Question

1. Name the feedstock materials used in the manufacture of Portland cement. Describe the process of cement production using these materials.   
2. Explain the importance of water in the setting reaction for cement and the reasons for selecting the correct water-cement ratio in concrete. Discuss the problems that might occur when the water-cement ratio is too low or too high.   
3. Write down the chemical reaction between atmospheric carbon dioxide and concrete and state what happens to the pH of concrete as a result of this process. Give the common name for this reaction. Explain the effect of this reaction on both the strength of concrete and on the integrity of steel reinforcement.   
4. State how the mechanical properties of concrete are altered by the addition of steel reinforcement and explain the mechanism of this effect. How would corrosion of the steel or degradation of the concrete affect the mechanical properties?

Answer 1

Solution

1. The two principal raw materials used for producing the Portland cement square measure chalky materials like stone, chalk or dirt and clayey materials like clay and sedimentary rock.

Cement producing may be a complicated method that begins with mining then grinding raw materials that embody stone and clay, to a fine powder, referred to as raw meal, that is then heated to a sintering temperature as high as 1450 °C during a cement oven. during this method, the chemical bonds of the raw materials square measure countermined then they're recombined into new compounds. The result's referred to as clinker, that square measure rounded nodules between 1mm and 25mm across. The clinker is ground to a fine powder during a cement mill and mixed with mineral to form cement. The pulverized cement is then mixed with water and aggregates to create concrete that's employed in construction.

Clinker quality depends on staple composition, that needs to be closely monitored to make sure the standard of the cement. Excess free lime, for instance, leads to undesirable effects like volume growth, redoubled setting time or reduced strength. many laboratory and on-line systems is used to make sure method management in every step of the cement producing method, as well as clinker formation.

2. Water is that the key ingredient, that once mixed with cement, forms a paste that binds the mixture along. The water causes the hardening of concrete through a method known as association. association could be a chemical process within which the main compounds in cement type chemical bonds with water molecules and become hydrates or association product. Details of the association method square measure explored within the next section. The water has to be pure so as to forestall aspect reactions from occurring which can weaken the concrete or otherwise interfere with the association method. The role of water is very important as a result of the water to cement quantitative relation is that the most crucial consider the assembly of "perfect" concrete. an excessive amount of water reduces concrete strength, whereas deficient can build the concrete infeasible. Concrete has to be possible so it's going to be consolidated and formed into completely different forms (i.e.. walls, domes, etc.). as a result of concrete should be each robust and possible, a careful balance of the cement to water quantitative relation is needed once creating concrete.

The strength of the concrete is expounded to the waterto cement mass quantitative relation and therefore the hardening conditions. A high water to cement mass quantitative relation yields an occasional strength concrete. this is often thanks to the rise in porousness (space between particles) that's created with the association method.

3. Carbonation of concrete

Carbonation of concrete is related to the corrosion of steel reinforcement and with shrinkage. However, it additionally will increase each the compressive and enduringness of concrete, thus not all of its effects on concrete ar dangerous.

Carbonation is that the results of the dissolution of carbon dioxide within the concrete pore fluid and this reacts with atomic number 20 from lime hydrate and atomic number 20 salt hydrate to create spar (CaCO3). mineral could type in hot conditions.

Within many hours, or each day or 2 at the most, the surface of contemporary concrete can have reacted with carbon dioxide from the air. Gradually, the method penetrates deeper into the concrete at a rate proportional to the root of your time. once a year approximately it's going to usually have reached a depth of maybe one millimeter for dense concrete of low porousness created with an occasional water/cement magnitude relation, or up to five millimeter or a lot of for a lot of porous and permeable concrete created employing a high water/cement magnitude relation.

Fibers ar typically utilised in concrete to control cracking due to plastic shrinkage and to drying shrinkage. They to boot reduce the body of concrete and then reduce damage of water. Some types of fibers end up larger impact, abrasion, and shatter–resistance in concrete. typically fibers do not increase the flexural strength of concrete, so cannot replace moment–resisting or steel reinforcement.[citation needed] therefore, some fibers actually reduce the strength of concrete.

The amount of fibers facet to a concrete mix is expressed as a proportion of the general volume of the composite (concrete and fibers), termed "volume fraction" . Vf typically ranges from zero.1 to 3%. The magnitude relation (l/d) is calculated by dividing fiber length (l) by its diameter (d). Fibers with a ellipsoid cross section use identical diameter for the calculation of magnitude relation. If the fiber's modulus of snap is quite the matrix (concrete or mortar binder), they assist to carry the load by increasing the lastingness of the material. Increasing the magnitude relation of the fiber typically segments the flexural strength and toughness of the matrix. However, fibers that ar too long tend to "ball" among the mix and create workability problems.

Some recent analysis indicated that exploitation fibers in concrete has restricted result on the impact resistance of the materials. This finding is improbably very important since traditionally, of us assume that plasticity can increase once concrete is bolstered with fibers. The results to boot indicated that the use of tiny fibers offers higher impact resistance thereto of longer fibers.

The High Speed one tunnel linings incorporated concrete containing one kg/m³ of plastic fibers, of diameter eighteen μm, giving the benefits noted below.

4. As a form of vital engineering material, steel fiber-reinforced concrete was used wide in applied science. Up to now, steel fiber-reinforced concrete was sometimes created by the normal combination methodology. For the explanation of uniform distribution of fiber, the reinforcement of mechanical properties of concrete was inadequately performed. during this paper, C50 steel fiber-reinforced concrete and C60 steel fiber-reinforced concrete were factory-made by ancient combination and moving combination strategies, severally, and then, the cube compression take a look at, flexural take a look at, ripping tensile take a look at, and therefore the bending take a look at were distributed. The reinforcement effects of mechanical properties were analyzed by comparison the normal combination and moving combination strategies. The results show that moving combination will effectively improve the distribution of steel fibers in concrete and may increase the density of steel fiber concrete, and so, it effectively improves the mechanical properties of steel fiber-reinforced concrete compared to the normal combination methodology.

You may suppose that corrosion in structures may be a simply a durability-related issue within the initial look. Well, that's removed from the reality. In fact, corrosion will directly have an effect on mechanical and structural properties of elements. Corrosion will have an effect on the world response of the structure. during this article, we'll review a number of the most structural effects of corrosion on steel structures and concrete structures.

Before we start, let’s review the fundamentals in corrosion science. Corrosion may be a chemical action, during which refined metals – steel in our case – revert back to their lower energy, a lot of natural and stable state of ore (iron oxides in our case). The phenomena is scientifically explained with the Law of Entropy. The reaction happens with losing steel material and manufacturing red rust, that is mostly four to seven times larger in volume.