Evaluation of Bond (Adhesive) Strength Between Conventional Concrete and Steel Fiber Reinforced Concrete Interface

- Good bond strength between overlay and substrate is a key factor in performance of concrete repairs. This thesis was aimed at studying the evaluation of bond strength between conventional concrete substrate and steel fiber reinforced concrete. Many factors such as surface roughness, existence of micro cracks, compaction, curing etc. influence `the bond strength. The quality assurance of the bond strength requires test methods that can quantify the bond strength as well as identify the failure mode. There have been numerous investigations led to development of different test methods. The forces which are applied in each test and the failure mode are important in order to choose the proper test. An interpretive study on test methods is presented. While this study can provide individually useful information on bond strength and bond characterization.


INTRODUCTION 1.1 GENERAL
Concrete is a predominant material used in construction and it competes directly with all other major construction materials like timber, steel, asphalt, and stone, because of its versatility in applications. However, concrete is a composite material and its properties can vary significantly depending on the choice of materials and proportions for a particular application. However, concrete does have weaknesses that limit its use in certain applications. Now-a-days a large number of existing concrete structures worldwide are in urgent need of effective and durable repair. It has been estimated that almost half of all concrete repairs fail due to the lack of reliable and perfect bond. Good bonding between repair materials and existing concrete repair substrate is of vital importance in the concrete repairs.
Fiber-reinforced concrete, Shrinkage-compensated concrete and Latex-modified concrete.

OBJECTIVES OF THE PRESENT WORK:
The main theme of this thesis is to study the bond strength between the concrete interfaces of Conventional concrete and steel fiber reinforced concrete. Concrete of different grades M20, M30 and M40 is designed and cast in to a mould of prism of dimensions 20cm*10cm*10cm up to the interface making an angle of interface 30 0 and 45 0 respectively. Then remaining portion is cast with fiber reinforced concrete of M20, M30, M40 grades respectively.

CHAPTER 2 LITERATURE REVIEW 2.1 RECENT STUDIES ON BOND STRENGTH BETWEEN THE CONCRETE AND CONCRETE INTERFACES:
The following points explain about research wok on the bond strength between the concrete and concrete interfaces. Hugo costa, Pedro santos, and Eduardo julio [1] -studied the bond strength behavior of thelight weight aggregate concrete (LWAC) to the normal weight concrete (NWC) interfaces. An experimental study is conducted to characterize the shear strength and tensile strength of NWC-to-NWC, LWAC-to-NWC and LWAC-to-LWAC interfaces and stated as follows 1. Two failure modes were observed, cohesive (at the weakest concrete) and adhesive (debonding of the interface). 2. For slant shear tests, the failure mode was mainly monolithic, for very rough surfaces (HS and CD), and mainly adhesive, for very smooth and smooth surfaces (SS and WB). 3. For rough surfaces, SF and SB, both failure modes were observed.

Radhakrishnan, Syam Prakash, and Prasad varmathampan [2]
evaluated the performanceof styrene butadiene rubber as a concrete repair material in tropical climate using slant shear test and splitting tensile strength of the repaired cylinder specimens of the standard dimensions, in which SBR is used as a bonding agent are determined and stated as 1. The results of sorption test showed that the conventional weathering coat of cement mortar of 1:3 proportions did not possess adequate water penetration resistance, to function as water proofing agent. Therefore a modifier is essential to make the repairs durable. 2. SBR modified cement mortar possess very good water penetration resistance and can be used as a repair material in the case of spalled roof slabs with exposed steel reinforcement.

CHAPTER 3 EXPERIMENTAL STUDY 3.1 PROGRAM OF EXPERIMENTAL WORK
The experimental program was designed to study the bond strength between old concrete and new concrete interface. For this purpose following interfaces are created. They are: 1. M20-M20, M20-SFRC0.4%, M20-SFRC0.8%, M20-SFRC1.

MIX PROPORTIONS
In this experimental study all the mix design were done according to IS456:2000 and IS 383:1970 and IS 10262:2009.The following were the mix ratios used for casting:

MATERIALS
The various materials used in the experimentation namely cement, fine aggregate and coarse aggregate have been tested in the laboratory. The specifications and properties of these materials were presented in the subsequent sections. All the materials used in the study were tested in the accordance to the Indian standards.

Cement
Cement used in experimental work was Ordinary Portland Cement of 53 grade from Ultra tech brand conforming to IS: 12269-1987. Cement used was fresh, of uniform colour, free from any lumps and foreign matter, and from the same batch. The properties of cement used were as shown in Table 3.3.1. Bulk Density (Rodded) in kg/m 3 1700 5 Fineness modulus 7.867

Fine Aggregate
River sand conforming to Zone-II as per IS 383:1970 was used. The fine aggregate was clean, inert and free from organic matter, silt & clay. The Fine aggregate was dried before use. The properties of fine aggregate were presented in the Table 3.3.3. To begin with all the dry materials (coarse aggregate, fine aggregate, cement) are mixed about two minutes then super plasticizer is thoroughly mixed with the water and this liquid component was added to the dry material mixture. This wet composition is allowed to mix for another four minutes. During this process fibers are sprinkled uniformly to the wet mixture. The care has been taken in allowing all materials to get mixed up uniformly and avoiding the material to get stuck up to walls of the mixer.

VIBRATOR
A plate vibrator was used for compacting the prisms.

EXPERIMENTAL SETUP
The prism specimens of the concrete were tested on Compression testing machine (CTM) capacity of 40Tonnes. The bearing surface of the machine is wiped off clean and any loose sand or any other materials removed from the surface of the specimen the specimen was placed in the machine in such a manner that the load was applied to opposite vertical faces of the prism. The axis of the specimen was carefully aligned at the centre of the loading frame and the load applied was increased continuously at a constant rate until the resistance of the specimen to increasing load breaks down and could not no longer sustained.

CHAPTER 4 RESULTS AND DISCUSIONS
4.1 GENERAL Details of the laboratory experimentation is carried out with different combinations of materials have been discussed in the previous chapter. In this chapter a detailed discussion on the results obtained from various laboratory tests are presented.       Referring to Fig 4.2.1.1, Fig 4.2.1.2, Fig 4.2.1.4 and Fig 4.2.1.5, it is clear that there is an increase of bond strength values as the percentage of steel fiber content is increased in the over laid concrete for M20 and M30 grades of concrete at both 45 0 and 30 0 angle of interfaces. This may be due to presence of steel fibers which act as the crack closing forces against the micro cracking caused by compressive loading. Referring to Table 4.2.4.1, it is noticed that there is an improvement of the toughness as the steel fiber content is increasing in the overlaid concrete. So, it may be due to the improvement in the energy absorption capacity due to the steel fibers.

Limitations in using of steel fibers:
1.) There is a reduction in the workability in the concrete as the percentage of steel fibers content is increasing from the 0 to 1.2 of volume fraction. 2.) Balling of fibers is noticed as the fiber content is more than 0.8%.