Concrete is a composite material that consists of a mixture of fine and coarse aggregates and fluid cement that hardens over time. It is the second most popular substance on earth after water and is the most common building material. The compound has a wide range of applications, ranging from roads to bridges.
Concrete decay is the result of a chemical reaction between water and carbon dioxide. The chemical reaction in concrete can damage a structure and can lead to cracks or bursts. It can also result in the corrosion of reinforcements. In order to minimize the risk of concrete degradation, concretes should be formulated with a low carbonation ratio.
There are several types of chemical reactions involved in the hydration of concrete. One of these is the sulfate attack. The severity of this chemical reaction depends on the type of sulfate used. MgSO4 is highly soluble in water at room temperature (20 deg). Sodium Sulfate has a much lower solubility.
In concrete containing only clinker and gypsum, the ettringite reaction is early, followed by the hydration reaction. As the cement continues to hydrate, monosulfate begins to replace ettringite. As the cement undergoes further hydration, the ratio of alumina to sulfate increases. This increases the concrete’s strength.
Another chemical reaction that occurs in concrete is the alkali-silica reaction. This occurs when alkali-sensitive silicate aggregates react with water within the concrete pore solution. The result is a gel-like substance that results in microcracks in the concrete. The chemical reaction can be controlled by using pozzolanic cement. These cements reduce the pH of the concrete mix, reducing the likelihood of damage to the concrete.
In addition to reducing the cost of cement, pozzolans also improve the durability of hardened concrete. They also improve sulfate resistance.
One of the most important factors to consider in concrete construction is the material’s durability. This refers to its ability to withstand a range of external and internal stresses. In addition to the materials used, there are other factors that may affect durability. External agents can include weathering, bacterial growth, and attack from natural gases and liquids. Internal agents include the presence of sulfates and the non-compatibility of aggregates and cement paste.
Another important property to consider is the amount of segregation. This occurs when constituent materials in concrete separate. In good concrete, these components are evenly distributed, but there are substantial differences in their specific gravities. The concrete’s natural tendency to separate is the result of these differences. When this happens, the paste and coarse aggregate separate from the rest of the material.
There are many other concrete properties. The most important one is its strength. The amount of cracking a structure can endure is determined by its tensile strength. A concrete structure that is too weak to resist a tensile force will develop cracks. One way to test this property is to perform a split-tensile strength test on a concrete cylinder.
During the drying process, concrete expands and contracts to depend on the exposure time. As the concrete ages, it becomes stronger. In just 28 days, it can increase by 70-75% of its final strength. A year later, it can reach 90 percent or more. In the end, it is this stress that leads to cracks.
Lastly, when it comes to the strength of concrete, the type of aggregate and cement used will determine the concrete’s durability and workability. Aggregates should be chosen according to the design requirements. In addition to density, other properties are important to consider when choosing aggregates.
The basic elements of a concrete composition are Portland cement, water, and sand. The proportion of each component is important, and they can be varied to enhance the properties of concrete. A variety of additives, including polymer-based coating modifiers, are used in the preparation of concrete for various applications.
The composition of concrete is determined by the data obtained in laboratory experiments and by the design characteristics of concrete. For example, concrete with high thermal resistance may be classified as heat-resistant concrete. The purpose of testing concrete for heat resistance is to ensure that it has the desired mechanical and physical properties. The degree of dehydration, for example, must be sufficient to allow it to be formed and deformed to the desired shape. In addition, the residual water content must be close to the normal density of the cement paste.