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CONTENTS
Volume 10, Number 3, September 2020
 

Abstract
An analytical model is developed in this paper to predict the shear capacity of reinforced concrete (RC) columns with corroded transverse reinforcements. The shear strength model for corroded RC columns is proposed based on modifying the existing strut-and-tie model, which considers the deformational compatibility between truss and arch mechanisms. The contributions to the shear strength from both truss and arch mechanisms are incorporated in the proposed model. The effects of corrosion level of transverse reinforcements are considered in the proposed model through the minimum residual cross-sectional area of transverse reinforcements and the reduction of concrete compressive strength for the cover area. The shear strengths calculated from the developed model are compared with the experimental results from Vu\'s study (2017), which consisted of RC columns with corroded transverse reinforcements showing shear failure under the cyclic loading. The comparison results indicate satisfactory correlations. Parametric studies are conducted based on the developed shear strength model to explore the effects of column axial loading, aspect ratios, transverse reinforcements and the corrosion levels in transverse reinforcements to the shear strength of RC columns with corroded transverse reinforcements.

Key Words
reinforced concrete; column; corrosion; shear strength; seismic

Address
Cao Thanh Ngoc Tran: Department of Civil Engineering, International University, Ho Chi Minh City, Vietnam; Vietnam National University, Ho Chi Minh City, Vietnam
Xuan Huy Nguyen: Faculty of Construction Engineering, University of Transport and Communications, Vietnam
Huy Cuong Nguyen: Faculty of Construction Engineering, University of Transport and Communications, Vietnam
Ngoc Son Vu: Department of Structural Mechanics, National University of Civil Engineering, Vietnam

Abstract
This study investigates the behavior of ultra-high-performance fiber-reinforced concrete (UHPFRC) with hybrid macro-micro steel and macro steel-polypropylene (PP) fibers. Compression, direct and indirect tension tests were carried out on cubic and cylindrical, dogbone and prismatic specimens, respectively. Three types of macro steel fibers, i.e., round crimped (RC), crimped (C), and hooked (H) were combined with micro steel (MS) and PP fibers in overall ratios of 2% by volume. Additionally, numerical analyses were performed to validate the test results. Parameters studied included, fracture energy, tensile strength, compressive strength, flexural strength, and residual strength. Tests showed that replacing PP fibers with MS significantly improves all parameters particularly flexural strength (17.38 MPa compared to 37.71 MPa). Additionally, the adopted numerical approach successfully captured the flexural load-deflection response of experimental beams. Lastly, the proposed regression model for the flexural load-deflection curve compared very well with experimental results, as evidenced by its coefficient of correlation (R2) of over 0.90.

Key Words
fiber reinforced concrete; high/ultra-high performance concrete; steel fiber reinforced concrete (SFRC); hybrid reinforcement; modeling

Address
Behrooz Dadmand: Department of Civil Engineering, Razi University, Kermanshah, Iran
Masoud Pourbaba: Department of Civil Engineering, Maragheh Branch, Islamic Azad University, Maragheh, Iran
Hamed Sadaghian: Department of Civil Engineering, University of Tabriz, Tabriz, Iran
Amir Mirmiran: Department of Civil Engineering, University of Texas at Tyler, Tyler, TX, USA

Abstract
In this paper, 18 single-sized pervious concrete mixtures were tested. The mixtures were prepared by altering: the amount and type of binder, type of aggregate, and the method of compaction. Concrete was compacted in layers in one of five different consolidation techniques: with standard tamping rod, wooden lath, concrete cylinder, or vibration of 12 and 40 s. Tests carried out on the specimens were: slump, density, porosity, coefficients of permeability, compressive strength and splitting strength. The relationships between porosity-density and porosity-strength were established. Two mixtures were selected for the preparation of test slabs on different subgrades and their permeability was tested according to ASTM C 1701-09 Standard. By comparing laboratory and field tests of permeability, it was concluded that the subgrade affects the test results. Measurements on the test slabs were repeated after 1 and 2 years of installation.

Key Words
pervious concrete; permeability; method of compaction; mechanical properties; test slabs

Address
Sandra Juradin, Nives Ostojic-Skomrlj, Ivan Brnas and Marina Prolic: Faculty of Civil Engineering, Architecture and Geodesy, University of Split, Matice hrvatske 15, 21000 Split, Croatia

Abstract
To reduce the CO2 emissions associated with the manufacture of portland cement (PC), an efficient alternative like an alkali-activated binder (AAB) is the requirement of the industry. To promote the use of AAB in construction activities, a practically implementable mix proportion is required. Owing to the several raw ingredients of AAB concrete and their associated uncertainties, partial replacement of PC by AAB may be adopted instead of complete replacement as per industrial requirements. Hence, the present study aims to determine an optimal proportion for partial replacement of PC with AAB and recommend a technique for it based on site conditions. Three modes of partial replacement are followed: combining all the dry ingredients for AAB and PC followed by the addition of the requisite liquids (PAM); combining the PC and the AAB concrete in two horizontal layers (PAH); and two vertical layers (PAV). 28-day old specimens are exposed to 10% v/v solutions of HCl, H2SO4, and HNO3 to evaluate changes in mechanical, physical, and microstructural characteristics through compressive strength, corrosion depth, and microscopy. Based on deterioration in strength and integrity, PAH or PAV can be adopted in absence of acid attack, whereas PAM is recommended in presence of acid attack.

Key Words
alkali-activated binder; mixing proportion; acid resistance; microstructure

Address
Kruthi K. Ramagiri: Department of Civil Engineering, BITS Pilani-Hyderabad Campus, Telangana, India
Swaraj Patil: Department of Civil Engineering, Politecnico di Milano, Italy
Harsh Mundra: Walter P Moore LLC, Houston, Texas, USA
Arkamitra Kar: Department of Civil Engineering, BITS Pilani-Hyderabad Campus, Telangana, India

Abstract
Past research efforts already established geopolymer as an environment-friendly alternative binder system for ordinary Portland cement (OPC) and recycled aggregate is also one of the promising alternative for natural aggregates. In this study, an effort was made to produce eco-friendly mortar mixes using geopolymer as binder and recycled fine aggregate (RFA) partially and study the resistance ability of these mortar mixes against the aggressive environments. To form the geopolymer binder, 70% fly ash, 30% ground granulated blast furnace slag (GGBS) and alkaline solution comprising of sodium silicate solution and 14M sodium hydroxide solution with a ratio of 1.5 were used. The ratio of alkaline liquid to binder (AL/B) was also considered as 0.4 and 0.6. In order to determine the resistance ability against aggressive environmental conditions, acid attack test, sulphate attack test and rapid chloride permeability test were conducted. Change in mass, change in compressive strength of the specimens after the immersion in acid/sulphate solution for a period of 28, 56, 90 and 120 days has been presented and discussed in this study. Results indicated that the incorporation of RFA leads to the reduction in compressive strength. Even though strength reduction was observed, eco-friendly mortar mixes containing geopolymer as binder and RFA as fine aggregate performed better when it was produced with AL/B ratio of 0.6.

Key Words
fly ash; ground granulated blast furnace slag; geopolymer; recycled fine aggregate; eco-friendly mortar; compressive strength; durability

Address
Suman Saha: Department of Civil Engineering, National Institute of Technology Calicut, Kozhikode, Kerala-673601, India
Chandrasekaran Rajasekaran, Prateek Gupta: Department of Civil Engineering, National Institute of Technology Karnataka, Surathkal, Mangalore, Karnataka-575025, India

Abstract
In this paper the possibility of using different regression models to predict the mechanical properties of limestone concrete after exposure to high temperatures, based on the results of non-destructive techniques, that could be easily used in-situ, is discussed. Extensive experimental work was carried out on limestone concrete mixtures, that differed in the water to cement (w/c) ratio, the type of cement and the quantity of superplasticizer added. After standard curing, the specimens were exposed to various high temperature levels, i.e., 200oC, 400oC, 600oC or 800oC. Before heating, the reference mechanical properties of the concrete were determined at ambient temperature. After the heating process, the specimens were cooled naturally to ambient temperature and tested using non-destructive techniques. Among the mechanical properties of the specimens after heating, known also as the residual mechanical properties, the residual modulus of elasticity, compressive and flexural strengths were determined. The results show that residual modulus of elasticity, compressive and flexural strengths can be reliably predicted using an artificial neural network approach based on ultrasonic pulse velocity, residual surface strength, some mixture parameters and maximal temperature reached in concrete during heating.

Key Words
residual mechanical properties; compressive strength; artificial neural network; non-destructive testing techniques; fire behavior; concrete

Address
Urska Blumauer, Tomaz Hozjan : Faculty of Civil and Geodetic Engineering, University of Ljubljana, Jamova 2, SI-1115 Ljubljana, Slovenia
Gregor Trtnik: Building Materials Institute, IGMAT d.d., Polje 351c, SI-1000 Ljubljana, Slovenia

Abstract
The aim of this study is to investigate the flexural performance of hybrid fiber reinforced self-compacting concrete (HFRSCC) having different ratio of micro and macro steel fiber. A total of five mixtures are prepared. In all mixtures, the sum of the steel fiber content is 1% and also water/binder ratio is kept constant. The amount of high range water reducer admixture (HRWRA) is arranged to satisfy the workability criteria of self-compacting concrete. Four-point bending test is carried out to analyze the flexural performance of the mixtures at 28 and 56 curing days. From the obtained load-deflection curves, the load carrying capacity, deflection and toughness values are investigated according to ASTM C1609, ASTM C1018 and JSCE standards. The mixtures containing higher ratio of macro steel fiber exhibit numerous micro-cracks and, thus, deflectionhardening response is observed. The mixture containing 1% micro steel fiber shows worst performance in the view of all flexural parameters. An improvement is observed in the aspect of toughness and load carrying capacity as the macro steel fiber content increases. The test results based on the standards are also compared taking account of abovementioned standards.

Key Words
hybrid fiber reinforced; self-compacting concrete; toughness; load carrying capacity; deflection

Address
Kazim Turk: Department of Civil Engineering, Engineering Faculty, Inonu University, Malatya, Turkey
Ceren Kina: Department of Civil Engineering, Faculty of Engineering and Natural Sciences, Malatya Turgut Ozal University, Malatya, Turkey
Erol Oztekin: Organized Industry Region Vocational High School, Construction Technology Program, Inonu University, Malatya, Turkey

Abstract
Quantifying the amount of damage of structures under earthquakes is an interesting issue that researchers have attended on and have presented some damage indices. Whereas a lot of damage indices have been introduced based on nonlinear dynamic analysis, computational effort, the calculus complicacy and time-consuming of this analysis are the main drawbacks to widespread use of these indices. The objective of this study is to quantify the damage of Shear Wall Reinforced Concrete Frames (SWRCFs) based on pushover analysis as a procedure that can reflect the behavior of structures from elastic to collapse. For this purpose, firstly, several SWRCFs are designed and the capacity spectrum of each one is achieved via pushover analysis. After that, the static damage indices of the designed frames are obtained. Then, nonlinear dynamic analyses are performed on these frames and the Park and Ang damage index as the basis damage criterion is achieved. Afterward, some relations are presented to predict the dynamic damage of these frames via pushover analysis. Eventually, to confirm the validity of the proposed relations, the values of Park and Ang damage index of three new SWRCFs are acquired once utilizing nonlinear dynamic analysis and again applying the introduced relations. Outcomes prove the validity of some presented damage indices.

Key Words
damage index; nonlinear dynamic analysis; pushover; shear wall; performance point

Address
Ali Reza Habibi: Department of Civil Engineering, Shahed University, Tehran, Iran
Mohammad Samadi: Department of Civil Engineering, Kurdistan University, Sanandaj, Iran
Mehdi Izadpanah: Department of Civil Engineering, Kermanshah University of Technology, Kermanshah, Iran


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