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To explore the effect of pressure on the combustion and luminescence properties of magnesium/nitrate pyrotechnics, four sets of zero-oxygen-equilibrium magnesium/sodium nitrate (N), magnesium/potassium nitrate (K), magnesium/barium nitrate (B), and magnesium/strontium nitrate (S) pyrotechnic samples were subjected to TG-DSC (thermogravimetric analysis-differential scanning calorimetry) testing and combustion tests at atmospheric pressure and 1 kPa. The combustion experiments showed that the flame height increased at 1 kPa due to the rapid diffusion of gas products. Moreover, the degree and rate of oxidation of magnesium are limited by the scarcity of oxygen in the environment, resulting in a decrease in both combustion temperature and luminous intensity at low pressure. Thermal analysis tests showed that B and S have higher combustion temperatures and better luminescence performance at 1 kPa because of their higher low-pressure reactions than N and K. In addition, the Mg/Sr(NO3)2 red light tracer has the best luminescence performance at low pressure because it still has a higher concentration of visible light emitter SrOH at 1 kPa. These scientific findings provide useful insights into the low-pressure combustion behavior of pyrotechnics and support the growing demand for military and civilian applications. [ABSTRACT FROM AUTHOR]

To explore the effect of pressure on the combustion and luminescence properties of magnesium/nitrate pyrotechnics, combustion tests and thermal analysis of magnesium/sodium nitrate (N) and magnesium/strontium nitrate (S) pyrotechnic samples with zero oxygen balance were conducted under the pressure range of 101kPa-1kPa in this study. The results show that the flame height of N increases continuously as the pressure decreases, and the flames gradually change from a steady-state convergent flame to a turbulent evanescent flame. However, due to the different diffusion rates of the gas-phase combustion products, the diffusion of S at low pressure is lower and the flame still maintains a stable laminar flow. Although the light intensity and burning speed of both N and S satisfy Vier's law, the luminous intensity of S is less sensitive to pressure and still has good luminous performance at 1 kPa. Thermal analysis test results show that N and S can react almost completely at atmospheric pressure, and their enthalpies of reaction are 6.75 kJ/g and 6.07 kJ/g, respectively. The difference in the thermal decomposition histories of strontium nitrate and sodium nitrate at 1 kPa results in a reaction enthalpy of 4.24 kJ/g for S and only 2.45 kJ/g for N. This indicates that the reaction degree of S at low pressure is higher than that of N. The SEM-EDS test results further confirm this opinion. These scientific findings provide useful insights into the low-pressure combustion behavior of pyrotechnics and support the growing need for military and civilian applications. [ABSTRACT FROM AUTHOR]

Abstract Supplementary cementitious materials (SCMs) play an essential role in sustainable construction due to their potential to reduce carbon emissions, promote circular economy principles, and enhance the properties of concrete. However, the inherent diversity of SCMs makes it challenging to predict their degree of reaction (DOR). This study applies machine learning techniques to predict DOR while exploring key parameters affecting it. Five machine learning models are utilized: linear regression, Gaussian process regression (GPR), decision tree regression, support vector machine and extreme gradient boosting, with GPR providing the most accurate and adaptable prediction. The study delves into the impact of various parameters on DOR, revealing their significance. Silica content emerges as the most critical, followed by particle size distribution, specific gravity, and water-to-cement (W/C) ratio. Optimizing DOR requires extending curing time, reducing particle size distribution, and considering optimal silica content and W/C ratio. This research emphasizes the importance of understanding the relationships between parameters and the DOR of SCMs, providing insights to enhance the efficiency of SCMs in cementitious systems through machine learning and data-driven analysis.

Supplementary cementitious materials (SCMs) play an essential role in sustainable construction due to their potential to reduce carbon emissions, promote circular economy principles, and enhance the properties of concrete. However, the inherent diversity of SCMs makes it challenging to predict their degree of reaction (DOR). This study applies machine learning techniques to predict DOR while exploring key parameters affecting it. Five machine learning models are utilized: linear regression, Gaussian process regression (GPR), decision tree regression, support vector machine and extreme gradient boosting, with GPR providing the most accurate and adaptable prediction. The study delves into the impact of various parameters on DOR, revealing their significance. Silica content emerges as the most critical, followed by particle size distribution, specific gravity, and water-to-cement (W/C) ratio. Optimizing DOR requires extending curing time, reducing particle size distribution, and considering optimal silica content and W/C ratio. This research emphasizes the importance of understanding the relationships between parameters and the DOR of SCMs, providing insights to enhance the efficiency of SCMs in cementitious systems through machine learning and data-driven analysis. [ABSTRACT FROM AUTHOR]

Determination and prediction of degree of reaction (DOR) of supplementary cementitious materials (SCMs) in hydrated Portland cement are important for designing concrete with lower levels of embodied carbon dioxide. Herein, a model for predicting the DOR of SCMs in hydrated cement was developed using a set of collected data and a machine learning algorithm based on genetic programming toolbox for the identification of physical systems. The results suggest that the model reliably predicts the DOR of slag, fly ash, metakaolin, and silica fume with a coefficient of determination (R2) value of 0.89. The predicted DOR of SCMs is found to be directly proportional to water-to-cement ratio and curing time, while it is highly reliant on the oxide composition and differs amongst SCMs. For instance, the DOR of slag substantially increased with a higher alumina content, while the DOR of metakaolin remained more stable, primarily influenced by the silica-to-alumina ratio. The proposed model is particularly useful for predicting phase assemblages of SCMs-blended Portland cement when experimental data and information on SCMs are limited and properties of SCMs are highly variable. The insights gained from this study offer a pathway towards more sustainable and efficient concrete design, aligning with contemporary environmental objectives. [ABSTRACT FROM AUTHOR]

A reaction degree of supplementary cementitious materials (SCMs) in hydrated Portland cement is an important factor that enables prediction of the performance of concrete, while conventional methods for estimating the degree of reaction of SCMs are generally time-consuming and complicated. This study investigated the applicability of thermodynamic modeling as an alternative and potentially less complicated means of predicting reaction degrees of SCMs. The reaction degrees and bound water contents of slag- and fly ash-blended Portland cement were experimentally measured at various sample ages by selective dissolution and thermogravimetric analysis, respectively, and compared with thermodynamic calculations. The results suggest that reasonably accurate and comparable predictions of bound water and degrees of reaction of SCMs can be made, which is promising and shows the potential of this approach to be used as an alternative and simple approach to predict the degrees of reaction of SCMs in hydrated Portland cement.

Geopolymers are miscellaneous materials with superior mechanical strength properties. Geopolymeric materials offer the advantage of simultaneously improving both environmental and engineering performance compared to cement-based materials used in the construction industry. This study presents the geopolymerization kinetics of fly ash-based geopolymer foams by using the Johnson–Mehl–Avrami–Kolmogorov (JMAK) model. The experiments were designed using several curing temperatures and alkali concentrations. The degree of reaction (α) of the fly ash was used as a measure of the changes that occurred during the geopolymerization reaction. The compressive strengths of the prepared samples were estimated by using the JMAK method as well as through real-time compression strength analysis, and the results were compared. The values of n were in the range of 0.0931–0.2321, while the values of k were in the range of 0.366–0.671. Regardless of alkali concentration and curing temperature, the degree of reaction continued to increase in all samples until the 28th day, after which the degree of reaction remained almost stable. Although alkalinity and curing temperature had a positive effect on strength gain, low alkalinity had no effect on strength even when the curing temperature was increased. The increase in alkalinity, curing temperature, and curing time had an increasing effect on strength in both measured and calculated values. The strength values obtained on the 1st, 7th, 28th, and 90th days for the samples were compared with the JMAK results, and it was concluded that the values calculated with JMAK were half of the measured strength values. [ABSTRACT FROM AUTHOR]

Coal gasification coarse slag (GFS) is a byproduct of coal gasification technology, which contains abundant amorphous aluminosilicate minerals. GFS has low carbon content, and its ground powder has potential pozzolanic activity, which can be used as a supplementary cementitious material (SCM) for cement. Herein, GFS-blended cement was studied in terms of ion dissolution characteristics, initial hydration kinetics, hydration reaction process, microstructure evolution process, and the development of the mechanical strength of their paste and mortar. Enhanced alkalinity and elevated temperature could increase the pozzolanic activity of GFS powder. The specific surface area of GFS powder and its content did not change the reaction mechanism of cement. The hydration process was divided into three stages: crystal nucleation and growth (NG), phase boundary reaction (I), and diffusion reaction (D). A higher specific surface area of the GFS powder could improve the chemical kinetic process of the cement system. The degree of reaction of GFS powder and blended cement had a positive correlation. A low GFS powder content (10%) with a high specific surface area (463 m2/kg) showed the best activation in cement as well as improving the late mechanical properties of cement. The results show GFS powder with low carbon content has the application value as SCM. [ABSTRACT FROM AUTHOR]

[Display omitted] • A study of fly ash based pressed and cast geopolymer was proposed. • Compressive strength of pressed geopolymer nearly twice that of cast geopolymer. • Flexural strength of pressed geopolymer was 5 times higher than cast geopolymer. • The highly compacted pressed geopolymer reduced the tendency of efflorescence. • The low alkali activator of pressing method lowered EE, ECO 2 and ECI of geopolymer. The high liquid content of cast geopolymer not only limits its strength development and durability but also leads to high energy consumption and carbon dioxide (CO 2) emissions. Thus, a study of the cast and pressed geopolymer was performed. The geopolymers were cured for 1, 7 and 28 d before testing and characterizations. With the incorporation of pressure compaction, higher bulk density (2158–2227 kg/m3) was recorded for pressed geopolymer in comparison to cast geopolymer (1842–1854 kg/m3). The dense matrix in pressed geopolymer improved the inter-particle contact, increasing the 28 d degree of reaction to 39.7%, higher than that of cast geopolymer (33.0%). This feature was proved by SEM micrographs wherein the pressed geopolymer was well-compacted and denser in microstructure, with less unreacted/partially reacted fly ash and pores. The compressive and flexural strengths of pressed geopolymer reached 114.2 and 29.9 MPa after 28 d, higher than that of cast geopolymer (60.0 and 6.2 MPa, respectively). The strength reduction of pressed geopolymer (31.7%) after the accelerated efflorescence test was lower than that of cast geopolymer (60.2%). The ecological analysis inferred that pressed geopolymer was ecologically superior to the casting method in terms of embodied energy (EE) and embodied carbon dioxide emission (ECO 2), in which 50% and 59% of reductions are acquired. Besides, the embodied carbon index (ECI) of pressed geopolymer was about 21% of cast geopolymer. [ABSTRACT FROM AUTHOR]

Knowing the reactivity of recycled brick powder (RBP) is fundamental for its correct and efficient utilization. In this work, the dissolution behavior of RBP in NaOH solution and the degree of reaction in cement matrix were studied to investigate the reactivity of RBP. The results revealed that the main active species of RBP, Si and Al, showed obvious lasting dissolution with a significant non-steady state dissolution stage, indicating that the reaction proceeds slowly. The dissolution mechanism controlled by the phase boundary reaction, with activation energies of 82.74 kJ/mol and 75.79 kJ/mol for Si and Al dissolution, respectively, further confirmed this finding. The strength activity index, thermogravimetric analysis, selective dissolution, BSE-IA-Mapping and MAS NMR all confirmed reactivity of RBP. Additionally, reaction rims were observed around RBP particles in cement paste. The low Ca/Si and Ca/Al ratios and their significant increases in a direction from the particle boundary to the paste demonstrate that the rim was a hybrid phase composed of the original RBP components and the reaction products. [ABSTRACT FROM AUTHOR]

• A moderate content of LCDGP polymerizes C-(N)-A-S-H gel and does not cause strength loss. • As the LCDGP content increases, the dominant phase changes from C-(N)-A-S-H to N -A-S-H. • High content of LCDGP reduces the reactivity of the precursors, causing significant strength loss. • The content of LCDGP that does not cause strength loss is up to 50 %. This study presents the feasibility of a combination of liquid–crystal display glass powder (LCDGP) and slag in alkali-activated materials using several techniques including nuclear magnetic resonance and thermodynamic modeling. Slag was replaced with LCDGP at a weight ratio of 25%, 50%, 75%, and 100%. Replacing slag with LCDGP up to 50% resulted in no strength loss and no significant changes in phase assemblages compared to alkali-activated slag. The incorporation of 25% LCDGP improved the pore structure and the reactivity of both precursors which result in increased compressive strength. This was because aluminum of LCDGP incorporated into the silicate which polymerized more C-(N)-A-S-H gel. However, the excessive use of LCDGP (more than 50%) caused a significant strength loss. Since LCDGP was responsible for lowering the pore solution's pH, its excessive use reduced the reactivity of precursors and caused a significant strength loss. This study suggests a guideline for using LCDGP to improve the mechanical property of alkali-activated slag. [ABSTRACT FROM AUTHOR]

• The dissolution rates of different raw materials and reaction products were investigated. • A quantitative analysis approach for the geopolymerization degree of MK was developed. • The GGBFS was almost completely reacted under the alkali- activated conditions. • Addition of GGBFS improved the reaction level of MK in most cases. The mechanical properties and durability of an alkali-activated metakaolin (MK)- ground granulated blast furnace slag (GGBFS) blend depend on its reaction degree during the alkali activation process. In the present study, the dissolution ratios of MK and GGBFS and their reaction products in hydrochloric acid with different pH values were investigated. The hydrochloric-acid-insoluble matter of MK and its geopolymers were analysed using an X-ray fluorescence spectrometer, X-ray diffractometry, and Fourier transform infrared spectroscopy. It was found that the MK was mostly insoluble and that the MK-based geopolymer was dissolved completely in the hydrochloric acid solution at a pH of 0, and the GGBFS and alkali-activated GGBFS were completely dissolved in the hydrochloric acid solution at a pH of 0–2. Based on the solubility of the raw materials and the alkali activated products, a quantitative analysis approach for the geopolymerisation degree of MK and an MK-slag blend was developed, and the degrees of reaction of the MK and MK-slag blend under alkali activation conditions were studied. It was found that the degree of geopolymerisation reaction of pure MK increases with the increase in the liquid–solid ratio and decreases with the increase in the activator modulus (molar ratio of SiO 2 to Na 2 O) with an activator concentration of 35%. The addition of GGBFS enhanced the degree of reaction of the MK in the MK-GGBFS blend in most cases, particularly under conditions of a low liquid–solid ratio, a high activator modulus, and a low activator concentration. The degree of reaction of the MK in the blend usually first increases and then decreases with the increase in the GGBFS content, and the 40% and 60% GGBFS contents often correspond to the highest degree of geopolymerisation reaction of the MK. However, the degree of the reaction of the MK will continue increasing with the increase in the GGBFS content when activated by an activator with a low concentration. [ABSTRACT FROM AUTHOR]

[Display omitted] • A ready-mix geopolymer were prepared with powder sodium silicate. • Geopolymer manufacture with powder activator was easy and simple. • Economic advantage for a process implementation at a commercial scale. • Powder and aqueous activator shows diferences in the geopolymeric gel development. • Powder-geopolymer showed better response to durability test. Geopolymer manufacturing by means a ready-mix procedure using powder sodium silicate as activator is described in this paper. Its characteristics are compared with conventional geopolymers using aqueous sodium silicate. Degree of reaction, mercury intrusion porosity and compressive strength were measured at different curing times. Three durability tests were carried out. The geopolymer obtained using powder activator showed slightly lower mechanical properties and better durability results than those found for geopolymers based on aqueous activators. In addition, the manufacture of geopolymers based on powder silicate was easier and simpler than the more common procedure using sodium silicate solutions, so the ready-mix manufacturing could be an alternative to produce geopolymers. [ABSTRACT FROM AUTHOR]