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Due to an increasing need of sustainability, durability of concrete structures has become a matter of prime importance. And as far as durability of concrete is concerned, it is inversely proportional to its tendency to allow the ingress of water. It is thus quite instrumental in relating the measure of concrete’s resistance to exposure in aggressive conditions. This paper presents the effect of adding steel fibers in concrete on the surface water absorption using sorptivity test. The variation in the sorptivity with varying percentage of steel fibers in concrete is determined by measuring the increase in the mass of specimens resulting from absorption of water as a function of time when only one surface of the specimen is exposed to water as per ASTM C1585.
Test results indicate that the presence of steel fibers in concrete reduce the surface water absorption significantly as compared to the plain concrete indicating increased resistance to the uptake of water and hence increased durability.
Keywords: Concrete, Corrosion, Durability, Steel Fibers, Sorptivity.
Due to increasing population and hence the rapidly increasing demand of infrastructure, there is undoubtedly an indispensible need of sustainable and innovative construction techniques. Concrete, a widely used construction material is being researched widely to achieve the desired quality in construction. And to have a sustainable concrete structure, it becomes important to take its durability into consideration. A durable concrete can be referred as one which resist weathering action or any sort of chemical exposure and the one which performs as expected under the prevalent conditions.
Moreover, any kind of composite that can hold its original arrangement and serviceability in spite of any environmental conditions can be referred as durable. Selection of concretes materials for a specific application is a crucial step in avoiding durability problems. And as far as durability of concrete is concerned, it is inversely proportional to its tendency to allow the ingress of water. Especially, the concrete structures that are exposed to marine water, de-icing salts, corrosive environments etc. need low permeability of water for enhanced durability. Apart from providing safety and performing well throughout the service life of a structure, the enhanced durability of a structure also eliminates the expenses or troubles that may arise due to recurring need for repairs and maintenance. Thus, a durable structure prevents the undue wastage or exploitation of the resources.
Concrete is well known to be Quasi-brittle material. And concrete alone cannot solve the key requirement of being a usable structural material. Reinforcement within concrete creates a composite material, with the concrete providing strength against the compressive stresses while the reinforcement provides the strength against the tensile stresses. Thus, concrete reinforced with steel is the foundation of our modern society.
On the contrary, while steel reinforcement solves one of the concretes greatest limitations, it creates an entirely new problem. Corrosion of steel rebar is the most common form of concrete deterioration. And it is accelerated with the ingression of water, salts and contaminants into the concrete. Several monitoring techniques and preventive measure have been reported in literature . The structure subjected to worse exposure conditions is able to maintain its durability through two main performance characteristics. The one is low permeability and the other is shrinkage. Lower permeability can be achieved by better micro structure and by preventing shrinkage cracks that may appear due to heat of hydration. Fibers in concrete are known for their crack arresting characteristic. On the other hand, if not skillfully incorporated, fibers may lead to porous concrete due to decreased workability. Transport properties of materials like permeability, might disturb the durability and structure of concrete composite. Therefore, it becomes important to investigate the role that fibers can play in regard to porosity or permeability of concrete.
Inorder to investigate the transport properties of concrete, researchers have been using enormous techniques namely, water absorption test, permeability test, Rapid chloride penetration test etc , , [7,8,9,10,11]. Sabir et al (1998) presented a test to measure the mortar and concrete’s water absorption in one direction the sorptivities of the specimens by detecting the changes between the sorptivities of specimens . Lockington et al (1999) also presented the study of unsaturated hardened concrete by determining the amount of water soaked by solid concrete at different intervals of time to check the sorptivity index of concrete . It was stated that this is the vital parameter which is instrumental to evaluate the concrete’s resistance to ingress of water or contaminants , , , . Though abundant investigation has been completed to recognize, examine, and investigating the mechanical properties of fibre strengthened concrete, slight exploration has focused on the transport qualities of this material. Concrete is transport properties, particularly permeability, may disturb the durability and internal structure of the composite. The rise in concrete permeability, due to the onset and advancement of cracks, delivers entrance of water, chlorides and other destructive deteriorating agents. Thus, the present investigation aims to examine the effect of adding steel fibers into concrete on rate of absorption of water by performing sorptivity test.
Inorder to investigate the effect of adding steel fibers in concrete on the rate of absorption of water, Sorptivity Test has been performed on different set of specimens as per ASTM C1589-04. According to it, this test strategy is utilized to decide the rate of assimilation (sorptivity) of water by pressure driven in cement concrete by estimating the expansion in the mass of a sample coming about because of ingestion of water as an element of time when just one surface of the sample is presented to water ,. In the present work, the fibers are added in concrete mix of M25 grade, represented with percentage of the entire volume of composite known as volume fraction (Vf). Steel fibers of hooked end type of dia 1 mm and length 50 mm are used.
Inorder to examine the effect of steel fibers on the sorptivity of concrete, the experimentation has been carried out on specimens with varying percentage of steel fibers (0%, 0.5% and 1%). The standard test sample is a 100±6 mm diameter disc, with a length of 50±3 mm . The absorption can be assessed at various separations from the uncovered surface. For obtaining the standard control samples, 150 mm ? 150 mm ? 150 mm cubes of grade M25 containing 0%, 0.5% and 1% hooked end steel fibers were casted and cured for a period of 28 days. A total of 12 test specimens consisting of a set of three samples for each case (0%, 0.5% and 1% steel fibers) were obtained from the drilled cores of the casted cubes as shown in the figure 2.1.
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