Abstract
This paper reports on the results of a parametric study, which examines the effects of varying aspect ratios on the dynamic response of cylindrical silos directly supported on the ground under earthquake loading. Previous research has shown that numerical models can provide considerably realistic simulations when it comes to the behavior of silos by using correct boundary conditions, appropriate element types and material models. To this end, a three dimensional numerical model, taking into account the bulk material-silo wall interaction, was produced by the ANSYS commercial program, which is in turn based on the finite element method. The results obtained from the numerical analysis are discussed comparatively in terms of dynamic material pressure, horizontal displacement, equivalent base shear force and equivalent bending moment responses for considered aspect ratios. The effects experienced because of the slenderness of the silo in regards to the seismic response were evaluated along with the effectiveness of the classification system proposed by Eurocode in evaluating the loads on the vertical walls. Results clearly show that slenderness directly affects the seismic response of such structures especially in terms of behavior and the magnitude of the responses. Furthermore the aspect ratio value of 2.0, given as a behavioral changing limit in the technical literature, can be used as a valid limit for seismic behavior.
Address
Aysegul Durmus Demir: Department of Civil Engineering, Karadeniz Technical University, 61080 Trabzon, Turkey
Ramazan Livaoglu: Department of Civil Engineering, Uludağ University, 16059 Bursa, Turkey
Abstract
The present study is focused on the mechanical and durability properties of ternary blended cement concrete mix of different grades 30 MPa, 50 MPa and 70 MPa. Three mineral admixtures (fly ash, silica fume and lime sludge) were used as a partial replacement of cement in the preparation of blended concrete mix. The durability of ternary blended cement concrete mix was studied by exposing it to acids HCl and H2SO4 at 5% concentration. Acid mass loss factors (AMLF), acid strength loss factor (ASLF) and acid durability factor (ADF) were determined, and the results were compared with the control mix. Chloride ions penetration was investigated by conducting rapid chlorination penetration test and accelerated corrosion penetration test on control mix and ternary blended cement concrete. From the results, it was evident that the usage of these mineral admixtures is having a beneficiary role on the strength as well as durability properties. The results inferred that the utilization of these materials as a partial replacement of cement have significantly enhanced the compressive strength of blended concrete mix in 30 MPa, 50 MPa and 70 MPa by 42.95%, 32.48% and 22.79%. The blended concrete mix shown greater resistance to acid attack compared to control mix concrete. Chloride ion ingress of the blended cement concrete mix was low compared to control mix implying the beneficiary role of mineral admixtures.
Abstract
Self-compacting concretes (SCC) are highly fluid concrete which can flow without any vibration. Their composition
requires a large quantity of fines to limit the risk of bleeding and segregation. The use of crushed sand rich in limestone fines could be an adequate solution for both economic and environmental reasons. This paper investigates the influence of quarry limestone fines from manufactured crushed sand on rheological, mechanical and durability properties of SCC. For this purpose, five mixtures of SCC with different limestone fines content as substitution of crushed sand (0, 5, 10, 15 and 20%) were prepared
at constant water-to-cement ratio of 0.40 and 490 kg/m3 of cement content. Fresh SCC mixtures were tested by slump flow test, V-funnel flow time test, L-box height ratio, segregation resistance and rheological test using a rheometer. Compressive and flexural strengths of SCC mixtures were evaluated at 28 days. Regarding durability properties, total porosity, capillary water absorption and chloride-ion migration were studied at 180 days. For the two test modes in fresh state, the results indicated
compatibility between slump flow/yield stress (t0) and V-funnel flow time/plastic viscosity (u). Increasing the substitution level of limestone fines in SCC mixtures, contributes to the decrease of the slump flow and the yield stress. All SCC mixtures investigated achieved adequate filling, adequate passing ability and exhibit no segregation. Moreover, the inclusion of limestone
fines as crushed sand substitution reduces the capillary water absorption, chloride-ion migration and consequently enhances the durability performance.
Key Words
crushed sand; limestone fines; self-compacting concrete; rheological properties; mechanical properties;
water permeability; chloride-ion migration
Address
Smain Benyamina, Belkacem Menadi, Said Kenai: Geomaterials Laboratory, Department of Civil Engineering, University of Blida 1, Algeria
Siham Kamali Bernard: Laboratory of Civil Engineering and Mechanical Engineering, National Institute of Applied Sciences, Rennes 35708, France
Abstract
In this paper, the workability and static stability were evaluated using a proposed test method.Workability and static stability represent a key property of self-compacting concrete (SCC) in fresh state. A number of standardized test methods were developed to assess these properties. However, no accelerated test method reliably predicts both workability and static stability of SCC. In the present work, a modified K-slump test method was developed to evaluate workability and static stability of SCC. In order to take implicit mixture variations of SCC constituents that can affect fresh SCC properties, a central composite design was adopted to highlight the effect of gravel to sand ratio (G/S), gravel 3/8 to gravel 8/15 ratio (G1/G2), water to cement ratio (W/C), marble powder to cement ratio (MP/C) and superplasticizer content (SP) on workability measured with slump and flow time (T50) tests and static stability measured with sieve stability test (Pi), segregation test index (SSI), Penetration test (Pd) and the proposed K-slump test (Km). The obtained results show that G/S ratio close to 1 and G1/G2 ratio close to 60% can be considered as optimal values to achieve a good workability while ensuring a sufficient static stability of SCC. Acceptable
relationships were obtained between Slump flow, Pi, Pd and Km. Results show that the proposed K-slump test allow to assess
both workability and static stability of fresh SCC mixtures.
Abstract
The possibility of using a combination of mineral admixtures as a replacement for cement may reduce the CO2
emission which causes global warming and climatic changes on the environment. By using the combination of different byproducts from various industries, for replacing cement in concrete leads to saving in energy and natural resources. In this article, an attempt has been made to study the mechanical and water absorption properties of concrete incorporated with combination of Fly ash (FA), Alccofine (ALC) and Collodial Nano Silica (CNS) at 7, 28 and 56 days curing period. Cement has been partially replaced by combination of FA at 25%, ALC at 10% and CNS at 0.5%, 1%, 2% and 3% with water cement ratio of 0.43. The result indicates that the incorporation of combination of FA, ALC and CNS can be very effective in improvement of mechanical and water absorption properties of concrete. The Mix with a combination of 25% FA, 10% ALC and 1% CNS is most effective in improvement of mechanical and water absorption properties as compared with all other mixes.
Key Words
ash; Alccofine; Collodial Nano Silica; tetranary blended concrete
Address
Avuthu Narender Reddy : Department of Structural and Geo-Technical Engineering, School of Civil Engineering (SCE), Vellore Institute of Technology (VIT-Vellore), Vellore, Tamil Nadu, 632014, India
Abstract
When designing reinforced concrete (RC) members, the rebar is assumed to resist all tensile forces, but the resistance of the concrete in the tension area is neglected. However, concrete can also resist tensile forces and increase the tensile stiffness of RC members, which is called the tension stiffening effect (TSE). Therefore, this study assessed the TSE, particularly after yielding of the steel bars and the effects of the steel ratio on the TSE. For this purpose, RC member specimens with steel ratios of 2.87%, 0.99%, and 0.59% were fabricated for uniaxial tensile tests. A vision-based non-contact measurement system was used to measure the behavior of the specimens. The cracks on the specimen at the stabilized cracking stage and the fracture stage were measured with the image analysis method. The results show that the number of cracks increases as the steel ratio increases. The reductions of the limit state and fracture strains were dependent on the ratio of the rebar. As the steel ratio decreased, the strain after yielding of the RC members significantly decreased. Therefore, the overall ductility of the RC member is reduced with decreasing steel ratio. The yielding plateau and ultimate load of the RC members obtained from the proposed equations showed very good agreement with those of the experiments. Finally, the image analysis method was possible to allow flexibility in expand the measurement points and targets to determine the strains and crack widths of the specimens.
Key Words
tension stiffening; post-yielding; reinforced concrete; image analysis; steel ratio
Address
Jong-Han Lee: Department of Civil Engineering, Inha University, Incheon, 22212, Republic of Korea
Chi-Young Jung: Seismic Simulation Test Center, Pusan National University, Yangsan, 50612, Republic of Korea
Tae-Ryeon Woo, Jin-Hwan Cheung: Department of Civil Engineering, Pusan National University, Busan, 46241, Republic of Korea
Abstract
Heterogeneous photocatalysis is developed rapidly in the field of engineering of environmental. It has a good potential to tackle with the enhancing traffic pollution. Adding photocatalyst to usual building materials such as cement and concrete makes friendly environmental materials against the air pollution. TiO2 nanoparticles are a good item for concrete structures for diminishing the air polluting affect by gasses of exhaust. In specific, the transformation of NOx to NO3- is studied and the interaction of TiO2 nanoparticles and concrete is investigated here by experimental test. This paper presents an overview of the principle of photocatalysis and the application in combination with cement, as well as the results of the laboratory research, especially towards air purifying action. In addition, by the analytical models, the influence of TiO2 nanoparticles is studied on the stiffness of the concrete. The Results show that TiO2 nanoparticles have significant effect on the reduction of
environmental pollution and increase of stiffness in the concrete structures
Key Words
TiO2 nanoparticles; concrete structures; environmental pollution; stiffness
Address
Javad Tabatabaei and Leila Gorji: Department of petroleum and geology, Meymeh branch, Islamic Azad University, Meymeh, Iran
