Bulking of Sand

Bulking of Sand

The presence of moisture in sand increases the volume of sand. This is due to fact that moisture causes film of water around the sand particles which result in the increase of volume of sand. For a moisture content of 5 to 8 percent, the increase in volume may be about 5 to 8 percent, depending upon the grading of sand. The finer the material, the more will be the increase in volume for a given moisture content. This phenomenon is known as bulking of sand.

When moisture content is increased by adding more water, sand particles pack near each other and the amount of bulking of sand is decreased. Thus the dry sand and the sand completely flooded with water have practically the same volume.

For finding the bulking of sand, a test is carried out with following procedure.

·     A container is taken and it is filled two third with the sample of sand to be tested.

·     The height is measured, say 20cm.

·     Sand is taken out of container.

·     The container is filled with water.

·     Sand is then slowly dropped in the container and it is thoroughly stirred by means of a rod.

·     The height of sand is measured say 16cm, then bulking of sand =

                         20-16                4

              =   ----------------  =  --------     or 25%

                       16                       16

Grading of Sand

Grading of Sand

According to the site of grains, sand is classified as fine, coarse and gravelly

·     Sand passing through a screen with clear opening of 1.5875mm is known as fine sand. It is generally used for masonry works.

·     Sand passing through a screen with clear openings of 7.62mm is known as gravely sand. It is generally used for plastering.

·     Sand passing through a screen with clear opening of 3.175mm is known as coarse sand. It is generally used for masonry work.

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.

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

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.

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.

Equipment Required in Ready Mix Concrete

Equipment Required in Ready Mix Concrete

Following are the equipments required in Ready Mix Concrete

1.Batching plant

2.Transit mixer

BATCHING

Batching plants are classified as

1.Manual

2.Semiautomatic

3.Fully automatic

STORAGE

Storage of the raw materials is done by following methods: -

INLINE BINS Inert raw materials like fine & coarse aggregates are stored in bins called as

“Inline Bins” where the trucks carrying fine & coarse aggregate can dump the material easily.

The aggregates required are fed by the means of aggregate belt conveyer. On the aggregate belt conveyer the aggregates are weighed automatically by means of computer form the computer room presents on the plant.

SILOS

Cement & Flash are stored in airtight container called as “Silos”. The required quantity of cement & fly ash is extracted by the silos. There are two cement silos and one silo of fly ash.

Check by Consumer Before Ordering the Ready Mix Concrete

Check by Consumer Before Ordering the Ready Mix Concrete

The following need to be looked into by the consumer:

·     Reliability of the plant and transit mixers for consistent and continuous concrete supply as per requirement.

·     Calibrations of all measuring devices and their accuracy.

·     Mode of operation of plant should preferably be fully automatic and not manual.

·     Quality of materials proposed to be used.

·     Adequacy of quantity of materials proposed to be used.

·     Compliance of concrete specifications based on the mix parameters specified.

·     Adequacy of testing facilities

·     Time likely to be taken by transit mixers from plant to site and back.

Information to be Supplied by the Producer

Information to be Supplied by the Producer

The Ready Mix Concrete supplier must provide the following information to the consumer if and when requested:

·     Nature and source of each constituent material including the name of the manufacturer in case of branded products like cement, admixtures etc.

·     Proportion of quantity of each constituent per CuM of fresh concrete.

·     Generic type of the active constituent of the chemical admixture and its solid content.

·     Chloride content in all constituent materials.

·     Compatibility of cement and chemical/mineral admixtures.

·     Compatibility of admixtures with one another when more than two types of admixtures are proposed.

·     Initial and final setting time of concrete when admixture is used.

·     Details of plant and machinery (capacity CuM/hr), storage (CuM) availability, type of facilities to dose admixtures, type of moisture measurement arrangement, type of mixer, rated capacity (CuM/min.) of the mixer.

·     Availability of number of transit mixers and their capacities.

·     Details of last calibrations done on various weighing /dosing equipments

·     Testing facilities available at RMC plant

·     Capacity and type of concrete pump and placing equipment available (if required).

Need to be Specified for Ready Mix Concrete

Need to be Specified for Ready Mix Concrete

The following need to be specified very clearly:

·     Characteristic strength or grade (N/mm2)

·     Target workability or slump in mm required at site

·     Exposure conditions for durability requirements

·     Maximum water to cement ratio

·     Minimum cement content

·     Maximum aggregate size

·     Type of cement

·     Mineral admixture and its proportion (Kg/m3)

·     Maximum aggregate size

·     Rate of gain of strength (for formwork removal or prestressing etc.)

·     Maximum temperature of concrete at the time of placing (in extreme climatic conditions or incase of massive concrete pours)

·     Type of surface finish desired

·     Method of placing

·     Rate of supply desired to match the placing and compaction speed planned at site.

·     Quantity of concrete required.

·     Lift and lead of concrete transportation and placement at site.

·     Frequency of concrete testing

·     Details of materials and their required tests.

·     Permeability tests required (if any)

·     Placing of concrete in formwork to be under scope of RMC supplier (if required)

·     Permissible wastage

·     Mode of measurement.

Admixtures

Admixtures

Ready Mix Concrete is generally transported to different construction sites and delivered with the help of revolving type transits mixers. These sites are located at long distances and the concrete delivered is workable, plastic and flowable. Experience shows that slump loss takes place with certain types of cement and to prevent this superpplasticiser are used.

Ready Mix Concrete's often use admixtures formulated for special purposes lik e:

(a) Improvement of screeds, renders, mortars and concrete for increased water resistance and less risk - from aggressive materials,

( b) Integral water proofers,

 (c) Foamed - for light weight insulation. void filling and semi structural support,

(d) Water repelling for semi-dry block concrete,

(e) Microsillica for use in high performance concrete. The introduction of microsillica was observed to improve the pore solution chemistry of HPC. For higher replacement of cement by silica fumes, the concentration of both K+ and OH-ions are substantially removed. However, up to 20% replacement will not cause a drop in pH below that of saturated CaOH solution, which is approx.12.5. Even at 30%

replacement,  pH does not drop below 11.5, which is considered to be a threshold value for maintaining a good passivity of embedded steel.

Testing of Concrete

Testing of Concrete

The results of concrete tests are used as the basis for deciding whether the delivered concrete is in accordance with the specification, if the reported results are below the compliance loyal, doubt is cast on the quality of the supplied concrete and the long term durability of the structure. If the investigation indicates that the sampling, preparation and or storage of the test specimens have not been in accordance with the required standard procedures, then the result will be invalid. Further valuable management time, better devoted to other management functions, will have been wasted.

It is, therefore, in everyone's interest that sampling and testing is done correctly so that the results provide a valid basis for logical decision making. Where the contractor is required to perform on-site concrete testing, it is imperative that suitable test facilities are available, that the appropriate equipment is calibrated and that the staff has been fully trained in the relevant test techniques, one can look the factors that affect the price compliance test, (i.e.) the compressive strength test.

As  a result is the average of the compressive test specimens made for the same sample of concrete. Individual variation should not be more than 15 Percent of the average. If more. The results of the average. If more, the results of the sample are invalid. This is because differences of this magnitude indicate poor sampling, cube making, curing or crushing. It is, therefore essential that correct test facilities are provided and the people with responsibility for sampling and testing concrete are suitably trained.

Slump test for predicting the workability of concrete is done at batching plant and working site. The main problem in the production of ready mixed concrete is maintaining the workability of the mix right to the time of placing. Concrete stiffens with time and the stiffening may also be aggravated by prolonged mixing and by high temperature. With the use of retarding admixtures, the time limit can be extended to 3 or even 4 hours, The United States Bureau of Reclamation provides for an extension of 3 to 6 hours in the time of contact between cement and wet aggregate in transport prior to mixing.  The general requirement is that concrete shall be discharged from the truck-mixer within 2 h of the time of loading. However, a longer period may be permitted if retarding admixtures are used or in cool humid weather or when chilled concrete is produced.

Sampling of Concrete

Sampling of Concrete

Critical decisions, often involving very high potential costs, are made on the basis of concrete test results. Correct sampling is paramount to the validity of these test results but is an aspect of testing that is frequently overlooked and often carried out by untrained people. It is therefore essential that the sampling is done correctly and is representative of the concrete delivered.

After the truck-mixer has re-mixed its delivery on site allow at least the first one-third of a m3 of concrete to be discharged prior to taking any samples. Take at least 4 incremental samples from the remainder of the load avoiding sampling the last cubic meter of concrete. Thoroughly re-mix this composite sample either on a mixing tray or in the sampling bucket and proceed with the required testing.

Describe the recommended sampling methods for ready mixed concrete in British code. Using a standard scoop, this can collect about 5kg of normal weight concrete. Each load of concrete to be tested should be nominally divided into a number of scoopfuls.

The Standard method: To ensure that the concrete is representative of the whole load is standard sample consists of scoopfuls taken from at least four different parts of the load and collected in buckets. The scoopfuls should be taken at equally spaced intervals; the scoop being passed through the whole width and thickness of the stream in a single movement. The first and the last 1/6th

portion of the discharge should be disregarded as unrepresentative. This is then thoroughly re-mixed on a non-absorbent surface before carrying out any individual test. This operation is necessary to even out any variation between individual scoopfuls and to counteract any segregation that may have occurred in transporting the sample from the sampling point to the testing area.

The Alter native Method: An alternative method of sampling concrete for slump testing from

a truck-mixer before the majority of the load has been discharged is permitted. This enables the concrete to be tested before being placed. When this alternate method is used, an initial discharge of at least 0.3 m3 is made before a sample of six scoopfuls is collected from the

moving stream; The sample is then r e-mixed on a non-absorbent surface and split into two equal parts. Each part is then tested or slump, with the average of the two tests recorded as the test result. This method of sampling is only applicable to the slump test. Concrete sampled by this method must not be used to make cubes for compliance testing, as it will produce erroneous results.

Ready Mix Concrete

Ready Mix Concrete

Ready Mix Concrete is a specialized material in which the cement aggregates and other ingredients are weigh-batched at a plant in a central mixer or truck mixer, before delivery to the construction site in a condition ready for placing by the builder. Thus, `fresh' concrete is manufactured in a plant away from the construction site and transported within the requisite journey time. The RMC supplier  provides two services, firstly one of processing the materials for making fresh concrete and secondly, of transporting a product within a short time.

Sometimes Materials such as water and some varieties of admixtures can be transit-mixed (also known as Transit Mixture), that is they can be added to the concrete at the jobsite after it has been batched to ensure that the specified properties are attained before placement. Here materials are batched at a central plant and are completely mixed in the Batching Plant or partially mixed intransit. Transit-mixing keeps the water separate from the cement and aggregates and allows the concrete to be mixed immediately before placement at the construction site (Dry Concrete). This method avoids the problems of premature hardening and slump loss that result from potential delays in transportation or placement of central-mixed concrete.

Additionally, transit-mixing allows concrete to be hauled to construction sites further away from the plant. There are several types of RMC plants varying in type of mixing and capacity of concrete production.

Capabilities of the intelligent building

Capabilities of the intelligent building

The overriding function of the intelligent building system is to support the capabilities inherent . Clearly it is necessary to consider an intelligent building as a single entity unifying objectives of the owner in delivering the building’s desired capabilities with the adaptability and functionality desired by the occupants.

As with the systems present in the intelligent building it is possible to list the capabilities. They include:

·     sensing human presence and/or occupancy characteristics in any part of the building and controlling the lighting and HVAC systems based on appropriate pre-programmed responses

·     performing self-diagnostics on all building system components

·     alerting security and fire alarm systems and monitoring the location of occupants in case of emergencies

·     sensing the intensity and angle of light and solar radiation, temperature and humidity, and adjusting the building’s envelope according to the desired interior performance levels

·     monitoring electrical outlets for malfunctioning equipment

·     monitoring access to the building and individual building spaces

·     detecting odors and pollutants and responding by increasing ventilation rates

·     distributing electric power to computers on demand or in accordance with a preset priority schedule and automatically activating reserve batteries or back-up systems

·     selecting the least cost carrier for long distance telephone calls

·     activating ice-making or heat storage systems when the utility signals that discounted rates are in effect

·     providing better acoustic privacy by activating white noise systems to mask background noise.

Concrete Curing

Concrete Curing

For high durability, concrete must not only be “strong” but also impermeable, especially in the areas near the surface. The lower the porosity and the denser the hardened cement paste, the higher the resistance to external influences, stresses and attack. To achieve this in the hardened concrete, measures have to be taken to protect the fresh concrete, particularly from

·     Premature drying due to wind, sun, low humidity etc.

·     Extreme temperatures (cold, heat) and damaging rapid temperature changes

·     Rain

·     Thermal and physical shock

·     Chemical attack

·     Mechanical stress

Protection from premature drying is necessary so that the strength development of the concrete is not affected by water removal. The consequences of too early water loss are:

·     Low strength in the parts near the surface

·     Tendency to dusting

·     Higher water permeability

·     Reduced weather resistance

·     Low resistance to chemical attack

·     Occurrence of early age shrinkage cracks

·     Increased risk of all forms of shrinkage cracking

Concreting Operation

Concreting Operation

In general, when concreting it is important to ensure that the release agent suffers as little mechanical stress as possible. If possible the concrete should not be poured diagonally against vertical formwork to prevent localized abrasion of the release film. The pour should be kept away from the form as much as possible by using tremies/pipes etc. When compacting, make sure that the poker vibrators do not come too close to the form work skin or touch it. If they do, they exert high mechanical stress on the form surface, which can result in abrasion of the release agent and later to localized adhesion (non-release) of the concrete.

Summary

The concrete industry cannot do without release agents. When correctly selected and used with the right formwork and concrete quality, they contribute to visually uniform and durable concrete surfaces. Inappropriate or wrongly selected release agents, like unsuitable concrete raw materials and compositions, can cause defects and faults in and on the concrete surface.

Sulphate resistant Sprayed Concrete

Sulphate resistant Sprayed Concrete

A sprayed concrete with a standard cement content of 400–450 kg/m³ has high sulphate resistance when it uses:

·     Cement combined with water reducer

·     a standard Portland cement combined with water reducer and added at > 5% or

·     a CEM III-S

Requirement: w/c < 0.50

Recommended mix design for wet sprayed concrete:

·     Granulometry                         0–8 mm

·     Cement content                        425 kg/m³        

Steel Fiber reinforced Sprayed Concrete

Steel Fiber reinforced Sprayed Concrete

Definition

Steel fiber reinforced sprayed concrete, like conventionally reinforced sprayed concrete, consists of cement, aggregates, water and steel. By using and adding steel fibers, the sprayed concrete is homogeneously reinforced. 

Reasons for using steel fiber reinforced sprayed concrete:

·     Saving on the costs for installation of steel mesh reinforcement

·     Reduction in slump due to higher early strengths

·     Elimination of “spray shadow” when spraying onto reinforcing mesh

·     Due to its homogeneity, steel fiber reinforced sprayed concrete can withstand forces of various kinds in various directions at any point on its cross-section. 

Additional notes:

·     The cement content may have to be increased because the fines content of steel fiber reinforced sprayed concrete must be higher than in standard wet sprayed concrete, to anchor the fibers.

·     Adding Silica fume helps to achieve the target values of the sprayed concrete because it also improves anchorage of the fibers.

·     improves the pump ability considerably.

·     The minimum diameter of the pump line should be at least double the maximum fiber length.

Test Methods of Sprayed Concrete

Test Methods of Sprayed Concrete

Determination of early strengths

To determine the very early strengths (in the range 0 to 1 N/mm²), the Proctor or Penetrating needle is used.

The following methods are well established for compressive strength testing between 2 and 10 N/mm²:

·     Kaindl/Meyco: Determination by the pull-out force of bolts.

·     HILTI (Dr. Kusterle): Determination of the impression depth (I) and pull-out force (P) of nails shot with a HILTI DX 450L shot bolt machine (load and nail size are standard).

·     Simplified HILTI method (Dr. G. Bracher, Sika):Determination of the impression depth (I) of nails shot with a HILTI DX 450L shot bolt machine (load and nail size are standard). Determining the required early strength by this method should be accurate to ±2 N/mm².