2010 S2 CVEN 2101 - Wk 9-2 (2 slides)

[CVEN 2101] Engineering Construction
Introduction to Concrete (Con’t)
•Be of proper workability so as to enable proper consolidation, prevent segregation, completely fill the forms, and provide achievement of a proper finish
•Slump-test
–Most widely used
–Measures the amount of slump from its original height
–/watch?v=higx_ktnKLI&feature=related
Introduction to Concrete (Con’t)•Concrete operation
–Batching the materials
–Mixing
–Transporting
–Placing
–Consolidating
–Finishing
Fi i hi
concrete is batched in a central batch plant and transported to the
p p job site in trucks
•/watch?v=0Aqq3a0GTjY&feature=related •Mixer output production rate
–Mixer size is measured by volume
–Mixer output is measured by m3/hr Æmixer size / mixer cycle time
–Mixer cycle time: loading time, mixing time, and discharging time
Transit mixed Central mixed
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Mixing Concrete (Con’t)•Freefall mixers
–Mix concrete by lifting the ingredients with the aid of fixed blades inside a rotating
drum and then dropping the material
S i bl f h iff –Suitable for concretes that are not too stiff (about 5-6 cm of min. slump)
•Power mixers
–Blend concrete by rapid rotary motion of paddles moving in centric or eccentric
courses inside the mixing drum
–Require a shorter mixing time to obtain
R i h t i i ti t bt i
homogeneous, high-quality concrete,
resulting in greater output
•/watch?v=q49_3 ePR5kw
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[CVEN 2101] Engineering Construction
–Remotely located projects
–Large scale projects
–Project located in busy, heavily trafficked urban areas •Smaller-scale self-contained concrete plant
–Operates similarly to a full-size permanent central plant
–Can be moved between sites either on trucks or in a trailer-mounted configuration
–Highly automated and can be operated by one worker
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[CVEN 2101] Engineering Construction
–Complementary means on projects utilizing cranes or pumps
C l t j t tili i
–Additional expenses of building ramps, runways, and similar setups should be taken into account
–Recommended for distances less than 60m
–Motor-propelled buggies (power buggies) can traverse up to 300m 14[CVEN 2101] Engineering Construction
[CVEN 2101] Engineering Construction
–Proper belt size and speed should be considered
–Particular attention must be given to points where the concrete leaves one conveyor and either continues on another conveyor
or is discharged, as segregation can occur at these points
–Optimum concrete slump for conveyed concrete is 6.5 –7.5 cm 16[CVEN 2101] Engineering Construction
/hr (up to the 58th floor);
•Consolidation
–To remove these entrapped air voids and to ensure complete filling of the forms
–Normally achieved through the use of mechanical vibrators
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•
Any work done to a concrete surface
after it has been consolidated will
weaken the surface strength
•Surface strength is very important on a
floor slab, sidewalk, or pavement
•Only the absolute minimum finishing
necessary to impart the desired texture
should be permitted
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[CVEN 2101] Engineering Construction
Finishing Concrete (Con’t)•Troweling
–To create a smoother surface after floating with a steel trowel
–Motor-propelled (power trowels)are used Motor propelled (power trowels)
to smooth and finish large concrete surfaces
such as floor slabs and the upper face of
horizontally concreted precast element –Improves the density of the upper concrete layer and seals plastic cracks that
developed in the face of the concrete –Floating is aimed at removing protruding aggregate grains, leveling off swells, filling。