Building Materials PDF

Chapter 3: Building Materials 3.1. Introduction Construction or building materials are any materials that are used in the construction work. They are of two major categories: natural and synthetic. Natural materials are like aggregates,sand, stones and wood are natural, while c...

Chapter 3: Building Materials 3.1. Introduction Construction or building materials are any materials that are used in the construction work. They are of two major categories: natural and synthetic. Natural materials are like aggregates,sand, stones and wood are natural, while cement, bricks, steel, concrete, or plastics are synthetic. 3.2. Aggregate Aggregates give the concrete its form and reduce its shrinkage.Aggregates represent about 70 to 80 % of concrete volume. Aggregates are classified according to shape and size. The shape of the aggregates is determined not only by the parent rock but also by the crushing machine used. According to shape, aggregates can be rounded, irregular or partly rounded, angular, flaky, elongated, and flaky and elongated aggregates. According to size, Aggregates are either fine (sand)or coarse (gravel)aggregates 3.3. Bricks Bricks are building materials used to build walls or paving roads. They can be connected using mortar., adhesives or by interlocking them. Bricks can be classified according to quality or the building process. Based on quality there are first, second and third class bricks. First class bricks have standard size, regular shape, uniform yellow or red color, and well burnt. Second class bricks almost have the same characteristics like first class except that the burning temperature is slightly lower than first class. Unlike first and second class, the third class has irregular shape and size, the color is soft and light red and is under burnt. According to building process, Bricks are classified into unburnt bricks, burnt bricks and over burnt bricks. 3.4. Lime Lime is used in construction workS as lime mortar. Lime can be hydraulic or non-hydraulic lime. The difference between these two types is that hydraulic lime sets under water but non-hydraulic lime do not set underwater. Quick Lime is a non-hydraulic lime manufactured by burning calcium carbonate containing lime stones. Lime used in construction works should exhibit good plasticity, should be flexible and easily workable, and should harden in short time. 3.5. Cement Cement is a fine powder which sets after a few hours when mixed with water, and then hardens in a few days into a solid, strong material. Cement is mainly used to bind fine sand and coarse aggregates together in concrete. Cement is a hydraulic binder, i.e. it hardens when water is added. Portland cement is made of lime stone (CaCO;) and clay (Kaolin Al,0,SiO,.2H,0) and some iron oxides (Fe,0;). Cements are classified as non-hydraulic or hydraulic, based on the ability of the cement to set in the presence of water. Non-hydraulic cement does not set in the presence of water. Oppositely, it sets as it dries and reacts with carbon dioxide in the air. It is resistant to attack by chemicals after setting. Hydraulic cements (e.g., Portland cement) set in the presence of water because of the formation of water insoluble metal hydrates. 3.5.1.Production of Portlandcement Basically, the cement production process involves two main steps; clinker formation step and cement formulation step. Clinker is produced by mixing the cement raw materials at high temperatures, up to 2000 "C,in a rotary kiln. The presence of some ferric oxide in the mixture of the raw materials helps in the formation of the clinker at lower temperatures (around 1300°C). Afterwards, the formed clinker is crushed and grinded in a cement grinding mill. Some additives, such as calcium sulphate or limestone, are grinded in a cement grinding mill too, leading to a fine and homogenous cement powder. The cement is then stored in storage tower before being shipped either in bulk or bagged. Clinker consists of four main phases: 1. C3S: Tri Calcium Silicate (Alite)(3CaO-SiO2) 2. C2S: Di Calciun Silicate (Belite) (2CaO-Si02) 3. C3A: Tri Calcium Aluminate (celite) (3CaO-AlI203) 4. CAAF: Tetra Calcium Alumino Ferrite (Brownmillerite)(4CaO-Al203-Fe203). The silicates are responsible for the cement's mechanical properties, the tricalcium aluminate and Tetra Calcium Alumino Ferrite are essential for the formation of the liquid phase during the burning process of clinker in the kiln. First, the limestone (calcium carbonate) is burned to eliminate its carbon, creating lime (calcium oxide) in what is known as a calcination reaction. This single chemical reaction is a main source of global carbon dioxide emissions. CaCO3 CaO +CO, The lime reacts with SiO, to yield dicalcium silicate and tricalcium silicate. 2CaO +Si02 2CaO-Si02 3CaO +Si02 3CaO-Si02 The lime also joins with aluminum oxide to produce tricalcium aluminate. 3CaO +AI203 3CaO-A1203 The lime also unifies with aluminum Oxide, and ferric oxide to give cement. 4CaO + A1203 + Fe203 4CaO-A1203-Fe203 (cement)  clay ime stone Concentration by fitrstion Aotary urnace oushing Ymaing Wet grinding Cooling ai cooing Cinker storaor Pucking Grinding and powder contro Fig. 2 Cement production steps 3.5.2.Main tests for cement quality: 5. Magnesium oxide percentage: This percentage should not exceed 5%, since its increase means that the quality of the used limestone is poor. Magnesia is rather refractory and does not take part in the cement reactions. 6. Powder size a yaill The prepared cement should be very fine, such that at least 98% of it should pass through mesh 200 (200 pinch per linear inch). 7. Setting time: This test is done to test the speed of cement solidification. For this purpose, samples of cement are mixed with standard amounts of water. In this test, the time at which a standard needle loaded with a standard weight cannot penetrate the prepared sample is measured. 8. Date of Manufacturing It is very important to check the manufacturing date because the strength of cement decreases with time. It's better to use cement before 3 months from the date of manufacturing. 3.6. Concrete A good quality concrete is basically a heterogeneous mixture of cement, coarse and fine aggregates and water which combines into a hard mass due to chemical action between the cement and water. In concrete production, each component has its specific role. The coarser aggregates (gravel) acts as fillers. The fine aggregates (sand) occupy the holes between the paste and the gravel. The cement with water acts as a binder. 3.6.1. Properties of Fresh Concrete: Concrete should preserve its fresh form the time it mixed until the time it compacted. The properties of the fresh concrete are very critical because it affects its quality after being hardened. Concrete consistency, workability, and settlement and bleeding are important properties that should be taken into account when working with concrete. 1. Concrete consistency Concrete consistency reflects the stiffness or sloppiness or the concrete fluid. For good handling, placing and compacting of the concrete, consistency must be the same for each batch. 2. Concrete workability The workability of a concrete is a measure of how easy a concrete can be placed, compacted and finished without parting of the individual materials. Workability is not the same thing as consistency. Workability is size dependent property; concrete mixes made up with smaller stones are more workable than that with larger stones.  3. Settlement and Bleeding Cement and aggregate particles are three times denser than water. Therefore, in concrete mix they have a tendency to to settle and displace mixing water which moves upward the concrete surface. This upward movement of mixing water is known as bleeding; from the rest of the concrete is called water that splits bleed water.