behaviour except for the zones that are subjected to severe mechanical or cyclic loading and aggressive environmental conditions. Therefore the methods of rehabilitation or strengthening of these zones should be reliable, effective and economical. Today, many scientists, academics and engineers understood the extremely low porosity and low permeability characteristics of ultra high performance fibre concrete (UHPFC) giving its enhanced durability over high performance concrete (HPC), thus making it potentially suitable for rehabilitation and retrofitting problematic RCS. The advantages of utilising the technology of UHPFC in repairing works includes (i) decrease the working time needed for the rehabilitation works; and (ii) increase the serviceability and durability to an extent where

The relationship between substrate roughness parameters and bond strength of ultra high-performance fiber concrete

The bonding that exists between the old concrete and the new concrete depends largely on the quality of substrate surface preparation. The accurate representation of substrate surface roughness can help determine very precisely the correct bonding behavior. In this work, an experimental investigation was carried out to quantify the normal concrete (NC) substrate roughness parameters and evaluate their relationship with the bonding performance of ultra high-performance fiber concrete (UHPFC), used as a repair material. The bond strength was quantified based on the results of the pull-off test, splitting cylinder tensile test, and the slant shear test. Three types of NC substrate surface preparation were used: as-cast (without surface preparation) as reference, wire-brushed, and sand-blasted (SB); the roughness of which was determined using an optical three-dimensional (3D) surface metrology device (Alicona

Flexural Strength Behavior of Composite UHPFC-Existing Concrete

Article Preview Article Preview Ultra high performance fiber concrete (UHPFC) is an advanced formula concrete that is proven to be more superior than conventional concrete because it embrace the qualities of steel and concrete. Therefore UHPFC properties which include high durability and strength are fully exploited in the research of rehabilitation and strengthening in concrete and even non-concrete structures. This article presents the findings of an experimental study carried out to examine the bonding strength behaviour between normal concrete (NC) substrate and UHPFC as a repair material, under flexural strength test by using third-point loading beam test method. Three types of NC substrate surface preparation were used: as-cast (without surface preparation) as a reference, wire-brushed, and sand-blasted. The flexural test results clearly indicated that all failures occurred through the NC substrate and no

Characterization of the interfacial bond between old concrete substrate and ultra high performance fiber concrete repair composite

The interfacial bond characteristics between normal concrete substrate as old concrete and ultra high performance fiber concrete as repair material have been investigated. Normal concrete substrates were first subjected to different surface preparation methods prior to bonding the ultra high performance fiber concrete to form repair composites. The interfacial mechanical bond of the composites was assessed using slant shear and tensile splitting strength tests. In addition, rapid chloride permeability test was performed to ascertain the potential chloride resistance of the composites. The microstructure of the transition zone between the normal concrete and ultra high performance fiber concrete was also studied using scanning electron microscope. The results generally indicate that surface preparation of the substrate is very much required to obtain superior mechanical bond of the composites; whereby the

Assessment of adhesion between RPC overlay and existing concrete substrate

Article Preview Article Preview The number of existing structures under repair and rehabilitation has extensively increased over the past two decades; these structures typically require performance enhancements including durable and safe repair and strengthening. The experimental program aimed to investigate the bond strength at the joint surfaces between conventional concrete substrate as existing concrete and reactive powder concrete RPC as new overlay concrete. Pull off test was used to quantify the direct tension of the bond strength. Different surfaces roughness were used for existing concrete. The obtained results, clearly showed that, RPC could be linked excellent to the existing concrete at early age; as a result, all failures occurred through the existing concrete, regardless of the surface roughness of existing concrete. RPC could be used as an excellent overlay concrete for increasing the durability at

Microstructural analysis of the adhesion mechanism between old concrete substrate and UHPFC

The performance of any repaired concrete structure, and thus its service life, depends on the quality of the interfacial transition zone of the composite system formed by the repair material and the existing concrete substrate. In this work, the properties of the interfacial transition zone between normal concrete (NC) substrate as an old concrete and ultra-high performance fiber-reinforced concrete (UHPFC) as a repair material was investigated. Pull-off and splitting cylinder tensile tests were performed to quantify the bond strength in direct and indirect tensions, respectively. The microstructure of the interfacial transition zone was also studied using scanning electron microscopy and energy dispersive X-ray spectroscopy (SEM/EDS). Different types of NC substrate surface preparation methods were used. An optical three-dimensional surface metrology device was used to estimate the substrate roughness parameters

Existing concrete textures: their effect on adhesion with fibre concrete overlay

This paper quantifies the roughness parameters of existing normal concrete substrate surfaces and evaluates their effect on adhesion strength with ultra-high-performance fibre concrete overlay. Three types of substrate surface textures are adopted: as-cast texture as control, wire-brushed texture and sand-blasted texture. The roughness profile of these substrate surfaces is assessed using an Alicona Infinite Focus device. Adhesion strength is quantified at 3, 7, 28 and 180 days based on the results of the pull-off test, splitting cylinder tensile test and slant shear test. The short- and long-term results of the splitting cylinder tensile and slant shear tests demonstrate that the surface texture profiles of the existing concrete substrate have an important effect on the adhesion strength between existing concrete and ultra-high-performance fibre concrete overlay. The behaviour of bonded ultra-high-performance fibre concrete/existing concrete with sand-blasted texture closely resembles that of monolithic normal samples under splitting cylinder and slant shear tests. The short- and long-term results of the pull-off test prove that failure occurs in the existing concrete, regardless of the type of existing concrete surface texture. A very good polynomial correlation (R2 > 80%) is observed between the average roughness parameter (Ra) of existing concrete textures and results of the splitting cylinder tensile and slant shear tests