Materials for making concrete 1/2/2019 Building Materials Sofia Sebastian

Introduction - Concrete Concrete is a composite construction material composed of cement (commonly Portland cement) and other cementitious materials such as fly ash and slag cement, aggregate (generally a coarse aggregate made of gravels or crushed rocks such as limestone, or granite, plus a fine aggregate such as sand), water, and chemical admixtures. 1/2/2019 Building Materials Sofia Sebastian

Introduction - Mortar Mortar Modern mortars are typically made from a mixture of sand, a binder such as cement or lime, and water. Mortar is a workable paste used to bind construction blocks together and fill the gaps between them. The blocks may be stone, brick, cinder blocks, etc. Mortar becomes hard when it sets, resulting in a rigid aggregate structure. 1/2/2019 Building Materials Sofia Sebastian

Introduction - Plaster Unlike mortar and cement, plaster remains quite soft after setting, and can be easily manipulated with metal tools or even sandpaper. suitable for a finishing, rather than a load-bearing material There are 3 types of plasters Gypsum (Plaster of Paris) Lime plaster Cement plaster Plaster is a building material similar to mortar or cement. Like those materials, plaster starts as a dry powder that is mixed with water to form a paste which liberates heat and then hardens 1/2/2019 Building Materials Sofia Sebastian

Gypsum Plaster/ Plaster of Paris Gypsum plaster, or plaster of Paris, is produced by heating gypsum to about 150 °C 2CaSO4·2H2O + Heat → 2CaSO4·½H2O + 3H2O (released as steam). When the dry plaster powder is mixed with water, it re-forms into gypsum. 1/2/2019 Building Materials Sofia Sebastian

Cement plaster Cement plaster Cement plaster is a mixture of suitable plaster, sand, portland cement and water which is normally applied to masonry interiors and exteriors to achieve a smooth surface. Interior surfaces sometimes receive a final layer of gypsum plaster.  1/2/2019 Building Materials Sofia Sebastian

Lime Plaster Lime Plaster To make lime plaster, limestone (calcium carbonate) is heated to produce quick lime (calcium oxide). Water is then added to produce slaked lime (calcium hydroxide), which is sold as a white powder. Lime plaster is a mixture of calcium hydroxide and sand (or other inert fillers). Carbon dioxide in the atmosphere causes the plaster to set by transforming the calcium hydroxide into calcium carbonate (limestone).  CaCO3 + Heat → CaO + CO2 CaO + H2O → Ca(OH)2 ( white powder) Ca(OH)2 + CO2 → CaCO3 + H2O 1/2/2019 Building Materials Sofia Sebastian

Composition of concrete Based on the composition , there are many types of concrete available Cement Water Aggregates Chemical admixtures 1/2/2019 Building Materials Sofia Sebastian

Cement – Portland cement Cement – adhesive and cohesive material capable of bonding together particles of solid matter into a compact durable mass. It has compounds of lime as their chief constituent. Its primary function is to bind the fine and coarse aggregates together. Portland cement is the most common type of cement - a basic ingredient of concrete, mortar, and plaster consists of a mixture of oxides of calcium, silicon and aluminium. Portland cement is made by heating limestone (a source of calcium) with clay, and grinding this product (called clinker) with a source of sulphate (most commonly gypsum). 1/2/2019 Building Materials Sofia Sebastian

Manufacture of Portland cement Cement is made from limestone, calcium, silicon, iron and aluminium, plus lesser amounts of other ingredients. Raw material process – The raw materials are collected, mixed together and ground in a grinding machine Burning process - This mixture is heated in large kilns to 1,482 degrees Celsius to form a product called clinkers, which roughly resemble marbles. Finishing process - These are ground to a powder and gypsum is added, creating the gray flour-like substance known as cement. 1/2/2019 Building Materials Sofia Sebastian

Aggregates – Fine aggregate “Fine   aggregate” are the aggregates whose size is less than 4.75 mm.  Example: Sand is used as fine aggregate in the preparation of concrete and cement mortar. For increased  workability  and for economy as reflected by use of less cement, the fine aggregate should have a rounded shape. The purpose of the fine aggregate is to fill the voids in the coarse aggregate and to act as a workability  agent. 1/2/2019 Building Materials Sofia Sebastian

Aggregates – Coarse aggregate Crushed stone or gravel used in concrete; will not, when dry, pass through a sieve with 6-millimeter diameter holes.  Coarse aggregates are the basic structural  members  of  the  concrete The coarse aggregate should have a rounded shape 1/2/2019 Building Materials Sofia Sebastian

Grading of aggregates Better the aggregate is graded (that is, the better the distribution of particles sizes), the more solidly all voids will be filled, and the denser and stronger will be  the  concrete. The voids between the larger coarse aggregate particles are filled by  smaller  particles.  The  voids  between  the smaller particles are filled by still smaller particles. Finally, the voids between the finest grains are filled  with  cement. 1/2/2019 Building Materials Sofia Sebastian

Water – Process of hydration Hydration – Process of combining water with a cementitious material to form a concrete paste which solidifies and hardens to rock-hard strength through a chemical process called hydration. Hydration involves many different reactions, often occurring at the same time. The cement paste glues the aggregate together, fills voids within it, and allows it to flow more freely. Less water in the cement paste will yield a stronger, more durable concrete; more water will give a freer-flowing concrete with a higher slump (fall or sink heavily). Impure water used to make concrete can cause problems 1/2/2019 Building Materials Sofia Sebastian

Water-cement ratio The water-cement ratio is one major factor influencing the strength of concrete. It is responsible for the porosity of the hardened cement paste. Water cement ratio is the water added to the cement quantity by weight w/c ratio should be from 0.4-0.6 1/2/2019 Building Materials Sofia Sebastian

Workability of concrete Workability is the ability of a fresh (plastic) concrete mix to fill the form/mold properly with the desired work (vibration) and without reducing the concrete's quality. Workability depends on water content Raising the water content or adding chemical admixtures will increase concrete workability. Excessive water will lead to increased bleeding 1/2/2019 Building Materials Sofia Sebastian

Admixtures The common types of admixtures are as follows. Accelerators – speed up the hydration of the concrete – CaCl2, NaCl Retarders - slow the hydration of concrete, and are used in large or difficult pours where partial setting before the pour is complete is undesirable - sugar Air- Entrainments - add and entrain tiny air bubbles in the concrete, which will reduce damage during freeze-thaw cycles thereby increasing the concrete's durability Plasticizers - increase the workability of plastic or "fresh" concrete Pigments – to add colour Corrosion inhibitors – to reduce corrosion for the reinforcement 1/2/2019 Building Materials Sofia Sebastian

Production of concrete Batching – measuring the quantity of cement, coarse aggregates, fine aggregates by weight or volume Mixing Transporting Placing Compacting Curing Finishing 1/2/2019 Building Materials Sofia Sebastian

Production of concrete Mixing – make the concrete mass homogenous and uniform – done by hand or machine Transporting Placing Compacting Curing Finishing 1/2/2019 Building Materials Sofia Sebastian

Production of concrete Transporting – concrete should be transported to the place of construction without the loss of homogeneity (max of 2 hours using trucks with agitator) Placing – placed with utmost care securing the homogeneity Compacting Curing Finishing 1/2/2019 Building Materials Sofia Sebastian

Production of concrete Compacting – consolidating the fresh concrete within the moulds, and around the steel reinforcement Curing - concrete slab retains moisture in the slab so that the concrete continues to gain strength. Finishing 1/2/2019 Building Materials Sofia Sebastian

Curing of concrete Curing time – 28 days Cement requires a moist, controlled environment to gain strength and harden fully Curing is the process where the concrete slab retains moisture in the slab so that the concrete continues to gain strength.  It delays drying shrinkage until the concrete is strong enough to resist shrinkage cracking. 1/2/2019 Building Materials Sofia Sebastian

Production of concrete Finishing – The concrete surface is roughened, cleaned and wetted. Over this a cement mortar of 1:3 is applied 1/2/2019 Building Materials Sofia Sebastian

Making of concrete 1/2/2019 Building Materials Sofia Sebastian

Properties of concrete -good Concrete has relatively high compressive strength, but significantly lower tensile strength, and as such is usually reinforced with materials that are strong in tension (often steel). It is durable It can be moulded into any form Concrete has a very low coefficient of thermal expansion, and as it matures concrete shrinks. It prevent steel from corrosion It is economical As it is heavy in weight, it is the ideal material for dam and retaining walls. 1/2/2019 Building Materials Sofia Sebastian