Nghiên cứu thực nghiệm về tính chất cơ lý của bê tông sử dụng cốt liệu lớn tái chế từ chất thải rắn xây dựng và ứng dụng cho cột bê tông cốt thép chịu nén đúng tâm.Nghiên cứu thực nghiệm về tính chất cơ lý của bê tông sử dụng cốt liệu lớn tái chế từ chất thải rắn xây dựng và ứng dụng cho cột bê tông cốt thép chịu nén đúng tâm.Nghiên cứu thực nghiệm về tính chất cơ lý của bê tông sử dụng cốt liệu lớn tái chế từ chất thải rắn xây dựng và ứng dụng cho cột bê tông cốt thép chịu nén đúng tâm.Nghiên cứu thực nghiệm về tính chất cơ lý của bê tông sử dụng cốt liệu lớn tái chế từ chất thải rắn xây dựng và ứng dụng cho cột bê tông cốt thép chịu nén đúng tâm.Nghiên cứu thực nghiệm về tính chất cơ lý của bê tông sử dụng cốt liệu lớn tái chế từ chất thải rắn xây dựng và ứng dụng cho cột bê tông cốt thép chịu nén đúng tâm.Nghiên cứu thực nghiệm về tính chất cơ lý của bê tông sử dụng cốt liệu lớn tái chế từ chất thải rắn xây dựng và ứng dụng cho cột bê tông cốt thép chịu nén đúng tâm.Nghiên cứu thực nghiệm về tính chất cơ lý của bê tông sử dụng cốt liệu lớn tái chế từ chất thải rắn xây dựng và ứng dụng cho cột bê tông cốt thép chịu nén đúng tâm.Nghiên cứu thực nghiệm về tính chất cơ lý của bê tông sử dụng cốt liệu lớn tái chế từ chất thải rắn xây dựng và ứng dụng cho cột bê tông cốt thép chịu nén đúng tâm.Nghiên cứu thực nghiệm về tính chất cơ lý của bê tông sử dụng cốt liệu lớn tái chế từ chất thải rắn xây dựng và ứng dụng cho cột bê tông cốt thép chịu nén đúng tâm.Nghiên cứu thực nghiệm về tính chất cơ lý của bê tông sử dụng cốt liệu lớn tái chế từ chất thải rắn xây dựng và ứng dụng cho cột bê tông cốt thép chịu nén đúng tâm.
MINISTRY OF EDUCATION AND TRAINING HANOI UNIVERSITY OF CIVIL ENGINEERING NGUYEN THANH QUANG EXPERIMENTAL STUDY OF THE MECHANICAL AND PHYSICAL PROPERTIES OF CONCRETE MADE OF RECYCLED COARSE AGGREGATES FROM CONSTRUCTION SOLID WASTES AND USED REINFORCED CONCRETE COLUMNS UNDER CONCENTRIC LOADS Major: Civil Engineering Code: 9580201 SUMMARY OF DOCTORAL DISSERTATION Hà Nội – Năm 2022 The thesis is completed at Hanoi University of Civil Engineering Supervisor 1: Assoc Prof Nguyen Hoang Giang Supervisor 2: Dr Nguyen Ngoc Tan Examiner 1: Dr Nguyen Dai Minh Examiner 2: Assoc Prof Nguyen Ngoc Phuong Examiner 3: Assoc Prof Nguyen Xuan Huy The thesis will be examined by the Examination Board of Hanoi University of Civil Engineering at The thesis can be found at the Library Hanoi University of Civil Engineering and the National Library INTRODUCTION The necessity of the research The vigorous development of construction activities generates a large amount of construction solid waste (CSW) In Vietnam, according to statistics in 2009, the amount of construction waste generated in big cities is about 1.46 - 1.92 million tons/year, but the recycling rate is very low, only about 1-2% Currently, construction waste is generated about 3000 tons/day, in 2020 the total amount of construction waste is estimated at 6.3 million tons and is expected to reach 11 million tons by 2025 However, the effective application of construction waste in large quantities to construction projects is facing many difficulties, especially in assessing the quality, mechanical properties of recycled materials and applicability in the structures such as columns, beams, foundations and linings for infrastructure works Therefore, the topic focuses on studying the mechanical behavior of concrete materials using recycled coarse aggregates (RAC) from construction waste, in order to evaluate the applicability of recycled aggregate concrete (RAC) in the load bearing structure in construction The recycle reduces the pressure of a large amount of construction waste discharged into the environment, reduces the causes of pollution and adverse impacts on human life, and provides the construction market with a large amount of recycled materials The process meets technical requirements in order to reduce exploitation of natural resources and create added value for materials with high scientific value Objective - Research on the development of some mechanical properties of concrete using recycled concrete aggregates with different replacement contents - Study on compressive behavior of reinforced concrete columns made of recycled aggregate concrete Comparison of mechanical behavior of recycled aggregate concrete columns with conventional reinforced concrete columns Object and scope of the study The concrete from the demolition of construction sites is grounded according to the design process for the crusher assembled in Vietnam The recycled aggregate particles in this study are from to 20 mm in diameter, the largest aggregate diameter is 20 mm Recycled concrete is designed with compressive strength grade B30 and tested at 3, 7, 14, 28, 60, 90, 120, 150, 180 and 360 days old, respectively, with coarse aggregate replacement rates by mass is r = 0%, 50%; 100%; respectively The recycled aggregate used for the column test with dimensions of 200 x 200 x 880 mm and the replacement rate of recycled aggregate for the column is r = 0%; 50%; 100% Columns are subjected to axial compression to study the behavior and bearing capacity of recycled aggregate concrete column members compared to natural aggregate concrete columns (NAC) Research Methodology Theoretical research: Based on research documents to conduct an overview research on the thesis topic Experimental research: The thesis is carried out mainly by experimental method The main results are obtained from tests performed on concrete specimens and reinforced concrete column members New contributions of the thesis - Proving the feasibility of manufacturing concrete with average strength of cylinders up to 40 MPa using recycled coarse aggregates (RCA) from construction solid waste (CSW) in Vietnamese conditions; - Provide experimental data sets on basic mechanical and mechanical properties of RCA concrete from CSW with aggregate replacement rates of 0, 50 and 100%, respectively, including: compressive strength, modulus elastic at the ages of 3, 7, 14, 28, 60, 90 and 360 days, thereby suggesting a mathematical relationship between these quantities over time; stress-strain relationship curve; shrinkage and creep deformation; - Conducted experimental research on the working of reinforced concrete columns subjected to axial compression using RCA concrete from CSW The results of this study have practical significance when proving the applicability of RAC in building structures in Vietnam Content of the thesis The thesis consists of an introduction, four content chapters, a conclusion and a list of references The thesis is 144 pages long, 72 drawings, 26 tables and 21 references in Vietnamese, 160 references in English CHAPTER 1: REVIEW OF CONSTRUCTION SOLID WASTE AND MECHANICAL CHARACTERISTICS OF CONCRETE USING RECYCLED CONCRETE AGGREGATE This chapter focuses on presenting the definition of construction waste, an overview of the management situation, and studying the properties and applications of concrete using RCA in the world and in Vietnam On that basis, draw the next research direction of the thesis 1.1 Construction solid waste: management and recycling actual state 1.1.1 Construction solid waste definition According to the definition in standard TCVN 6705:2000 on Nonhazardous solid waste – Classification: waste from construction activities is waste discharged due to demolition, renovation of old construction items/works, or due to the construction of new items/constructions (houses, bridges, roads ); such as lime mortar, broken bricks, concrete, water pipes, roofing sheets and other materials Thus, construction waste is generated during construction, total demolition, or partial demolition of construction works Figure 1.1 shows some examples of construction waste components from different types of demolition sources, for example: High-rise buildings, residential buildings, bridges, roads and structures with use concrete Figure 1.1 Some examples of construction waste composition from different sources 1.1.2 Actual status of construction waste recycling management in Vietnam a) Actual status of CSW management With the rapid urbanization along with economic development in all aspects, construction activities are taking place in many places, especially in big cities in Vietnam According to the 2011 National Environment Report on Solid Waste Management of the Ministry of Natural Resources and Environment, the total amount of municipal solid waste is shown in Table 1.1 Table 1.1 CSW volume of some localities City Volume of CSW Collection rate (%) (ton/day) Hanoi 1000 – 1500 70 Ho Chi Minh city 2000 – 2500 75 Hai Phong 400 – 450 40 - 45 Da Nang 500 - 600 60 Others 100 - 200 20 - 30 The recycling of construction waste has been emphasized in the national strategy on solid waste management to 2025 and vision to 2050 Accordingly, 50% - 60% of the collected solid waste will be recycled b) Existing problems The concept of construction waste management is still quite new in Vietnam The Vietnamese government is facing a major challenge in construction waste management Construction technology is outdated, so it generates a large amount of waste The indiscriminate dumping of construction waste also affects human health and the environment, such as obstructing traffic (CSW on pavements) leading to many accidents, causing impacts on urban landscapes and air pollution (due to dirt), degrades infrastructure (clogged water pipes), wastes land resources In addition, the lax management of hazardous construction materials such as drywall (generating H2S gas) and asbestos materials (possibly carcinogenic) poses high health risks to humans Besides, Vietnam has not had much attraction from the public's perceptions and attitudes towards waste generated from construction and demolition 1.1.3 Actual status and potential of construction waste recycling The management of construction waste is part of the Government's solid waste management and treatment strategy, in which Directive No 41/CT-TTg (reducing landfill to less than 20% while the remaining provinces reduce to less than 25% by the year) 2025) Circular 08/2017/TT-BXD stipulates the reporting on the collection and treatment of construction waste in the provinces and cities of Vietnam Therefore, it is very urgent and important to introduce a management process and crushing method to manufacture recycled materials from concrete It can be seen that construction waste is a great resource that can be used as new recycled materials for infrastructure construction: - Producing recycled aggregate from construction waste and applying it as a foundation and lining for roads - Producing materials to build traffic infrastructure: concrete using recycled aggregates, embankment, road filling, leveling, etc - Additives in cement production; production of reinforced concrete piles - Waste water treatment: Using recycled products as filter materials - Treating oil-contaminated water and seawater, overcoming coastal erosion 1.2 Overview research on concrete using RAC 1.2.1 Properties of recycled concrete aggregates The main properties of concrete using recycled aggregate greatly affect the properties of the concrete mix, such as: mineral composition, porosity, particle composition, water absorption, shape properties, form, strength of aggregate The material composition of recycled aggreagate concrete (RAC) is similar to that of original waste concrete, with two main components being natural stone and artificial mortar (sand, stone, cement) Therefore, this content will greatly affect the amount of mixing water, workability and workability loss, volumetric weight, permeability and durability of concrete using RAC When using crushing and screening technology, the particle composition of RAC is equivalent to that of natural aggregate (NA) and conforms to the technical requirements of the standard TCVN 7570: 2006, standard TCVN 11969:2018 used for large aggregates for concrete RAC always has a much greater water absorption than NA Specifically, the water absorption of RAC from concrete is usually 312%, from mixed construction waste is 20-25%, while that of NA is only 0.5-1.2% 1.2.2 Mechanical properties of concrete using RAC a) Compressive strength of concrete using RAC Studies from the 70s-80s of the last century on concrete using RAC have shown that the compressive strength of this type of concrete in general tends to decrease compared to concrete using natural aggregates of the same grade (Table 1.2) Table 1.2 Reduction rate of compressive strength of RAC concrete in some research results Decreasing compressive Replacement Author (year) strength at 28 days of age rate (%) (%) Nixon (1978) 100 20 Ravindrarajah and Tam (1985) 100 8-24 De Oliveira and Vazquez (1996) 100 10 Topỗu and Sengel (2004) 100 23,5-33 20 4-6 Kou (2006) 50 13-17 100 16-22 30 5,6 50 12 Xiao (2018) 70 10 100 11,5 Due to limitations in mechanical properties, some countries have clear regulations for the use of RAC For example British standard BS 8500:2 (20% alternative, maximum strength 40MPa), German DIN 4226100:200 (20-35% alternative, maximum strength 30MPa), Hong Kong WBTC No 12/2002 (20-100% replacement, maximum strength 35MPa) In Vietnam, the standard TCVN 11969:2018 on recycled coarse aggregates for concrete mainly evaluates the input quality of recycled coarse aggregates suitable for concrete production b) Elastic modulus of concrete using RAC The modulus of elasticity is the mechanical property studied in most publications on concrete using RAC Summary of the rate of reduction of elastic modulus in some typical publications when replacing 100% of NA with RAC It can be seen that the elastic modulus of concrete used when using 100% RAC is about 17.5% - 45% lower than that of concrete using natural aggregates c) Shrinkage of concrete using RAC The use of RAC instead of NA often increases the shrinkage of concrete The main reason is that the high mortar content in RAC has a system of open pores of different sizes, which greatly increases the water absorption and air permeability of concrete Shrinkage can be increased by 10-25% or 20-70% d) Feasibility of using RAC in column structure Compared with conventional concrete, the application of concrete using RAC in load-bearing structures is often carefully considered Figure 1.2 Cross-section of RAC reinforced concrete columns subjected to eccentric loads and proportional deformation distribution chart Research on the reliability of columns using RAC reinforced concrete under the effect of eccentric loads (Figure 1.2) and conclude that reinforced concrete columns have compressive capacity distributed over a wide range In China, they also conducted a test of RAC concrete column subjected to eccentric loads to determine the load capacity, drawing a relationship curve between longitudinal force N and bending moment M (Figure 1.3) Figure 1.3 Experimental curve of relationship between axial force N and bending moment M with different rates of recycling aggregate 1.3 Conclusion The use of RAC for concrete structures is still limited due to the lack of reliable information on the origin of recycled aggregates and workability RAC can add value by high quality recycling Practical application of RAC recycling can benefit the construction industry, thus encouraging the management of RAC and 3R in the country Therefore, this study focuses on evaluating the mechanical properties of concrete materials using RAC and the working ability of the reinforced concrete column structure under load From previous studies, it can be seen that the quality of RAC depends a lot on the quality of the input materials as well as the mixing process and quality control The standards in the world are developed for materials suitable to the region and locality, of which in Vietnam, there is only a standard for recycled coarse aggregate that has no specificity from recycled concrete Concrete types in Vietnam with different characteristics will affect the development of strength of materials as well as components from concrete using different RAC Therefore, more in-depth studies are needed for RAC in accordance with standard requirements as well as adjustment coefficients for the appropriate calculation and design process in Vietnam Currently, Vietnam also does not have a process for technology and management of coarse aggregates after the crushing and demolition process and a suitable mixing process for concrete using RAC Therefore, it is necessary to research, experiment and develop this process in order to put the recycling and application of RAC into practice There is a need for research for reinforced concrete from demolished concrete and this process needs to take into account the development of reinforced concrete over time as well as the work of reinforced concrete on a typical structure and compare with the reinforced concrete to have adjustments and appropriate recommendations for the effective use of this material in practice 11 2.1.3 Mechanical properties of recycled concrete aggregates The experiment was carried out in the SATREPS laboratory, Hanoi National University of Civil Engineering (HUCE) according to the standard TCVN 7572:2006 in order to determine the input quality of the RCA The properties of the recycled materials in this study are shown in Table 2.2 The experiments were conducted including: (i) Humidity, (ii) water absorption, (iii) mass by volume, (iv) Los Angeles (LA) abrasion, (v) Determination of elongation and flaskiness index The results show that the RAC used meets the type I criteria of the TCVN 11969:2018 standard and is also consistent with the standards published in the world Table 2.2 Properties of RAC Physical properties of recycled coarse aggregate Humidity (%) Water absortpion (%) Volume mass (g/cm3) Los Angeles abrasion, % Elongation and flaskiness index, % JIS A 5022:2018 - Loại M Result TCVN 11969:2018 Loại I GB/T 251772010 1,87 -