TÓM TẮT ĐÓNG GÓP MỚI CỦA LUẬN ÁN 1. Nghiên cứu đã khẳng định được sự cần thiết áp dụng kết cấu dầm đúc sẵn sử dụng bê tông cường độ cao trong xây dựng công trình cầu ở vùng Đông Nam Bộ. 2. Thiết kế được các cấp phối bê tông C60, C70, C80 có độ sụt cao sử dụng vật liệu địa phương khu vực Đông Nam Bộ, với cốt liệu thô sử dụng đá dăm Phú Mỹ - Bà Rịa và cốt liệu mịn phối trộn giữa cát sông và cát nghiền với tỉ lệ 60/40, phù hợp cho sản xuất dầm bê tông dự ứng lực đúc sẵn với quy mô công nghiệp. 3. Đối với các cấp phối C60, C70, C80 sử dụng vật liệu vùng Đông Nam Bộ, nghiên cứu đã đưa ra cách xác định một số chỉ tiêu cơ lý để phục vụ cho công tác thiết kế kết cấu dầm cầu bê tông dự ứng lực đúc sẵn khi sử dụng các cấp phối đó như mô đun đàn hồi, cường độ chịu kéo khi uốn, hệ số quy đổi khối ứng suất tương đương. 4. Đã đề xuất các thông số kích thước mặt cắt phù hợp đối với kết cấu dầm I cánh rộng sử dụng bê tông cường độ cao với các chiều dài nhịp 24m, 33m, 60m. 5. Khẳng định được tính hiệu quả của việc dùng dầm I cánh rộng với bê tông cường độ cao so với các loại hình dầm truyền thống sử dụng bê tông thông thường hiện nay trong khu vực Đông Nam Bộ: Giảm chiều cao dầm từ 150mm đến 450mm; giảm khối lượng vật liệu từ 10% đến 50%.
Trang 1MINISTRY OF EDUCATION AND TRAINING UNIVERSITY OF TRANSPORT AND COMMUNICATIONS
VÕ VĨNH BẢO
RESEARCH FOR APPLICATION OF PRECAST PRESTRESSED CONCRETE GIRDER WITH HIGH STRENGTH CONCRETE FOR TRAFFIC DEVELOPMENT
IN THE SOUTHEAST REGION
Majors: Transport Construction Engineering
Code: 9580205
SUMMARY OF DOCTORAL THESIS
HA NOI - 2022
Trang 2The thesis was completed at: University of Transport and Communications
Academic supervisors:
1 Prof Dr Tran Duc Nhiem
2 Assoc Prof Dr Nguyen Ngoc Long
The thesis can be found at:
1 University of Transport and Communications Library
2 National Library
Trang 3INTRODUCTION
1 The urgency of research
In the South of Vietnam, the key economic area whose nucleus is the Southeast region has potential and resources for strong development, many new urban areas are quickly formed, and urbanization of the Southeast region is among the highest in the country, from which the demand for building technical infrastructure systems is also required To meet the needs of building an urban transport system in the Southeast region, it is necessary to have many beam structure solutions for urban bridge construction projects The type of prestressed concrete beam structure with high strength concrete has been applied by many countries in the world to traffic construction, the advantage of high strength concrete is that it can increase the bearing capacity of the structure thereby helping to design structures with smaller size, lighter weight, longer span and increased durability due to better concrete quality However, currently, in the Southeast region, bridge construction projects only use concrete with a strength of 50MPa or less This is an open issue and needs to be addressed With the available potential of the Southeast region in terms of materials to produce high-strength concrete, the study and application of high-strength concrete in the construction of traffic bridges in the Southeast region is a right direction
2 Purpose of research
- Research on manufacturing high-strength concrete using materials in the Southeast region and experimentally evaluate some important mechanical properties of the material such as elastic modulus, tensile
Trang 4strength in bending, development strength over time, to serve the design and manufacture of prestressed concrete beam structures
- Analyze and select the type of precast concrete beam structure that
is applicable to high strength concrete in the design and manufacture
of precast concrete beams using materials in the Southeast region
- Application to calculate and design typical girder structure for the type of beam selected in step 2 using concrete mixed with concrete in step 1 for application in traffic projects in the Southeast region
3 The object and scope of the study of the thesis
Materials: research of using local materials in the Southeast region
to manufacture high-strength concrete mixes with suitable characteristics for the construction of pre-stressed concrete beams
Structural: Research and application of wide-flange girder made
of prestressed concrete with simple span for traffic development in the Southeast region
About the load: The research load limit is a static load problem
4 Research Methods
The main research method is theoretical research combined with experimental research
CHAPTER 1 OVERVIEW 1.1 Traffic development demand in the Southeast region
The SouthEast is a region with a high degree of urbanization and rapid development Population density is high in industrial zones and surrounding areas
The provinces in this region have a very high urbanization rate, due to the income gap with other regions leading to massive migration from neighboring provinces to urban areas The general situation of these cities is: the demand for housing is large, the demand for
Trang 5personal transport and the large movement of goods exceeds the capacity of the existing infrastructure system
In the existing urban areas, the land fund for traffic is still quite limited, the compensation and site clearance costs are very large, so the elevated roads and underground routes will be more focused on development
1.2 Types of precast - prestressed concrete beam structures are being applied and developed in bridge construction
In Vietnam, with small and medium span bridges (length from 60m or less), simple girder span structure is the most applied span structure
Table 1-1: Statistics of commonly used precast - prestressed beams
in Vietnam
No Bridge girder type Fabricating method
2 Slab girder 12m Pre-tensioning
3 Slab girder 15m Pre-tensioning
4 Slab girder 18m Pre-tensioning
5 Slab girder 21m Pre-tensioning
6 Slab girder 24m Pre-tensioning
1 I-beam 18,6m Pre-tensioning and Post-tensioning
2 I-beam 24,54m Pre-tensioning and Post-tensioning
3 I-beam 33m Pre-tensioning and Post-tensioning
1 Super-T beam 38,2m Pre-tensioning
E SOME NEW TYPES OF BEAM BEEN INTO VIETNAM
1 Reverse T Beam 25m Pre-tensioning
Trang 6Currently in the world, types of prestressed concrete beams are being widely applied, including Bulb-Tee girder, Wide Flange Girder, U-Beam girder, Bath-Tub beam, Pi girder
1.3 Application situation and development trend of high strength concrete (HSC), high performance concrete (HPC) in bridge construction and repair
High-strength concrete and high-performance concrete have been researched and widely applied in many countries around the world, led
by the US, Germany, France, and Japan Many other countries are also very interested in developing high-strength concrete structures such as China, Korea, Australia, Norway, UK, Canada
In the current bridge span structure design in Vietnam, concrete
is commonly used with the usual strength range [4050]MPa for prestressed girder structures, for commonly used cast-in-place deck slabs concrete with strength [3035]MPa
In the area of Ho Chi Minh City and neighboring provinces in the Southeast region, now many concrete factories have put into production high strength concrete up to 80MPa but still mainly used
to manufacture precast - prestressed pile
CHAPTER 2 RESEARCH FOR PRODUCTION OF HIGH STRENGTH CONCRETE 60MPA TO 80MPA USING LOCAL MATERIALS IN THE SOUTHEAST AREA,
GIRDER
2.1 Overview of high-strength concrete
High-strength concrete is made based on the following adjustments:
Trang 7 Reducing the ratio of water to cement (N/X): using a new generation of high water reducing additives, the N/X ratio can be greatly reduced while still ensuring the required slump
Adding some products with high fineness: there are 3 types of commonly used products: fly ash, silica fume and activated metakaolin
2.2 Research and design concrete mix composition of 60MPa to 80MPa strength using local materials in the SouthEast region
The Southeast region has an abundant supply of good quality crushed stone The rock origin is mainly basalt, with strength ranges from 100Mpa to 200Mpa High intensity rock sources are concentrated in the areas of Tan Cang, Dinh Quan, Dong Nai province, Chau Pha in Ba Ria-Vung Tau, Di An in Binh Duong
The main source of sand supplied in the Southeast region is from the Tien River, Tan Chau yellow sand (An Giang) is a popular material due to its abundant supply and low cost However, the modulus of magnitude is only about 1.75 (according to TCVN 7572-2:2006), if only river sand is used, it will not satisfy the requirements for grading Currently, in the Southeast region, crushed sand produced in Phu My,
Ba Ria - Vung Tau province is a reasonable alternative and supplement for fine aggregates to manufacture high strength concrete The topic proposes to use fine aggregate with a mixing ratio of 60% river sand with 40% crushed sand for application in the next research sections
Design of concrete mix C60 using materials in the Southeast
region
+ Design requirements:
- The 28-day compressive strength of the cylinder specimen: 60Mpa or more
Trang 8- Required slump: 160mm
+ Design steps: according to ACI211.4R-08
The design results are presented in Table 2-13
Table 2-13: C60 mix selected after testing
Kí hiệu
BT N/CKD
Đ (kg)
C (kg)
N (lit)
X (kg)
FA (kg) (kg) SF PGSD (lít) C60 0.3145 1120 720 150 477 0 0 4
Design of concrete mix C70 using materials in the Southeast
+ Design steps: according to ACI211.4R-08
The design results are presented in Table 2-15
Table 2-15: C70 mix selected after testing
Kí hiệu
BT N/CKD
Đ (kg)
C (kg)
N (lit)
X (kg)
FA (kg) (kg) SF PGSD (lít) C70 0.264 1120 700 140 530 0 0 4.77
Design of concrete mix C80 using materials in the Southeast
+ Design steps: according to ACI211.4R-08
The design results are presented in Table 2-17
Table 2-17: C80 mix selected after testing
Trang 9Kí hiệu
BT N/CKD
Đ (kg)
C (kg)
N (lit)
X (kg)
FA (kg) (kg) SF PGSD (lít) C80 0.26 1120 780 140.4 540 0 0 5.2
Evaluation of compressive strength of test mix C60, C70,
C80 using local materials in the Southeast region
The characteristic compressive strength of the selected mix C60, C70, C80 is determined according to the results of compression test of
a cylinder specimen of 15x30(cm) with the number of 12 specimen s for each mix The experimental results are shown in Table 2-19 Table 2-19: Results of determination of compressive strength for 3
Modulus of rupture
Modulus of rupture is determined by laboratory testing of beam samples of size 15x15x60 (cm), standard used for testing is ASTM C78-02, number of test samples used to determine tensile strength when bending is 12 samples for each mix
Compare the value obtained from the experiment with the estimated value according to TCVN 11823 for 3 grades C60, C70, C80
as follows:
Mix Strength
(MPa)
f r (TCVN 11823) (MPa)
f r from test (MPa)
Difference (%)
Trang 10The experimental values obtained are more than 30% higher than the estimate according to the formula of TCVN 11823:2017, so to estimate the elastic modulus value of 3 concrete mix C60, C70, C80 accurately more precisely, the proposed bending strength estimation formula can be used as follows:
23
Table 2-23: Test results of elastic modulus of cylinders
Sample E c (Mpa) Sample E c (Mpa) Sample E c (Mpa)
C60-M25 52580.0 C70-M25 54109.5 C80-M25 62751.0 C60-M26 53832.8 C70-M26 51866.0 C80-M26 56443.0 C60-M27 55815.9 C70-M27 51131.5 C80-M27 57818.9 C60-M28 54085.1 C70-M28 57881.9 C80-M28 58187.2 C60-M29 55441.7 C70-M29 60778.6 C80-M29 58541.7 C60-M30 56695.0 C70-M30 59997.1 C80-M30 52114.2 C60-M31 56754.3 C70-M31 58279.4 C80-M31 58169.2 C60-M32 67927.6 C70-M32 57878.2 C80-M32 61192.9 C60-M33 56754.3 C70-M33 54899.6 C80-M33 62727.4 C60-M34 55386.7 C70-M34 60454.9 C80-M34 59985.9 C60-M35 48569.5 C70-M35 59971.3 C80-M35 56113.3 C60-M36 52129.2 C70-M36 59913.0 C80-M36 58503.2
Trang 11Average: 55497.7 Average: 57263.4 Average: 58545.6
Based on the experimental results, the thesis proposes to use the formula to estimate the elastic modulus for high-strength concrete with mix C60, C70, C80 using materials in the SouthEast region in the form:
5 2.55 0.285
Graph of strength development over curing time
In the content of this research, the topic uses the results of the compression test of samples according to the age of 1, 3, 5, 7 and 28 days to evaluate the strength development of high-strength concrete with materials in the SouthEast region by date of age The number of test samples used to determine the strength over time was 6 samples per day of age With the experimental results obtained, the following formula can be used to estimate the strength development time for all
Constructing the stress-strain relationship equation of
high-strength concrete using local materials in the SouthEast region and determining the coefficients α 1 and 1
To perform the test to determine the stress-strain relationship curve, use the test of 1530 (cm) cylindrical concrete samples with strain gauges on opposite sides along the specimen height to measure the strain of the concrete Real-time samples, combined with experimental compressors with real-time compression force measurement, can determine the stress-strain relationship graph with the condition that the failure of the sample occurs in the middle region
Trang 12of the cylinder body The number of test samples used to determine the stress-strain relationship curve is 6 samples for each mix
The Strain gauge used is Kyowa KC-70-120-A11-11, 67mm long, glued to concrete with the included special glue The data acquisition frequency (compression force and strain) of the devices is adjusted at 62ms (1000 times/min)
Figure 2-17: Sample image before compression
Because the amount of data obtained from the measuring device for each sample is quite large, to simplify the representation of the stress-strain relationship graph, the test data results for each concrete sample will be filtered to take 15 values corresponding to the following times:
Maximum force value (f’c) and the corresponding strain at time f’c (o)
Maximum strain value max
Force increase phase from 0 to f’c : take 9 more values at the corresponding stress times about (0.1; 0.2; 0.3; 0.4; 0.5; 0.6; 0.7; 0.8; 0.9)f’c
Period from o to max : take 4 more values at times with corresponding strain about + (0.2; 0.4; 0.6; 0.8)( - )
Trang 13The process of testing 18 concrete samples with 3 mixes of C60; C70; C80 obtained the results of 15 samples (1 sample with an error
of the experimenter not storing the strain signal, 2 samples with an error of the strain data series)
With the results obtained, the topic evaluates and selects the type of equation used to represent the stress-strain relationship for high-strength concrete using materials in the Southeast region as follows:
; is the parameter to be determined
Parameter value is determined for each sample by the method
of least squares, the results of parameter determination according to table 2-37
Table 2-37: Result of parameter based on experimental data
C60-M3 19.5 C70-M3 16.9 C80-M2 22.7 C60-M4 14.3 C70-M4 53.4 C80-M3 10.6 C60-M5 24.9 C70-M5 16.9 C80-M4 35.4 C60-M6 14.1 C70-M6 72.1 C80-M5 10.2
Giá trị trung bình t/b = 28.08 Based on the calculation results, the topic proposes to use the parameter value =28.1
To build a complete stress-strain relationship graph, it is necessary to determine the value of cu as well as the relative ratio of
cu to o, so we consider the correlation between o and max according
to the following table: