Abstract
After passing through a magnetic field, the physical quality of water improves, and magnetic water (MW) is produced. There are many investigations on the effects of magnetic field on water that shows MW properties like saturation and memory effect. This study investigates the fresh and hardened properties of concrete mixed with MW, which contains silica fume (SF) and superplasticizer (SP). The test variables included the magnetic field intensity for producing MW (three kinds of water), SF content replaced cement (0 and 10 percent), water-to-cementitious materials ratio (W/CM=0.25, 0.35 and 0.45) and curing time (7, 28 and 90 days). The results of this study show that MW had a positive impact on the workability and compressive strength of concrete. By rising the intensity of the magnetic field which was used for producing MW, its positive influence on both workability and compressive strength improved. MW had greater positive impacts on samples containing SP that did not have SF. Moreover, the best compressive strength improvements of concrete achieved as W/CM ratio decreased.
Key Words
magnetic water; silica fume; superplasticizer; concrete
Address
Moosa Mazloom and Sayed Mojtaba Miri: Department of Civil Engineering, Shahid Rajaee Teacher Training University, Tehran, Iran
Abstract
Cement kiln dust (CKD) is one of the most important waste materials in the cement industry. The large amount of this material, has encouraged researchers to propose new ways to recycle and reuse it. In this paper, effects of adding cement kiln dust to the ordinary Portland cement, on the physical and mechanical properties of ordinary and lightweight concrete were investigated. Results showed that concrete containing CKD, presents lower workability and modulus of elasticity; however, improvements in strength was observed by adding particular amounts of CKD. Eventually, it was found that adding 10% of cement weight CKD is the appropriate percentage for utilizing in manufacturing ordinary and lightweight concrete.
Address
Parham Shoaei: Department of Civil Engineering, Sharif University of Technology, Tehran, Azadi Avenue, Iran
Sina Zolfaghary: Department of Civil Engineering, K.N. Toosi University of Technology, Tehran, Mirdamad Blvd, Iran
Navid Jafari and Mehdi Dehestani: Department of Civil Engineering, Babol Noshirvani University of Technology, Babol, Shariati Street, Iran
Manouchehr Hejazi: Department of Civil Engineering, Amirkabir University of Technology, Tehran, Hafez Avenue, Iran
Abstract
The attack of environmental aggressive agents progressively reduces the structural reliability of buildings and infrastructures and, in the worst exposition conditions, may even lead to their collapse in the long period. A change in the material and sectional characteristics of a structural element, due to the environmental damaging effects, changes its mechanical behaviour and varies both the internal stress redistribution and the kinematics through which it reaches its ultimate state. To identify such a behaviour, the evolution of both the damaging process and its mechanical consequences have to be taken into account. This paper presents a computational approach for the analysis of reinforced and prestressed concrete elements under sustained loading conditions and subjected to given damaging scenarios. The effects of the diffusion of aggressive agents, of the onset and development of the corrosion state in the reinforcement and the corresponding mechanical response are studied. As known, the corrosion on the reinforcing bars influences the damaging rate in the cracking pattern evolution; hence, the damage development and the mechanical behaviours are considered as coupled phenomena.
The reliability of such an approach is validated in modelling the diffusion of the aggressive agents and the changes in the mechanical response of simple structural elements whose experimental behaviour is reported in Literature.
A second set of analyses studies the effects of the corrosion of the tendons of a P.C. beam and explores potentially unexpected structural responses caused by corrosion under different aggressive exposition. The role of the different types and of the different positions of the damaging agents is discussed. In particular, it is shown how the collapse mode of the beam may switch from flexural to shear type, in case corrosion is caused by a localized chloride attack in the shear span.
Key Words
corroded R.C. and P.C. beams; time-variant bending and shear capacity; carbonation; chloride attack; corrosion
Address
Pier Giorgio Malerba, Diego Ielmini and Giordano Gotti: Department of Civil and Environmental Engineering, Politecnico di Milano, Milano, Italy
Luca Sgambi: Faculty of Architecture, Architectural Engineering and Urbanism (LOCI), Université catholique de Louvain, Louvain-la-Neuve, Belgium
Abstract
In the present day scenario, concrete construction is rapidly becoming uneconomical and non sustainable practice, due to the scarcity of raw materials and environmental pollution caused by the manufacturing of cement. In this study an attempt has been made to propose recycled aggregates from demolition wastes as coarse aggregate in geopolymer concrete (GPC). Experimental investigations have been conducted to find optimum percentage of recycled aggregates (RA) in GPC by replacing 20%, 30%, 40%, 50% and 60% of coarse aggregates by RA to produce recycled aggregate geopolymer concrete (RGPC). From the study it has been found that the optimum replacement percentage of recycled aggregates was 40% based on mechanical properties and workability. In order to study and compare the flexural behaviour of RGPC and GPC four beams of size 175 mmx150 mmx1200 mm were prepared and tested under two point loading. Test results were evaluated with respect to first crack load, ultimate load, load- deflection characteristics, ductility and energy absorption characteristics. Form the experimental study it can be concluded that the addition of recycled aggregate in GPC causes slight reduction in its strength and ductility. Since the percentage reduction in strength and behaviour of RGPC is meager compared to GPC it can be recommended as a sustainable and environment friendly construction material.
Key Words
recycled aggregate; geopolymer concrete; mechanical properties; flexural behaviour
Address
Deepa Raj S and Jithin Bhoopesh: Department of Civil Engineering, College of Engineering Trivandrum, Kerala, India
Abstract
The phenomenon of concrete column shortening has been widely acknowledged since it first became apparent in the 1960s. Axial column shortening is due to the combined effect of elastic and inelastic deformations, shrinkage and creep.
This study aims to investigate the effects of ambient temperature, relative humidity, cement hardening speed and aggregate type on concrete column shortening. The investigation was conducted using a column shortening prediction model which is underpinned by the Eurocode 2.
Critical analysis and evaluation of the results showed that the concrete aggregate types used in the concrete have significant impact on column shortening. Generally, aggregates with higher moduli of elasticity hold the best results in terms of shortening. Cement type used is another significant factor, as using slow hardening cement gives better results compared to rapid hardening cement. This study also showed that environmental factors, namely, ambient temperature and relative humidity have less impact on column shortening.
Key Words
concrete; creep and shrinkage; mid-rise buildings; column shortening
Address
Ali B-Jahromi: Department of Civil Engineering, School of Computing and Engineering, University of West London, W5 5RF, London, UK
Abdulazeez Rotimi and Shivan Tovi: School of Computing and Engineering, University of West London, W5 5RF, London, UK
Charles Goodchild: The Concrete Centre, SW1V 1HU, London, UK
Joseph Rizzuto: Department of Civil Engineering, School of Computing and Engineering, University of West London, W5 5RF, London, UK
Abstract
This paper is aimed at determining the shear and impact strength of waste plastic fibre reinforced concrete. M30 grade of concrete is prepared with waste plastic door fibres cut into 5 mm width and aspect ratios of 30, 50, 70, 90 and 110. Fibres are used in a volume fraction of 0 to 1.5% with an increment of 0.25%. L shaped specimens are cast for shear strength tests and flat plates of size 250x250x30 mm are used for impact tests. \"Drop ball method\" is used for checking the impact strength. Shear strength is checked with L shaped specimens under UTM with a special attachment. It was found that up to 1.25% of waste plastic fibres can be effectively used for better strength of concrete both in shear and impact. Shear and impact strength were found to be increasing up to a volume fraction of fibres of 1.25%.
Key Words
concrete; waste plastic fibres; aspect ratio; volume fraction; plates; L shaped specimens; shear strength; impact strength; drop ball method
Address
Savithri S Karanth: Department of Civil Engineering, Global Academy of Technology, Bangalore, India
Vaishali G Ghorpade: Department of Civil Engineering, JNTU College of Engineering Anantapuram, Andhra Pradesh, India
H Sudarsana Rao: JNTUA, Anantapuram, Andhra Pradesh, India
