Strength Gain Research Articles

High-volume recycled glass cementitious and geopolymer composites incorporating graphene oxide

This study presents the development of high-volume recycled glass construction materials using recycled glass aggregate (RGA) as a 100 % sand replacement, recycled glass powder (RGP) as 40 wt% of the binder, and 0.1 wt% graphene oxide (GO) as nano-reinforcement. The research investigates the individual and their combined effects on the engineering performance, reaction kinetics (using calorimetry, X-ray diffraction-XRD, Fourier Transform Infrared-FTIR and Thermogravimetric analysis-TGA), and microstructure (Scanning Electron Microscopy/ Energy Dispersive X-ray Spectroscopy-SEM/EDS) for both cementitious and geopolymer systems. The results indicate that while RGA reduces strength and exacerbates alkali-silica reaction (ASR), the presence of 40 wt% RGP significantly mitigates ASR despite a lower strength gain in both systems. Geopolymers exhibit significantly lower ASR expansion compared to cementitious matrices owing to their superior alkali-binding capacity and denser microstructure, which restricts water and alkali ion mobility. 0.1 wt% GO was found to accelerate geopolymerisation, enhancing the strength of geopolymer mixes, but it decreased compressive strength in cement-based mixes due to self-desiccation-induced micro-cracking under ambient curing condition. The study also highlights that cement and metasilicate, as well as slag, are the main contributors to cost and CO2 emissions in cementitious and geopolymer systems, respectively. Overall, geopolymers exhibit a significantly lower global warming potential (< 180 kg CO2-eq/m3) compared to cement-based mixes (> 365 kg CO2-eq/m3) with a comparable cost (190–230 AUD/m3). The results indicate the potential for sustainable construction applications using high volumes of recycled glass, incorporating over 70 % of the mixture by weight.

Effect of particle size distribution and content of limestone powder on compressive response of high-early-strength cement mortars

This study examined the effect of particle size distribution and content of limestone powder on the compressive response of high-early-strength portland cement mortars cured either in water or under ambient conditions. Nineteen mortar mixtures were classified into three groups based on the particle size distribution of the pulverized limestone powders: L (blaine = 3467 cm2/g), M (blaine = 4710 cm2/g), and H (blaine = 5764 cm2/g). The design equations for the compressive strength gain rates and stress–strain relationship of ordinary portland cement (OPC) concrete were adapted for the present mortars. The test results revealed that the 28-d compressive strength (fc′) of the mortars tended to decrease with an increase in limestone powder content, even for mortars containing 5 % limestone powder with small particle sizes. This contrasts with the common trend of the positive effect of limestone powder on the compressive strength of OPC concrete up to a certain substitution level. Furthermore, mortars containing finer limestone powders exhibited a greater rate of decrease in fc′, regardless of the curing conditions. The modified equations show promise for reliably assessing both the compressive strength gain rates at different ages and the stress–strain behavior of high-early-strength portland cement mortars containing limestone powders.

Early-age shrinkage behavior of cement mixtures regulated with metakaolin-based internal conditioning

Shrinkage occurs in concrete during its hardening and strength gain process leading to undesired deformation, cracking, and decreases in strength and durability. While metakaolin-based internal conditioning (MIC) has been validated as a promising technique for modifying cement and mitigating alkali-silica reactions in concrete, its impact on the early-age shrinkage behavior of cement remains unexplored. This study delves into the effects of MIC and its coupling with lithium on the chemical shrinkage, autogenous shrinkage, and drying shrinkage of portalnd cement incorporating 30 % metakaolin with varying degrees of saturation (50 %, 75 %, and 100 %). The results indicate that the hydration of cement can be substantially enhanced by MIC with 29.0 % more heat released and a 32.3 % decrease in calcium hydroxide content. As a result of the enhanced hydration, cement with MIC yielded increased chemical shrinkage. Compared with dry MK, the autogenous shrinkage and drying shrinkage of cement were decreased by 38.0 % and 11.0 %, respectively, in the presence of MIC. A synergistic effect between MIC and lithium was suggested by the higher efficacy in suppressing autogenous shrinkage.

Analytical Overview of the Methods of Controlling the Parameters of Vibratory Compaction of the Concrete Mixes

Introduction. A historical (retrospective) overview of the evolution and application of the methods of concrete mixture compaction by vibration, as well as an overview of the breakthrough scientific+ advancements in the studied field have been presented. The use of the dry concrete mixes that reduce cement consumption, accelerate the strength gain of concrete, reduce the shrinkage strain and heat emission and increase the strength and durability of products has been proposed. The theoretical and practical issues of vibratory compaction of the concrete mixes, the research on the effect reached by the various vibration modes of the vibrating tables, the issues of choosing an efficient mode of vibration impact during compacting the concrete mixes and optimisation of their parameters have been studied. The vibrating table design, the installation layout of the vibrator’s eccentric weights to obtain a given value of the exciting force and the layout of a vibration module with the directed vibrations have been studied in detail. The criteria of duration of the concrete mixture compaction have been defined, changes of the impact parameters during compacting the concrete mixes have been characterised and technical specifications of the vibrating tables have been defined. In the article considerable attention has been paid to the main parameters of the vibrocompacting machines: frequency, amplitude and acceleration of the working member. Most often, the parameter of intensity is used to assess the efficiency of the vibration impact received by the mixture during the compaction process.Materials and Methods. A mixture that turns into concrete after compaction, setting and hardening was selected for the research. The various methods and parameters of concrete mixture compaction to obtain the high-quality concrete were studied. The impact of the various vibration modes on the process of compaction of concrete mixes was investigated, the criteria for the efficient selection and optimisation of the vibration impact parameters were revealed. The paper presents the criteria for assessing duration of the concrete mixture compaction and describes the changes in the parameters during compaction of the concrete mixes. The technical specifications of the vibrating tables of different types and sizes were also presented. The choice of the vibration compaction mode for the concrete mixture is a complicated task, which includes many parameters.Results. Upon the research, the data on the process of concrete mixture compaction under the impact of vibration forces has been obtained. The process results in the destruction of the structural bonds and weakening the bonds between the particles, which leads to the emergence of a variable stress-strain condition. It has also been found that under such settings, the mineral particles get transferred and a denser packing is formed.Discussion and Conclusion. The resulting denser packing of the concrete mixture particles ensures the undoubted economic advantage due to reduced consumption of a binder without loss of the strength properties of concrete.

Auxotonic training in muscle strength and power performance of professional young volleyball players

Auxotonic training unexplained on isotonic and isometric muscular contraction combination to develop strength and power gain. The study aimed to investigate muscle strength and power changes of professional young volleyball players on the auxotonic training effect. Volleyball players divided in AUT (auxotonic group: 16.32 y, 1.72 m, 63.63 kg) trained over 8 week and per week 2 day performing isotonic + isometric contraction combination periodization and IKT (isokinetic group: 16.23 y, 1.69 m, 60.22 kg) performed only isokinetic contraction periodization. The linear muscle strength and power processes of training periodization preferred for maximize performance. The strength changes of this study resulted on AUT and IKT for 1RM strength test and activforce isometric muscular strength adaptation test were similar, however, AUT obtained high improvement power performance (p &lt; .05). Auxotonic training developed on strength and power for AUT. Additionally, showing of comparison between AUT and IKT concluded CMJ (90°) ES = 1.09 very large, vertical jump ES = 1.31 very large and handgrip right ES = 0.05 small effect size. Based on the results we obtained, current auxotonic contraction was determined on resistance training applied to young volleyball players effective in strength and power development. Auxotonic training performed on young volleyball players will bring a perspective to the coaches and athletes work in this field as a resistance training model. The auxotonic training strategy for long term performance changes on outcomes of using aimed potential muscle isotonic + isometric contraction combination may be effective maximize strength and power performance.

Направления обеспечения качества гипсоизвестковых вяжущих при реставрации

Purpose: to consider issues related to the standard definition of the strength characteristics of an air binder and a cement binder. To show a technological solution to the problem of regulating the strength of an air binder stone by stabilizing care during setting and hardening. Methods: during the research, GOST 23789- 2018 “Gypsum binders. Test methods”. Results: a distinctive feature of restoration plaster solutions is that structure formation and strength gain occur only in an air-dry environment. As a result, the availability of approved and applied standards for the manufacture and use of restoration plaster solutions does not fully guarantee the creation of a reliable and safe environment for the life of an architectural heritage monument. It has been established that the mechanical characteristics (compressive and bending strength limits), as well as elastic parameters should be the same or lower in historical and restoration solutions in order to avoid changes in stress distribution. Practical significance: developed taking into account the comprehensive care of hardening stone, gypsum-lime binders can have a wide range of applications. They can be used as mortars for the preservation of architectural heritage and in the reconstruction of modern buildings, self-supporting partitions, fire protection elements or drywall (in places where a higher mechanical load is expected).

Evaluation of cement-treated recycled concrete aggregates for sustainable pavement base/subbase construction

Rapid urbanization and population growth have caused a substantial rise in the generation of all kinds of waste globally. The use of recycled waste not only can replace the enormous volume of virgin materials used in construction but also alleviate environmental concerns by lowering landfilling loads. This study aims to evaluate the feasibility of using non-treated and cement-treated recycled concrete aggregates (RCA) in pavement base and subbase layers. A detailed study focused on the strength, durability and microstructural aspects of treated RCA. To fulfill this, experimental test program and analysis covered particle-size distribution, Los Angeles abrasion, aggregate impact value, modified Proctor compaction, unconfined compressive strength (UCS), weight loss under wet-dry cycles, and scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) analysis. The recycled aggregates are found to show excellent physical and mechanical characteristics in terms of abrasion and aggregate impact values. Cement treatment has shown to significantly enhance the strength and durability characteristics of RCA, rendering it suitable for pavement base/subbase layer application. RCA samples treated with a cement content of 3 % and above (by weight) are found to satisfy the minimum specified unconfined compressive strength (UCS) values of 2 MPa at 7 days of curing, according to the Texas Department of Transportation (TxDOT) and Austroads guidelines for pavement base and subbase layer applications. However, a relatively higher cement contents (5 % and 7 %) is required to meet the minimum 7-days UCS criterion of 3 and 4.5 MPa for base layer applications of low- and high- volume roads, respectively, according to Indian road standards (IRC SP 72 (2015) and IRC 37(2018)). Cement-treated samples with 2 % cement or above showed minimal weight loss after 12 alternate wet-dry cycles, which was well within the maximum permissible limit (14 %) specified in various standards for stabilized materials. Additionally, microstructural investigations have clearly showed formation of hydration products corroborating the mechanism behind strength gain with time. Findings from this study provide references to promote the use of RCA in construction of pavement base and subbase layer, contributing towards the goal of net zero set by the United Nations.

Performances enhancing of supersulfated cement (SSC) using waste alkaline activators: Red mud and carbide slag

Supersulfated cement (SSC), since its invention, showed lower early-age strength gain, which has limited its practical applications. The urgent issue is how to regulate and enhance its early-age performance. In this context, solid waste materials such as bauxite residue-red mud (RM) and carbide slag residue (CS) from acetylene production by calcium carbide hydrolysis were used to improve the hydration and performance of SSC. By utilizing a range of analytical techniques such as isothermal calorimetry (IC), X-ray diffraction (XRD), backscatter scanning electron images (BSE), and thermogravimetric analysis (TGA), the hydration process, phase assemblages and microstructure of CS/RM-modified SSC were systematically investigated. It’s found that CS, as a calcareous alkaline activator, act as a regulator for adjusting the two main hydration reactions of C-A-S-H deposition and ettringite formation in SSC. The alkaline activator induces the hydration of slag and promotes the formation of hydration products. However, an excessively high dosage of carbide slag delays the primary ettringite formation reaction because it inhibits the dissolution of slag and promotes the formation of outer products. It leads to a looser and more porous paste matrix, resulting in higher expansion strain and poor strength gain at full curing ages. In contrast, red mud improves the hydration rate and enhances the hydration degree of SSC within the studied content (up to 30 wt%). With addition of red mud, SSC hydration is significantly advanced and deepened, resulting in more hydrates, particularly inner products. Red mud facilitates the depolymerization of the slag glass network and promotes the forming of nuclei and growth of hydration products. However, an excessively high red mud content would lead to a looser and more porous paste matrix due to the characteristics of red mud particle itself. An optimal red mud content has been identified as 20 wt%.

Rapid CO2 catalytic activation of binary cementing system of CSA and Portland cement

This study presents a novel approach to activating a binary cementing system composed of calcium sulfoaluminate (CSA) cement and ordinary Portland cement (OPC) using an instant CO2 catalysis. The activation led to significant and rapid strength enhancement, with the binary cement achieving a strength of 15.42 MPa immediately after activation, all within 1 min. The rapid CO2 activation catalyzed a notable heat release, accelerating the hydration of ye'elimite to form ettringite, which is a crucial component capable of bridging gaps and imparting high initial strength. Simultaneously, the CO2 activation catalyzed the increase in sulfur concentration, which in turn, also facilitated the formation of ettringite at an early age. Subsequent strength development was attributed to belite hydration. Apart from the rapid strength gain, employing CO2 activation facilitated control over the pH value of the pore solution, thus enabling the manipulation of ettringite's crystal morphology to strategically enhance the microstructure. Samples with lower pH values exhibited needle-like ettringite formations, whereas samples with higher pH values yielded rod-like and column-like ettringite crystal structures. Comprehensive analytical investigations were analyzed using XRD, FTIR, TGA, 27Al NMR, MIP, SEM, and ICP-OES. The present study provides a new perspective on the potential application of CSA-based cement, such as precast concrete element, instant concrete product delivery, and urgent reconstruction.

Enhancing upper extremity muscle strength in individuals with spinal cord injury using low-intensity blood flow restriction exercise.

This study explores the feasibility and effects of low-intensity blood flow restriction exercise on forearm muscle strength and function in individuals with spinal cord injury. Pilot randomized clinical trial. Ten male and female adult participants with chronic cervical and thoracic spinal cord injury underwent an 8-week low-intensity blood flow restriction exercise programme that targeted forearm muscles. Each participant's contralateral forearm served as the control. Grip strength was the primary outcome measure, and participants also provided qualitative feedback on their experiences. The study revealed a significant increase in participants' forearm muscle strength on the experimental side engaged in low-intensity blood flow restriction training, with an average strength gain of 7.5 ± 0.36 kg after 16 exercise sessions (Cohen's d = -6.32, 95% CI -8.34, -6.68). In comparison, the control side, following a conventional high- intensity exercise regimen without BFR, showed a more modest strength increase of 4.4 ± 0.67 kg. A mean Patient's Global Impression of Change score of 2.2 reflected overall improvements in participants' daily activities and health status. This study highlights the feasibility and effectiveness of low-intensity blood flow restriction exercise as a safe and promising approach to enhancing forearm muscle strength in individuals with spinal cord injury. The observed positive outcomes, coupled with a high level of participant satisfaction, underscore the potential of this innovative method to significantly improve limb muscle strength, thereby contributing to greater functional independence in this population.

Multi-experimental seismic analysis of low-rise thin reinforced concrete wall building with unconnected elastomeric isolators using real-time hybrid simulations

In response to the pressing need for housing and streamlining construction processes, the building industry has embraced innovative construction techniques. One such method, known as the Industrialized Housing Construction (IHC) system, departs from traditional framing systems by utilizing thin-reinforced concrete walls (TRCW). These TRCWs, characterized by high flowability and rapid strength gain, enable quick and efficient monolithic construction of walls and slabs. However, challenges have arisen regarding the structural behavior of these elements, potentially compromising their seismic performance. Given the significant seismic risk, there is a compelling need to develop resilient buildings by using this cost-efficient structural system. This study proposes the use of passive control systems such as base isolation to address this problem. While base isolation has proven effective in other countries, its feasibility in structures using TRCW and its performance during actual seismic events warrants further investigation. This paper presents an innovative approach using Multi-Axial Real-Time Hybrid Simulation (M-RTHS), which combines numerical and experimental components to gain deeper insights into the seismic response of low-rise TRCW buildings with base isolation using unconnected fiber-reinforced elastomeric isolators (U-FREIs). The methodology is detailed and includes the division of the structure into numerical and experimental segments and the use of transfer systems to replicate real seismic excitations, including those from El Centro (USA, 1940), Pizarro (Colombia, 2004), Chihuahua (Mexico, 2013), Loma Prieta (USA, 1989), and Kobe (Japan, 1995), with a maximum amplitude of 7.36 [Formula: see text] (0.75 g). The results highlight a remarkable reduction in upper structure floor drifts of over 57.47%, the characterization of the behavior and energy dissipation of each experimental specimen, and the optimal evaluation of M-RTHS. This research paves the way for improving the seismic resistance of buildings in regions prone to seismic activity, especially those using innovative construction methods such as TRCW.

Neck Strength Variations in Dental Students with and without Neck Pain: A Longitudinal Study

Neck pain can induce specific motor responses and alterations in muscle strength. Therefore, this study aimed to investigate and compare the progression of cervical muscle strength within and between students with and without neck pain over the course of their first semester of clinical training. We used an online Nordic Musculoskeletal Questionnaire for group allocation, and neck strength in flexion, extension, and lateral flexion on both sides was measured using the KForce Bubble Pro hand-held dynamometer. Forty-four students were divided into neck pain (n = 21) and asymptomatic (n = 23) groups. Both groups increased neck strength by the end of the semester in flexion, extension, and left and right lateral flexion (p &lt; 0.001). Students experiencing neck pain showed a significantly lesser degree of improvement (p = 0.036) in right lateral flexion. The agonist/antagonist ratios revealed an enhanced role of neck extensors across both groups. Dental students showed overall increased cervical strength in their first semester of clinical training. Those with neck pain exhibited a diminished rate of strength gain in right lateral flexion when compared with students without pain by the semester’s end, suggesting different neuromuscular adjustments to clinical practice in students experiencing pain, which may lead to functional impairments in later training stages.

Performance of self-compacting concrete with treated rice husk ash at different curing temperatures

Self-compacting concrete (SCC) is currently gaining traction as a replacement to conventional vibrated concrete. Its distinct microstructure leads to varied mechanical behaviour under different curing temperatures. In the past various supplementary cementitious materials (SCMs) were used in SCC to investigate their respective effects on the performance. However, there has been no systematic studies conducted to determine the effect of different curing temperature on the sensitivity reaction of rice husk ash (RHA) in SCC. This research focuses on high-strength SCC with SCMs such as RHA, silica fume (SF), fly ash (FA), and ground granulated blast-furnace slag (GGBS), exploring their applicability for concrete structures under varying curing temperatures. Heat of hydration, compressive strength and open porosity of SCC specimens were assessed at various temperature. Results indicate high curing temperatures expedite the hydration and pozzolanic reaction, refining the microstructure and increasing the early-age concrete strength, but compromising the long-term performance, potentially mitigated by the use of SCMs. Conversely, lower curing temperature, impedes hydration leading to gradual strength gain, particularly with SCMs, yet yielding significant strength increases at later concrete age. SCMs presence and curing temperature significantly influence maturity function-based strength predictions, impacting strength trends in the samples studied.

FEATURES FOR OPTIMISING THE PROPERTIES OF COMPOSITE MATERIALS BASED ON ACRYLIC MONOMERS

Further development of research in the field of acrylic composites is aimed at creating modifiers with specified properties that will improve the characteristics of composites in specific application conditions; developing optimal ratios of composite components to ensure the required properties; developing universal mathematical models that will predict the properties of composites depending on the composition and curing conditions; searching for new applications for acrylic composites, such as industrial and civil engineering. Among all organic compounds, acrylic compounds demonstrate the highest rate of strength gain over a wide temperature range. This is due to the low activation energy of the polymerisation process of acrylic monomers, which is triggered by special initiators. Due to this feature, acrylic composites can cure even at low temperatures and gain high strength in a short time. However, despite the obvious advantages, there are a number of questions that require further research: how does the rate of strength gain and other properties of acrylic composites change at different temperatures? How does changing the ratio of composite components (pliable, filler, initiator) affect its properties? How does the curing process of acrylic composites work at the molecular level? Determining the answers to these questions will make it possible to select the optimal ratio of components to obtain a material with the required properties, control the rate of strength gain of the composite by changing the temperature and composition, and use acrylic composites in a wider range of temperature conditions. Thus, a deep understanding of the processes that occur during the curing of acrylic composites is a prerequisite for their effective use in various industries and construction. The aim of the study is to comprehensively study the properties of composite materials based on methyl methacrylate (MMA) for the purpose of their effective use. Research objectives: determination of the optimal temperature regime to achieve maximum composite strength in the shortest possible time (1.5-2 hours). Study the effect of various fillers and other components on the strength, durability and other properties of the material. Identification of effective ways to modify MMA to increase the strength of the composite. Development of methods for controlling the rate of strength gain to ensure optimal operation. Assessment of the durability of the adhesive bond under various operating conditions. Comparison of the properties of the developed composites with existing materials. The results of the study will make it possible to develop new, more efficient composite materials for repair work that will be widely used in construction, industry and other sectors. Keywords: acrylic composites, modification, methyl methacrylate, strength, temperature, curing, repair.

Exploring the Dose-Response Relationship Between Estimated Resistance Training Proximity to Failure, Strength Gain, and Muscle Hypertrophy: A Series of Meta-Regressions.

The proximity to failure in which sets are terminated has gained attention in the scientific literature as a potentially key resistance training variable. Multiple meta-analyses have directly (i.e., failure versus not to failure) or indirectly (e.g., velocity loss, alternative set structures) evaluated the effect of proximity to failure on strength and muscle hypertrophy outcomes categorically; however, the dose-response effects of proximity to failure have not been analyzed collectively in a continuous manner. To meta-analyze the aforementioned areas of relevant research, proximity to failure was quantified as the number of repetitions in reserve (RIR). Importantly, the RIR associated with each effect in the analysis was estimated on the basis of the available descriptions of the training interventions in each study. Data were extracted and a series of exploratory multilevel meta-regressions were performed for outcomes related to both strength and muscle hypertrophy. A range of sensitivity analyses were also performed. All models were adjusted for the effects of load, method of volume equating, duration of intervention, and training status. The best fit models for both strength and muscle hypertrophy outcomes demonstrated modest quality of overall fit. In all of the best-fit models for strength, the confidence intervals of the marginal slopes for estimated RIR contained a null point estimate, indicating a negligible relationship with strength gains. However, in all of the best-fit models for muscle hypertrophy, the marginal slopes for estimated RIR were negative and their confidence intervals did not contain a null point estimate, indicating that changes in muscle size increased as sets were terminated closer to failure. The dose-response relationship between proximity to failure and strength gain appears to differ from the relationship with muscle hypertrophy, with only the latter being meaningfully influenced by RIR. Strength gains were similar across a wide range of RIR, while muscle hypertrophy improves as sets are terminated closer to failure. Considering the RIR estimation procedures used, however, the exact relationship between RIR and muscle hypertrophy and strength remains unclear. Researchers and practitioners should be aware that optimal proximity to failure may differ between strength and muscle hypertrophy outcomes, but caution is warranted when interpreting the present analysis due to its exploratory nature. Future studies deliberately designed to explore the continuous nature of the dose-response effects of proximity to failure in large samples should be considered.

Superficial Heat Therapy and Therapeutic Exercise in Individuals with Knee Osteoarthritis

Introduction: Knee Osteoarthritis is a major cause of pain and locomotor disability worldwide. Several physical therapy modalities have been recommended in reviewed clinical guidelines and systematic reviews, such as exercises, and electro and thermotherapy resources. Objective: This study evaluated the influence of the application of superficial heat therapy and/or therapeutic exercise on reducing pain and improving functional capacity in patients with knee osteoarthritis. Methods: 30 patients were divided into three groups (superficial heat, exercises, superficial heat plus exercises) and underwent 10 treatment sessions. Pain intensity was assessed using the visual analog scale; muscle flexibility with Wells’ bank test; strength gain with testing of one maximum repetition; walking time was analyzed with a walking test over a distance of 10 meters; and the Lequesne functional questionnaire was used to assess the functional activities of patients. Results: All treatments performed reduced knee pain. The exercise group showed an improvement in flexibility and quadriceps muscle strength. And the group that received superficial heat and therapeutic exercise showed better performance in time over a fixed distance covered. Conclusions: Therapeutic exercise and superficial thermotherapy performed in isolation showed beneficial effects in individuals with knee osteoarthritis. However, the therapeutic intervention carried out in combination showed better results in all parameters evaluated, suggesting that the clinical treatment can improve the quality of life of these individuals.

Flexural Behavior of Reinforced Concrete One-way Slabs with Longitudinal Hollows

This paper presents an experimental investigation of the flexural behavior of reinforced concrete one-way slabs with longitudinal hollows. Hollow ratios (weight reductions) used in this work are 11.43% and 22.86%. Two longitudinal reinforcement ratios (ρ = 0.58 % and 1.03 %) and four steel fibers volumetric ratios (Vf = 0, 0.2, 0.4, and 0.8%), were used. Results show that slabs with longitudinal hollows having weight reduction up to 22.86%, show reductions in strength (ultimate load) up to 32% and toughness (energy absorption) up to 45% and higher deflections compared to corresponding solid slabs. However, these reductions lowered to 27.5% and 24.5%, respectively using 0.8% steel fibers or 6.3% and 25.5%, respectively by increasing longitudinal reinforcement from 0.58% to 1.03%. Furthermore, increasing longitudinal reinforcement from 0.58% to 1.03% along with using 0.4% steel fibers in a hollow slab gives a strength gain of 17.5% with a reduction in toughness of only 9.8% compared to reference solid slab with 0.58% longitudinal reinforcement and 0% steel fibers. Results also showed that hollow slabs offer stiffer load-deflection behavior (lower deflections) and less maximum crack width as longitudinal reinforcement and/or steel fibers.

Reaction mechanism of Ca(OH)2-based carbon storage suitable for the production of building materials

The development of CaCO3 oxyfuel combustion and calcium looping techniques offers opportunities for Ca(OH)2 production with near-zero CO2 emissions. This study investigated the viability of Ca(OH)2-based CO2 storage for use in the production of building materials. To resolve the deficient strength gain of Ca(OH)2 carbonation, siliceous materials, using fly ash as a model compound, were introduced into the raw mixture, and hydrothermal curing was applied to promote the pozzolanic reaction. Two microstructural features, i.e., inner and outer CaCO3 formations, were identified during Ca(OH)2 carbonation via backscattered electron imaging. Inner CaCO3 formation is characterized by Ca(OH)2–CaCO3 conversion within the edge of Ca(OH)2 particles. Outer CaCO3 formation is characterized by the dissolution of Ca(OH)2 and the precipitation of CaCO3 in capillary pores, which generates hollow microstructures. The hollow space can be further filled by Al-tobermorite during hydrothermal curing. The prepared materials are capable of storing up to 16 % CO2 by the mass of the raw mixture. Furthermore, the pore structure influenced by inner and outer CaCO3 formation demonstrates the feasibility of adjusting the material's mechanical and CO2 storing properties by controlling the carbonation and hydrothermal curing schemes.

Performance assessment of pervious concrete incorporated with calcium silicate hydrates (C-S-H) cultivated on rice husk ash substrates – A trend surface analysis interpretation

Pervious concrete is a special type of concrete designed to allow water to pass through by omitting fine aggregates from the mix, or by using special techniques to create interconnected voids within the concrete. The current study investigates a novel method of cultivating calcium silicate hydrate (CSH) precipitates on a supplementary cementitious material (SCM), Rice husk ash (RHA), substrate and integrating the RHA substrate into pervious concrete to improve mechanical and durability properties. Scanning electron microscopy (SEM) images indicates the formation of precipitates of calcium silicate hydrates on the surface of RHA particles. The silica to RHA (Si/RHA) ratio and curing age of pervious concrete specimens serve as focal points for assessing the mechanical characteristics. Trend surface analysis is utilized to analyse the results, using a polynomial equation to identify underlying trends or patterns within the dataset. The analysis reveals that the Si/RHA ratio and curing days have minimal impact on permeability, while an increase in RHA substrate volume reduces permeability, indicating microstructure densification rather than macro void filling. For compressive strength, the results show that higher Si/RHA ratios and longer curing times positively correlate with strength, with accelerated hydration suggested by the quadratic coefficients of curing age. In terms of split tensile strength, increasing substrate volume enhances strength, while linear terms of Si/RHA ratio and curing age also exhibit positive correlations, although quadratic terms indicate minimal change in strength gain rates. Flexural strength correlates positively with both Si/RHA ratio and curing age, while abrasion resistance negatively correlates with Si/RHA ratio and substrate volume, suggesting enhanced resistance with increased values. CSH seeds grown on RHA enhances the microstructure of concrete, resulting in a denser material facilitating rapid strength development and improved durability.

Ultrasonic diagnostics of concrete destruction under the influence of corrosion environment

Introduction. Modern methods of studying the corrosion damage of concrete are quite lengthy and time-consuming, which makes their use difficult. This necessitates the search for new approaches to study the destruction of concrete under the influence of aggressive media. Currently, the ultrasound diagnostic method is effectively used to identify various structural defects, but the possibility of its use for concrete corrosion studies is poorly understood. This work is devoted to filling this gap.The methods of research. Concrete samples of 2.5x2.5x10 cm and 2.5x2.5x16 cm of various composition (cement: placeholder = 1:9, 1:7, 1:5). The control samples hardened under normal conditions, the test samples were stored in various aggressive environments. The samples of all storage media were subjected to periodic tests on the Pulsar-2.2 ultrasound diagnostic device. In parallel, the strength parameters obtained by the destructive method on the PGM-100MG4 hydraulic press, as well as the resistance coefficient, were determined.Results. The relationship between the growth periods, extremes and abrupt changes in the velocity of passage of ultrasonic waves and the stages of strength gain, the conditions of hardening of samples, and time factors has been established. It is shown that ultrasound diagnostics is quite sensitive to the processes caused by the corrosion destruction of concrete and allows us to obtain reliable data, while the strength and coefficient of resistance do not always adequately reflect the development of corrosion processes. It has been established that the use of ultrasound diagnostics makes it possible to increase the reliability of the results of concrete corrosion studies.Conclusion. The use of the ultrasound diagnostic method enables to obtain new data on the processes of concrete destruction under the influence of aggressive media, which makes it possible to increase the reliability of the results of concrete corrosion studies.