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CONTENTS
Volume 12, Number 5, November 2021
 


Abstract
This study experimentally investigated the improvement of bond strength and durability of concrete containing high volume fly ash. Concrete mixtures made with 0%, 25% and 60% replacement of cement with class F fly ash were prepared. Water-binder ratios ranged from 0.28 to 0.72. The compressive, flexural and pullout bond strength, the resistance to chloride-ion penetration, and the water permeability of concrete were measured and presented. Test results indicate that except for the concretes at early ages, the mechanical properties, bond strength, and the durability-related chloride-ion permeability and water permeability of concrete containing high volume (60% cement replacement) fly ash were obviously superior to the concrete without fly ash at later ages of beyond 56 days. The enhanced bond strength for the high volume fly-ash concrete either with or without steel confinement is a significant finding which might be valuable for the structural application.

Key Words
bond strength; durability; high volume fly ash concrete; mechanical properties

Address
Chung-Hao Wu: Department of Civil Engineering, Chung Yuan Christian University, No. 200 Chung Pei Road, Chung Li Dist., Taoyuan City 320, Taiwan
Chien-Jung Chen: Architecture and Building Research Institute, Ministry of the Interior, 13F., No.200, Sec. 3, Beisin Rd., Sindian District,New Taipei City 23143, Taiwan
Yu-Feng Lin: Department of Civil Engineering, Chienkuo Technology University, No.1, Chiehshou North Road, Changhua City 500, Taiwan
Shu-Ken Lin: Department of Civil Engineering, National Chung Hsing University, No. 145 Xingda Rd., South Dist., Taichung City 402, Taiwan

Abstract
Reinforced concrete vertical silos are universal structures that store large amounts of granular materials. Due to the asymmetric structure, heavy load, uneven storage material distribution, and the difference between the storage volume and the storage material bulk density, the corresponding earthquake is very complicated. Some scholars have proposed the calculation method of horizontal forces on reinforced concrete vertical silos under the action of earthquakes. Without considering the effect of torsional effect, this article aims to reveal the expansion factor of the silo group considering the torsional effect through experiments. Through two-way seismic simulation shaking table tests on reinforced concrete column-supported group silo structures, the basic dynamic characteristics of the structure under earthquake are obtained. Taking into account the torsional response, the structure has three types of storage: empty, half and full. A comprehensive analysis of the internal force conditions under the material conditions shows that: the different positions of the group bin model are different, the side bin displacement produces a displacement difference, and a torsional effect occurs; as the mass of the material increases, the structure

Key Words
flat torsional vibration; group silos; seismic response; shaking table test; storage materials

Address
Xuesen Li, Yonggang Ding and Qikeng Xu: School of Civil Engineering, Henan University of Technology, Zhengzhou 450001, China

Abstract
This paper presents an experimental study exploring impact resistant properties of Kagome truss reinforced composite panels. Three types of panels with different materials and reinforcements, i.e., ultra-high-performance mortar, steel fiber, and Kagome truss, were designed and manufactured. High-velocity projectile impact tests were performed to investigate the impact response of panels with dimensions of 200 mmx200 mmx40 mm. The projectile used in the testing was a steel slug with a hemispherical front; the impact energy was 1 557 J. Test results showed that the Kagome truss reinforcement was effective at improving the impact resistance of panels in terms of failure patterns, damaged area, and mass loss. Synergy effects of a combination of Kagome truss and fiber reinforcements for the improvement of impact resistance capacity of ultra-high-performance mortar were also observed.

Key Words
composite; impact resistance; Kagome truss; projectile impact

Address
Jeong-Il Choi: Biohousing Research Center, Chonnam National University, Gwangju 61186, Republic of Korea
Se-Eon Park: Department of Architecture and Civil Engineering, Chonnam National University, Gwangju 61186, Republic of Korea
Sang-Kyu Lee: Department of Architecture and Civil Engineering, Chonnam National University, Gwangju 61186, Republic of Korea
Jae-Seung Hwang: Department of Architecture and Civil Engineering, Chonnam National University, Gwangju 61186, Republic of Korea; School of Architecture, Chonnam National University, Gwangju 61186, Republic of Korea
Bang Yeon Lee: Department of Architecture and Civil Engineering, Chonnam National University, Gwangju 61186, Republic of Korea; School of Architecture, Chonnam National University, Gwangju 61186, Republic of Korea

Abstract
The existing method to improve the coordination performance of the inner and outer parts of concrete-encased concrete-filled steel tube (CFST) composite columns by increasing the volume-stirrup ratio causes difficulties in construction due to over-dense stirrups. Thus, this paper proposes an open polygonal composite stirrup with high strength and high ductility CRB600H reinforced rebar, and seventeen specimens were constructed, and their axial compressive performance was tested. The main parameters considered were the volume-stirrup ratio, the steel tube size, the stirrup type and the stirrup strength. The test results indicated: For the specimens restrained by open octagonal composite stirrups, compared with the specimen of 0.5% volume-stirrup ratio, the compressive bearing capacity increased by 14.6%, 15.7% and 21.5% for volume-stirrup ratio of 0.73%, 1.07% and 1.61%, respectively. For the specimens restrained by open composite rectangle stirrups, compared with the specimen of 0.79% volume-stirrup ratio, the compressive bearing capacity increased by 7.5%, 6.1%, and -1.4% for volume-stirrup ratio of 1.12%, 1.58% and 2.24%, respectively. The restraint ability and the bearing capacity of the octagonal composite stirrup are better than other stirrup types. The specimens equipped with open polygonal composite stirrup not only had a higher ductility than those with the traditional closed-loop stirrup, but they also had a higher axial bearing capacity than those with an HPB300 strength grades stirrup. Therefore, the open composite stirrup can be used in practical engineering. A new calculation method was proposed based on the stress-strain models for confined concrete under different restrain conditions, and the predicted value was close to the experimental value.

Key Words
axial compression; CRB600H; composite column; concrete-filled steel tube; open polygonal composite stirrup

Address
Xiaojun Ke: College of Civil Engineering and Architecture, Guangxi University, Nanning 530004, China; Key Laboratory of Disaster Prevention and Structural Safety of Ministry of Education, Guangxi University, Nanning 530004, China
Wen Ding: College of Civil Engineering and Architecture, Guangxi University, Nanning 530004, China
Dingguo Liao: College of Civil Engineering and Architecture, Guangxi University, Nanning 530004, China

Abstract
Roller compacted concrete (RCC) used in the island reef airport runway will be subjected to the coupling actions of the fatigue impacts and the salt spray cycles, which will accelerate the deterioration of runway concrete and even threaten the flight safety. A cyclic impact testing machine and a climatic chamber were used to simulate the low-velocity fatigue impact and the salt spray cycles, respectively. The physical properties, the microstructures and the porosity of RCC were investigated. The results show the flexural strength firstly increases and then decreases with the increase of the fatigue impacts and the salt spray cycles. However, the decrease in the flexural strength is significantly earlier than the compressive strength of RCC only subjected to the salt spray cycles. The chlorine, sulfur and magnesium elements significantly increase in the pores of RCC subjected to 30000 fatigue impacts and 300 salt spray cycles, which causes the decrease in the porosity of RCC. The coupling effects of the fatigue impacts and the salt spray cycles in the later period accelerates the deterioration of RCC.

Key Words
damage; fatigue impacts; roller compacted concrete (RCC); salt spray cycles

Address
Longxin Gao: School of Transportation Science and Engineering, Beihang University, Beijing, China
Yong Lai: China Airport Construction Group Co.,Ltd., Beijing, China
Huigui Zhang: School of Transportation Science and Engineering, Beihang University, Beijing, China
Jingsong Zhang: School of Transportation Science and Engineering, Beihang University, Beijing, China
Wuman Zhang: School of Transportation Science and Engineering, Beihang University, Beijing, China

Abstract
The overuse level of cement for civil industry has several undesirable social and ecological consequences. Substitution of cement with industrial wastes, called by-products, such as fly ash, ground granulated blast furnace slag, silica fume, metakaoline, rice husk ash, etc. as the mineral admixtures offers various advantages such as technical, economical and environmental which are very important in the era of sustainability in construction industry. The paper presents the experimental investigations for assessing the mechanical properties of the concrete made using the Pozzolanic waste materials (supplementary cementitious materials) such as fly ash and silica fume as the cement replacing materials. These materials were used in eight trial mixes with varying amount of ordinary Portland cement. These SCMs were kept in equal proportions in all the eight trial mixes. The chemical admixture (High Range Water Reducing Admixture) was also added to improve the workability of concrete. The compressive strengths for 7, 28, 40 and 90 days curing were evaluated whereas the flexural and tensile strengths corresponding to 7, 28 and 40 days curing were evaluated. The study corroborates that the Pozzolanic materials used in the present investigation as partial replacement for cement can render the sustainable concrete which can be used in the rigid pavement construction.

Key Words
concrete; fly ash; rigid pavement; pozzolanic materials; silica fume; strength

Address
Hemant Sharad Chore: Department of Civil Engineering, Dr. B.R. Ambedkar National Institute of Technology, G.T. Road Bye Pass, Jalandhar-144011, India
Mrunal Prashant Joshi: Department of Civil Engineering, Datta Meghe College of Engineering, Airoli, Navi Mumbai-400708, India

Abstract
In the era of building engineering the intensification of Self Compacting Concrete (SCC) is world-shattering magnetism. It has lot of rewards over ordinary concrete i.e., enrichment in production, cutback in manpower, brilliant retort to load and vibration along with improved durability. In the present study, the mechanical strength of CM-2 (SCC containing 10% of rice husk ash (RHA) as cement replacement and 600 grams of glass fibers per cubic meter) was investigated at various dosages of cement replacement by fly ash (FA) and GGBS. A total of 17 SCC mixtures including two control SCC mixtures (CM-1 and CM-2) were developed for investigating fresh and hardened properties in which, ten ternary cementitious blends of SCC by blending OPC+RHA+FA, OPC+RHA+GGBS and five quaternary cementitious blends (OPC+RHA+FA+GGBS) at different replacement dosages of FA and GGBS were developed with reference to CM-2. For constant water-cement ratio (0.42) and dosage of SP (2.5%), the addition of glass fibers (600 grams/m3) in CM-1 i.e., CM-2 shows lower workability but higher mechanical strength. While fly ash based ternary blends (OPC+RHA+FA) show better workability but lower mechanical strength as FA content increases in comparison to GGBS based ternary blends (OPC+RHA+GGBS) on increasing GGBS content. The pattern for mixtures appeared to exhibit higher workablity as that of the concentration of FA+GGBS rises in quaternary blends (OPC+RHA+FA+GGBS). A decrease in compressive strength at 7-days was noticed with an increase in the percentage of FA and GGBS as cement replacement in ternary and quaternary blended mixtures with respect to CM-2. The highest 28-days compressive strength (41.92 MPa) was observed for mix QM-3 and the lowest (33.18 MPa) for mix QM-5.

Key Words
fly ash (FA); glass fibers; ground granulated blast furnace slag (GGBS); mechanical strength; self compacting concrete (SCC)

Address
Ashish Kumar: Department of Civil Engineering, Samalkha Group of Institutions, Panipat, Haryana, India
Abhinav Singh: Department of Civil Engineering, Swami Vivekanand Subharti University, Meerut, Uttar Pradesh, India
Kapil Bhutani: Department of Civil Engineering, Samalkha Group of Institutions, Panipat, Haryana, India

Abstract
In recent years, nano-reinforcing materials are widely utilized in cement composites due to their unique multifunctional properties. This study incorporated multi-walled carbon nanotubes (MWCNTs) into the cementitious composites at ratios of 0.1%, 0.3%, and 0.5%, and investigated their influence on the flowability, mechanical strength, and hydration heat properties. The addition of MWCNTs enhanced the compressive and split tensile strengths approximately by 18-51%. In the semi-adiabatic temperature rise test, the internal hydration heat of the composites reduced by 5%, 9%, and 12% with the increase of MWCNTs in 0.1%, 0.3%, and 0.5%. This study further performed hydration heat analysis and estimated the adiabatic temperature rise, thermal stress, and thermal crack index. The internal hydration heat of the concrete decreased by 5%, 10%, and 13% with the increase of MWCNTs. The thermal stress of the concrete decreased with increase in the addition of MWCNTs, and the obtained temperature crack index was effective in controlling the thermal cracks.

Key Words
carbon nanotubes; hydration heat; semi-adiabatic temperature rise test; thermal crack; thermal stress

Address
Sung-Jin Ha: Office of Water Works, Yeongcheon City Hall, Yeongcheon 38819, Korea
Rajagopalan Sam Rajadurai: Department of Civil Engineering, Daegu University, Gyeongsan 38453, Korea
Su-Tae Kang: Department of Civil Engineering, Daegu University, Gyeongsan 38453, Korea


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