ABSTRACT
The quality of the bonded concrete overlay depends on the bonding at the layer’s interface, which is affected by parameters such as fibre inclusion and content in new concrete, moisture condition and surface roughness of old concrete surface. This research presents an experimental study carried-out to assess the interfacial bond strength behaviour of Steel Fibre Reinforced Concrete (SFRC) and Plain Concrete (PC) substrate. The objective of this study is to quantify the interface shear bond strength affected by fibre inclusion and content in new concrete, moisture condition and surface roughness of old concrete surface. Steel wire fibre was incorporated as reinforcing agent in the FRC to determine its effect on bonding strength. To better understand the bonding mechanism at the interface, overlaid square prism specimens were fabricated with three moisture conditions (air dry, SSD, and wet). Five different fibre volume fraction of 0%, 0.5%, 1.0%, 1.5%, and 2.0% were prepared and used as the overlay concrete on three different surface texture (As Cast surface, Grooved surface, and Wire brush surface). It was observed that the bond strength of the FRC samples at all moisture condition (SSD, W and AD) is higher than that of the control specimens in the presence of the three surface texture. The bond strength of FRC with 1% fibre volume was observed to have consequently improved. This improvement is influenced through grooved surface texture at SSD moisture condition of the old concrete surface. Steel fibre of 1.0% produced sample with the highest interfacial bond strength of 15.19N/mm2. It was observed that, the bond strength of FRC was more than the control specimen. Based on ACI Concrete Repair Guideline, all the roughened surface textures used in this study were able to meet the minimum bond strength it specified. Considering all inferences and appraisals from this research, 1% steel FRC, grooved surface treatment type and SSD surface condition are recommended in the production of retrofitting/repair concretes with the sole aim of achieving an enhanced interfacial shear bond strength.
CHAPTER ONE
1.0 INTRODUCTION
1.1 Background to the Study
Concrete infrastructures in most countries around the world are facing a rapid loss of serviceability, safety and suffering damages from increasing and unpredictable live loads which they are exposed and subjected to in service (Shin & Wan, 2010; Banthia et al., 2014). These civil infrastructures such as roads, sewers, and the built infrastructure of commercial, domestic and public buildings are the basis of any community’s health, safety and prosperity. Consequently, they must be kept in good and functional state at all time (Banthia et al., 2014). In response to infrastructure damaged, new construction materials that are reliable, effective and economical such as Steel Fibre Reinforced Concrete are used in constructing overlay and patching the damaged or deteriorating part of the structures (Tayeh et al., 2013a; Denarié & Brühwiler, 2006). The usage of Steel Fibre Reinforced Concrete in engineering application is meant to achieve the target of creating an effective ductile and high tensile concrete.
Concrete-to-concrete interfaces are present both in new and existing structures. Two distinctive situations can be identified: (1) placing hardened concrete against hardened concrete parts, such as the case of precast members for viaducts and bridge decks; and (2) placing fresh concrete against hardened concrete parts, such as the rehabilitation and strengthening of existing structures by concrete jacketing or concrete overlay (Aysha et al., 2014).
The security strength of the substantial to-concrete or Concrete to fix material interface is impacted by a few boundaries however fundamentally by the harshness of the interface mode, the utilization of holding specialists; the pressure opposition of more vulnerable concrete, the dampness substance of the substrate, the relieving conditions, the pressure state at the interface, the presence of breaking and, the measure of steel support crossing the interface among others. Similarity of the maintenance material with the current substrate is a significant thought if the maintenance is to withstand every one of the burdens prompted by impacts, for example, volume changes and compound and electrochemical impacts (Aysha et al., 2014; Casal, 1960).
Application of Steel Fibre Reinforced Concrete (SFRC) in enhancing the bonding of concretes will gradually help to increase the efficiency of the building system. The mechanism behaviour of the combination of concretes plays an important role in the structural system. Many applications involved in the bonding of concretes such as repairing, casting joints or precast element connection requires large amounts of cement in them for them to develop an adequate bond with the substrate. The use of SFRC as replacement of existing conventional concrete to be used for repairing and rehabilitation purpose may give a great impact in engineering application towards sustainability.
Investigated result has shown SFRC to have the possibilities that make it reasonable for fix, retrofitting and restoration of Supported Substantial Designs (RCS) and as new development material (Banthia et al., 2014). Any remaining pieces of the designs stay in ordinary primary concrete as these parts are exposed to generally sensible openness. Ordinarily, there consistently exists a feeble association between the bond strength of the old and new substantial constructions during reinforcing and restoration (Momayez et al., 2005; Gorst & Clark, 2003; Mu et al., 2002). To effectively rehearse restoration of decaying structures, the comprehension of the practices at the interface between the old and the new development materials is convenient (Tayeh et al., 2013a; Tayeh et al., 2013b; Ueda & Dai, 2005). The bond between the composite materials is an element of certain variables, like surface unpleasantness and surface extremity of the composite segments. In estimating the surface energies and bond strength of the composite material, a comprehension of the interfacial attachment between the fibre and the network must be resolved. This exploration will assist with understanding the Interfacial bond conduct of Concrete made with steel fibre and Plain concrete.
1.2 Statement of the Research Problem
The deterioration of concrete structures is a matter of critical concern as it threatens the durability and strength of concrete structures. SFRC can be used with advantage in new structures such as precast and cast insitu elements, as well as the strengthening, repair and rehabilitation of old structures to improve their resilience properties.
Bonded concrete overlay is a viable option to increase structural capacity and improve reliability of concrete structures. However, property mismatch of new overlaid concrete to old concrete usually create bond problems that lead to early age failure and a shortened service life of concrete composite (Momayez et al., 2005; Gorst & Clark, 2003). Consequently, to better understand the bonding mechanism at the interface between new and old concrete surface, it is essential to measure bond strength at the interface and to investigate parameters that affect properties (Tayeh et al., 2013a; Tayeh et al., 2013b; Ueda & Dai, 2005).
1.3 Aim and Objectives
The aim of this research is to investigate the interfacial bond strength behaviour of Steel Fibre Reinforced Concrete and Plain Concrete Substrate with a view to establishing the parameters affecting the bond strength at the interface.
The objectives of the research work are to:
i. Determine the effects of three different conditions at substrate surface on the interfacial bond strength.
ii. Investigate the influence of Steel fibre content on the interfacial bond strength of the composite concrete members
iii. Determine the influence of surface roughness of the substrate on the bond strength of the interface of the composite concrete members
1.4 Scope of the Study
The research work would be experimental in nature and centres on the development and application of SFRC. Fibre volume fraction inclusion in concrete ranges from 0.5% to 2.0% at 0.5% interval at a corresponding fibre length of 40 mm. The study emphasizes on the bond strength of the composite using slant rectangular test specimens to measure the bond stress behaviour in shear. Three conditions (air dry, Saturated Surface Dry (SSD), and wet) were made on the Plain (existing/old) concrete surface. Also, three different surface texture of the old concrete substrate was used in assessing the bonding interface strength of the specimens. A constant water:cement (w/c) ratio of 0.55 was chosen as overlay (repair/rehabilitation) concrete. To assess the variation of the parameters in the result, triplicate samples were fabricated and tested.
1.5 Justification of Study
Several research studies (Aslani & Nejadi, 2013; Arango, 2010; Abdul Awal et al., 2013; Swamy & Mangat, 1974) have been performed on mechanical properties of steel fibre reinforced concrete and concrete structural members reinforced with fibres under various loading conditions. However, studies on interfacial shear bond strength properties of concrete with steel fibres and plain concrete are very limited. In the present investigation, the interfacial shear bond strength behaviour of SFRC and plain concrete substrate was investigated by slant shear bond strength methods. Besides, influence of percentage of fibres, moisture condition of surface and the texture of bond surface on interfacial bond strength was studied.
The critical discoveries of this exploration will be valuable in the accompanying manners:
i. Facilitate in advancing financially savvy fix materials that has decent interfacial security strength with old Concrete thinking about the vital boundaries.
ii. This exploration will help analysts, planners, fabricators and architects to comprehend the Interfacial bond conduct of Concrete made with steel fibre and Plain concrete.
iii. Application of SFRC in upgrading the holding of Concretes will steadily assist with expanding the effectiveness of the structure framework
iv. The utilization of SFRC as substitution of existing customary Concrete to be utilized for fixing and recovery reason may give an incredible effect in designing application towards manageability.
v. Encourage creation of SFRC for fix and retrofitting decaying and break surfaces of Concrete.
vi. Aid in giving curiosity data set of interfacial bond strength of old Concrete to new substantial utilizing SFRC as a maintenance material its application in the development business.
vii. Assist fabricators and specialists in improving the nature of Concrete to substantial interfaces present in both old existing and new designs giving proper materials and strategy.
viii. Provide critical market value where the eventual outcome can be popularized as an oddity in Nigeria.
ix. The findings of this research can be directly adapted in the rehabilitation of concrete pavements and bridges.
This material content is developed to serve as a GUIDE for students to conduct academic research
INTERFACIAL BOND STRENGTH BEHAVIOUR OF STEEL FIBRE REINFORCED CONCRETE AND PLAIN CONCRETE SUBSTRATE
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