Natural materials are remarkably efficient because they fulfill the complex requirements posed by the biological functions and they do so using as little material as possible. Most natural materials are complex composites whose mechanical properties are often outstanding, considering the weak constituents from which they are assembled. Moreover, most natural materials are sustainable, recyclable and, when disposal is necessary, biodegradable, making them a model for environmentally conscious engineering. These complex structures, which have risen from hundreds of millions years of evolution, are inspiring Materials Scientists in the design of novel materials.

Most living tissues or organisms can heal themselves, provided the incurred damage is moderate. Most engineered materials are developed on the basis of the damage prevention paradigm and deteriorate with time irreversibly, which limits the life of various components and sometimes causes catastrophic damage. It would be then very desirable to implement the ability of self-healing in inorganic materials. A material (concrete, polymers, ceramics, etc.) that can intrinsically correct damages caused by normal usage could lower production costs of a number of different industrial processes through longer service life, reduction of inefficiency over time caused by degradation, as well as avoidance of costs incurred by material failure. For a material to be defined as self-healing, it is necessary that the healing process occur without human intervention. In this research will be discussed as self-healing materials, Concrete.

The development of self-healing cementitious composites are focused both on the natural ability of hydrates to heal cracks over time, requiring a external trigger, like heat or light (autogenic) and artificial means of crack repair that are man-made inclusions, but do not require any external trigger, to activated the damage itself is the stimulus for the healing (autonomic).

Concrete is the most used construction material because of its high compressive strength and low cost. But, it is sensitive to crack formation and as a consequence of its limited tensile strength; these cracks endanger the durability of concrete buildings as aggressive liquids and gases may penetrate into the matrix along these cracks and cause further damage. Hence, inspection, maintenance and repair of concrete cracks are all indispensable.

Many developed countries, are experiencing unprecedented amounts of civil infrastructure deterioration, so much so that the annual outlay for repair and rehabilitation has outstripped the cost of new infrastructure construction. The annual economic impact associated with maintaining, repairing, or replacing deteriorating structures is estimated at 18-21 billion in the U.S. only. The American Society of Civil Engineers estimates that 2,2 trillion is needed over the next five years to repair and retrofit; a cost of 2 trillion has been estimated for Asia’s infrastructure. In Europe, 50 percent of the annual construction budget is spent on rehabilitation and repairing existing structures. For United Kingdom, repairing and maintenance accounts for almost 45 percent of the UK’s activity in the construction and building industry. In case of Netherlands, one third of the annual budget for large civil engineering works is spent on inspection, monitoring, maintenance, upgrade, and repair. To make matters worse, repairs of concrete structures are often short-lived. In the US, it is estimated that half of all field repairs fail and require re-repairs. The concerns related to civil infrastructure deterioration are not limited to the economic cost of repairing and rehabilitation, but extend to social and environmental costs. While there is little documentation and quantification of the social and environmental costs, it is generally agreed that repeated repairs of civil infrastructure over their service life is decidedly unsustainable.

Van Breugel, suggested a conceptual life cycle performance and cost model. The current practice of periods of gradual infrastructure deterioration punctuated by discrete repair events leads to increasingly high cumulative costs that many match or even exceed the initial construction cost.

In contrast, infrastructure built with self-healing concrete may have higher initial cost, but the self-healing functionality maintains the quality of infrastructure with minimum or no additional cost accumulation over the life cycle, resulting in a life-cycle cost that could be competitive with the cost of current concrete infrastructure. It is for these reasons that the self-healing ability would be desirable for concrete.

Therefore, first it is important to perform different tests of three-point-bending with different healing agent and then to determine the flexural strength and elastic modulus for each one of the samples with the different healing agents proposed. When these results were known, should be selected the healing agent, with the best properties that must meet the self-healing concrete. The process to select the different healing agents were made in the Department of Applied Science and Technology (DISAT) of the Politecnico di Torino; and the process to determine the physical properties were made in the Department of Structural, Geo-technical and Building Engineering (DISEG) of the Politecnico di Torino. This research is performed with the aim of achieving sustainable development in the economy and environment areas, using capsules with healing agent for the production of the Self-Healing Concrete.

Consequently of all this, it is necessary to formulate the following questions:

1.2. RESEARCH OBJECTIVES

- What characteristics must possess the capsules to allow a total output of the healing agent when will fracture the concrete?

- Which healing agent reacts with concrete fractured allowing to achieve the recovery of their mechanical properties (flexural strength and elastic modulus)?

- Which are the recovery percentage of the flexural strength and the elastic modulus of the self-healing concrete?

Therefore, once developed the mixing of self-healing concrete and that present the best flexural strength and elastic modulus for subsequent implementation; will be able to know the Load Recovery Index and the Stiffness Recovery Index.

1.2. RESEARCH OBJECTIVES

Principal Objective

- Evaluate flexural strength and elastic modulus recovery in self-healing concrete repaired by inorganic solutions.

Specific Objectives

- Obtain a cementitious capsule with the necessary characteristics that allows a total output of the healing agent when will fracture the concrete.

- Identify the healing agent which reacts with concrete fractured allowing to achieve the recovery of their mechanical properties (flexural strength and elastic modulus).

- Indicate the recovery percentage of the flexural strength and the elastic modulus of the self-healing concrete.

1.3. JUSTIFICATION AND IMPORTANCE

Over the last decade, the concept of concrete infrastructure able to repair itself without human intervention has emerged as a possible cure for overcoming civil infrastructure deterioration. While the idea remains a novelty in practice, it has attracted a significant amount of attention in the research community. Many different approaches to functional-izing concrete to posses self-healing ability have been investigated. Given that damage in concrete is dominated by cracks, much attention has been given to self-repair of cracks. Being promising to the feasibility of future civil infrastructure smart enough to detect its own damage and undergo repair by itself. Thus self-healing concrete has significant implications in extending service life, and reducing economic, social and environmental

costs of civil infrastructure, That is, self-healing concrete could be a major enabling technology towards sustainable civil infrastructure.

Cracks in concrete are a common phenomenon due to the relatively low tensile strength. Durability of concrete is impaired by these cracks since they provide an easy path for the transportation of liquids and gases that potentially contain harmful substances. If microcracks grow and reach the reinforcement, not only the concrete itself may be attacked, but also the reinforcement will be corroded. Therefore, it is important to control the crack width and to heal the cracks as soon as possible. Self-healing of cracks in concrete would contribute to a longer service life of concrete structures and would make the material not only more durable but also more sustainable.

The present research is to study Self-Healing Concrete using a capsule with inorganic solutions to achieve sustainable development. The use of self- healing concrete can contribute with the reduction of the rate of deterioration, extension of service life, and reduction of repair frequency and cost over the life of a concrete infrastructure. These benefits may be expected to lead to enhanced environmental sustainability since fewer repairs implies lower rate of material resource usage and reduction in energy consumption and pollutant emission in material production and transport, as well as that associated with traffic alterations in transportation infrastructure during repair/reconstruction events.