Chapter5 Cement concrete
1
Main topics
5.1
Technical Performances of Concrete
5.2
Concrete Mixture Design
5.3
Concrete Admixture
5.4
Concrete for Road
2
5.1
Technical Performances
of Concrete
3
5.1
Technical Performances of Concrete
——Introduction
 Cement concrete is a man-made stone material, which is
compound that consists of cement, aggregates and water
in proper proportion.
 Cement concrete is widely used in civil engineering, its
characteristics are:
——richness in resources and simple for construction;
——concrete and reinforcement have same linear
expansion coefficient and fine bond strength between them,
which is much beneficial to make reinforcement concrete
and prestressed concrete;
——through changing the composition proportion, different
feature concretes can be obtained to meet different
requirements；
——good mechanical behaviors and better durability.
4
5.1
Technical Performances of Concrete
——Construction workability
 Definition:
——workability is a property which means fresh
cement concrete mixture is easy to construction
operation (including mixing, transportation,
concreting, vibrating and surface treatment) ,
uniformity on quality and dense in structure.
 Workability including:
——flowability (流动性): is easy to fill formwork in
uniformity and compactness；
——tamping feasibility (捣实性): is likely to remove
all air in concrete mixture to be dense.
5
5.1
Technical Performances of Concrete
——Construction workability
——cohesiveness (黏聚性): without
separation and disintegration to fresh
concrete depending on some cohesion;
——water-retaining (保水性): to have good
water retention abilities without bleeding
problem.
6
5.1
Technical Performances of Concrete
——Construction workability
 Workability test method:
——slump test(坍落度试验)
——Vebe consistometer test(维勃稠度试验)
7
5.1
Technical Performances of Concrete
——Construction workability
 Influencing factors on workability
(1) internal cause: component materials:
——water and cement ratio (W/C);
——quantity of water per unit；
——sand percentage；
——raw materials: cement and cement fineness,
aggregates;
——admixture;
(2) external causes
——environmental factor: temperature, humidity,
wind speed;
——time.
8
5.1
Technical Performances of Concrete
——Strength Characteristics
 Concrete strength
——cubic compressive strength;
——axis compressive strength;
——flexural strength;
150mm
300mm
——splitting strength.
150mm
150mm
15
150mm
150mm
150mm
150mm
Test diagram of
150mm
150mm
150mm
150mm
150mm
compressive
strength
Test
diagram
Test diagram of of axis
Test
diagram
compressive
strength
splitting
strengthof
flexural strength
9
5.1
Technical Performances of Concrete
——Strength Characteristics
 Cubic compressive strength( f cu )
——definition: the compressive strength of a
cubic with 150mm length on each side;
——method of calculation:
F
f cu 
A
——the standard values on the cubic
compressive strength ( f cu，k ): the strength
satisfied the requirement of assurance rate under
standard condition:
fcu , k  f  1.645
10
5.1
Technical Performances of Concrete
——Strength Characteristics
 Grades of concrete strength
——there are 12 concrete strength grades
in our country nowadays. Each of them can
be expressed as “C” plus “standard value of
strength” :
——C7.5, C10, C15, C20, C25, C30, C35,
C40, C45, C50, C55, C60.
11
5.1
Technical Performances of Concrete
——Strength Characteristics
 Flexural strength
150mm
150mm
150mm 150mm150mm
PL
Test diagram of flexural strength
bh 2
where : P —maxi mum l oadi ng( N) ;
L—span（450mm）;
f cf 
b, h—wi dt h and hi gt h( nor mal l y 150mm, r espect i vel y) .
12
5.1
Technical Performances of Concrete
——Strength Characteristics
 Influencing factors on concrete strength
(1) concrete composition:
——cement strength: the higher cement
strength, the higher concrete strength;
——water cement ratio (W/C): concrete
strength has close relationship to W/C
according to a lot experience, which is the
lower W/C, the higher concrete strength is.
13
5.1
Technical Performances of Concrete
——Strength Characteristics
——Characteristics of aggregate:
① rough surface and plentiful edges preferred;
② closely to cubic or round shape, rather than
elongated or flat;
③ larger of maximum size is beneficial to compressive
strength but unbeneficial to flexural strength, and when
size of coarse aggregate is too larger, it is unfavorable to
workability. Normally, nominal maximum size of coarse
aggregate for concrete is no more than 31.5mm;
④ concrete mixture in continuous gradation has better
workability and more dense; Comparatively speaking, gap
gradation has less cement consumption compare with
continuous concrete, but it is poor in workability;
⑤ Generally, sand with less specific surface area and
less void ratio is preferred which has the ideal gradation. 14
5.1
Technical Performances of Concrete
——Strength Characteristics
(2) curing condition
——curing temperature;
——curing humidity;
——aging.
15
5.1
Technical Performances of Concrete
——Strength Characteristics
 Evaluation on the quality of concrete strength
 Statistical method—Unknown standard deviation
method：
fcu  1S  0.90 fcu ,k
fcu ,min  2 fcu ,k
 Nonstatistcal method:
fcu  1.15 fcu ,k
fcu ,min  0.95 fcu ,k
16
5.1
Technical Performances of Concrete
——Deformation Characteristics
 Elastic deformation
——it can be expressed by the secant modulus
stress
(割线模量);
σ
 Creep deformation
——it is the deformation under sustained loading
condition;
 Temperature deformation
α
ε
 Dry shrinkage deformation
strain
Diagrams of secant modulus
17
5.1
Technical Performances of Concrete
——Durability Characteristics
 Impermeability of concrete
——it is a capability that concrete resists permeability of
gas or water;
——according to the behavior of concrete standard
specimen without water seepage (渗水) under specified
water pressure, 6 grades on impermeability are set;
 Frost resistance
——it is a capability that concrete resists freeze/thaw
cycling (冻融循环) ；
——there are 9 grades to evaluate concrete freezingthawing durability;
 Resistance to chemical attack
 Abrasive resistance.
18
Asphalt Pavement Abrasive Experiment
19
5.2
Concrete Mixture Ratio Design
20
5.2
Concrete Mixture Ratio Design
——Technical requirements for raw materials
 Cement
——types of cement: according to cement
adaptability which is affected by the project
features and environmental condition, proper type
of cement is selected;
——grades of cement: concrete grade and cement
grade should be matched;
 Coarse aggregate
——quality: satisfied the specified quality
requirements, such as strength, soundness etc.;
21
5.2
Concrete Mixture Ratio Design
——Technical requirements for raw materials
——detrimental (有害的) impurity: including clay, sludge(泥
土), sulfate and organic materials etc., they are affect
mostly on cohesive property between cement and
aggregate;
 Fine aggregate:
Besides requirements on the quality and detrimental
impurity same as coarse aggregate, particular
requirements are
——grading: based on the cumulative on the sieve size
0.6mm, the grading of fine aggregate can be classified as I,
II, III types, among them type II is better on the
characteristics, because it has higher density and lower
specific surface area, which gives concrete good waterretaining and less cement consumption;
22
5.2
Concrete Mixture Ratio Design
——Technical requirements for raw materials
——fineness modulus: normally medium
sand shows better performance;
 Water
——any domestic water can be used in
concrete mixture;
 Admixture
——it is a special material which uses a little
quantity but influence very much on the
concrete properties.
23
5.2
Concrete Mixture Ratio Design
——Basic concept about mixture design
 Representation of concrete proportions
——unit volume method: mass of each material
per one cubic meter, for example:
cement : water : sand : coarse aggregate.
300 : 150 : 600 : 1200 (kg/m3)
——relative quantity method: which means that
mass of cement considered as one unit while
other materials convert into a relative units related
to cement, for example:
cement : sand : c.agg., water/cement ratio =
1 : 2.00 : 4.00 , W/C= 0.50
24
5.2
Concrete Mixture Ratio Design
——Basic concept about mixture design
 Design requirements
——meet strength requirement: put forward a
preparation strength(配制强度
) which is
higher than the design strength(设计强度 f cu , k );
——meet workability requirement: select
appropriate workability based on dimension or
shape of the structure, reinforced layout
situation and construction method.
25
5.2
Concrete Mixture Ratio Design
——Basic concept about mixture design
——meet durability requirement: control
concrete “maximum W/C ratio” and
“minimum cement requirement” according to
environmental conditions;
——meet economic requirement: use local
materials or waste materials based on
qualified requirement of workability and
mechanics.
26
5.2
Concrete Mixture Ratio Design
——Basic concept about mixture design
 Design parameters
——W/C: it is a key parameter which affects
concrete performances: such as strength,
workability and durability;
——water requirement: it decides quantity of
cement paste under same W/C ratio;
——sand-ratio: it is closely related to
concrete cohesiveness and water-retaining.
27
5.2
Concrete Mixture Ratio Design
——Basic concept about mixture design
 Design processes
(1)stage of initial design: according to
requirement of the design document, initial mix
proportion is found by experience way based on
the characteristics of raw materials;
(2)stage of testing, adjusting and confirming:
final mix proportion is determined in lab by the way
of slump test and strength test;
(3)stage of work site design: the process is to
find the mix proportion to construction based on
moisture content of aggregate in the site.
28
5.2
Concrete Mixture Ratio Design
——(1)Stage of initial design
 Determining the preparation strength:
f cu ,o  f cu ,k  1.645
where : f cu ,o —preparation strength ( MPa );
fcu ,k  f  1.645
f cu ,k —design strength ( MPa );
1. 645—assurance coefficienat in 95% assurance;
 —standard deviation ( MPa ).
Calculation of W/C:
W /C 
 a  f ce
f cu ,o   a   b  f ce
Types of agg.
Crushed agg.
gravel
αa
0.46
0.48
αb
0.07
0.33
Coefficient
where
f ce : 28d actual strength of cement ;
 a ,  b : regression coefficient related witht types of coarse aggregate.
29
5.2
Concrete Mixture Ratio Design
——(1)Stage of initial design
mwo ):
——can be get through checking the table when
W/C comes within the range of 0.4~0.8;
 Determining of sand ratio (  s ):
——also get through checking the table by
interpolation (插入法);
 Calculation of cement requirement:
 Determining of water requirement (
mwo
mco 
W /C
W/C=0.40
=0.45
=0.50
砂率： 27~32%
？
31%
30~35%
30
5.2
Concrete Mixture Ratio Design
——(1)Stage of initial design
Calculation of sand and coarse aggregate
requirements, respectively ( mso , mgo ):
——Volume method
mco mwo mso mgo



 0.01a  1
c  w s g
——Density method
mco  mwo  mso  mgo  cp
ms
100  （%
）
s
ms  mg
ms
100  （%
）
s
ms  mg
cp  2400 ~ 2450kg / m3
So the initial mix proportion of this stage is:
mco : mwo : mso : mgo
31
5.2
Concrete Mixture Ratio Design
——(2)Stage of adjustment
 Basic mix proportion
——It is the process that adjusts initial
concrete design based on slump test;
——one of the possibilities for the test is
shown in the following table;
——this stage result can be expressed as:
mca : mwa : msa : mga
32
Possibilities of Slump Test
Possibility
Slump value
Cohesiveness and
water-retaining
1
good
good
No improving.
good
Keeping W/C constant to
adjusting quantity of
cement paste.
poor
Increasing sand ratio
properly.
poor
Adjusting quantity of
cement paste and
increasing sand ratio
properly.
2
3
4
poor
good
poor
Improvement measures
33
5.2
Design mix proportion
——finding the relationship between strength and W/C ratio, so to
determine final W/C ratio to ensure the strength which meets the
requirement:
f cu , o
compressive strength (MPa)

Concrete Mixture Ratio Design
——(2)Stage of adjusting design
35
33
31
29
27
0.43
W/C
0.48
W/C ratio
0.53
34
5.2
Concrete Mixture Ratio Design
——(2)Stage of adjusting design
——based on the final W/C and basic water
requirement considered as mwb , to calculate the
final cement requirement again ( mcb );
——then calculating the sand and coarse
aggregate requirements under new cement and
water requirements mcb , mwb , so this stage
result can be expressed as:
mcb : mwb : msb : mgb
35
5.2
Concrete Mixture Ratio Design
——(2)Stage of adjusting design
——according to correction factor of density
(  ) to calculate final mix proportion:

 c ,t
 c ,c
where :
c ,t —actual measurement destity (kg / m 3 );
c ,c —calculation desity (kg / m 3 )
——final mix proportion in lab can be expressed
as:
mc : mw : ms : mg
36
5.2
Concrete Mixture Ratio Design
——(3)Stage of construction design
 Because sand and coarse aggregate materials in
construction site are kept moist, so mix proportion
for construction site should be adjusted according
to moisture content of sand and coarse
aggregate( ws %, wg % ):
cement :
sand :
mc  mc
ms  ms  (1  ws %)
coarse aggregate : mg  mg  (1  wg %)
water :
mw  mw  (ms  ws %  mg  wg %)
37
5.3
Concrete for Road
38
5.3
Ordinary concrete for road
——Special requirements
 Composition
——there are some special characteristics in cement
composition, which are higher C4FA and lower content of
C3A;
 Workability
Ordinaryof
Portland
Mineral very much
Chemical
Cement
for road
 depends
on the method
Concrete
paving,
compositions
compositions
(%)
normally paving
method are: cement (%)
——Concrete
synovial paving method(滑膜摊铺法): slump
Tricalcium
3CaO·Al2O3
0～15
≤7
25~30mm;
aluminate
——Concrete track paving method(轨道摊铺法): slump
40~60mm;
Tetracalcium 4CaO·Al2O3·Fe2O
5～15
≥15
——Concrete paving
method
with
three
roll
shaft(三辊轴摊铺
aluminoferrite
3
法) : slump 30~50mm；
——Small machine paving method(小型机具法) :slump
39
10~40mm.
5.3
Ordinary concrete for road
——Special requirements
 Durability
——Besides controlling the maximum W/C
ratio and the minimum requirement,
durability of concrete for road has the
requirement on air content;
——amount of air entraining content should
consider normally environment condition,
and nominal maximum size of coarse
aggregate.
40
5.3
Road Concrete Design
——Determining preparation strength
Common concrete
f cu ,o  f cu ,k  1.645
where
f cu ,o ：preparation strength (MPa);
f cu ,k：design strength (MPa);
1.645：assurance coefficienat in
95% assurance;
 ：standard deviation (MPa).
Concrete for road
fr
 ts
fc 
1  1.04Cv
where
f r : design strength, MPa ;
s : standard deviation;
t : assurance coefficient;
Cv : coefficient of variation
41
5.3
Road Concrete Design
——Calculation W/C
Common concrete
W /C 
 a  f ce
f cu ,o   a   b  f ce
where
f ce : 28d actual strength of cement;
 a ,  b : regression coefficient related
witht ypes of coarse aggregate.
Concrete for road
W /C 
1.5684
f c  1.0097-0.3595 f s
(for crushed agg.)
1.2618
W /C 
f c  1.5492  0.4709 f s
(for gravel agg.)
where
f c : concrete preparation strength (MPa )
f s : cement actual flexuel strength (MPa ).
42
5.3
Road Concrete Design
——Find sand ratio
Common concrete
By table lookup method.
related factors:
——slump value;
——type of coarse aggregate;
——nominal maximum size of
aggregate.
Concrete for road
By table lookup method.
Related factors:
——fineness modulus;
——type of coarse
aggregate;
43
5.3
Road Concrete Design
——Find water requirement
Common concrete
Through the look-up table method
to find water requirement；
Related factors:
——W/C ratio;
——type of coarse aggregate;
——nominal maximum size of
aggregate.
Concrete for road
Through the calculation method to find
water requirement；
mwo  104.97  0.309 SL  11.27(W / C )  0.61 s
mwo
(for crushed aggregate)
 86.89  0.370 SL  11.24(W / C )  1.00  s
(for gravel aggregate)
where
SL : slump value (mm);
 s : sand ratio(%).
44
5.3

Road Concrete Design
——Calculation requirements of cement,
and aggregates
There is no differences on the
calculation method of mix
design for cement, fine and
coarse aggregates requirements
between common concrete and
road concrete;
 It should emphasize that
filling volume of coarse
aggregate is calculated,
which is not less than 70%.
(mass over tap density of
coarse aggregate).
mwo
mco 
W /C
mco
c

mwo
w

mso
s

mgo
g
 0.01a  1
ms
100  （%
）
s
ms  mg
mco  mwo  mso  mgo  cp
ms
 100  （%
）
s
ms  mg
45
5.4
Concrete Admixture
46
5.3
Concrete Admixture
——introduction
 Concrete admixture is a special compound which
mixed into concrete during mixing process.
 Quantity of admixture added is not much
(generally no more than 5% by weight of the
cement) , but it brings about significant impact on
concrete performances, such as workability,
strength etc.;
 The main function of admixture is reducing
construction cost, obtaining desirable workability
and meeting some special requirements.
47
5.4
Concrete Admixture
——introduction
Improving
rheological behavior
Water reducer,
Air entraining agent,
Pumping aid,
Water-retaining agent.
Adjusting speed of
setting and hardening
Retarder,
Early strength agent,
Accelerating agent.
Adjusting
air content
Air entraining agent,
Foam agent,
Defoamer.
Classification
Improving
durability
Air entraining agent,
Antifreeze agent,
Anti-permeability agent,
Corrosion inhibitor. 48
5.4
Concrete Admixture
——Ordinary admixtures
 Reducing water agent
——it is an agent that can reduce water requirement
without affecting workability of concrete, especially
flowability;
——the main functions of this admixture are:
(1) because of reducing water requirement and lowering
W/C ratio, so concrete strength corresponding is improved;
(2) remarkably improving workability under the condition of
no any change on concrete component and strength;
(3) without change on workability and strength, it can
reduce cement consumption so to cut coast.
49
5.4
Concrete Admixture
——Ordinary admixtures
——Mechanism of action：
(1) oriented absorption and dispersion (定向吸附和
分散作用);
(2) lubrication (润滑作用)；
(3) promotion hydration(促进水化作用) ；
——types of reducing water agent:
(1) common type: reducing water requirement
about 5~15%;
(2) superplasticizer: reducing water requirement
about over about 20%;
(3) compound type: besides reducing water
requirement, also having other characteristics.
50
5.4
Concrete Admixture
——Ordinary admixtures
 Air entraining agent
——this admixture can bring a larger
number of microscope air-bubbles dispersed
throughout the concrete;
——the benefit of this entrained is that
causes disruption of the continuity of
capillary pores (毛细管) , thus reducing the
permeability of concrete and reducing
internal stresses caused by expansion of the
pore water on freezing.
51
5.4
Concrete Admixture
——Ordinary admixtures
 Retarder
——it can prolong the setting time of concrete with
no adverse effects on post strength;
——the mechanism of retarder is because that
retarder can be attracted on the cement particles
surface to form a film which is not soluble, so as to
prevent cement from hydration for a period of time;
——retarder applies for mass concrete,
construction in summer season and long distance
translocation.
52
5.4
Concrete Admixture
——Ordinary admixtures
 Early strength agent
——it is a kind admixture that promote concrete
early strength but no adverse effect on post
strength;
——the mechanism relies on the catalytic role of
hydration;
——it applies to the construction under room and
low temperature, even under negative temperature
condition. But it has to pay more attention in
corrosion of steel bar because this admixture
normally contains some chloride.
53
An example of admixture application
 According to the following example to know
how to calculate the concrete mix proportion
when some reducing water agent mixed to
concrete.
 Known conditions: initial concrete proportions
cement : water : sand : coarse aggregate
372 : 175 : 596 : 1268 (kg/m3);
Sand ratio: 32%;
Admixture adding amount : 0.5% in cement;
water reducing ratio: 8%.
54
Solution 1
Strength remains constant, while flowability of
fresh concrete increases significantly .
After mixed 1.9kg reducing water agent
( m a d  mc,ad  0.5%  372  0.5%  1.9kg / m ), finding
slump value increasing obviously, from original
25mm into 120mm, and cohesiveness and
water-retaining are still desirable.
3
55
Solution 2
Keep concrete flowability (slump value) and strength the
same to save cement consumption.
Calculating water
requirement
when added
reducing water
admixture
Calculating
cement
requirement
Calculating
Admixture
quantity
Finally determining the
fine and coarse
aggregate requirements
mw, ad  mw (1  ad )  175(1  0.08)  161kg / m 3
mc , a d  mw,ad / (W / C )  161  0.47  343kg / m 3
m a d  mc , ad  0.5%  343  0.005  1.7kg / m 3
sand : 617kg / m3， coarse aggregate :1310kg / m3
56
Solution 3
Flowability (slump value) remains constant, while
strength of concrete is improved.
Calculating water
requirement
when added
reducing water
admixture
Cement
requirement
keeps constant
Calculating
Admixture
quantity
Finally determining the
fine and coarse
aggregate requirements
mw, ad  mw (1  ad )  175(1  0.08)  161kg / m 3
mc , ad  372kg / m 3
m a d  mc,ad  0.5%  372  0.5%  1.9kg / m 3
sand : 609kg / m3， coarse aggregate :1294kg / m 3
57
Summary of the example
cement
water
sand
c.agg
W/C
Original
proportion
372
175
596
1268
0.47
Solution 1
372
175
596
1268
0.47
Solution 2
343
161
617
1310
0.47
Solution 3
372
161
609
1294
0.43
58