what is compressive strength of concrete| how to find compressive strength of materials
Compressive strength is the capacity
to oppose pressure loads. When all is said in done, utilizing RCA in the
substantial blend decline compressive strength contrasted with virgin total.
How ewer, at 28 days, all mix designs usually exceed 50 MPa compressive
strength. One study showed the compressive strength of virgin concrete
was 58.6 MPa and the RCA concrete ranged from 50.9 to 62.1 MPa.
There were higher values for
concrete made with 50% RCA compared to 100% RCA. The deficiency of compressive
strength is in the scope of 30-40% for the substantial made with RCA at 28
days. There was a minor reduction in 28 and 56 days compressive strength when
virgin aggregate was partially replaced with RCA and a much greater reduction
when RCA was used in full.
The most influential parameter
affecting compressive strength in the w/c ratio. Other influential parameter
include fine RCA content, cleanness of aggregate, interaction between fine RCA
content and crushed brick content and interaction between w/c ratio and coarse
RCA content . Keeping a constant w/c ratio, air-dried RCA containing concrete
had the highest compressive strength compared to oven-dried and saturated
surface dry RCA. Using unwashed RCA reduces compressive strength particularly
at lower w/c ratios. Compressive strength is 50% of virgin concrete at 0.38 w/c
and 75% at 0.6 w/c.
When comparing laboratory made RCA
and field demolished RCA, there was the same basic trend in all strength
developed. Admixtures in the original concrete has no signification impact on
the compressive strength of the new RCA concrete. At the point when slag is
added to the RCA concrete, it creates strength throughout a more extended
timeframe contrasted with ordinary cement.
Some research suggest
that compressive strength is dependent on the amount of time the RCA spent in
the stockpile after crushing. For example, concrete made with RCA that was in
the stockpile one day had a 25% higher compressive strength than concrete made
with RCA that was in the stockpile 28 days. Concrete made with RCA that was in
the reserve seven days had a seven percent lower compressive strength than
substantial that was in the store 28 days.
RCA concrete showed good
performance when exposed to temperatures up to 600 C with a loss in compressive
strength of 20-25%. When RCA concrete fails it is usually because cracks passed
through the RCA: however, when virgin concrete fails it is usually due to bond
failure at the aggregate paste interface.
There are several barriers to overcome in order for
RCA to become widely accept. Initially there is high investment cost to
purchase concrete crushers. In addition, maintenance cost of concrete crushers
is significant.
As reasonable obstacles are present if crushing of
concrete is done by concrete crushers. Similarly problems are there if crushing
process is done by man power. Both these methods of crushing have their
advantages and disadvantages. Machine
crushing has advantage of smooth crushing but increase the cost which is major
concern in the project.
On the other hand, manual crushing has advantage
according to the major purpose of the project i.e., cost but having
disadvantage of ineffective smoothness in crushing aggregate and chance of
breaking of aggregates particles into small pieces. So, there are some problems
identified during crushing
There is a problem to make the RCA surface free the
mortar mechanically or manually for its proper usage in the concrete to make
bond. If the surface is not free from mortar than its bond become weak and it
gives no better strength.
Another complication is related to quality of RCA. Highways
require quality material that meets engineering, economic an environment
consideration. RCA cannot be used where high performance is required,
Concrete that RCA has less compressive and flexure
strength, increase dry shrinkage. There is also lack of knowledge on how RCA
affects durability.
Government agencies have been show down to embrace to use of RCA due to concern about quality and reluctance to change the past practices. The use of material specification is a crunches in use in RCA. However, specific standards to use RCA in new concrete are not currently available
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