Compressive Strength Index Research Articles

Assessment of short and long-term pozzolanic activity of natural pozzolans using machine learning approaches

This investigation introduces the optimal performance models for predicting the compressive strength (CS) and pozzolanic activity index (PAI) by comparing the machine learning models. The machine learning models, i.e., multilinear regression (MLR), support vector machine (SVM), gaussian process regression (GPR), decision tree (DT), random forest (RF), and gene expression programming (GEP) have been trained (TRN) and tested (TST) by 28 and 7 data points. For the first time, the SiO2, Al2O3, Fe2O3, SiO2 +Al2O3 +Fe2O3, reactive SiO2, Blaine specific surface area, and specific gravity have been used as input variables to compute the CS, and 28 days PAI (28PAI), and 90 days PAI (90PAI) of the natural pozzolans. The multicollinearity analysis showed the SiO2, Al2O3, Fe2O3, SiO2 +Al2O3 +Fe2O3, reactive SiO2, and specific gravity have problematic multicollinearity (variance inflation factor – VIF > 10). Therefore, the root mean square error (RMSE), mean absolute error (MAE), correlation coefficient (R), performance index (PI), and variance accounted for (VAF) metrics have been implemented to evaluate the model's performance and multicollinearity impact. From the comparison of models, it has been recorded that model GPR outperformed the MLR, SVM, DT, RF, and GEP models in predicting CS (PI = 1.29, VAF = 71.31, R = 0.8473, MAE = 0.9390 MPa), 28PAI (PI = 1.87, VAF = 94.88, R = 0.9744, MAE = 0.7295 %), and 90PAI (PI = 1.72, VAF = 88.11, R = 0.9393, MAE = 1.2444 %) in the TST phase, close to ideal values. The score, generalizability. Wilcoxon test, uncertainty analysis, Anderson-daring test, and accuracy metrics have confirmed the superiority of GPR models in predicting CS, 28PAI, and 90PAI of natural pozzolans.

Effects of silicon content and test conditions on the dry wear behaviour of Zn–30Al–3Cu–(0–5)Si Alloys

ABSTRACT Dry sliding wear performance of Zn-30Al-3Cu-(0-5)Si alloys was studied using a block-on-disc type test apparatus. Their microstructure consisted of β dendrites, α, η, and ϵ (CuZn4) phases, and silicon particles. Hardness and tensile strength of the alloys increased with silicon content but above 1% Si the trend reversed for the tensile strength. Total percent elongation, impact energy, compressive strength, and quality index of the alloys decreased with silicon content. However, the friction coefficient and wear volume showed different changes with silicon content, sliding distance, contact pressure, and sliding velocity. Worn surface examinations indicated that the wear of these alloys occurs by both abrasion and adhesion. Non-linear regression analysis showed that the friction coefficient and wear volume of the alloys can be calculated in terms of silicon content and either sliding distance or contact pressure and sliding velocity using the empirical equations developed in this work. Zn-30Al-3Cu-0.5Si alloy exhibited the highest quality index and wear resistance among the alloys tested. It was concluded that the hardness and tensile strength of the alloys containing hard and brittle phases have opposite effects on their dry wear behaviour. The wear volume of such alloys decreases with increasing hardness but increases with tensile strength.

Microstructural behavior of mortars containing thermo-activated crushed demolition residue (TCDR)

The construction industry has been constantly expanding and is, consequently responsible for a high consumption volume of natural raw materials and for generating large amounts of waste. In detriment of this scenario, this research proposes the reuse of Construction and Demolition Waste (CDW), especially that from plaster for making mortars. The residue was thermo-activated at 650 °C for a period of 2h, a heating rate of 10 °C/min, it was crushed in a jaw crusher and passed through an ABNT N° 16 sieve. The mortars were prepared with a (cement:sand) ratio of 1:6 by mass, the sand was partially replaced by the residue in proportions of 0, 10, 20 and 30%, using Ordinary Portland Cement (OPC). Tests were carried out on consistency index, mass density, incorporated air content, isothermal calorimetry, water retention, mass density in the hardened state, flexural strength, compressive strength, water absorption and void index, in addition to testing techniques characterization, such as laser granulometry, pozzolanic activity using the Modified Chapelle method and Lúxan method, X-Ray Fluorescence (XRF), X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) as well as Mercury Intrusion Porosimetry (MIP). It was possible to observe that the residue has amorphous phases, through XRD and heterogeneous nucleation of smaller particles, proven by the calorimetry test, contributing to the increase in mechanical strength. The results indicate that the mixture with 30% replacement achieved a greater increase in mechanical strength, lower absorption rates and consequently, a reduction in the distribution of pore sizes.

High-Strength Controllable Resin Plugging Agent and Its Performance Evaluation for Fractured Formation.

Lost circulation is a common and complicated situation in drilling engineering. Serious lost circulation may lead to pressure drop in the well, affect normal drilling operations, and even cause wellbore instability, formation fluid flooding into the wellbore, and blowout. Therefore, appropriate preventive and treatment measures need to be taken to ensure the safe and smooth operation of drilling operations. So, it is necessary to conduct in-depth research on the development and performance of the plugging materials. In this study, urea formaldehyde resin with high temperature resistance and strength was used as the main raw material, and the curing conditions were optimized and adjusted by adding a variety of additives. The curing time, compressive strength, temperature resistance, and other key performance indexes of the resin plugging agent were studied, and a resin plugging agent system with excellent plugging performance was prepared. The formula is as follows: 25% urea formaldehyde resin +1% betaine +1% silane coupling agent KH-570 + 3% ammonium chloride +1% hexamethylenetetramine +1% sodium carboxymethyl cellulose. The optimal curing temperature is between 60 and 80 °C, with a controllable curing time of 1-3 h. Experimental studies examined the rheological and curing properties of the resin plugging agent system. The results showed that the viscosity of the high-strength curable resin system before curing remained stable with increasing shear rates. Additionally, the storage modulus and loss modulus of the resin solutions increased with shear stress, with the loss modulus being greater than the storage modulus, indicating a viscous fluid. The study also investigated the effect of different salt ion concentrations on the curing effect of the resin plugging system. The results showed that formation water containing Na+ at concentrations between 500 mg/L and 10,000 mg/L increased the resin's curing strength and reduced curing time. However, excessively high concentrations at lower temperatures reduced the curing strength. Formation water containing Ca2+ increased the curing time of the resin plugging system and significantly impacted the curing strength, reducing it to some extent. Moreover, the high-strength curable resin plugging agent system can effectively stay in various fracture types (parallel, wedge-shaped) and different fracture sizes, forming a high-strength consolidation under certain temperature conditions for effective plugging. In wedge-shaped fractures with a width of 10 mm, the breakthrough pressure of the high-strength curable resin plugging agent system reached 8.1 MPa. As the fracture width decreases, the breakthrough pressure increases, reaching 9.98 MPa in wedge-shaped fractures with an outlet fracture width of 3 mm, forming a high-strength plugging layer. This research provides new ideas and methods for solving drilling fluid loss in fractured loss zones and has certain application and promotion value.

The effect of operating conditions on neutral sulphite semi-chemical pulping properties: an industrial pilot plant study

The influence of pulping variables on the pulp and black liquor properties for a neutral sulphite semi-chemical pulping system was investigated in a pilot plant pulping setup situated at an industrial paper mill. Eucalyptus chips were used as raw material and the operating variables were Na2SO3 charge (8–18% w/w on oven-dry wood), Na2CO3 charge (0.5–3.0% w/w on oven-dry wood) and maximum cooking temperature (160–180 °C). Response surface methodology was used to parametrize empirical models to find the optimal conditions for maximizing the short-span compression strength index of the pulp. The derived regression models for the black liquor properties and the pulp hypo number had R2-adjusted values above 0.8 and p-values for overall significance below 0.05. The derived regression models for the handsheet strength properties had R2-adjusted values between 0.3 and 0.45 and p-values for overall significance either below 0.05 or between 0.05 and 0.1. The sulphite charge, followed by the carbonate charge, had the most notable effect on the evaluated properties with the effects of temperature being less significant. Optimization of the pilot plant system showed that the short-span compression strength index of the pulp could be maximized to 26.7 N m/g, using a sulphite charge of 9.4% (w/w on oven-dry wood) and a carbonate charge of 1.94% (w/w on oven-dry wood), similar to short-span compression strength indices typically achieved using other pulping processes.

Effects of Process Variables on Physico-Mechanical Properties of Abura (Mitrogyna ciliata) Sawdust Briquettes

Efficient utilization of biomass requires conversion into forms that can be optimally applied in energy generation. Briquetting involves the compaction of biomass into solid blocks that are more efficient than raw biomass, and provides ease of transport and handling. These are improved when the briquettes possess a high density, shatter index, and compressive strength. Due to differences in nature and composition, it is imperative to define optimum conditions for the production of quality and durable briquettes for individual biomasses that are compacted into briquettes. This study investigated the effects of process variables on the strength, durability, and density of biomass briquettes produced using Abura sawdust. The lateral compressive strength and drop shatter index were investigated whilst varying the temperature (100–150 °C), pressure (9–15 MPa), and hold time (15–30 min). The compressive strength ranged between 2.06 and 5.15 MPa, whilst the shatter index was between 50 and 600. Briquette density was between 518.8 and 822.9 kg/m3. The pressure was significant to the determination of the compressive strength (p < 0.1) and the shatter index (p < 0.05). The pressure, temperature, and hold time are significant to the briquette density. Physical and mechanical characteristics of the binderless Abura sawdust briquettes can be improved by optimizing the densification variables during the briquetting process when moderate pressures are used for compaction.

Effect of grain size on ductility and failure mechanism of fiber-reinforced coral sand cement-based composites

Fiber offers the potential for enhancing the resistance to deformation in engineering cement-based composites (ECC). However, replacing quartz sand in ECC with coral sand containing a large number of internal pores will make the interaction between aggregate, interface transition zone, and cementitious materials more complex. To investigate the influence of coral sand particle size and Polyvinyl alcohol (PVA) fiber content on the compression behaviour and internal microstructure of fiber-reinforced coral sand cement-based composites (FRCSCC), we conducted uniaxial compressive strength tests and real-time measurements of P-wave and S-wave velocities. We tested various mechanical parameters, such as density, elastic modulus, compressive strength, wave velocities, and toughness index. The findings revealed a notable trend in relation to the coral sand particle size. Specifically, as the particle size increased, the compressive strength of FRCSCC decreased by 26 % and the elastic modulus reduced by 11 %. During uniaxial compression, the calculated cumulative voltage energy (CVE) from P-wave and S-wave can be divided into three stages: elastic deformation, microcrack and macrocrack propagation, and main crack formation. Moreover, the increase of coral sand particle size from 0.075 mm to 1.00 mm resulted in the rise of residual stress from 8.7 % to 18.2 %, followed by the increase of toughness index from 2.5 to 3.2. Scanning electron microscope (SEM) images reveal that the main failure modes of PVA fiber in FRCSCC specimens during uniaxial compression are debonding pull-out and tearing. Larger particle sizes of coral sand are associated with uneven fiber dispersion, increased fiber fractures, and diminished ductility of the specimens. The results establish a theoretical foundation for offshore engineering construction.

Scalable fabrication of collagen fiber-waterborne polyurethane foams with enhanced toughness and thermal insulation by constructing energy dissipation networks

Natural fiber-based foams demonstrate outstanding potential for energy-efficient building and personal protective equipment applications due to their lightweight, high porosity, and sustainability. However, the weak interfacial interaction among fibers, functional additives, and the matrix hampers effective stress dissipation, largely affecting the material performance. Herein, this paper demonstrates a facile strategy for fabricating high-performance collagen fiber-based foams by constructing efficient energy dissipation networks using tannin-modified leather collagen fibers (T-LCF) and waterborne polyurethane (WPU). Tannin acts as a coupling bridge, linking the fiber and polyurethane to create a hydrogen-bonded network, enhancing energy dissipation and imparting excellent mechanical properties. Compared to WPU foam (WPUF), the T-LCF-based foam (WPUF/T-LCF) showed 65%, 34 times, and 35% improvements in tensile strength, compressive strength, and ultimate oxygen index, respectively. This study provides new insights into the cleaner production of high-performance natural fiber-based foam composites and a new way for the high-value utilization of collagen solid waste.

Association of osteoporotic fractures of femoral neck and femoral neck geometric parameters in native Chinese women

BackgroundAlthough it is generally believed that the femoral neck fracture is related to the femoral neck geometric parameters (FNGPs), the association between the risk of osteoporotic fracture of the femoral neck and FNGPs in native Chinese women is still unclear.MethodsA total of 374 female patients (mean age 70.2 ± 9.32 years) with osteoporotic fracture of the femoral neck, and 374 non-fracture control groups were completely matched with the case group according to the age ratio of 1:1. Using DXA bone densitometer to measured eight FNGPs: the outer diameter (OD), cross-sectional area (CSA), cortical thickness (CT), endocortical diameter (ED), buckling ratio (BR), section modulus (SM), cross-sectional moment of inertia (CSMI), and compressive strength index (CSI) at the narrowest point of the femoral neck.ResultsCompared with the control group, the average values of OD (2.9%), ED (4.5%), and BR (26.1%) in the patient group significantly increased (p = 0.015 to < 0.001), while CSA (‒15.3%), CT (‒18.2%), SM (‒10.3%), CSMI (‒6.4%), and CSI (‒10.8%) significantly decreased (all p < 0.001). The prevalence of osteoporosis in the lumbar spine, femoral neck, and total hip was, respectively, 82%, 81%, and 65% in fracture patients. Cox proportional hazard model analysis showed that in the age adjusted model, the fracture hazard ratio (HR) of CSA, CT, BR, SM, and CSI significantly increased (HRs = 1.60‒8.33; 95% CI = 1.08‒16.6; all p < 0.001). In the model adjusted for age and femoral neck BMD, HRs of CT (HRs = 3.90‒8.03; 95% CI = 2.45‒15.1; all p < 0.001) and BR (HRs = 1.62‒2.60; 95% CI = 1.20‒5.44; all p < 0.001) were still significantly increased.ConclusionThese results suggest that the majority of osteoporotic fractures of the femoral neck of native Chinese women occur in patients with osteoporosis. CT thinning or BR increase of FNGPs may be independent predictors of fragility fracture of femoral neck in native Chinese women unrelated to BMD.

Quantitative Insight into the Compressive Strain Rate Sensitivity of Polylactic Acid, Acrylonitrile Butadiene Styrene, Polyamide 12, and Polypropylene in Material Extrusion Additive Manufacturing

Herein, a research and engineering gap, i.e., the quantitative determination of the effects of the compressive loading rate on the engineering response of the most popular polymers in Material Extrusion (MEX) Additive Manufacturing (AM) is successfully filled out. PLA (Polylactic Acid), ABS (Acrylonitrile Butadiene Styrene), PP (Polypropylene), and PA12 (Polyamide 12) raw powders were evaluated and melt-extruded to produce fully documented filaments for 3D printing. Compressive specimens after the ASTM-D695 standard were then fabricated with MEX AM. The compressive tests were carried out in pure quasi-static conditions of the test standard (1.3 mm/min) and in accelerated loading rates of 50, 100, 150, and 200 mm/min respectively per polymer. The experimental and evaluation course proved differences in engineering responses among different polymers, in terms of compressive strength, elasticity modulus, toughness, and strain rate sensitivity index. A common finding was that the increase in the strain rate increased the mechanical response of the polymeric parts. The increase in the compressive strength reached 25% between the lowest and the highest strain rates the parts were tested for most polymers. Remarkable variations of deformation and fracture modes were also observed and documented. The current research yielded results with valuable predictive capacity for modeling and engineering modeling, which hold engineering and industrial merit.

Влияние древесного наполнителя и магнезита на прочность композиционного материала

Research in the field of creating new composite materials, including those based on magnesia binder and wood shavings – wood raw material - plays an important role in solving strategic tasks of construction complex development. Differences in the shape, size, and fractional composition of chips and wood shavings, which is used in the manufacture of the material-analogue (arbolite), determine the need to substantiate the composition of mixture main components. According the research, we obtained the relationship between the strength properties of wood-mineral composite (WMC) and the proportion of wood filler in the structure of the material. The study revealed relation of change in the compressive and bending strength indices of WMC with increasing mass content of wood shavings. It is recommended to maintain the ratio of wood shaving : magnesia binder at the level of 20 : 80, taking into account the intensity of strength properties change in the development of rational WMC composition.

The infrared thermal effect of coal failure with different impact types and its relationship with bursting liability

There are significant differences in the infrared thermal effect of coal failure with different impact types. It will be of great significance to determine the bursting liability of coal by using the infrared thermal effect characteristics of coal failure. In this paper, the infrared monitoring experiments of coal failure with different impact types is carried out. The infrared thermal effect characteristics of coal failure with different impact types are analyzed, and the quantitative relationship between the thermal effect index and the bursting liability index is established. The results show that the infrared radiation temperature (IRT) changes of coal failure with different impact types have great differences. With the increase of bursting liability, the increment of IRT gradually increases, and the infrared high temperature area (IHTA) gradually increases and concentrates. The average infrared radiation temperature (AIRT) increment of the strong and weak impact coal is 2.38 times and 1.62 times that of the no impact coal, respectively. The maximum infrared radiation temperature (MIRT) increment is 12.95 times and 5.42 times that of the no impact coal. The percentages of IHTA in coal with no, weak, and strong impact are 3.49 %, 57.83 %, and 81.43 %, respectively. Based on the quantitative relationship between AIRT, MIRT, IHTA and bursting liability index, the type of bursting liability of coal can be determined. For the uniaxial compressive strength index (RC), when the AIRT and MIRT are greater than 0.19 °C and 0.87 °C, and the IHTA is greater than 59.60 %, the coal belongs to the strong bursting liability. The research results propose a new approach to use infrared thermal effect characteristics to determine the bursting liability of coal, which is of great significance for improving the theory and method of infrared monitoring and early warning of rock burst.

Activation of Low-Quality Coal Gangue Using Suspension Calcination for the Preparation of High-Performance Low-Carbon Cementitious Materials: A Pilot Study

Although the calcination-based activation of coal gangue is important for its valorization in the form of cementitious materials, the related works mainly focus on high-quality coal gangue, neglecting its low-quality counterpart. To bridge this gap, we herein conducted the pilot-scale suspension calcination of low-quality coal gangue; explored the effects of calcination temperature, particle size, and O2 content on the phase composition of the calcined product, kaolinite decomposition, decarbonization, and silica/alumina dissolution; and evaluated calcination-product-based cementitious materials. Under optimal conditions (temperature = 875–900 °C; particle size = 39.71–46.84 μm; and O2 content = 12–14%), the carbon content of the calcined product equaled 1.24–1.87 wt%, and the dissolution rates of activated alumina and silica were 77.6–79.5% and 49.4–51.1%, respectively. The 28 d compressive strength (50.8–55.7 MPa) and true activity index (98.8–108.4%) of the cementitious material prepared at a calcination product dosage of 30–38 wt% met the standard of 42.5 grade cement. This study demonstrated the suitability of suspension calcination for the preparation of high-performance low-carbon cementitious materials from low-quality coal gangue, thus providing a basis for further industrialization and technological development.

Cementitious properties of coal-based metakaolin prepared from coal gangue via Fe3O4-Assisted microwave activation

Coal gangue is the largest emission of solid waste in the coal industry, and its large accumulation has posed serious hazards to environment. Low-quality coal gangue can be transformed into an auxiliary cementing material (coal-based metakaolin) with pozzolanic activity after calcination. However, the conventional calcination has slow heating rate, high energy consumption and serious pollution issues. Therefore, the fast and efficient calcination of coal gangue must be explored. In this study, coal series kaolinite (coal gangue with a kaolinite content of more than 80%) from Inner Mongolia was calcined by Fe3O4-assisted microwave calcination craft to prepare coal-based metakaolin (CBM). Results indicated that the efficiency of the microwave calcination of coal series kaolinite powder (CSKP) was considerably increased by adding analytical-grade Fe3O4 to CSKP. After substituting 30% of cement with CBM prepared by Fe3O4-assisted microwave calcination of CSKP to prepare cement–coal based metakaolin mortar (CCBMM), the mortar specimen made of CBM prepared at 675 °C showed the highest compressive strength (61.3 MPa) and activity index (112%). The analytical-grade Fe3O4 particles in CSKP will form spherical hematite microparticles (Fe2O3) with good dispersion after microwave calcination at appropriate temperatures (650 °C and 675 °C), which acted as microaggregates to optimize the pore structure of CCBMM, thereby enhancing the strength of CCBMM. The findings of this study confirmed that analytical-grade Fe3O4 addition not only increased the efficiency of preparing CBM by microwave calcination and reduced energy consumption, but also improved the cementitious performance of CBM.

Characterization of the Time–Space Evolution of Acoustic Emissions from a Coal-like Material Composite Model and an Analysis of the Effect of the Dip Angle on the Bursting Tendency

Rock bursts pose a grievous risk to the health and lives of miners and to the industry. One factor that affects rock bursts is the dip angle of the coal seam. Because of the uniquely high gas content of the coal in a mine in Shanxi Province, China, coal specimens were obtained from this mine to produce coal–rock combination specimens and test the effects of various seam inclinations. Using a DYD-10 uniaxial compression system and a PCI-8 acoustic emission (AE) signal acquisition system, we investigated the spatial and temporal evolution characteristics of the burst tendency of specimens with different coal seam inclination angles (0°, 10°, 20°, 30°, 35°, 40°, and 45°). Uniaxial pressure was applied to the specimens, and we found that, as the inclination angle increased, the coal–rock combination specimens exhibited structural damage and destabilization, which was attributed to the generation of an interface slip phenomenon. In all tests, the coal exhibited greater damage than the rock. There was an energy convergence at the coal–rock interlayer interface, which was the main carrier for the accumulated energy. The impact energy dissipation index is defined according to the energy dissipation properties of the loading process of coal–rock composites. As the inclination angle increased, the impact energy dissipation index, energy storage limit, compressive strength, elastic modulus, and other indexes gradually decreased. This effect was strongest where the angles were 40° and 45°. The indexes used to assess the impact propensity decreased to a notable degree at these angles, revealing that the burst tendency of coal–rock is curtailed as the inclination angle increases. The results of this research are of great importance to the early evaluation of mine burst risks and the sustainable development of coal utilization.

Prediction of the axial compression capacity of stub CFST columns using machine learning techniques.

Concrete-filled steel tubular (CFST) columns have extensive applications in structural engineering due to their exceptional load-bearing capability and ductility. However, existing design code standards often yield different design capacities for the same column properties, introducing uncertainty for engineering designers. Moreover, conventional regression analysis fails to accurately predict the intricate relationship between column properties and compressive strength. To address these issues, this study proposes the use of two machine learning (ML) models-Gaussian process regression (GPR) and symbolic regression (SR). These models accept a variety of input variables, encompassing geometric and material properties of stub CFST columns, to estimate their strength. An experimental database of 1316 specimens was compiled from various research papers, including circular, rectangular, and double-skin stub CFST columns. In addition, a dimensionless output variable, referred to as the strength index, is introduced to enhance model performance. To validate the efficiency of the introduced models, predictions from these models are compared with those from two established standard codes and various ML algorithms, including support vector regression optimized with particle swarm optimization (PSVR), artificial neural networks, XGBoost (XGB), CatBoost (CATB), Random Forest, and LightGBM models. Through performance metrics, the CATB, GPR, PSVR and XGB models emerge as the most accurate and reliable models from the evaluation results. In addition, simple and practical design equations for the different types of CFST columns have been proposed based on the SR model. The developed ML models and proposed equations can predict the compressive strength of stub CFST columns with reliable and accurate results, making them valuable tools for structural engineering. Furthermore, the Shapley additive interpretation (SHAP) technique is employed for feature analysis. The results of the feature analysis reveal that section slenderness ratio and concrete strength parameters negatively impact the compressive strength index.

Reliability assessment of carbon fiber mortar: Combined pulse velocity, point load, and compressive strength tests

Cement mortar is used as an adhesive and plaster for brick walls, drainage channels or irrigation with river stones or mountain stones, and in the manufacturing of short revetments. The performance of cement mortar requires continuous improvement by construction materials researchers, scientists, and building contractors. Recently, carbon fiber sheet has gained popularity for use in retrofitting and improvement to the performance of building elements. This study aims to recycle small sheets of unused carbon fiber by cutting them into short carbon fiber (SCF) with a uniform length of 12 mm, which is used as an internal reinforcement in the cement mortar. All plain and fibrous mortar were prepared with a 50 mm cube mold. In addition, tests were conducted to provide reliable data regarding the application of recycled carbon fiber sheets as discrete fiber reinforcement in the improvement of cement mortar; these include ultrasonic pulse velocity (UPV), compressive strength, and point load strength index (PLSI) (known for performance rock testing in geotechnical and geological environments) tests. The test results for UPV, PLSI, and compressive strength showed that the addition of carbon fiber improves the performance of the mortar when compared to plain mortar. Furthermore, two simplified relationships are made: the first correlation was for PLSI with compressive strength, and the second correlation was for UPV with compressive strength. Finally, these correlations were compared with those of experimental tests obtained from published literature, thus demonstrating the correctness of the PLSI, compressive strength, and UPV values obtained in this study.

The investigation of the frost resistance of the aggregate-sand mixes

Problem. Recently there is a steady trend to the increase of the intensity of traffic and of the loads from the wheels of the rolling stock on the whole structure of the road pavement, therefore during the building of the road pavement layers the most important thing is a rational choice of the materials for the base layers and for the top layers which will provide the performance of the entire structure during the designed service life under the working conditions which are getting worse all the time. Nowadays the most widespread material for the road base layers is aggregate mix strengthened by cement. One of the ways of the base layers materials improving is the increase of their frost resistance. One of the ways to solve this problem can be the different additive and fibers usage as a reinforcing component of the aggregate mix. But until today the influence of the internal factors such as size of mineral grains, granulometric composition and binder content on the indexes of frost resistance is still not investigated.&#x0D; Goal. The aim of the research is the investigation of the maximum grain size and content and also mineral binder concentration influence on the indexes of frost resistance of the aggregate mixes strengthened by cement. Methodology. To achieve this goal in the laboratory of the Department of Highway Building and Maintenance named after O. Birulia the samples of sand, fine-grained, medium-grained and coarse-grained aggregate mixes with cement content from 2 to 10 % were prepared. Results. For the frost resistance indexes determination of the aggregate mixes of different compositions strengthened by cement according to the maximum grain size the cement concentration influence on the grade strength indexes was found. The research results have shown that: with the increase of cement content the compressive strength indexes in the fine, medium and coarse-grained mixes are increasing; the increase of the maximum grain size of the same cement concentration shows that compressive strength and tensile strength indexes are increasing. The repeated freezing and thawing is one of the main aggressive factors of the external environment influence which reduces strength and durability of the materials, therefore the influence of this factor on the compressive strength and tensile strength was evaluated. In Ukraine according to the current standard the frost resistance of the aggregate mixes is evaluated only in terms of compressive strength index of samples which were subjected to certain number of freeze-thaw cycles. It is determined that the aggregate mixes with the same cement content with larger mineral grains in its composition have higher indexes of the frost resistance coefficient. Also it was found that the influence of the freeze-thaw cycles is more informatively shown at the samples testing according to the split tensile test. Conclusions: 1. The increase of the binder content in the composition of strengthened aggregate mixes leads to the decrease of the freeze-thaw cycles influence on the compressive strength and splitting strength for all studied compositions of aggregate mixes. 2. The aggregate mixes strengthened by the same cement amount with the larger size of mineral grains in its composition have higher values of frost resistance coefficients in comparison with strengthened aggregate mixes with smaller maximum size of mineral grains in its composition. 3. The influence of the freeze-thaw cycles is showed more informatively by the split tensile scheme.

Pemanfaatan Limbah Ampas Tebu Menjadi Briket Bio-Batubara Menggunakan Perekat Tapioka

The research carried out aims to utilize bagasse waste and determine the characteristics of bio-coal briquettes made from bagasse waste with the addition of coal. This research was conducted with reference to a completely randomized design (CRD) with two factors and three replications. The first factor is the comparison of the composition of the main raw materials in the form of bagasse and coal (P) which includes four treatment levels, namely 100%: 0% (P0), 40%: 60% (P1), 60%: 40% (P2) and 80 %: 20% (P3).The second factor is the concentration ratio of tapioca adhesive which includes three treatment levels, namely 10% (K1), 15% (K2) and 20% (K3). There are seven parameters tested in this study, namely density, moisture content, compressive strength, shatter resistance index, calorific value, combustion rate and basic temperature of the cooking pancie when burning briquettes.The results showed that the higher the percentage of coal in the composition of the main raw material tends to increase the compressive strength and decrease the burning rate of the briquettes. Meanwhile, the lower the tapioca adhesive concentration used tends to increase the density, compressive strength, and shatter resistance index and reduce the burning rate of briquettes. The briquettes produced in this study resulted in the following characteristics: briquette density ranged from 0.36 to 0.44 g / cm3, the moisture content ranges from 4.04% - 6.42%, compressive strength ranges from 26.87 - 46.15 N / cm2, the shatter resistance index ranges from 96.02% - 96.78%, the actual heating value ranges from 3266.1 - 4588.5 cal / g, the theoretical calorific value ranged from 1988.1 to 4483.6 cal / g, the briquette combustion rate ranged from 1.818 to 3.125 g / min, and the highest basic cooking pancie temperature was obtained in the P1K1 treatment combination of 229ºC. Keywords: Briquettes, Coal, Tapioca Glue, Waste Bagasse.

Effect of calcination on the physical, chemical, morphological, and cementitious properties of red mud

Red mud (RM), a by-product of aluminum production, poses environmental concerns with its disposal. This study explored calcining RM at 600 °C for 0–6 hours to utilize it as a cement substitute. Calcination up to 2 hours decreased particle size and increased surface area due to moisture loss, while further calcination reversed these effects. XRF analysis showed high Fe2O3, Al2O3, SiO2 contents. XRD revealed goethite transformed to hematite and gibbsite to alumina. SEM images displayed a loose then denser structure over time. 10% calcined RM incorporated into cement showed 2-hour calcined RM exhibited optimal properties, including high strength (46.27 MPa) and strength activity index (117.24%). SEM confirmed improved C-S-H gel formation with 2-hour calcined RM. In summary, calcining RM optimally at 600 °C for 2 hours allows its effective use as a sustainable cementitious material, providing environ- mental and technical benefits of RM utilization in cement composites.