Study on the influence of the shape of machine-made sand particles on the rheological properties of mortar
Zhou Xinwen 1,2, Liu Jianzhong 2,3, Liu Guangyan 3, Liu Jiaping 1,2
(1. School of materials science and engineering, Southeast University, Nanjing 211189; 2. State Key Laboratory of high performance civil engineering materials, Nanjing 210008; 3. Jiangsu subote new materials Co., Ltd., Nanjing 211103)
Abstract: in order to study the influence of the shape of manufactured sand particles on the rheological properties of mortar, the digital image processing technology (DIP) was used to quantitatively characterize the shape of sand particles. The rheological curve of mortar was measured by design test and the yield stress and apparent viscosity of mortar were calculated. The results show that the aspect ratio (E) and aspect ratio (f) of machine-made sand are 14% and 18% larger than that of natural river sand respectively, which indicates that the rod-shaped and flaky degree of machine-made sand is higher than that of natural river sand; the rheological curve of mortar reflects that the irregular shape of sand particles will increase the flow resistance of mortar, which is more significant under high volume fraction; the yield stress of 40% volume fraction machine-made sand mortar fitted by Chateau model is The results show that the apparent viscosity of machine-made sand mortar is higher than that of natural sand, especially at low shear rate.
Key words: machine made sand; particle shape; rheological property; yield stress; apparent viscosity
Study on the construction of 3D printing cement-based materials
Zhang Suyang, Jiang Yaqing, Wang Yu, pan tinghong
(School of mechanics and materials, Hehai University, Nanjing 211100)
Abstract: through the time-varying tests of plastic strength, static yield stress and jumping table fluidity, the influence of the synergistic action of nano clay and water reducer on the constructability of 3D printing cement-based materials (3dpc) was studied, and the evaluation index of 3dpc constructability was established based on the rheological properties. The results show that the time-dependent plastic strength and the time-dependent static yield stress of 3dpc mixed with nano clay and tackifying polycarboxylic acid water reducer increase with the increase of nano clay content, the appropriate content of nano clay is 0.8%, and the rate of change is 2.0 ~ 4.2 when the static yield stress increases At PA / s, the extrudability and constructability of 3dpc can be realized; in printable and constructable window time, the flow rate of 3dpc jumping table is 170-190 mm. It is an effective way to control the rheological parameters of 3dpc by adding nano clay and tackifying polycarboxylic acid water reducer.
Key words: cement based materials; 3D printing; constructability; rheological properties
Study on the mechanism of improving the impermeability of concrete with high corrosion resistance Portland cement
Ren Xuemei 1,2, song Jiamao 1,2, Hao Tingyu 1,2
(1. China Metallurgical Construction Research Institute Co., Ltd., Beijing 100088; 2. China Metallurgical High Performance Concrete Engineering Technology Center, Beijing 100088)
Abstract: in order to explore the mechanism of improving the impermeability of concrete with high corrosion resistance Portland cement, the compressive strength, chloride diffusion coefficient and DC step resistivity of ordinary portland cement concrete and special high corrosion resistance Portland cement concrete were studied. The results show that the high corrosion-resistant Portland cement can improve the impermeability of concrete not by improving the strength of concrete, but mainly by reducing the internal void ratio and connectivity.
Key words: high corrosion resistant Portland cement; concrete; resistivity; chloride diffusion coefficient
Experimental study on SO42 diffusion in concrete in saline soil
Wang Yanfeng 1, Jing Hao 2, Yan Changwang 3, Sun Wei 2
(1. Inner Mongolia Electric Power Economic and Technological Research Institute, Hohhot 010040; 2. Civil engineering college, Inner Mongolia University of technology, Hohhot 010051; 3. Mining college, Inner Mongolia University of technology, Hohhot 010051)
Abstract: in order to study the SO42 - diffusivity of concrete in Western saline soil environment, the SO42 - content in concrete of different depth was measured under different solution and different dry and wet cycle age. Using Fick's second law as the basic model, considering the combination ability of SO42 - and concrete and the characteristics of concrete as non-uniform medium, the SO42 diffusion coefficient is analyzed and discussed. In addition, based on the XRD results, the growth of ettringite in the erosion process was analyzed to explain the influence of ettringite formation on SO42 diffusion. The results show that Cl - can promote the erosion speed of SO42 - in the early stage of erosion; the diffusion coefficient of SO42 - in the concrete under the Western saline soil environment has a negative correlation with the binding capacity and a positive correlation with the erosion depth; the higher the concentration of SO42 - is, the faster the growth of ettringite is, and the expansion of ettringite will fill the existing cracks in the concrete, thus inhibiting the diffusion of SO42 -.
Key words: SO42 ion; diffusivity; saline soil environment; dry wet cycle; X-ray diffraction
Preparation of shrinkage compensating concrete for large area slab beam structure
Yan Peiyu 1, Chen Weiyi 1, Zhao Haitao 2, Wang Hailong 3, Huadong BANNER 2, Li xishuo 2, Qi Zhixiang 2, Kang Kai 2
(1. Department of civil engineering, Tsinghua University, Beijing 100084; 2. China Construction First Engineering Bureau Group Construction Development Co., Ltd.; Beijing 100102; 3. Wuhan Sanyuan special building materials Co., Ltd., 430082)
Abstract: in order to meet the requirements of crack resistance in the construction of large area floor beam structure of large-scale electronic industrial workshop, the properties of HCSA expansion agent and composite expansion agent (MgO expansion agent and HCSA expansion agent mixed) were compared and studied, and the high crack resistance compensating shrinkage concrete was prepared. The test results show that C40 shrinkage compensating concrete made of two kinds of expansion agents has the effect of shrinkage compensating and preventing cracking. The early strength and temperature rise of the shrinkage compensating concrete with composite expansion agent are slightly lower, but the shrinkage compensating ability is stronger, which is beneficial to improve the crack resistance of the concrete structure with large volume of deep beam and thin slab cast at the same time.
Key words: shrinkage compensating concrete; HCSA expansion agent; MgO expansion agent; crack resistance
Industrial preparation and properties of bulk polymerized solid polycarboxylic acid slump retention agent
Chen Guoxin 1,2,3,4, Zhu Yiran 1,2,3,4, Du Zhiqin 1,2,3,4, Wen Jinbao 1,2,3,4
(1. Nanjing Research Institute of water resources, 210029; 2. Nanjing Ruidi High Tech Co., Ltd., 210024; 3. Research center of new materials engineering technology of Ministry of water resources, Nanjing 210029; 4. Anhui Ruihe new materials Co., Ltd., Maanshan 243000)
Abstract: pc-702s2, a bulk solid polycarboxylic acid slump agent, was prepared by using TPEG, AA and MAH as the main raw materials, adjusting the process and selecting industrial equipment. The conversion, molecular weight and PDI of pc-702s2 were studied by GPC, and the structure of pc-702s2 was discussed based on the results of FTIR. The results show that the conversion rate of pc-702s2 is 94.43% and PDI is 1.283, which can reach the performance of conventional water solution polymerization slump retention agent. The particle size range after slicing is less than 300 μ m, which is suitable for industrial promotion and has a good development prospect.
Keywords: bulk polymerization; polycarboxylic acid system; slump retention agent; industrial preparation
Analysis on the current situation of water use in ready mixed concrete industry
Guan Chen 1, Zhou Jiheng 1, Wei Jianxun 1, Hu Zhiying 1, Shi Haixia 2, Wang Jianhua 3, Yan Xiaobo 1, Jia Jia 2, Yuan Mata Cheng 1
(1. Beijing guojianlianxin Certification Center Co., Ltd., 100831; 2. Ready mixed concrete branch of China Association of concrete and cement products, Beijing 100831; 3. Henan Academy of Building Science Co., Ltd., Zhengzhou 450053)
Abstract: through data investigation and field visit, the water consumption of ready mixed concrete industry in China is studied. Based on the water balance test results, the water consumption of each production link is analyzed, which provides reference for the research of water consumption in ready mixed concrete industry and the formulation of relevant standards.
Key words: ready mixed concrete; water resources; current situation of water use
Study on the influence of longitudinal crack on the bearing capacity of BCCP
Sun Yueyang 1, Hu Shaowei 1, 2, mingpan 1, Xue Xiang 2
(1. Nanjing water conservancy research institute, 210024; 2. Chongqing University, 400045)
Abstract: in order to study the influence of the longitudinal crack of the pipe core on the internal and external pressure bearing capacity of BCCP (reinforced spiral steel tube concrete pressure pipe), the appropriate material constitutive model is selected, and the internal and external pressure calculation models of DN1800 BCCP are established by using ABAQUS software. The internal and external pressure pipe core of the internal pressure pipe and the internal pressure pipe core of the external pressure pipe are respectively set at 1000 mm, 2000 mm, 3000 mm and 4 mm The longitudinal crack of 000 mm is compared with that of intact pipe. The results show that for the internal pressure pipe, the longitudinal crack of the outer pipe core only affects the internal pressure value corresponding to the tensile limit of the outer pipe core, and this value has nothing to do with the length of the longitudinal crack, which is about 2.95 MPa, 0.25 smaller than the intact pipe MPa; for the external pressure pipe, the longitudinal crack in the pipe core at the pipe top only affects the external pressure value corresponding to the tensile limit at the crack location, which is also independent of the length of the longitudinal crack, all of which are about 1200 kn, 300 smaller than the intact pipe Kn; whether it is internal pressure pipe or external pressure pipe, the corresponding load value when the protective layer, steel cylinder and reinforcement reach the ultimate strength is independent of whether the pipe core has cracks or not and the length of cracks.
Key words: steel reinforced concrete pressure pipe; crack; internal pressure; external pressure; tensile strength
Experimental study on seismic behavior of pva-ecc columns under composite stress
Liang Xiao 1, Shao Yongjian 1, Ling Zhi 1, Wang guozuo 2
(1. School of civil engineering, Suzhou University of science and technology, 215011; 2. China Yifeng Construction Group Co., Ltd., Suzhou 215131)
Abstract: Based on the seismic performance test of six ECC columns strengthened with steel bars and one ordinary concrete column under the condition of Compression Bending Shear Torsion composite stress, the hysteretic curve, skeleton curve, strength degradation, stiffness degradation and failure mode of the component are studied, and the influence of stirrup ratio, longitudinal reinforcement ratio and fiber content on the seismic performance of ECC columns subjected to torsion is analyzed. The test results show that the hysteretic curve of ECC column is fuller than that of ordinary RC column, and the yield torque, ultimate torque and ultimate torsion rate are increased by 64.4%, 74.8% and 123.3% respectively; the fiber content of test piece is increased from 1% to 2%, and the ductility coefficient is increased from 2.30 to 4.04; with the increase of stirrup ratio, the torsional performance of test piece is enhanced, and the stirrup spacing is 75% compared with that of test piece without stirrup The ductility coefficient of MM specimen is increased by 66.2%, and the ultimate torque is increased by 34.0%.
Key words: pva-ecc; composite torsion; hysteretic performance; seismic performance
Experimental study on fatigue of reinforced concrete beams in corrosive environment
Zhang Qiuyue 1, Wang Hui 1, Han Wenchen 2
(1. School of civil engineering and architecture, Shandong University of science and technology, Qingdao 266590; 2. Qingdao Tengyuan Design Office Co., Ltd., 266101)
Abstract: the fatigue tests of 8 reinforced concrete beams were carried out in the atmosphere, fresh water and sea water environment, and the mechanical properties and stiffness damage evolution law were studied. Furthermore, the failure mode, deflection development rule and fatigue life of the beam under the combined action of three environments and cyclic loads are analyzed. The results show that there is a coupling effect between corrosion and fatigue, and the fatigue life of the beam is the shortest under the sea water corrosion environment and 5%~70% load level. According to the theoretical analysis and test results, the fatigue life and its law of reinforced concrete beams in the harsh marine environment are further studied. Referring to the existing literature and test results, the fatigue life prediction model based on the evolution law of the rigidity damage of reinforced concrete beams is given. After calculation, the error between the measured results and the calculation results of the prediction model is not more than 13%.
Key words: reinforced concrete beam; seawater corrosion environment; fatigue life; stiffness damage
Design and application of type Ⅲ heavy duty concrete sleeper