Advances in the hydration of reactive MgO cement blends incorporating different magnesium carbonates

Hydration of reactive magnesia cement (RMC) is limited by the formation of a Mg(OH)2 surface-layer on unreacted MgO particles. This study improved RMC hydration by using magnesium acetate (MA), along with hydromagnesite (H) and magnesite (M) as RMC replacements. While MA accelerated hydration and resulted in the formation of needle-like artinite, inclusion of M led to rosette-like crystals. The accumulated nucleation and growth of low-crystallinity Mg(OH)2 on H particles in a bird nest-like arrangement was observed for the first time in literature. This low-crystallinity Mg(OH)2 could be prone to carbonation. The replacement of up to 40% RMC with M in the presence of MA improved the compressive strength of RMC samples by 240%. This performance enhancement was supported by microstructure densification via the compact formation of hydrate and carbonate phases, defining M as a feasible partial RMC substitute

Environmental impact assessment of the pangasius sector in the Mekong Delta

In the past seven years the export of white pangasius fillets grew fast. The culture method shifted to intensive production of striped catfish (Ca Tra) in deep ponds because this is more efficient than the pen and cage culture of Ca Basa. Today, striped catfish comprises more than 90 % of the culture. The increased production was achieved by producers investing in large ponds. The market chain is gearing towards vertical integration. Most farms keep fish at relatively high densities of 15 to 25 fish/m3 in ponds having a depth of up to 4m, and are advised to exchange daily 20 to 40% of the water. The sustainability of the sector is threatened due to the increased environmental pressure, and hampered by the growing cost of inputs and reduced farm-gate prices of the fish. The Environmental Impact Assessment (EIA) intends to identify measures for preventing or mitigating the environmental impacts of catfish culture in the Mekong Delta. The EIA was a seven-step process during which we interacted twice with part of the main stakeholders. To build trust among the stakeholders from the sector, we conducted the scoping and goal setting with them

FAMEBASE VER. 2.0 – Hệ quản trị cơ sở dữ liệu cho người sử dụng đầu cuối

FAMEBASE VER. 2.0 – Hệ quản trị cơ sở dữ liệu cho người sử dụng đầu cuối

Performance of reactive MgO concrete under increased CO2 dissolution

The strength gain of reactive MgO cement (RMC) samples depends on carbonation, which is limited by the formation of an initial carbonate layer and the low dissolution of CO2. This study investigates the use of seeds and NaHCO3 (SBC) to extend the surface area for carbonation and increase CO2 dissolution, respectively. The influence of seeds and SBC on the hydration kinetics of RMC was evaluated by isothermal calorimetry and pH measurements. Mechanical performance results were supported by XRD, TG-DTG and SEM, which identified the amount and morphology of final phases. The introduction of well-dispersed seeds within the initial mix design enabled the enhanced nucleation of carbonates, while the dissolution of CO2 was improved by the increased initial pH and HCO3– provided by SBC. The simultaneous use of seeds and SBC led to dense microstructures composed of interconnected carbonate networks, resulting in 142% increase in 28-day strengths (24 vs. 58 MPa)

Carbonated MgO concrete with improved performance: The influence of temperature and hydration agent on hydration, carbonation and strength gain

Carbonation plays a key role in the strength gain of reactive MgO cement (RMC)-based concrete formulations. Low hydration of MgO limits the subsequent carbonation and associated strength gain. This study improves the mechanical performance of carbonated RMC concrete mixes with the introduction of a hydration agent (HA) and high temperature pre-curing (HTPC). The influence of HA and HTPC on hydration, carbonation and microstructural development was investigated through isothermal calorimetry, TGA, XRD, ATR-FTIR and SEM. Implementation of HA and HTPC increased the rate and degree of hydration. The increased brucite content led to higher carbonation degrees, accompanied by lower water absorption and higher density and strength values. Improvement of the morphology of carbonates resulted in 40% higher strengths than the control mix, reaching 56 MPa at 28 days. These mixes provided equivalent strengths to the 28-day strength of the control mix at 7 days, therefore shortening the curing period by 75%

Improving the performance of reactive MgO cement-based concrete mixes

Low hydration and high water demand of MgO limits strength gain in MgO cement-based formulations. This study enhanced the microstructure and performance of MgO concrete mixes by increasing hydration and lowering water demand via the introduction of hydration (HA) and dispersion (DA) agents. Hydration and carbonation mechanisms were evaluated by isothermal calorimetry, TGA, XRD, FTIR and SEM. HA increased MgO dissolution and brucite precipitation. DA reduced water content and resulted in denser microstructures by increasing CO2 diffusion. Formation of dense carbonate networks with improved morphologies resulted in 28-day strengths of 45 MPa, which were >50% higher than the control sample

Potential additives for magnesia-based concrete with enhanced performance and propensity for CO2 sequestration

This study focuses on the development of carbonated reactive magnesia cement (RMC) concrete formulations involving hydromagnesite (H), magnesite (M) and hydration agent (HA). Partial replacement of RMC by H and M stimulated the formation of hydrate and carbonate phases. Use of H increased the rate and degree of hydration, resulting in the formation of a bird nest-like structure containing poorly-crystalline brucite. The higher propensity of this poorly-crystalline phase for carbonation increased the utilisation of RMC as a binder and facilitated its conversion into strength-providing HMCs. Synergistic combination of M and HA led to significant strength gain via increased carbonate content and reduced w/b ratio. Presence of M provided micro-aggregates that facilitated the enhanced formation of large carbonate crystals with improved morphologies, resulting in microstructure densification and 113 % strength increase. Furthermore, partial replacement of RMC with M enabled reduction of natural resources, CO2 emissions and energy consumption associated with RMC production

Development of MgO concrete with enhanced hydration and carbonation mechanisms

This study proposed the use of hydration agent (HA) and seeds to improve the hydration and carbonation of reactive magnesium cement (RMC)-based concrete formulations. Hydration of RMC was evaluated by isothermal calorimetry. Water absorption and compressive strength results were used to assess the mechanical performance of RMC-based concrete samples. Quantification of hydrate and carbonate phases was performed via XRD and TGA. Formation and morphology of carbonates were observed via BSE and SEM. In addition to increasing the utilization of RMC in the carbonation reaction and facilitating early strength development, the use of HA formed large carbonate phases, while the addition of seeds improved sample microstructures via the development of dense carbonate networks. The improvements in morphology, microstructure and carbonate content in samples involving the simultaneous use of HA and seeds resulted in 56% lower water absorption values and 46% higher 28-day compressive strengths (70 MPa) in comparison to the control sample

Sequestration of CO 2 in reactive MgO cement-based mixes with enhanced hydration mechanisms

Strength development of reactive MgO cement-based concrete is limited by the low hydration and carbonation of MgO. This study aims to improve the hydration and mechanical performance of carbonated MgO mixes with the introduction of various hydration agents (HAs) at different concentrations. Influence of these HAs on the hydration and carbonation mechanisms under ambient and accelerated curing conditions was evaluated through isothermal calorimetry, TG, XRD and FTIR analyses. Introduction of HAs enabled extensive carbonation and strength development reaching up to ∼60 MPa at 28 days, which was 107% and 53% higher than the corresponding MgO and PC-based control mixes, respectively