Experimental determination of the remaining prestress force in a prestressed concrete crosstie
Page(s): 97-105 Linh Le Ha, Tu Do Anh, Hieu Nguyen Minh, Hung Le Xuan, Cuong Nguyen TuanAbstractCurrently, prestressed concrete (PC) crossties are widely used to replace wooden crossties in the Vietnam railway system, and effectively used in urban railroads due to their advantages in strength, durability, cost, and environmental impact. PC crossties use high strength steel wires to a create pre-compression state in concrete. For many reasons, the remaining prestress force is partially lost during fabrication and operation. Therefore, there is a need for a method to determine the effective remaining force in the crossties. This paper presents an experimental method to determine the remaining prestress force in a crosstie through a 4-point bending test. A sample set of 03 crossties was tested until cracks appeared. By re-loading until the pre-cracks begin to open, the critical force is recorded and the remaining prestress force in the crosstie is determined. This test method allows to determine the remaining prestress force, which is used to assess the current status and predict the service life of a PC crosstie
Evaluation of cracking resistance of stone matrix asphalt with copolymer styrence-butadiene-styrence
Page(s): 106-117 Lan Nguyen Ngoc, Cham La Van, Viet Nguyen Tien, Youngik Kim, Son Nguyen KimAbstractStone Matrix Asphalt Mixture (SMA) is a high-performance asphalt mixture used for the pavement structures with a heavy vehicle load, or the airport pavements. Because SMA has a stone-on-stone structure and the mixture is often made with additives, leading to increasing the rutting resistance. There are many types of additives used in SMA with different prosperities of short-term and long-term performance. This paper presents experimental results to evaluate the cracking resistance of SMA using original styrene-butadiene-styrene (SBS) additive, commercially called Rubber Modified Compound (RMC). The graded asphalt (DGA) and SMA using PMB III bitumen were compared with the SMA. The crack resistance properties are assessed by the fracture failure energy (Gf), the post-peak slope (|m75|), and the cracking resistance index (Cracking Tolerance Index - CTIndex) of the indirect tensile asphalt cracking test. Experimental results show that the SMA using RMC additive has higher crack resistance than DGA but lower than that of SMA using PMB III
Page(s): 118-131 Lam Dang Hong, Thinh Phi HongAbstractA shear module plays an important role in modeling of soil behavior, especially in small strain structures such as vibration equipment foundation, wind turbine foundation, bridge foundation, retaining wall, tunnel, and so on. There are a lot of studies on soil shear modulus depending on the allowable shear strain in the world, but there is not much that study in Vietnam, especially in small strain structures. In this paper, to study the relationship between the shear modulus and the allowable shear strain, the authors used downhole seismic tests, cycle triaxial tests and standard penetration tests performed on coastal sand in Quang Binh province, Vietnam. The results from the shear modulus are compared with those in the classical literature to enrich the database of the shear modulus for engineering practices in Vietnam. The experimental results from the shear modulus show that the correlation between the shear modulus and the allowable shear strain is close to the lower limitation of the classical correlation curve in the literature
Page(s): 132-146 Hung Tran Ngoc, Hieu Tran TrungAbstractSunway-Quoc Oai quarry’s aggregate has been known and widely used for polymer modified hot mix asphalt in Vietnam. Evaluating the difference as well as the efficiency of other types of stone aggregates to replace Sunway stone is necessary, especially to help in better understanding the chemical composition and mechanical properties of aggregates and asphalt mixtures. The article conducts experimental studies, showing the possibility of using stone aggregate at Khau Dem-Lang Son quarry to replace traditional stone aggregate Sunway-Quoc Oai quarry for the SBS (Styrene Butadiene Styrene) polymer modified hot mix asphalt. As a result from analyzing X-ray fluorescence spectroscopy, the mineral compositions of the two types of stone Khau Dem and Sunway have high similarities, both are strongly magmatic rock, with SiO2 content of 43,17% and 45,24% respectively. When considering BTNP12,5-Sunway and BTNP12,5-Khau Dem, experimental results and statistical analysis showed that the Marshall parameters and rutting resistance were similar. Research results show that the high suitability of some igneous rocks used for polymer modified asphalt mixture in Vietnam
Page(s): 147-159 Thuy Nguyen Tien, Anh Nguyen TuanAbstractThe Glass Fiber Reinforced Polymer (GFRP) shape and systems have been using commercially since 1970 and is increasingly applying in construction. The design standard for GFRP materials is gradually being developed and improved to meet the increasing demand from manufacturers and designers. The preparation of a design standard would require sufficient numbers of experimental data, both on material properties and structural behavior under difference boundary and loading conditions to propose design equations and factors. Longitudinal elastic modulus and major possion’s ratio are those important values that being used frequently in design. This paper presents experimental work to determine those values. It is found that the elastic modulus of flanges and the web can be significantly different when comparing together. It is also found that they are 27-43% higher than that provided by the manufacturer in the design manual. For Major Poisson’s ratio, the measured value is very close to that of design manual
Page(s): 160-174 Duc Dang VietAbstractPhat Tich – Dai Dong Thanh Bridge in Vietnam locates at the interfering area with number of spiritual and cultural places; therefore, the its structure was specially designed with concentration of aesthetic appearances. Because of the geometrical specialties with great width dimension and only one surface of suspension cables, the suspension anchorages which located in transverse middle of the girder section, the distribution of transverse flexural moment is significant, especially around the suspension anchorage location and inducing the complicated local stress-strain distribution. In this paper, with application of Non-linear FEM model, author investigates the local structural behaviour of the concrete box girder. A computating model for burning beams based on the theory of finite element method and Concrete Damaged Plasticity was developed. In addition to that, a detailed analysis based on simulation results and practical factors were performed. The findings are able to contribute into ensure the structural safety in stages of construction and service
Effects of rejuvenators on penetration and softening point of bitumen blends
Page(s): 175-185 Quyet Truong Van, Lan Nguyen Ngoc, Dong Dao Van, Trang Pham MinhAbstractThe use of Reclaimed Asphalt Pavement (RAP) to produce asphalt concrete is becoming more and more popular in the world because of its technical, economic and environment. However, when a high RAP is used, causing a negative effect on the performances of the mixtures. Therefore, rejuvenators are used to improve the properties of bitumen and to recycle asphalt mixtures. This paper presents a study on the influence of the type and content of the rejuvenators on the penetration and the softening point of bitumen. The types of bitumen were evaluated including the virgin bitumen, aged bitumen recovered from RAP and bitumen blends (including virgin bitumen, RAP aged bitumen with the recycled binder ratio (RBR) of 0.3, and rejuvenator). Two rejuvenators used in the study are petroleum-based recycling agent (HS1 rejuvenator) and vegetable oil-based (Prephalt@FBK rejuvenator) with different contents from 0%, 4%, 8% and 12%. The obtained results have shown the effectiveness of rejuvenators in restoring the physical properties of bitumen. In order to meet the requirements of the penetration and softening point as bitumen 60/70, the rejuvenator content should be about 9.0% with HS1 and about 5.0% with Prephalt@FBK
Page(s): 186-198 Hoai Ho Thi, Tai Dinh Huu, Cuong Nguyen Huy, Thuy Pham Thi ThanhAbstractNowadays, textile reinforced concrete (TRC) is one of the effective methods for strengthening existing reinforced concrete (RC) structures. However, many studies pointed out that it is difficult to determine the tensile strength of the textile reinforcement in TRC when it subjects to the complex loading at the corners of the beams and columns. In this paper, the authors present an experimental study to determine the tensile strength of curved carbon textile reinforcement in TRC under both tensile and compressive loading. The results showed that all test specimens failed at the curvature region. The average tensile strength of the curved reinforcement in TRC under both tensile and compressive loading only reached 33 % to 48 % of the theoretical strength of the carbon textile. The direction change of the textile mesh and the effect of compression loading are the reasons for the strength degradation. The proposed experiment in this paper contributes to developing the experimental program for determining the mechanical properties of TRC when it is used as a strengthened material for RC structures
Page(s): 199-215 Hanh Vu Kim, Cuong Doan Danh, Khoat Vu VanAbstractIn urban areas, the amount of daily solid waste (CTRSH) is increasing with the growth rate of population and urbanization. The article presents a survey and an assessment of the existing state of domestic solid waste management (DSWM) in 10 wards of Lao Cai city, Vietnam, following with suggestions for enhancing management effectiveness. The research results showed that the proportion of households performing DSWM classification at the source reached 96.85%, the quality of classification reached 86.7% and the collection rate reached 95-97%. The rate of domestic solid waste being recycled, reused, produced fertilizer or recovered energy in Lao Cai city was reached 63%, the remaining 37% was buried at landfill in Toong Mon village, Dong Tuyen commune. Based on that, we proposed to apply QGIS technology to support the use of existing infrastructure in DSWM, collection management, and collection mapping. That is aimed to optimization of collection and transportation routes and reduction of waste collection costs, and improve the efficiency of DSWM in the direction to a circular economy
Research on proposing mixture composition of geopolymer using sea sand by experimental design method
Page(s): 216-229 Chi Dang Thuy, Son Trinh HoangAbstractThe research on geopolymer concrete (GPC) using sea sand in the world has been carried out over 10 years. In Vietnam, the studies on the GPC with sea sand are shortage. Also, the potential of the the GPC with sea sand in coastal infrastructure construction has not been significantly considered. In this paper, to initially evaluate the ability the sand taken from Cua Lo coast, Nghe An province, Vietnam to manufacture GPC without any futher treatment, an experiment design method we carried out in our university laboratoty. The result outcome has successfully proposed 03 GPC mixtures with the graded factor of 15, 25, and 35 MPa, respectively. The achievement of the study suggested that it is possible to replace conventional coarse sand by sea sand in the production of GPC. Thus, our study will in turn contribute to the efficient use of sea sand resources, reducing exploitation of amount of depleted traditional coarse sand
Page(s): 230-241 Tho Pham Duc, Hung Tran NamAbstractIn order to decrease the thermal stress in the slab, a thin isolation layer between the slab and the base is installed which reduces friction and adhesion forces at the contact interface to certain values. So far in Vietnam, for the calculation of rigid pavement concrete slab, it is basically assumed that there is no friction between the slab and base layer or they bond with each other. Based on the finite element method this paper presents a numerical estimation of stress-deformation state of the slab taking into account the behavior of the isolation layer. In the study, the isolation layer is modeled by Goodman contact elements that can consider both the friction and adhesion forces at the contact interface. The results show that, in case of considering this layer the stress-deformation state in the concrete slabs changes significantly in comparison with case of bond condition imposed between the slab and the base. Therefore, when modeling the rigid pavement concrete slab, it is necessary to take into account the effect of the isolation layer to more closely reflect the real working condition of the pavement, and in this procedure the finite contact element could be used to simulate this layer
