Xinyuan Ke

Chloride binding and mobility in sodium carbonate-activated slag pastes and mortars

This study evaluates the chloride binding capacity and the migration of chloride in sodium carbonate-activated slag cements and mortars. The effect on chloride mobility and binding of adding a calcined layered double hydroxide (CLDH) to the binder mix was also assessed. Significantly improved durability characteristics can be achieved for sodium carbonate-activated slag mortars by the addition of small fractions of CLDH, as a consequence of a higher degree of reaction, higher chloride binding capacity, and the refined pore structures present in these modified materials, in comparison with alkali-activated cements produced without CLDH. The addition of CLDH enables the production of sodium carbonate-activated slag cements with notably reduced chloride ingress compared to silicate activated slag cements.

Structural ordering of aged and hydrothermally cured metakaolin based potassium geopolymers

This study evaluates the potential correlation between natural aging and hydrothermal curing (accelerated aging), related to the crystallisation of zeolites in potassium-based metakaolin geopolymer binders. 7-year old sealed-cured specimens, formulated with varying silicate contents, were evaluated. The effect of different accelerated aging durations on the mineralogy of these potassium-based geopolymers was also assessed. The results show that although zeolite formation is favoured under both natural and accelerated aging in potassium-based geopolymers, different types of zeolites are formed depending on the silicate content added to the mix, and the curing conditions of the specimens.

Metakaolin-Based Geopolymers for Nuclear Waste Encapsulation

The UK nuclear industry has a significant and challenging stockpile of nuclear wastes, and geopolymers produced from activation of the calcined clay metakaolin offer a valuable alternative to Portland cement-based systems. The characteristics of different formulations of metakaolin-based geopolymers, reacted with sodium and potassium silicate, are therefore of interest. As preliminary steps, the compressive strength and rheology of some metakaolin geopolymer grouts have been studied. This work showed that a potassium silicate-based geopolymer binder, with a sufficiently high water content can be produced to be highly workable. These grouts have a shear stress of approximately 80 Pa at a shear rate of 110 s−1 and can achieve compressive strengths of up to 40 MPa after 7 days of curing. This study is to be expanded in future and compared to the results produced from further analysis performed on the chemical structure of the geopolymer, as well as the overall physical characteristics achieved, to support the immobilisation, incorporation and retention of metal and oil based nuclear wastes.

Alternative inorganic binders based on alkali-activated metallurgical slags

Alkali-activation technology has been used to produce inorganic cements for over a century, as a means of valorizing wastes or industrial by-products derived from different commercial activities. Granulated blast furnace slags (GBFS), derived from the iron-making industry, have been widely utilized for the production of alkali-activated cements. Significant advances in understanding the roles of different factors which govern the properties of alkali-activated GBFS cements have been made in recent decades, to the point that concretes based on alkali-activated GBFS are commercially deployed in several parts of the world. However, GBFS is not the only slag that can be used as a raw material for producing Portland clinker-free inorganic binders. Various other metallurgical slags, which currently have little or no commercial value, can also be utilized as raw materials for producing inorganic cements. The main difficulty to overcome in this area is the generally lower hydraulic reactivity of these slags compared with GBFS, and the high content of heavy metals which can limit the utilization of some such slags as building materials. Alkali-activation can thus, in some instances, also be seen as a means for the consolidation and safe disposal of such materials, which may otherwise pose an environmental hazard. This chapter provides an overview of inorganic cements produced via alkali-activation, particularly those which utilize nonblast furnace metallurgical slags including steel, ferronickel, titaniferous, stainless steel, lead, copper, zinc, nickel, manganese, silicomanganese, and phosphorus slags.