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Quality Assurance of Cement from Production to Construction
Presented by : K.K. Choi 14th February 2006
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Content
Cement Standardin HK
Cement ManufacturingProce
QualityAssurance Planning
QualityControlSchemes
ss
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QUALITY PLANS: • Product Specification • Process Specification • Procedures • Sampling & Testing Plans • Work Instruction/Records • Testing Data QA
Raw Material Constrains
National Standards
Process Constrains
Customer Requirements
Market Positioning
Quality Planning
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Cement Standard Migration
Portland Cement Standard HK Adoption year
BS12:1989 1992
BS12:1991 -
BS12:1996 2003
BSEN197-1:2000 2005
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Major Changes since BS12:1991
BS12:1989 Since BS12:1991
Test method Mortar and Concrete cube Mortar prism test to EN196 tests to BS4550
Classification By Fineness and early strength, into CFPC, OPC and RHPC
4 major Strength Classes in BS, and 3 major strength classes in BSEN197:2000
Minor constituents Not permitted Up to 5%
Compliance Based on single sample Employs statistical method in and single test. strength class classification, Compliance based on and Single Sample Acceptance absolute limits based on deviations.
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Conformity Criteria
LLAutoControlLimits LLSS For class 52.5 N
50.0 52.5
20.018.02 days strength
28 days strength
P<=5%
S is standard Deviation KA is no. of test dependent
Population
Measured Value
>LLAC +KA xS
Arithmetic Mean
ULAutoControl
P<=10%
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Target 28 days’ Strength
56.23 57.68 No. of test =55, Pk =2.07
55.74 57.00 No. of test = 310 Pk = 1.80
SD=1.8 SD = 2.5
+1.94
Reduce SD = Reduce target 28 d strength = Reduce production cost = Improve operation stability
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What is Cement ?
Cement - A finely ground powder which has hydraulic properties when mix with water It is the most essential element in concrete for civil structures
Water
7%
Admixture
0%
Aggregates
75%
Cement
18%
C40
Typical C40 Concrete Composition
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What’s Inside the Cement
Clinker
Additives
Gypsum
Cement Clinker •Major strength contributor
Gypsum •Regulate the setting properties
Additives •Such as Flyash, Limestone •Performance modifier
Inter-grinding
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Typical Type I Cement Clinker
C3A
C4AF C3S
C2S
Others,
C3S & C2S •Calcium Silicates, xCaO.SiO2 •Amount up to 72-78 % •Strength contributor
C3A & C4AF •3CaO.Al2O3, •4CaO. Al2O3. Fe2O3 •Flux for the pyroprocess
Such as free lime, MgO, Alkali, sulphates
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Composition Type I cement clinker C3S 45 - 65 % CxS 72 - 78 % C3A 8 - 12 % C4AF 10 - 11 %
Elementary Composition CaO 63 66 % SiO2 20 23 % Al2O3 4 6 % Fe2O3 3 4 %
Bogue’s formulas for calculating potential composition
+3.043 C4AF
-1.692 +2.650 C3A
+1.079 +5.068 +8.602 -3.070 C2S
-1.430 -6.719 -7.602 +4.071 C3S
Fe2O3Al2O3SiO2CaO
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Cement Processes Quarrying Provide raw material
Proportion of Raw Material
Provide correct chemistry
Raw Grinding Provide surface area for heating process
Precalcination Decomposition of CaCO3 to CaO
Sintering Formation of Clinker mineral
Finish Grinding Provide surface area for cement hydration and properties modification
I
II
III
Clinker
Cement
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Cement Plant Schematic Process Flow
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Quarrying Most limestone quarry are not uniform Origin from organisms like corals, algae in “Shallow marine carbonate platform” Complex structure due to formation mechanism, faults, foldings. Quarry planning ¢ Resource conservation – Overburdens, Low Ca layers,
High MgO layers, Gypsum ¢ Controls of harmful elements, such as Alkali, Chloride,
MgO
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Pre-blending & Homogenizing Further reduce quality variation from quarry Applicable to limestone, clay, coal
1 2 3 4 5 6 7 8 9
Stacking
Reclaiming
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Raw Meal Proportioning
Raw Mix design ¢ Clinker performance – Bogue’s formulas ¢ Burnability – Free lime VS temperature ¢ Coal ash correction ¢ Cost
Control parameters – LSF, S/R, A/R Material dosing, drying and grinding
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Impact Flowmeter
Total enclosure, ideal for powder
Less accurate
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Belt Weight Feeder
Belt Scale Speed Sensor
Flow (tph) = Weight x Speed
Accuracy : Better than 1%
Suitable for very high flow rate
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Tacho Speed Sensor
Torque Load Cell Feed in
C
Z
Feed out
Coriolis Flowmeter
Flowrate * Angular speed * Radius^2 = Torque Totally enclosure, ideal for powder Very accurate : For Coal, Cement Additives Dosing
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Clay, FlyashLimestone
Typical Close Circuit Raw Grinding with High Efficiency Separator
Homo Silo
Si Fe
Raw mill
High Efficiency Separator
Product XRF analyzer
KilnFeedBelt analyzer RawMixController
Main Components Correctives
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Raw Mill Controls
Processes Objectives
Raw Material Dosing
Ensure correct potential clinker chemistry
Raw meal fineness Ensure proper heat transfer in Preheater
Provide data for ash correction Coal ash analysis
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Typical Precalciner-Kiln System Kiln Feed
Kiln To Clinker Silo
850oC
1100oC
380oC
1000oC
870oC
750oC
600oC
1450oC900oC
110oC
800-1000 C : Decomposition of CaCO3, with formation of CS,CA,
Cooler
100-400 C : Escape of adsorbed water
600-900 C : Decomposition of clay, metakaolinites & others, with formation of reactive oxide mixture
CA + 2C => C3A
CA +3C +F => C4AF
CS + C => C2S
2C + S => C2S
C2S + C => C3S
80oC
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Cement Kiln Controls Kiln Feed
Kiln To Clinker Silo
850oC
1100oC
380oC
1000oC
870oC
750oC
600oC
1450oC900oC
110oC Cooler
Combustion air control ® Reduce excess air ® Prevent reducing atmosphere ( Fe2+ formation)
Precalciner temperature control Provide reactive oxide for sintering Reduce kiln thermal loading
Burning zone temperature control Reduce residue free lime Complete transform C2S to C3S
Clinker cooling rate Control crystal and glass formation Control of alite size Control periclase (MgO) crystal
80oC
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Finish mill
Gypsum Clinker
Typical Close Circuit Finish Grinding With High Efficiency Separator
Cement Cooler
Cement Silo
High Efficiency Separator ∑Control particle size distribution
Water spray
Gypsum dosing ® Control hydration reaction ® Obtain optimal dosing
Additives
Additives dosing Reduce strength deviation Regulate strength Mill temperature control
Control false setting during grinding
Cement cooling ®Control false setting during storage
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e
Comparison of Size distribution on Separator product
0.00
1.00
2.00
3.00
4.00
5.00
6.00
7.00
8.00
0.10 1.00 10.00 100.00 1000.00
size (u)
resu
lt i
n %
Conventional H.Efficiency
Inert
Active
Over-grind
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Comparison of Separator Specific Power Blaine, 45um residue, Consumption,
cm2/g % kWh/t
Open Circuit 3800 14% -
Mechanical 3600 14% 49 Separator H. E. 3200 8% 45 Separator (-8%)
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Conflict between BS12:1989 & HE Separator
325 330 >350 >275 Fineness, m2/kg
68.5 69.0 >52 >47 <67
34.0 35.5 >25 >25 Mortar Strength 3 days, MPa 28 days, MPa
Japan HK RHPC OPC
2002 Average BS12:1989 Limits Test items
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Standards & Cement Process
HE Separator drove the review of BS12:1989. Auto-Control scheme of BS12:1991 provides incentives to reduce SD through QA. Provision of 5% additive enables better control of strength variation and cost saving. End-users are benefit from the addition of 5% pozzolanas.
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Thank You