Questions about concrete and cement..

What is the difference between cement and concrete??

• Cement and concrete often are used interchangeably, but cement is actually an ingredient of concrete.
• Concrete is basically a mixture of aggregate and paste while aggregate are sand and gravel or crushed stone; the paste is water and portland cement. .
• Cement comprises from 10 to 15 percent of the concrete mix. Nonetheless, measuring exact volumes of the materials is difficult. Thus, the mix proportions are usually expressed as the weight of each material required in a unit volume of the concrete production,usually in kg/m.
• Through a process called hydration, the cement and water harden and bind the aggregates into a rocklike mass. This hardening process continues for years. This means that concrete gets stronger as it gets older.
• So, there is no such thing as a cement sidewalk or a cement mixer; the proper terms are concrete sidewalk and concrete mixer.

What does it mean to 'cure' concrete??

• Curing is one of the most important steps in concrete construction as the proper curing greatly increases concrete strength and durability.
• Concrete hardens as a result of hydration, which is the chemical reaction between cement and water. But, hydration occurs only if water is available and if the concrete's temperature stays within a suitable range.
• During the curing period, from 5 to 7 days after placement for conventional concrete, the concrete surfaces needs to be kept moist to permit the hydration process.
• New concrete can be wet with soaking hoses, sprinkles or covered with wet burlap, or can be coated with commercially available curing compounds, which seal in moisture.

Can it be too hot or too cold to place new concrete??

• Temperature extremes make it difficult to properly cure concrete.
• On hot days, too much water is lost by evaporation from newly placed concrete.
• If the temperature drops too close to freezing, hydration slows to nearly a standstill. Under these conditions, concrete ceases to gain strength and other desirable properties.
• so, the temperature of new concrete should not be allowed to fall below 10 ºC.

Will concrete harden under water??

• Portland cement is a hydraulic cement which means that it sets and hardens due to a chemical reaction with water. Consequently, it will harden under water.

How to make a BRICK....

Production process for cement

The production process for cement consists of drying, grinding and mixing limestone and additives like bauxite and iron ore into a powder known as “raw meal”. The raw meal is then heated and burned in a pre-heater and kiln and then cooled in an air cooling system to form a semi-finished product, known as a clinker. Clinker (95%) is cooled by air and subsequently ground with gypsum (5%) to form Ordinary Portland Cement (“OPC”). Other forms of cement require increased blending with other raw materials. Blending of clinker with other materials helps impart key characteristics to cement, which eventually govern its end use.The production process for cement consists of wet and dry process dry process .

The basic differences between these processes are the form in which the raw meal is fed into the kiln, and the amount of energy consumed in each of the processes. In the dry process, the raw meal is fed into the kiln in the form of a dry powder resulting in energy saving, whereas in the wet process the raw meal is fed into the kiln in the form of slurry. There is also a semi-dry process, which consumes more energy than the dry process but lesser than the wet process.

All J.K. Cement plants are dry process plants. Limestone is crushed to a uniform and usable size, blended with certain additives (such as iron ore and bauxite) and discharged on a vertical roller mill, where the raw materials are ground to fine powder. An electrostatic precipitator dedusts the raw mill gases and collects the raw meal for a series of further stages of blending. The homogenized raw meal thus extracted is pumped to the top of a preheater by air lift pumps. In the preheaters the material is heated to 750°C. Subsequently, the raw meal undergoes a process of calcination in a precalcinator (in which the carbonates present are reduced to oxides) and is then fed to the kiln. The remaining calcination and clinkerization reactions are completed in the kiln where the temperature is raised to between 1,450°C and 1,500°C. The clinker formed is cooled and conveyed to the clinker silo from where it is extracted and transported to the cement mills for producing cement. For producing OPC, clinker and gypsum are used and for producing Portland [Pozzolana] Cement (“PPC”), clinker, gypsum and fly ash are used. In the production of Portland Blast Furnace Stag Cement (“PSC”), granulated blast furnace slag from steel plants is added to clinker

Properties of AGGREGATE for concrete

Mechanical Properties

STRENGTH AND ELASTICITY

• Strength is a measure of the ability of an aggregate particle to stand up to pulling or crushing forces.
• Elasticity measures the "stretch" in a particle.

High strength and elasticity are desirable in aggregate base and surface courses. These qualities minimize the rate of disintegration and maximize the stability of the compacted material.

Bond

• Interlocking of aggregates and the hydrated cement paste
• Clean and rougher surface improve the bonding

Toughness

• Defined as resistance to failure by impact
• Determined by carrying out aggregate impact test
• Important for concrete used in road pavement

Hardness

The hardness of the minerals that make up the aggregate particles and the firmness with which the individual grains are cemented or interlocked control the resistance of the aggregate to abrasion and degradation.

• Soft aggregate particles are composed of minerals with a low degree of hardness.

Physical Properties

DENSITY AND SPECIFIC GRAVITY

• Density is the weight per unit of volume of a substance.
• Specific gravity is the ratio of the density of the substance to the density of water.

The density and the specific gravity of an aggregate particle is dependent upon the density and specific gravity of the minerals making up the particle and upon the porosity of the particle.

These can be defined as

1) All of the pore space (bulk density or specific gravity)

2) Some of the pore space (effective density or specific gravity)

3) None of the pore space (apparent density or specific gravity)

ABSORPTION, POROSITY, AND PERMEABILITY

The size, the number, and the continuity of the pores through an aggregate particle may affect the strength of the aggregate, abrasion resistance, surface texture, specific gravity, bonding capabilities, and resistance to freezing and thawing action.

· Absorption → the particle's ability to take in a liquid.

· Porosity → a ratio of the volume of the pores to the total volume of the particle.

· Permeability → the particle's ability to allow liquids to pass through.

SURFACE TEXTURE

• the pattern and the relative roughness or smoothness of the aggregate particle.
• affects the workability of hot mix asphalt, the asphalt requirements of hot mix asphalt, and the water requirements of portland cement concrete
• develop the bond between an aggregate particle and a cementing material.

rough surface texture→ produce a stronger bond, and thus creating a stronger hot mix asphalt or portland cement concrete.

PARTICLE SHAPE

Effect :

• The asphalt demands of hot mix asphalt
• The workability and the strength of both portland cement concrete and asphalt pavements

Best aggregates→ crushed stone / crushed gravel

Crushed aggregate→ have irregular, angular particles that tend to interlock when compacted or consolidated.

COATING

• a layer of substance covering a part or all of the surface of an aggregate particle.
• could even increase the quantity of bonding agent required in the mixture.
• prevent a good bond from forming between the aggregate surfaces and the cementing agent.(Coating should be removed )

Natural coating→ mineral deposits formed in sand and gravel by ground water

Artificial coating→ dust formed by crushing and handling

Types Of Portland Cement

Portland cement is the most commonly used type of cement in the world today. Portland cement can be found in both concrete and mortar, not to mention other construction medium such as stucco and some types of grout, where it acts as a binding agent. On a chemical level, Portland cement is a fine powder comprised of a minimum of 66% calcium silicate, with the remainder largely being a mix of aluminum, and iron. Portland cement is a hydraulic material, which requires the addition of water in order to form exothermic bonds, and is not soluble in water.

Type 1. Ordinary Portland Cement (OPC)
-The most common type of cement and referred to as general purpose Portland cement.
-Unless is specified as being of another type, it is normally safe to assume
-Is suitable for most construction applications,especially those in which the cement will not be in contact with or buried in the ground.
-The least expensive




Type 2. Rapid-Hardening Portland Cement (RHPC)
This is similar in price to Type1 cement, but it has higher sulfate resistance, and is therefore more suitable for applications in which concrete will come in contact with the ground, or be buried in the ground.
*i. Having higher C3S and lower C2S content in the cement.
  ii.Grinding the cement clinkers to finer particles.

Type3. Ultra-high early strength Portland Cement 
-Develops strength quickly, but is slightly less strong in the long run than other types of Portland cement.
-Used in applications where quick hardening and strength is required.
(Concrete made with this cement achieves the 3 days strength of rapid hardening cement in 16 hours and its 7 days strength in 24 hours.)




Type4. Low-heat Portland cement
-Has low heat of hydration, which simply means that it gives off less heat as it sets and hardens than other types of Portland cement.
-Sets very slowly,but it much stronger after curing than other types of cement.
-Required for thick concrete work




Type5. Sulphate resisting Portland Cement
-used where there is presence of sulphates (sulfates) from external sources
e.g in industrial wastes, sulphate bearing soils and in sewage wastes.
-Sulphates react chemically with the hydration products of calcium aluminates,causing cracking
-The solution is to reduce tricalcium aluminate(C3A) in the cement during manufacture (not exceeding3.5%)

White Portland Cement
-the grey color of Portland cement is due to ferrite(C4AF)in the limestone or clay
-white cement is made from white china clay
-white cement is more expensive than normal Portland cements.




Portland blast-furnace cement
-adding about 30-35% by weight blast furnace slag to ordinary Portland cement clinker before grinding.
-the rate of hardening of this cement in the first 28days and the heat evolved is less, so the cement is not suitable for use at low curing temperatures.
-the strength of mature concrete is the same with concrete made from ordinary Portland cement






Pozzolanic cement
-made from pulverized fuel ash and opc
-low heat cement (initially slower in hardening but attains strength equal to that of OPC after 3 months)
-good resistance to sea water and sulphates

Aggregates

Aggregates are inert granular materials such as sand, gravels or crushed stone that, along with water and portland cement, are an essential ingredient in concrete. For a good concrete mix, aggregates need to be clean, hard, strong particles free of absorbed chemicals or coatings of clay and other fine materials that could cause the deterioration of concrete. Aggregates, which account for 60 to 75 percent of the total volume of concrete, are divided into two distinct categories-fine and coarse. Fine aggregates generally consist of natural sand or crushed stone with most particles passing through a 3/8-inch(9.5-mm) sieve. Coarse aggregates are any particles greater than 0.19 inch(4.75mm), but generally range between 3/8 and 1.5 inches(9.5mm to 37.5mm) in diameter. Gravels constitute the majority of coarse aggregate used in concrete with crushed stone making up most of the remainder.

Natural gravel and sand are usually dug or dredged from a it, river, lake or seabed. Crushed aggregate is produced by crushing quarry rock, boulders, cobbles or large-size gravel. Recycled concrete is a viable source of aggregate and has been satisfactorily used in granular subbases, soil-cement and in new concrete. Aggregate processing consists of crushing, screening and washing the aggregate to obtain proper cleanliness and gradation. If necessary, a benefaction process such as jigging or heavy media separation can be used to upgrade the quality.

Once processed, the aggregates are handled and stored in a way that minimizes segregation and degradation and prevents contamination. Aggregates strongly influence concrete's freshly mixed and hardened properties, mixture proportions and economy. Consequently, selection of aggregates is an important process. although some variation in aggregate properties is expected, characteristics that are considered when selecting aggregates include:

• grading
• durability
• particle shape and surface texture
• abrasion and skid resistance
• unit weights and voids
• absorption and surface moisture

Grading refers t the determination of the particle-size distribution for aggregates. Grading limits and maximum aggregate size are specified because grading and size affect the amount of aggregate used as well as cement and water requirements, workability, pumpability and durablity of concrete. In general, if the water-cement ratio is chosen correctly, a wide range in grading can be used without a major effect on strength. When gap-graded aggregate are specified, certain particle sizes of aggregate are omitted from the size continuum. Gap-graded aggregate are used to obtain uniform textures in exposed aggregate concrete. Close control of mix proportions is necessary to avoid segregation.

SHAPE AND SIZE MATTER

Particles shape and surfaces texture influence the properties of freshly mixed concrete more than the properties of hardened concrete. Rough-textured, angular and elongated particles require more water to produce workable concrete that smooth, rounded compact aggregate. Consequently, the cement content must also be increased to maintain the water-cement ratio. generally, flat and elongated particles are avoided or are limited to about 15 percent by weight of total aggregate. Unit-weight measures the volume that graded aggregate and the voids between them will occupy in concrete. The void content between particles affects the amount of cement paste required for the mix. Angular aggregate increase the void content. Larger sizes of well-graded aggregate and improved grading decrease the void content. absorption and surface moisture of aggregate are measured when selecting aggregate because the internal structure of aggregate is made up of solid material and voids that may or may not contain water. The amount of water in the concrete mixture must be adjusted to include the moisture conditions of the aggregate. Abrasion and skid resistance of an aggregate are essential when the aggregate is to be used in concrete constantly subject to abrasion as in heavy-duty floors or pavements. Different minerals in the aggregate wear and polish at different rates. Harder aggregate can be selected in highly abrasive conditions to minimize wear.

Limestone quarry

10 mm graded crushed rock aggregate, used in concrete, called " blue metal" in Australia

20mm graded aggregate

Concrete Water Curing Process - Bass Fishing Manufacturing Building - Wa...

Concrete Curing and Sealing

Curing Process Of Concrete

What is CURING ?

Curing is the process of controlling the rate and extent of moisture loss from concrete during cement hydration (Hydration means the chemical combination of cement and water). Since the hydration of cement does take time – days, and even weeks rather than hours – curing must be undertaken for a reasonable period of time if the concrete is to achieve its potential strength and durability.

When to cure?
Curing is done just after finishing the concrete surface, as soon as it will not be damaged. However, In hot and/or windy weather a concrete mix may stiffen rapidly and not be workable. IN COLD WEATHER Frozen or very cold water will also slow down the setting time which can cause costly delays. In extremely cold weather water turns to ice, EXPANDS and can CRACK hardened concrete. In these conditions, we must take extra care while curing.

How to cure?
In hot weather : Keep the concrete continuously moist.

Method 1 →APPLYING WATER
Put a continuous fine, misty spray of water over the concrete or else it will damage the surface of the concrete.

Method 2 →PLASTIC SHEETS

Slow down water loss. The sheets must be held down to stop them blowing away and the concrete surface drying out. The sheets also can be overlapped and stuck together or held down with sand, timber or bricks to prevent them blowing away. We must always check under the plastic from time to time to make sure the concrete is evenly moist. If it feels dry, sprinkle with water and put back the plastic sheets carefully.

Method 3→MEMBRANE-FORMING CURING COMPOUNDS
Curing compounds are liquids which are usually sprayed directly onto concrete surfaces and which then dry to form a relatively impermeable membrane that retards the loss of moisture from the concrete.

Method 4→WET COVERINGS

Fabrics such as hessian, or materials such as sand, can be used like a ‘mulch’ to maintain water on the surface of the concrete. On flat areas, fabrics may need to be weighed down. Also, it is important to see that the whole area is covered. Wet coverings should be placed as soon as the concrete has hardened sufficiently to prevent surface damage. They should not be allowed to dry out as they can act as a wick and effectively draw water out of the concrete.

How Long To Cure?
Concrete keeps getting HARDER AND STRONGER over TIME. Household concrete jobs MUST be cured for AT LEAST 3 DAYS while for better strength and durability, cure concrete for 7 DAYS. The longer concrete is cured, the closer it will be to its best possible strength and durability.

Types of Bricks

Types of Bricks

     Bricks are made in 4 materianls :

• Burnt/fired clay
• Calcium silicate
• Dense concrete
• Lightweight concrete

     6 types of bricks : 

• Facing Bricks,
• Commons  Bricks ,
• Engineering  Bricks ,
• Concrete or Calcium Silicate Bricks,
• Reclaimed Bricks 
• Specials  Bricks .

Facing Bricks

•  Attractive appearance 
•  good quality and durability

Wirecut Bricks

•  Have variations of colour and texture in the bricks.

Stock  Bricks

• An irregular shape
• More expensive than wirecuts bricks.

Handmade  Bricks

• Handmade bricks is the most expensive bricks compare to facing bricks because it has a specified value.

Fletton Bricks

• Also called as "London Bricks"
• The main ingredients of fletton bricks is coal traces because it can reduce the quantity of fuel demand for the kiln.
• Fletton bricks helps us to keep down the cost

Commons Bricks

• Useful rather than attractive.

Engineering Bricks

• Not very pretty but tough
• Strong and hard-wearing
• Good resistance to frost and to water

Concrete or Calcium Silicate Bricks

• Scarce is a good making clay and it cost is cheapest.

Reclaimed Bricks

• Is kind of salvaged bricks which is reclaimed from the old building and cleaned up for a new fashion design.

Specials Bricks

•  Has a wonderful design possibility and make brickwork in a tasteful way.

Portland cement

THE PRODUCTION PROCESS OF CEMENT

Production Process of Cement

chalk & clay  + water ------> slurry or dried powder

 the slurry or dried powder will undergo wet process or dry process

WET PROCESS

1.) Slurry fed into higher end of inclined rotary kiln.

2.) Heated as mixture passes down the kiln under combination of action of rotation and gravity.

3.) Mixture under increasing temperature as it passes down the kiln undergoes four physical and chemical changes.

i. Drying

ii. Preheating

iii. Calcining

iv. Clinkering

DRY PROCESS

1.) Dried powder preheated and some calcining in heat exchanges.

2.) Mixture fed into the higher end of inclined rotary kiln.

3.) Mixture undergoes two chemical changes with increasing temperature.

i. Calcining

ii. Clinkering 

( part 1)

( part 2 )

Cement, how it is made.

Cement

~Cement~
Concrete is a compound material made from sand, gravel and cement. The cement is a various minerals which when mixed with water, hydrate and rapid become hard binding the sand and gravel into a solid mass. Cement can be used to bind two materials together e.g wood, brick, tiles etc.

The first recorded use of cement was by the Egyptians, who used it to built their pyramids, in around 2500 BC. They used mud mixed with straw to bind dried bricks made from clay. They also used gypsum mortars and mortars of lime in the pyramids. In the later periods of civilization, volcanic materials were ground with lime and sand to produce better cement. The Romans from 300BC found that by mixing a pink sand like material which they obtained from Pozzuoli with their normal lime-based concrete they obtained a far stronger material. The pink sand turned out to be fine volcanic ash and they had inadvertently produced the first 'pozzolanic' cement. The Romans used pozzolana cement near Mt.vesuvius to build the Appian Way, Roman baths, Coliseum, Pantheon in Rome and Pont du Gard aqueduct in South France. They were the first who invented what today we called hydraulic cement-based concrete. In 1824, Joseph Aspdin of England invented Portland cement by burning finely ground chalk with finely divided clay in lime kiln until carbon dioxide was driven off. The sintered product was then ground and he called it Portland cement, name after the high quality building stones quarried at Portland, England. Today, the term is generally synonymous with Portland Cement, which is one of several cement types produced.

Good quality concrete (a strong hard building material composed of sand, gravel, cement and water ) has many advantages that add to its popularity. First, it is economical when ingredients are readily available. Concrete's long life and relatively low maintenance requirements increase its economic benefits. Concrete is not as likely to rot or decay as other building materials. Concrete has the ability to be molded or cast into almost any desired shape. Building of the molds and casting can occur on the work-site, which reduces cost.

In Malaysia, infrastructure projects using cement as a building material (for example highways, dams, airports,housing area, office buildings) are the foundation of our future growth. Cement is an important means for everyday life of human beings and is widely use in all building throughout the world.

Exterior concrete

CONCRETE HOMES

LANDSCAPE BORDERS

WATER FEATURES

CONCRETE PATIOS

CONCRETE POOL DECKS