Autogenous shrinkage of CARDIFRCRTM

Durability requirements have become a major issue in the design of concrete structures today. The hardening process plays a key role in the quality of the concrete. Autogenous shrinkage is considered to be a factor that may cause damage to the concrete structure during hardening. The concept of autogenous shrinkage is relatively new and in the case of conventional concrete with fairly high water to cement ratios these self-induced volume changes are found to be relatively small and therefore are neglected. Self-desiccation and autogenous shrinkage are pronounced phenomena in the case of low water to cement ratio concretes. The current study deals with the development of autogenous shrinkage strains in a new class of High Performance Fibre Reinforced Cementitious Composites (HPFRCCs) designated CARDIFRC that has been recently developed at Cardiff University. The scope of the study was to investigate how the self-induced shrinkage strains develop in CARDIFRC matrix without fibres and what was the effect of the inclusion of a large amount of fibre on the autogenous shrinkage. Both experimental and theoretical studies were undertaken as a part of this investigation. Autogenous shrinkage strains were measured on large and small prisms of CARDIFRC under isothermal conditions. The experiments revealed a relatively large scatter in the measured values for the case of large beams with fibres, whereas the beams of same size but without any fibres gave consistent results. This large scatter has been confirmed to be a result of the uneven distribution of fibres in the large prisms. Small prisms with and without fibres gave very consistent results, with autogenous shrinkage taking place up to 75 days. The autogenous shrinkage strains have been modelled using a thermodynamic approach which follows the continuous change in the moisture content, pore volume and stiffness of the mix with degree of hydration. The predictions of the model are in good agreement with the measured strains in all specimens with and without fibres

Effect of Metallic Waste Addition on the Physical and Mechanical Properties of Cement-Based Mortars

© 2018 by the authors. Licensee MDPI, Basel, Switzerland. This is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).This paper investigates the influence of the type and amount of recycled metallic waste on the physical and mechanical properties of cement-based mortars. The physical and mechanical properties of cement mortars, containing four different amounts of metallic waste (ranged 4 to 16% by cement weight), were evaluated by measuring the bulk density, total porosity, flexural and compressive resistance, and dynamic elastic modulus by ultrasonic tests. All the properties were measured on test specimens under two curing ages: 7 and 28 days. Additionally, the morphological properties and elemental composition of the cement and metallic waste were evaluated by using Scanning Electron Microscopy (SEM), energy dispersive X-ray spectroscopy (EDXS), and X-ray fluorescence (XRF). Main results showed that the addition of metallic waste reduced the bulk density and increased the porosity of the cement-based mortars. Furthermore, it was observed that flexural and compressive strength proportionally increased with the metallic waste addition. Likewise, it was proven that elastic modulus, obtained by compressive and ultrasonic tests, increases with the metallic waste amount. Finally, based on a probability analysis, it was confirmed that the addition of metallic waste did not present a significant effect on the mechanical performance of the cement-based mortars.Peer reviewedFinal Published versio

Recycling mine tailings as precursors for cementitious binders – Methods, challenges and future outlook

© 2021 Elsevier Ltd. All rights reserved. This is the accepted manuscript version of an article which has been published in final form at https://doi.org/10.1016/j.conbuildmat.2021.125333Increase in demand for mineral commodities such as coal, copper, iron, aluminium, gold, tungsten, zinc etc., has led to higher quantity of mineral waste produced such as solids, crushed rocks, overburden soil and tailings. The fine-grained mineral waste left after removal of valuable material from ore is called mine tailing and is one of the major wastes of the mining processes. Mineral wastes from mines, quarries and excavations are typically rich in SiO2, Al2O3, CaO and Fe2O3. This chemical composition makes them very attractive candidates to be used in the production of construction materials, as these oxides are also the main constituents of cement as well as of key alkali-activated binders. This contribution aims to provide a comprehensive overview of the nature of mine tailings, the current state-of-the-art in their utilisation in cementitious binders and the future potential. A rational summary of limitations associated with use of mine tailing in cementitious binder due to its low reactivity and potential solutions to overcome it is also provided. The study concludes with how the use of mine tailings in cementitious binder could benefit in achieving the global sustainability goals.Peer reviewe

THE EFFECT OF MINING WASTE ON THE DURABILITY INDICATORS OF CEMENT-BASED COMPOSITES

© 2021 The Authors.The need for infrastructure development is of major importance and the projected global infrastructure investment between 2013-2030 is estimated in the excess of £30 trillion to support the rapid growth of societies and economies worldwide (1). This trend puts civil infrastructure industry under immense stress to plan properly, construct fast and deliver resilient structures. Concrete is the dominant construction material and the key element in most infrastructure assets. However, concrete’s manufacture is extremely energy and resource intensive: >4 Billion tonnes of cement are produced annually, accounting to ~8% of global anthropogenic CO2 and resulting to an annual production of ~2 tonnes of concrete for every person on the planet. The production of concrete is a process associated with very high energy consumption. In Europe, the construction sector alone is responsible for the 36% of CO2 emissions and the 40% of all energy consumption. The utilisation of mining waste in cement-based composites is an area of growing interest worldwide, with mining and excavation waste increasing considerably the last decade. Our work focuses on the replacement of cement with mineral wastes and the initial findings suggest that even at 20% replacement, the mechanical properties are marginally affected. This contribution will discuss some preliminary data on the effect of mining waste on the durability indicators of cementitious composites (oxygen permeability, capillary sorption and ion diffusion). Keywords: Mining waste, Silicates, capillary water absorption,Peer reviewedFinal Published versio

An investigation of CSR orientations among Greek university students

This paper presents the results of a survey of the corporate social responsibility (CSR) orientations of commerce students at the University of Piraeus. The study utilised the instrument developed by Aupperle (1982, cited in Aupperle, Carroll, & Hatfield, 1985) based on Carroll's (1979) social responsibility framework. Comparisons are made with the results of other surveys that have used the same method.peer-reviewe

Assessing the quality of concrete – reinforcement interface in Self Compacting Concrete

© 2019 Elsevier Ltd. This manuscript is made available under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International licence (CC BY-NC-ND 4.0). For further details please see: https://creativecommons.org/licenses/by-nc-nd/4.0/Research has shown that even self-compacting concrete (SCC) mixtures can exhibit the so-called “top-bar effect” which impacts bond and anchorage. Several instances of conflicting results have nevertheless been published regarding interfacial bond between self-compacting concrete and steel reinforcement. The scope of this paper is to present an experimental methodology for assessing the quality of the interface between self-compacting concrete and ribbed reinforcement. For this purpose, seven different self-compacting and four normally vibrated concrete (NVC) mixtures with diverse rheological characteristics were examined. Digital Image Analysis of cut sections containing reinforcing bars at different cast-heights was used as a diagnostic tool. The study illustrates that the quality of the interface is strongly affected by the viscosity of the SCC mixtures and by the slump values in NVC. Self-compacting concrete mixtures show greater inherent robustness and cohesion at the steel–concrete interface compared to conventionally vibrated concretes.Peer reviewe

Experimental and numerical study of behaviour of reinforced masonry walls with NSM CFRP strips subjected to combined loads

© 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).Near surface mounted (NSM) carbon fibers reinforced polymer (CFRP) reinforcement is one of the techniques for reinforcing masonry structures and is considered to provide significant advantages. This paper is composed of two parts. The first part presents the experimental study of brick masonry walls reinforced with NSM CFRP strips under combined shear-compression loads. Masonry walls have been tested under vertical compression, with different bed joint orientations 90ffi and 45ffi relative to the loading direction. Different reinforcement orientations were used including vertical, horizontal, and a combination of both sides of the wall. The second part of this paper comprises a numerical analysis of unreinforced brick masonry (URM) walls using the detailed micro-modelling approach (DMM) by means of ABAQUS software. In this analysis, the non-linearity behavior of brick and mortar was simulated using the concrete damaged plasticity (CDP) constitutive laws. The results proved that the application of the NSM-CFRP strips on the masonry wall influences significantly strength, ductility, and post-peak behavior, as well as changing the failure modes. The adopted DMM model provides a good interface to predict the post peak behavior and failure mode of unreinforced brick masonry walls.Peer reviewe

Performance of joints in reinforced concrete slabs for two-way spanning action

A series of tests on filigree slab joints was performed with the aim of assessing whether such joints can be reliably used in the construction of two-way spanning reinforced concrete slabs. The test results were compared with code requirements. Adequate joint performance is shown to be achievable when the joints are appropriately detailed. Further research is recommended for the formulation of a more generic understanding when the design parameters are varied from those studied in this work