0708 Solutions Concrete
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Transcript of 0708 Solutions Concrete
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Higher temp means quicker hydrationj
Assume 100g of cement for 40g of water
Vol of cement = 31.8 ml (Specific gravity of cement = 3.15)
Vol of water = 42ml
0% Hydration 100% HydrationWater = 40 ml Capillary pores
Gel poresSolid products of hydration
Cement = 31.8
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PFA Slaaaaaaag! Silica fume Metakaolin
Physics Data
Surface AreaBulk density
Specific gravityChemical Data
SiO2Fe2O3
Al2O3
CaO
MgONa2O + K2O
Table 1
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PFA
y Increase in long term strength,y lower water demandy improve workabilityy increase durabilityy lower early strength.
GGBFS
y Higher long term strengthy increased resistance to sulphatesy reduced early strength
Silica fume
y to development of strengthy increased workabilityy better long term strengthy improved chemical resistance
Metakaolin
y twice the reactivity of most other pozzolansy the filler effect, the acceleration of OPC hydration, and the pozzolanic reaction. The filler
effect is immediate, while the effect of pozzolanic reaction occurs between 7 to 14 days.[4]#
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y --------------
Hydration is required to
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Environmental Impact of OPC
y Quarrying of materials impacts environment visually and also energy is requiredy Energy is used to heat the materials to 1500degC and to grind the resulting clinkery Fossil fuel is burned to produce the energy resulting in greenhouse gas emissionsy As a result of the calcining (burning) process, calcium carbonate breaks down releasing
carbon dioxide.
y For 1ton of cement, 1 ton ofCO2 is releasedAlternatives
y Blended cements (composite cements)o Partial replacement of OPC with cementitious or pozzolanic materialso Most benefit when they are by products of other industries(e.g. slag (40-70%
replacement) and PFA (20-50%))
o Other replacements such as silica fume and metakolin but less benefit as they havelower levels of replacement and metakolin is manufactured rather than a by product
o Binding by CSHo When used properly, cement has superior quality to straight OPC
y Low energy cemento Lower temperature of manufacture (1200C -1300C) c.f Portland (1450C -1500C )o Belite cement (based on C2S)
Requires less calcium carbonate for its production (c.fC3S) Lower manufacturing temperature, lower emissions Low rate of strength gain so undesirable for normal construction Cement is quenched at end of manufactuing stage then blended with C3S or
OPC or with calcium sulfoaluminate which is used in easern Europe.
y Calcium sulfoaluminate cement (CSA)o
Save energy 25%, reduce CO2 by 40%o Can be used with cement replacement materials (PFA, slag etc)o Based on Kliens compound and pure CSA is C4A3 ( is SO3)o Binding material ettringiteo High early strength (most in 7days and is double that of OPC)o Pore fluid low in pH so could be useful in systems sensitive to alkalis (e.g glass fibre
reinforcement)
o Fire stability lower than OPC
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o Used in Chinao Inherent sulphate resistanceo When used with OPC, can produce either high early strength or shrinkage
compensating effect reducing cracking
y Alkali activation of Slago
Slag can be used as sole binder (without any OPC) when activated by an alkalisolution (sodium silicate)
o High strength and may be suitable for structural applicationso Sensitive to poor curingo Binding through CSH
y Geopolymerso Alkali activation of aluminosilicate materials containing no calciumo Early dayso Potential route for activating many wastes and by products materials containing
alumuinosilicates that havent been exploited yet
o High temperature (60C ) curing required with strengths of 50MPa at day 1 recordedo Binding through chains of alumina, silica and oxygen
Where
= flow rate (cm3/s)
a= cross sectional area of specimen (m2)
L = length of specimen (m)
p =fluid pressure across the head of specimen (N/m2)
= viscosity of the fluid (Ns/m2)
K = intrinsic permeability (m2)
Flow rate considered at the avg pressure across the specimen.
Gas flow rate, R (cm3/s), is measured at down stream pressure P1 bar (atmospheric pressure). If
input pressure (upstream) is P2 bar (absolute) then:
barAverage pressure, Flow rate at avg pressure 1 bar = 10
5N/m2
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With
R in cm3/s
P1 and P2 in barL in m
A in m2
Avg pressure = 1 bar so P1=P2=Pavg
y Gas permeability values are influenced by the test pressure.o Low pressure, gas molecules have fewer collisions with pore walls so the gas can
slip through.o At high pressure, the flow is impeded by large number of molecular collisions due to
shorter mean free path (the distance between gas molecules)
o At extreme pressure, the gas may resemble a liquid and may give similarpermeability values.
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Indentify method of degradation
Concrete could deteriorate in the following ways:
Physical Chemical
Abrasion Sulphate attack
Salt crystalisation Corrosion of steeleinforcement
Ice formationAlkal-aggregate reaction
Other than abrasion, degradation caused by internal expansion leading to cracking (when the tensile
strength of the concrete is exceeded). Then most reactions involve the ingress of either
y Liquids (water)y Gases (oxygen, CO2)y Ions (chlorides, sulphates)
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y Sulphate attacko Locations
Foundations and bellow ground works in locations where soil orgroundwater is naturally high in sulphates
Re development of old industrial sites (gas works especially) where theground may have been contaiminated with sulphate salts)
Maritime works (immersed in water or subject to sea spray) Tunnel works (Pyrites) Sewage works (sulphur oxidising bacteria)
o Types Classic sulphate attack
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Remedial measures