4. Tóm Tắt Lats Tiếng Anh (Ncs Lvh).Pdf

MINISTRY OF EDUCATION AND TRAINING HANOI UNIVERSITY OF CIVIL ENGINEERING Le Viet Hung Study on the production of high strength lightweight concrete using hollow microspheres from fly ash (cenospheres)[.]

MINISTRY OF EDUCATION AND TRAINING

HANOI UNIVERSITY OF CIVIL ENGINEERING

Le Viet Hung

Study on the production of high-strength lightweight concrete using

hollow microspheres from fly ash (cenospheres)

Major: Material engineering

Code: 9520309

SUMMARY OF DOCTORAL DISSERTATION

Ha Noi - 2023

The work was completed at: Ha Noi University of Civil Engineering (HUCE)

Academic supervisor:

1 Prof Dr Nguyen Van Tuan – HUCE

2 Prof Dr Le Trung Thanh – VIBM

Peer reviewer 1: Prof Dr Luong Duc Long - VIBM

Peer reviewer 2: Prof Dr Nguyen Duy Hieu - HAU

Peer reviewer 3: Prof Dr Nguyen Thanh Sang - UTC

The doctoral dissertation will be defended at the level of the University Council of Dissertation Assessment's meeting at the Hanoi University of Civil Engineering

at hour ', day month year 2022

The dissertation is available for reference at the libraries as follows:

- National Library of Vietnam;

- Library of Hanoi University of Civil Engineering;

INTRODUCTION

1 NECESSARY OF THE STUDY

Research and development of lightweight concrete for load-bearing structures in construction projects are being carried out in many places around the world This type of concrete ensures both strength and durability like conventional concrete while providing various benefits such as reducing the structural load, decreasing the size of structures, enhancing soundproofing, insulation, earthquake resistance, fire resistance, easy transportation, construction, installation, and more The concrete used for load-bearing structures in construction increasingly demands high strength and long-term durability The concrete used for prestressed structures requires higher quality compared to concrete used for conventional structures, specifically, the compressive strength often requires more than 40 MPa, rapid strength development, and the criteria for impermeability, water absorption, and long-term durability are also higher than those for conventional concrete

In the past decade, there has been significant research interest in using hollow spherical particles derived from fly ash (Fly Ash Cenospheres - FAC) for the production of lightweight concrete in construction Utilizing FAC as a lightweight material in concrete manufacturing offers several advantages, such as achieving compressive strength over 40 MPa and low water absorption, comparable to conventional concrete This type of lightweight concrete can be classified as high-strength lightweight concrete with many superior characteristics compared to traditional lightweight aggregate concrete However, the research and development of high-strength lightweight concrete using FAC still face limitations worldwide, especially in Vietnam FAC can be recovered from fly ash generated by coal-fired thermal power plants in Vietnam, with a recovery rate of 80-85% from

an annual total fly ash production of approximately 17 million tons (in 2021) With an average FAC content in fly ash ranging from 0.3% to 1.5%, the theoretical amount of recoverable FAC could be (32,640-163,200) tons per year

Based on practical requirements and scientific challenges in developing high-strength lightweight concrete, the chosen research direction is to explore the production of lightweight concrete using hollow spherical particles derived from fly ash in thermal power plants in Vietnam With this

objective in mind, the proposed dissertation topic is "Study on the production of high-strength

lightweight concrete using hollow microspheres from fly ash (cenospheres)”

2 PURPOSE OF THE STUDY

The study focuses on manufacturing high-strength lightweight concrete for load-bearing structures in construction projects using hollow spherical particles derived from fly ash The objective is to achieve

3 OBJECTIVE AND SCOPE OF THE STUDY

3.1 Objective of the study

The type of high-strength lightweight concrete using hollow spherical particles derived from fly ash cenospheres (FAC-HSLWC) has a compressive strength greater than 40 MPa and a density not exceeding 2000 kg/m3, based on the available materials in Vietnam The research focuses on investigating the mechanical and physical properties and applications of this type of concrete, with a

3.2 Scope of the study

✓ Selection of materials and mix proportions for high-strength lightweight concrete using hollow spherical particles derived from fly ash (FAC-HSLWC) with a compressive strength greater than

materials include pozzolanic cement (XM) and mineral admixtures consisting of silica fume (SF) and finely ground granulated blast furnace slag (GGBFS); Aggregates: natural sand and hollow spherical particles derived from fly ash (FAC), in combination with superplasticizers and polypropylene fibers (PP fibers)

✓ Development of a predictive model for the compressive strength of FAC-HSLWC

✓ Development of a method for calculating the mixture proportions of FAC-HSLWC

✓ Technical properties of FAC-HSLWC: properties of the concrete mix, mechanical and durability characteristics

✓ Performance of a reinforced concrete floor slab using FAC-HSLWC

4 SCIENTIFIC BASIC

✓ The study on production of FAC-HSLWC is based on the theoretical principles of enhancing the strength and durability of concrete, which include the following principles: optimizing the particle composition to achieve the highest packing density of the material mixture; enhancing structural homogeneity by selecting the appropriate maximum aggregate size; increasing the strength of the cementitious matrix and the transition zone between aggregate and cement paste; improving flexural/tensile strength and crack resistance through dispersed fiber reinforcement

✓ The predictive model for compressive strength is built on the relationships between concrete compressive strength, cement compressive strength, water-to-cement ratio (w/c ratio), and key factors of mixture proportions The predictive model for FAC-HSLWC is established using nonlinear regression functions derived from experimental results

✓ The mixture design method for FAC-HSLWC is developed based on the optimal composition of aggregate particle sizes, the optimal ratio of binder to aggregate (binder/aggregate), the formula for calculating density of concrete based on the replacement ratio of FAC for sand, and the predictive model for compressive strength based on the key parameters of concrete mixture proportions obtained from the research

5 RESEARCH METHODOLOGY

The dissertation utilizes the following research methods:

✓ Theoretical research: Gathering relevant technical literature to synthesize, analyze, and provide a basis for establishing the research program

✓ Experimental research: Conducting experiments using both standard and non-standard methods Standard methods are primarily performed according to Vietnamese technical standards (TCVN) and some commonly used international standards Non-standard methods are commonly applied

in material research, concrete, and concrete structure fields, such as scanning electron microscopy (SEM), differential thermal analysis/thermogravimetric analysis (DTA/TGA), determination of compactness of material mixtures, and determination of viscosity of cement mortar mixtures

✓ Established a mixture proportion design method for FAC-HSLWC, ensuring the target

✓ Investigated several physical and mechanical properties of FAC-HSLWC applicable to structural elements, including: (1) workability characteristics of the fresh concrete mixture, (2) mechanical properties of the hardened concrete (compressive strength, flexural strength, modulus of elasticity, Poisson's ratio), and (3) durability properties of the concrete (drying shrinkage, water absorption, chloride ion permeability, resistance to sulfate attack)

✓ Evaluated the performance of structural slabs using FAC-HSLWC in comparison to slabs made with conventional concrete of the same compressive strength grade

7 STRUTURE OF THE THESIS

The thesis consists of an Introduction, 6 chapters, General Conclusion and Recommendations, 36 tables, 97 figures, presented within 151 pages excluding the appendix

1 CHAPTER 1: INTRODUCTION OF LIGHTWEIGHT CONCRETE AND

CENOSPHERE-BASED LIGHTWEIGHT CONCRETE

1.1 LITERATURE REVIEW ON STRUCTURAL LIGHTWEIGHT CONCRETE

1.1.1 Concept and classification on lightweight concrete

1.1.2 Situation on research and application of structural lightweight concrete

For structural lightweight concrete used in construction, the minimum specified compressive strength

is usually 17 MPa In practice, lightweight concrete is commonly used with compressive strengths ranging from 21 to 35 MPa High-rise buildings and bridge structures often employ high-strength lightweight concrete, with compressive strengths typically ranging from 35 to 41 MPa and a density

The lightweight aggregates used in the production of such lightweight concrete are typically artificial lightweight aggregates made from clay, shale, and expanded shale Depending on the quality and density of the lightweight aggregates, the compressive strength of lightweight structural concrete can

aggregates is their porous structure, which results in a high water-absorption capacity (typically 25%) This poses challenges in controlling the workability of the concrete mix and the properties of the concrete, such as changes in density and volume when exposed to a moist environment

10-1.1.3 High-strength lightweight concrete and its application

According to ACI 213-14, high-strength lightweight concrete (HSLWC) is a type of lightweight structural concrete with a compressive strength greater than 40 MPa

1.1.4 Situation research and application of lightweight concrete in Viet Nam

In Vietnam, there have been studies and applications of common lightweight concretes such as cellular concrete, lightweight aggregate concrete using keramzit, fly ash, and polystyrene beads However, research on using cenospheres for lightweight concrete is a new issue in Vietnam, and currently, there have been no studies conducted Cenospheres in Vietnam have the potential for large-scale recovery from coal-fired thermal power plants

1.2 LIGHWEIGHT CONCRETE USING CENOSPHERE

1.2.1 Introduction of lightweight concrete using cenospheres

Fly Ash Cenosphere Lightweight Concrete (FAC LWC) refers to a type of lightweight concrete that utilizes cementitious material and hollow fly ash cenospheres This type of lightweight concrete has

a lower density compared to conventional concrete

Figure 1.1 Cenosphere and typical cenosphere-containing concrete structure

The research on the use of FAC as a lightweight aggregate in cementitious binder systems began in

1984 However, it was not until the late 20th century that the role of FAC as a lightweight aggregate for low-density, low-strength concrete, primarily fulfilling insulation requirements, was extensively studied Recently, several studies have successfully produced a type of lightweight concrete called

compressive strength at 28 days ranges from 33.0 to 69.4 MPa, and the flexural strength is around 8 MPa The thermal conductivity coefficient of ULWC typically ranges from 0.3 to 0.8 W/m·K, which

is significantly lower than that of conventional concrete, approximately 1.9 W/m·K

1.2.2 Hollow microsphere from fly ash (Cenosphere)

Cenospheres are hollow spherical particles composed mainly of alumino-silicates, similar to fly ash particles Their bulk density typically ranges from 0.4 to 0.9 g/cm3, with particle sizes ranging from

1 to 400 μm The majority of cenospheres fall within the range of 20 to 300 μm, with wall thicknesses ranging from 1 to 18 μm Cenospheres possess good compressive strength and high resistance to gas and water permeability Therefore, they are suitable for use in lightweight concrete to enhance strength and reduce bulk density The cenosphere content in fly ash is approximately 0.3 to 1.5%, and considering an estimated annual fly ash generation of around 17 million tons, the theoretical recoverable amount of cenospheres would be between 32,640 to 163,200 tons per year The chemical composition and mineralogy of cenospheres are similar to those of fly ash particles FAC particles contain amorphous silica minerals, which have the ability to react pozzolanically and contribute to the formation of calcium-silicate-hydrate (C-S-H) gel in the cementitious binder system However, this reactivity is relatively low at room temperature and increases with the curing temperature of the concrete

1.2.3 Properties of the concrete using cenosphere

1.2.3.1 Fresh concrete

There have been very few studies determining the properties of FAC concrete mixtures The workability of FAC lightweight concrete is typically assessed using the flowability test method for mortar The flowability of FAC lightweight concrete mixtures is usually controlled within the range

of 150-220 mm The air void content in FAC lightweight concrete mixtures is higher compared to conventional concrete

1.2.3.2 Concrete Properties

1.2.3.2.1 Density and Compressive Strength

The volume mass of FAC lightweight concrete depends on the FAC content, the ratio of fine aggregate to cementitious material, and the presence of coarse and fine aggregates It can range from

studies do not use any aggregates other than FAC The current compressive strength and bulk density properties of FAC lightweight concrete typically range from 30-68 MPa and 40-47 kPa/kg.m-3, respectively

1.2.3.2.2 Flexural Strength and Flexural/Tensile Strength: Similar to other lightweight concrete types, FAC lightweight concrete exhibits relatively low flexural and tensile strength compared to its compressive strength (indicating the brittle nature of the concrete) Therefore, studies on FAC lightweight concrete often incorporate fiber reinforcement such as PVA, PE, or PP to improve its flexural resistance The flexural strength of FAC concrete, when combined with fiber reinforcement

1.2.3.2.3 Elastic Modulus: The elastic modulus of concrete primarily depends on its compressive strength and volume mass Due to its low density, similar to other lightweight concretes, FAC concrete has a lower elastic modulus compared to its compressive strength and decreases proportionally with its volume mass With compressive strengths ranging from 33-69.4 MPa, the elastic modulus of FAC lightweight concrete is typically between 10.4-17.0 GPa

1.2.3.2.4 Durability: The water resistance of FAC lightweight concrete has not been extensively studied Research has shown that FAC particles have a water absorption capacity 18 times greater than sand, but the difference in water absorption is not significant while the water permeability rate

is higher than that of conventional concrete The ability to resist water, liquids, and gases is an important factor related to the durability of concrete in aggressive environments Therefore, in-depth research is needed to clarify these characteristics regarding FAC lightweight concrete

1.2.3.2.5 Shrinkage: To date, there have been very few studies on the shrinkage of FAC lightweight concrete However, since FAC lightweight concrete is a cementitious binder system with a high cement content and does not use a dense reinforcement framework like conventional concrete, its shrinkage is expected to be greater than that of conventional concrete

2 CHAPTER 2: SCIENTIFIC BASIC OF MATERIAL SELECTION, COMPRESSIVE

STRENGTH MODELING, AND MIX DESIGN FOR FAC-HSLWC

Unlike conventional concrete, including commonly used lightweight aggregate concrete such as expanded clay aggregate (keramzit), coarse aggregates are not typically used in high-strength lightweight concrete using FAC (FAC-HSLWC) to ensure low density as well as to reduce the risk

of segregation These characteristics lead to several challenges in the mix design of FAC-HSLWC: 1) Increased surface area leading to higher water demand and W/B ratio: Incorporating a large amount

of FAC hollow particles into the concrete mixture to achieve the desired density results in a significant increase in the interfacial contact area between phases in the system This reduces the workability of the concrete mixture, leading to compromised product quality Moreover, the higher water absorption capacity of FAC compared to sand also contributes to an increase in the water demand

2) Weak transition zone and poor adhesion between cement paste and FAC particles: FAC particles have a rough surface texture, resulting in a low bond strength between the particle surface and the cement paste This diminishes the bond strength within the concrete matrix, affecting its strength and durability

3) Brittle behavior and significant shrinkage of FAC-HSLWC: To ensure the compressive strength and long-term durability of the concrete, a high cement content and low water-to-cement ratio are necessary However, these conditions increase the likelihood of generating internal stresses that exceed the tensile capacity of the concrete, leading to cracking Additionally, the lack of a solid reinforcing framework in FAC-HSLWC, as found in conventional concrete, and the high cement content contribute to its brittle behavior

4) Lack of a unified mix design method for FAC concrete: Due to the absence of coarse aggregates

in FAC-HSLWC, common mix design methods for lightweight concrete, such as ACI 211.2 or CEB/FIP, cannot be directly applied Developing a mix design method specifically for FAC-HSLWC requires identifying the factors that influence the concrete's properties, with strength and density being the fundamental characteristics The following sections present the scientific foundations to address the aforementioned challenges

2.1 SCIENTIFIC BASIS FOR MATERIAL SELECTION IN FAC-HSLWC

2.1.1 Scientific Basis for Aggregate Selection in FAC-HSLWC

To mitigate segregation in concrete mixtures, several principles have been identified: (1) increasing the packing density of aggregate mixtures reduces segregation; (2) continuous gradation of aggregates leads to less segregation compared to discontinuous gradation; (3) reducing the maximum size of aggregates reduces segregation compared to using aggregates with the same particle size distribution but larger Dmax; (4) increasing the proportion of fine particles in the mixture decreases the degree of segregation; (5) minimizing the difference in thermal conductivity of the aggregates reduces segregation Based on these principles, the aggregates for FAC-HSLWC are selected to have a high compaction factor, small Dmax, increased proportion of fine particles, and materials with minimal variation in thermal conductivity The FAC particles primarily have sizes ranging from 45-250 μm Therefore, in this study, the aggregates for FAC-HSLWC are chosen to include FAC combined with natural sand aggregates with a maximum particle size of 5.0 mm to ensure a continuous particle size distribution and limit segregation

2.1.2 Scientific Basis for Using Pozzolanic Materials in FAC-HSLWC

Pozzolanic materials are used in this study to improve adhesion and enhance the strength characteristics of the interfacial transition zone (ITZ) between the FAC particles and the cement paste

in FAC-HSLWC In this study, pozzolanic materials, specifically silica fume (SF) and ground granulated blast furnace slag (GGBFS), with particle sizes ranging from fine to ultrafine, are oriented

in the CKD component of FAC-HSLWC These pozzolanic particles, along with cement, can fill the voids created by larger-sized particles such as sand and FAC particles with an average particle size

of approximately 100-120 μm, thereby creating a dense structure for the concrete

2.1.3 Scientific Basis for Using Polypropylene Fiber

Polypropylene (PP) fibers are commonly used in concrete Concrete reinforced with PP fibers is known to improve crack resistance by controlling crack propagation within the concrete structure PP fibers in concrete act as bridging elements for cracks formed under load, thus impeding crack development Additionally, the use of PP fibers has been shown to be an effective measure in reducing concrete shrinkage

2.2 SCIENTIFIC BASIS FOR BUILDING A COMPRESSIVE STRENGTH PREDICTION

MODEL FOR FAC-HSLWC

2.2.1 Some Models for Predicting Concrete Strength

Several models for predicting the compressive strength of concrete have been developed One of the earliest models is Feret's model (1892) This concrete strength model has been further developed by researchers such as Abrams (1919), Bolomey (1935), De Larrard (1993), and Popovics (1965) Bolomey (1935) simplified Feret's formula into a linear model:

f′c= 24,6 [c

The model by De Larrard (1993) takes into account multiple factors influencing concrete strength,

aggregates in concrete (through the maximum paste thickness, MPT):

It can be observed that De Larrard's strength prediction model is comprehensive, as it considers the influence of cement paste (based on the strength and composition of cement paste using Feret's

system, when applying De Larrard's compressive strength prediction model, the aggregates will

will be a multiple-component system composed of OPC cement and pozzolanic materials These factors will affect the coefficients in the concrete strength prediction model

2.2.2 Some Models for Predicting Lightweight Aggregate Concrete Strength

Several models for predicting the compressive strength of lightweight aggregate concrete (LWAC) have been proposed, such as the CEB/FIB model (1983) Other models have also been developed based on improvements to the CEB/FIB formula or in the form of logarithmic functions of the strength

of lightweight aggregate and mortar Generally, the current models for predicting LWAC strength take into account various factors such as the W/C ratio, compressive strength of cement or mortar, the thermal conductivity of lightweight aggregates (LWA), compacted LWA strength, and the volume

of LWA However, applying these strength prediction models to the FAC-HSLWC system is challenging due to the difficulty in determining the compressive strength of small-sized particles like FAC particles

2.2.3 Proposed Approach for Building a Compressive Strength Prediction Model for

FAC-HSLWC

The proposed compressive strength prediction model for FAC-HSLWC is based on key factors influencing concrete strength, including the strength of binder, paste volume, type and content of aggregates (sand and FAC), and type and content of dispersed fiber reinforcement The 28-day compressive strength (R28) of FAC-HSLWC is a function of these factors The quantification of factors influencing R28 of FAC-HSLWC is established based on some concrete strength prediction formulas mentioned earlier in the introduction Details regarding the construction of the compressive strength prediction model for FAC-HSLWC are presented in Chapter 4

2.3 SCIENTIFIC BASIS FOR DEVELOPING MIX PROPORTIONING METHOD FOR HSLWC

FAC-2.3.1 Methods for Mix Proportioning of Concrete and Lightweight Concrete

For the FAC-HSLWC system, due to the distinct characteristics of FAC particles compared to lightweight sand particles and the absence of large aggregates, conventional mix proportioning methods for lightweight concrete like the ACI 211.2-98 (2004) method cannot be used The mix proportioning methods for high-performance concrete nowadays are mainly based on selecting

appropriate materials and optimizing the particle size distribution For a concrete mixture with the same W/B ratio, increasing the compactness of the material mixture will increase the amount of free water in the system Conversely, for a concrete mixture with the same cementitious content, increasing the compactness of the larger aggregates will increase the amount of excess water in the system Some mix proportioning methods for LWAC have been established based on this principle With this approach, the designed concrete mix will have a good W/B ratio and compactness, minimizing the voids between particles, thereby enhancing the structural integrity of the LWAC system

2.3.2 Proposed Approach for Developing Mix Proportioning

Method for FAC-HSLWC The proposed approach for developing a mix proportioning method for FAC-HSLWC ensures two factors: compressive strength and workability of concrete, based on the following principles The mix proportioning for FAC-HSLWC is based on optimizing the CKD (binder) component, including cement (XM), SF, and GGBFS, through experimental work using compaction or calculations from De Larrard's compaction model The relationship between the B/A ratio and workability, compressive strength is established The relationship between compressive strength and key influencing factors such as W/B ratio, binder/aggregate (B/A ratio), FAC/aggregate (FAC/A) ratio is established The relationship between the workability of lightweight concrete, concrete with 100% sand aggregate, is established to determine the amount of lightweight aggregate

to replace sand aggregate

3.1 MATERIALS USED IN THE STUDY

3.1.1 Cement: The cement used in the study is PC50 Nghi Son Portland cement, with an average particle size of 15 μm

3.1.2 Silica fume: The silica fume (SF) used in the study is a loose uncompacted microsilica product, with an average particle size of 0.151 μm

3.1.3 Ground granulated blast furnace slag: The ground granulated blast furnace slag (GGBFS) used

in the study is of type S95, with the main particle size ranging from 1-45 μm and an average particle size of 7.8 μm

3.1.4 Cenosphere: The study utilizes cenospheres (FAC) obtained from the fly ash of the Pha Lai 2 thermal power plant The FAC used has a particle size range of 10-300 μm, with a significant concentration in the range of 45-250 μm and an average particle size of 117 μm

Figure 3.1 Cenosphere and its particle shape by SEM3.1.5 Sand aggregate: The aggregate used in the study is river sand, specifically sand suitable for concrete The sand is categorized into different types based on the largest particle size (Dmax), which are 0.315, 0.63, 1.25, 2.5, and 5.0 mm, determined through sieving

3.1.6 Superplasticizer admixture: The chemical admixture used for the experimental samples is ViscoCrete 3000-20 superplasticizer from Sika It has a water-reducing capacity of 36.5%

3.1.7 Polypropylene fibers (PP fibers): Polypropylene fibers (PP fibers) are non-water-absorbent fibers that are alkali-resistant and chloride-resistant The type of fiber used in the study is monofilament fibers with a length of 12-18 mm

3.1.8 Mixing water: The water used for concrete mixing in the research is tap water from Hanoi city's domestic supply The mixing water meets the requirements specified in the TCVN 4506:2012

"Concrete and Mortar Mixing Water - Technical Requirements" standard

3.2 EXPERIMENTAL METHODS

3.2.1 Standard Test Methods: The study utilized both Vietnamese and international standard test methods to experimentally determine the mechanical and physical properties of the materials used,

as well as the properties of cement paste, fresh mixed concrete, and concrete

3.2.1.1 Load-bearing capacity test of precast FAC-HSLWC components: Precast concrete components made with FAC-HSLWC were subjected to load-bearing capacity tests following the TCVN 9347:2012 standard, but using a continuous loading method with a hydraulic jack

3.2.2 Non-standard Test Methods: Modern physical and chemical analysis methods were employed, including X-ray diffraction (XRD), X-ray fluorescence (XRF), laser diffraction, and scanning electron microscopy (SEM) The viscosity of fresh concrete was determined using a viscometer, and the cement hydration degree was analyzed using thermogravimetric analysis (TGA) to measure the

CH content The compaction degree of the FAC-HSLWC mixture was evaluated using the Compressive Packing Model (CPM) proposed by De Larrard (1999) and verified through experimental methods using vibration and compaction with a pressure of 10 kPa

3.2.2.1 Concrete Mixing Method: Hobart mixers with capacities of 5 L and 20 L, as well as a horizontal shaft mixer with a capacity of 60 L, were used in the study

3.2.2.2 Concrete Curing Methods: The maintenance regimes for the FAC-HSLWC specimens included: (1) standard curing regime, and (2) thermal and moisture curing regimes at 70°C and 90°C,

as well as autoclave curing at 210°C

FAC-HSLWC

4.1 RESEARCH ON SELECTING SUITABLE CKD COMPONENTS FOR FAC-HSLWC

4.1.1 Selection of CKD (binder) components based on optimal compaction

At the first step, the binder components, including XM, SF, and GGBFS, are selected based on the optimal packing density of binder The calculated packing density (PD) of the binder with different types and proportions of admixtures is shown in Figure 4.1 The results indicate that the compaction

of CKD mainly depends on the proportion of SF, reaching the highest value of 0.767 with an SF proportion of 30% and an XM proportion of 70% by volume, corresponding to SF and XM proportions by weight of 23.3% and 76.7%, respectively When the SF proportion exceeds 30%, the compaction of CKD decreases

Figure 4.1 Packing density of the binder with various

SMCs

Figure 4.2 Response ssurface and contour plot of the packing density with the binder ternary system (XM-SF-GGBFS)

4.1.2 Selection of CKD components based on optimal workability and compressive strength

From the CKD components optimized using theoretical compaction calculations, the rational composition of CKD is selected based on ensuring the optimal workability and maximum compressive strength of CKD using the experimental design method

Table 4.1 Mix proportions and experimental results of binder for D-optimal design

Flow (mm)

Flow (mm)

a) Consistency of the binder mortar

Based on the experimental results presented in Table 4.1, applying the D-Optimal design yields a second-order experimental model for the workability of binder as follows:

Flow = 194,6*A +19,4*B + 227,0*C + 112,1*AB -47,0*AC + 113*BC

Figure 4.3 Response Surface and contour plot of

the workability model for CKD

Hình 4.4 Response Surface and contour plot

of the R28 and ingredients of the binder From the response surface and contour plot in Figure 4.3, obtained from the experimental model, it can be observed that increasing the SF content from 0% to 30% significantly reduces the workability

of the binder from approximately 200 mm to below 160 mm When the binder consists only of OPC and SF, there exists a maximum SF content that ensures a workability of the mortar mix of 180 mm

or above, which is approximately 12.5% based on the experimental model When combining SF with GGBFS, the workability of CKD is improved

b) Compressive strength of binder

Based on the experimental results presented in Table 4.1, applying the D-Optimal method yields an

The results depicted in Figure 4.4 show that the compressive strength of CKD increases as the SF content increases from 0% to 30% However, the rate of increase in compressive strength tends to decrease when the SF content exceeds approximately 20% Conversely, with the presence of SF, increasing the GGBFS content from 0% to 60% decreases the early-age strength of CKD However, there exists an optimal GGBFS content (approximately 36%) to achieve the maximum compressive strength (R28) of CKD at 28 days, after which the strength decreases with further increases in GGBFS content These results are consistent with the experimental findings regarding the dependence of packing density on the CKD mixture's components, SF and GGBFS, as mentioned earlier

c) Optimization of CKD components containing OPC-SF-GGBFS

Design-Expert® Software

Độ chảy vữa (mm)

Design points above predicted value

Design points below predicted value

Two CKD compositions were selected as the base components to investigate the properties of HSLWC:

FAC-1) CKD system consisting of XM-SF: XM/CKD ratio = 90%; SF/CKD ratio = 10% (ratios calculated by weight)

2) CKD system consisting of XM-SF-GGBFS: XM/CKD ratio = 54%; SF/CKD ratio = 10%; GGBFS/CKD ratio = 36% (ratios calculated by weight)

4.2 DESIGN OF MIXTURE COMPONENTS FOR FAC-HSLWC

4.2.1 Selection of Sand Aggregate Particle Size for FAC-HSLWC

segregation of fresh mixture with W/B ratios of 0.5, 0.4, 0.3, and binder/aggregate ratio of 0.667, and FAC/aggregate ratio of 0.5 by volume From the experimental results, it was found that the required PSD content to ensure the workability of concrete mixtures in the range of 180-200 mm increased as

the segregation rate of the fresh concrete, as shown in Figure 4.5, indicating that as the Dmax of the aggregate increased from 0.315 mm to 5 mm, the stratification level of SCC increased significantly The stratification levels were in the range of (1.35-7.29)%, (3.26-10.67)%, (6.22-18.21)% for the W/B ratios of 0.3, 0.4, and 0.5, respectively Based on the research findings regarding the influence

study selected sand aggregate with a Dmax of 0.63 mm as the base aggregate for investigating the properties of FAC-HSLWC

Figure 4.5 Effect of D max of aggregate on segregation of the fresh FAC-HSLWC

Figure 4.6 Effect of D max of aggregate on R 28 of the fresh FAC-

HSLWC

4.2.2 Selection of Aggregate/CKD Ratio for FAC-HSLWC

Based on the rational selection of binder ingredients discussed in section 4.1, with binder composed

of 90% XM and 10% SF, further research is conducted to optimize the ratio of material mixtures for the production of FAC-HSLWC, which consists of three components: sand, FAC, and binder To optimize the particle composition of this mixture, the study utilizes an experimental method to determine the packing density of the material mixture, following the approach proposed by De Larrard This method determines the packing density of the dry particle mixture, taking into account the influence of compression pressure

4.2.3 Selection of Aggregate and CKD Ratio based on Optimal Packing Density

From the experimental results presented in Table 4.2, a second-order function model of the packing density of the CKD-CL mixture for FAC-HSLWC is represented as follows:

PD = 0,63*Sand+ 0,66*FAC + 0,58*CKD + 0,65*Sand*CKD+ 0,54*FAC*CKD

Using the optimization tool of the Design-Expert software to find the optimal proportions of Sand, FAC, and CKD for FAC-HSLWC based on maximum compactness For the aggregate system consisting of Sand+FAC, the ratio of Sand:FAC:CKD is 0.20:0.39:0.41 For the aggregate system consisting of only FAC, the ratio of FAC:CKD is 0.60:0.40 Therefore, two mixtures are selected as the base mixtures to investigate the properties of FAC-HSLWC, converted into the following parameters: Sand/A, FAC/A, and CKD/A as follows:

1) In the FAC-HSLWC system with only FAC as the aggregate, the ratio of FAC/A is 1, and the ratio of CKD/A is 0.667 (by volume)

Table 4.1 Mixture ratios and experimental results based on the D-Optimal design

No

Input variable: Objective

function: Response surface

4.2.4 Study on the selection of binder and aggregate ratios using the experimental method

To investigate the influence of binder content on the workability and compressive strength of HSLWC, the study examines the binder content with a fixed W/B ratio (fixed binder composition) Therefore, for each binder with a specified W/B ratio, the influence of material proportions on the concrete properties mainly depends on three variables: Sand/Total Volume of Materials (Sand/VLK), FAC/VLK, and CKD/VLK, where VLK includes binder, sand, and FAC

FAC-The compressive strength of FAC-HSLWC is represented as a second-degree polynomial function, which is constructed based on an experimental plan From the surface plots showing the influence of the three components and the graph showing the influence of two components on the compressive strength (R28) in Figure 4.7a, b, c for different W/B ratios (0.5, 0.4, and 0.3), it can be observed that

compressive strength (R28) tends to increase up to a certain value and then decrease

optimal binder content to achieve the maximum compressive strength When the amount of cementitious material surrounding the aggregate particles is thinner or thicker than the optimal value,

it will reduce the compressive strength of the concrete

Using the optimization tool in the Design-Expert software to determine the suitable material composition for making FAC-HSLWC Based on the criteria set forth to determine the optimal material composition, the software has selected the following proportions for maximum compressive

A: Cát 1

B: FAC 1