Some aspects of therapy on a girl's psychiatric ward

Thesis (M.S.)--Boston University, 195

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

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

Efficient mix design of alkali activated slag concretes based on packing fraction of ingredients and paste thickness

Many studies have been dedicated to the properties of alkali-activated slag concretes as a form of low-carbon high performance concrete, but less work has been focused on the application of mix design procedures to have a dense, durable and cost-efficient alkali-activated concrete. This study proposes a method for selecting the mix proportions of alkali-activated concretes based on the packing fraction of materials. The design method is based on the selection of the volumetric proportions of sand and coarse aggregate according to an ideal particle gradation curve. To validate this method, trial castings were carried out for concrete mixes containing alkali activated slag (AAS) with different paste contents to suggest the most cost-efficient concrete for different classes of workability and applications. Compaction and pore structure of these mixes studied by optical microscopy have shown that the design of AAS concretes based on the proposed method resulted in a dense and workable mix

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

Effect of temperature on the strength development of mortar mixes with GGBS and fly ash

The concrete mixes used in this study had 28 d mean strengths of 50 and 30 MPa and also had Portland cement (PC) partially replaced with ground granulated blast-furnace slag (GGBS) and fly ash (FA). These mixes were the same as those used in a UK-based project that involved casting of blocks, walls and slabs. The strength development of ‘equivalent’ mortar mixes was determined in the laboratory for curing temperatures of 10, 20, 30, 40 and 50°C. High curing temperatures were found to have a beneficial effect on the early-age strength, but a detrimental effect on the long-term strength. GGBS was found to be more sensitive to high curing temperatures than PC and FA, as reflected in its higher ‘apparent’ activation energy. The accuracy of strength estimates obtained from maturity functions was examined. The temperature dependence of the Nurse–Saul function (i.e. concrete strength gain rate varies linearly with temperature) was not sufficient to account for the improvement in early-age strengths resulting from high curing temperatures. The Arrhenius-based function, on the other hand, overestimated them because of the detrimental effect of high curing temperature on strength starting from a very early age. Both functions overestimated the long-term strengths, as neither function accounts for the detrimental effect of high curing temperatures on the ultimate compressive strength. </jats:p

The use of waste bricks and tiles as a precursor for alkali activated binders

Currently, the most common treatment of construction and demolition waste (CDW) in Europe, other than disposal, is backfilling with a very small amount being effectively reused. In an attempt to optimize the use of construction and demolition waste (CDW), potential recycling and reuse routes exist, with the most popular method being to use CDW as recycled aggregates. Another viable route, however, would be to use bricks and tiles (BT) waste, collected from CDW, as a precursor for alkali activated binders as they can make up a larger proportion of CDW[i]. The work was performed in the framework of RE4, “Reuse and Recycling of CDW materials and structures in energy efficient prefabricated elements for building refurbishment and construction”, a European project founded by the European Commission in the framework of H2020 Research and Innovation Program (call H2020-EEB-04, GA n. 723583 I project website: www.re4.eu) Two sources of recycled waste have been collected from Northern and Southern Europe. They were ultimately sorted and were found to contain 14 % and 27 % by weight of bricks and tiles waste respectively. Upon separation, the BT waste from both sources were ground together to form a fine powder to be used as a precursor for alkali activation. To assess the potential use of BT waste as a precursor, mortars were prepared to measure workability and strength evolution (measured on 50 mm cubes), fixing the sand to binder ratio at 2.75. The activating solution made use of both NaOH and Na2SiO­3,varying the alkali dosage M+ (M+ = Na2O/BT) and alkali modulus AM (AM = Na2O/SiO2). The original water/solids (w/s) ratio was fixed at 0.37 and was increased in increments up to 0.45 to assess its impact on strength and workability. Mortars, prepared replacing up to 80 % of BT waste with GGBS by weight, were also tested. It was found that mortars, containing BT as the sole precursor, cured at room temperature did not set after one day. In order to accelerate reaction, subsequent mortars were cured at 70°C. Mortars prepared with a low alkali dosage (M+ ≤ 5.5%) reached low to moderate strengths after 28 days of curing; the strongest mixes reached strength values of 15 MPa. Increasing the M+ up to 7.5 % led to higher strength, up to 30 MPa. However, the strength plateaued, and even reduced marginally, at higher M+ values. Interestingly, varying the AM ratio had very limited effect on strength. Partial substitution of BT with GGBS led to the possibility of room temperature curing. Strength also increased as the GGBS content increased. Mortars containing 20 % by weight of GGBS of precursor reached a modest strength value of 28 MPa, whereas mortars containing 80 % by weight reached an ultimate strength of 79 MPa. The mortars were found to be workable, albeit very cohesive. When measured using the flow table test mortars prepared with a w/s = 0.37 spread to an average diameter of 14 mm. The value was near constant regardless of the AM value, ranging from 0.5 up to 1.5, for a fixed M+ = 7.5%. Only mortars prepared with NaOH as the sole activator (AM = ∞) showed a reduction in workability. Increasing the water content of the mortars led to more workable mortar. When the w/s was increased up to 0.45, the spread reached an ultimate diameter of 20 mm. The increase in w/s, from 0.37 up to 0.45, however, resulted in a 25 % drop in strength. Work to date suggests the potential use of BT as an alkali active binder. However, more work is needed in order to understand the reaction mechanisms in an attempt to further optimize BT as a precursor for alkali activated binders, including microstructural analysis. [i] ROBAYO, F.A., MULFORD, A., MUNERA, J., MEJIA DE GUTIERREZ, R., Alternative Cements Based on Alkali-Activated Red Clay Brick Waste, Construction and Building Materials, 128, pp 163-169, 201

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