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 CO

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

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

- 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

- 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: Tct

- 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: Designedgradationand 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

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]

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

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 = 28-350C, 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

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

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

3.2 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

PC40 cement (kg)

Fly ash (kg)

Sand (kg)

Crushed stone (0,5x1) (kg)

Super plastticizer (kg)

VMA (kg)

Water (kg)

M1 SF1 650 0,30 B45 444,9 147,4 808 770 5,92 0,2 185,9 M2 SF2 710 0,35 B35 409,3 140 808 770 5,49 0,19 197 M3 SF3 795 0,315 B35 328,8 236,4 808 770 5,65 0,20 189 4.1.2 Experimental conditions

Table 4.2 Weather conditions of experimental environment

Sign Characteristics Temperature (0C) humidity (%) Relative air Wind speed (m/s)

- 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

Figure 4.1 Decreasing SF and T500 againts degrees with grout

temperature and retention time

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

SF3 Figure 4.2 Decreasing SF and T500 by method and retention time 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

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

Figure 4.7 Transform of T500 and Vfunnel

of M2 against weather conditions and

time

Figure 4.8 Transform of Lbox and Jring of M1 against weather conditions and time The temperature factor clearly affects the decrease in viscosity of the mixture through

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