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8. Selection of Concrete Composition
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Transcript of 8. Selection of Concrete Composition
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Selection of Concrete Composition
UK term: Mix Design selection of mix ingredients and their proportions (DOE approach)
Ref: Design of normal concrete mixes, DOE, 1988)
American term: Mixture Proportioning (ACI approach)
Ref: Standard practice for selecting proportions for
normal, heavyweight, and mass concrete, ACI Manual of
concrete practice, Part 1: Materials and general
properties of concrete, ACI 211.1-91, 1994
The process aims to select constituent materials and their
proportions for concrete to meet specified requirements,
i.e. characteristic strength, consistence and durability
for exposure conditions in service and any special needs
The selected composition is adjusted based the results of a
trial batch applying knowledge on influencing factors Page 1 of 62
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Selection of Concrete Composition
Important factors in selection of concrete composition:
Compressive strength
Commonly at 28-day characteristic value adopted in
structural design (structural adequacy)
Consistence (depends on construction processes)
Suitable for ease of placing, compacting and method of
transporting to point of placing after delivery
Durability (intended working life for exposure condition)
Currently deem-to-satisfied approach based on choice of
types of cement, maximum w/c ratio, minimum cement
and cover thickness based on qualitative classification of
exposure condition
Cost and other special requirements, e.g. surface finish Page 2 of 62
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Selection of Concrete Composition
Exact determination of constituent proportions is NOT possible due to:
Variability of materials of nominal qualitative classification e.g. shape, texture and grading of aggregates
Lack of truly quantitative properties exactly linked to properties in quantitative terms e.g. water demand for given consistence
Empirical methods adopt tables and charts to provide first approximation of proportions as these are prepared from past experience for initial estimation only
For a new set of materials or requirements, initial test (trial mix) is conducted to assess resultant properties
Adjustment to proportions as necessary to achieve and/or to optimize composition for desired concrete properties, checked with further trials often needed
Page 3 of 62
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Fundamentals Concepts
Duff Abrams (1918) formulated relationship between
compressive strength of concrete and water-cement
ratio in the form:
c = K1/K2(w/c)
c = compressive strength
A = empirical constant (96.5 MPa)
B = Constant that depends on cement properties (~4)
w/c = water to cement ratio by weight
Bcwc
A)/(5.1
c = 234 X3 (MPa) reported by Powers (1958)
Page 4 of 62
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Fundamentals Concepts
Feret (1896) established relationship:
c = K [c/(c + w + a)]2
where c = compressive strength
c, w, and a = absolute volumetric proportions of cement, water and air respectively
K = constant
This relationship includes volume of air and has been applied to cementitious systems with high air content e.g. foamed concrete (aerated or cellular concrete)
Air content up to 3% by volume in normal concrete taken into consideration in empirical approach
Higher air content by air-entraining admixture has to be compensated for reduction in compressive strength with lower water-cement ratio for similar strength
Page 5 of 62
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Fundamentals Concepts
Ideal aggregate grading Most dense aggregate-packing with a minimum content of voids
will be the most economical in theory
In practice, it is adequate to follow the grading limits specified by standards
Some basic rules for consistence (workability) Flowability
For a given slump, water requirement when
Max aggregate size
Content of angular or rough-textured aggregate particles
Content of entrained air
Cohesiveness
Improve cohesiveness
Increase sand/coarse aggregate ratio
Partial replacement of coarse sand by a fine sand
Increase cement/aggregate ratio (at given w/c)
Water content is main factor influencing consistence Page 6 of 62
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Mix Design Process
Determine the job parameters
Strength
Durability requirements (if needed)
Consistence (Slump)
aggregate properties, max. aggregate size
water/cement ratio
Admixtures (for specific performance)
Calculate batch weights
Adjusting to the batch weights based on trial mix
Comment:
High durability concrete is expected to be also high
in strength, may be higher than used in structural
design Page 7 of 62
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ACI Method (Mindess, 2002)
Step 1: Required information on materials to be used, properties on fine and coarse aggregates, dimensions of structural elements,
concrete strength and exposure conditions
Step 2: Choice of slump guidance from Table 10.1
Step 3: Maximum aggregate size depends of bar spacing and cover
Step 4: Estimation of mixing water (and air content if entrained air needed) guidance from Table 10.2
Step 5: Water/cement or water/cementitious material ratio guidance from Table 10.3 and Table 10.4 (severe exposure condition)
[Tables 10.5, 10.6 and 10.7 from CSA for specific exposure class]
Step 6: Calculation of cement or cementitious material content based on water content and water/cement ratio selected
Step 7: Estimation of coarse aggregate content guidance from Table 10.8
Step 8: Estimation of fine aggregate content guidance from Table 10.9 for fresh concrete density or based on volume of each ingredient to make
up 1 cubic meter
Step 9: Adjustment for moisture in the aggregates for batching weights
Step 10: Trial batch based on test results to adjust ingredient proportions to achieve required level Page 8 of 62
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Required average strength ACI 214
(1) The probable frequency of the average of 3 consecutive tests below specified strength fc will not exceed 1 in 100
fcr = fc + 2.33 s/3 = fc + 1.34 s
where
fcr = required average compressive strength
fc = specified compressive strength
s = standard deviation
(2) (a) For fc 35 MPa, the probable frequency of tests more than 3.5 MPa below fc should not exceed 1 in 100
fcr = fc + 2.33 s - 3.5 (MPa)
(b) For fc > 35 MPa, the probable frequency of tests below 0.90fc should not exceed 1 in 100
fcr = 0.90 fc + 2.33 s
The required average compressive strength fcr is determined as the larger value of the above
(fcr and fc are cylinder compressive strength) Page 9 of 62
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Required Average Strength (When Data Are Available to Establish a Standard Deviation)
Specified
compressive
strength, f'c, MPa
Required average
compressive strength, f'cr,
MPa
35
f'cr = f'c+ 1.34s
f'cr = f'c + 2.33s 3.5
Use larger value
> 35
f'cr = f'c+ 1.34s
f'cr = 0.90f'c + 2.33s
Use larger value
(ACI 214) Page 10 of 62
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Number of tests
Modification factor for
standard deviation
Less than 15 Use Table 15.3
15 1.16
20 1.08
25 1.03
30 or more 1.00
Modification Factor for Standard Deviation
( 30 Tests)
s is multiplied by the above factor
(ACI 318)
Page 11 of 62
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Required Average Strength (When There Are Insufficient Data to Establish s)
Specified compressive
strength,
f'c, (MPa)
Required average
compressive strength,
f'cr, (MPa)
Less than 20 f'c + 7.0
20 to 35 f'c + 8.5
Over 35 1.1f'c + 5.0
These estimates are very conservative, and should not be
used for large projects (over-design, non-economical)
(ACI 318)
Page 12 of 62
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1. Required information Sieve analysis of fine and coarse aggregate, fineness
modulus
Dry-rodded unit weight of coarse aggregate
Bulk specific gravity of materials
Absorption capacity, or free moisture in the aggregate
Information on structure including the type and
dimensions of structural members, minimum space
between reinforcing bars
Required strength
Exposure conditions
Relationship between strength and w/c for available
combinations of cement and aggregate
Job specifications [e.g., max w/c, min. slump, strength at
early age (normally 28d), early temperature] Page 13 of 62
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2. Choice of slump
Recommended Slump Ranges
Concrete construction Slump, mm
Maximum Minimum
Reinforced foundation walls and
footings 75 25
Plain footings, caissons, and
substructure walls 75 25
Beams and reinforced walls 100 25
Building columns 100 25
Pavements and slabs 75 25
Mass concrete 50 25
[(ACI 211.1) Table 10.1 Mindess] Page 14 of 62
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3. Choice of maximum size of aggregate
Using a large max size of a well-graded aggregate
will produce less void space than using a smaller
size
Large aggregates minimize the amount of water
required, therefore reduce the amount of cement
required.
The maximum allowable aggregate size is limited by
the dimensions of the structural elements and
space between reinforcement
capabilities of construction equipment
Page 15 of 62
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150
250
10
30 30 30 30
- Form: 150/5=30 mm
- Space between bars =30x3/4=22.5 mm
- Space between bar & form=25x3/4=19 mm
(assume: cover thickness = 25 mm)
Select aggregate with max. size 19 mm
(19 mm = 3/4 in. and 25 mm = 1 in.)
25 mm
Situation Maximum aggregate size
Form dimensions 1/5 of minimum clear distance
Clear space between reinforcement or prestressing
tendons
3/4 of minimum clear space
Clear space between reinforcement and form 3/4 of minimum clear space
Unreinforced slab 1/3 of thickness
Mindess
Page 16 of 62
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4. Estimation of mixing water & air content
The quantity of water required to produce a given
slump is
dependent on the max size, shape and grading of
aggregate, amount of entrained air
not greatly affected by cement content
Estimation of water from Table 10.2 if no data are
available for a given aggregate
The recommendations in Table 10.2 are reduced for
other aggregate shapes than angular:
Shape Reduction in kg/m3
Sub-angular 12
Gravel with crushed particles 21
Round gravel 27
Page 17 of 62
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Water and Air Requirements for Different Slumps and Sizes of Aggregate
Water, kg/m3 of concrete,
for indicated sizes of aggregate
Slump, mm 9.5
mm
12.5
mm
19
mm
25
mm
37.5
mm
50
mm
75
mm
150
mm
25 to 50 210 200 185 180 160 155 130 113
75 to 100 225 215 200 195 175 170 145 124
150 to 175 240 230 210 205 185 180 160
Approximate amount of
entrapped air in non-air-
entrained concrete,
percent
3 2.5 2 1.5 1 0.5 0.3 0.2
Non-air-entrained concrete (Extra from Table 10.2)
Based on well-shaped, angular coarse aggregate
[(ACI 211.1) Table 10.2 Mindess] Page 18 of 62
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Air entrainment requirements
Air entrainment is required whenever concrete is
exposed to freeze-thaw conditions
Air entrainment is also used for workability
The amount of the air required varies with
exposure conditions
mild: indoor or outdoor service where concrete
is not exposed to freezing and de-icing salts.
AEA may be used to improve workability
moderate: some freezing exposure occurs but
concrete not exposed to moisture
severe
size of the aggregates
Page 19 of 62
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Water and Air Requirements for Different Slumps and Sizes of Aggregate
Water, kg/m3 of concrete,
for indicated sizes of aggregate
Slump, mm 9.5
mm
12.5
mm
19
mm
25
mm
37.5
mm
50
mm
75
mm
150
mm
25 to 50 180 175 165 160 145 140 120 107
75 to 100 200 190 180 175 160 155 135 119
150 to 175 215 205 190 185 170 165 155 -
Recommended average total air content,
percent, for level of exposure
Mild exposure 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0
Moderate exposure 6.0 5.5 5.0 4.5 4.5 4.0 3.5 3.0
Severe exposure 7.5 7.0 6.0 6.0 5.5 5.0 4.5 4.0
Air-entrained concrete (Extract from Table 10.2
[(ACI 211.1) Table 10.2 Mindess] Page 20 of 62
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5. Selection of w/c or w/cm
Strength (Comment: Cylinder compressive strength)
Page 21 of 62
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Cylinder
Compressive
strength at 28
days, MPa
Water/Cement Ratio by mass
Non-air-entrained
concrete
Air-entrained
concrete
45 0.37 -
40 0.42 -
35 0.47 0.39
30 0.54 0.45
25 0.61 0.52
20 0.69 0.60
15 0.79 0.70
If no historical data are available
- make trial batches with different w/c, establish a relationship between
strength and w/c
- estimation of w/c for the trial mixes from Table 10.3
Not applicable to ASTM Type II, III, IV, and V cements and blended
cements with very high quantities of pozzolans or GGBFS
[(ACI 211.1) Table 10.3 Mindess] Page 22 of 62
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5. Selection of w/c or w/cm
Durability
Checking w/c against the max. allowable w/c for
exposure conditions
Generally, more severe exposure conditions
require lower w/c
The minimum of the w/c for strength and durability
is selected for proportioning of the concrete
Page 23 of 62
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6. Calculation of cement or cementitious material content
= mixing water (step 4) divided by the w/c (step 5)
if the concrete is used in flatwork, check minimum
cement content requirement
Nominal maximum size
of aggregate, mm
Cementing materials,
kg/m3
37.5 280
25 310
19 320
12.5 350
9.5 360
(ACI 318) Page 24 of 62
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Cementitious Materials Requirements for
Concrete Exposed to Deicing Chemicals
Cementitious materials
Maximum % of
cementitious
materials
Fly ash and natural pozzolans 25
Slag 50
Silica fume 10
Total of fly ash, slag, silica fume
and natural pozzolans 50
Total of natural pozzolans and
silica fume 35
(ACI 318) Page 25 of 62
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7. Estimation of coarse aggregate content
increase V, less workability (pavement)
reduce V, increased workability (pumping, shotcrete)
Maximum size of
aggregate, mm
Volume of dry-rodded coarse aggregate for
different fineness moduli of sand
2.40 2.60 2.80 3.00
9.5 0.50 0.48 0.46 0.44
12.5 0.59 0.57 0.55 0.53
19 0.66 0.64 0.62 0.60
25 0.71 0.69 0.67 0.65
37.5 0.76 0.74 0.72 0.70
50 0.78 0.76 0.74 0.72
75 0.82 0.80 0.78 0.76
150 0.87 0.85 0.83 0.81
Volume of Coarse Aggregate per Unit volume of Concrete
[(ACI 211.1) Table 10.8 Mindess Page 26 of 62
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Coarse Aggregate Content per m3 of Concrete
Assume: Max. aggregate size = 9.5 mm
Fineness modulus of sand = 2.8
Volume of coarse aggregate in concrete
= 0.46 m3 of coarse aggregate/m3 concrete
Assume: Dry rodded unit weight = 1567 kg/m3 (oven dry)
Coarse aggregate content (Oven dry)
= 0.46 x 1567 kg/m3 = 715.5 kg/m3
Coarse aggregate content (SSD)
= 715.5 x (1+ A/100) [ A = Absorption capacity in %]
Page 27 of 62
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8. Estimation of fine aggregate content
Mass (Weight) method
Wfa = Wc - Weight of other ingredients
Wfa = weight of fine aggregate
Wc = unit weight of concrete
Estimate according to Table 10.9
[(ACI 211.1) Table 10.9 Mindess]
Page 28 of 62
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8. Estimation of fine aggregate content
Volume method
The components weight and specific gravity are used to
determine the volumes of the water, coarse aggregate, and
cement. These volume + volume of air are subtracted from
a unit volume of concrete to determine the V of fine
aggregate
1000 liters kg kg/l
convert the V to weight (generally using bulk SSD specific
gravity)
awcacemcon
awcacemconfa
VWWWV
VVVVVV
1/65.2/15.3/
Page 29 of 62
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9. Adjustments for aggregate moisture
The mix proportions determined by steps 1 to 7 are
assumed to be on a saturated surface dry (SSD) basis.
If aggregate contains free moisture, the mixing water should
be and aggregates correspondingly according to the
amount of free moisture in the aggregates.
If aggregate is air dry, the mixing water should be and
aggregates correspondingly
Total water in aggregate absorption = free moisture
Page 30 of 62
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Example:
Coarse aggregate, absorption capacity = 1%,
effective absorption = 0.5% (from air-dry to SSD)
Fine aggregate, absorption capacity = 1.3%, total
moisture content 4.5%
Assume a concrete mix proportion based on SSD:
Cement = 400 kg/m3, Water = 200 kg/m3, Coarse
aggregate = 1050 kg/m3, Fine aggregate = 710 kg/m3
Estimated unit weight = 2360 kg/m3
Actual mix proportion with the given aggregates
CA: 1050 1050x0.5% = 1045 kg/m3 (diff. = 5 kg/m3)
FA: free moisture = 4.5% 1.3% = 3.2%
710 + 710x3.2% = 733 kg/m3 (diff. = 23 kg/m3)
Water: 200 + 1050x0.5% - 710x3.2% = 182 kg/m3
Estimated unit weight = 2360 kg/m3
(Batching tolerance: 3% for aggregates, ?% for water) Page 31 of 62
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10. Trial batch
Purpose
Verifies that a concrete mixture meets design requirements prior to use in construction.
Determine
Fresh concrete: slump, cohesiveness, segregation tendency, unit weight, air content, finishing
Hardened concrete: strength 28 days or other ages
Durability parameters if specified
Adjust concrete mixture accordingly
Strength does not meet requirement (workability ok)
Reduce w/c
Keep water content unaltered
Increase cement, reduce aggregate Page 32 of 62
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10. Trial batch - continued
Adjust concrete mixture accordingly (contd)
Workability does not meet requirement (strength ok)
Keep w/c unaltered
Slump too low
Increase water and cement content
( 6 kg/m3 water will slump by ~25 mm)
Use WRA or superplasticizer
Slump too high
Reduce water and cement content
Reduce the dosage of WRA or SP
Segregation
Increase fine aggregate and reduce coarse aggregate
accordingly
Replace coarse sand with a finer sand
Air content: 1% air, reduce water by 3 kg/m3 Page 33 of 62
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UK Approach DOE Method (Neville, 2011)
Step 1: Water/cement ratio based on typical relationships between compressive strength and water/cement ratio in Fig. 14.12, curve
for use selected from past experience of 28 day compressive
strength of concrete at water/cement of 0.5
Step 2: Water content for required consistence (slump) from Table 14.10 related to type of coarse aggregate (uncrushed or crushed) and
maximum aggregate size
Step 3: Cement content based on selected water/cement ratio and water content (at least equal to minimum cement content for durability,
guidance not provided)
Step 4: Total aggregate content for range of specific gravity of crushed or uncrushed coarse aggregate and fresh concrete density for
water content and specific gravity of coarse aggregate in Fig. 14.13
Step 5: Proportions of fine aggregate in total aggregate based on level of slump and free water /cement ratio for different percentage of fine
aggregate passing 600 m sieve and maximum aggregate size (20
mm or 40 mm) in Fig. 14.14
Comment:
In both ACI and DOE approach, guidance not provided on use of chemical
admixture and recommendations for different specific exposure conditions. Page 34 of 62
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UK Approach Adopted in Singapore
Target mean strength, = characteristic strength + margin
fm = fcu,28 + ks
where
fm = mean cube compressive strength
fcu,28 = specified characteristic cube compressive strength
s = standard deviation
k = constant (= 1.64 for 5% defective)
EN 206: 2013 Annex A (normative) Initial Test
For initial testing, margin = 2 x standard deviation (6 to 12 MPa)
Comment:
Typical values for standard deviation range from 3 to 5 MPa for
most RMC plants.
Common margin selected = 7.5 to 8 MPa (s 4.5 to 5.0)
Page 35 of 62
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1. Selection of water/cement ratio
Target mean strength is based on value adopted in design of concrete
structure (may not be the same for all
structural elements)
DOE method based on assuming certain strengths are related to
water/cement ratio of 0.5 for different
types of cements and aggregates Table 14.9 Neville
Current CEM l (42,5R) is similar to former rapid hardening Portland
(ASTM Type lll)
[w/c 0.5 50 MPa, approximately linear to w/c 0.3 80 MPa]
Fig. 14.12 Neville
Comment: Cube compressive strength
Page 36 of 62
a0104388Line
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2. Selection of free water content for consistence
Free water content assumed main factor to achieve various levels of consistence (in terms of slump) (Table 14.10 Neville)
Three maximum size coarse aggregates : 10, 20, 40 mm
Two types of coarse aggregates considered:
Uncrushed (e.g. river gravel)
Crushed (higher water demand)
(Neville, 2011)
Page 37 of 62
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3. Determination of cement content
Cement content = (water content)/ (water/cement ratio)
Limit for minimum cement content for durability
(EN 206 Table F.1 Annex F (informative)
Cement is the most costly not only on per unit mass basis but also for the amount in each unit volume of concrete
Cement has highest carbon footprint of all constituent materials in concrete
Minimum cement content achieved with minimum water content for consistence (including use of superplasticizers)
Limit for maximum cement content for development of heat of hydration in thick sections
Page 38 of 62
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Durability Design of Concrete Structures
SS EN 206-1:2009
Clause 4.1 Exposure classes related to
environmental actions
NOTE The exposure classes to be selected
depends on the provisions valid in the place of
use of the concrete.
SS 544-1:2009 Concrete Complimentary Singapore Standard to SS EN 206-1 Part 1: Method of specifying and guidance for the
specifier
Table A.2 Classification of ground conditions
provides more detailed criteria for sulfate and
Tables A.1, A.4 and A.5 for exposure classes
(presentation on durability)
Page 39 of 62
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4. Determination of total aggregate content
Estimate density of fully compacted fresh concrete indicated for selected water content (Step 2) and specific gravity of coarse
aggregate from chart (Fig. 14.13 Neville)
If specific gravity of coarse aggregate in not known, recommend value of 2.6 for uncrushed aggregate and 2.7 for crushed
aggregate
Total aggregate = concrete density cement content water content
(Neville, 2011)
Page 40 of 62
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5. Determination of proportion of fine aggregate
Bases for selection include level of consistence, water/cement ratio and fineness of fine aggregate (percentage of fine aggregate
passing 600 m sieve (likely range 40 to 60%)
Determine proportion of fine aggregate in term of percent of total aggregate (Step 4) - Fig. 14.14 Neville
Fine aggregate content = % fine aggregate x total aggregate content
Coarse aggregate content = total aggregate content minus fine aggregate content
Recommend coarse aggregate divided into different single sized aggregates in proportions shown below
Total coarse aggregate 5 10 mm 10 20 mm 20 40 mm
100 33 67 -
100 18 27 55
Comment: approximately 1:2 between adjacent sizes Page 41 of 62
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5. Determination of proportion of fine aggregate
Neville, 2011
Comment:
Commonly
20 mm max. size
60-180 mm slump
Page 42 of 62
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Volumetric Proportions of Concrete Mass proportions of concrete batching control
Volumetric proportions for consideration of contribution of
components on properties of concrete
Density of concrete = Mc + Mw + Mca + Mfa (M = mass content, kg/m3)
where
c = cement, w = water, ca = coarse aggregate, fa = fine aggregate
Density of components:
Gc, Gw, Gca, Gfa are density of components with
c = cement, w = water, ca = coarse aggregate, fa = fine aggregate
Per cubic metre of concrete, Vcon
Vc, Vw, Vca, Vfa and Vair are volume of components with
c = cement, w = water, ca = coarse aggregate, fa = fine aggregate
Vcon = Vc + Vw + Vca + Vfa + Vair = 1 m3
Vcon = Mc/Gc + Mw/Gw + Mca/Gca + Mfa/Gfa + Vair = 1 m3
(Comment: Entrapped air content 2%, or max. 3% with chemical admixture)
Nominal or determined density to indicate volume supplied in delivery truck
Page 43 of 62
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Selection of Ingredient Proportions
Both ACI and DOE approaches do not provide guidance on use of chemical admixtures (use manufacturers recommendation)
The data used are based on experience in temperature climate and temperature effects for tropical climate not included
In most RMC plants, past experience with available constituent materials for concrete has led to typical proportions for common
range of characteristic strengths (C25/30 to C50/60)
As set-retarding and plasticizing admixtures are typically used in tropical climatic conditions, adjustment of consistence is often
provided by adjusting dosage of admixtures
(Water reducing admixture: G1 10%, G2 20% and G3 30% or higher water reduction for similar slump)
Typically strength/water-cement ratio is approximately linear over limited range of values, e.g. Fig. 14.12 (Neville 2011) shows
approx. 10 MPa from w/c = 0.60 to 0.50 and approx. 15 MPa for
each change in w/c = 0.10 between 0.50 and 0.30
Page 44 of 62
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Durability Design of Concrete Structures - Sulfate
SS EN 206-1:2009
Clause 4.1 Exposure classes related to
environmental actions
NOTE The exposure classes to be selected
depends on the provisions valid in the place
of use of the concrete.
SS 544-1:2009 Concrete Complimentary Singapore Standard to SS EN 206-1 Part 1: Method of specifying and guidance for the
specifier
Table A.2 Classification of ground
conditions provides more detailed criteria
for sulfate attack
Page 45 of 62
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Durability Design of Concrete Structures - Sulfate
SS 544-1: 2009 (BS 8500-1: 2006)
Page 46 of 62
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Durability Design of Concrete Structures - Sulfate
SS 544-1: 2009 (BS 8500-1: 2006)
Page 47 of 62
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Durability Design of Concrete Structures - Sulfate
SS 544-1: 2009 (BS 8500-1: 2006)
Page 48 of 62
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Durability Exposure classes related to environmental influence
Chemical attack (XA classes) BS EN 206-1:
Where concrete is exposed to chemical attack from natural soils and ground water, the exposure shall be classified in Table 2. The classification of sea water depends on the geographical location, therefore the classification valid in the place of use of the concrete applies.
Class
designation
Description of the environment Informative examples where
exposure class may occur
XA1 Slightly aggressive chemical environment
according to Table 2
XA2 Moderately aggressive chemical
environment according to Table 2
XA3 Highly aggressive chemical environment
according to Table 2
Replacement for XA classes in BS EN 206-1, Table (shown above) with BS 8500-1 Annex A (informative) Table A.2 to determine the ACEC-class (see BRE Special Digest 1 for guidance on site investigation)
Refer in BS EN 206-1 Table 2 Limiting values for exposure classes for chemical attack from natural soil and ground water
Page 49 of 62
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Extract from Table A.2 of SS 544-1 Classification of ground conditions (refer to the BS 8500-1 for the details)
Sulfate and magnesium Design
sulfate
class
Natural soil Brownfield A) ACEC-
class
(design
sulfate
class)
2:1 water/soil
extract
Groundwater Total
potential
sulfate B)
Static
water
Mobile
water
Static
water
Mobile
water
SO4 Mg C) SO4 Mg
C) SO4
mg/l mg/l mg/l mg/l % pH pH pH D) pH D)
500
to
1500
400
to
1400
0.24 - 0.6 DS-2
> 3.5 AC-1s
> 5.5 >6.5 AC-2
2.5 to 3.5 AC-2s
2.5 to 5.5 5.6 to 6.5 AC-3z
4.5 to 5.5 AC-4z
2.5 to 4.5 AC-5z
1600
to
3000
1500
to
3000
0.7 to 1.2 DS-3
> 3.5 > 5.5 AC-2s
> 5.5 > 6.5 AC-3
2.5 to
3.5
2.5 to 5.5
AC-
3s
2.5 to 5.5 5.6 to 6.5 AC-4
2.5 to 5.5 AC-5 Page 50 of 62
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Extract from Table A.9 of SS 544-1 Selection of the nominal cover and DC-class or designated concrete and the number of APM for in-situ concrete elements where the hydraulic gradient due to groundwater is five or less (refer to the BS for details)
ACEC-class Lowest nominal cover E), mm
Intended working lifeF)
At least 50 years G), H)
At least 100 years
AC-1s, AC-1 50I), 75 J) DC-1 (RC25/30 if reinforced)
DC-1 (RC25/30 if reinforced)
AC-2s AC-2 50I), 75 J) DC-2 (FND2) DC-2 (FND2)
AC-2z 50I), 75J) DC-2z (FND2z) DC-2z (FND2z)
AC-3s 50I), 75J) DC-3 (FND3) DC-3 (FND3)
AC-3z 50I), 75J) DC-3z (FND3z) DC-3z (FND3z)
AC-3 50I), 75J) DC-3 (FND3) DC-3 + one APM of choice, FND3 + one APM or choice, DC-4 or FND4
AC-4 50I), 75J) DC-4 (FND4) DC-4 + one APM from APM2 to APM5, or FND4 + one APM from APM2 to APM5
AC-5 50I), 75J) DC-4 (FND4) + APM3 K)
DC-4 (FND4) + APM3K)
I) For concrete cast against binding J) For concrete cast directly against the soil (Designation within brackets refers to Designated Concrete in BS 8500-1)
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Extract from Table A.11 of BS 8500-1 Limiting values of composition and properties for concrete where a DC-class is specified
DC-
class
Max.
w/c ratio
Min. cement or combination content
(kg/m3) for max. aggregate size
Cement and
combination types
Grouping used in
BRE SD1:
2005[1]
40 mm 20 mm 14 mm 10 mm
DC-1 A) All in Table A.6 A to G
DC-2
0.55 300 320 340 360 IIB-V+SR, IIIA+SR,
IIIB+SR, IVB-V
D, E, F
0.50 320 340 360 380 CEM I, SRPC, IIA-D,
IIA-Q, IIA-S, IIA-V, IIB-
S, IIB-V, IIIA, IIIB
A, G
0.45 340 360 380 380 IIA-L or LL 42.5 B
0.40 360 380 380 380 IIA-L or LL 32.5 C
DC-2z 0.55 300 320 340 360 All in Table A.6 A to G
DC-3
0.50 320 340 360 380 IIIB+SR F
0.45 340 360 380 380 IVB-V E
0.40 360 380 380 380 IIB-V+SR, IIIA+SR,
SRPC
D, G
DC-3z 0.50 320 340 360 380 All in Table A.6 A to G
A) If the concrete is reinforced or contains embedded metal, the minimum concrete quality for 20 mm maximum aggregate
size is C25/30, 0.65, 260 or designated concrete RC25/30.
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Exposure Classes
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Exposure Classes
National Foreword to SS 544-1: 2009
Guidelines are highlighted to guide local
users:
Annex A (informative) Exposure classes related to environmental conditions
In order to cater to the higher ambient
temperatures in Singapore compared to
UK, the recommendation is to consider
the required concrete for at least one
class higher than that based on exposure
conditions in accordance with the
requirements for UK exposure conditions
(refer to Table A.3).
The specifier should take into
consideration the nature of the element,
intended working life, its importance and
the cost of maintenance and repair to
select the same or higher performance
concrete.
Different elements in the same structure
may be specified with different concrete
to optimise cost-effectiveness. Page 54 of 62
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SS EN 544-1: 2009 Annex A (informative)
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SS EN 544-1: 2009 Annex A (informative)
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SS EN 544-1: 2009 Annex A (informative)
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SS EN 544-1: 2009 Annex A (informative)
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Durability Design of Concrete Structures - Examples
Example Prescribed limits on w/c, cement content and cement type
Exposure class: Corrosion induced by carbonation (XC classes)
Concrete for
nominal cover
of 25+c (mm)
Exposure class: XC3/4: (intended working life of at least 50 years, 20 mm
maximum size aggregate) Cement type: All in Table 6, except IVB-V
Strength class SS 544-1 Table A.4 With + 2 MPa With + 5 MPa
Designation C30/37-XC3/4 (0.55 300) C32/40-XC3/4 (0.52 310) C35/45-XC3/4 (0.50 320)
Comment UK conditions May not be adequate Preferred
Increase
nominal cover
to 30+c (mm)
Exposure class: XC3/4: (intended working life of at least 50 years, 20 mm
maximum size aggregate) Cement type: All in Table 6, except IVB-V
Strength class SS 544-1 Table A.4 With + 2 MPa With + 4 MPa
Designation C28/35-XC3/4 (0.60 280) C30/37-XC3/4 (0.55 300) C32/40-XC3/4 (0.52 310)
Comment UK conditions May not be adequate Preferred
Concrete for
nominal cover
of 30+c (mm)
Exposure class: XC3/4: (intended working life of at least 100 years, 20 mm
maximum size aggregate) Cement type: All in Table 6, except IVB-V
Strength class SS 544-1 Table A.5 With + 5 MPa With + 10 MPa
Designation C40/50-XC3/4 (0.45 340) C45/55-XC3/4 (0.40 380) C50/60-XC3/4 (0.35 380)
Comment UK conditions Preferred For off-form finish Page 59 of 62
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Durability Design of Concrete Structures - Examples
Example Prescribed limits on w/c, cement content and cement type
Exposure class: Corrosion induced by carbonation (XC classes)
Concrete for
nominal cover
of 25+c (mm)
Exposure class: XC2: (intended working life of at least 50 years, 20 mm
maximum size aggregate) Cement type: All in Table 6
Strength class SS 544-1 Table A.4 With + 3 MPa With + 5 MPa
Designation C25/30-XC2 (0.65 260) C28/30-XC2 (0.60 280) C30/37-XC2 (0.55 300)
Comment UK conditions, same
for higher covers
May not be adequate Preferred
Concrete for
nominal cover
of 30+c (mm)
Exposure class : XC2: (intended working life of at least 100 years, 20 mm
maximum size aggregate) Cement type: All in Table 6
Strength class SS 544-1 Table A.5 With + 3 MPa With + 5 MPa
Designation C25/30-XC2 (0.65 260) C28/30-XC2 (0.60 280) C30/37-XC2 (0.55 300)
Comment As for 50 years, but
with larger cover
May not be adequate Preferred
Note:
XC2: for foundations, often with nominal cover of 50 mm
XC3/XC4: for above ground structures (see also XS1 airborne salts) Page 60 of 62
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Comparison of Approach Information provided:
Characteristic strength = C40/50 (target 48/60 MPa)
Coarse aggregate: Dry-rodded density = 1650 kg/m3
S.G. (SSD) = 2.65, Absorption 1%, Effective absorption = 0.5%
Fine aggregate: Free moisture content 8% (total 9.5% absorption 1.5%)
S.G. (SSD) = 2.50
Fineness modulus = 2.60, % passing 600 m = 50%
CEM I (ASTM Type 1), S.G. = 3.15
Durability: XO (no special requirement)
(a) Select concrete composition without admixture (SSD aggregates)
(b) Select concrete composition with admixture (SSD aggregates)
Admixture to be taken as part of added water (dosage < 2 kg/m3)
Water reduction = 15% when added at recommended dosage
Compute batch quantities for 1m3 in each case (adjusted for moisture)
Comment on differences in composition between ACI and DOE methods
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Review of Results
Each method is based on different approaches to the selection of values
to arrive at the concrete composition.
The results may differ within a narrow range between different persons
as interpolation may be needed using the tables and figures provided
in the presentation
You are encouraged to carry out case (a) for both approaches and send
their compositions by e-mail to [email protected]
A summary of submitted results will be presented for review at the end
of the next presentation
Adjust concrete composition if Initial Test show:
(Each case taken separately, all others data remain as before)
(a) Mean cube compressive strength is 5 MPa below target
(b) Fineness modulus changed to 2.30 (% passing 600 m = 60%)
(c) Fine aggregate total moisture content = 12%
Page 62 of 62