Nghiên cứu nâng cao cường độ chịu kéo khi uốn và khả năng chống mài mòn của bê tông cát mịn đối với mặt đường bê tông xi măng tt tiếng anh

MINISTRY OF EDUCATION AND TRAINING MINISTRY OF CONSTRUCTION VIETNAM INSTITUTE OF BUILDING SCIENCE AND TECHONOLOGY --- NGO VAN TOAN RESEARCH OF IMPROVEMENT OF TENSILE STRENGTH IN BENDI

MINISTRY OF EDUCATION AND TRAINING MINISTRY OF CONSTRUCTION

VIETNAM INSTITUTE OF BUILDING SCIENCE AND TECHONOLOGY

-

NGO VAN TOAN

RESEARCH OF IMPROVEMENT OF TENSILE STRENGTH IN BENDING AND ABRASION RESISTANCE OF FINE SAND CONCRETE FOR

CEMENT CONCRETE PAVEMENT

Specialization: Materials engineering Code : 9520309

SUMMARY OF DOCTORAL THESIS

THE DISSERTATION IS COMPLETED AT:

VIETNAM INSTITUTE FOR BUILDING SCIENCE AND TECHONOLOGY

Academic supervisor:

1 Dr HOANG MINH DUC

INSTITUTE OF CONCRETE TECHONOLOGY - VIETNAM INSTITUTE FOR

BUILDING SCIENCE AND TECHONOLOGY

2 Dr NGUYEN NAM THANG

VIETNAM INSTITUTE FOR BUILDING SCIENCE AND TECHONOLOGY

Reviewer 1: A/Prof Dr Vu Dinh Dau

Reviewer 2: A/Prof Dr Nguyen Duy Hieu

Reviewer 3: Dr Nguyen Duc Thang

This dissertation will be defended by Academy Doctoral Examination Boar at Institute of Building Science and Techonology, 81 Tran Cung street, Nghia Tan, Cau Giay District, Ha Noi at …… on the day of 2019

The dissertation may be read at:

- National Library of Vietnam

- Library of Vietnam Institute of Building Science and Techonology

LIST OF PUBLISHED SCIENTIFIC WORKS

OF AUTHOR RELATED TO THE DISSERTATION

1 Hoang Minh Duc, Ngo Van Toan "Study the effect of mortar residual coefficient

on the properties of concrete and fine sand concrete mixture using as cement concrete pavement", Construction Magazine - Ministry of Construction No 11,

2018

2 Hoang Minh Duc, Ngo Van Toan "The impact of limestone grit on the abrasion

and shrinkage of fine sand concrete on cement concrete pavement", Journal of

Transport - Ministry of Transport, No 12, 2018

3 Hoang Minh Duc, Ngo Van Toan "Study on improving tensile strength in

bending and abrasion resistance of fine sand concrete using to make cement concrete roads", Transport Magazine - Ministry of Transport, No 6, 2019

4.Hoang Minh Duc, Nguyen Nam Thang, Ngo Van Toan "Selecting concrete

components using fine sand according to tensile strength when bending", Journal

of Construction Science and Technology - Institute of Construction Science and Technology, No 2, 2019

5 Ngo VanToan, Hoang Minh Duc "Selection of concrete components using fine

sand and stone grit mixing according to tensile strength when bending for cement concrete pavement", Transport Magazine - Ministry of Transport, No 7, 2019

INTRODUCTION

1 Abstract

The more and more developed the country, the greater the need for travel, that requires the construction of a higher and higher traffic system, resulting in an increasing demand for materials used in the concrete industry This leads to the current general trend of making the best use of locally available aggregate materials in concrete production to reduce construction costs At present, the raw sand source in the country is increasingly scarce while the fine sand source has very large reserves distributed in many regions across the country that are less interested in using in the concrete industry To meet the needs of materials for construction works, transportation besides the traditional materials such as raw sand, it is impossible not to mention the fine material used for cement concrete in

general, especially concrete roads Prior to this fact, the topic "Research of

improvement of tensile strength in bending and abrasion resistance of fine sand concrete for cement concrete pavement" was conducted, contributing to

demonstrate the ability to use fine sand sources instead of raw sand to make concrete used for cement concrete pavement and evaluate the feasibility of applying this type of concrete to transportation and construction works, construction, irrigation in our country

2 Rationale of the Study

Raw sand reserves are limited, unevenly distributed, while fine sand is available in many localities across the country that can be used to make cement concrete for road surface However, due to the size modulus of the small fine sand, in the past, standards and technical guidelines used only fine sand for concrete with compressive strength less than 30MPa and proportional correlation with compressive strength above tensile strength when bending to reach level 1 (tensile strength when bending only reaches 4.0MPa), abrasion is only <0.6g/cm2 Therefore, if there is no improvement, the fine sand concrete is only suitable for cement concrete pavement of grade IV or lower roads and yards For I, II, III level concrete roads, compressive strength over bending strength (Rn/Rku, MPa) requires higher values, corresponding to not less than 40/5.0 for calves single-layer pavement or I, II - level road and 35/4.5 pavement pavements for III-level concrete pavement The abrasion of concrete to the surface of cement concrete roads of grades I, II and III also requires less than 0.3g/cm2 Therefore, the study to improve the tensile strength of bending and abrasion resistance of fine sand concrete meeting technical requirements for cement concrete pavement to grade I roads is essential

3 Research subject and scope

The research objective of the dissertation is to improve tensile strength in bending and abrasion resistance of fine sand concrete used as cement concrete pavement for

I - level road

4 Subjects and research content

4.1 Research subjects:

Concrete uses fine sand and uses fine sand in combination with limestone grit to make concrete pavement construction according to the normal vibration method, namely: a) Concrete using fine sand: the tensile strength when bending is greater than 4.5MPa, the abrasive value is obtained from (0.3÷0.6) g/cm2 for concrete pavement of IV level road and below and yard; b) Concrete using limestone grit combined with fine sand in a reasonable proportion: tensile strength when bending

is greater than 5.0MPa, abrasion less than 0.3g/cm2 for concrete pavement to I level road

- Research and choose input materials

- Research to improve tensile strength when bending and abrasion resistance of fine sand concrete for cement concrete pavement

- Research some properties of fine sand concrete for concrete pavement surface

- Researching practical applications and assessing the economic efficiency of fine sand concrete for cement concrete pavement

5 Scientific significance

By theoretical and experimental research, the dissertation has established a number

of influential and dependent correlations in concrete with a small aggregate of fine sand, fine sand mixture with stone grit, strong water reducing admixture in Rku tensile strength (4.0÷7.0) MPa, as follows:

- Amount of water used for concrete;

- Correlating compressive strength of concrete with compressive strength of cement and N/X ratio;

- Correlating tensile strength of concrete with cement tensile strength and N/X ratio;

- Correlation between compressive strength and tensile strength of concrete;

- The impact of fine aggregate of fine sand, fine sand combined with stone grit on the abrasion resistance of concrete;

- The effect of fine aggregate of fine sand, fine sand combined with stone cool to some properties of concrete: soft shrink, dry shrink, strength development, water resistance, elastic modulus of concrete;

- A number of technological requirements to restrict concrete surface cracking during construction

6 Practical significance

Using fine sand combined with stone grit and superplasticizer admixture, cement (PC40, PCB40) can produce concrete for cement concrete pavement to grade I

roads with reduced cost from 10% to 15% compared to when using rough sand transported remotely

7 New scientific contributions of the dissertation

Experiments and practical applications have proved that:

- Using fine sand with fineness modulus (Mdl=1.2÷1.9) combined with crushed stone (Mdl=3.6), cement (PC40, PCB40) and polycarboxylate ether can make concrete with tensile strength when bending over 5.0MPa, compressive strength over 40MPa and abrasion < 0.3g/cm2, suitable for making cement concrete pavement to level I road

- Using fine sand without crushed stone with cement and additives as above, the tensile strength of concrete can be enhanced to be equivalent to that of concrete when there is a combination of crushed stone (tensile strength when bending > 5.0MPa, compressive strength over 40MPa), but does not reduce the abrasion of concrete to < 0.3g/cm2 Beside, concrete using fine sand is also dehydrated, splitting mortar, softening stronger than concrete using coarse sand and concrete using fine sand with crushed stone Therefore, this type of concrete can only be used as a concrete pavement of 4 - level roads or yards when appropriate technological measures are applied to limit cracking of concrete surfaces

Chapter 1 OVERVIEW OF RESEARCH AND USING OF FINE SAND CONCRETE 1.1 Overview of research situation and using of fine sand concrete

1.1.1 Classification and technical requirements for sand as aggregate for concrete

In the Russian Federation, according to the GOST 8736-93 standards; GOST 26633-91 and "Instructions for use of fine sand and very fine sand for concrete pavement and airport" In the United States, applying the AASHTO M6-93 standard; ASTM C33-03 In Vietnam, according to Vietnam standard TCVN 7570:

2006 "Aggregates for concrete and mortar - Technical requirements"; According to Decision 778/1998/QD-BXD, "Technical instructions for selecting concrete components of all kinds" and according to TCXD 127:1985 standard, "Fine sand for making concrete and construction mortar - Instructions for use" Standards of countries have not agreed on the scope of application of fine sand, generally, all standards stipulate that sand is considered fine sand when the modulus of magnitude is less than 2 (Mdl < 2)

1.1.2 The situation of research and use of fine sand concrete in the world

In the world, the study and use of fine sand to make cement concrete mainly in two main directions: a) Using fine sand as aggregate in the manufacture of small-grained concrete (also called sand concrete - concrete without large aggregates); b) Use fine sand instead of all or part of the rough sand (Mdl> 2), in ordinary concrete (with large aggregate)

 Using fine sand as aggregate in manufacturing small-grained concrete, which

has been studied and used by many countries in the world: as in the former Soviet Union; Russian Federation today; Algieri and France However, the research

orientation of the thesis is to use fine sand instead of all raw sand in manufacturing and producing ordinary concrete Therefore, it is necessary to focus on the studies

of countries in the world in the following direction:

 Using fine sand to replace all or part of raw sand (M dl >2), in conventional concrete, these studies have been researched and used by many countries in the world: in the Soviet Union (former) Research on fine sand used in concrete has

been carried out quite early, especially for hydraulic concrete Until the year of 1950s of the twentieth century, fine sand was standardized in "Technical guidelines for using fine sand in hydraulic concrete" In the year of 1970 of the twentieth century, Do-nhi-ep fine sand and Bar-khan was applied to concrete in a number of hydraulic construction projects A number of research works by Ki-ri-en-co, S.ton-nhi-cop and Gu-Ba have also been published By the year of 1980s of the twentieth century, it was studied to use sand from the Enisei river to build Sayano-Shushenskaia hydroelectricity Also during this period, one of the areas where fine sand was widely used was in the transport, especially the manufacture of concrete for roads and airports, which was done in the research of Research on road construction) is considered as the basis for preparing the "Guidelines for the use of fine sand in cement concrete for roads and airport pavements" and "Guidance for the use of low-aggregate concrete of large quantities using fine sand in building pavement of cars and airports” In China since the year of 1965 of the twentieth century, fine sand was also studied and put into use in concrete, this is mentioned

in the BGY Regulation 19-65, allows the use of sand with a module size greater than 0.7 to make concrete In 2009, the DuBai City project in the United Arab Emirates used cement concrete that uses fine sand of (300÷400) kg per cubic meter

of concrete, resulting in compressive strength of the value of 45MPa

Fine sand may be river sand but fine sand can also be desert sand, so in the Middle East countries, many studies have been conducted with desert fine sand of high fineness, moderately fine sand from 0.45 to 0.88 In China, the Tenggeli and Maowusu desert sands with modules of 0.334 and 0.194 magnitudes have been studied for use in mortar and concrete In Australia, research on the use of desert fine sand is also of interest During the study of river sand used in concrete, Kim et

al Studied cracked properties of concrete using crushed sand from limestone in Korea, the results showed that when used in combination with sand grinding from limestone and sand has improved the intensity of concrete In the study of author XieZhi-Hua, took advantage of sand and crushed powder from seashells to make cement concrete, the results showed that strength The degree of concrete is also improved In Asia, research by ‟RSNaidu, M Zai University Malaysia, Malaysia and SE Ang, Open University Kebangsaan Malaysia ” studied the compressive strength of concrete using fine sand, crushed sand and mineral additives, the results showed that when replacing 20% of fine sand by sand grinding dust in concrete, compressive strength of concrete is lower than when using fine sand alone, when using 10% fly ash to replace adhesives in concrete components, the compressive

strength of concrete is increased Concrete using dust grit sand combined with 10% silica fume instead of the binder component shows that the strength of concrete reaches the highest value

1.1.3 The situation of research and use of fine sand concrete in Vietnam

The use of fine sand for concrete in Vietnam has been studied for a long time, such

as the topic ‟Using black sand of the Red River to produce concrete (CCA)" – Doc Nguyen Van and Lan Hoang Phu chaired and reported the Conference of Concrete throughout the North - 1967 ” By the 70s of the twentieth century, the Institute of Water Science Research and the Institute of Construction Science and Technology had studied and applied fine sand concrete with the compressive strength  30 MPa for a number of hydraulic works and civil construction The study on “using fine sand for concrete and construction mortar” - Nguyen Manh Kiem and Duong Duc Tin, has been conducted with a number of different fine sand types in the Northern region (Cao Lang, Vinh Phu, Ha Nam Ninh, Thai Binh, Hanoi) Types of sand used in the study (Mdl=0.47÷1.97), compared with concrete using rough sand (Mdl= 2.20÷2.26) with the same compressive strength and tensile strength, prismatic strength, elastic modulus, bonding strength between concrete and reinforcement, water absorption, softening coefficient and contraction of concrete using fine fine sand equivalent to raw sand The abrasion resistance of concrete using fine sand is inferior to that of concrete using raw sand The topic also mentioned the use of plasticizers as a cement saving measure However, these are just initial studies, the role of plasticizers when using fine sand has not been clearly defined By the 90s of the twentieth century, there were studies using fine sand of the Red River (Mdl=1.1÷1.72) in intermittent concrete mixtures with intermittent levels of sand loam different from (19÷40)%, the ratio of N/X from (0.40÷0.55), the amount of cement used (233 ÷ 526) kg/m3, indicating that the slump of concrete mixes may vary from (0 ÷ 18) cm, the intensity reaches from (28÷50)MPa In 2005, studies using fine sand to manufacture high-strength concrete at Hanoi University of Construction were conducted with an additive system including mineral admixtures and superplasticisers and fine sand (Mdl=1.08) used in research; compressive strength of concrete to achieve values up to 98MPa (sample 10x10x10cm) In 2006, Vung Tau and Binh Thuan sands with modules of 0.95 and 1.31 respectively and NaCl content of about 0.06% are studied to make cement concrete for highways construction The research results show that the fine sand in the sea can be used to make cement concrete for the construction of high-grade pavement, the surface of low-grade automobile pavement and the pavement of rural roads in suburban sea provinces In 2006, a study on using Red river black sand made low strength concrete, proposed fine sand (Mdl=1.1) used to make concrete with required strength over 10MPa, the authors also propose to use roller compaction method for low strength concrete construction using fine sand By

2010, there was a study on the use of fine sand and the mixture of rice husk slag ash additives to produce high strength concrete, resulting in the compressive

ash-strength of concrete at the age of 28 days gained from (67÷80) MPa, chloride ion permeability level is very low In 2012, there was a study on the use of Song Hong black sand (Mdl=1.0;1.5;2.0) and the workability of D3, D4 to produce 40MPa concrete for local constructions in Hanoi In 2013, fine sand in the Mekong Delta (Mdl=1.21) was studied in concrete fabrication with a ratio of sand to the aggregate

of 0.34 to 0.40 The results show that when using fine sand, the decrease is about (23÷25)% but the decrease level over time is less, compressive strength decreases from (9÷15)% The elasticity of the modulus is reduced (5÷7)% compared to when using raw sand (Mdl=2.71) Fine sand concrete has a higher shrinkage than raw sand concrete at age 60 days Fine sand concrete has higher water absorption and chloride permeability than raw sand concrete, but the waterproofing is equivalent (declining at a high N/X ratio) In 2010, there was a study of mechanical properties and applicability of sand concrete for building roads, the author used sand (Mdl=1.73) used for sand concrete, achieving the value of the intensity of compressive strength of concrete at the age of 28 days from (30÷40) MPa In the field of manufacturing concrete products, fine sand is also commonly used At Song Day Construction Material Joint Stock Company, Hong river sand (Mdl=1.2÷1.5) has been used to produce culverts, manholes, box culverts At Song Day Joint Stock Company - Hong Ha Petroleum also used fine Hong River fine sand (Mdl=1,5) to produce autoclaved aerated concrete block (AAC) of compressive strength 3 and 4

 Regarding research on improving tensile strength in bending and abrasion resistance for fine sand concrete, there have been some research works The outstanding contents and rules can be drawn from these studies: fine sand concrete

follows the general rules with cement concrete The influence of fine sand on the properties of concrete and concrete mixtures is reflected in changing the amount of water used, the workability and the strength of concrete However, the characteristics and the degree of influence depend on the characteristics of the sand

as well as the use of concrete On the other hand, in the standards and technical guidelines of some countries around the world, the use of fine sand is still in the open trend, so if appropriate and optimal technology measures are used component

of concrete, concrete can be made using fine sand to meet the technical requirements and the amount of cement equivalent to the concrete using coarse

 Summary of studies in the world and in Vietnam, it can be seen that fine sand was initially used to make cement concrete roads at all levels In order to develop and expand these applications in practice, especially in the context of Vietnam, more in-depth studies are needed as well as further clarification of one of the points

of particular interest, when using fine sand, there are some disadvantages such as bending strength in bending and abrasion resistance of concrete using fine sand lower than coarse sand Therefore, the study to improve the tensile strength of bending and abrasion resistance of concrete using fine sand equivalent to coarse sand, meeting technical requirements for cement concrete pavement for roads at all

levels is very necessary and has a scientific basis The current surface of cement concrete roads is usually constructed using roller-compacted and vibratory technology, in the conditions in Vietnam, especially in remote areas, Northwest areas with complex terrain, the work vibratory technology can be considered more reasonable Therefore, the thesis focuses on construction methods based on normal vibration technology

1.2 Characteristics and properties of cement concrete for road construction

Technological characteristics of cement-concrete for road construction are cast in situ place concrete without cased beam and solidified in natural conditions Concrete cast, compaction and finishing are carried out by means of a specialized apparatus which are suitable for the construction of relatively dry concrete mixtures Strength is the most important characteristic of cement concrete for road construction, evaluated by two criteria: tensile strength during bending and compressive strength in which tensile strength when bending is the main criterion The compressive strength used to evaluate the wear resistance of surface concrete Abrasion is also a major indicator of concrete for roads Stability and deformation properties are also an important characteristic of concrete for roads Elastic modulus of concrete characterizes the ability of concrete to deform under the effect

of a load Shrinkage of concrete is an important property of concrete for making roads

1.3 Characteristics, properties and technical requirements for concrete pavement surface

1.3.1 Characteristics and properties for cement concrete pavement

Cement concrete pavement is a high-grade hard pavement The surface layer is a cement concrete with very high stiffness, the computational model is on the elastic floor (soil and road foundations) The main strength reinforcement of the sheet is tensile strength during bending

1.3.2 Technical requirements for cement concrete pavement

According to standard 22TCN 223-95; According to Article 5.2.a, Circular No.12/2013/TT-BGTVT; According to the Minister of Transport's Decision No 1951/QD-BGTVT of August 17, 2012: a) Tensile strength in bending: with cement concrete surface of highways, grades I and II less than 5.0MPa, with pavements of cement concrete grade III or lower not less than 4.5MPa b) Abrasion: with the cement-concrete pavement of expressways, I,II,III lever not bigger than 0.3g/cm2, with pavements of cement concrete IV lever or lower not exceeding 0.6g/cm2

1.4 The scientific basis of the dissertation

As analyzed above, the disadvantage of fine sand concrete is that it has compressive strength, tensile strength when bending lower than coarse sand concrete (10÷15)% when using the same amount of cement and have the same construction slump In addition, fine sand concrete has low abrasion resistance, the abrasion is usually from (0.3÷0.6) g/cm2 compared to the value (<0.3 g/cm2) in rough sand concrete Therefore, in order to use fine sand for road concrete,

improving the tensile strength of bending and the abrasion resistance of concrete plays an important role

1.4.1 Improvement of tensile strength when bending of concrete

The compressive strength (Rn) is closely related to the tensile strength of concrete (Rku) The ratio between them commonly used in the concrete road design standard is: Rn/Rku=30/4.0; 35/4.5; 40/5.0; 50/5.5 According to the relationship Rn (Rku) and the ratio of water / cement (N/X), in order to improve Rn (or Rku), it is necessary to improve the cement strength, reduce N/X and improve the quality of aggregate In specific field conditions, when the commonly used cement is PC40 (or PCB40), aggregate is mined on site, the most feasible solution is to reduce N/X For road concrete (usually using stone with Dmax=40 mm, the slump of 2 ÷ 3 cm), the use of water reducing admixture can compensate for the increase of water due to fine sand without increasing cement Water reducing admixture for road concrete is rarely used due to the fear that they may reduce Rku of concrete due to the smoothing effect of cement stone structure However, in the case of using strong water-reducing additives (polycarboxylate-based additives), it can be expected that Rns will increase sharply (30 ÷ 40)% and lead to it Rk also increase, although the increase is not expected as increase Rn (can be 20÷25% or higher if the additive increases the uniformity of the structure of concrete) In addition, when choosing concrete components, the application of mortar data higher than conventional compressive concrete approximately (0.10÷0.20) also increases (5÷8)% Rku

1.4.2 Improvement of the abrasion resistance of concrete

According to the studies in the overview, fine sand concrete has poor abrasion resistance because fine sand usually contains fine particles (≤ 0.14 mm) to 35% compared to no more than 10% in standard sand of TCVN 7570:2006 For abrasive concrete ASTM C33-03, also specify the amount of grain (≤ 0.075 mm) must not exceed 3% This fine-grained sand often flakes off the surface when rubbing or grinding from the outside To improve the abrasion resistance, it is possible to mix more grit to reduce the percentage of fine particles in the small aggregate, while creating a solid aggregate frame in the concrete mortar to keep the remaining fine particles, increasing area of aggregate directly subjected to grinding In addition, the abrasion resistance of fine sand concrete can be enhanced by the use of large aggregates with good abrasive resistance such as basalt, granite, high strength limestone and when increasing their density in the concrete cardboard In the context of the priority to use large amounts of locally exploited aggregate, the increase in their density (reduction of mortar residue coefficient) leads to the reduction of Rku so solution to use a part of stone grit from the mines themselves will be the most feasible and practically feasible solution

=> Thus, improving the tensile strength of bending (Rku) and abrasion resistance of fine sand concrete to make cement concrete pavement in this topic is based on the main scientific hypothesis:

- Use strong water reducing admixture (polycarboxylate based superplasticiser) to simultaneously increase the tensile strength of bending and compressive strength

of concrete;

- Use a part of grit combined with fine sand to improve abrasion resistance and tensile strength when bending for concrete

1.5 Objectives of the research

Improvement of bending tensile strength and abrasion resistance of fine sand concrete used as cement concrete pavement for I level road construction

1.6 Subjects and research content

1.6.1 Research subjects

Concrete using fine sand and fine sand combined with limestone grit to make concrete pavement construction by normal vibration method, namely: a) Concrete using fine sand: tensile strength when bending greater than 4.5MPa, the value of abrasion is obtained from (0.3÷0.6) g/cm2 used for concrete pavement of IV level roads or lower and yards; b) Concrete using limestone grit combined with fine sand

in a reasonable proportion: tensile strength when bending is greater than 5.0MPa, abrasion less than 0.3g/cm2 for concrete pavement to I level road

- Research and choose input materials

- Research to improve tensile strength when bending and abrasion resistance of fine sand concrete for cement concrete pavement

- Research some properties of fine sand concrete for cement concrete pavement

- Researching practical applications and assessing the economic efficiency of fine

sand concrete for cement concrete pavement

Chapter 2: MATERIALS AND RESEARCH METHODS

2.1 Materials used in the study

+ Cement: PCB40 Nghi Son; (PC40 But Son used to test the water reduction efficiency of superplasticizer according to TCVN 8826:2011);

+ Coarse aggregates: Stone (Dmax=20mm) - Dong Ao - Ha Nam;

+ Crushed sand: M (<5mm) - Ha Nam;

+ Fine aggregate: Fine sand: C1 (Mdl=1.2); C2 (Mdl=1.6); C3 (Mdl=1.9) - Red River; Raw sand: CV (Mdl=2.5) - Lo River;

+ Additive: Daltonmat-RDHP of Vietnam Spemat;

+ Mixture water: Hanoi

2.2 Research Methods

2.2.1 Standard test methods

TCVN 6017:2015 (ISO 9597:2008); TCVN 6016:2011 (ISO 679:2009); TCVN 4030:2003; TCVN 7572-2:2006; TCVN 4506:2012; TCVN 7572-4:2006, ASTM

C469-10; TCVN 3016:1993; TCVN 3015:1993; TCVN 3108:1993; TCVN 3109:1993; ASTM C231-10; TCVN 3114:1993; TCVN 3116:1993; TCVN 3118:1993; TCVN 3119:1993; TCVN 3120:1993; TCVN 8864:2011; TCVN 8867:2011; TCVN 8866:2011

2.2.2 Non-standard test methods

- Determination of dehydration and elasticity of concrete mixture is determined based on TCVN 9204:2012, with some modified

- Determine the shrinkage of concrete based on ASTM C157/157M-08, with some modified

Chapter 3: IMPROVEMENT OF TENSILE STRENGTH IN BENDING AND ABRASION RESISTANCE OF FINE SAND CONCRETE FOR CEMENT

CONCRETE PAVEMENT

Tensile strength when bending is an important property for cement concrete pavement In Vietnam today, the selection of concrete components that meet the requirements on tensile strength when bending is done under Decision No 778/1998/QD-BXD Accordingly, concrete gradation is still selected in accordance with the compressive strength based on the Bolomey-Skramtaev formula (1):

Rb = A Rx ( + B) (1) Where: Rb, Rx - Concrete and cement intensity; X, N - Amount of cement and

water used; A - Material quality coefficient; B - Equation factor

When designing components according to compressive strength, the value of Rb,

Rx is the compressive strength of concrete and cement, the coefficient B is taken by

± 0.5 depending on the X/N ratio, coefficient A is determined according to the investigation table depending on the quality of materials used

According to Y.M.Bazenov, formula (1) can also be used to select concrete components according to tensile strength in bending Then Rb, Rx is the tensile strength when bending of concrete and cement, coefficient B is taken by -0.2, coefficient A is taken from the lookup table However, the values shown in (1) are based on cement test data using the method of plastic mortar and the use of materials in the former Soviet Union Therefore, these coefficients are likely not suitable for the current situation in Vietnam Besides, when designing concrete components according to tensile strength in bending, attention should be paid to mortar residuals (reasonable mortar residuals should increase by about 0.15÷0.20 compared to when designed according to compressive strength) When increasing the mortar balance calculation, the work of concrete mixture will be reduced, so it

is recommended to select the appropriate initial amount of water to ensure workability On the other hand, using fine sand in concrete, the tensile strength of bending and the abrasion resistance of concrete are reduced compared to when using coarse sand In order to improve the tensile strength of bending and abrasion resistance of fine sand concrete equivalent to coarse sand, meeting the technical requirements for concrete pavement to grade I, the use of water-reducing

admixture, increasing mortar residues and adding grit combined with fine sand is

really necessary

3.1 Properties of concrete mixtures

3.1.1 Selecting concrete components for research

The dissertation has used the same type of PCB40 Nghi Son cement, stone (Dmax = 20mm), superplasticizer Daltonmat-RDHP, fine sand (C1,C2,C3), coarse sand (CV), dust limestone (M) combines fine sand with the rate of replacing 40% of fine sand with crushed stone workability of concrete, Rku, amount of cement and N/X ratio as recommended by Decision No.1951/QD-BGTVT To ensure appropriate construction conditions, the workability in the study is not immediately after mixing but takes into account the loss of slump depending on the actual conditions and weather of the construction The use is higher than that required for cement concrete pavement Therefore, the amount of cement selected is 350 kg/m3, the rate

of additives according to the manufacturer's recommendations is 1% of the weight

of cement, the ratio of X/N=1.80; 2.00 and 2.30 Given an X/N ratio and sand magnitude module, the experimental gradients are designed with two different reasonable mortar residues for Rn and Rku according to Decision No.778/1998/QD-BXD and TCXD 127:1985 In particular, the reasonable mortar residual coefficient according to Rku was chosen higher than Rn from 0.15 to 0.20, Based on batches and volume of concrete mixture using fine sand and concrete using fine sand combined with crushed stone, calculated the actual concrete composition and research results are presented in Table (3.1, 3.2)

3.1.1.1 Selection of concrete components using fine sand

Table 3.1 Studied components of concrete used (fine sand, rough sand)

No Symbol Material quantity, kg/m

3.1.1.2 Selection of concrete components using fine sand and limestone grits

Table 3.2 Components of concrete used (fine sand combined with grit, coarse sand)

No Symbol Material quantity, kg/m

3

Distribution parameters Cement Water M Sand Stone PG M dl M dlhh M/CLN K d X/N

3.1.2 The relationship between the used amount of water and the workability

of the concrete mixture

3.1.2.1 Relationship between the used amount of water and the performance of the concrete mixture using fine sand

Research results show that the slump of concrete mixture tends to decrease with increasing mortar residual coefficient The volumetric mass of a concrete mixture

is less affected by the sand category but only depends on the sand magnitude module The air bubbles content of the concrete mixture using different types of sand in the study is not much different The sand modulus has a significant effect

on the correlation between water use and the slump of the concrete mixture When using finer sand, the ratio of surface area increases the level of water absorption, so the amount of water mixed to reach the same slump tends to increase with decreasing sand modulus Based on the above test results, combined with the recommendations of Decision No.778/1998/QĐ-BXD, it is possible to create Table 3.6 to reference the initial preliminary water required for 1m3 of concrete using fine sand When using polycarboxylate-based superplasticizers for concrete components to make cement concrete roads (priority for tensile strength in bending) as follows:

Table 3.6 The initial amount of mixing water required for 1 m 3 of concrete, liters

No Slump, cm

Maximum particle size of large aggregate D max =20mm

Modulus of magnitude of sand, M dl

mixture The amount of mixing water to achieve the same slump tends to increase gradually in the direction of decreasing the modulus of the magnitude of the fine

sand mixture with crushed stone

3.1.3 Ability to maintain the working properties of the concrete mixture

3.1.3.1 The ability to maintain the workability of concrete mixtures using fine sand

The study results showed that after 60 minutes, the slump of the concrete mixture using fine sand decreased over time about 3cm, using coarse sand decreased by about 2cm

3.1.3.2 The ability to maintain the workability of a concrete mixture using fine sand and limestone grit

The results of the study showed that after 60 minutes the slump of the concrete mixture using fine sand and stone grout decreases over about 2cm equivalent to the use of coarse sand and magnitude modulus

3.1.4 Stratification of concrete mixture

3.1.4.1 Stratification of concrete mixture using fine sand

The research results show that with the same X/N ratio, the level of mortar separation tends to increase gradually with the decrease of the sand bulk module, the increase of mortar residual coefficient, the level of mortar separation for fine sand value of (1.8÷2.8)%, coarse sand is equal to 0% and all meet technical requirements within the allowable limits according to TCVN 9340:2012 Mortar separation for concrete using fine sand is of great value when the mortar residual coefficient is high

3.1.4.2 Stratification of the concrete mixture using fine sand combined with limestone grit

Research results show that the use of grit combined with fine sand has limited the splitting of mortar of concrete mixture compared to when using fine sand alone, which means that the ability to improve the resistance abrasion of concrete to cement concrete pavement

3.2 Properties of concrete

3.2.1 Relationship compressive strength of concrete with compressive strength of cement and X/N ratio

Analysis of experiment results in the former Soviet Union recommends that the value of

B coefficient be equal to -0.5 when the ratio of X/N <2.5 and equal to +0.5 when the ratio

of X/N>2.5 Then, formula (1) has the form: