Please enable JavaScript.
Coggle requires JavaScript to display documents.
Cement Technology and Sustainable Materials - Coggle Diagram
Cement Technology and Sustainable Materials
Concrete
widely used construction materials
easy to maintian
versatile
Typical Composition of concrete
Cement 8 to 20%
Water 10 to 25%
Aggregate (60 to 75%)
Admixture <1%
Air Void around 2%
What is Concrete?
Concrete consists of
Sand (fine aggregate)
Cement
Stones (coarse aggreagate)
Water
Additional materials: admixtures
to modify different pproperties
Cement
generally refers to binders
materials exhibiting cohesive or adhesive properties
Aggregates
do not take part in reaction
acts as fillers to improve strength and durability of concrete
Reactivity
Reactivity of cement is brought into effect by water
Cement
Danger
Demantities
Concrete burn due to skin moisture and concrete hardening
Cause skin to blister, swell and bleed
Manufacture of Portland Cement
Grinding raw Materials such as limestone and Clay/Shade into very fine powder in a predetermined proportioned.
Burn them in a large kiln of about 1400 degree Celsius to form clinker
What happens?
Cement reacts with water and chemical reaction takes place (Hydration)
Physical process of hardening is called stiffening or hardening
Setting
Stiffening of cement paste
Changing from fluid to rigid state
Initial setting time: 60 min (to allow mixing and handling to take place)
Final setting time: Max 10 h (to gain strength before formwork removal)
Hardening
Gaining of strength in cement
BS-EN 197 -1:2000 class 42.5N and 42.5R must gain strength of 10 and 20 MPa in 2 days respectively
Refer to BS-EN 197 for more details
Other types of cement (Sustainability)
Portland Blast Furnace Cement
Blending of Portland Cement Clinkers with around 6 to 35% granulated blast furnace slag
Depending on the amount of slag, specific gravity is around 2.9
Maybe use in mass concrete and sea water construction
Major types of Portland Cement
Ordinary Portland Cement
most commonly used
medium rate of setting and hardening
suitable for most concrete work
specific gravity around 3.15
Relevant Standard
Eurocodes SS EN 197
Singapore Standard SS 26
Relevant Standard for testing cement
SS 397
BS EN 196
Rapid Hardening Portland Cement
Develop strength faster than OPC
Use when early formwork removal is necessary
Construction at low temperature to safeguard against frost damage
Should not be used in mass concrete construction due to higher rate of heat development
specific gravity around 3.15
Sulphate Resisting Portland Cement
Use when sulphates are present in concentration that would damage concrete
Higher cost due to special composition of raw materials
applied in sewage treatment work or sub or super structures contacting seawater
specific gravity around 2.97 to 3.10
Low heat Portland Cement
Low heat of hydration
applied in large gravity dams and large raft slabs to control thermal cracks
specific gravity around 3.15
White & Coloured Cement
use for architectural purposes
white cement to fill gaps between floor tiles, cover cracks or touch up work for false ceiling, dry wall partition etc
colour cement apply on a concrete structure usually not a fresh coat
specific gravity of 3.05 to 3.1
Water
Water for concreting
portable water or drinking water is best
should be free from deleterious materials affecting setting and hardening rates of concrete
Relevant standards
BS EN 1008
BS 3148
use of water from underground sources, natural surface water and industrial waste water is possible but must be subjected to testing preliminary inspection and harmful contaminants
preliminary inspection may be present of oils and detergent, colour not yellowish, pH more than or equals to 4
seawater or brackish water may be used without embedded metals
sewage water not suitable as a material
testing procedures BS EN 1008:2002, clause 6.1
Roles of water
Chemical
Hydration: cement + water
water content of mix is expressed in water/cement ratio
Binding properties of cement
hydration process of cement forms calcium silica hydrate binding elements together
stronger bond will form with more cement however workability will decrease
weaker bond will form with less cement however workability will increase
Physical
water reacts with cement to provide bonding agent for composite
fresh concrete it provides lubricating element
Aggregates
Aggregates used in construction
Natural Aggregate
aggregate from mineral sources subjected to mechanical processing
Manufactured Aggregate
aggregate of mineral origin resulting from an industrial process involving thermal or other modification
Recycled Aggregate
aggregate resulting from processing of inorganic material previously used in construction
Why are aggregates needed?
much cheaper than cement
maximum economy obtained using as much aggregate as possible in concrete
improve volume stability and durability of concrete
3 types of aggregates
Normal weight = SG bet 2&3
Light weight = SG below 2
Heavy weight = SG above 3
Classification of Aggregate
Sieving method (EN 933-1) to determine particle size distribution
Coarse Aggregates
Aggregate retained on a 4.00mm test sieve
specific gravity for granite around 2.55 to 2.67
Fine Aggregate
aggregate passing a 4.00mm sieve and retainedon a 63 micrometer test sieve
specific gravity around 2.6 to 2.7
All in aggregates
mixture of coarse and fine aggregates
Aggregate Graduation
Well-graded aggregates have particle sizes distribution evenly from fine to coarse
requiring less cement
more gaps can be filled and mix will be denser
Conditions of Aggregate
Oven Dry
Bone dry from oven set at 103 degree Celsius for 24 hours.
Saturated Surface Dry
Surface is dry but pores within the aggregate is filled with water.
Wet
Surface and pores within the aggregate is filled with water
Absorption
determine the amount of water that the aggregate can absorb into it's pore structure
also to adjust the amount of water to be added to the mix based for different concrete batches (w/c ratio)
Effects of Impurities from fine aggregate
Organic Impurities
decaying vegs and etc retard setting of cement
Inorganic Salts
chlorides etc corrodes reinforcement steel
Silt/Clay
high water demand, low strength and high shrinkage
Reactive materials
Alkali-Silica Reaction affects durability of aggregates
Admixtures
introduction
give a desired and beneficial modification of the behaviour of concrete in the freshly mixed and/or hardened state
changes are effected through process of hydration, liberation of heat, development of gel structure and formation of pores
only use where composition and proportion of the mix cannot be modified or economical
Types of admixtures
Chemical Admixtures
A chemical substance which is added in small amounts during or immediately before the mixing stage of concrete production.
Workability
Durability
Compressive strength
Admixture is introduced to concrete to alter or improve the properties of the fresh and hardened concrete
Two types most commonly used in SG
Type D
Water reducing and retarding
Type F
High range water- reducing, normal set
Mineral Admixture
Air Entraining Admixture
Classifications
Accelerators
used in cold weather concreting
expediting demoulding and stripping of formworks
suitable for emergency repair work and water leakage
e.g. sodium carbonate, sodium sulphate and calcium chloride
Set- retarders
used for work which requires a prolonged set-retardation
used for large pours such as dam, retaining wall
suitable for hot weather concreting where hot temperatures can reduce the normal setting and hardening times
prevention of the formation of cold joints between successive lift
e.g.Calcium sulphate, Sugars or Carbohydrate derivatives, soluble zinc salts, soluble borates
Water reducers
increase strength by reducing w/c at given workability
reduce cement content at given workabililty and strength
increase workability for a given w/c ratio and strength
e.g. lignosulphonate salts : obtained from pulping wood
High range water reducing
self-levelling concrete mix is achievable
very-high strength concrete is achievable with a water reduction of 25 to 30 per cent
slumps in excess of 200 mm is achievable with no increase in water content
very suitable for heavily reinforced and inaccessible sections or where rapid placing of concrete is required
suitable in underwater, bored pile and diaphragm wall concreting using a tremie
used to produce self compacting or self consolidation concrete
What is self compacting or self consolidation concrete
is a highly flowable and non-segregating concrete
as the ability to flow under its own weight, fill the required space/formwork completely to produce a dense and adequately homogenous material without the need for compaction
spread (slump flow) of SCC typically ranges from 25mm to 815mm depending on the requirements for the project
Concrete Mix
Design
By method
can be referred as prescribed mix as mix is specified by mix proportion
producers just follow the recipe
Design Mix
specify quantifiable properties
producer uses his skill to meet the requirements
supplier is responsible for all the requirements