The Many Uses of Ready-Mix Concrete

The Many Uses of Ready-Mix Concrete

Concrete is a popular building material. You can see it in homebuilding sites, commercial building sites and government projects such as bridges and highways. It is easier to complete big projects like these by using ready-mix concrete. Completing projects on a tight deadline is possible and achieved in less than half the time it would when not using this product.

Ready-mix concrete comes from manufacturers and plants ready for delivery and mixing at work or project sites. With the use of a concrete mixer, one can get a precise mixture of concrete for the project. Using this type of cement material eliminates too much confusion at the work site. It also saves considerable amount of time because it requires less time to prepare than concrete prepared from scratch.

Cements, sands, aggregates (gravels) and water are the main contents of the mixture. It has the same ingredients as the ones that are not except that instead of carrying and mixing the raw materials at the site, the ready-mix arrives at the site on mixer trucks already pre-mixed and ready to use. Adding different additives and aggregates offsite and then delivering onsite for a different project based upon the specification of the customer is another feature of the ready-mix concrete. Different textures, finishes and colors are also available in ready-mix form.

Using ready-mix concrete eliminates having to carry and mixing the materials on site, which is a painstaking process. It eliminates errors that come with wrong measurement of water and the concrete materials. Using ready-mix saves time and effort. Big projects take less time to complete after pouring in the mixture using the transit mixer. The quality of the product is also much better than those that come in a non-ready mixed form.

Ready-mix concrete has a big potential in a lot of building projects. Aside from using it on big infrastructure projects such as building bridges, highways and huge buildings, we see this type of concrete as the choice of homeowners when building driveways, walkways made of concrete. Some homeowners choose concrete for their kitchen and bathroom countertops and as floorings. Stained concrete floors and counters provide a rustic look and patina adding more character to the interior of the home.

When using ready-mix concrete one must work with caution. One must ensure that there is enough space for the transit mixer. In addition, the location should be strong enough to handle the weight of the transit mixer and the concrete. The workers practice caution when working with the concrete mixer, by avoiding standing near the way of the mixer, especially when operating and pouring concrete. Accidents can and do happen which can endanger the well-being of the workers.

Characteristics of sand

Characteristics of sand

·     It should be chemically inert

·     It should be clean and coarse. It should be free from organic matter.

·     It should contain sharp, angular and durable grains.

·     It should not contain salts, which attract the moisture from atmosphere.

·  It should be well graded (i.e.) should contain particles of various sizes in suitable proportions.

Sand

Sand

Sand is an important building material used in the preparation of mortar, concrete, etc.

·     Sources of Sand: Sand particles consist of small grains of silica (Si02). It is formed by the decomposition of sand stones due to various effects of weather. The following are the natural sources of sand.

·     Pit Sand: This sand is found as deposits in soil and it is obtained by forming pits to a depth of about 1m to 2m from ground level. Pit sand consists of sharp angular grains, which are free from salts for making mortar, clean pit sand free from organic and clay should only be used.

·     Rive Sand: This sand is obtained from beds of rivers. River sand consists of fine rounded grains. Color of river sand is almost white. As the river sand is usually available in clean condition, it is widely used for all purposes.

·     Sea Sand: This sand is obtained from sea shores. Sea sand consists of rounded grains in light brown color. Sea sand consists of salts which attract the moisture from the atmosphere and causes dampness, efflorescence and disintegration of work. Due to all such reasons, sea sand is not recommendable for engineering works. However be used as a local material after being thoroughly washed to remove the salts.

Uses of Cement

Uses of Cement

1. Cement mortar for masonry work, plaster, pointing etc.

2. Concreter for laying floors, roofs and constructing lintels, beams, weather sheds, stairs, pillars etc.

3. Construction of important engineering structure such as bridges, culverts, dams, tunnels storage reservoirs, light houses, deckles etc.

4. Construction of water tanks, wells, tennis courts, septic tanks, lampposts, roads, telephone cabins etc.

5. Making joints for drains, pipes etc.

6. Manufacture of pre cast pipes, piles, garden seats, artificially designed urns, flowerpots, etc dustbins, fencing posts etc.
7. Preparation of foundations, watertight floors, footpaths etc.

Types of Cement

Types of Cement

In addition to ordinary cement, the following are the other varieties of cement.

·     Acid Resistance Cement : This is consists of acid resistance aggregates such as quartz, quartzite’s, etc, additive such as sodium fluro silicate (Na2SiO6) and aqueous solution of sodium silicate. This is used for acid-resistant and heat resistant coating of installations of chemical Industry. By adding 0.5 percent of unseed oil or2 percent of ceresil, its resistance to water is increased and known as acid water resistant cement.

·     Blast Furnace Cement: For this cement slag as obtained from blast furnace in the manufacture of pig iron and it contains basic elements of cement, namely alumina, lime and silica. The properties of this cement are more or less the same as those of ordinary cement and prove to be economical as the slag, which is waste product, is used in its manufacture.

·     Colored Cement: Cement of desired color may be obtained by intimately mixing mineral pigments with ordinary cement. The amount of coloring may vary from 5 to 10 percent and strength of cement if it is exceeds 10 percent. Chromium oxide gives brown, red or yellow for different proportions. Colored cements are used for finishing of floors, external surfaces, artificial marble, windows.

·     Expanding Cement : This type of cement is produced by adding an expanding medium like sulpho – aluminate and a stabilizing agent to ordinary cement. Hence this cement expands where as other cement shrinks. Expanding cement is used for the construction of water retaining structures and also for repairing the damaged concrete surfaces.

·     High alumina Cement: This cement is produced by grinding clinkers formed by calcining bauxite and lime. The total content should not be less than 32 percent and the ratio by weight of alumina to lime should be between 0.85 and 1.30.

Functions of Ingredients in Cement

Functions of Ingredients in Cement

1.Lime : Lime is the important ingredient of cement and its proportion is to be maintained carefully. Lime in excess makes the cement unsound and causes the cement to expand and disintegrate. On the other hand, if lime is in deficiency the strength of the cement is decreased and it causes cement to set quickly.

2. Silica : This also an important ingredient of cement and it gives or imparts quick setting property to imparts strength to cement.

3. Alumina : This ingredient imparts quick setting properly to cement. Express alumina weakens the cement.

4. Calcium Sulphate : This ingredient is in the form of gypsum and its function is to increase the initial setting time of cement.

5. Magnesia : The small amount of this ingredient imparts hardness and color to cement.

6. Sulphur : A very small amount of sulphur is useful in making sound cement. If it is in excess, it causes the cement to become unsound.

7. Alkalies : Most of the alkalies present in raw material are carried away by the flue gases during heating and only small quantity will be left. If they are in excess in cement, efflorescence is caused.

About Cement

About Cement

Cement in its broadest term means any substance which acts as a binding agent for materials natural cement (Roman Cement) is obtained by burning and crushing the stones containing clay, carbonates of lime and some amount of carbonate of magnesia. The clay content in such stones is about 20 to 40 percent. Natural cement resembles very closely eminent hydraulic lime. It is not strong as artificial cement, so it has limited use in practice.

Artificial cement is obtained by burning at very high temperature a mixture of calcareous and argillaceous materials in correct proportion. Calcined product is known as clinker. A small quantity of gypsum is added to clinker and it is then pulverized into very fine powder is known as cement. Cement was invented by a mason Joseph Aspdin of leeds in England in 1824. The common variety of artificial cement is known as normal setting cement or ordinary cement or Portland cement.

Manufacture of bricks

Manufacture of bricks

To minimize breakages in cold weather, increase the cement content of the mix or the curing period before moving blocks.

Ordering and stockpiling materials

Aggregates and cement should be ordered in good time. Stocks should be sufficient to prevent stoppages due to lack of material.

As a rough guide, using an aggregate: cement ratio of 8:1 by loose volumes, three and a half bags of cement and a cubic meter of aggregate will be enough to make about 400 bricks. The number of blocks produced from the same quantity of material will depend on block size and whether they are solid or hollow.

Aggregates must be stockpiled in such a way that contamination is prevented and mixing of different types is prevented.

Cement must be stored in such a manner that it is kept dry. Cement in bags should be used within one month of being delivered.

Batching

Cement, if supplied in bags, should preferably be batched by the full bag. Cement supplied in bulk may be weighed (preferable) or batched by loose volume (not recommended).

It is important to batch all materials accurately. Batching containers, e.g. wheelbarrows, buckets, drums and wooden boxes, should be loosely filled to the brim and struck off flush with it. To avoid errors, there should be enough containers for a full batch to be made without using any container more than once. Dented or broken containers must not be used. The amount of water to be added to the mix is judged by eye and by doing some simple tests

Water content

Water content is critical. The mixture must be wet enough to bind together when compacted, but it should not be so wet that the blocks slump (sag) when the mould is removed. A common mistake is the use of mixes that are too dry, resulting in incomplete compaction. The moisture content should be as high as possible as this allows better compaction and thus gives the best strength.

Mixing

Hand mixing with the use of shovels should be done on a level concrete slab or steel plate.

First spread the sand out 50 to 100 mm thick. Then distribute the cement, and stone if any, evenly over the sand. Mix aggregate and cement until the color is uniform. Spread the mixture out,

sprinkle water over the surface and mix. Continue with this process until the right amount of water has been mixed in.

Molding

Hand operated machines should be used as instructed by the manufacturer.

The mould of a powered machine should be filled until approximately six to eight cycles of compaction are required to bring the compacting head to its stops. Too little or poor compaction should be avoided as it results in greatly reduced strengths.

Curing

Curing is the process of maintaining a satisfactory moisture content and a favorable temperature in the blocks to ensure hydration of the cement and development of optimum strength.

Bricks

Bricks

Bricks are obtained by moulding clay in rectangular blocks of uniform size and then by drying and burning these blocks. As bricks are of uniform size, they can be properly arranged, light in weight and hence bricks replace stones.

Composition Manufacture Process.

Composition – Following are the constituents of good brick earth.

Alumina : - It is the chief constituent of every kind of clay. A good brick earth should contain 20 to 30 percent of alumina. This constituent imparts plasticity to earth so that it can be molded. If alumina is present in excess, raw bricks shrink and warp during drying and burning.

Silica -A good brick earth should contain about 50 to 60 percent of silica. Silica exists in clay either as free or combined form. As free sand, it is mechanically mixed with clay and in combined form; it exists in chemical composition with alumina. Presence of silica prevents crackers shrinking and warping of raw bricks. It thus imparts uniform shape to the bricks. Durability of bricks depends on the proper proportion of silica in brick earth. Excess of silica destroys the cohesion between particles and bricks become brittle.

Lime– A small quantity of lime is desirable in finely powdered state to prevents shrinkage of raw bricks. Excess of lime causes the brick to melt and hence, its shape is last due to the splitting of bricks.

Oxide of iron - A small quantity of oxide of Iron to the extent of 5 to 6 percent is desirable in good brick to imparts red colour to bricks. Excess of oxide of iron makes the bricks dark blue or blackish.

Magnesia - A small quantity of magnesia in brick earth imparts yellow tint to bricks, and decreases shrinkage. But excess of magnesia decreases shrink leads to the decay of bricks.

The ingredients like, lime, iron pyrites, alkalies, pebbles, organic matter should not present in good brick earth

Grading of Aggregates

Grading of Aggregates

Grading of aggregates consists of proportioning the fine and coarse aggregates in such a ratio, so as to get strongest and densest mix with the least amount of cement. Grading the aggregates is so graded as to have minimum voids when mixed with all ingredients, and water should render a concrete mass of easy workability.

The grading of aggregates are done by the following methods

·     By trail – In this method, proportioning of aggregates as to give heaviest weight for same volume, yield the densest concrete

·     By finesse modules method (sieve analysis method): in this method, the samples of both coarse and fine aggregates are passed through a set of nine standard sieve and the percentage of sample retained on each of the said sieves is determined. The total of these percentages divided by 100 gives the finesses modulus of sample

·     By minimum voids method: This method is based on the fact, that so obtain dense concrete the quantity of cement should also be slightly in excess of voids more that the fine aggregates. In this method the voids in the fine and coarse aggregates are separately found out with the help of graduated cylinder and water. The percentage of voids I aggregate, “X” given by the equation.

X = (V1 – V2) x 100

                                                                                       V2

Where v1, volume of water filled

Where v2, volume of aggregates.

·     By arbitrary standards: It is a commonly adopted method of propitiating the aggregates in a concrete mix for small works of moderate importance. This method is not recommended for large works or important works in this method, the volume of cement, sand and coarse aggregates are taken in the proportion of 1:n:2n respectively. The quantity of water to be used a varied suit the workability descried.

Ex:                           1:1:2 M250 rich mix for columns, beams

                                   1:1:3 – M200 Water retaining structures etc

                                  1:3:6 – M150 slab’s columns roads etc

                                  1:3:6 – M100 – foundations,

                                   1:4:8 - For mass concrete.

Aggregates as Building & Construction Materials

Aggregates as Building & Construction Materials

Aggregates - Grading: Aggregates is derived from igneous, sedimentary and metamorphic rocks or is manufacture from clays, slag etc. The properties of concrete are directly related to those of its constituents and should be hard, strong, durable, and free from clay, loam, vegetables and other such foreign matters. The presence of clay or dirt coating prevents the adhesion of cement on the surface of aggregates and ultimately retards the setting and hardening of cement and reduces the strength, durability and soundness of concrete. Depending upon their size, the aggregates are classified as (i)Fine Aggregative (ii) coarse aggregates.

Fine Aggregates: The material, most of when passes through 4.75mm I.S. sieve size, is termed as fine aggregates. It should not contain more than 1 to 8% of fine particles, which may be obtained from sea, river, lake or pit may be used as fine aggregates but care should be taken all its impurities must be removed.

Coarse Aggregates: The material whose particles are of such size as are retained on 4.75mm, I.S sieve are called coarse aggregates. The size of the coarse aggregates used depends upon the nature of work. The maximum size may be 23mm for mass concrete such as dams etc. and 63mm for plain concrete. Crushed hard stone and gravel is the common materials used as coarse aggregates for structural concretes. Coarse aggregates usually obtained by crashing granite, gneiss, crystalline lime stone and good variety of sandstone etc.

Advantages of artificial stones

Advantages of artificial stones

1.Cavities may be kept in artificial stones to convey pipes, electric wires etc.

2.Grooves can be kept in artificial stone while it is being cast which are useful for fixing various fittings.

3.It can cast in desired shape

4.It can be made in a single piece and hence trouble of getting large blocks of stone for lintels, beams etc is avoided.

5.It can be made stronger than natural stone

6.It is cheap and economical

7.It is more durable than natural stone

8.Natural bed is absent in artificial stones and hence, the question of taking precautions with respect to the natural bed of stones does not arise.

Characteristics of stones

Characteristics of stones

In order to ensure suitable selection of stone of particular work, one must be conversant with its composition, characteristics, uses and place of availability.

Granite

1. Igneous rock

2. Composed of quart, felspar and mica and minerals

3. Available in grey, green, brown and pink and red

4. Hard and durable

5. High resistance to weathering

6. The texture varies with its quality

7. Specify gravity 2.7 and compressive strength 700 to 1300kg/cm2

8. Used for ornamental, road metal, railway ballast, aggregate for concrete; for construction of bridges, piers and marine works etc.

Balast

1. Igneous rock

2. It is compact, hard and heavy

3.Available in red, yellow grey, blue and greenish black color

4. Specific gravity is 3 and compressive strength varies 1530 to 1890 kg/cm2.

5. Used for ornamental, rail road ballast, aggregates for concrete etc.

Sand Stone

1.Sedimentary rock

2.It is available in variety of formations fine grained, coarse grained compact or porous

3.Available in white, green, blue, black, red and yellow.

4.Specific gravity 2.65 to 2.95

5.Compressive strength is 650kgs / cm

6.Used for ashlars works

Lime Stone

1. Sedimentary rock: It is available in a variety of forms which differ from one another in color Compaction, texture, hardness and durable

a. Compact lime stone

b. Granular lime stone

c. Magnesia lime stone

d. Kanker lime stone

f. Used for paving, road metal, etc

Artificial stones: These are also known as cast stones or reconstructed stones. Artificial stones may take up various forms such as

a. Cement concrete: This is the mixture of cement, fine aggregates, coarse aggregates and water. It may be cast in site or pre-cast if steel is used with cement concrete, it is known as reinforced cement concrete.

b. Mosaic tiles: Pre-Cast concrete tiles with marble chips at top surface are known as tiles. They are available in different shades and widely adopted at present.

c. Terrazo :This is a mixture of marble chips and cement. It is used for bathrooms residential buildings, temples etc.

Qualities of a good building stone

The following are the qualities or requirements of a good building stone.

1. Crushing strength: For a good building stone, the crushing strength should be greater than l000kg per cm2.

2. Appearance: Good building stone should be a uniform color, and free from clay holes, spots of other color bands etc capable of preserving the color for longtime.

3. Durability: A good building stone should be durable. The factors like heat and cold alternative wet and dry, dissolved gases in rain, high wind velocity etc affect the durability.

4. Fracture: For good building stone its fracture should be sharp, even and clear.

5. Hardness: The hardness greater than 17, treated as hard used in road works. It is between 14 to 17, medium hardness, less 14 said be poor hardness.

6. Percentage wear: For a good building stone, the percentage wear should be equal to or less than 3 percent.

7. Resistance to fire: A good building stone be fire proof. Sandstone, Argillaceous stone resists fire quite well.

8. Specific gravity: For a good building stone the specific gravity should be greater than 8.7 or so.

9. Texture: A good building stone should have compact fine crystalline structure should be free from cavities, cracks or patches of stuff or loose material.

10. Water absorption: For a good building stone, the percentage absorption by weight after 24 hours should not exceed 0.60.

11. Seasoning: Stones should be well seasoned before putting into use. A period of about 6 to 12 months is considered to be sufficient for proper seasoning.

12. Toughness Index: Impact test, the value of toughness less than 13 – Not tough, between 13 and 19 – Moderate, greater than 19- high

Uses of stones

Uses of stones

1.Structure: Stones are used for foundations, walls, columns, lintels, arches, roofs, floors, damp proof course etc.

2.Face works: Stones are adopted to give massive appearance to the structure. Wall are of bricks and facing is done in stones of desired shades. This is known as composite masonry.

3.Paving stones: These are used to cover floor of building of various types such as residential, commercial, industrial etc. They are also adopted to form paving of roads, foot paths etc.

4.Basic material: Stones are disintegrated and converted to form a basic material for cement concrete, morum of roads, calcareous cements, artificial stones, hallow blocks etc.

5.Misalliances: Stones are also used for (i) ballast for railways (ii) flux in blast furnace (iii) Blocks in the construction of bridges, piers, abutments, retaining walls, light houses, dams etc.

Stone

Crushed Stone

All the building structures are composed of different types of materials. These materials are either called building materials or materials of construction. It is very essential for a builder, may be an architecture or engineer or contractor, to become conversant thoroughly with these building materials. The knowledge of different types of material, their properties and uses for different purposes provides an important tool in the hands of the builders in achieving economy in material cost. The material cost in a building ranges 30 to 50 percent cost of total cost construction. In addition to material economy, the correct use of material results in better structural strength, functional efficiency and esthetic appearance.

Classification of Rocks:

Building stones are obtained from rocks occurring in nature and classified in three ways.

1. Geological classification

2. Physical classification

3. Chemical classification

Geological Classification:

According to this classification, the rocks are of the following types.

Igneous rocks: Rocks that are formed by cooling of Magana (molten or pasty rocky material) are known as igneous rocks. Eg: Granite, Basalt and Dolerite etc.

Sedimentary rocks: these rocks are formed by the deposition of production of weathering on the pre-existing rocks. Examples: gravel, sandstone, limestone, gypsum, lignite etc.

Metamorphic rocks. These rocks are formed by the change in character of the pre-existing rocks. Igneous as well as sedimentary rocks are changed in character when they are subject to great heat and pressure. Known as metamorphism. Examples: Quartzite, Schist, Slate, Marble and Gneisses.

Central Mixed Concrete

Central Mixed Concrete

Central-mixing concrete batch plants include a stationary, plant-mounted mixer that mixes the concrete before it is discharged into a truck mixer. Central-mix plants are sometimes referred to as wet batch or pre-mix plants. The truck mixer is used primarily as an agitating haul unit at a central mix operation. Dump trucks or other non-agitating units are sometimes be used for low slump and mass concrete pours supplied by central mix plants. About 20% of the concrete plants in the use a central mixer. Principal advantages include:

·     Faster production capability than a transit-mix plant

·     Improved concrete quality control and consistency and

·     Reduced wear on the truck mixer drums.

There are several types of plant mixers, including:

·     Tilt drum mixer

·     Horizontal shaft paddle mixer

·     Dual shaft paddle mixer

·     Pan mixer

·     Slurry mixer

The tilting drum mixer is the most common American central mixing unit. Many central-mix drums can accommodate up to 12 yd3 and can mix in excess of 200 yd3per hour. They are fast and efficient, but can be maintenance-intensive since they include several moving parts that are subjected to a heavy load.

Horizontal shaft mixers have a stationary shell and rotating central shaft with blades or paddles. They have either one or two mixing shafts that impart significantly higher horsepower in mixing than the typical drum mixer.

Pan mixers are generally lower capacity mixers at about 4 to 5 yd3 and are used at precast concrete plants.

Slurry Mixing The slurry mixer is a relative newcomer to concrete mixing technology. It can be added onto a dry-batch plant and works by mixing cement and water that is then loaded as slurry into a truck mixer along with the aggregates. It is reported to benefit from high-energy mixing. Another advantage is that the slurry mixer reduces the amount of cement dust that escapes into the air.