Cise Unluer

Preliminary Laboratory-Scale Model Auger Installation and Testing of Carbonated Soil-MgO Columns

This paper presents details of the installation and performance of carbonated soil-MgO columns using a laboratory-scale model auger setup. MgO grout was mixed with the soil using the auger and the columns were then carbonated with gaseous CO2 introduced in two different ways: one using auger mixing and the other through a perforated plastic tube system inserted into the treated column. The performance of the columns in terms of unconfined compressive strength (UCS), stiffness, strain at failure and microstructure (using X-ray diffraction and scanning electron microscopy) showed that the soil-MgO columns were carbonated very quickly (in under 1 h) and yielded relatively high strength values, of 2.4–9.4 MPa, which on average were five times that of corresponding 28-day ambient cured uncarbonated columns. This confirmed, together with observations of dense microstructure and hydrated magnesium carbonates, that a good degree of carbonation had taken place. The results also showed that the carbonation method and period have a significant effect on the resulting performance, with the carbonation through the perforated pipe producing the best results.

XPS Study on the Stability and Transformation of Hydrate and Carbonate Phases within MgO Systems

MgO cements have great potential for carbon sequestration as they have the ability to carbonate and gain strength over time. The hydration of reactive MgO occurs at a similar rate as ordinary Portland cement (PC) and forms brucite (Mg(OH)2, magnesium hydroxide), which reacts with CO2 to form a range of hydrated magnesium carbonates (HMCs). However, the formation of HMCs within the MgO–CO2–H2O system depends on many factors, such as the temperature and CO2 concentration, among others, which play an important role in determining the rate and degree of carbonation, the type and stability of the produced HMCs and the associated strength development. It is critical to understand the stability and transformation pathway of HMCs, which are assessed here through the use of X-ray photoelectron spectroscopy (XPS). The effects of the CO2 concentration (in air or 10% CO2), exposure to high temperatures (up to 300 °C) and curing period (one or seven days) are reported. Observed changes in the binding energy (BE) indicate the formation of different components and the transformation of the hydrated carbonates from one form to another, which will influence the final performance of the carbonated blends.

Carbon dioxide sequestration in magnesium-based binders

Abstract Reactive magnesia cement (RMC) has emerged as a sustainable and technically promising novel binder because of its lower production temperatures than Portland cement and ability to gain strength by sequestering significant quantities of CO 2 . Other benefits of RMC include its improved durability under aggressive environments where reinforcement is not present, because of the higher resistance of its hydrate and carbonate phases. The low sensitivity of RMC to impurities enables the utilization of large quantities of wastes and industrial by-products. From an environmental standpoint, the ability of RMC to gain strength via the carbonation process and be fully recycled in concrete mixes, in which it is used as the sole binder, indicates potential for impact on a large scale. This chapter focuses on the reaction mechanisms and associated strength and microstructural development of RMC systems. It reviews the production, characterization, properties, and applications of the main binder phase, MgO, that control the performance of RMC samples. The influence of key factors, such as binder properties, mix design, curing conditions, and presence of additives on the hydration and carbonation reactions, is discussed. Current state of the art and gaps in existing literature are highlighted, supported by recommendations to turn limitations into potential advantages.

Investigating the Carbonation and Mechanical Performance of Reactive MgO Cement Based Concrete Mixes

Carbonation governs the microstructure and the overall mechanical performance of mixes involving MgO cements as the main binder. Aggregate grading has a significant influence on the carbonation process due to the different particle arrangements that determine the porosity and permeability of the resulting formulations. This work investigates the effect of aggregate particle size distribution on the carbonation of blocks containing reactive MgO. Samples containing four different aggregate profiles were subjected to accelerated carbonation at 20% CO2 concentration for up to 28 days. While the influence of gap grading on strength development was not very pronounced, mixes with the lowest initial porosity indicated the greatest increase in density at the end of 28 days. This also translated into the highest strength results obtained due to the formation of hydrated magnesium carbonates, reaching 10 MPa only after 1 day of carbonation. The porosity values measured before carbonation were inversely correlated with the corresponding densities and final strengths of each mix. An inverse correlation between porosity and permeability values before carbonation led to the conclusion that the connectivity of pores rather than the total pore volume controls the carbonation reaction. Mixes with higher initial permeabilities achieved the highest strengths, proving that the extent of CO2 diffusivity is mainly dependent on pore connectivity.