Influence of Early Oven Curing on the Alkali Activated Binders with Reactive Magnesia Replacement

Magnesia is widely used an expansive agent in construction materials due to its delayed hydration, which will compensate for the thermal shrinkage. This study investigates the influence of magnesia and early oven curing on the mechanical performance and microstructures of alkali-activated natural clay samples under different curing regimes after 28 days. Microstructural analysis and pH measurements were conducted to assess the strength of the samples. Results indicate that the strength was greatly improved (in comparison with the control samples) by the incorporation of magnesia due to the formation of nesquehonite. Meanwhile, oven curing is an effective method in the fast strength development in alkali-activated natural clay. The results also demonstrated the possibility of CO2 curing in the strength development of the magnesia-modified alkali-activated natural clay. Keywords: magnesia, natural clay, oven curing, compressive strength, microstructur

Testing Rheological Properties of Alkali-Activated Cement Using Non-Traditional Test Methods

In this paper, the rheological parameters of alkaline activated cement (AAC) paste tailored for continuous extrusion using the non-traditional test method of the direct shear box test are presented. Characteristic changes of the material’s rheological behaviour are estimated in response to variations in the water-to-solid ratio and addition of a cellulosic rheology aid. The results indicate that the increase of the water-to-solid ratio from 0.18 to 0.19 does not impact the internal angle of friction (φ) but does, however, reduce the shear yield strength, or cohesion (c), by 85%. For mixes containing cellulosic rheology aid, the internal angle of friction shows no significant change also. However, the shear yield strength for the mix with a water-to-solid ratio of 0.18 is 51% higher. The shear yield strength increases by a further 28% for the mix with a water-to-solid ratio of 0.19. These results indicate that the cellulosic rheology aid does not necessarily increase the "flow-like" characteristics of the mix which provides it plasticity and the ability to move through the extruder. It does however significantly improve its ‘green strength’, even at an increased water-to-solid ratio of 0.19, which would ultimately assist with lowering the binder density

Environmental assessment of magnesium oxychloride cement samples: A case study in Europe

This study is the first in the literature to systematically assess the environmental impacts of magnesium oxychloride cement (MOC) samples, which are regarded as a more eco-friendly construction material than Portland cement. The environmental impacts of MOC samples prepared with various molar ratios of MgO/MgCl2∙6H2O and sources of reactive magnesia were obtained via a life cycle assessment (LCA) approach (from cradle to grave), and the obtained outcomes were further compared with the counterparts associated with the preparation of Portland cement (PC) samples. Meanwhile, a sensitivity analysis in terms of shipping reactive magnesia from China to Europe was performed. Results indicated that the preparation of MOC samples with higher molar ratios led to more severe overall environmental impacts and greater CO2 sequestration potentials due to the difference of energies required for the production of MgO and MgCl2∙6H2O as well as their various CO2 binding capacities, whereas in terms of CO2 intensities, the molar ratios in MOC samples should be carefully selected depending on the strength requirements of the applications. Furthermore, various allocation procedures and MgO production processes will greatly influence the final outcomes, and allocation by mass is more recommended. Meanwhile, the environmental impacts associated with the transportation of reactive magnesia from China to Europe can be ignored. Finally, it can be concluded that MOC concrete is no longer a type of ‘low-carbon’ binder in comparison with PC concrete in terms of CO2 emissions, and in view of the single scores and mixing triangles for weighing, MOC concrete can only be identified as a type of more sustainable binder than PC concrete when the main component MgO in MOC samples is obtained through the dry process route rather than the wet process route

Effects of lactic and citric acid on early-age engineering properties of Portland/calcium aluminate blended cements

In this study, Portland/calcium aluminate blended cement (PC/CAC) was combined with citric acid or lactic acid as additives to investigate the effects of the aforementioned carboxylic acids on the hydration reactions of PC/CAC as a potential fast hardening and low cost repair material for concrete. Mortar specimens with the carboxylic acid additives of either 0.5%, 1% or 3% by weight, prepared with a binder:sand:water ratio (by weight) of 1:3:0.5, were subjected to flexural and compressive strength tests at early ages up to 28 days. In order to understand the phase composition of the hydrates in the PC/CAC systems, XRD analyses were conducted on ground PC/CAC mortars with and without carboxylic acid at 7, 14 and 28 days. In combination with this, SEM images of selected mortar specimens were also taken at the same times for visual analyses of hydrates. Citric acid did not have any beneficial effect on enhancing the calcium silicate phase as initially assumed and instead reduced the strength of PC/CAC cement at all levels of concentration. The experiment analyses revealed that Portlandite crystals were the major hydrate phase in PC/CAC with lactic and citric acids. Lactic acid below 2% wt. improved both compressive and flexural strength gained at early ages due to improved crystallinity of the calcium hydroxide crystals. Combined with its inherent rapid setting time, PC/CAC blended cements have a potential to be developed into a suitable repair material for concrete

Development and Optimisation of Phase Change Material-Impregnated Lightweight Aggregates for Geopolymer Composites Made from Aluminosilicate Rich Mud and Milled Glass Powder

Macro-encapsulated aggregates (ME-LWAs) consisting of expanded clay lightweight aggregates (LWAs) impregnated with a paraffin wax phase change material (PCM) was produced. To fully exploit the thermal energy retaining properties of PCM, it is fundamental to retain as much of the PCM as possible within the pores of the LWA. This paper investigates 3 different commercial materials to create a total of 14 different coating regimes to determine the most efficient coating method and material regarding its ability at retaining the PCM. The ME-LWAs are then further used as aggregates in geopolymer binders made from a combination of aluminosilicate rich mud and waste glass. Physical properties such as thermal conductivity and mechanical strength are determined for the geopolymer binder with and without the addition of the ME-LWA. A polyester resin was determined to be the most suitable choice of coating material for the ME-LWA, producing a practically leak-proof coating. The ME-LWA was also determined to be chemically neutral, showed a 42% higher thermal conductivity than the LWA in their raw state and maintained a latent heat of 57.93 J/g before and after being used in the geopolymer binder. Carbon fibres and graphite spray were used to improve the thermal conductivity of the resin coating, however no significant increase was detected. Finally, the compressive strength and thermal conductivity results achieved are acceptable for applications in buildings for enhancement of their energy efficiency.Partial finance support from the European Commission Horizon 2020 MARIE Skłodowska CURIE Research and Innovation Staff Exchange Scheme through the grant 645696 (i.e. REMINE project) is greatly acknowledged

Environmental Assessment of Magnesium Oxychloride Cement Samples: A Case Study in Europe

This study is the first in the literature to systematically assess the environmental impacts of magnesium oxychloride cement (MOC) samples, which are regarded as a more eco-friendly construction material than Portland cement. The environmental impacts of MOC samples prepared with various molar ratios of MgO/MgCl2∙6H2O and sources of reactive magnesia were obtained via a life cycle assessment (LCA) approach (from cradle to grave), and the obtained outcomes were further compared with the counterparts associated with the preparation of Portland cement (PC) samples. Meanwhile, a sensitivity analysis in terms of shipping reactive magnesia from China to Europe was performed. Results indicated that the preparation of MOC samples with higher molar ratios led to more severe overall environmental impacts and greater CO2 sequestration potentials due to the difference of energies required for the production of MgO and MgCl2∙6H2O as well as their various CO2 binding capacities, whereas in terms of CO2 intensities, the molar ratios in MOC samples should be carefully selected depending on the strength requirements of the applications. Furthermore, various allocation procedures and MgO production processes will greatly influence the final outcomes, and allocation by mass is more recommended. Meanwhile, the environmental impacts associated with the transportation of reactive magnesia from China to Europe can be ignored. Finally, it can be concluded that MOC concrete is no longer a type of ‘low-carbon’ binder in comparison with PC concrete in terms of CO2 emissions, and in view of the single scores and mixing triangles for weighing, MOC concrete can only be identified as a type of more sustainable binder than PC concrete when the main component MgO in MOC samples is obtained through the dry process route rather than the wet process route

Alkali activated binders valorised from tungsten mining waste: materials design, preparation, properties and applications

This thesis was submitted for the award of Doctor of Philosophy and was awarded by Brunel University LondonAlkali-activated binders (AABs) are the third-generation class of binders after lime and Portland cement. These binders have the potential to be made from a variety of industrial waste sources, many of which have remained largely unexplored. Significant drawbacks of AABs are the requirement of highly alkaline solutions for its production and the lack of available data regarding its implementation in the field. To bridge this gap, this study aimed to research the recycling and valorization of tungsten mining waste (TMW) to produce AABs, using waste glass (WG) as a supplementary material for reducing the alkali activator demand. Finally, a connection was made between the fundamental research on AABs and a practical engineering application. A detailed approach was undertaken to determine the most appropriate TMW-WG AAB preparation methods and curing conditions, an understudied area, with a strong emphasis on the microstructural development during hardening. The alkali activator appeared to be sensitive to prolonged stirring, which appeared to induce a stripping effect of the water molecules from the alkali metal ions, leading to a less intense attack on the silicon-oxygen bonds in precursor material. The effects of WG (dissolution and chemical reaction) were investigated to understand its contribution to the AAB system. WG was observed to provide an additional source reactive silica, contributing to the formation of a calcium-containing N-A-S-H gel, and significantly improve the mechanical strength. PCM macro-encapsulated aggregates (ME-LWAs) were also researched and incorporated into the TMW-WG AAB for the development of an energy-saving building material. The ME-LWAs stood out to be leak proof, with excellent thermal stability and thermal conductivity, latent heat capacity and abrasion resistance. It was also found out it is feasible to produce foamed lightweight alkali-activated materials using tungsten mining waste (TMW-WG FAAB) and other precursor materials. FAAB can be used in several applications where low density and fire resistance is required. The TMW-WG FAAB was also designed to suit a wide range of densities and compressive strengths using chemical foaming, achieving very low thermal conductivity. Finally, the TMW-WG AAB proved itself to be convenient to prepare on-site, demonstrating in service its ease of preparation, rapid hardening and durability as a novel road repair mortar

Covert integration of core state powers : renegotiating incomplete contracts

This chapter argues that the integration of core state powers in the European Union, as defined and investigated in this volume, has frequently occurred not manifestly in the formal central political arena but rather in a process of covert integration, without being explicitly mandated by formal political actors. It has arguably led to a ‘competence creep’ from the national to the supranational level, and from legislative to executive and judicial actors. Deepening integration through covert integration happens because it is politically more expedient and politically less costly. It reveals different patterns that may be theoretically grasped by rational choice institutionalism and the theory of incomplete contracts developed and applied in a multi-level context. The chapter will theorize and overall empirically analyse the conditions and processes of covert integration and their ‘stopping points’ on the basis of the empirical policy areas discussed in this volume and some additional examples from my own research

Alkali-activated binders based on incinerator bottom ash combined with limestone-calcined clay or fly ash

This study investigates the feasibility of improving the properties of alkali-activated bottom ash (AABA) binders by incorporating limestone-calcined clay (LC2) or fly ash (FA) with the aim of treating and utilising bottom ash in a large-scale as a potential resource for construction materials. Experimental results revealed that increasing the substitution with LC2 or FA in the AABA binders increased both the compressive strength and the immobilization capacity of heavy metal when compared to the pure AABA binders. Given a Na2O content of 5%, the compressive strength of the AABA binder with 30% bottom ash substituted by FA was almost 200% higher than that of the pure AABA binder. However, further increase in the Na2O dosage did not necessarily lead to higher compressive strength, which was found to be controlled by the volume fraction of air voids and large pores. When greater Na2O dosages were employed, i.e., 6 % and 7 %, LC2 was found to be more useful in improving the properties of AABA binders than FA. Furthermore, the substitution of bottom ash with FA resulted in the formation of N-A-S-H gels, whereas the substitution with LC2 led to the formation of more C-A-S-H gels. Finally, the immobilization capacity appeared to be influenced by many factors, such as hydration products, capillary pores and different types of heavy metals