How to set up formwork in high rise structures

Aluminum formwork is very effective for both high and low-rise concrete construction projects. Aluminum formwork technology can significantly minimize the labor costs as well as makes the project cycles shorter.

WTF aluminum formwork is a highly recognized construction system for building up cast in place concrete structures. WTF offers aluminum formwork for reinforced concrete construction ranging from single and multi-story buildings and facilitates the walls and slab to be positioned monolithically in the similar operation. It enhances efficiency and builds up an extremely robust structure with superb concrete finish.

The WTF Aluminum Formwork System is excellent since it builds all of the components in the structure along with walls, floor slabs, columns, beams, stairs, window details, balconies, and different decorative features with adherence to the architect’s design.

WTF aluminum formwork technology is a complete system that can be employed for simple column, beam and slab constructions through to more complicated features like curved structures, staircases, and all architectural features.

Go through the following video tutorial to learn how WTF aluminum form is set up in high rise structure.

Video Source: Civil Engineering

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Published By
Arka Roy
http://www.constructioncost.co
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Some useful tip on placing of Reinforcement

Reinforcement should be perfectly arranged and sufficiently supported prior to placing of concrete as well as safeguarded against displacement within allowable tolerances which are given below.

The tolerances, given below, should be maintained while placing reinforcement unless otherwise mentioned by the engineer:

(a) Tolerances for depth d, and minimum concrete cover in flexural members, walls and compression members should be as follow :-

Tolerances for Placing Reinforcement

Tolerance for d – Tolerance for Minimum Concrete Cover

d ≤ 200 mm ±10 mm –10 mm
d > 200 mm ±13 mm –13 mm

(b) Regardless the provision of (a) above, tolerance for the clear distance to formed soffits should be minus 6 mm and tolerance for cover should not be in excess of minus 1/3 the minimum concrete cover stated in the design drawings or specifications.

(c) Tolerance for longitudinal location of bends and ends of reinforcement should be ± 50 mm, excluding at discontinuous ends of brackets and corbels, where tolerance should be ± 13 mm and at discontinuous ends of other members, where tolerance should be ±25 mm. The tolerance for concrete cover should also be used in discontinuous ends of members.

Welded wire reinforcement (with wire size not more than MW30 or MD30) applied in slabs not over and above 3 m in span should be allowed to be curved from a point adjacent to the top of slab over the support to a point near the bottom of slab at midspan, in case such reinforcement is either continuous over, or securely anchored at support.

Welding of crossing bars should not be allowed for assembly of reinforcement unless the concerned engineer approve.

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Benefits and drawbacks of air entrained concrete

Air entrained concrete is formed by providing little air bubbles into concrete is called air entrainment. Air entrainment is performed with the use of air entraining Portland cement or air entraining agents like admixture.

The amount of air in such concrete is normally kept among four to seven percent of the volume of concrete.

Various types of methods like galvanometric method, volumetric method and pressure method are used to work out the concrete volume. The air bubbles mitigate internal pressure on the concrete by arranging chambers for water to be extended at the time of getting freezed.

Method – Air in concrete in integrated in the following ways:

 By utilizing gas forming materials like aluminium powder, zinc powder and hydrogen peroxide.  With the application of surface active agents that minimizes surface tension. These may contain natural wood resins and their soaps, animal or vegetable fats or oils, alkali salts of sulfonated or sulphated organic compounds.  With the help of cement dispersing agents.

Benefits – Given below, some of the benefits of air entrained concrete:

1. Workability of concrete is raised significantly.
2. The impact of freezing and thawing is reduced with air entraining agent.
3. Bleeding, segregation and laitance in concrete are decreased.

4. Entrained air makes the sulphate repelling strength of concrete.
5. Minimizes the chance of shrinkage and crack development in the concrete surface.

Drawbacks – Given below, some of the drawbacks of air entrained concrete:

a. The strength of concrete is reduced.
b. Air entraining agent can raise the porosity of concrete and consequently the unit weight is decreased.
c. Air-entrainment in concrete should not be performed if the site control is not superior because the air entrained in a concrete differs with the alteration in sand grading, errors in proportioning and workability of the mix and temperatures.

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Published By
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Brief explanation of Cement Hydration Process

This construction video tutorial provides useful information for the students who will appear in SSC and JE exam. The video is presented by the renowned civil engineer Mr. Parag Pal and it sheds light on cement hydration process. Mr. Pal briefly explains the term rate of heat liberation throughout pouring of concrete.

Before delve into the video, first learn the definition of hydration :-

When series of unchangeable exothermic chemical reactions occur among cement and water, it is defined as hydration.

With existence of water, the silicates and aluminates develop the products of hydration which in due course form a rigid (solid) and hard mass i.e. the hydrated cement paste.

Production of hydration products ultimately results in stiffening (loss of adaptability), setting (consolidation), hardening (strength gain).

Hydration process is ceaseless still the heat and moisture exist in the cement.

To gather sufficient knowledge on the fundamentals of hydration is very important for the following reason :-

Assure the strength and longevity of concrete.

Identify and alleviate the stresses to resist cracking.

Recognize the significance of superior curing and construction practices.

Go through the following video tutorial to learn the detail hydration process.

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Published By
Arka Roy
http://www.constructioncost.co
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Brief overview of rise and fall table in land surveying

This construction video tutorial is very useful for land surveyor. The tutorial sheds light on the rise and fall table in land surveying. Get some useful tricks to resolve the rise and fall table.

Rise and fall method is applied to resolve the levelling to detect the variation in elevation and elevation of points..

By resolving this table, it is possible to work out the reduced level of each point captured at staff rod with leveling machine. In order to work out the reduced level of an individual point, it is necessary to compute the rise and fall of points. After that, for reduced level, the following formula is applied :-

new R.L = old R.L – Fall
new R.L = old R.L + Rise

The table contains various heads like number, B.S (back sight), I.S (inter sight), F.S (fore sight), Rise, Fall, R.L (reduced level) and remarks.

B.S – Back sight (BS) is the abbreviation for “back sight reading”. It means the first staff reading captured by the surveyor as soon as the levelling instrument is arranged and levelled. B.S is normally captured on the point of known reduced level as on the benchmark or a change point. The normally applied datum is mean sea level.

Fore sight (FS) is the abbreviation for “fore sight reading”. It means the last staff reading captured prior to modify the instrument to the other position. It refers to the staff reading captured on point whose RL is to be ascertained. This sight is treated as negative and assumed from Height of Instrument to find out RL of the point.

Reduced Level (RL) in surveying stands for equating elevations of survey points relating to a common assumed datum. It refers to a vertical distance among survey point and selected datum plane. Therefore, it is taken as the base elevation that is applied as reference to consider heights or depths of other important places.

To get more detailed information, watch the following video tutorial.

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Published By
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Details of chain surveying – Benefits and Drawbacks

Chain surveying is the sort of surveying in which only linear measurements are selected in the jobsite.

This type of surveying is undertaken for surveys of small span to specify the boundaries of plot of land to detect the existing features on them.

Chain surveying is the simplest form of survey in which surveying area is segregated into a number of triangles and the sides of different triangles are calculated directly in the field through a chain or a tape and no angular measurements are chosen. Chain is most recommended for initial survey process.

Chains stands for the measuring devices which are applied in surveying. These are produced with the 100 links of 4mm galvanized mild steel wire. These links are attached with 3 circular or oval wire rings. These rings make the chains flexible.

The chain comprised of several small segments to manage or study the measurements.

At the ends chain contains brass handle with swivel joint to simplify the process for rolling or unrolling the chain devoid of twisting and knots.

At each 10th link is arranged with a total of one teeth, 20th link with a total of two teeth and so on till 40th link. With these arrangements, the reading of measurements can be taken efficiently.

At the center of the chain, there is a circular talley used for easy reading.

Chain surveying devices: 1. Chain, 2. Tape, 3. Arrows, 4. Ranging Rods, 5. Offset Staff, 6. Optical Square

Types of Chains utilized in Surveying – The chains are categorized as follow depending on the length of the chain:

Metric chains, Steel band or Band chain, Gunter’s chain or surveyor’s chain, Engineer’s chain, Revenue chain

Benefits of chains :-

a. The chains can be read easily and instantly
b. They can resist wear and tear
c. They can be repaired in the jobsite without any difficulty

d. There is no requirement to adjust measuring tape
e. This type of survey work is very effective for a small plain ground.
f. It needs simple instruments.
g. Plotting of maps is very simple and trouble-free.

Drawbacks of chain:

a. They are heavy and take long time to open or fold.
b. They turn to be longer or shorter because of repeated use.
c. If measurement is done in suspension the chain sags greatly.
d. Error in measurement may occur because of temperature, sagging and marking.
e. Requires more manpower to complete the layout.

This type of surveying is recommended for undulation land where chaining operation is tiresome and prone to errors. This method should not be undertaken for a crowded city containing a huge numbers of buildings and obstacles since it cannot be separated into well-conditioned triangles. As for instance route surveying.

For conducting the survey work of a road, irrigation canal, railways, water and sewer lines, tunneling etc., this method is not suitable at all.

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Published By
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Fast Form Bracket System offers complete slab wall & sheet pile capping formwork Solution

Fast-Form provides complete solution for different types of pile cap, slab, base, beam, wall and sheet pile capping beam formwork whether they come in straight or radius, single or double sided.

This system can efficiently bolts together to facilitate casting kickers, plinths, hang bolts as well as monolithic bund walls etc.

There are 2 types of bases to pin directly to hard-core and ground by means of road pins, or bolt with re-usable concrete bolts to slabs and blinding concrete or even fasten them to decking with wood screws.

This system can be used without any difficulty. Just attach the brackets in a line and plumb up, screw on your ply from behind and pour your concrete.

Brackets are angled forward or back to make adjustment with sloping and battered pours along with irregular ground, thus making them much more compliant as compared to timber or panel systems.

The brackets are generated from superior grade galvanized steel to get rid of rust and they have longevity of 25 years plus. They are strong and do not get damaged. They can be also used underwater. Different sizes are available which range from 150 / 200 / 400 / 600 / 800 / 1200 & 1800mm high.

KEY BENEFITS:

• SAFETY: Access, handrails & toe boards, lightweight system that can be easily set up manually instantly and securely.
• SPEED: No need of de-nailing, lightweight and user-friendly system much faster as compared to conventional process and very simple to use with low labour skill levels.

• COST: It is very cost-effective as compared to timber with reduced labour and plant costs.
• ENVIROMENTAL: Little or no timber wastage and 100% completely recyclable materials which significantly minimize carbon emission deliveries.
• BETTER FINISH: Fair face finishes are obtained easily. The brackets are available with an F4 finish. So, fewer remedial works are required. Ply is fixed from behind systems, so, there is no marks on face of the concrete and any grade ply can be utilized as per your requirement.

To get more information, visit www.fastformsystems.com

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Published By
Arka Roy
http://www.constructioncost.co
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Maturity Index is the latest method to find out concrete maturity & in-place strength during curing

The Maturity Index offers a simple process to estimate the in-place strength of concrete throughout curing. It is developed on the basis of the principle that the strength is can be obtained depending on the temperature-time history throughout the curing process.

By applying a thermocouple data logger with simple thermocouple temperature sensors implanted in the concrete, the data can be recorded easily. This data can then be instantly evaluated with excel spreadsheet to work out the maturity index.

Concrete maturity belongs to a measuring system of how much a batch of freshly poured concrete has cured. It is a quick indicator of the in-place strength at that point in time corresponding to the ultimate strength when the concrete is completely cured. Usually, the concrete strength is calculated on the basis of compression tests. The maturity method works out an index on the basis of time-temperature data that offer a relative indicator of strength.

This method is very useful since it can be performed instantly on-site with a temperature data logger and thermocouple sensors implanted in the pour. Besides, the method can save significant time and enhance safety by facilitating form removal, post-tensioning, joint sawing or putting structures in service ensuring that necessary strength has been achieved.

What is the Maturity Index?

The maturity is created on the perception that strength of concrete is dependent on the hydration of cement in the mix. This hydration stands for an exothermic reaction that emits heat. By recording the temperature profile at regular time gaps throughout the curing process, the strength of concrete can be computed on-site in real-time.

The American Society for Testing Methods (ASTM) developed a standard method for measuring the concrete strength with the maturing method, ASTM standard C 1074. This method is based on initial calibration process that needs assessment of the maturity index in line with more traditional compressive strength test to create the maturity index vs. strength curve. Once this curve is set it is supposed to be applicable for any pours which employ the identical mix recipe.

The maturity index is computed from the raw time temperature data with the following 2 expressions:

The temperature-time factor:
M(t)= ∑▒〖(Ta-To)∆t〗

Where:

M(t)= Maturity temperature-time factor
Ta = Average temperature during time interval ∆t
To = Datum temperature below which no hydration occurs
Δt = time interval between measurements

Equivalent age using an Arrhenius function:
t_e= ∑▒e^(-Q(1/Ta- 1/Ts)) ∆t

Where:
te = Equivalent age
Q = Activation energy divided by gas constant K
Ta = Average temperature during time interval ∆t
Ts = Datum temperature below which no hydration occurs

Δt = time interval between measurements

To get more details go through www.DataLoggerInc.com

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Published By
Arka Roy
http://www.constructioncost.co
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Some useful tips for reinforcement detailing

Given below, some useful tips for reinforcement detailing :-

Create drawings perfectly. Try to mark every bar and demonstrate its shape for transparency.

Cross section of retaining wall that falls quickly as soon as soil backfill is arranged since ¼” dia is used instead of 1 ¼” dia. Errors happen as exact rebar dia is covered with a dimension line.

If required, generate bar bending schedule.

Denote perfect clear cover, nominal cover or effective cover to reinforcement.

Settle detailed location of opening/hole and provide sufficient information for reinforcement around the openings.

Utilize the size of bars and spirals which are easily accessible. For a single structural member, there should limited numbers of various sizes of bars.

The grade of the steel should be mentioned properly in the drawing. Deformed bars should not contain hooks at their ends.

The enlarge details at corner, intersections of walls, beams and column joint should be demonstrated at identical situations. There should not be congestion of bars at points where members overlap and ensure that all reinforcements are placed perfectly.

For bundled bars, lapped splice of bundled bars should be formed by connecting one bar at once; such separate splices inside the bundle should be staggered.

Ensure that the hooked and bent up bars are arranged and there is sufficient protection for concrete.

Specify all expansion, construction and contraction joints on plans and provide details for such joints.

The position of construction joints should be at the point of minimum shear roughly at mid or adjacent to the mid points. It should be created vertically instead of a sloped manner.

Article Source: onlinecivilforum.com

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Published By
Arka Roy
http://www.constructioncost.co
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Definition, causes and remedies of efflorescence in masonry & other building surfaces

Efflorescence stands for a fine, white or greyish, powdery deposit of water-soluble salts that is present on brick, concrete, stone, stucco or other building surfaces when the water vaporizes. Besides, efflorescence also exists on floors and walls and requires special attention. It is often mentioned as “whiskers”.

These efflorescent salt deposits is found at the worst times, normally about a month as soon as the building is developed, and sometimes as long as a year after finishing of structure.

Efflorescence is found in both indoors and exterior, and it can differ in frequency and intensity because of the existence of moisture and temperature.

The efflorescence happens for the following three factors :-

• Existence of water-soluble
• Salts are converted into a soluble solution because of moisture content.
• The transmission of salts through a material to its surface that leads to vaporization of the moisture and cause the salts to crystallize and thus efflorescence is formed.

Moisture is mainly formed due to water, rain and snow and may affect the extent of efflorescence. Condensation, groundwater tapering and interior activities also may influence the extent of moisture formation.

In several cases it is found that efflorescence may happen throughout home construction. If masonry units are left behind all through the night during construction, they can consume moisture from damp soil and rain. It is recommended that masonry units should be wrapped and left in pallets to reduce the risk of efflorescence during a construction project.

The following installation issues associated with building surface result in creating efflorescence

• Improper application of through-wall flashing
• Utilization of masonry devoid of adequate ventilation
• Utilization of masonry in areas where a perfect moisture barrier does not exist
• Joint material failure
• Imperfect ground storage

How to get rid of efflorescence – The following measures should be taken to avoid efflorescence:

1) Hydrophobic Sealant: Use a saturating hydrophobic sealant to a building material surface to resist the immersion of water. The sealant also will resist water from passing through a building material.

2) Capillary Breaks: Set up capillary breaks like polyethylene sheeting among a building material and soil to reduce the risk of salt penetrating the material.

3) Standard Masonry Construction: Apply overhanging copings, eaves and flashings will help in reducing the risk of entering water into a wall.

4) Better Emphasis on Landscaping and Sprinklers: Give concentration to landscaping and sprinklers will guarantee to avoid water from reaching permeable building materials.

5) Set up Grout with Mechanical Vibration: Compile grout with mechanical vibration will control the occurring of voids in the grout.

6) Apply Dense Tooled Mortar Joints: Provide dense tooled mortar joints to minimize the permeable nature of a wall, making it strong for salts to pass through it.

7) Utilizing Grout Admixtures: Various grout admixtures like chemical additives should be used since they can make flow of a grout mix better and minimize its water content all together to lessen voids in grout.

8) Preserve Masonry Materials Properly: Retain masonry materials off the ground and wrap them with water-resistance materials to safeguard these materials from groundwater and precipitation.

Article Source: www.nitterhousemasonry.com

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Published By
Arka Roy
http://www.constructioncost.co
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