ABSTRACT
Illustrating the influence of Fe dosage and temperature on the formation of sulfoaluminate hydrates is of great significance to understand the early hydration process of high ferrite cement ...under steam curing. Herein, the impact of Fe dosage on the ettringite formation at different temperatures was revealed through the combination of experiments and computational simulations. A Fe dosage no more than 20% conspicuously accelerated the crystal growth of ettringite by increasing the surface energy in the (0 0 1) direction, whereas a higher dosage suppressed the formation of ettringite as the high incorporation of Fe ions into the ettringite crystal was energetically unstable. The chemical environment analysis of Fe in products shows that Fe(OH)63−, compared with Al(OH)63−, prefers to participate in the formation of Al2O3‐Fe2O3‐mono than ettringite, which is also confirmed by the calculated thermodynamic properties’ results. The understanding of the impact and mechanism of Fe on the formation of ettringite under steam curing conditions plays a pivotal role in the utilization of high ferrite cement.
•The carbonation capacity of 20% CO2 is higher than that of pure CO2.•The carbonation strength is proportional to CO2 uptake, but not to reaction time and pressure.•The highest strength is obtained ...under proper combination of carbonation and hydration.•The carbonation mechanism for the flue gas and pure CO2 is analysed.
Carbonation curing of cement-based materials is an important pathway for CO2 utilization and sequestration. Most previous studies focused on pure CO2 carbonation curing. In this work, we demonstrate superior CO2 uptake and enhanced compressive strength with flue gas (20% CO2 concentration) carbonation curing. The flue gas carbonation rate is smaller at the beginning of curing, but the CO2 uptake and compressive strength are larger than that of pure CO2 curing at 12 h carbonation. Moreover, the growth rate of the post hydration strength is inversely proportional to the CO2 uptake, but under proper combination of carbonation and hydration curing, the 28d strength of the flue gas carbonated specimen can be higher than that of the hydration specimen. The carbonation curing mechanism for the flue gas and pure CO2 is discussed from a microscopic perspective. The higher carbonation capacity of lower concentration CO2 in cement carbonation curing may inspire new pathways in carbonation management.
•The influence of curing conditions on the sorptivity, electric flux and carbonation depth were investigated.•Longer curing time, higher humidity and appropriate temperature was helpful to improve ...the impermeability of concrete.•The relationship between water absorption and other permeability was discussed.
The influence of mineral admixtures and curing conditions on the permeability of concrete with high volume mineral admixtures is investigated. Fly ash and ground granulated blast furnace slag (GGBFS) are used to replace 50% cement, the water absorption, capillary water absorption, sorptivity coefficient, electric flux and carbonation depth of concrete with mineral admixtures are tested under different curing conditions, such as the curing time, curing humidity and curing temperature. The test results show that the water absorption, capillary water absorption, sorptivity coefficient, electric flux and carbonation depth of concrete decrease with the longer standard curing time, higher curing humidity and appropriate curing temperature, and decrease with the increasing of GGBFS content. It is also shown that the permeability of concrete with high volume mineral admixtures is very sensitive to the curing conditions.
On‐demand adhesive dismantling has the potential to improve multimaterial product recycling, but its implementation has been hampered by a critical trade‐off between strong bonding and easy ...debonding. As a result, the temperature range in which these temporary adhesives can be used is relatively limited. Here, a new class of dynamic epoxy resins is reported that significantly extends this upper temperature limit and still achieves fast debonding. Specifically, two types of dynamic polyamidoamine curing agents for epoxy hardening are developed, being polysuccinamides (PSA) and polyglutaramides (PGA). As the dynamic debonding/rebonding process of PSA and especially PGA linkages is more thermally demanding and at the same time more thermally robust than previously reported dynamic covalent systems, the resulting materials can be triggered at high temperatures, and at the same time remain bonded over a wide temperature range. The versatility of the PSA and PGA dynamic adhesive curing system is demonstrated in classical bulk adhesive formulations, as well as in dynamic covalent linking to a PSA‐ or PGA‐functionalized surface. As a result, an attractive drop‐in strategy is achieved for producing debondable and rebondable epoxy adhesives, with high complementarity to existing adhesive resin technologies and applicable in an industrially relevant temperature window.
A new class of on‐demand debondable epoxy adhesives showing fast debonding, while staying stable until high temperatures, is reported. In this context, two types of dynamic polyamidoamine curing agents are synthesized and their versatility is demonstrated in classical bulk adhesive formulations, as well as in dynamic covalent linking to functionalized surfaces.
Influences of limestone powder on the resistance of concretes to the chloride ion penetration and sulfate attack with a constant water/binder ratio and a constant 28-day compressive strength were ...studied. The sensitivity of the properties of concrete to the initial moist curing time was also explored. The results indicate that, under a constant water/binder ratio condition, the resistance to sulfate attack of concrete deteriorates with the increasing of limestone powder content, and the resistance to chloride ion penetration decreases when the replacement ratio of limestone powder is 24%. As the initial moist curing time declines, the reducing magnitude of the properties of concrete containing limestone powder is larger than that of plain cement concrete. Nevertheless, lowering the water/binder ratio of concrete containing limestone powder can significantly reduce the sensitivity of the properties of the concrete to the initial moist curing time. No matter how long the initial moist curing time is, replacing cement with 8% limestone powder can improve the resistance of concrete to sulfate attack. Concrete with up to 24% limestone powder addition can still obtain a resistance to chloride ion penetration and sulfate attack similar to plain cement concrete on the premise of a constant 28-day compressive strength. Moreover, it was found that both the crystallization of sodium sulfate and the formation of ettringite collectively result in the deterioration of concrete subjected to the sulfate solution.
Display omitted
•Lowering the w/b ratio can significantly reduce the sensitivity.•2. Adding 8% limestone powder can improve sulfate attack resistance.•3. Na2SO4·10H2O and AFt result in the deterioration of the concrete.
This study aims to establish a development model for the compressive strength of 3D printed concrete (3DPC) under the coupling influence of temperature and humidity, utilizing the maturity method. ...Initially, diverse curing conditions were applied to 3D printed specimens, incorporating varying temperatures (10 °C, 20 °C, 40 °C) and relative humidity levels (100% RH, 80% RH, 60% RH, 40% RH), with strength value assessed at different ages. Subsequently, a maturity model for humidity modification was proposed, and the model was calibrated through experimental results. The results show that the strength of the specimens increases over time, irrespective of the variations in curing temperatures and humidity levels. Moreover, with a decrease in humidity level, a more pronounced decline in strength is observed. Furthermore, the anisotropy index values of the rate constant in the Y-direction specimen, when cured at temperatures of 10 °C and higher humidity conditions, such as 100% RH and 80% RH, exhibit significant variations across different temperatures and moisture levels, leading to increased anisotropies. The modified maturity model can be used to predict and evaluate the strength development of 3D PC under different environmental conditions with high accuracy.
•Low temperature and high humidity conditions lead to increased anisotropic behavior.•The proposed model accurately predicts the strength development of 3DPC under various temperature and humidity conditions.•The anisotropy index exhibits notable variations across different temperatures and humidity levels.
•Recommendations are provided for kinetic analysis of thermal polymerization.•Main focus is on analysis of DSC measurements.•Multi-step nature of polymerization kinetics is emphasized.•Model-fitting, ...isoconversional, and deconvolution analyses are discussed.•Specific advices are offered for efficient usage of each analysis.
The present recommendations have been developed by the Kinetics Committee of the International Confederation for Thermal Analysis and Calorimetry (ICTAC). The recommendations provide guidance on kinetic analysis of thermal polymerization, which incorporates both linear and crosslinking polymerization (curing). The focus is on treating the kinetics as measured by differential scanning calorimetry (DSC). The recommendations discuss basic reaction mechanisms and emphasize the multi-step nature of the polymerization kinetics. An overview of mechanistic and phenomenological models is provided for polymerization controlled by reaction kinetics and diffusion. Three different approaches to evaluation of kinetic parameters (activation energy, preexponential factor, reaction model) for individual steps are considered. These approaches comprise model-fitting, isoconversional, and deconvolution analyses. Practical advices are offered for effective usage of each approach. Attention is paid to the typical problems and to the ways of addressing them. The recommendations are intended to assist with efficiently conducting kinetic analysis and interpreting its results.
In order to integrally recycle urban solid wastes as secondary resource materials, cold bonded lightweight aggregates (CBLAs) comprising 100% wt. solid wastes, including incineration sewage sludge ...ash (ISSA) and concrete slurry waste (CSW), were produced. This study focused on assessing the feasibility of using ISSA in CBLAs and its improvement on thermal stability; studying the influence of CSW as an alternative binder instead of ordinary Portland cement (OPC); quantifying the benefits of using CO2 curing compared to steam curing; and evaluating the addition of waste wood fine (WF) on the properties of CBLAs. The experimental results showed that the combined use of ISSA and CSW to produce CBLAs resulted in better properties than the one produced with ISSA and OPC; and increasing the CSW content had positive influence on the pellet strength. CO2 curing could help to achieve rapid strength development and lower water absorption of the pellets compared to steam curing. The use of WF increased the porosity of CBLAs, resulting in lower bulk densities and higher water absorption values. In comparison, the CBLAs prepared with ISSA had good thermal stability, and showed more than 30% residual strength after exposure to 800 °C. Additionally, the CO2 cured CBLAs can sequestrate 3.9–7.6% per unit wt. of CO2 during the curing process.
•Cold bonded lightweight aggregates were produced with 100% wt. of solid wastes.•Concrete slurry waste was recycled as a cementitious binder for CBLAs.•Accelerated CO2 curing was applied on CBLAs incorporating cementitious waste innovatively.•CBLAs with ISSA had good thermal stability.•CO2 uptake of the produced CBLAs was between 3.9% - 7.6% wt.
Three oxazolidine‐2‐one based acrylates monomers were synthesized by the reaction of oxazolidine‐2‐one with 1,6‐hexanediol diacrylate (HDDA), neopentyl glycol diacrylate (NPGDA) and ...trimethylolpropane triacrylate (TMPTA). The molecular structures of the products were characterized by FT‐IR, 1H NMR and electrospray ionization high resolution mass spectrometry (ESI‐HRMS). The photo‐polymerization kinetics of the synthesized oxazolidine‐2‐one based acrylates were investigated by real‐time infrared spectroscopy. The results showed that the oxazolidine‐2‐one based acrylates with 1 wt% 2‐isopropylthioxanthone (ITX) could be cured to form a transparent film under UV irradiation. The UV curing speed of oxazolidine‐2‐one based acrylates with 1 wt% ITX was better than that of TMPTA with 1 wt% ITX and 3 wt% ethyl 4‐(dimethylamino) benzoate (EDB) as co‐initiator. Based on the HRMS analysis of oligomers extracted from the UV‐cured film, the plausible photopolymerization mechanism was proposed. The synthesized monomer formula with CN996 resin can be 3D printed forming various models with smooth surface, good accuracy, excellent thermal stability and 99.4% gel content.
•A practical model framework is developed to assess the CO2 uptake of cement mortar.•High-concentration CO2 accelerates diffusion process and has little effects on carbonation process.•The CO2 uptake ...for different sizes of specimens tends to be the same after sufficient curing.•Achieving overall curing is an effective way to ensure high carbonation rate and CO2 uptake.
CO2 curing of cement-based materials is considered a promising carbon–neutral technology for large-scale storage of CO2, and CO2 uptake is the key parameter for evaluating CO2 storage capacity. This study assessed the CO2 uptake of cement mortar subjected to flue gas curing through theoretical modeling and experimental validation. It is found that the CO2 uptake for the high-concentration group is higher at early stages but becomes the same after sufficient curing, asthe higher CO2 concentration accelerates the diffusion process but has little effect on the carbonation process. Meanwhile, although the initial CO2 uptake for the smaller specimens is larger, the difference gradually decreases with curing time after overall curing. Achieving overall curing is an effective way to ensure high carbonation rate and CO2 uptake. The CO2 uptake at overall curing increases with increasing specimen size or decreasing CO2 concentration. For fixed-depth CO2 curing, the CO2 uptake decreases significantly with increasing specimen size, while the curing time and carbonation degree change little. The findings of the present work will be beneficial to improve the CO2 storage capacity of cement-based materials and push forward the application of CO2 capture, utilization and storage (CCUS) technology in the construction industry.
