IN-SITU 2015). The process involves batching, mixing,

IN-SITU
CONCRETE FRAME METHOD

INTRODUCTION

In-situ concrete frame is
generally used as a structure for both single and multi-storey buildings such
as residential buildings and commercial spaces. Since several years, in-situ
concrete is raised from an experimental material to the widest form of building
construction. This method is used as a structural material for buildings as a
frame with a combination of beams, columns, concrete roofs and floors. Portland
cement is easily manufactured by burning shale and limestone; aggregates such
as sand and crushed limestone are easily attained. Steel minimills use scrap
iron to feed their furnaces inturn producing reinforcing bars for local
operation (Hartman 2014). In-situ concrete is used for foundations and for
structural skeleton frames.

PROCESS

In-situ concrete frame
involves pouring liquid concrete into removable forms and dismantling the forms
once the concrete has been hardened to leave a solid wall behind (Din 2016).
The pouring liquid concrete includes cement type, aggregate size and type,
amount of water, mineral and chemical admixtures (Din 2016). In the mix, the
aggregates are graded in size, the water combines chemically with the cement
paste to form a strong bond gel structure (The Structural Frame 2015). The
process involves batching, mixing, placing, consolidation, finishing and curing
(Hartman 2014).

BATCHING

The concrete is usually
batched in the ready mix central plants where varieties of cement, aggregates
and equipments are available and operated under controlled conditions. The
process is completed inside the plant and loaded to a truck or it can be mixed
in the truck while transporting to the site. The quality is high and consistent
due to exact weighing of materials and is often suitable for small jobs
depending upon the travel distance.

Fig1(Left):
Ready mix plant. Right: – Fresh
mixed concrete being filled in the truck (Hartman 2014)

MIXING

Mixing of concrete is an
important process to achieve good quality of concrete with the right equipment.
Good mixing removes all the air voids between the aggregates and clusters
formed with cement giving a high strength to concrete. Bad mix design always
leads to bad quality of concrete hence most of the times ready mix concrete is
used.

 

 

Fig2:
Mixing of concrete (Hartman 2014)

PLACING

The concrete must always be
deposited as near as possible into the formwork on the site. The rebar is to be
provided before the placing of concrete into the formwork. Concrete can be transported
using special concrete pumps by hoses or by buckets using cranes if the
deposition place is not accessible.

Fig3:
Placing of wet concrete into the rebar produced formwork (The Structural Frame
2015)

CONSOLIDATION

In this process, the concrete
is compacted after placing through a rolling compactor or vibrator. The
vibrator is an equipment that transfers shear energy into the concrete through
a certain depth to remove excess air voids. The roller is used only in
construction of roads, dams with a heavy roll in front and is driven on the
concrete. While concrete should be placed in many layers, each layer is
compacted first and then the next layer is placed over it.

Fig4:
Compaction of fresh placed concrete (Din 2016)

FINISHING

The concrete floors and
pavements are finished using a wide blade after consolidation to bring out the
smooth surface and attractive. However, the finishing depends on the type of
floor or pavement and for what purpose it is used for. The finishing is carried
out before the concrete is hardened.

Fig5:
Finishing of concrete using wide blade (The Structural Frame 2015)

CURING

The concrete must be cured
after its hardened using damped bags, filling the roof with water or by
spraying water periodically. This process is important as it avoids cracks,
strength loss, durability of concrete. If the curing is not carried out
properly there might be cracks developed or sometimes the collapse of the
building takes place.

 

Fig6:
Curing of concrete by storing water without drying (Hartman 2014)

ADVANTAGES
OF IN-SITU CONCRETE FRAME

ü  Building
design and architectural interest is feasible because of today’s technology.

ü  It
provides thermal insulation resisting from earthquakes, insects penetrating
walls, explosion and collision.

ü  It can
be moulded into numerous geometrical shapes with less maintenance cost.

ü  No
cranes and skilled labours are required for the erection.

ü  Before
or during the construction, any adjustments or alterations is flexible.

ü  Durable
and stable for long time because of minimal deflection and less movement.

ü  Doesn’t
require any storage place and the whole process can be carried onsite.

ü  Preferred
for basement walls and foundations because of its high strength.

ü  It can
withstand any climatic conditions because of its high compressive and tensile
strength.

ü  In-situ
concrete is the most economical material for construction of foundations,
piers, dams and columns.

ü  The
total construction time in in-situ concrete frame is relatively short.

DISADVANTAGES
OF IN-SITU CONCRETE FRAME

·        
It is tough to make the alterations once the
concrete is hardened.

·        
It requires more number of labours which
increases the wages.

·        
The improper process of mixing, placing and
curing affects its final strength which causes shrinkage, cracks and collapse
of the building.

·        
It is a complicated process with many inputs
and flows which takes 28days for attaining the concrete final strength hence,
speed of construction is relatively low.

·        
It need to be carried out under certain
climatic conditions to maintain the hydration of concrete.

·        
The cost is increased due to more temporary
works and falsework of labours.

·        
The formwork costs more and its erection is
time consuming.

·        
Crushed concrete cannot be used for a new
building hence, its scrap value is nil.

·        
Maintaining the quality of concrete is
difficult due to poor mix design.

·        
The surrounding environment of the site is
affected as the process is carried out in an unprotected environment.

·        
Concrete can harden even before placing and
surface finishing is not assured due to variable workmanship.

·        
Climate, large areas can be problematic during
construction and curing.

 

REFERENCES

1)    Din, R. (2016)
“Advantages and Disadvantages of Reinforced Concrete”. Reza
Din

2)    Hartman, D. (2014)
“The Advantages and Disadvantages of Cast-In-Place Concrete”. Dennis
Hartman

3)    “Steel Structure
Vs RCC (Concrete) Structure Buildings -Pros, Cons & Application”
(2013)

4)    The Structural Frame (2015)
available from

21 December 2017