Chapter 5 Flashcards
(25 cards)
a composite material composed of gravels or crushed stones (coarse aggregate), sand (fine aggregate) and hydrated cement (binder)
Concrete
are granular materials obtained from rocks and crushed stones.
Coarse aggregate
The sand obtained from river beds or quarries is used as
Fine Aggregate
The nominal maximum coarse aggregate size is limited by the lowest of the following quantities.
1) 1/4 times the minimum thickness of the member
2) Spacing between the tendons/strands minus 5 mm
3) 40 mm.
The deleterious substances that should be limited in aggregate are clay lumps, wood, coal, chert, silt, rock dust (material finer than _________), organic material, unsound and friable particles.
75 microns
cement is a mixture of lime stone and clay heated in a kiln to
1400 - 1600ºC.
Ordinary Portland cement confirming
33 Grade – Specification.
Portland Slag Cement
Specification, but with not more than 50% slag content.
Rapid-hardening Portland cement
Specification
Water used for mixing and curing shall be clean and free from injurious amounts of ___________________________
oils, acids, alkalis, salts, sugar, organic materials or other substances that may be deleterious to concrete and steel
chemical admixtures
1) Air-entraining admixtures
2) Water reducing admixtures
3) Set retarding admixtures
4) Set accelerating admixtures
5) Water reducing and set retarding admixtures
6) Water reducing and set accelerating admixtures.
mineral admixtures (Contains cementous and pozzolanic materials)
1) Fly ash
2) Ground granulated blast-furnace slag
3) Silica fumes
4) Rice husk ash
5) Metakoline
The concrete in prestressed applications has to be of good quality. It requires the following attributes.
1) High strength with low water-to-cement ratio
2) Durability with low permeability, minimum cement content and proper mixing, compaction and curing
3) Minimum shrinkage and creep by limiting the cement content.
The compressive strength of concrete is given in terms of the characteristic compressive strength of ________ size cubes tested at ________
150 mm
28 days
The minimum grades of concrete for prestressed applications are as follows.
30 MPa for post-tensioned members
40 MPa for pre-tensioned members
60 MPa for maximum grade members
It is measured by testing beams under 2 point loading (also called 4 point loading including the reactions).
Flexural tensile strength
It is measured by testing cylinders under diametral compression.
Splitting tensile strength:
It is measured by testing rectangular specimens under direct tension
Direct tensile strength
In absence of test results, the Code recommends to use an estimate of the flexural tensile strength from the compressive strength by the following equation.
fcr=0.7√fck
fcr = flexural tensile strength in N/mm2
fck = characteristic compressive strength of cubes in N/mm2 .
The modulus of elasticity for short term loading (neglecting the effect of creep)
Ec =5000 √fck
common durability problems in concrete
1) Sulphate and other chemical attacks of concrete.
2) Alkali-aggregate reaction.
3) Freezing and thawing damage in cold regions.
4) Corrosion of steel bars or tendons.
attributes of high performance concrete
1) High strength
2) Minimum shrinkage and creep
3) High durability
4) Easy to cast
5) Cost effective.
Some special types of high performance concrete
1) High strength concrete
2) High workability concrete
3) Self-compacting concrete
4) Reactive powder concrete
5) High volume fly ash concrete
6) Fibre reinforced concrete
Achorage blocks are also called.
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