Alkali-activated concrete for the production of building blocks: research achievements and future challenges

This is the final version.Several global challenges identified by the UN Sustainable Development Goals are either directly or indirectly linked to the construction sector. The need for decent and affordable houses is an urgent problem for many developing countries, whereas the concerns about the carbon emissions related to the manufacture of Portland cement are growing worldwide. A number of possible solutions are currently offered by the research, which has been investigating the recycling of waste/by-products into sustainable building materials during the last decades. This paper discusses the experience gathered in the manufacture of building blocks using alkali-activated concrete produced from waste streams such as fly ash, slag, or cement kiln dust. Laboratory investigations on binder development, concrete mix proportioning, and building block sample production, as well as full size factory trials with industrial equipment, were carried out for assessing the potential and the challenges of this technology. Obtained results demonstrated the technical feasibility of manufacturing building blocks with alkali-activated concrete, and highlighted the challenges for a viable and sustainable application of this technology

Use of Vietnamese rice husk ash for the production of sodium silicate as the activator for alkali-activated binders

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this record.Geopolymer and Alkali-Activated Binders (AAB) has recently emerged as a new, green material with the potential to replace Portland cement in several applications. They can reduce the CO2 footprint of concrete by up to 80% and this is in addition to being more durable in certain aggressive environments. However, commercial alkaline activators contribute significantly to the cost and CO2 footprint of AAB concrete mixes. This research investigates the production of a low cost, low environmental impact sodium silicate solution (waterglass) from Rice Husk Ash (RHA) and more specifically RHA from Vietnam. A hydrothermal process for the dissolution of RHA in sodium hydroxide solution was developed. Sodium hydroxide solution concentration, process temperature and duration were studied. Optimised procedure parameters were found to be: NaOH concentration 3M, heating temperature 80 °C and heating duration 3h. The obtained solution was used for the production of AAB mortar made with a blend of fly ash and ground granulated blast furnace slag. Obtained compressive strength of mortar was in the range of 60 MPa at 28 days, matching the strength obtained from control samples produced with commercially available activators. Microstructural investigation (isothermal calorimetry, infrared spectroscopy, X-ray diffraction and thermogravimetric analysis) on pastes confirmed the equivalence between the solution produced with the optimised method and commercially available options. Cost analysis indicated that the proposed method could allow a reduction of almost 55% of the cost for the activation of AAB. Results from a simplified preliminary environmental analysis suggested increased sustainability of the RHA-derived solution when compared with commercially available waterglass.This research is funded by National University of Civil Engineering (NUCE) under grant number 108-2018/KHXD-TĐ. The authors also gratefully acknowledge the financial support provided by the National Foundation for Science and Technology Development- Vietnam (NAFOSTED); Queen’s University Belfast and the National University of Civil Engineering for sponsoring Dr Kien Tong’s partnership study programme. The Authors would also like to thank Dr Le Trung Thanh and Dr Bui Danh Dai for their guidance and valuable discussions; Dr Mark Russell for his assistance in the characterisation of both raw materials and reacted samples. The Authors are also grateful to Angkor Bio Cogen Co. Ltd., Cambodia, for their useful information on burning technologies available and information on power plants currently using rice hulls

The role of water content and paste proportion on physico-mechanical properties of alkali activated fly ash-ggbs concrete

This is the author accepted manuscript. The final version is available from the publisher via the DOI in this recordt The growth of the construction industry worldwide poses a serious concern on the sustainability of the building material production chain, mainly due to the carbon emissions related to the production of Portland cement. On the other hand, valuable materials from waste streams, particularly from the metallurgical industry, are not used at their full potential. Alkali-activated concrete (AAC) has emerged in the last years as a promising alternative to traditional Portland cement-based concrete for some applications. However, despite showing remarkable strength and durability potential, its utilisation is not widespread, mainly due to the lack of broadly accepted standards for the selection of suitable mix recipes fulfilling design requirements, in particular workability, setting time and strength. In this paper, a contribution towards the design development of AAC synthesised from pulverised fuel ash (60 %) and ground granulated blast furnace slag (ggbs) (40 %) activated with a solution of sodium hydroxide and sodium silicate is proposed. Results from a first batch of mixes indicated that water content influences the setting time and that paste content is a key parameter for controlling strength development and workability. The investigation indicated that, for the given raw materials and activator compositions, a minimum water-to-solid (w/s) ratio of 0.37 was needed for an initial setting time of about 1 h. Further work with paste content in the range of 30–33 % determined the relationship between workability and strength development and w/s ratio and paste content. Strengths in the range of 50–60 MPa were achieved.European Union Seventh Framework Programm

Effects of slag substitution on physical and mechanical properties of fly ash-based alkali activated binders (AABs)

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this recordNeat fly ash-based alkali activated binders require high activator dosages and high temperature curing in order to develop satisfactory mechanical properties. Blending ground granulated blast furnace slag (GGBS) with fly ash can give medium to high strengths without the need for high temperature oven curing. An extensive investigation was carried out for understanding the effects of GGBS substitution of fly ash in mortar. GGBS substitution in the mix has an impact on mix proportions, fresh and hardened properties, and microstructure of reaction products. The strength of fly ash/GGBS blends cured at room temperature increased with the increase of GGBS content, whilst setting time showed an opposite trend. Fly ash/GGBS blends required lower activator dosages for obtaining high compressive strength, which has cost and environmental benefits. XRD, FTIR, TGA, and SEM/EDX results confirmed the presence of C-A-S-H gel as a reaction product with as low as 20% GGBS content.European Union FP7Government of the Sultanate of Oman ( Ministry of Manpower

Magnetic Properties And Giant Magnetoresistance Of Melt-spun Granular Cu100-x-cox Alloys

Room-temperature measurements of magnetization and giant magnetoresistance were performed on rapidly solidified granular Cu100-xCox systems (x=5,10,15). The magnetoresistance of melt-spun Cu100-xCox ribbons was enhanced either by suitable furnace annealings or by exploiting the dc Joule-heating technique in the attempt of precipitating smaller magnetic particles. The particle-size distribution, the particle density, and mean distance are obtained for all compositions and heat treatments through a suitable analysis of the magnetic behavior of samples. The magnetoresistance is plotted as a function of the reduced magnetization, and a significant deviation from the quadratic behavior predicted by the independent-moment approach is observed at low fields. A simple theory taking explicitly into account the correlation existing among the magnetic particles is proposed. A general expression for the magnetoresistance in granular magnetic systems is obtained, and shown to accurately fit all the experimental curves, indicating that this effect is basically determined by the ratios between two distinct correlation ranges for the magnetic-moment fluctuations and the electronic mean free path. © 1995 The American Physical Society.5221153981541

Sustainable concrete construction – from recycled demolition aggregate to alkali activated binders

This is the author accepted manuscript. The final version is available from IOP Publishing via the DOI in this record.14th International Conference on Concrete Engineering and Technology (CONCET 2018), 7-10 August, Kuala Lumpur, MalaysiaInvestigations into the economics, practicalities and technicalities of using recycled demolition aggregate in concrete precast products started in 2001. At that time, there were six demolition contractors around Liverpool and they were using mobile crushers which were suited for road subbase material but not for the smaller sized aggregate required for precast concrete products. It was estimated that if all six worked round the clock, i.e. assuming there was enough feed material, they would still have found it difficult to maintain the required supplies for a single precast factory. Investment in equipment was therefore required to guarantee supply and improve the quality of the recycled demolition aggregate. The market forces and the incentives/drivers for construction companies to adopt sustainable practises have encouraged investment of several million pounds to be made in new recycling plants and this has resulted in “urban quarries”. Work on reducing the carbon footprint of concrete construction needs to consider not only the replacement of the aggregate with recycled ones but also to consider a reduction or complete replacement of Portland cement in concrete mixes. Alkali activated binders and geopolymers have seen applications in ceramics, hazardous waste containment, fire-resistant construction materials and refractories but the most interesting application is their use to replace Portland cement-based concretes. Several factors affecting the reactivity of fly ash as a precursor for geopolymer concrete have been investigated. These include physical and chemical properties of various fly ash sources, inclusion of ground granulated blast furnace slag (ggbs), chemical activator dosages and curing temperature. Alkali-activated fly ash was found to require elevated curing temperatures and high alkali concentrations. A mixture of sodium hydroxide and sodium silicate was used and this was shown to result in high strengths, as high as 70 MPa at 28 days. The partial replacement of fly ash with ground granulated blast furnace slag (ggbs) was found to be beneficial in not only avoiding the need for elevated curing temperatures but also in improving compressive strengths. It became apparent that the main obstacle to commercialisation of these new alternative binders was the cost of the activating solutions, i.e. the sodium hydroxide and the sodium silicate. The latter is the most expensive one and results in geopolymer concretes that cannot compete on price with Portland cement concretes. Attempts therefore concentrated on developing a procedure for the production of sodium hydroxide from waste streams, which in this case was ground glass cullet. Production of eco-friendly concretes thus becomes commercially possible.The authors are grateful to the Veolia Environmental Trust, the Flintshire Community Trust Ltd (AD Waste Ltd) and the Northwest European Regional Development Fund (ERDF) Programme for funding the several phases of some of the projects described. One of the projects was carried out at the University of Liverpool in the framework of the Carbon Trust Applied Research Grant 0911-0252 “Ultra High Performance Fibre Reinforced Cementless Precast Concrete Products”. The work was then continued at Queen’s University of Belfast with the financial support of the SUSCON project, which has received funding from the European Union Seventh Framework Programme (FP7/2007-2013) under Grant Agreement No. 285463 (Call FP7-2011-NMP ENV-ENERGY-ICT-EeB). The authors would like to thank Innovate UK-EPSRC for providing funding for the project RESCIND “REcovery and uSe of Cement kIlN Dust as the alkali activator for Geopolymeric (Cementless) Concrete Building Blocks”, Grant Ref. EP/N508962/1, which achieve the production of an alternative activator

Noise-based core monitoring and diagnostics: overview of the cortex project

This paper gives an overview of the CORTEX project, which is a Research and Innovation Action funded by the European Union in the Euratom 2016-2017 work program, under the Horizon 2020 framework. CORTEX, which stands for CORe monitoring Techniques and EXperimental validation and demonstration, aims at developing an innovative core monitoring technique that allows detecting anomalies in nuclear reactors, such as excessive vibrations of core internals, flow blockage, coolant inlet perturbations, etc. The technique is based on primarily using the inherent fluctuations in neutron flux recorded by in-core and ex-core instrumentation (often referred to as neutron noise), from which the anomalies will be differentiated depending on their type, location and characteristics. In addition to be non-intrusive and not requiring any external perturbation of the system, the method allows the detection of operational problems at a very early stage. Proper actions could thus be taken by utilities before such problems have any adverse effect on plant safety and reliability

Magnetic properties and giant magnetoresistance of melt-spun granular Cu-100-x Co-x alloys

Room-temperature measurements of magnetization and giant magnetoresistance were performed on rapidly solidified granular Cu100-xCox systems (x=5,10,15). The magnetoresistance of melt-spun Cu100-xCox ribbons was enhanced either by suitable furnace annealings or by exploiting the de Joule-heating technique in the attempt of precipitating smaller magnetic particles. The particle-size distribution, the particle density, and mean distance are obtained for all compositions and heat treatments through a suitable analysis of the magnetic behavior of samples. The magnetoresistance is plotted as a function of the reduced magnetization, and a significant deviation from the quadratic behavior predicted by the independent-moment approach is observed at low fields. A simple theory taking explicitly into account the correlation existing among the magnetic particles is proposed. A general expression for the magnetoresistance in granular magnetic systems is obtained, and shown to accurately fit all the experimental curves, indicating that this effect is basically determined by the ratios between two distinct correlation ranges for the magnetic-moment fluctuations and the electronic mean free path

Magnetic hysteresis in granular CuCo alloys

Room-temperature hysteresis loops of granular Cu100-xCox alloys (5 less than or equal to x less than or equal to 15) obtained by planar flow casting in air and submitted to proper annealing treatments have been measured up to a field of 10 kOe by means of a vibrating sample magnetometer. In major loops (\H-vert\ = 10 kOe), the reduced remanence-to-saturation ratio m(r) = M-r/M-s and the coercivity H-c measured on all studied materials appear to be related by an almost linear law of the type m(r) approximate to 1/3 (mu H-c/kT), mu being the average magnetic moment on Co particles. A similar relation is also observed on minor symmetrical loops (100 Oe less than or equal to\H-vert\ less than or equal to 9 kOe). The observed results are accounted for by a model which considers the hysteresis as originating by magnetic interactions among nearly superparamagnetic Co particles. (C) 1999 American Institute of Physics. [S0021-8979(99)51408-4]

Sustainable solutions for the construction sector: integration of secondary raw materials in the production cycle of concrete

The construction industry is one of the largest consumers of raw materials and energy and one of the highest contributor to green-houses gases emissions. In order to become more sustainable it needs to reduce the use of both raw materials and energy, thus lim-iting its environmental impact. Developing novel technologies to integrate secondary raw materials (i.e. lightweight recycled aggre-gates and alkali activated “cementless” binders - geopolymers) in the production cycle of concrete is an all-inclusive solution to im-prove both sustainability and cost-efficiency of construction industry. SUS-CON “SUStainable, Innovative and Energy-Efficiency CONcrete, based on the integration of all-waste materials” is an European project (duration 2012-2015), which aim was the inte-gration of secondary raw materials in the production cycle of concrete, thus resulting in innovative, sustainable and cost-effective building solutions. This paper presents the main outcomes related to the successful scaling-up of SUS-CON concrete solutions in traditional production plants. Two European industrial concrete producers have been involved, to design and produce both pre-cast components (blocks and panels) and ready-mixed concrete. Recycled polyurethane foams and mixed plastics were used as aggre-gates, PFA (Pulverized Fuel Ash, a by-product of coal fuelled power plants) and GGBS (Ground Granulated Blast furnace Slag, a by-product of iron and steel industries) as binders. Eventually, the installation of SUS-CON concrete solutions on real buildings has been demonstrated, with the construction of three mock-ups located in Europe (Spain, Turkey and Romania