adsense analytic

Showing posts with label Concrete Aggregate. Show all posts
Showing posts with label Concrete Aggregate. Show all posts

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
~~~~~~~~~~~~~~~~~~~~~~~~

Wednesday, December 5, 2018

The role of Viscosity Modifying Admixture (VMA) in Concrete

Viscosity Modifying admixtures or VMAs belong to the admixtures which are applied to modify various properties of fresh concrete ranging from viscosity, workableness, cohesiveness etc.
The functionality and uses of VMA for several types of concrete are given below.


Function of Viscosity Modifying Admixture (VMA) in Concrete

The prime objective of viscosity modifying admixture in a concrete mix is to modify the rheological properties of concrete- particularly the plastic viscosity of fresh concrete. If VMA is added to concrete mix, the plastic viscosity of concrete is raised and a slight surge in yield point is observed.

Yield point is another rheological property of concrete that should also be improved together with the plastic viscosity to attain perfect concrete rheology. The yield point of concrete is not impacted with VMA.

Therefore, besides, VMAs plasticizers or super plasticizers are also included to modify the yield point of concrete mix.

Advantages of Viscosity Modifying Admixtures (VMAs)

Given below, the details of various types of concretes which show different behavior with the inclusion of viscosity modifying admixture to their design mixes:

1. Self-compacting Concrete, 2. Pumped Concrete, 3. Under Water Concrete, 4. Light weight concrete, 5. Semi-dry Concrete, 6. Sprayed Concrete, 7. Porous Concrete, 8. Concrete with Poorly Graded Aggregates

1. Self-compacting Concrete: When Self-compacting concrete blends with less powder content, it remains unsafe against moisture variations and as a result segregation may take place.

Inclusion of viscosity modifying admixture to self-compacting concrete raises the segregation resistance as well as enhances the strength to moisture variations.

VMAs improve the strength of self-compacting concrete mixes.

VMAs also minimize bleeding from concrete mix.

Pumped Concrete

a. Obstacle of aggregates at bends in pipe is the issue found in general that occurs for pumped concrete.
b. When Viscosity modifying admixture is included, pumped concrete turns out to be more consistent and segregation while pumping can’t occur.
c. The friction among pump-wall and concrete mix while pumping is minimized by lubricating effect resulting from VMA.


Sprayed Concrete
a. Use of viscosity modifying admixture reduces the rebound of aggregates from sprayed concrete by enhancing the cohesion of concrete mix.


Porous Concrete
a. Viscosity modifying admixtures resist the discharge of cement paste from porous concrete mix.
b. VMA makes the bond better among cement paste and aggregate thereby raises the strength of concrete.


To get more details, go through the following link theconstructor.org

The role of Viscosity Modifying Admixture (VMA) in Concrete

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

Monday, October 9, 2017

Specification of M50 concrete mix design

Concrete mix design belongs to the method of determining the ratios of concrete mix in terms of proportions of cement, sand and coarse aggregates.

As for instance a concrete mix of proportions 1:2:4 signifies that cement, fine and coarse aggregate are in the ratio 1:2:4 or the mix comprises of one part of cement, two parts of fine aggregate and four parts of coarse aggregate.

The concrete mix design proportions are both by volume or by mass. The water-cement ratio is normally stated in mass.
The mix design M-50 grade (with Admixture –Sikament) presented here is for reference purpose only. Actual site conditions may fluctuate and consequently, this should be modified as per the location and other factors.
M50 Grade concrete is mostly suitably in heavily reinforced structures to withstand dynamic loading.
Given below the specifications of M50 Concrete Mix Design
Grade Designation = M-50
Type of cement = O.P.C-43 grade
Brand of cement = Vikram ( Grasim )
Admixture = Sika [Sikament 170 ( H ) ]
Fine Aggregate = Zone-II
Sp. Gravity
Cement = 3.15
Fine Aggregate = 2.61
Coarse Aggregate (20mm) = 2.65
Coarse Aggregate (10mm) = 2.66
Minimum Cement (As per contract) =400 kg / m3
Maximum water cement ratio (As per contract) = 0.45
Mix Calculation: –
1. Target Mean Strength = 50 + ( 5 X 1.65 ) = 58.25 Mpa
2. Selection of water cement ratio:-
Suppose water cement ratio = 0.35
3. Calculation of water: Estimated water content for 20mm max. Size of aggregate = 180 kg /m3 (As per Table No. 5 , IS : 10262 ). As plasticizer is projected, water content is decreased by 20%.
Water content is taken as 180 X 0.8 = 144 kg /m3
For more details, click on the following link engineeringcivil.com
Specification of M50 concrete mix design

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