Abstract
The production of alkali-activated materials (AAMs) is known for its environmentally friendly processing method, where several amorphous-rich aluminosilicate material sources combine with an alkali media solution to form solid, ceramic-like materials. In terms of the Si:Al, Na(K):Al, and Na(K):H2O ratios, the theory of AAM formation is quite well developed, but some open questions in the technology process remain, especially with regards to the means of curing, where the generation of defects can be persistent. Knowing that deformation is extremely high in the early ages, this study investigates the effects of temperature and moisture on shrinkage behavior within the first 72 h of AA pastes made from ladle (LS) and electric arc furnace (EAF) slag and activated by sodium silicate (Na2SiO3). The method to determine the deformation of alkali-activated slag-based materials, in terms of both autogenous and drying shrinkage, was based on the modified ASTM C1698-19 standard for the measurement of autogenous shrinkage in cement pastes. Autogenous deformation and strain were measured in four samples, using the standard procedure at room temperature, 40 and 60°C. Furthermore, using an adjusted method, nine samples were characterized for strain and partial surface pressure, while drying at room temperature, 40, or 60°C at a relative humidity of 30 or 90%. The results show that the highest rate of autogenous shrinkage occurred at a temperature of 60°C, followed by drying shrinkage at 60°C and 30% relative humidity, owing to the fact that the rate of evaporation was highest at this moisture content. The study aimed to provide guidance regarding selection of the optimal curing set in order to minimize deformations in slag-based alkali-activated materials. In the present case, curing at a temperature of around 40°C under lower moisture conditions for the first 24 h provided optimal mechanical properties for the slags investigated. The methodology might also be of use for other aluminosilicate sources such as metakaolin, fly ash, and mineral wool–based alkali-activated materials.
Highlights
The consumption of 33 billion tons of concrete per year (ISO/TC 071 Strategic business plan, Date: 4/14/2016, Version: Final) necessitates the adoption of a new approach toward the production of more environmentally friendly materials
The measuring procedure in standard C1698-09 was followed, which specifies curing at room temperature for 72 h, with parallel measurements made at elevated temperatures of 40 and 60°C in order to evaluate the deformation caused at higher temperatures
The autogenous shrinkage is greater, and deformation continues rapidly within the first 10 h, at which point it slows down to the rate of −8,000 μm/m in the specimen dried at room temperature
Summary
The consumption of 33 billion tons of concrete per year (ISO/TC 071 Strategic business plan, Date: 4/14/2016, Version: Final) necessitates the adoption of a new approach toward the production of more environmentally friendly materials. AAMs possess good properties, similar to concrete or ceramic materials, and can be processed at low temperatures, given that all the thermal pretreatment of precursors is performed when either producing steel (metallurgical slags) or burning coal fuel (ashes) in the steam power plants at the point when the electrical energy is produced (Fernandez-Jimenez et al, 2015). Another advantage of using AAMs is the chance to recover material from landfills, which are often overloaded with industrial by-products, eventually leading to air and water pollution (Natali Murri et al, 2013). Most of the studies regarding the deformation of AAMs have been made in terms of drying shrinkage, where some authors have found that overall shrinkage is far greater than in the case of OPC
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