**1. Introduction**

Carbonatable binders have emerged as one of the alternative binders to Portland Cementbased materials that could assist in the global trend of reducing CO2 emissions [1]. Carbonated Reactive Magnesia Cement (CRMC), which is based on the transition of Magnesia to Hydrated Magnesium Carbonates (HMCs), such as Dypingite (Mg5(CO3)4(OH)2·5H2O), Hydromagnesite (Mg5(CO3)4(OH)2·4H2O), and Nesquehonite (MgCO3·3H2O), through Accelerated Carbonation Curing (ACC) [2–5], is among this group of binders.

However, the success of the ACC of CRMC-based materials is highly dependent on a wide range of factors, such as the conditions to which the fresh CRMC-based material is exposed (e.g., CO2 environment, curing temperature, period of exposition, and relative humidity), the raw materials' properties (e.g., Magnesia source, Magnesia calcination history, and type of aggregates used), the blend design (e.g., water content, pH, additives used, and the use of Magnesia replacement), and both geometry and porosity of the fresh material [6]. In addition to the previously mentioned carbonation-curing influencing

**Citation:** Grünhäuser Soares, E.; Castro-Gomes, J.; Magrinho, M. The Influence of Casting Static Compaction Pressure on Carbonated Reactive Magnesia Cement (CRMC)-Based Mortars. *Mater. Proc.* **2023**, *13*, 5. https://doi.org/10.3390/ materproc2023013005

Academic Editors: Katarzyna Mróz, Tomasz Tracz, Tomasz Zdeb and Izabela Hager

Published: 13 February 2023

**Copyright:** © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

factors, the compaction pressure on the specimens' casting process of carbonatable binders is another factor that may significantly influence the compressive strength obtained in this group of binders, mainly due to its influence on the porosity of the material [7]. However, it seems that this approach has not yet been investigated regarding CaO-based materials.

For this purpose, an exploratory approach was developed aiming to investigate how a CRMC-based mortar exposed to ACC behaves when modifications in the static compaction pressure of the casting process are made. A total of 16 specimens were produced and tested for four different static compaction pressures (i.e., 10, 30, 50, and 70 MPa). Moreover, the mixture, the production method, and the ACC conditions were defined based on previous studies [8–10], which used a reactive compound (MgO), a waste-based material as filler, and sand as fine aggregate to produce CRMC-based mortars that were moulded through static compaction and cured under pressurized ACC for 24 h under controlled conditions.

With the aim of understanding the CRMC-based mortar development, the devised mortars were then evaluated through compressive strength tests, Mercury Intrusion Porosimetry (MIP) analysis, Thermogravimetry and Derivative Thermogravimetry (TG-DTG), and Fourier-transform Infrared Spectroscopy (FTIR) analyses.
