adsense analytic

Tuesday, March 26, 2019

Specifications of cement concrete in detail

Cement, fine aggregates, coarse aggregates and water are mainly used to form cement concrete. While writing detailed specifications, explain The specifications of every single component should be narrated briefly at the time of formulating detail specifications.

CEMENT: Cement belongs to the elementary and most vital component of cement concrete. The quality of cement should be fresh while utilizing it for construction work and it should satisfy the standard specifications.

FINE AGGREGATE: Sand is utilized as fine aggregate in cement concrete. Sand particles should comprise of coarse, sharp and angular edges. Size of sand particles should be maintained in such a manner that it can move through 4.75mm sieve. Sand should be clean and does not contain dust and organic matters. Sea sand should not be applied for construction work due to extreme salt contents.

Stone dust is also applied as fine aggregate in cement concrete, but prior to application, check that it adheres to specifications.

COARSE AGGREGATE: Normally, pieces of feverous rocks are applied as coarse aggregates. These stones should be solid, strong, long-lasting and clean. The shapes of aggregates should be cubic or closed to cubic shape. The shape of coarse aggregates should not be laminated and elongated. It should be clean and does not contain from any irrelevant organic matters.

The size of coarse aggregates should satisfy the approved construction work requirements. It should not move through the sieve size of 5mm and coarse aggregates should be graded. Voids should not go beyond 42%.

PROPORTIONING: Based on their fixed ratios, cement, sand and coarse aggregates should be calculated. Prepare a standard measuring box as per the volume of one cement bag. Volume of one cement bag is 1.25 cubic foot.

When, it is required to calculate the ratio of sand, bulking of sand should be taken into consideration. Choose dry sand at the time of making calculation of proportioning. Work out the moisture content in sand and include extra volume of sand. Constantly work out moisture content throughout construction work and include extra volume of sand based on the amount of moisture. It is suggested not to compact coarse aggregates at the time of proportioning.

CONCRETE MIXING: Mixing machine is suitable for large scale construction works whereas hand mixing is chosen since it is cost-effective for smaller concrete works.

CONCRETE CONSISTENCY: Concrete consistency is based on water to cement ratio. Surplus amount of water reduces the strength of concrete and also concrete constituents can be easily detached. The quantity of water given below should be applied against 50kg cement bag.

Concrete Ratio - Amount of Water
1:3:6 - 34 liters
1:2:4 - 30 liters
1:2:3 - 27 liters
1:1:2 - 25 liters


If vibrator is utilized for concrete compaction, then the amount of water should be reduced as per suggestion of engineer in charge.

 Specifications of cement concrete in detail
Read more
~~~~~~~~~~~~~~~~~~~~~~~~
Published By
Rajib Dey
www.constructioncost.co
~~~~~~~~~~~~~~~~~~~~~~~~

Monday, March 25, 2019

Some useful tips to examine concrete formwork in job site

The finalized inspection of concrete formwork should be examined prior to set the reinforcement bars in exact location. By implementing perfect form work, honey combing, blow holes, grout less or discoloration of concrete can be circumvented and consequently the finished surface of concrete becomes superior.

Prior to commencement of concreting work, shuttering surface should be fully cleansed and does not contain any defect/deposits in order to provide rightly straight smooth concrete surface. Shuttering surface does not contain any damage and unnecessary roughness to its surface.

While building concrete form work, the following should be examined properly.

1. Any member to be retained in position once the general dismantling is completed, should be labeled perfectly.
2. The applicable materials should be thoroughly examined in order that no incorrect items/rejects are utilized.
3. When excavations exist nearby reformatory and strengthening action should be undertaken to impact the safety of form work.
4. The quality of bearing soil should be strong and it should be arranged properly and the sole plates should bear well on the ground. Sole plates should be perfectly placed on their bearing pads or sleepers. The bearing plates of steel props should not be deformed. There should be adequate bearing areas for the steel sections on the bearing members.

5. There should be proper safety provisions to get rid of impact of traffic, scour caused by water and accidental impacts.
6. To maintain proper strength and durability of form work at intermediate stage, bracing, struts and ties should be provided together with the advancement of form work. Avoid ‘Tilting and overturning of steel sections.
7. While applying customizable steel props, no damage and evident bents should be observed; steel pins should be arranged, restricted latterly near each end.
8. Screw adjustments of adaptable props should not be over extended.

9. When settlement/elastic shortening of props happens, double wedges should be arranged for correction of the form to the desired position. Wedges are applied only at bottom end of single prop and should not be very steep and one of the pair should be secured/clamped down after correction to avoid their shifting.
10. No member should be eccentric over vertical member.
11. There should sufficient number of bolts and nuts and cantilever supports.
12. Props shall remain directly under one another in multistage construction.
13. Guy ropes or stays should be perfectly tensioned.
14. Provision should be arranged for movement and operation of vibrator and other plant and equipment.
15. Required camber should be arranged over long spans.
16. Supports shall be sufficient and in plumb.


Some useful tips to examine concrete formwork in job site

Read more
~~~~~~~~~~~~~~~~~~~~~~~~
Published By
Rajib Dey
www.constructioncost.co
~~~~~~~~~~~~~~~~~~~~~~~~

Wednesday, March 20, 2019

Some useful guidelines to develop a building foundation

While building up a foundation for a building, adequate knowledge is required with some particular steps to make sure that the footings will retain the weight of the building through rest of time.

The purpose of building foundations is to bear the load of the structure as well as disperse the load to the soil in greater cross sectional area. The foundation should have the capacity to resist the load of the structure along with the live loads and environmental factors.

A safety factor is arranged for safety all through the foundation design. The foundation is built up on the basis of the design. Given below, some vital steps, which should be abided by, at the time of constructing & designing building foundation.

1: Survey and Stake Out Footprint - A professional surveyor should execute this step. The surveyor will settle on the exact distances from the property lines. It makes sure that the building will set out perfectly and abide by the code. The corners of the building will be marked with surveyor’s stakes.

Then the surveyor will arrange offset stakes about two feet out from the surveyor’s stakes. The digging for the foundation will start by applying the offset stakes as the guides. It accomodates extra room so the work can be performed on the exterior foundation walls.

2: Excavation - A structural engineer is required to define the depth of the excavation. All surface soils should be eliminated to uncover the soil that is properly compressed to carry the weight of the building.

The depth will differ for each building. The top of the footing should remain underneath the frost line since it resists the concrete from cracking when the freeze-thaw cycle happens in the soil that encircles the building.

3: Footings - A footing stands for a poured concrete pathway that is applied to expand the weight of the building from the foundation walls to the soil. They are larger as compared to the foundation walls that they are supporting and create the perimeter of the building. In some cases, there exist extra footings which are provided inside the perimeter to provide support to the load-bearing walls.

4: Sub Slab - Normally, plumbing lines are arranged from the street to the building’s basement by passing over or even below the footing. It occurs for the buildings which contain their own separate sewage facility or drain field. A poured concrete slab is used to cover these lines.

5: Foundation Drainage System - Subsurface water is preserved and pushed away from the foundation to get rid of pooling water or flooding. The foundation drainage tile is constructed with an incessant run of punched drainage pipes which are implanted in gravel along the foundation of the building. In some areas, a sump pump may also be needed to facilitate accumulating the subsurface water.

To gather knowledge on other steps, go through the following link civilengineersforum.com

Some useful guidelines to develop a building foundation

~~~~~~~~~~~~~~~~~~~~~~~~
Published By
Rajib Dey
www.constructioncost.co
~~~~~~~~~~~~~~~~~~~~~~~~

Tuesday, March 19, 2019

How to measure minimum bar spacing for Bundle Bars in Cast-in Place Concrete as per AASHTO provisions

Minimum Bar Spacing: As per AASHTO LRFD, section 5.10, the minimum bar spacing for bundled bars should be measured on the basis of the acquired diameter rather than computing from individual diameters.

As for instance, if there are 2 nos. 32 mm dia bars, the similar diameter in accordance with 2×32 is 45mm. Therefore, 45 should be employed to utilize the following clauses from AASHTO.

For 2×32 dia bars, clear spacing should be provided as ~68mm for Cast-in Place concrete and 60mm for precast concrete.

Refer following Clauses from AASHTO LRFD 5th Edition 2010


5.10.3.1.1—Cast-in-Place Concrete
For cast-in-place concrete, the clear distance among parallel bars in a layer should not be under :
5 times the minimal diameter of the bars,
5 times the maximum size of the coarse aggregate, or 1.5 in.
5.10.3.1.2—Precast Concrete
For precast concrete fabricated under plant control conditions, the clear distance among parallel bars in a layer should not be under :
The minimal diameter of the bars,
33 times the maximum size of the coarse aggregate, or 1.0 in.
5.10.3.1.5—Bundled Bars
The number of parallel reinforcing bars bundled in contact to function as a unit should not go beyond four in any one bundle, apart from flexural members, the number of bars greater than No. 11 should not go beyond two in any one bundle.
Bundled bars should be attached within stirrups or ties. Individual bars in a bundle, cut off inside the extent of a member, should be abandoned at several points with minimum a 40-bar diameter stagger. Where spacing limitations are dependent on bar size, a unit of bundled bars should be considered as a single bar of a diameter taken from the corresponding total area.
How to measure minimum bar spacing for Bundle Bars in Cast-in Place Concrete as per AASHTO provisions
~~~~~~~~~~~~~~~~~~~~~~~~~~
Published By
Rajib Dey
www.constructioncost.co
~~~~~~~~~~~~~~~~~~~~~~~~~~

Monday, March 18, 2019

Common methods for concrete construction

In this civil engineering article, you will get detail information on the most common methods for developing a concrete structure.

Designing the concrete mix: The most vital part in the method is to find out the components that will form the concrete and their ratios. Several types of variables should be taken into consideration at the time of designing which range from cement type, aggregate size and type, amount of water, and mineral and chemical admixtures.

A good mix design can also lead to improper or substandard quality concrete when it is accomplished inappropriately. Based on the type of project, it is decided who will take responsibility for designing the mix. For large, publicly funded projects, a licensed civil engineer should be liable for the final design.

For residential projects like foundations and driveways it is the private contractor, who will prepare the mix design. For do-it-yourself projects it is of course the homeowner who should take responsibility to design his own mix.

To produce an exact mix design, initially, detect the properties that the fresh and solidified concrete should have and then move backwards to opt for the most inexpensive mix design that provides these properties.

Here, focus should be given on the following factors :

Supported Loads: Concrete is formed with different types of strengths, so this is considered as the gateway of the mix design. As the cost of concrete scales rather narrowly with its strength, one does not like to make the concrete stronger than it should have been.

However, if the application provides support to considerably small loads, it is generally not a good idea to indicate weak concrete since weak concrete does not have good stability. For low load applications the quality of the concrete is settled with other factors like resistance to freezing or wear resistance.

Workability: The necessary workability is mainly based on how the concrete will be arranged. Concrete can be poured, pumped, and even sprayed into place, and it will impact the desired workability. Various other factors like the shape of the molds, the rebar spacing, and the accessible equipment at the site for solidifying the fresh concrete once it is placed should also be taken into consideration.

Workability is generally settled with the slump, the tendency for the fresh concrete is to expand under its own weight when it is arranged onto a flat surface.

Environmental conditions: When the concrete is uncovered to severe conditions, then this may perfectly ascertain the required concrete quality in spite of the applied loads. In cold-weather locations the concrete should have the strong resistance capacity against freezing. Besides, it must have the ability to resist the corrosive effects of salt. Underground applications should have the capability to withstand the penetration of moisture and aggressive species from the soil. For almost any type of conditions or mode of attack, the most effective way for defense is to retain the w/c low.

Surface wear: For some applications the physical loads can erode the concrete rather than breaking it. For roads, parking garages, driveways, and industrial floors, the longevity of the structure depends on the hardness and wear resistance of the top layer of concrete.

Common methods for concrete construction

Read more
~~~~~~~~~~~~~~~~~~~~~~~~
Published By
Rajib Dey
www.constructioncost.co
~~~~~~~~~~~~~~~~~~~~~~~~

Saturday, March 16, 2019

Smart Concrete – The newest upcoming technology to detects cracks in concrete earlier

The concrete is extensively used as a composite material for several types of structures but the concrete lacks the strength to resist tension and as a result it can be cracked easily. Therefore, the concrete should be examined thoroughly for cracks and proper and timely repairs should be undertaken so that the quality of the concrete is not deteriorated.

In this way, the safety and stability of different structures are maintained. Another process for determining cracks is to attach sensors to the structure but the installation charge is costly.

Smart concrete technology is the newest concept for examining the health of reinforced concrete structures. The type of concrete is reinforced with carbon fiber comprising of 0.2% to 0.5% of the volume. It can determine the pressure on the concrete structure well in advance. Smart concrete technology has witnessed broad laboratory testing, but has not launched yet.

It becomes functional with the addition of a small amount of short carbon fiber to the concrete with a traditional concrete mixer to change the electrical resistance of the concrete with regards to tension or pressure.

Accordingly, contact among the fiber and the cement matrix is impacted while the concrete is deformed or depressed, thus affecting the electrical resistivity of the concrete volume. Tension is then exposed by calculating the level of electrical resistance.

Smart concrete has the ability to recognize very small structural weaknesses before it gets significant and therefore becomes applicable in checking the internal conditions of the structure, especially after an earthquake.

Besides, identifying small cracks, smart concrete also allows stopping the development of cracks in traditional concrete and reinforce it to make it stronger. Besides, it takes a lot of strength to bend smart concrete, and consume more energy before breaking.

Smart concrete can also be applied in the construction of highways since they can easily find out the weight of the vehicle. Roads constructed with smart concrete can detect the position, weight, and speed of the vehicle.

Smart Concrete – The newest upcoming technology to detects cracks in concrete earlier

Read more
~~~~~~~~~~~~~~~~~~~~~~~~
Published By
Rajib Dey
www.constructioncost.co
~~~~~~~~~~~~~~~~~~~~~~~~

Friday, March 15, 2019

Properties and benefits of self compacting concrete

Self-consolidating alias self-compacting concrete is an extremely flowable type of concrete that does not need vibration for setting and compaction.

It is compressed into each corner of a formwork perfectly with its self weight exclusive of any external vibrators. It is a fully engineered concrete with greater fluidity.

Self compacting concrete retains all the strength and characteristics of concrete satisfying desired performance requirements.

In some specific conditions the inclusion of superplasticizers and viscosity modifier with the mix, the bleeding and segregation is significantly reduced. The strength is decreased for the concrete that segregates and as a result honeycombed areas are produced next to the formwork. A properly designed SCC mix does not segregate and it retains extreme deformability and outstanding stability characteristics.

Advantages of SCC:

a. Curtailment in site manpower
b. Problems due to vibrators are reduced
c. Easy to set
d. Rapid construction
e. Superior surface finish
f. The strength is enhanced because of superior compaction and uniformity of concrete.


Characteristics Of Self-Compacting Concrete

Self-compacting concrete has strong resistance capacity against segregation with mineral fillers or fines as well as special admixtures. It should have the flexibility to be flown and filled special forms under its own weight, it should be flowable enough to move across highly reinforced areas, and should have the capability to get rid of aggregate segregation. This type of concrete should fulfill special project requirements regarding placement and flow.

Self-compacting concrete having a similar water cement or cement binder ratio will generally contain a marginally higher strength with regard to conventional vibrated concrete, without proper vibration, a superior interface among the aggregate and hardened paste will be created.

The concrete mix of SCC should be set at a considerably higher velocity as compared to traditional concrete. Self-compacting concrete should be set at heights greater than 5 meters devoid of aggregate segregation. It can also be applied in areas with normal and congested reinforcement, with aggregates as large as 2 inches.

Self-Compacting Concrete Uses - Self-compacting concrete is mostly found in bridges and even on pre-cast sections.

a. Conclusion
b. Self compacting concrete can save time, cost as well as improve strength.
c. SSC can be efficiently transformed into congested reinforced areas like columns, drilled shafts.


To get more details, go through the following link csengineermag.com

Properties and benefits of self compacting concrete

~~~~~~~~~~~~~~~~~~~~~~~~
Published By
Rajib Dey
www.constructioncost.co
~~~~~~~~~~~~~~~~~~~~~~~~