Lets Explore the Diverse Types of Civil Engineering
The excessive presence of silt in the sand reduces the
bonding between cement and aggregates. It increases water demand for concrete.
This reduces the strength of the concrete.
It also modifies the setting times of concrete. It can cause
cracks in hardened concrete. Hence, silt content is undesirable in the sand.
Here is a simple method to find out the silt content in sand.
The permissible limit of silt
content
The silt content should be less than 8 % by volume.
What to do if silt content is
more than the allowable limit?
The sand having silt content more than 8 %, should not be
used in concrete. However, the sand can be used after washing. It brings the
sand content below the permissible limit.
Frequency of Testing of silt
content
The silt content should be tested daily and once for each
truck at the time of unloading at sites.
The preparation of estimates represents one of the most
important functions performed in any business enterprise. In the construction
industry, the quality of performance of this function is paramount to the success
of the parties engaged in the overall management of capital expenditures for
construction projects.
The estimating process, in some form, is used as soon as the
idea for a project is conceived. Estimates are prepared and updated continually
as the project scope and definition develops and, in many cases, throughout
construction of the project or facility.
The parties engaged in delivering the project continually
ask themselves “What will it cost?” To answer this question, some type of
estimate must be developed. Obviously, the precise answer to this question cannot
be determined until the project is completed. Posing this type of question
elicits a finite answer from the estimator. This answer, or estimate,
represents only an approximation or expected value for the cost. The eventual
accuracy of this approximation depends on how closely the actual conditions and
specific details of the project match the expectations of the estimator.
Extreme care must be exercised by the estimator in the
preparation of the estimate to subjectively
weigh the potential variations in future conditions. The
estimate should convey an assessment of the
accuracy and risks.
Estimating Defined
Estimating is a complex process involving collection of
available and pertinent information relating to the scope of a project,
expected resource consumption, and future changes in resource costs. The
process involves synthesis of this information through a mental process of
visualization of the constructing process for the project. This visualization
is mentally translated into an approximation of the final cost.
Estimating at any stage of the project cycle involves
considerable effort to gather information. The estimator must collect and
review all of the detailed plans, specifications, available site data,
available resource data (labor, materials, and equipment), contract documents,
resource cost information, pertinent government regulations, and applicable
owner requirements. Information gathering is a continual process by estimators
due to the uniqueness of each project and constant changes in the industry environment.
Unlike the production from a manufacturing facility, each product of a
construction firm represents a prototype. Considerable effort in planning is
required before a cost estimate can be established. Most of the effort in
establishing the estimate revolves around determining the approximation of the
cost to produce the one-time product.
The estimator must systematically convert information into a
forecast of the component and collective costs that will be incurred in
delivering the project or facility. This synthesis of information is
accomplished by mentally building the project from the ground up. Each step of
the building process should be accounted for along with the necessary support
activities and embedded temporary work items required for completion.
The estimator must have some form of systematic approach to
ensure that all cost items have been
incorporated and that none have been duplicated. Later in
this chapter is a discussion of alternate
systematic approaches that are used.
The quality of an estimate depends on the qualifications and
abilities of the estimator. In general, an
estimator must demonstrate the following capabilities and
qualifications:
• Extensive knowledge of construction
• Knowledge of construction materials and methods
• Knowledge of construction practices and contracts
• Ability to read and write construction documents
• Ability to sketch construction details
• Ability to communicate graphically and verbally
• Strong background in business and economics
• Ability to visualize work items
• Broad background in design and code requirements
Design and Construction of Concrete Formwork
Concrete formwork serves as a mold to produce concrete
elements having a desired size and configuration. It is usually erected
for this purpose and then removed after the concrete has cured to a satisfactory
strength. In some cases, concrete forms may be left in place to become part of
the permanent structure. For satisfactory performance, formwork must be
adequately strong and stiff to carry the loads produced by the concrete,
the workers placing and finishing the concrete, and any equipment or materials
supported by the forms. For many concrete structures, the largest
single component of the cost is the formwork. To control this cost, it
is important to select and use concrete forms that are well suited for the job.
In addition to being economical, formwork must also be constructed with
sufficient quality to produce a finished concrete element that meets job
specifications for size, position, and finish. The forms must also be designed,
constructed, and used so that all safety regulations are met.
Formwork costs can exceed 50% of the total cost of the
concrete structure, and formwork cost savings should ideally begin with
the architect and engineer. They should choose the sizes and shapes of the
elements of the structure, after considering the forming requirements and
formwork costs, in addition
to the usual design requirements of appearance and strength.
Keeping constant dimensions from floor to floor, using dimensions that
match standard material sizes, and avoiding complex shapes for elements in
order to save concrete are some examples of how the architect and structural
engineer can reduce forming costs.
Ready-mix concrete is a type of concrete that
is manufactured in a factory or batching plant, according to a set recipe, and
then delivered to a work site, by truck mounted transit mixers . This results
in a precise mixture, allowing specialty concrete mixtures to be developed and
implemented on construction sites. The first ready-mix factory was built in the
1930s, but the industry did not begin to expand significantly until the 1960s,
and it has continued to grow since then.
Ready-mix
concrete is sometimes preferred over on-site concrete mixing because of the
precision of the mixture and reduced work site confusion. However, using a
pre-determined concrete mixture reduces flexibility, both in the supply chain and
in the actual components of the concrete.
The
leading ready-mix concrete supplier worldwide is the Mexican concrete
company Cemex;
its main competitor is France-based Lafarge
Ready
Mixed Concrete is also referred as the customized concrete products for
commercial purpose. the Ready-mix Concrete Company offer different concrete
according to user's mix design or industrial standard.
The
Ready mixed concrete company is required to equip themselves with up-to-date equipment’,
such as transit mixer, concrete pump, and Concrete Batching Plant, which needs
visualized production management software and also PLC controller.
Ready
Mixed Concrete, or RMC as it is popularly called, refers to concrete that is
specifically manufactured for delivery to the customer's construction site in a
freshly mixed and plastic or unhardened state. Concrete itself is a mixture of
Portland cement, water and aggregates comprising sand and gravel or crushed
stone. In traditional work sites, each of these materials is procured
separately and mixed in specified proportions at site to make concrete. Ready
Mixed Concrete is bought and sold by volume - usually expressed in cubic
meters. RMC can be custom-made to suit different applications.
Ready
Mixed Concrete is manufactured under computer-controlled operations and
transported and placed at site using sophisticated equipment and methods. RMC
assures its customers numerous benefits.
Advantages of Ready mix
Concrete over Site mix Concrete
§
A centralized concrete batching
plant can serve a wide area.
§
The plants are located
in areas zoned for industrial use, and yet the delivery trucks can service
residential districts or inner cities.
§
Better quality concrete
is produced.
§
Elimination of storage
space for basic materials at site.
§
Elimination of
procurement / hiring of plant and machinery
§
Wastage of basic
materials is avoided.
§
Labor associated with
production of concrete is eliminated.
§
Time required is greatly
reduced.
§
Noise and dust pollution
at site is reduced.
§
Reduce cost.
§
Disadvantages of
Ready-Mix Concrete
§
The materials are
batched at a central plant, and the mixing begins at that plant, so the
traveling time from the plant to the site is critical over longer distances.
Some sites are just too far away, though this is usually a commercial rather
than technical issue.
§
Generation of additional
road traffic; furthermore, access roads, and site access have to be able to
carry the weight of the truck and load. Concrete is approx. 2.5tonne per m³.
This problem can be overcome by utilizing so-called 'minimix' companies, using
smaller 4m³ capacity mixers able to access more restricted sites.
§
Concrete's limited
timespan between mixing and going-off means that ready-mix should be placed
within 90 minutes of batching at the plant.
