Nghiên cứu tính công tác hỗn hợp bê tông và kỹ thuật bảo dưỡng bê tông tự lèn trong điều kiện khí hậu việt nam tt tiếng anh

MINISTRY OF EDUCATION AND TRAINING
NATIONAL UNIVERSITY OF CIVIL ENGINEERING

Nguyễn Hùng Cường

RESEARCH OF WORKABILITY OF CONCRETE MIXTURE AND
TECHNIQUES FOR CURING OF SELF-COMPACTING CONCRETE
UNDER VIETNAM CLIMATE CONDITIONS

Area: Construction Engineering
Code: 9580201

SUMMARY OF DOCTORAL DISSERTATION

Hà Nội - 2020


This dissertation has been completed at the National University of Civil
Engineering

Scientific Principal Instructor 1: Hồ Ngọc Khoa, Ph.D., Associate
Professor
Scientific Principal Instructor 2: Bùi Danh Đại, Ph.D.

Reviewer 1:
Reviewer 2:
Reviewer 3:

The dissertation is defended at the Dissertation Committee at the National
University of Civil Engineering
At: …. o’clock…………………………….. 2020

1

INTRODUCTION
1. Research topic necessity
Self-compacting concrete (SCC) was first introduced in Japan in 1983. SCC technology
in Vietnam is rather new. The composition of the concrete mixture differs from
traditional concrete such as fine filler content, more superplasticizer, more cement
volume and lower W/P ratio. Therefore, the factors of work and curing techniques have
specific characteristics. Vietnam is located in the tropical monsoon region, during the
year there are many adverse weather cycles adversely affecting the properties of concrete
mixes, curing and strength development of concrete. How the workability of the SCC
mixture and the initial curing process of SCC change and behave in Vietnamese weather
conditions? What technical measures and processes need to be applied to ensure
workability? What concrete curing techniques need to be applied to ensure the curing
process? Research results have been conducted and published in Vietnam and the
documents compiled from abroad on this issue are incomplete and unclear. Meanwhile,
the trend of developing and applying SCC technology in construction practice in Vietnam
is increasingly critical. Therefore, the study of the workability of concrete mixtures and
the curing of concrete techniques is scientific and necessary.
2. Research purposes
Research purposes: Propose the process and technical requirements to ensure the
workability of the concrete mixture; Propose procedures and technical instructions for
curing of concrete construction in the climatic conditions of Vietnam.
3. Research goals
Research and produce SCC mixture; Empirical research on the decline in workability;
study dehydration and plastic shrinkage; building ANN model forecasting the initial
workability based on manufacturing materials; Building ANN model to estimate the
decline in workability based on technology and climate; Propose a technical process to

ensure workability and curing of SCC technicals.
4. Research objects and scope
4.1. Research objects
- Workability of SCC mixture
- Curing of SCC
4.2. Research scope
- Research applied to conventional reinforced concrete structures constructed by on-site
concrete pouring method, excluding large concrete structures.
- SCC with the ratio of W/P = 0,256-0,374; Fly-ash/P= 0,081-0,418; B35-B50.
- Experimental conditions: weather conditions in Hanoi area with weather cycles and
parameters of temperature, relative humidity of air are relatively similar to different areas
across the country.
5. Scientific background
- The workability of the concrete mixture is influenced by materials, technology and
climate. ANN network is a suitable technique for predicting the workability of the
concrete mixture.
- Speed and quality of hydration and hardening process of concrete depend on the
moisturizing method, the composition of cement minerals, admixture and curing


2

- temperature. Initial curing time depends on the control of evaporation and plastic
shrinkage. The period of follow-up curing is started after initial curing with 2
parameters: TctBD and RthBD.
6. Research methodology
- Analysis and theoretical synthesis.
- Experimental methods
- Statistical method (ANN - Artificial Neural Network model).
7. Scientific Value and Significance:

- Scientific value: Systematizing the scientific basis of technology of SCC; qualitatively
and quantitatively change the workability of concrete mixture, the dehydration and
plastic shrinkage of concrete mixture in the climatic conditions of Vietnam.
- Significance: Designed gradation and manufactured SCC; propose the process and
technical instructions to ensure the workability of SCC, procedures and technical
instructions for curing of SCC
8. Novelty and contributions of the dissertation
- Determines the rule and quantifies the change of SCC mixed work under the influence
of technological and climate factors through experimenting and applying ANN
network model.
- Determines the rules and quantifies the process of dehydration and plastic shrinkage
in the initial hardening period of SCC under the influence of technological and climatic
factors through experiments in natural conditions.
- Proposes the process and technical requirements to ensure the workability of SCC
before pouring concrete and effective curing of SCC in Vietnamese climatic
conditions.


3

CHAPTER 1: OVERVIEW OF WORKABILITY OF CONCRETE MIXTURE
AND CURING OF SELF-COMPACTING CONCRETE
1.1. Definitions and Terminologies
1.1.1. Self-compacting concrete
Self-compacting concrete (SCC) is a type of concrete that when has not been cured, is
capable of flowing under the force of gravity itself and is capable of filling itself in every
corner of the formwork even in places with dense reinforcement. SCC does not need any
mechanical impact but still ensures uniformity and consistency.
1.1.2. Workability of self-compacting concrete mixture
Workability of the concrete mixture is an engineering feature of the concrete mixture,

which determines the ease of pouring, leveling, compaction at every position of the
formwork without stratification and water separation.
1.1.3. The dehydration of self-compacting concrete
Dehydration of concrete is the process of evaporating water from concrete into
surrounding environment (the process of changing substances) through an open surface.
1.1.4. Plastic shrinkage of concrete
Plastic shrinkage is the phenomenon of changing the volume (shrinking or expansion) of
concrete without developed strength, or very small strength developed.
1.1.5. Concrete curing
Concrete curing is the curing of suitable moisture and heat in concrete for a period
immediately after pouring and finishing of the surface to facilitate the curing of the
concrete, ensuring development and achieving physical properties of concrete.
1.1.6. Artificial Neural Network
The Artificial Neural Network (ANN) is an information processing mathematical model
that is modeled to mimic the behavior of the nerve system of animals, including large
number of neurons attached.
1.2. Fundamentals of self-compacting concrete technology
1.2.1. Characteristics of the materials that produce self-compacting concrete
1.2.1.1 Powder: consists of cement, pozzolan and fine fillers, with a particle size of less
than 125µm
a) Cement: Ordinary Portland cement, belite rich cement (specified amount of C2S in the
range 40-70%), Low-heat dissipation cement with less C3A and C4A.
b) Fly ash: Fly ash is classified into two types: Type F and Type C.
c) Silica is a by-product of the manufacturing industry of silicon-containing products,
escaping in the form of extremely fine flying smoke.
d) Blast furnace slag: The blast furnace slag is a fine filler of particle size approximately
the size of a cement particle.
1.2.1.2. Aggregate:
a) Large aggregate – crushed stone: usually 12-20mm, with size of 10-15mm concrete
will be more stable [84], 9.5-12.7mm is prefered for high strength concrete size.

b) Small aggregate - sands: Standards of Japan, China, Europe, and the US stipulate that
the particle size greater than 5mm (and 8mm according to Swedish and Norwegian
standards) of small aggregate does not exceed 10% [82].


4

1.2.1.3. Chemistry admixture:
a) Superplasticizer admixture: disperses cement particles and gives high flow concrete
mixture without adding water. Polycarboxylate Ether (PCE) based superplasticiser is
used for SCC production.
b) Viscosity denaturing admixture: Used to adjust the viscosity of concrete mixtures.
1.2.2. Principle of gradation and component structure:
The characteristics of SCC are high strength (> 40 MPa), long service life, good
waterproofing, small shrinkage level. SCC is made on the principle of using active
mineral additives, low W/P ratio, minimizing large aggregate content, high amount of
superplasticizer.
1.2.3. Classification of self-compacting concrete
1.2.3.1. Classified by workability
According to European codes, classification based on slump flow, viscosity, passability,
stability. Corresponds to each type of concrete with appropriate application instructions.
1.2.3.2. Classified by materials
- SCC mixture based on fine powder effect.
- SCC mixture using viscosity modifier additives.
- SCC mixture of combined type.
1.3. Self-compacting concrete applications in the world
1.3.1. An overview of the history of the self-compacting concrete research in the
world
In 1983, the issue of sustainability of concrete structures was a hot topic in Japan. In
1988, an SCC prototype was made in Japan. After that, SCC research was spread to

European countries, North America and many countries around the world. Up to now,
there have been 9 international RILEM seminars on SCC held in countries around the
world.
1.3.2. Self-compacting concrete applications in the world
In Japan, in 1990, SCC was first used for housing construction. In 1998, SCC was used
in the construction of two 3m-anchor piles of the Akashi-Kaikyo Bridge project., SCC
was used in the CCTV TV Building In Beijing - China, in Alturki Business Park - Saudi
Arabia. SCC has been used in Thailand since 1992, for some buildings such as the pillars
of the Office Building in Bangkok. In Philippines SCC was used to build the 71-story
Eaton Holiday hotel in Makati. Sweden, in 1998, SCC was used at Sodra Lanken
Infrastructure Project. In 2007, ACI rated SCC as a new technology and encouraged its
adoption in the US.
1.3.3. Research and application of self-compacting concrete in Vietnam
In Vietnam, SCC has been a topic for research since 2001. In recent years, high-flow
concrete has been used for some buildings such as Keangnam, Lotte Center Hanoi,
Viettinbank Tower, The Landmark 81 in Ho Chi Minh City and some small irrigation
works.
1.3.4. Research situation of workability and curing of self-compacting concrete
1.3.4.1. The state of the art of the research of the workability of self-compacting concrete
mixture
Abdullah's research results; Marar and Eren; ACI report 238.1 in 2008; Felekoglu has
studied the workability of concrete. In 2009, ASTM issued standards to check the


5

operation of SCC mixture including ASTM C1611, ASTM 1621, ASTM C1610. In 2010,
Europe issued the EN12350 standard for testing methods of workability parameters of
SCC mixtures. Nehdi and Yeh used ANN model to study SCC workability.
In Vietnam, Nguyen Duy Hieu (2009) studied the decrease in mixed work of SCC using

hollow aggregate keramzit. According to the research results of Ho Ngoc Khoa, the speed
and value of reducing the workability of SCC mixture depend mainly on mortar retention
time, and is influenced by factors such as gradation and weather.
1.3.4.2. Study the curing of self-compacting concrete
Currently, there is no specific guideline for high-quality concrete maintenance (high
performance - HPC) in general and SCC in particular. The difference between curing of
HPC concrete and ordinary concrete. The purpose of HPC curing is not only to ensure
the strength of concrete but also to the requirement of concrete's durability.
CHAPTER 2: SCIENTIFIC FUNDAMENTALS OF THE WORKABILITY OF
CONCRETE MIXTURE AND THE CURING OF SELF-COMPACTING
CONCRETE
2.1. The influence of Vietnamese climatic conditions on concrete workability
2.1.1. Climate characteristics of Vietnam: Survey in 3 representative areas of Hanoi, Da
Nang and Ho Chi Minh, showing that there are 4 typical weather conditions are humid
(T = 15-300C, W = 70- 95%), dry (T = 18-300C, W = 40-65%), hot and humid (T = 28350C, W = 65-85%), hot sunny (T> 350C, W = 40-65) %).
2.1.2. Impact on concrete workability: Speeding up the starting time and setting speed of
cement; accelerate the process of evaporation, increase the rate of deterioration of the
workability of SCC mixture, water amount is not enough for the hydration process; Fast
growing plastic shrinkage. These factors reduce the intensity and durability of concrete.
2.2. Workability of self-compacting concrete
2.2.1. Specifications of workability of self-compacting concrete mixture: ability to
fill, ability to flow through (pass), and resistance to stratification.
2.2.2. Effects of component materials on the performance of the SCC mixture
2.2.2.1. Effect of powder content: Increasing the powder content with a reasonable W/P
ratio will increase leading to increased filling capacity, flowability and stability.
2.2.2.2. Effect of aggregate: Friction between aggregates will consume the flow energy
of the lake during concrete pouring, thus reducing slump flow (SF).
2.2.2.3. Effect of additives
a) Active additives: fineness, particle composition, particle shape, mineralization,
chemical contents, activity, specific gravity all affect the SF, required water volume,

maintain workability, viscosity, and separation of water.
b) Superplasticizer: In a rational grade design, superplasticizer has the effect of increasing
the SF, passability and stability.
c) Lubricant additives: In the right proportion, VMA has little effect on filling capacity
but has the effect of promoting flowability and increasing stability.
2.2.2.4. Effect of mixing water
2.2.3. Influence of technological and climate factors to the workability of SCC
2.2.3.1. Effect of initial temperature of concrete mixture
2.2.3.2. Effect of shipping and storage times
2.2.3.3. Effects of climatic conditions
2.3. Artificial neural network in studying the workability of SCC


6

2.3.1. ANN artificial network structure: Including neurons connected with one another
through weights, functions to receive input signals, synthesize and process input signals
to calculate the output signal.
2.3.2. Types of ANN artificial neural networks: Linear, multi-layer linear transmission,
feedback network ...
2.3.3. ANN network application predicts workability parameters of SCC mixture: In
recent years, ANN network has been studied and applied successfully to model the
behavior of materials.
2.4. The process of forming self-compacting concrete structure
2.4.1. The process of hydration and formation of the initial structure of concrete:
including mineralization process of minerals: Mineral C3A, C3S and C2S, C4AF.
2.4.2. Curing process and structure development
2.4.2.1 Stages of curing process: include dissolution phase; forming coagulating
structure; forming the original structure; forming solid structure; intensity development.
2.4.2.2. Products created during the SCC curing process: include calcite solid mass,

cement gel, non-hydrated cement and voids.
2.4.3. Factors affecting the hydration and curing process of SCC
2.4.3.1. Effect of cement: more C3A, C3S will hydrate and reach strength faster; C2S
affects the later strength of concrete; C4AF has less effect on concrete strength.
2.4.3.2. Effect of W/C ratio and amount of water used: SCC has a small W/C ratio,
together with the process of self-drying of concrete, resulting in insufficient water for the
hydration reaction.
2.4.3.3. Effect of activated mineral additive components: fly ash, silicon soot; blast
furnace slag; limestone powder has a certain influence on the time and speed of cement
hydration of self-compacting concrete to different degrees, thus affecting the time and
duration of concrete curing.
2.4.3.4. Effect of superplasticizer admixture: superplasticizer admixture is used so the
setting time is prolonged, so curing time is usually longer than that of traditional concrete.
2.4.3.5. Effect of temperature factor: Curing temperature affects the hydration speed of
cement and puzzolanic reaction, thus affecting the strength development of concrete.
2.4.4. Effect of hydration on concrete pore structure: The continuity of the capillaries
inside the concrete depends on the level of hydration of cement, for concrete with low
W/C ratio, the capillary holes become discontinuous after a few days of hydration.
2.4.5. The physical process during the concrete curing process
2.4.5.1. The process of dehydration of self-compacting concrete: Is the process of
metabolism between concrete and the external environment.
2.4.5.2. Plastic shrinkage of Self-compacting concrete: Plastic shrinkage takes place
during the first 8-10 hours of curing of concrete.
2.5. The curing of self-compacting concrete
2.5.1. Nature of self-compacting concrete curing: facilitates temperature and humidity
for cement hydration and puzzolanic reactions with the participation of the active mineral
admixture puzzolan occurring in the early stages of curing. These conditions must be
maintained until concrete develops and the desired properties are achieved.
2.5.2. Curing specifications: including initial curing form, follow-up curing start and
finish time, follow-up curing form, required maintenance time for required curing time

TctBD and critical RthBD curing intensity.


7

2.5.3. Curing methods: 1) maintaining the existence of mixing water in concrete at the
early curing stage; 2) minimizing the process of dehydration of concrete by covering
concrete surfaces.
CHAPTER 3: MATERIALS USED AND RESEARCH METHODS
3.1. Materials used in research
3.1.1. Cement
In the study, PC40 cement of But Son factory was used. The mechanical properties of
cement followed TCVN 2682:2009.
3.1.2. Aggregates
3.1.2.1. Large aggregates: Limestone originates in Kien Khe - Ha Nam with Dmax = 510mm. The mechanical properties of limestone followed TCVN 7570:2006.
3.1.2.2. Fine agreegates: size modulus is 2.62 and clay dust content is 0.12%. These
mechanical and physical properties meet the standard TCVN 7570:2006.
3.1.3. Admixture
3.1.3.1. Mineral admixture: Pha Lai thermoelectric fly ash that meet the technical
requirements of F-type fly ash ASTM C618:12 and TCVN 10302:2014.
3.1.3.2. Superplasticizer admixture: new generation superplasticizer, polycarboxylate
BiFi HV298 that complies with ASTM C494 type G.
3.1.3.3. Viscous additives: Culminal MHPC400, a white powder, derived from cellulose,
easily soluble in water.
3.1.4. Water: Water for concrete meets the technical requirements according to TCVN
4506: 2012 Water for concrete and mortar mixing - Specification.
3.2. Designing gradation and manufacturing self-compacting concrete
3.2.1. Method of gradation design: there is no standard on gradation. The methodology
is mainly based on the criteria of workability as a basis for the design of gradation. Carry
out the design of grading by optimizing the amount of mortars surrounding aggregate or

empirically using calculations.
3.2.2. Define gradedation design specifications: Refer to the US, European, and
Japanese standards.
3.2.3. Define material composition
3.2.2.1. Calculation of material composition: Calculated 30 gradations of SCC.
3.2.2.2. Self-compacting concrete mixture mixing: the mixture follows the principle of
free fall.
3.2.2.3. Test the SCC mixture work: using European standard EN 12350: 2010.
3.2.2.4. Testing compressive strength: R28 reaches from 41.5 to 67.9 MPa.
3.3. Research methods and experiments
According to the methods of Europe, Vietnam, the experimental research methods carried
out by scientists in the former Soviet Union, of the Russian Federation, have been applied
by some concrete technology researchers in Vietnamese climatic conditions.
CHAPTER 4: PROPOSAL OF RESEARCH PROCEDURES, TECHNICAL
REQUIREMENTS FOR ASSURANCE OF WORK OF THE SCC
COMBINATION
4.1. Sample, Condition and Experimental content
4.1.1 Self-compacting concrete mixture test sample
Table 4.1 SCC mixture gradation used for workability evaluation test


8

Sign

Type
SF
(mm)

W/P

P
(MPa)

PC40
cement
(kg)

Fly
ash
(kg)

Sand
(kg)

Crushed
stone
(0,5x1)
(kg)

Super
plasttic
izer
(kg)

VMA

Water

(kg)

(kg)

SF1
0,30
147,
444,9
808
770
5,92
0,2
185,9
650
B45
4
SF2
0,35
M2
409,3
140
808
770
5,49
0,19
197
710
B35
SF3
0,315
236,
M3

328,8
808
770
5,65
0,20
189
795
B35
4
4.1.2. Experimental conditions
Table 4.2 Weather conditions of experimental environment
Temperature
Relative air
Wind speed
Sign
Characteristics
(0C)
humidity (%)
(m/s)
ĐK1
Humid
15 ÷ 30
70 ÷ 95
1÷2
ĐK2
Dry
18 ÷ 30
40 ÷ 65
1 ÷ 2,5
ĐK3

Hot and humid
28 ÷ 35
65 ÷ 85
1 ÷ 2,5
ĐK4
Hot
28 ÷ 40
40 ÷ 65
1 ÷ 2,5
4.1.3. Experimental content
- Assessing the impact of initial heat on concrete to reduce workability.
- Assessing the effect of storage conditions on the workability over time.
- Assessing the influence of climatic conditions on the workability over time.
4.2. Results of experiments
4.2.1. Initial temperature of the mixture to workability
It is observed from the
results of the study: The
higher
the
initial
temperature, the faster the
decline in work speed: SF
decreases faster and T500
also increases. The reason
is
that
the
high
temperature of the mixture
promotes the speed and

value of dehydration due
to
evaporation
and
accelerates the setting of
cement. However, after
120 minutes of storage,
both samples remained at
SF1 and SF2 classification,
and T500 was still within
Figure 4.1 Decreasing SF and T500 againts degrees with grout
permitted
limits
(<5
temperature and retention time
seconds).
M1


9

4.2.2. Effect of storage conditions on workability
SF and T500 of the mixture
in static containers, free
evaporation of water
decline very quickly. T500
after more than 15
minutes has been greater
than 5 seconds, exceeding
the

construction
specifications according
to EN standards. SF
plummeted after the first
30 minutes, to a value less
than 650mm, did not meet
the
criteria
for
classification according to
the spread of SF2, after 75
minutes decreased to
550mm, did not meet the
classification criteria for
Figure 4.2 Decreasing SF and T500 by method and retention time
SF3.
The mixture is kept in a tightly closed mixing container, turning at a slow speed, similar
to storage conditions - transported by tank truck, maintaining very good workability: The
spread of SF spread after 60 minutes of storage is still satisfactory. Technical
specifications are 670mm, T500 in the allowable value is 4.85 seconds. However, for up
to 90 minutes, SF approaches the limit of 650mm, and the T500 exceeds the allowed limit
of 5s.
4.2.3. Impact of climatic conditions on workability
Performed with 3 gradients M1, M2, M3 in 4 weather conditions DK1,2,3,4

Figure 4.3 SF decreasement of M1 against weather conditions and time


10

Figure 4.4. Transform of T500 and Vfunnel of
M1 against weather conditions and time

Figure 4.5 Transform of Lbox and Jring of
M1 against weather conditions and time

DK1, M1, M2, M3 maintain good spread and ensure working after 120 minutes according
to classification criteria (SF1 ≥ 550, SF2 ≥ 660, SF3 ≥760). In DK2, M1 maintained good
SF after 120 minutes, M2 decreased to min classification criteria after 105 minutes and
M3 - after 60 minutes. In hot and humid conditions, M1, M2 still maintained good
workability after 120 minutes according to classification criteria, M3 retention time of
M3 reduced to 90 minutes. Particularly in hot DK4 conditions, both M2 and M3
decreased SF below the classification criteria after 45 minutes of retention; M1 - after 60
minutes; construction criteria after only 30 minutes of storage (Figures 4.3, 4.6, 4.9).

Figure 4.6 The SF decreasement of M2 against weather conditions and time


11

Figure 4.7. Transform of T500 and Vfunnel
Figure 4.8 Transform of Lbox and Jring of
of M2 against weather conditions and
M1 against weather conditions and time
time
The temperature factor clearly affects the decrease in viscosity of the mixture through
Vfunnel and T500. Humid conditions, parameters Vfunnel samples M2, M3 decreased beyond
the use standard after 120 minutes of storage, M1 after 90 minutes, T500 all 3 gradients
maintained under the usage criteria for 120 minutes. In dry condition, Vfunnel of M1, M2
exceeded 60 minutes after standard use, M3 after 105 minutes; M1 and M2 T500 exceeded

the standard after 75 minutes, M3 after 120 minutes. In hot and humid condition, Vfunnel
M1 exceeded the standard after 75 minutes, M2 after 105 minutes, M3 after 120 minutes;
T500 M2, M3 exceed the standard after 120 minutes, M1 after 90 minutes. Especially in
hot conditions, M1's Vfunnel exceeded construction regulations (12 seconds) after 30
minutes, M2 and M3 after 60 minutes; M1, M2 T500 exceeded construction standards
after 60 minutes, M3 after 75 minutes (Figures 4.4, 4.7, 4.10).

Figure 4.9. The SF decreasement of M3 against weather conditions and time


12

Figure 4.10 Transform of T500 and Vfunnel
of M3 against weather conditions and
time

Figure 4.11 Transform of Lbox and Jring
of M3 against weather conditions and
time

There are similarities in the influence of weather conditions to the mobility, self-flow,
flowability of SCC mixture through Lbox and Jring criteria as for the viscosity of the
mixture. In DK1, Jring parameters of M1 and M2 maintained construction criteria up to
90 minutes, M3 maintained up to 120 minutes; Lbox guarantee construction criteria up to
120 minutes. In DK2, Jring of M1, M2 maintained for 60 minutes, M3 maintained for 75
minutes. Conditions DK3, Jring of graded M1, M2 maintained up to 75 minutes, M3
maintained up to 90 minutes; Lbox parameters maintained up to 120 minutes for all 3
gradients. Especially in DK4, Jring graded M1 maintained up to 30 minutes, M2, M3 to
45 minutes; Lbox all 3 gradients maintain the construction limit to 45 minutes of storage
(Figures 4.5, 4.8, 4.11).

4.2.4. Impact of reduced workability on SCC's R28
Table 4.9. SCC compressive strength corresponding to the time of storing different
concrete mixes


13

Grad
e

M1

M2

M3

Climatic
condition
Humid
Humid
Humid
Dry
Hot humid
Hot
Hot
Humid
Humid
Humid
Dry
Hot humid

Hot
Hot
Humid
Humid
Humid
Dry
Hot humid
Hot
Hot

Temperatur
e (0C)

Moisture
(%)

11,7
17,2
23,4
30,5
31
35,1
43,1
11,4
17,8
23,6
29,7
31,8
35,6
43,6

11,2
17,7
24,5
30,1
32,7
34,5
43,2

89
87
81
50
75
65
43
80
72
68
51
74
53
31
82
75
70
50
72
64
40

R28 (MPa)
At pouring sample time(minutes)
0
30
60
90
120
7,7
56,9
55,7
53,8
52,3
58,7
57,9
55,2
54,1
52,7
58,6
57,1
53,2
52,1
46,4
65,9
57,4
52,8
52,3
51,2
61
62,3
60

53
46
58
62
57
54
50,7
58
63
55
47
40
52,9
51,7
47,3
46,1
43,7
53,1
52,3
46,9
45,7
44,5
51
50,3
45,7
43,9
38,9
52,3
52,9
52,3

51,8
50
52
57
54
50
45
50
49,5
47,1
46,2
44,9
52
53
51
45,5
43,3
44,5
43,8
42,7
40,9
38,9
45,7
44,9
43,2
41,2
39,5
45
43,5
41,7

40,5
37
45,1
42,5
41,9
39,5
38,5
42
43
42,5
41
39
45,1
43,7
43,5
42,6
42,1
45,2
41,5
42
36
32

4.3. Predicting the workability of self-compacting concrete mixture by ANN model
4.3.1 Predictive model of workability and concrete strength against fabrication
materials
4.3.1.1. Building ANN1 network training data
- Building a model with 7 input
variables: volume of cement,
flyash, stone, sand, water,

superplasticizer, VMA.
- Output: SF, T500, Jring, Lbox,
Vfunnel, SR, R28 workability
parameters.
- Number of hidden layers: a
hidden layer; Number of
Figure 4.12 ANN1 model predicting workability
neurons in the hidden layer: 4.
parameters by materials
Number of samples to study
- Number of samples to test: 30 randomly selected
(training): 180 samples per
samples for each network.
network.
4.3.1.2. MLP-ANN1 network results predict parameters of workability at the batching
plant by material composition


14

Figure 4.13 Test results of parameters SF and T500

Figure 4.14 Vfunnel and Lbox parameters test

Figure 4.15 Test results of Jring and SR parameters

Figure 4.16 R28 compressive strength
parameter test results

Figure 4.17 Example of correlation

between outputs and Lbox target values


15

4.3.2. Predictive model for workability against temperature and retention time
4.3.2.1. Developing ANN2 network training data
Building ANN2 model includes: 3
input variables: ambient, concrete
temperature, retention time; Outputs
include: SF, T500, Jring, Lbox, Vfunnel,
SR, R28; Number of hidden layers: a
hidden layer; Number of neurons in
the hidden layer: 5; Number of
Figure 4.18 MLP-ANN2 model
samples to study: 35/NW
4.3.2.2. MLP-ANN2 results predict the workability and R28 of self-compacting concrete

Figure 4.19 Predicted SF and T500 of M1

Figure 4.20 Predicted Vfunnel and Lbox of M1
Jring approximation

20

R28 approximation

70
y

y

Jring

d Jring

18

R28

d R28

65

16
60
14
55
12
50
10
45

8

6

0

5

10

15

20

Sample number

25

30

35

40

0

5

10

15

20

25

30

35

Sample number

Figure 4.21 Predicted Jring and R28 of M1
MLP-ANN2 network processing results showed very high accuracy of the model with a
very small difference between the desired d-line (red yellow line) and the predicted ynetwork line (blue line). The training task was conducted with 35 sets of data for each


16

parameter of SCC mixture with performance assessed by the values: MAE (Mean
Absolute Error), MRE (Mean Relative Error), Max AE with low values and the
correlation coefficient between MLP output and actual target value and approach 1
(Table 4.11).
Table 4.11. Predicting errors and correlation coefficients of the model MLP-ANN2
Output
MAE
MRE (%)
MaxAE
Correlation
SF
2,12
0,33
11,30
0,98
T500
0,075
1,76

0,42
0,99
Vfunnel
0,13
1,08
0,73
0,97
Lbox
0,003
0,33
0,021
0,99
Jring
0,26
2,70
0,93
0,98
R28
0,49
0,91
1,68
0,99
4.4. Propose the process and technical requirements to ensure the workability of
self-compacting concrete mixture
4.4.1. Fundamental process of designing, mixing, storing and transporting selfcompacting concrete mixture

Figure 4.28
Process of
designing, mixing,
storing and

transporting selfcompacting
concrete mixture
using ANN model


17

4.4.2. Developing the ANN model to predict the workability parameters of SCC
Step 1: Select parameters
to predict (parameters for
work calculation at the
batching plant or at the
construction site)
Step 2: Identify variables
that affect the parameters
to predict.
Step 3: Develop data to
train the network
Step 4: Establish network
structure, train and test
ANN model.
Step 5: Check errors to
confirm the model
Step 6: Use the ANN
model results to predict
new cases.
Figure 4.29 General process to establish the ANN
model for the predict problem
4.4.3 Gradation design process using the ANN1 model
Step 1: Identify SCC

mixed
properties
according to construction
requirements.
Step 2: Prepare component
materials: the supply and
technical requirements.
Step 3: Calculate materials
and gradation.
Step 4: Run the ANN1
model and select the
appropriate
SCC
gradation.
Steps 5, 6: Mix SCC
mixture in laboratory
conditions and check the
workability.
Step 7: Check the strength
and mechanical properties
of concrete.
Step 8: Mix SCC in
factory
conditions,
Figure 4.30 Design process of SCC mixture using
calibrate.
ANN1
Step 9: Issue the standard
gradation.

18

4.4.4. Ensuring the workability of self-compacting concrete mixture in
transportation - storage in climatic conditions in Vietnam
Step 1: Define input
parameters.
Step 2: Select the
appropriate SCC mixtures.
Step 3: Using ANN2 to
predict the reduction of
workability
of
SCC
mixture at the site.
Step 4: Building and
piloting the model of
transporting and storing
SCC mixture.
Step 5: Check the
workability
parameters
and concrete strength R28.
Step 6: Decide on a plan to
transport and store SCC
mixtures.
Step 7: Organize SCC
mixed transport.
Figure 4.31 Process to guarantee workability of selfcompacting concrete mixture
Table 4.14. Recommendations of transit time - storage of SCC mixture

Maximum transit time (minutes)
Type of SCC
Humid
Dry
Hot humid
Hot
SF1 (SF = 550 – 650)
75
45
75
30
SF2 (SF = 660 – 750)
90
60
75
45
SF3 (SF = 760 – 850)
120
75
90
45

CHAPTER 5: RESEARCH ON THE TECHNIQUES TO CURE SELFCOMPACTING CONCRETE IN THE WEATHER CONDITIONS IN
VIETNAM
5.1. Sample, conditions and content of the experiment
5.1.1. Samples for experiment
Table 5.1 Mixed gradation of SCC used for concrete curing test
Sign
Type
W/P

PC40
Fly
Sand
Crushed
Super
VM
Water
cemen
ash
stone
plastic
A
(kg)
SF
P
t
(kg)
(kg)
(0,5x1)
izer
(mm)
(MP
(kg)
(kg)
(kg)
(kg)
a)
SF1
0,30
147,

M1
444,9
808
770
5,92
0,2
185,9
650
B45
4
SF2
0,35
M2
409,3
140
808
770
5,49
0,19
197
710
B35


19

5.1.2. Content of experiment:
- Study the effect of curing conditions on dehydration and plastic shrinkage processes.
- Study the effect of curing conditions on concrete quality;
- Analysis of experimental results as a basis for selecting curing methods;

- Identify elements and specifications of the selected SCC curing method.
5.2. Experiments studying the physical process in the early curing period
5.2.1. Measured dehydration and plastic shrinkage results

Figure 5.1 Evaporation and plastic shrinkage
of grade M1 in dry condition

Figure 5.2 Evaporation and plastic shrinkage
of grade M2 in dry condition

Figure 5.3 Evaporation, plastic shrinkage of
grade M1 in hot humid condition

Figure 5.4 Evaporation, plastic shrinkage of
grade M2 in hot humid condition


20

Figure 5.5 Evaporation, plastic shrinkage of
grade M1 in hot condition

Figure 5.6 Evaporation and plastic shrinkage
of grade M2 in hot condition

Evaporation and deformation take place mainly during the first 6-7 hours. Curing with
nylon has the smallest amount of water evaporation, then the Water-on sample and the
largest water vapor occur in the Non-Curing sample. Condition dry nylon cover 5.05%
and 5.25%; Water-on: 27.1%; and 28.2%; Non-Curing: 30.72% and 32.58%; hot humid
nylon cover 4.85% and 5.10%; Water-on: 17.56% and 18.90%; and Non-Curing: 20.91%

and 19.5%; hot samples nylon cover 6.25% and 5.95; Water-on: 30.1% and 31.97%;
Non-Curing: 32.3% and 33.80%.
Along with the evaporation of water is the plastic shrinkage of concrete. In all 3 climatic
conditions, nylon cover maintenance has the smallest plastic shrinkage value, then
Water-on and the largest occur in the Non-Curing sample. dry and nylon cover conditions
give plastic shrinkage values of 0.71mm / m and 0.74mm / m; Water-on: 2.09mm / m
and 2.13mm / m and Non-Curing: 2.31mm / m and 2.43mm / m; in hot and humid, nylon
cover curing samples 0.68mm / m and 0.70mm / m; Water-on: 1.18mm / m and 1.21mm
/ m and Non-Curing: 1.46mm / m and 1.50mm / m; Hot conditions, soft deformed nylon
cover 0.81mm / m and 0.82mm / m; Water-on: 2.15mm / m; 2.25mm / m and NonCuring: 2.37mm / m and 2.51mm / m.
In the first 10 hours, the max surface dehydration rate of the two gradients is: The dry
rate reaches the max value at 3 o'clock. The largest values in Non-Curing are 1.6 kg / m2
/ hour and 1.9 kg / m2 / hour; Water-on: 1.35kg / m2 / hour; 1.55 kg / m2 / hr, nylon cover:
0.44kg / m2 / hr; 0.47kg / m2 / hour; Hot humid speed reaches the max value at 2 o'clock.
The max rate of Non-Curing sample is 1.02 kg / m2 / hour; Water-on is 0.9 kg / m2 / hour
and 0.9 kg / m2 / hour; nylon cover: 0.41kg / m2 / hour and 0.45kg / m2 / hour. Especially
hot speed reaches the max value at the time of 1 hour. The largest value Non-Curing 1.4
kg / m2 / hour and 1.57 kg / m2 / hour; Water-on: 1.22 kg / m2 / hour and 1.44 kg / m2 /
hour; nylon cover: 0.47kg / m2 / hour and 0.48kg / m2 / hour.


21

5.3. Choose a method of curing of suitable self-compacting concrete
5.3.1. Effect of dehydration and plastic shrinkage on concrete quality
5.3.1.1. Effect on compressive strength of concrete
There is a negative correlation between dehydration value, plastic shrinkage and
compressive strength: dehydrated concrete and small plastic shrinkage have greater
strength than concrete with high dehydration value and large plastic shrinkage.
Table 5.5 SCC compressive strength corresponding to curing conditions

Dry
Grade

Curing method

R28
(MPa)

Hot and humid

%Rtc28

R28
(MPa)

%Rtc28

Hot
R28
(MPa)

%Rtc28

Non-Curing
49,4
85
50,3
84,8
50,7
84,4

Water-On
53,2
90
53,5
90,2
54,3
90,4
Nylon Cover
59,1
100,5
59,7
100,6
60,8
101
Standard-Curing
58,8
100
59,3
100
60,1
100
Non-Curing
39,4
80,57
41,0
82,1
41,7
82,9
M2
Water-On

42,1
86,09
42,7
85,5
44,4
88,2
Nylon Cover
49,0
100,2
50,1
100,4
50,7
100,7
Standard-Curing
48,9
100
49,9
100
50,3
100
5.3.2.2. Effect on the quality of concrete surface
Through visual observation, in hot condition, samples curing with Water-on and NonCuring samples appeared with many crow's feet cracks on the surface, while the surface
cured by nylon cover had no cracks.
5.3.2. Choose a method of curing of suitable self-compacting concrete
Based on analysis of empirical data related to hardening, structure formation, strength
development shows that the method (nylon cover) is more preeminent (Water-on),
suitable for SCC in climatic conditions in Vietnam.
5.4. Define curing specifications
5.4.1. Determining the initial curing time: Results of compressive strength R28 of
concrete samples are shown in Figure 5.15, 5.16, 5.17.

M1

Figure 5.15 SCC initial curing time in dry
condition

Figure 5.16 SCC initial curing time in dry
condition


22

In both dry and hot and humid
weather conditions, concrete samples
of both M1 and M2 gradation with 1
hour of initial curing have the highest
compressive strength R28, reaching
and exceeding Rtc28 (H.515, H. 5.16).
In hot weather, plastic cover for
concrete as soon as possible, initial
curing is the shortest possible,
preferably less than 0.5 hours; The Figure 5.17 SCC initial curing time in hot
maximum is less than 1 hour (Figure condition
5.17).
5.4.2. Determine the required curing time
Table 5.7. Compressive strength of SCC M1-W/P = 0.35 and M2-W/P = 0.3
Concrete strength,% compared with Rtc28 in the
different climatic conditions
Follow- Rn, Rn+t
up
(t=28–

ĐK2
ĐK3
ĐK4
curing
n)
Rtc28= 49,3MPa
Rtc28=49,9MPa
Rtc28 = 50,2MPa
(days)
M1
M2
M1
M2
M1
M2
1

R1

35,1

36,1

35,6

36,3

41.6

42,5

R1+27
84,8
85,3
85,1
85,5
92,9
93,1
R2
35,8
37,3
35,9
37,7
46,3
46,9
2
R2+26
88,9
89,1
89,1
89,5
93,1
93,9
R3
36,8
39,1
36,9
39,4
50,6
50,7

3
R3+25
89,1
90,4
91,2
92,4
94,1
94,7
R4
46,7
47,3
47,3
48,1
54,6
54,8
4
R4+24
92,9
93,5
93,9
94,2
97,8
95,7
R5
51,7
51,9
52,1
52,5
61,5
63,5

5
R5+23
96,1
97,2
96,8
97,9
100,4
100,9
R6
55,3
55,9
56,7
57,6
64,6
65,1
6
R6+22
96,9
97,9
97,2
98,9
101,8
102,5
R7
60,1
61,5
61,3
62,5
68,8
69,1

7
R7+21
100,2
100,5
100,6 100,8
102,9
103,9
8
R8
65,3
66,5
66,2
67,4
73,1
74,1
R8+20
100,9
101,1
100,7 101,5
103,5
104,2
Under dry and hot and humid conditions, SCC needs continuous curing for 7 days. In hot
condition, need continuous curing for 5 days (Table 5.7).
5.4.3 Curing technique of self-compacting concrete by nylon cover method


23

5.4.3.1. Curing process

Figure 5.21 Process of SCC curing technology continuous
pouring without stopping

Figure 5.22 Process of SCC curing technology noncontinuous pouring with horizontal stops

Figure 5.23 Process of SCC curing technology noncontinuous pouring with vertical stops

(1-formwork, 2-concrete pump
nozzles, 3-concrete, 4-nylon curing,
5-concrete structures; I-erection of
formwork, II-pouring concrete, IIIcuring boards first, IV-follow-up
curing, V-finish curing)

(1-formwork, 2-hose pump, 3concrete, 4-nylon, 5-concrete; Ifitting formwork; II1,2-concrete
casting phase 1,2; III1,2-initial curing
of concrete pouring batch 1,2;
IV1,2- follow-up curing concrete
with batch 1,2; V-finish curing)
1-formwork, 2-nozzle, 3-concrete,
4-nylon, 5-concrete structure; Ierection of formwork; II1,2-dumped
batch 1,2; III1,2-initial curing bt 1st,
2nd batch; IV1-continued curing
after the first batch; IV2-curing bt
the whole structure; V - finish curing

5.4.3.2. Technical guidelines
- Initial concrete curing: 1-After finishing concrete surface, no curing method is required;
2-Allow steam to evaporate freely from concrete; 3-Initial curing time depends on the
composition of concrete and weather climatic conditions: in humid weather initial
concrete curing is not required; in dry and humid for about 1 hour; under high heat for

no more than 1 hour.
- Follow-up curing: After finishing initial concrete curing, cover the surface of concrete
with moisture-curing material, plastic film at least 0.1mm, with two layers of plastic.
Required curing time: humid – no curing required; dry and hot-humid TctBD = 7 days;
RthBD ≥ 60%Rtc28; high heat TctBD = 5 days; RthBD ≥ 62%Rtc28.
- End of curing: Curing plate is carefully dismantled, sanitized and warehoused for
subsequent uses.