Concept of Quality Control
Quality control or quality assurance is
giving quality to the product or service by taking necessary actions and using
correct and adequate materials. Building and Construction Materials. A quality product may not be high cost. User
decides whether a product is good quality or not. Low priced product or service
can be having high quality if it comes to standard or expectations of
consumers. User expectations depends on performance characteristics, economics
and aesthetics of the products.
Quality Assurance
Quality assurance considers design,
assuring quality of raw materials, development, production and services related
to production and inspection processes. Quality assurance consists of four
steps, 1. Planning 2. Design 3. Checking 4. Action (PDCA). PDCA is an effective
tool for monitoring quality assurance as it analyses existing conditions and
methods used to provide products to clients. For example the quality of
concrete depends not only on quality of materials and structure but also the
environment, safety, reliability, serviceability requirements.
Quality Control through Testing
Testing is a process of determining certain
qualities of a material. There are field and laboratory testing. When the
results lie within a certain limits then the engineer is confident that the
material behavior is almost satisfactory. The quality control has 2 purposes.
One to ensure workmanship and the other is
quality of material. In the case of concrete the quality depends on many
factors so testing is very important. For cube testing of concrete the types of
control are standard deviation and coefficient of variation.
Advantages of Quality Control
Quality control has no extra cost. The materials can be selected from reliable sources after testing which reduces the cost. Without quality control one can not ensure that over spending in one area will compensate in another. One extra bag of cement does not ensure good compaction. Building and Construction Materials. In the absence of quality control the designer will over design that raises the cost. QC reduces maintenance cost.
Storage of Cement the important Building material
Cement may be stored for a long time
particularly when deliveries are irregular. The cement will retain its strength
if moisture is kept away from it. 1 or 2% of water absorption is no harm but
more than that retards the hardening process. If the cement is powdered more it
will become more reactive. Once the cement is stored properly it is not
disturbed. If the cement is stored more than 3 months it must be retested.
Test for Physical Properties of Cement
Fineness
Fineness is the measure is size of
particles of the cement and is expressed in terms of specific surface of
cement. It is determined by air permeability method. When the cement is fine it
has more surface area for chemical reaction.
Setting
Time
When cement is mixed with water it will
harden after a certain time it with stand a fixed amount of pressure. The time
taken is called setting time. The time taken when the paste looses plasticity
is called initial setting time. Final setting time is the time taken from
adding water to become hard. Initial time should not be too less because it is
to be mixed transported and placed. Initial setting time should not be less
than 30 minutes and final setting time should not be more than 600 minutes.
Soundness
Unsoundness is the undesirable expansion.
It results in disintegration and cracking. There is a test for soundness called
Le-Chatelier test.
Compressive
strength
It is the ability of cement giving
compressive strength to concrete. More cube crushing test and concrete
compression tests are there to determine compressive strength.
Vistar associates is a consulting engineers
and project management firm giving consultation in civil engineering.
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