Strength Development Research Articles

A green binder for cold weather applications: enhancing mechanical performance of alkali-activated slag through modulus, alkali dosage, and Portland cement substitution

Below 5 °C, Portland cement (PC) experiences delayed hydration, slowing strength development, making it unsuitable for winter. Alkali-activated slag (AAS) emerges as a viable alternative with continuous hydration in low-temperature conditions. The effect of the activator nature on the performance of AAS cured at normal temperatures is well known, but further studies are required for low-temperature conditions. This study investigates the synergistic impact of activator modulus (1.2 and 1.5), alkali dosage (5, 7, and 9%), and PC substitution rates (0, 10, and 20%), on low-temperature cured AAS properties. Eighteen mixtures were prepared and cured at 2 °C. Compression and ultrasonic pulse velocity tests were conducted after 7, 28, and 90 days. Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy analyses were performed to examine the microstructure of the samples. Elevating alkali dosage enhanced early age strength but resulted in a drop in 90-day strength. Simultaneous increases in modulus and PC substitution rate reduced strength due to shrinkage-induced crack formation. Optimal mixture design options included using 10% PC in the 1.2 modulus and omitting PC when the 1.5 modulus was selected. Despite low temperatures, the use of PC significantly accelerated the setting time. Altering modulus and alkali dosage caused a considerable change in the intensity of the peaks in the FTIR spectrum. The findings indicate that AAS shows promise when adjusting the mixture design for temperatures below 5 °C, which are unfavorable for the hydration of PC.

Effect of temperature on binding process of calcium carbonate concrete through aragonite crystals precipitation

This study investigated the impact of temperature on the strength development of calcium carbonate concrete (CCC) comprising calcium carbonate and concrete waste. CCC exhibited its highest compressive strength when manufactured at temperatures between 60 and 70 °C, thereby demonstrating strengths 1.5 and 2.7 times greater than those achieved at 40 and 90 °C, respectively. At this temperature range (60–70 °C), CCC showed the highest amount of precipitated aragonite with large acicular aragonite crystals, which decreased the porosity of CCC. This temperature range governed the homogeneous distribution of calcium carbonate deposition within the CCC specimen. Moreover, the carbonated cement paste particles within the CCC continuously underwent aqueous carbonation, thereby providing an additional Ca source for calcium carbonate precipitation in CCC. At high temperatures, this process promotes the precipitation of Ca ions as needle-like aragonite crystals during reprecipitation with accelerating the transformation of calcium carbonate polymorphs. The CCC strength arose from the deposition of calcium carbonate from input calcium bicarbonate solution and the reprecipitation of calcium carbonate during aqueous carbonation. The calcium carbonate precipitation from aqueous carbonation accounts for 30 % of the total calcium carbonate precipitation of CCC. Needle-like aragonite crystals functioned as interlocking bridges between the particles and frame connections, effectively strengthening the CCC composite.

Experimental study and prediction of the long-term strength development of high-flowability concrete made of mixed sand and high-content fly ash

To comprehensively utilize the abundant solid wastes of superfine river sand and fly ash, a mixed sand of superfine river sand with coarse manufactured sand and high-flowability concrete made of mixed sand and high-content fly ash were developed. To address the critical question about the long-term strength of this new concrete, this paper presents an experimental study on the long-term development of cubic compressive and tensile strengths of the concrete over a curing age from 7 days to 360 days. In the study, the mixed sand was a hybrid of 40 % superfine river sand and 60 % coarse manufactured sand, and the fly ash content varied from 30 % to 75 % of the total binders by weight. The law of strength development of concrete with fly ash content was analyzed, combined with explanations of the mechanism and observations of hydration exotherms and microstructures of the concrete. Equations were proposed for predicting the long-term development of cubic compressive and tensile strengths, incorporating coefficients to reflect the effects of fly ash on the binder’s compressive strength and the development tendency of concrete strength. The validity of the proposed prediction equations was verified against the test results and compared with the extended application of the equation specified in CEB-FIP MC 2010.

Magnesium-silicate-hydrate cement pastes: Rheological behavior and strength development

In contrast to Portland cement (PC), magnesium-silicate-hydrate (MgO-SiO2) cement mixes offer a significant advantage due to their lower calcination temperature requirement during production, reduced carbon footprint and energy consumption linked with the manufacturing process. This study presents a detailed investigation of the rheological characteristics and strength development of magnesium-silicate-hydrate cement mixes, along with a series of microstructural analyses to examine the hydration process and phase compositions of the prepared mixes. Results indicated that an increase in the water-to-binder (w/b) ratio decelerated the growth rate of both storage and loss moduli over time. Samples with magnesia-to-silica (m/s) ratios of 4:6 exhibited not only the highest modulus during the initial stages of hydration, but also the most rapid increase. The reaction of MgO and dissolution of SiO2 were limited in the fresh state, initially resulting in low brucite and M-S-H contents. Although samples with m/s ratios of 5:5 exhibited the highest 28-day compressive strength (38.5 MPa), those with m/s ratios of 4:6 had the highest M-S-H content at 28 days. These findings contributed to existing knowledge by revealing the relationship between rheological characteristics, reaction mechanisms and strength development within MgO-SiO2 system and highlighted the impact of key factors such as w/b and m/s ratios on both the fresh and hardened properties.

Studying the hydration kinetics and mechanical-microstructural properties of Portland cements made with and without dredged sediment: experimental and numerical approaches

This research focused on two objectives: (i) investigating the impacts of sediment substitution in the raw meal on the hydration and mechanical-microstructural properties of cement; (ii) assessing the reliability of CEMHYD3D code for modeling the properties of hydrated cement. The experimental results indicated that a maximum rate of sediment up to 7.55% had no impact on the formation of mineralogical phases of clinker, the hydration and mechanical-microstructural development of cement. The degree of hydration and strengths of cement made of sediment substitution were slightly higher than those of reference cement, whereas the critical diameter of pores of both hydrated cements was nearly identical. Comparing the modeling results with the experimental measurements showed good predictions for the degree of hydration, hydration heat as well as strength development. However, the formation of hemi-and mono-carboaluminate phases was not predicted in the model, and the porosity prediction was also limited to the capillary porosity.

Role of polyferric sulphate in hydration regulation of phosphogypsum-based excess-sulphate slag cement: A multiscale investigation

Current demand for waste recycling, phosphogypsum-based excess-sulphate slag cement (PESSC) as a sustainable cement prepared by solid wastes, urges enhancing its performance development based on microstructure optimisation. For the purpose of improving the performance and durability of PESSC used in normal or corrosive environments, it is deemed an efficient technique to produce iron-doped compounds with high thermodynamic stability. This paper presents a systematic study of the effect of iron modification on PESSC binders by introducing 0%–2% polyferric sulphate (PFS) from a multiscale viewpoint. XPS, 29Si and 27Al NMR, and TEM were used to characterise the nanostructure of solid particles firstly at Level I. Then, the chemical composition and phase assemblage of PESSC binders were revealed at Level II in terms of ICC, ICP, DTG-DSC, FTIR, BSE-EDS and XRD. Finally, setting time and strength development were determined at Level III. Results indicated that the soluble FeOH4− supplied by the hydrolysis of PFS promotes the generation of iron-doped ettringite with a greater length-to-diameter ratio and thermodynamic stability. Seeding effect of iron doping also promotes the production of spherical and retiform gels with a slight influence on the chemical components and polymerisation. Despite the fact that iron doping weakens the early strength of PESSC mortars, it promotes the persistent hydration rate by retarding precipitation and encapsulation of hydrates on the surface of the slag, showing excellent strength in the later stages. In view of microstructure evolution and performance development during each stage, PFS supplementation within 1.0% is considered a feasible modification of PESSC relying on the formation control of iron-doped hydrates.

Experimental investigation on rehabilitation effectiveness of ductile RC beams with various seismic damage levels using dynamic and static-cyclic loading protocols

With respect to the seismic damage of a ductile reinforced concrete (RC) beam in an RC building structure with seismic design, since the functionality of the building must be recovered, the maximum strength and ductility of the member must be restored by repair or retrofit. Therefore, this work focuses on the effectiveness of the selected repair and retrofit methods in rehabilitating a ductile RC beam with a specified damage level. For this purpose, eight RC beam specimens are designed based on the seismic design requirements in ACI 318-19 to investigate their mechanical properties using the test. In the experiment, loading protocol tests of two types - traditional static-cyclic loading protocol and earthquake-then-cyclic loading protocol—are conducted to quantify the effectiveness of rehabilitation of the RC beam specimens with the selected repair or retrofit methods. The repair and retrofit methods include surface treatment, epoxy low-pressure injection, epoxy resin mortar coating, rebar planting and steel plate retrofitting. Finally, the test results related to the development of strength, stiffness and cracking are used to quantify the effectiveness of rehabilitation of the ductile RC beams with various seismic damage levels using the selected repair or retrofit methods.

Effects of Dry Land Speed Training on 100-Meter Freestyle Swimming in Adolescent Swimming

Background and Aim: The specific strength development in swimming tends to start at a younger age, so it becomes particularly important to conduct effective Specific strength training during adolescence. It is essential to utilize training methods and means that align with the developmental characteristics of Specific strengths in young swimmers. Thus, this study has developed a specific dry-land training program to enhance the 100-meter freestyle swimming speed of adolescent swimmers. Methods: This study selected 30 male adolescent swimmers from the Shaanxi Provincial Swimming Team and divided them into an experimental group and a control group (15 individuals in each group) based on their 100-meter freestyle speed. Both groups underwent a 12-week training intervention, with 12 training sessions per week, each lasting 2 hours. The total training time and water-based training content were the same for both groups, but the content of dry-land training differed. The experimental group followed a specific dry-land training program, while the control group followed a traditional training program. Comprehensive tests were conducted before and after the 12-week training intervention for both groups, using the physical fitness and test scores of swimmers in the experimental and control groups as research indicators. Experimental and analytical methods, including experimental and statistical methods, were employed to conduct a targeted study on the changes in physical fitness and test scores before and after the training. Results: show that after 12 weeks of training, the scores for both groups are as follows: Pull-ups (Experimental group: P=0.000<0.01, Control group: P=0.777>0.05), Vertical jump (Experimental group: P=0.032<0.05, Control group: P=0.848>0.05), Abdominal muscle endurance (Experimental group: P=0.000<0.01, Control group: P=0.396>0.05), and Back muscle endurance (Experimental group: P=0.004<0.01, Control group: P=0.583>0.05). The post-test results reveal that swimmers in the experimental group performed significantly better in pull-ups, vertical jumps, abdominal muscle endurance, and back muscle endurance compared to the control group. Conclusion: The specialized training program effectively increased the upper limb strength of the participants, with no significant advantage over the traditional training program.

A novel polyurethane-based mortar for pavement crack repair: Development, characterization, and performance evaluation

In light of the severe hazards posed by pavement cracks on traffic safety and infrastructure longevity, the development of a convenient and effective pavement repair material has become essential. The excellent cohesive strength and resilience of PU offer significant potential as a crack repair material, ensuring enhanced durability and reliability in pavement crack repairs. This study systematically explored the workability, mechanical properties, interface bonding performance, and fracture behavior of PUM as a pavement repair material through mechanical strength tests, interfacial tensile tests, and three-point bending tests based on DIC. The results indicate that the fluidity of PUM can be adjusted through the binder-sand ratio and PD content, enabling customization for various repair scenarios. PUM demonstrates exceptional one-day compressive and flexural strengths, achieving 18.8 MPa and 7.1 MPa, respectively. Furthermore, the bond tensile strength of PUM reaches 4.3 MPa, exhibiting accelerated strength development that meets the requirements for vehicle traffic after repairs. The lower elastic modulus of PUM, ranging from 0.28 to 0.63, indicates improved deformation adaptability. SEM analysis reveals a complex interfacial bonding network between PU and aggregates, considerably enhancing the energy dissipation capacity of PUM with a peak GF value of 205.05 N/m. DIC technology robustly captured the crack progression, revealing significantly reduced stress concentration at the crack tip of PUM, with no through-thickness cracks detected during the three-point bending fracture process. It is recommended that PUM be prepared with an 80 % binder-sand ratio and 5 % PD to achieve an optimal balance of workability, mechanical, and fracture properties.

Effects of unstable load vs stable load on muscle activation and bar velocity during a bench press

Unstable load (UL) resistance exercises have gained popularity due to the potential to increase strength and neural development compared to traditional resistance exercises (Costello, 2022, J Strength Cond Res, 36, 881-887). It is assumed that training with an UL will increase the recruitment and activation of stabilising muscles, which is beneficial for daily activities and sport performance Kohler et al. (2010, J Strength Cond Res, 24, 313-321). Despite the recent increase in popularity, there is a limited amount of research that has been conducted using a UL and its impact on primary mover muscle activity. The purpose of this study was to investigate if a UL increases muscle activity of primary movers (pectoralis major sternocostal head [PEC] and triceps brachii long head [TRI]) during a bench press compared to a stable load (SL), measured via a Biopac electromyography (EMG) device. Additionally, bar velocity (m/s) using a GymAware device was compared between both UL and SL conditions. Following ethical approval, thirteen resistance-trained males were recruited (age = 21 ± 2 years; height = 178 ± 3 cm; mass = 79 ± 12 kg). Participants attended a familiarisation session, where 1RM and EMG maximum voluntary contraction (MVC) were determined. Following this, participants took part in a randomized crossover design at pre-determined loads. For the SL trial, participants performed 3 sets of 8 repetitions at 65% 1RM using a standard Olympic barbell. The US trial followed an identical protocol; however, an earthquake bar was loaded with 50% 1RM. The two-way repeated measures ANOVA revealed a significant interaction effect for the PEC activation, where there was an increase during UL but not SL condition (P = 0.001, ŋ2 = 0.633). No difference was found in the TRI between conditions (P > 0.05). There was a significant 17% loss in velocity in the UL condition (P = 0.022, ŋ2 = 0.273). A significant difference was revealed in the eccentric phase for the UL condition (P = 0.001, ŋ2 = 0.473). In conclusion, muscle activation was increased in the pectoralis major muscle during the UL compared to SL resistance training. There was also an increase in velocity loss during the UL. In addition, the time of the eccentric phase was significantly longer during the UL condition. Therefore, despite the reduction in intensity, a UL may elicit greater activation of primary movers when compared to traditional resistance training alone.

Effect of Zr-based metal–organic framework (MOF-808) on strength development of cement pastes and its phase transition on mechanisms of cement hydration

Nanostructured materials can regulate the performance of cement-based materials at the nanoscale and thus attract intense interest in the cement community. However, there are still few studies on modifiable and large specific surface area metal–organic frameworks (MOFs) to regulate cement properties, which are still in the preliminary exploration stage. In this work, the nanoporous Zr(IV)-based MOF-808-modified cement-based composites have been investigated, focusing on the effects of MOFs on various aspects of compressive strength and microstructure of hardened cement pastes as well as cement hydration, and so on. Results showed that MOF-808 can chemically adsorb Ca2+, Fe3+, and Al3+ released from cement, and the adsorption capacity of Ca2+ increased greatly when the crystalline MOF-808 was transformed into an amorphous state. With the MOF-808 dosage of 0.15 wt%, the compressive strength at 3, 7, and 28 d increased by 15.56%, 25.53%, and 13.03% in comparison with the Blank group, respectively. Additionally, MOF-808 delayed the hydration of cement, reduced the heat of hydration, and shortened the delay time, which was reduced when the dosage of MOF-808 was increased. The addition of MOF-808 promoted the generation of C-S-H gels, refined the pore structure within the hardened cement paste, and reduced the content of pores larger than 10 μm. Finally, the influence mechanism of MOF-808 on cement hydration and strength development was proposed.

Compressive Strength and Microstructure of Carbide Slag and Alkali-Activated Blast Furnace Slag Pastes in China

The alkali-activated blast furnace slag is attracting significant attention in replacing Portland cement due to several characteristics similar to cement hydration. However, there are a few practical problems with commercial alkali activators, such as the fast setting time, relatively high costs, and significant CO2 emissions during preparation. Thus, discovering industrial residues possessing inherent alkalinity are urgent. This study proposes the use of carbide slag at levels of 0%, 5%, 10%, 15%, 20%, and 30% and alkali at levels of 1%, 2%, 3%, 4%, 5%, 6%, 8%, and 10% activated blast furnace slag. The compressive strength and microstructure of carbide slag and alkali-activated blast furnace slag (CAB) pastes were examined using X-ray diffraction analysis (XRD), Differential Scanning Calorimetry/Thermogravimetric Analysis (DSC/TG), Fourier transform infrared spectroscopy (FTIR) and Scanning electron microscopy (SEM). The results revealed that the addition of carbide slag produced more hydrotalcite-like phase as well as decreased the content of ettringite (AFt) and the calcium–silicate–hydrate (C-S-H) gel, which decreased the compressive strength of the CAB pastes. At the age of 28 days, when the dosage was 5%, 10%, 15%, 20%, and 30%, the compressive strength of CAB mixes decreased by 2.1%, 7.1%, 9.2%, 9.8%, and 28.1%, respectively. The addition of NaOH promoted the formation of AFt, and there was an optimum level of NaOH corresponding to the high compressive strength of paste. At the age of 3 days and 7 days, the compressive strength reached its maximum at the dosage of 6% NaOH, which was 24.8 MPa and 36.3 MPa, respectively. However, at the ages of 14 days and 28 days, the compressive strength increased as the dosage of NaOH increased to 5%, which was 43.3 MPa and 44.5 MPa, respectively. The water curing could both enhance the early and later strength, the compressive strength of 23.3 MPa was gained at 3 days, and this increased by 16.3%, 24.0% and 36.9% at 7 days, 14 days and 28 days, respectively. Therefore, water curing was suitable for the strength development of CAB pastes.

Mechanical properties of low calcium alkali activated binder system under ambient curing conditions

These days, the construction industry is facing sustainability issues, leading to the selection of greener, low-carbon, alkali-activated materials. This study examines a low calcium alkali activated system composed of three constituents (ceramic brick, metakaolin waste, and phosphogypsum). The AAB compositions consist of the primary precursor, waste ceramic brick, which is increasingly (20–100 wt%) replaced with waste metakaolin. The alkaline solution was made of sodium hydroxide and water; dosage depended on the Na2O/Al2O3 ratio (1.00–1.36). The AAB specimens were inspected by using XRD (X-ray diffraction) and FT-IR (Fourier transform infrared spectroscopy) methods for the evaluation of mineral composition, accompanied by SEM–EDS (scanning electron microscopy & energy dispersive X-ray spectroscopy) for the analysis of the microstructure. The compressive strength after 7, 28 and 90 days, along with water absorption and softening coefficient were determined. Also, mixture calorimetry was established. The results have shown that the initial materials are suitable for producing medium-strength alkali-activated binder under ambient temperature. The maximum compressive strength was reached by using the combination of 80% CBW and 20% MKW (13.9 and 21.2 MPa after 28 and 90 days respectively). The compressive strength development was linked with the formation N–A–S–H gel and faujasite type zeolite. A higher level of geopolymerization in composition with metakaolin waste led to lower compressive strength. Consequently, binding materials with low demand of high final and especially early compressive strength could be produced under ambient temperature curing, making them more sustainable.

An innovative strategy for maximizing CO2 reduction in concrete through preparing carbon sequestration precursors by accelerated carbonation

Concrete possesses significant potential as a medium for CO2 sequestration. Nevertheless, conventional approaches like CO2 mixing and carbonation curing have shown limited efficacy in this regard. The present work introduces a groundbreaking method for enhancing CO2 reduction in concrete production. It involves preparing carbon sequestration precursors (CSP) through carbonation of cement reinforced by mechanochemical effects. The study investigated the kinetics and phase assemblage during the CSP production process, along with examining the impact of CSP on the reaction kinetics and strength development of cement composites. Due to the mechanochemical effects, CSP was characterized by the prevalence of metastable calcium carbonate (Cc) with a small crystalline size. Moreover, CSP not only accelerated the hydration of cement composites but also led to increased compressive strength at all ages, even with the replacement of 30 wt% of cement by CSP. The multifunctional attributes of CSP, including nucleation, reactant, and inert filler roles, contributed to its exceptional performance. Furthermore, utilizing the CSP method demonstrated a significant capacity for CO2 reduction, exceeding 36.5 %, which is more than seven times that of the traditional CO2 mixing method. The positive outcomes from this study underscore the high efficacy of the CSP method for efficient CO2 sequestration in concrete.

Structuration and yield strength characterization of hybrid alkali-activated cement composites (HACC) for ultra-rapid 3D construction printing

This study investigates the critical time-dependent rheological properties, including structuration rate and yield stress, of hybrid alkali-activated cement composites (HACC). HACC, a blend of geopolymer and cement paste, is examined to evaluate its suitability for ultra-rapid 3D construction printing (3DCP), which refers to a material’s ability to attain rapid structuration and buildability within 5–10 min after mixing, essential for additive manufacturing of 3D structures. The investigation extends to the impact of filler materials like silica sand and PVA fibers on HACC’s rapid structuration. Vicat needle, fast- and slow-penetration resistance measurements indicate that setting time increases with decreasing the Silicon/Aluminum (S/A) molar ratio and the addition of silica sand. Conversely, the addition of fibers reduces setting time while enhancing yield strength. Specifically, HACC mixtures with 0.5% and 1% PVA fiber additions, alongside combined sand (30%, 40%) and fiber (0.5%) mixtures, demonstrate ultra-rapid setting behavior within 3–5 min. Notably, mixtures with 40% silica sand and 0.5% PVA fiber exhibit highest yield strength development, i.e., 14 MPa at 12 min. Remarkably, incorporating 1% fibers into the HACC mixture yields the highest 28-day compressive strength (∼80 MPa) and flexural strength (∼11 MPa). The synergistic interplay between geopolymer and cement facilitates rapid setting time and high early-age strength development in HACC mixtures. The varying effects of silica sand and PVA fiber on setting time and yield strength provide opportunities for designing suitable structuration profiles. These findings underscore the exceptional rapid setting, structuration, and mechanical properties of HACC, positioning it as a promising material for ultra-rapid 3D construction printing.

Experimental investigation of the effect of longitudinal tensile reinforcement ratio on ductility behaviour in GPC beams

This research first determined the strength of the cylindrical geopolymer concrete materi- als under compressive stresses. Secondly, conventional and geopolymer-reinforced concrete beams were manufactured in different reinforcement ratios, and their mechanical properties were compared under bending. The main aim of this study is to experimentally compare the effect of reinforcement ratio on the ductility behavior of an alkali-activated geopolymer con- crete (GPC) beam with that of an ordinary Portland cement (OPC) beam. First, balanced reinforcement calculations were made considering the mechanical properties obtained from the material tests. The load-displacement, moment-curvature, and crack development results obtained from beam tests are interpreted with this information. OPC and GPC beams exhibit- ed similar strength and crack development behavior. However, the behavior of GPC and OPC concretes differs regarding the ductility index. Therefore, to achieve similar ductility in the conduct of GPC and OPC beams, the balanced reinforcement ratio and section dimensions of GPC beams should be chosen to be larger than OPC.

Tailoring high-magnesium cements for enhanced carbonation hardening and CO2 sequestration

The reduction of CO2 emissions from the cement industry remains a major challenge worldwide. This study investigates the feasibility of using high-magnesium limestone to prepare high-magnesium and low-calcium cementitious materials (HM-LCCs) with improved carbonation reactivity and CO2 sequestration capacity. The carbonation reactivity, hardening properties, phase assemblage, microstructure, and pore distribution of HM-LCCs synthesized with varying proportions of high-magnesium limestone were characterized by XRD, TGA, FT-IR, SEM, and LF NMR. It is found that with increasing substitution of high-magnesium limestone, the main mineral phases in clinker transformed from C2MS2 to C3MS2 and eventually to β-C2S and MgO, along with markedly enhanced grindability. The carbonation reactivity and degree increased progressively with increasing substitution of high-magnesium limestone. Properly tailored HM-LCCs exhibited excellent strength development up to 94.56 MPa after carbonation, dense microstructure, and significantly higher CO2 uptake. This study provides new insights into developing low-carbon cement by utilizing high-magnesian raw materials. The carbonation hardening and CO2 sequestration capacity of cement can be optimized by tailoring the Mg/Ca ratio and calcium silicate phase assemblage.

Appreciative inquiry and strengths development in the workplace: a dual comparative study

ABSTRACT Research has shown that Appreciative Inquiry (AI) and strengths development interventions can foster well-being, engagement, and performance in the workplace. However, additional studies are needed to develop effective interventions and test their effects on these variables, notably from a comparative perspective. The objective of this research was therefore to measure and compare the effects of AI and strengths development interventions on employee well-being, engagement, and performance at work. Two quasi-experimental studies were conducted among workers in France (n = 202; in-person intervention protocol) and Canada (n = 70; online intervention protocol). Results of analyses of variance indicate that AI and strengths development interventions led to improvements in well-being and engagement. Additionally, results suggest that AI and strengths development interventions produce distinct effects on the studied variables. Theoretical and practical implications are discussed.

Influence of weak acid salts and curing condition on supersulfated cement mortar

This study explores the impact of weak acid salt agents (citrate and tartrate) in the mixture and various curing conditions on the properties of supersulfated cement (SSC) mortar. Compressive strength tests were conducted on prism-shaped samples measuring 4 × 4 × 16 cm. A comprehensive analysis of the phase assemblage of hardened products was carried out using X-ray diffraction (XRD), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDS). The results reveal the abundant formation of ettringite (E) and hydrotalcite (Ht) when weak acid salt agents are added, especially in chloride and sulfate-rich curing solutions, leading to a notable increase in compressive strength, up to 200% compared to the control sample. Furthermore, the study demonstrates a substantial improvement in early and overall strength under temperature-stimulated curing conditions, accelerating the hydration reaction of SSC. These findings provide deeper insights into the factors influencing SSC hardening and strength development, offering valuable information for enhancing the efficiency and utilization of SSC in the construction industry, aligning with the goals of sustainable development.

Properties of CO2-cured cement incorporating fly ash and slag subjected to further water curing

In the present work, the synergetic effect of fly ash (FA) and ground granulated blast furnace slag (GGBS) on the compressive strength and microstructure development of mortars subjected to CO2 curing coupled with further water curing was investigated. The calcite content in pure cement was first increased and then decreased, while it decreased gradually in cement incorporating FA and GGBS during further water curing. Ettringite was interlocked with calcium carbonate and MC and was only observed in pure cement paste. Two distinct forms of C–S–H were observed in pure cement with one being interlocked with calcite, while the other one was pure amorphous phase. The incorporation of FA and GGBS showed a negative effect on the polymerization decrease of silica-rich phase. FA showed a negligible effect on the decrease of porosity, while GGBS had a positive effect on it. A positive correlation was found between the increase of compressive strength subsequent to water curing and three parameters, i.e., crystal size of calcite, carbonation degree and capillary pore percentage after CO2 curing, where the carbonation degree had a negative effect, while the other two parameters had a positive effect. The incorporation of GGBS and FA had a positive effect on the strength increase rate during further water curing. Notably, GGBS showed a more obvious effect on the strength development during further water curing and normal curing at later age. When GGBS content was lower than 10 % or cement content was lower than 10 %, the increase of FA content had a positive effect on the strength increase.