Surfactants, short for surface-active agents, are compounds that
are commonly used in various industries for their ability to reduce
surface tension and increase the wetting and spreading properties of
liquids. In the context of concrete, surfactants are sometimes added to
the mix to modify certain properties of the concrete.
how the addition of surfactants can affect the water-cement ratio, strength, and density of concrete:
Water-Cement Ratio:
Surfactants
can act as water-reducing agents, allowing for a reduction in the
amount of water needed in the concrete mix while maintaining
workability. This is known as water reduction or plasticizing effect.
The
use of surfactants may enable a lower water-cement ratio, which is
generally desirable as it contributes to increased strength and
durability of the concrete.
Strength:
Surfactants
can influence the strength of concrete both directly and indirectly.
The reduction in water content due to the addition of surfactants can
lead to improved strength.
Some surfactants may also have a
chemical effect that enhances the cement hydration process, potentially
contributing to increased compressive strength.
Density:
Surfactants
can impact the density of concrete. As the water content is reduced,
the concrete mix may become more compact, potentially leading to higher
density.
However, the specific impact on density may vary
depending on the type of surfactant used and its interactions with other
components in the mix.
It's important to note
that the effects of surfactants on concrete properties can depend on
various factors, including the
type and dosage of surfactant,
the
characteristics of the cement,
aggregate properties,
and the overall mix
design.
While surfactants can offer advantages such as
improved
workability,
reduced water content,
and enhanced strength,
it is crucial
to carefully evaluate their impact and consider the specific
requirements of the concrete application.
It's recommended to
conduct laboratory tests and trials to assess the performance of
surfactants in a particular concrete mix before widespread use in
construction projects. Additionally, consulting with concrete experts
and following industry standards and guidelines is essential for
achieving the desired concrete properties while ensuring long-term
durability and performance.
Here are some examples of chemical classes and specific
surfactants commonly used in different applications:
Surfactants belong to a diverse group of chemicals, and they can
be classified into various categories based on their chemical structure
and properties.
In
concrete applications, the choice of surfactant depends on the specific
requirements of the mix design and desired properties. Water-reducing
agents, plasticizers, and air-entraining agents are common types of
surfactants used in concrete to improve workability, reduce water
content, and enhance other performance characteristics.
It's
important to note that the selection of a surfactant should consider
factors such as compatibility with other components in the mix,
long-term durability, and potential environmental and health
considerations. Consulting with concrete experts and following industry
standards is crucial to ensure the successful and safe use of
surfactants in concrete formulations.
The use of surfactants in concrete mixes can have specific effects on
various properties. Here's more information on when and how certain
surfactants are commonly used and their corresponding impacts on
concrete properties:
Sodium Lauryl Sulfate (SLS):
When Used:
SLS is often used as an air-entraining agent in concrete mixes to
introduce tiny air bubbles. This helps improve freeze-thaw resistance
and workability.
Property Effects: Enhances workability, improves durability in freezing conditions.
Sodium Dodecylbenzenesulfonate (SDBS):
When Used: SDBS can be used as a plasticizer in concrete mixes to improve workability and reduce water demand.
Property Effects: Increases plasticity, reduces water content, enhances workability.
Cetyltrimethylammonium Bromide (CTAB):
When Used: CTAB is a cationic surfactant that can be used as a plasticizer and water reducer in concrete mixes.
Property Effects: Improves workability, reduces water content.
Alkyl Ethoxylates:
When Used:
Alkyl ethoxylates, such as nonylphenol ethoxylate, are often used as
nonionic surfactants to enhance the workability of concrete.
Property Effects: Improves workability, reduces water demand.
When Used: Tweens are nonionic surfactants that can act as water reducers and plasticizers in concrete mixes.
Property Effects: Enhances workability, reduces water content.
Cocamidopropyl Betaine (CAPB):
When Used: CAPB is an amphoteric surfactant used in concrete to reduce water demand and improve workability.
Property Effects: Enhances workability, reduces water content.
Fluorinated Surfactants (PFOA, PFOS):
When Used: Fluorinated surfactants may be used for their water-repelling properties in specific concrete applications.
Property Effects: Improves water resistance, can enhance durability in some conditions.
Biosurfactants (Rhamnolipids, Sophorolipids):
When Used: Biosurfactants may be used as environmentally friendly alternatives in concrete mixes.
Property Effects: Can improve workability and reduce surface tension.
It's
crucial to note that the effectiveness of surfactants depends on
factors like dosage, mix design, and environmental conditions.
Additionally, while surfactants can provide benefits, their use should
be carefully considered, and compatibility with other additives and
long-term performance should be evaluated through testing and analysis.
Consulting with concrete professionals and following industry guidelines
is essential for successful surfactant use in concrete applications.
Too coarse aggregate results in hardness, segregation and bleeding and
too fine aggregate requires too large w/c ratio for adequate work-ability.
The statement is highlighting the importance of the proper gradation of aggregates in concrete mixtures, specifically coarse and fine aggregates, and its impact on various properties of concrete. Let's break it down:
"Too coarse aggregate results in hardness, segregation, and bleeding":
Hardness: Excessively large coarse aggregates can make the concrete mixture difficult to work with, leading to a concrete mix that is harder to place and compact.
Segregation: Coarse aggregates that are too large may settle at the bottom during the mixing and transportation process, causing uneven distribution of aggregates and resulting in a non-uniform concrete mixture.
Bleeding: This refers to the separation of water from the concrete mix, where excess water tends to rise to the surface. Coarse aggregates that are too large can contribute to bleeding issues.
Example: Imagine a construction project where the concrete mix contains very large pebbles as coarse aggregates. The resulting concrete might be difficult to pump, place, and finish due to the challenges posed by the excessively coarse aggregates.
"Too fine aggregate requires too large w/c ratio for adequate workability":
W/C ratio (Water-to-Cement ratio): The water-to-cement ratio is a critical factor in concrete mix design. Too much water is generally undesirable as it can affect the strength and durability of concrete.
Adequate workability: Workability refers to how easily the concrete can be mixed, placed, and finished. If the fine aggregate content is too high, it may require more water to maintain workability.
Example: Consider a concrete mix with an excess of fine sand as the fine aggregate. To maintain workability, a higher water-to-cement ratio might be needed. This can lead to a weaker and less durable concrete, impacting the overall performance of the structure.
Negligence in Considering aggregate properties
There have been instances where negligence in considering aggregate properties led to issues and damages in structures. One notable example is the case of the Alamillo Bridge in Seville, Spain.
Example of Negligence - Alamillo Bridge in Seville, Spain
The Alamillo Bridge, designed by architect Santiago Calatrava and completed in 1992, features a distinctive asymmetrical design with a single leaning pylon and cables supporting the bridge deck. The bridge experienced structural problems, including cracking, which were attributed to issues with the concrete mix.
Negligence and Consequences:
Aggregate Issues: It was found that the concrete mix used for the bridge had a high percentage of reactive silica in the aggregates, leading to alkali-silica reaction (ASR).
ASR Impact: ASR is a chemical reaction between alkaline cement and reactive silica in certain aggregates, resulting in the formation of a gel. This gel can cause expansion and cracking in concrete, compromising its structural integrity.
Consequences of Negligence:
Cracking: The alkali-silica reaction caused significant cracking in the concrete elements of the bridge, affecting its structural stability.
Structural Repairs: Extensive repairs were required to address the damages, leading to additional costs and efforts.
This example underscores the importance of carefully considering aggregate properties and potential reactivity in concrete mix designs. Neglecting such factors can lead to serious structural issues and the need for costly repairs. In this case, a more thorough evaluation of the aggregates' properties could have prevented or mitigated the alkali-silica reaction and the subsequent damage to the Alamillo Bridge.
Studying examples like the Alamillo Bridge provides invaluable lessons, emphasizing the critical importance of meticulously analyzing aggregate properties and avoiding potential issues such as the Alkali-Silica Reaction.
Alamillo Bridge and ASR: Case Study
Design and Construction:
The
Alamillo Bridge in Seville, Spain, was designed by Santiago Calatrava
and completed in 1992. Its distinctive design features a single leaning
pylon and a cable-stayed bridge deck.
During construction, the concrete mix used for the bridge included aggregates with a high percentage of reactive silica.
Alkali-Silica Reaction (ASR):
Nature of ASR:
ASR is a chemical reaction that occurs in concrete when certain types
of reactive silica present in aggregates react with the alkaline
substances in cement.
Formation of Gel: The
reaction results in the formation of a gel-like substance within the
concrete. This gel can absorb water and expand, leading to the
development of internal pressure.
Consequences of ASR:
Cracking:
The expansion caused by the ASR gel exerts pressure on the concrete,
leading to the development of cracks. These cracks compromise the
structural integrity of the concrete elements.
Reduced Durability: The continuous expansion and contraction due to ASR can result in a loss of durability and overall structural performance.
Identification of Issues:
Crack Formation: Over time, the Alamillo Bridge exhibited visible cracks in its concrete elements, signaling the presence of structural issues.
Investigation:
Detailed investigations were conducted to determine the cause of the
cracks, leading to the identification of the alkali-silica reaction as a
primary factor.
Mitigation and Repairs:
Repairs Needed:
To address the damages caused by ASR, extensive repairs were required.
This involved repairing and reinforcing the affected concrete elements.
Costs and Delays: The repairs incurred significant additional costs and delays in the project timeline.
Lessons Learned:
Importance of Aggregate Selection: The Alamillo Bridge serves as a cautionary example of the critical role that aggregate selection plays in concrete mix design.
Avoidance of Reactive Aggregates:
The experience emphasizes the importance of avoiding aggregates with
high reactivity, especially reactive silica, to prevent detrimental
effects like ASR.
In summary, the Alamillo
Bridge case illustrates how neglecting the properties of aggregates,
specifically the potential for alkali-silica reaction, can lead to
structural issues, compromising the integrity of a concrete structure.
The example underscores the need for meticulous consideration of
aggregate properties in concrete mix design to ensure the long-term
durability and performance of structures.
Understanding Alkali-Silica Reaction (ASR) is crucial for gaining comprehensive insights into the behavior of concrete, cement, and mortar, as well as the formation and long-term performance of structures.
The Alkali-Silica Reaction (ASR)
The Alkali-Silica Reaction (ASR) is a chemical reaction that can
occur in concrete when certain types of reactive silica present in
aggregates react with the alkaline substances in cement. Here's a more
detailed explanation of ASR:
Ingredients Involved:
Silica in Aggregates:
Aggregates, which are the inert granular materials (such as sand,
gravel, or crushed stone) in concrete, may contain certain forms of
silica minerals.
Alkali in Cement: Cement contains alkali compounds, such as sodium and potassium oxides.
Initiation of ASR:
Contact Between Silica and Alkali: When concrete is mixed, the alkaline cement comes into contact with the silica present in the aggregates.
Formation of ASR Gel:
In the presence of moisture, a chemical reaction occurs between the
reactive silica and the alkali. This reaction forms a gel-like
substance, commonly referred to as ASR gel.
Characteristics of ASR Gel:
Hygroscopic Nature: The ASR gel is hygroscopic, meaning it can absorb and retain water.
Expansive Behavior: The gel expands as it absorbs water, creating internal pressure within the concrete.
Effects of ASR:
Crack Formation: The internal pressure generated by the expanding ASR gel can lead to the development of cracks in the affected concrete.
Loss of Strength and Durability: Continuous expansion and contraction due to ASR can result in a gradual loss of concrete strength and durability over time.
Visual Indicators:
Cracking Patterns: ASR-induced cracks typically exhibit distinctive map-like patterns on concrete surfaces.
Location of Cracks: Cracks often form in areas with high moisture exposure, as moisture is essential for the ASR reaction to occur.
Prevention and Mitigation:
Aggregate Selection:
One of the primary methods to prevent ASR is to carefully select
aggregates with low reactivity during the concrete mix design process.
Use of Supplementary Cementitious Materials:
The addition of supplementary cementitious materials, such as fly ash
or silica fume, can help mitigate the effects of ASR by reducing the
availability of alkalis in the concrete.
Understanding
ASR is crucial in the context of concrete durability and structural
performance. Proper aggregate selection and mix design considerations
play a pivotal role in preventing or mitigating the detrimental effects
of ASR, ensuring the long-term stability of concrete structures.
Such case studies underscore the need for a thorough understanding of concrete behavior, aggregate selection, and mix design to ensure the structural integrity and durability of construction projects.
For self-compacted concrete water/powder ratio by volume should be
0.80 to 1.0
1.2 to 1.4
0.6 to 0.8
1.0 to 1.2
.8 to 1;
Indicative proportions of materials are shown below for self-compactible concrete:
1) Water/powder ratio by volume is to be 0.80 to 1.00
2) Total powder content to be 160 to 240 litres (400-600 kg) per m3
3) The sand content may be more than 38% of the mortar volume.
4) Coarse aggregate content should normally be 28 to 35% volume of the mix.
5) Water/cement ratio is selected based on the strength required. In any case, water content should not exceed 200 litres/m3.
i. Expanding cement is used for filling the cracks
ii. White cement is mostly used for decorative works
iii. Portland Pozzolana cement produces less heat of hydration
iv. High strength Portland cement is produced from the special materials
All correct Expanding Cement: It is obtained from mixing sulpho-aluminate. It has a property to expand, thus used in the elimination of shrinkage cracks. It is used in the treatment of expansion joints and for grouting.
White Portland cement: The white colour of this cement is due to less proportion of iron oxide, which is replaced by Sodium Alumino Ferrite. Colouring agents can be added to white cement to produce coloured cement.
Portland Pozzolana Cement: It is formed by inter grinding of OPC clinker to 10% to 25% of pozzolanic material. It produces less heat of hydration and offers greater resistance to the attack of aggressive water than OPC. It is useful in marine and hydraulic constructions.
High strength Portland cement: This cement is produced by a special technique called Macro Defect Free (MDF) innovation. In this process 4-7% of one of several water-soluble polymers (such as hydroxypropyl methylcellulose, polyacrylamide of hydrolyzed polyvinyl acetate is added for generating high strength.
Cubical aggregate has maximum strength in concrete as it has good packing and strength in all direction.
Rounded aggregate is not suitable for concrete.
Flaky means have less thickness, elongated means having more length. These aggregate can be easily crushed and having a minimum strength.
Reasons:
Generally, in normal concrete loads are taken by aggregates only and cement acts as a binder, therefore, a normal concrete can have maximum strength till the aggregates are not broken.
If the aggregates fail under a load before failure of cement sand matrix. The concrete produced with that aggregates will not achieve the desired strength.
So using flaky and elongated aggregates might lead to failure of concrete and hence should be avoided.
Classification of aggregates on basis of shape –
Rounded aggregates / spherical - Rounded aggregates result the minimum percentage of voids (32 – 33%) hence gives more workability. They require lesser amount of water-cement ratio. They are not considered for high strength concrete because of poor interlocking behaviour and weak bond strength.
Irregular or partly rounded aggregates - Irregular aggregates may result 35- 37% of voids. These will give lesser workability when compared to rounded aggregates.
Angular aggregates -
Angular aggregates result maximum percentage of voids (38-45%) hence gives less workability
Flaky aggregates -
When the aggregate thickness is small when compared with width and length of that aggregate it is said to be flaky aggregate. Or in the other, when the least dimension of aggregate is less than the 60% of its mean dimension then it is said to be flaky aggregate.
Elongated aggregates -
When the length of aggregate is larger than the other two dimensions then it is called elongated aggregate or the length of aggregate is greater than 180% of its mean dimension.
Flaky and elongated aggregates -
When the aggregate length is larger than its width and width is larger than its thickness then it is said to be flaky and elongated aggregates. The above 3 types of aggregates are not suitable for concrete mixing
Important Point:
Split tensile strength(fct) = 0.66 × Modulus of Rupture
Due to the difficulty in applying uniaxial tension to a concrete specimen, the tensile strength is determined by indirect methods.
It is the standard test to determine the tensile strength of concrete indirectly as per IS: 5816-1970
A standard test cylinder of a concrete specimen of 300 mm × 150 mm diameter is placed horizontally between the loading surfaces of the compression testing machine.
The compression load is applied diametrically and uniformly along the length of the cylinder until the failure of the cylinder along vertical diameter.
Modulus of rupture:
It is a measure of the tensile strength of concrete beams or slabs.
Flexure strength of concrete is determined as a modulus of rupture. Flexural strength of concrete/ Bending tensile strength of concrete/Modulus of rupture of concrete (fcr) is given by,
fcr = 0.7×√fck
Compressive strength of concrete:
It is determined by the compressive strength test on a standard 150 mm concrete cube in a compressive testing machine as per IS 516: 1959. The test specimens are generally tested after 28 days of casting and continuous curing.
In USA standard cylinder of height to diameter ratio of 2 is taken. (150 mm diameter, 300 mm height) for determining.
It is observed that the Cube strength of concrete is nearly 1.25 times the cylinder strength.
1. Pith : It is the inner most part of tree consist of cellular tissue which is used for nourishment of tree in young age.
2. Sapwood : It is outer annual rings between heartwood and cambium layers. It is the living, outermost portion of a woody stem or branch.
3. Heartwood : It is the dead, inner wood, which often comprises the majority of a stem's cross-section.
4. Cambium Layer : It is a thin layer of sap between sapwood and inner bark.
A good building stone has the following properties:
Percentage of wear in the attrition test should not be more than 3
Specific gravity should be at least 2.7
Coefficient of hardness should be greater than 17
Percentage of water absorption by weight of stone should be less than 5
Toughness index should not be less than 13
Crushing strength should be greater than 100 N/mm2
Chemical composition: The various tests are carried out to determine the chemical constituents of cement. Following are the chemical requirements of ordinary cement as per IS: 269- 1998:
Ratio of percentage of alumina to that of iron oxide: This ratio should not be less than 0.66.
Ratio of percentage of lime to those of alumina, iron oxide, and silica: This ratio is known as the lime saturation factor (LSF) and it should not be less than 0.66 and it should not be greater than 1.02, when calculated by the following formula:
Total loss on ignition: This should not be greater than 4 percent.
Total sulphur content-The sulphur content is calculated as SO3 and it should not be greater than 2.75%.
Weight of insoluble residue-This should not be greater than 1.5%.
Weight of magnesia-This should not exceed 5%.
Note:
As per IS 12269: 2013, the loss on ignition for OPC 53 should not be greater than 4%.
As per IS 8112: 2013, the loss on ignition for OPC 43 & 33 should not be greater than 5%.
Colored cement:
Colored pigment is manufactured by mixing of color pigments (5-10 %) with OPC.
The pigment is mixed in a finest powdered state.
The main modern white hiding pigment is Titanium dioxide. Zinc oxide is a weaker white pigment with some important usages.
Some pigments are toxic, such as those used in lead paint. Paint manufacturers replaced lead white with a less toxic substitute, which can even be used to colour food titanium white (titanium dioxide).
Portland slag cement:
This cement is prepared by mixing granulated blast furnace slag, hard burnt gypsum, and cement clinkers in suitable proportions.
This cement offer:
The heat of hydration of Portland slag cement is lower than OPC. Therefore, this cement can be used in mass concreting.
Higher resistance against the attack of chlorides and sulfate.
Better refinement of pore structure.
Higher water tightness. so this cement can be used in the marine structures.
Rapid hardening cement:
It is the type of cement that developed a higher rate of gain of strength and must not be confused with quick setting cement which only set quickly.
The cement attains the strength at the age of 3 days equivalent to that attained by OPC in 7 days.
This Higher strength in the initial stage is attributed to the higher fineness of the cement and increases the proportion of C3S (specific surface area should not be less than 3250 cm2/gm and C3S is approximate 56%).
Application
Pre-fabricated construction
Cold weather concreting
Emergency repair work
Pavement construction
High alumina cement:
This cement is obtained by fusing a mixture, in suitable proportions, of alumina and calcareous materials and grinding the resultant product to a fine powder. The raw material used for the manufacture of high alumina cement is limestone and bauxite.
The proportion of alumina in the cement must not less than 32% and the ratio of the percentage of alumina to that of lime is in the range of 0.85 to 1.3.
The cement offers a higher initial setting time (3.5 hours) and a lower final setting time (5 hours), hence more time is available to work with the cement along with speedy construction.
The cement can also resist high temperatures.
It can resist the action of acid up to a greater extent.
It also offers a higher rate of gain of strength.
When Water and Cement mix, heat is generated. This process is known as Hydration.
Hydration is a chemical reaction in which the major compounds in cement form chemical bonds with water molecules and become hydrates or hydration products.
Major compounds of cement clinker (also known as Bogues compounds) are:
Tricalcium aluminate (C3A): Celite is the quickest one to react when the water is added to the cement. It is responsible for the flash setting. The increase of this content will help in the manufacture of Quick Setting Cement. The heat of hydration is 865 J/Cal.
Tricalcium silicate (C3S): This is also called as Alite. This is also responsible for the early strength of the concrete. The cement that has more C3S content is good for cold weather concreting. The heat of hydration is 500 J/Cal.
Dicalcium Silicate (C2S): This compound will undergo reaction slowly. It is responsible for the progressive strength of concrete. This is also called as Belite. The heat of hydration is 260 J/Cal.
Tetra calcium Alumino ferrite (C4AF): This is called as Felite. The heat of hydration is 420 J/Cal. It has the poorest cementing value but it responsible for long term gain of strength of the cement.
Non-destructive Tests
Non-destructive tests are used to ascertain the quality of hardened concrete (strength, durability, elastic properties), generally following test are characterized as non-destructive test are:
1. Schmidt Rebound hammer test
2. Ultrasonic Pulse velocity test
3. Penetration method
4. Pull out Test method
5. Radioactive and nuclear test method
Destructive Test
In the case of destructive tests, the concrete specimens (cube, cylinder, etc) are loaded till destruction in the laboratory, and strength properties are determined from the tests. The following test are characterized as destructive test are:
1. Compressive strength
2. Tensile strength
Splitting tensile test
Modulus of rupture test
3. Bond strength
Different type of strength of timber:
Compressive strength:
The compressive strength is found to be the highest when acting parallel to the axis of growth.
The compressive strength perpendicular to the fibers of wood is much lower than that parallel to fibers of the wood.
Tensile strength:
Tensile strength along a direction parallel to the grains is found to have the greatest strength that can be developed under any kind of stress.
Tensile strength parallel to fibers is of the order 80.0 to 190.0 N/cm2.
Shearing strength:
Resistance to shear in across direction is found 3 to 4 times greater than that along fibers.
The shear strength along the fiber is found of the order 6.5 to 14.5 N/mm2.
Explanation:
The strength of timber is the highest parallel to the grains and minimum perpendicular to grains.
Timber:
The wood that is going to use for the building. The structure of the wood is:
Pith:
The innermost central portion or core of the tree is called the pith or medulla.
As the plant becomes old, the pith dies up and decays.
Sap Wood:
Outer annual rings between the heartwood and cambium layer are the sapwood.
It is light in color and weight.
It takes an active part in the growth of the trees.
It does not impart any strength.
Cambium Layer:
A thin layer of sap in between the sapwood and inner bark is referred to as the cambium layer.
It indicates the portion of the sap which is yet to be converted into the sapwood.
Bark:
The Outer protective layer or covering provided around the cambium layer is referred as bark.
Bulking of Sand:
The increase in the volume of sand due to an increase in moisture content is known as the bulking of sand. A film of water is created around the sand particles which forces the particles to get aside from each other and thus the volume is increased.
The increase in moisture in sand increases the volume of sand. The volume increase in dry sand is known as the bulking of sand. Bulking of sand depends on the quantity of moisture in the sand and also the size of the particles. Five to eight percent of the increase in moisture in the sand can increase the volume of sand up to 20 to 40 percent. Again the finer the sand is more will be the increase in volume and the increase in volume will be relatively less for coarser sand.
So, From the figure, We can say that With an increase in moisture content, the bulking of sand First increases to a certain maximum value and then decreases.
Fineness modulus of an aggregate is an indicator of the mean size of particles. The coarser the particle, the higher the fineness modulus.
Type of SandFineness Modulus Range
Fine Sand2.2 – 2.6
Medium Sand2.6 – 2.9
Coarse Sand2.9 – 3.2
Resins:
The resin is a natural or synthetic compound that begins in a highly viscous state and hardens with treatment
Many different kinds of resins may be used to create a varnish
Natural resins used for varnish include amber, kauri gum, dammar, copal, rosin, sandarac, balsam, elemi, mastic, and shellac
Varnish may also be created from synthetic resins such as acrylic, alkyd, or polyurethane
Typically, it is soluble in alcohol, but not in the water
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Vee - Bee Consistometer
It is the method used to determine the workability of very dry mixes with low workability.
It measures the time required for complete remoulding of concrete in seconds after placed in the mould with a slump cone.
It is expressed in seconds.
Note:
As slump increases, Vee - bee time decreases, and the compaction factor increases as it becomes easier for concrete to flow.
The degree of workability in Vee - Bee test is classified based on the time taken in seconds as shown below:
Degree of workability Vee - Bee degree (seconds)
Extremely low > 20
Very low 12 - 20
Low 6 - 12
Medium 3 - 6
High 0 - 3
Pointing is the finishing of the joints in brick masonry using either cement mortar (1 (cement): 3 (sand)) or lime mortar (1 (fat lime): 2 (sand)).
Facing is an outer layer or coating applied to a surface like brick wall for protection or decorative purpose.
Guinting is the process of repairing the already damaged concrete surface. In this method, cement is mixed with sand in 1: 3 or any other specified proportion and this mixture is applied over damaged concrete surface with a cement gun under some pressure. By doing so, a highly impervious surface is achieved.
Plastering is the process of covering rough walls and uneven surfaces in with a material, called plaster, which is a mixture of lime or cement and sand along with the required quantity of water.
Efflorescence:
It is a whitish coloured powdered deposition of salts on the concrete surface that is formed due to evaporation of water from the concrete.
It is caused when water soluble salts are present in the concrete material, which comes on to the surface while evaporation of water from the concrete.
These salts are sulphate and carbonate salts of calcium and sodium and can come from bricks, cement, aggregates, water, or admixtures.
The following water soluble salts are generally leads to efflorescence:
∴ Sulphates and carbonates of sodium, and calcium leads to efflorescence, but not due to those of iron.
Stones
Quarrying is the process of removing the rock, sand, gravel or other minerals from the ground in order to use them to produce materials for construction or other uses.
Natural bed of stone is the plane along which stone can easily be split. It thus indicates the plane or bed on which the sedimentary stone was originally deposited.
Dressing of Stone is the working of quarried stone into the shape and size required for use. This can be necessary as stones obtained from quarrying generally do not have the exact required dimensions or finish.
Seasoning of stone means to expose the stone in the open air for a period of 6 to 12 months. It removes quarry sap and makes the stone-hard and compact.
Basic Runway Length Correction for Elevation, Temperature and Gradient Correction for Elevation Corrections in runway length (i) correction ...
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