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CONTENTS
Volume 4, Number 4, December 2016
 

Abstract
The major problem of a coal combustion-based power plant is that it creates large quantity of solid wastes. So, to achieve the gainful use of waste materials and to avoid other environmental problems, this study was undertaken. The quantity of coal ash by-products, particularly coal fly ash and coal bottom ash has been increasing from the coal power plants around the world. The other objective of this study was to explore the possibility of utilization of coal ash in the production of ash bricks. In 15 different mixes, Mix Designation M-1 to M-15, the varying percentages of lime and gypsum were used and sand was replaced with coal bottom ash. Further, it has been noticed that the water absorption and compressive strength of mix M-15 is 13.36% and 7.85 MPa which is better than the conventional bricks. The test results of this investigation show that the prism strength of coal ash masonry prisms was more than that of the conventional bricks.

Key Words
coal fly ash; coal bottom ash; sand; lime; gypsum; compressive strength; water absorption; masonry prism

Address
Surender K. Verma, Joginder Singh: Department of Civil Engineering, PEC University Technology, Chandigarh 160-012, India
Deepankar K. Ashish:
1) Department of Civil Engineering, PEC University Technology, Chandigarh 160-012, India
2) Maharaja Agrasen Institute of Technology, Maharaja Agrasen University, Baddi 174-103, India

Abstract
This research study focuses on utilizing sandstone which is overburden waste rock in coal mines to use in concrete as a replacement of fine aggregate. Physical properties of sandstone like water absorption, moisture content, fineness modulus etc., were found to be similar to conventional fine aggregate. Scanning Electron Microscope (SEM) analysis was carried out for analysing elemental composition of sandstone. There was no sulphur content in sandstone which is a good sign to carry the replacement. Fine aggregate was replaced with sandstone at 25%, 50%, 75% and 100% by volume and moulds of concrete cubes and cylinders were prepared. Compressive strength of concrete cubes was tested after 3, 7 and 28 days and split tensile & flexural strength was determined after 28 days. The strength was found to be increasing marginally with increase in sandstone content. Fine aggregate that was replaced by 100% sandstone gave highest strength among all the replacements for the compressive, split tensile and flexural strengths. Though increase in strength was marginal, still sandstone can be an effective replacement for sand in order to save the natural resource and utilize the waste sandstone.

Key Words
coal mine overburden; waste rock; sandstone; fine aggregate; concrete; strength

Address
K. Ram Chandar, B.C. Gayana: Department of Mining Engineering, NITK, Surathkal, India
V. Sainath: NITK, Surathkal, India

Abstract
Concrete continues to be the most consumed construction material in the world, only next to water. Due to rapid increase in construction activities, Construction and Demolition (C&D) waste constitutes a major portion of total solid waste production in the world. It is important to assess the amount of C&D waste being generated and analyse the practices needed to handle this waste from the point of waste utilization, management and disposal addressing the sustainability aspects. The depleting natural resources in the current scenario warrants research to examine viable alternative means, modes and methods for sustainable construction. This study reports processing Recycled Coarse Aggregates (RCA) using a rod mill, for the first time. Parameters such as amount of C&D waste for processing, nature of charge and duration of processing time have been optimized for obtaining good quality RCA. Performance of RCA based concrete and performance enhancement techniques of 50% RCA based concrete are discussed in this paper.

Key Words
compressive strength; demolished concrete; recycled coarse aggregate; performance; performance enhancement

Address
Subhash C. Yaragal, Dumpati C. Teja and Mohammed Shaffi: Department of Civil Engineering, National Institute of Technology, Surathkal, Karnataka, India

Abstract
Several types of industrial byproducts are generated. With increased environmental awareness and its potential hazardous effects, the utilization of industrial byproducts in concrete has become an attractive alternative to their disposal. One such by-product is ground granulated blast furnace slag (GGBS), which is a byproduct of the smelting process carried out in the iron and steel industry. The GGBS is very effective in the design and development of high-strength and high-performance concrete. This paper reviews the effect of GGBS on the workability, porosity, compressive strength, splitting tensile strength, and flexural strength of concrete.

Key Words
compressive strength; flexural strength; split tensile strength; porosity; workability

Address
Rakesh Kumar Patra: Department of Civil Engineering, National Institute of Science and Technology, Palur Hills, Brahmapur, Odisha, India
Bibhuti Bhusan Mukharjee: Department of Civil Engineering, Veer Surendra Sai University of Technology, Burla, Sambalpur, Odisha, India


Abstract
Methods for designing the post-tensioned anchorage zones at ultimate limit state has been specified in current design codes based on strut-and-tie models (STM). However, it is still not clear how to estimate the serviceability behavior of the anchorage zones. The serviceability is just indirectly taken into account by means of the reasonable reinforcement detailing. To address this issue, this paper is devoted to developing a modified strut-and-tie model (MSTM) to predict the behavior of concentric anchorage zones throughout the loading process. The principle of stationary complementary energy is introduced into STM at each load step to satisfy the compatibility condition and generate the unique MSTM. The structural behavior of anchorage zones can be achieved based on MSTM from loading to failure. Simplified formulas have been proposed to estimate the first cracking load, bearing capacity and maximum crack width with the consideration of the details of reinforcement bursting bars. The proposed model provides a definite method to control the bursting crack width in concentric anchorage zones. Four specimens with different bearing plate ratios have been designed and tested to validate the proposed method.

Key Words
maximum crack width; modified strut-and-tie model; post-tensioned anchorage zones; serviceability behavior

Address
(1) Shangda Chen:
School of Civil Engineering, Changchun University of Architecture and Civil Engineering, Changchun, Jilin, 130607, China;
(2) Linyun Zhou:
School of Science, Nanjing University of Science and Technology, Nanjing 210096, China.

Abstract
Porous materials such as concrete could be subjected to aggressive ions transport. Durability of cement paste is extremely depended on water and ions penetration into its interior sections. These ions transport could lead different damages depending on reactivity of ions, their concentrations and diffusion coefficients. In this paper, chloride diffusion process in cement hydrates is simulated at atomistic scale using molecular dynamics. Most important phase of cement hydrates is calcium silicate hydrate (C-S-H). Tobermorite, one of the most famous crystal analogues of C-S-H, is used as substrate in the simulation model. To conduct simulation, a nanopore is considered in the middle of simulation cell to place water molecules and aggressive ions. Different chloride salts are considered in models to find out which one is better for calculation of the transport properties. Diffusion coefficients of water molecules and chloride ions are calculated and validated with existing analytical and experimental works. There are relatively good agreements among simulation outputs and experimental results.

Key Words
molecular dynamics; C-S-H; cement; diffusion; durability; porosity; chloride ion; water molecule

Address
Behnam Zehtab and Amir Tarighat: Department of Civil Engineering, Shahid Rajaee Teacher Training University, Tehran, Iran

Abstract
In most cases strengthening reinforced concrete columns exposed to high strain rate is to be expected especially within weak designed structures. A special type of loading is instantaneous loading. Rapid loading can be observed in structural columns exposed to axial loads (e.g., caused by the weight of the upper floors during a vertical earthquake and loads caused by damage and collapse of upper floors and pillars of bridges).Subsequently, this study examines the behavior of reinforced concrete columns under rapid loading so as to understand patterns of failure mechanism, failure capacity and strain rate using finite element code. And examines the behavior of reinforced concrete columns at different support conditions and various loading rate, where the concrete columns were reinforced using various counts of FRP (Fiber Reinforcement Polymer) layers with different lengths. The results were compared against other experimental outcomes and the CEB-FIP formula code for considering the dynamic strength increasing factor for concrete materials. This study reveals that the finite element behavior and failure mode, where the results show that the bearing capacity increased with increasing the loading rate. CFRP layers increased the bearing capacity by 20% and also increased the strain capacity by 50% through confining the concrete.

Key Words
reinforced concrete column; failure; rapid loading; axial load; CFRP

Address
Soheil Esfandiari: Department of Civil Engineering, College of Engineering, Sistan and Balouchestan University, Daneshgah Street-Zahedan, Iran
Javad Esfandiari: Department of Civil Engineering, College of Engineering, Kermanshah Branch, Islamic Azad University Kermanshah, Iran

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