Analisi geomeccanoiche per la stabilità degli scavi in sotterraneo della Pietra del Cardoso

L'articolo decsrive sperimentazione, caratterizzazione e modellazione relative alla pietra del Cardoso, nella quale sono impostate cave sia a giorno sia in ostterraneo. In particolare lo studio è stato rivolto proprio al passaggio in sotterraneo della coltivazione

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

Muck classification: raw material or waste in tunnelling operation.

Tunnel construction, structural diaphragms, debris from quarry exploitation require careful consideration of the spoil management, as this involves environmental, economic and legal requirements. In this paper a classification that considers the interaction between technical and geological factors in determining the features of the resulting muck is proposed. This gives indications about the required treatments as well as laboratory and field characterisation tests to be performed to assess muck recovery alternatives. While this reuse is an opportunity for excavations in good quality homogeneous grounds (e.g. granitic mass), it is critical for complex formation. It is therefore necessary to define a procedure that enables to assess the properties of natural ground and of the relative spoil or waste arising from the excavation or exploitation phases. This approach is presented in this paper for usual tunnelling cases, where the materials are resulting from the tunnel excavation carried out by drill and blasting and mechanised tunnelling. Physical parameters and technological features of the materials have to be assessed, according to their valorisation potential, for defining re-utilisation patterns. The methodology has proved to be effective in some cases tested by the Authors and the laboratory tests carried out on the materials allowed the suitability and treatment effectiveness for each muck recovery strategy to be defined

Mechanical and physical properties of stabilised compressed coal bottom ash blocks with inclusion of lateritic soils in Niger

This is the final version. Available on open access from Elsevier via the DOI in this recordThis paper describes the results from an investigation on the production of compressed block made with coal combustion by-products and local clayey soil in Niger. Stabilisation with Portland cement and a mixture of Portland cement and lime was adopted. Mechanical, physical, hydric, and thermal characterisation of the produced bricks was carried out. Blocks with satisfactory compressive strength were produced, with samples consistently exceeding the compressive strength of 4 MPa. Stabilisation with Portland cement proved to be the most effective in terms of strength development. However, satisfactory results were obtained with partial substitution of cement with lime (up to 30%). Porosity was found to be in the range 33% to 40% for all samples. The low thermal conductivity (in the range 0.31 to 0.48 W/m•K) was presumably influenced by the high porosity. Water absorption of the bricks was found to be very fast, although total water absorption (in the range 20.6 to 28.7%) was lower than the calculated porosity, suggesting that some of the pores were not accessible by water. Samples subjected to heating showed very promising results in terms of strength and mass loss. An increase in compressive strength was recorded up to temperatures of 400°C. This might be due to the triggering of other reactions in the binding matrix due to the chemistry of the bottom ash. A change in colour of samples (from grey to red) was observed, due to the dehydroxilation of iron hydroxide turning into ferric oxide

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

Overburden management in open pits: options and limits in large limestone quarries

This is the 'In press corrected proof' version. The final version is available from Elsevier via the DOI in this recordThe management of overburden is an important task in open pit exploitations. Site topography and morphology as well as geological and geotechnical properties of natural and remoulded materials are the most important factors affecting the disposal phase. Economic and environmental requirements must be followed in order to achieve the best reclamation results, keeping into account site constraints such as slope stability, hauling and dumping issues, and interactions with groundwater. This paper deals with the above mentioned issues, illustrating a rational approach applied on the case of a large limestone quarry where the thickness of the overburden is relevant and the spoil material has to be dumped in a flooded pit. The proposed multidisciplinary approach led to the selection of most suitable methods for excavation, transportation and disposal. The selection was based on a detailed laboratory and site characterisation that defined favorable and adverse factors to be considered during the preliminary study of a large quarrying project.Thanks are due to Mr G. Torchio for the graphics of the 3D simulation of overburden disposal from fixed discharge points. Special and extended thanks are due to the technical and support staff of CCB in Gaurain (Belgium) and Italcementi CGT in Bergamo (Italy), which supported part of this research by means of a research contract with Politecnico of Turin, DIATI (coordinator A. Godio

Chemical and Microstructural Properties of Fly Ash and Fly Ash/Slag Activated by Waste Glass-Derived Sodium Silicate

This is the final version. Available on open access from MDPI via the DOI in this recordSodium silicate is commonly used for activating alumina silicates to produce alkali-activated binders that can compete with conventional Portland cement in concrete. However, the cost and emissions related to activators can hinder the use of alkali-activated materials in the industry. The novel, waste-based activators have been developed in the last years, using Si-rich waste streams. Processing waste glass cullet not only reduces the glass landfill disposal but also allows the production of sodium silicate for alkali activation. In this article, the chemical and microstructural properties of neat fly ash and blended 60 fly ash/40 slag pastes activated by sodium silicate produced from glass cullet were studied and compared to equivalent ones activated by commercially available sodium silicate and sodium hydroxide solutions. Fourier transform infrared (FTIR) spectroscopy, X-ray powder diffraction (XRD), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM) coupled with energy dispersive X-ray (EDX) were used to determine the microstructure and composition of the gel phase. Findings have confirmed that pastes activated by the processed waste glass showed chemical and microstructural properties comparable to pastes produced with commercially available activators.Innovate UKEngineering and Physical Sciences Research Council (EPSRC)Newton Fun

Properties of non-conventional waste and geomaterials for reuse in excavation sites

This is the author accepted manuscript.Reuse and recycling of waste material from excavation and mining/quarrying activities is a global issue that received significant attention in the last decades. The links among local geology, excavation methods, spoil treatment and strategies for recycle have been identified as unavoidable in terms of early physical, chemical and mechanical characterisation of spoils. The emergence of a range of industrial waste streams and the environmental, economic and technical considerations arising from their recycle and reuse still need a comprehensive technical and validated procedure for acceptance. This paper describes the screening tests and treatment options for material recycling in the framework of an original spoil classification system, also for specific applications, such as drainage layers, covering of dumps, rehabilitation of abandoned sites. The experience learnt by the Authors from the development of suitable methodologies for characterisation and management of spoil waste can be extended to other waste such as glass waste, gypsum, rockwool, glasswool, granulates, chipping particles, polymeric cuttings which show similarities with soils and geomaterials in terms of ‘bulk behaviour