Split Test Research Articles

An open innovative inventory management based demand forecasting approach for the steel industry

This research focuses on accurately forecasting steel wire mesh demand to ensure timely order fulfillment. Various univariate time series forecasting methods were employed, including Prophet, Support Vector Regression (SVR), 1-Dimensional Convolutional Neural Network (1D-CNN), Recurrent Neural Network (RNN), Gated Recurrent Unit (GRU), and Long Short-Term Memory (LSTM). These RNN-based models were implemented to enhance the dynamics of open innovation. The study also employed the split test method to assess the impact of data size on model performance. Following a comprehensive comparative analysis, LSTM outperformed other models at 80:20 data split ratio, achieving the lowest RMSE of 51,473 and MAPE of 1.43. The robust performance of LSTM underscores its ability to expertly predict complex demand patterns. Moreover, forecast accuracy was enhanced using ensemble models, with RNN-LSTM delivering the best results (RMSE of 45,931 and MAPE of 1.20) at the same data split ratio. This accurate forecasting supports steel wire mesh companies in making informed decisions regarding inventory management. The study additionally demonstrated the integration of forecasting results into inventory strategies to improve decision-making for cost optimization.

Evaluation of Concrete Fatigue Damage with Elastic Wave-based Measurement Techniques

Fatigue damage is a progressive and permanent change in the internal material structure due to cyclic loading. The cyclic loads can be due to wind, waves, temperature variation, and traffic loads. Each cyclic load application introduces micro-damages that accumulate to induce failure. Detecting these micro-damages requires sensitive measuring techniques. Hence this research compares the sensitivity of different measuring techniques applied to fatigue experiments of concrete. The applied NDT are the passive acoustic emission technique (AET) and active ultrasonic measurements. In addition, linear variable differential transformers (LVDTs) are applied as a reference measurement. Accordingly in this research, cylindrical concrete samples are subjected to monotonic and cyclic Brazilian splitting tests. The cylinders are 100 mm in diameter and 150 mm in length. The cyclic load is applied to these samples with a loading frequency of 5 Hz. During the tests, the damage evolution is monitored with AET, ultrasonic measurements and LVDTs. There are eight AE sensors attached to the sample. The two LVDTs are positioned at the center of the sample's front and back side. Besides passively monitoring the acoustic emissions, the AET sensors are also used to do active ultrasonic measurements. The research reports the comparison conducted on the deformations and cracks measured with the LVDTs, the damage growth identified with the AET, and the change in the ultrasonic pulse velocity measurements. In addition, the study also presents the damage analysis capacity of the methods across different types of loading: monotonic, constant amplitude, and stepped fatigue loading. The comparison shows that combination of AET and ultrasonic velocity measurement is a sensitive indicator for damage growth.

Dynamic behavior of fractured gabbro treated by high temperatures

Rock masses in deep engineering are often subjected to high geothermal effect, and blasting is a key technique for deep rock excavation. It is crucial to study the dynamic characteristics of fractured rock masses under high geothermal conditions and blasting excavation. This paper focuses on fractured gabbro, examining the effects of high temperatures on its surface chromaticity and mass. Dynamic splitting tests were conducted using a Split Hopkinson Pressure Bar (SHPB) apparatus, and the microstructure was analyzed with scanning electron microscopy (SEM). The results indicate that: (1) High temperatures significantly affect the surface chromaticity and mass of gabbro samples. (2) Elevated temperatures lead to the progression from a microstructure with no noticeable microcracks to the development of extensive microcracks and mineral particle fragmentation. (3) The impacts of high temperatures on the splitting strength, peak strain, and dynamic elastic modulus of gabbro samples reach a critical point around 500 °C. At this temperature, the strengthening effect of high temperature is evident, whereas at 800 °C, these properties significantly decrease due to extensive mineral crystal fragmentation and microcrack expansion, weakening the sample's strength, stiffness, and deformation resistance. (4) From 25 °C to 600 °C, the fissure angle significantly influences the splitting strength, peak strain, and dynamic elastic modulus of gabbro. Although the fissure angle still impacts these properties at 800 °C, the overall effect of high temperature is more pronounced. (5) The failure of fractured gabbro samples is primarily characterized by tensile and shear failures, with the crack initiation angle closely related to the fissure angle.

Incorporation of Nanoalumina in Potassium Feldspar-based Phosphoric Acid Activated Geopolymer Composites: A Sustainable Approach

This study investigates the potential of potassium feldspar-phosphate-based geopolymer concrete as a sustainable replacement to traditional concrete, addressing the environmental concerns associated with CO2 emissions during cement production. While geopolymer concrete offers a promising path towards sustainability, its performance often falls short of Portland cement concrete. This study investigates the use of nanoalumina in improving the performance of geopolymer concrete. A ternary mix was formulated with potassium feldspar powder, metakaolin and rice husk ash, incorporating varying percentages of nanoalumina geopolymer concrete mixes. The mechanical characteristics of the resulting geopolymer composites were assessed through compressive and split tensile strength tests. The findings revealed that a 4% nanoalumina dosage (GC-N4) yielded the most significant improvement in strength and durability. The GC-N4 mix performed superior in all metrics, demonstrating the highest compressive (41.82 MPa) and split tensile (3.7 Mpa) strengths. Reduction in water absorption and durability aspects were also optimum in GC-N4. These results highlight the potential of incorporating nanoalumina into a ternary mix of potassium feldspar powder, metakaolin and rice husk ash to significantly enhance the overall performance of geopolymer concrete, promoting its wider adoption as a sustainable construction material.

Efficacy-focused and autonomy-supportive messaging in social media vaccine campaigns: insights from a Facebook split test

ABSTRACT Background In the context of social media vaccine campaigns, understanding the impact of message framing on audience engagement is crucial. This study examines the efficacy of messages centered on efficacy versus autonomy, informed by theoretical frameworks: the Extended Parallel Process Model (EPPM) and Self Determination Theory (SDT). Methods Utilizing the Facebook A/B Split Test (FBST) feature, an online experiment was conducted to compare the response to two different messages: one emphasizing vaccine efficacy (EPPM-informed) and the other focusing on individual autonomy in making vaccine decisions (SDT-informed). The primary measure of interest was the number of clicks on a link directing to a pro-vaccine website. Results The findings indicated that the autonomy-centered (SDT-informed) message resulted in a significantly higher click-through rate to the pro-vaccine website, particularly among users aged 65 and above. Furthermore, analysis of comments from Facebook users identified factors potentially contributing to vaccine hesitancy, with mistrust being the most dominant. Conclusions The study underscores the importance of tailoring social media vaccine campaigns to address the autonomy needs of the target audience while considering trust-related issues to mitigate vaccine hesitancy. Emphasizing individual autonomy in vaccine decision-making processes can enhance engagement with pro-vaccine content, especially in older demographics.

Evaluation of Bond Strength of Concrete Repaired Using Polyurethane Grout Material under Static and Impact Loads Coupled with Statistical Analysis.

The effectiveness of repair work relies on whether the interface substrate can achieve sufficient bond strength when subjected to numerous stresses. This study investigated the bond properties of repaired normal concrete (NC-to-NC) elements, including cube, beam, and U-shaped specimens, after undergoing natural fracture due to flexural and tensile stresses. The specimens were repaired using a polyurethane (PU) matrix by gluing the two parts and applying compression, splitting, and drop-weight impact (DWI) tests to evaluate the bond strength properties. The results revealed that the PU matrix effectively repairs NC substrate with adequate bond strength, which exceeds the minimum allowable bond strength specified in the ASTM ACI 546-06 to rehabilitate damage concrete structures. The reference beams exhibit a peak applied load capacity of 15.6 kN with less deflection than the repaired samples. The compressive strength of the NC-to-NC repaired specimens loaded along and parallel to the interface plane revealed a decrease in compressive strength of 47.3% and 31.5% compared to the NC-R samples, respectively. The mean number of blows at the cracking stages appeared nearly equal for reference and repaired NC-to-NC specimens. The reference specimens exhibited an average number of 24 and 31 blows at the initial and failure stages, respectively, which were higher by 9.1% and 5.2% than the NC-to-NC repaired specimens. The PU binder showed promising results in achieving adequate interfacial bond strength under static and impact loads.

Performance Study of Asphalt Mixtures Reinforced with Gradated Basalt Fibers of Mixed Lengths

The length of basalt fibers affects the performance of asphalt mixtures. To explore the influence of different lengths of basalt fibers on the performance of asphalt mixtures, this study selected basalt fibers with lengths of 6 mm, 9 mm, and 12 mm to design gradations that were incorporated into asphalt mixtures to prepare specimens. High-temperature rutting tests, immersion Marshall tests, freeze-thaw splitting tests, and low-temperature splitting tests were conducted, resulting in 11 test mix designs and 12 test indicators. Then, a multi-objective grey target decision method was used to optimize the optimal combination ratio of basalt fiber lengths. The results indicate that compared to asphalt mixtures with single-length basalt fibers, incorporating well-combined basalt fibers significantly enhances the high-temperature, low-temperature, and water stability performance of asphalt mixtures. According to the grey target decision method, this study determined that a basalt fiber combination ratio of 3:4:3 for lengths of 6 mm, 9 mm, and 12 mm provides the best overall performance of asphalt mixtures. Additionally, when designing asphalt mixtures with graded basalt fibers, the inclusion of 9 mm fibers should be the primary control point. These research findings provide important guidance for the enhanced application of basalt fibers in road engineering.

Experimental Study on Pavement Performance of Warm High Modulus Mixture WHMM-13

In order to solve the dusting and rutting problems of hot mix asphalt mixture during construction and operation, rutting test, bending test, Marshall stability test, freeze-thaw splitting test, uniaxial compression dynamic modulus test, overlay test, and four-point bending fatigue life test are applied on WHMM-13 to study the high-temperature stability, low-temperature cracking resistance, water stability, anti-reflection crack performance and fatigue durability in comparison with HMM-13. The results show that, compared to HMM-13, the dynamic stability and dynamic modulus (45 ℃, 10 Hz) of WHMM- 13 are improved by 10.0% and 47% respectively, and the rutting depth is reduced by 27.3%, indicating that the high temperature stability of WHMM-13 has been greatly improved. As for low temperature cracking resistance, the bending failure strain, stiffness modulus, flexural tensile strength and rupture energy of WHMM-13 are slightly lower than those of HMM-13. As for water stability, the residual stability of WHMM-13 in immersion Marshall test is 87.5%, and the splitting strength is 82.3%, both higher than that of HMM-13. As for anti-reflection crack performance, the total tensile rupture energy of WHMM-13 is 2.32 times that of HMM-13, with cracking resistance index (CRI) increased by 25%, which shows that WHMM-13 has better strength, can effectively prevent the crack from spreading and effectively improve the cracking resistance capacity of asphalt pavement. As for fatigue durability, the fatigue life of WHMM-13 is 5.4% lower than that of HMM-13, with bending stiffness modulus and cumulative dissipation energy reduced by 11.3% and 2.8% respectively, indicating that the fatigue durability of WHMM-13 is slightly reduced.

Performance of Asphalt Mixtures Modified with Desulfurized Rubber and Rock Asphalt Composites

This study explores the performance of asphalt mixtures modified with North American rock asphalt and desulfurized rubber particles at varying rubber-to-asphalt ratios ranging from 18% to 36% by weight. A comprehensive set of laboratory tests, including high-temperature rutting tests, low-temperature bending tests, indirect tensile tests, and freeze–thaw splitting tests, were conducted to evaluate the modified mixtures. The results indicate that both wet and dry blending methods produce mixtures that meet technical requirements, with the optimal asphalt-to-aggregate ratio determined to be 7.1%. At a rubber-to-asphalt ratio of 18%, the wet blending method slightly improves high-temperature rutting resistance compared to the dry method. However, an increase in rubber content generally enhances rutting resistance regardless of the blending technique. The wet blending method excels in low-temperature crack resistance, possibly due to better rubber dispersion, while an increase in rubber content diminishes crack resistance due to a thinning asphalt film. In terms of fatigue performance, the dry blending method results in significantly longer fatigue life, with a 27% rubber-to-asphalt ratio exhibiting optimal balance. The dry method consistently outperforms the wet method in water stability, and the resistance to water damage increases with rubber content. In conclusion, this study provides valuable insights into optimizing rubber-to-asphalt ratios and blending methods for various application needs, showcasing the benefits of rock asphalt and desulfurized rubber particles in asphalt modification.

Dynamic fracture toughness and crack propagation mechanism of a heterogeneous heterostructured material under combined strengthening mechanisms

Developing fracture-resistant high-strength steels is an attractive prospect for various structural applications. In this work, a combination of carburizing heat treatment (CHT) and shot peening (SP) was used to develop combined strengthening (CS) mechanisms and to improve the mechanical strength and dynamic fracture toughness of 18CrNiMo7-6 alloy steel. Standard tensile tests and split Hopkinson pressure bar tests were conducted to investigate the strength and dynamic fracture toughness of the 18CrNiMo7-6 alloy steel. The crack initiation and propagation of samples were studied using scanning electron microscopy and transmission electron microscopy. Microstructure characterization and molecular dynamic simulations indicated that the excellent dynamic fracture toughness of the CS samples could be attributed to the grain refinement after strengthening and the formation of numerous slip bands at the crack tips, reducing the stress concentration at the crack tips. The Cr23C6 precipitates have a positive effect on the strength improvement of 18CrNiMo7-6 alloy steel. The results showed that this research can be used to guide the design of steels with high-strength and high-dynamic fracture toughness.

Effects of Different Cooling Treatments on Heated Granite: Insights from the Physical and Mechanical Characteristics.

The exploration of Hot Dry Rock (HDR) geothermal energy is essential to fulfill the energy demands of the increasing population. Investigating the physical and mechanical properties of heated rock under different cooling methods has significant implications for the exploitation of HDR. In this study, ultrasonic testing, uniaxial strength compression experiments, Brazilian splitting tests, nuclear magnetic resonance (NMR), and scanning electron microscope (SEM) were conducted on heated granite after different cooling methods, including cooling in air, cooling in water, cooling in liquid nitrogen, and cycle cooling in liquid nitrogen. The results demonstrated that the density, P-wave velocity (Vp), uniaxial compressive strength (UCS), tensile strength (σt), and elastic modulus (E) of heated granite tend to decrease as the cooling rate increases. Notably, heated granite subjected to cyclic liquid nitrogen cooling exhibits a more pronounced decline in physical and mechanical properties and a higher degree of damage. Furthermore, the cooling treatments also lead to an increase in rock pore size and porosity. At a faster cooling rate, the fracture surfaces of the granite transition from smooth to rough, suggesting enhanced fracture propagation and complexity. These findings provide critical theoretical insights into optimizing stimulation performance strategies for HDR exploitation.

Experimental investigation on the mechanical characteristics of ultra-high-molecular-weight polyethylene (UHMWPE) based fiber-reinforced concrete

This study investigates the static and dynamic mechanical properties of ultra-high-molecular-weight polyethylene (UHMWPE) fiber-reinforced concrete (FRC). The properties were assessed by conducting compressive strength, flexural strength, split tensile strength, and impact resistance. The pneumatic dispersion method was used for the UHMWPE fiber pretreatment. The concrete mix was prepared with a water-to-cement ratio of 0.6 and an aggregate fineness modulus of 5.39. UHMWPE fibers, measuring 6 mm and 12 mm in length and incorporated at addition rates of 5 wt‰, 10 wt‰, 15 wt‰, and 20 wt‰ of the fiber-to-cement weight ratio, were added to the concrete specimens for testing. The results showed that the FRC with 12 mm UHMWPE fiber and 15 wt‰ fiber-to-cement weight ratio achieved the best performance in the compressive strength test, and it increase 51.92 % compared with benchmark specimen. For the flexural test results, the 6 mm UHMWPR fiber performed best at a 15 wt‰ addition ratio, and it increase 18.77 % compared with benchmark specimen. Moreover, the FRC with 12 mm UHMWPR fiber excelled at a 20 wt‰ addition ratio in split tensile strength test, and it increase 92.14 % compared with benchmark specimen. The drop weight test indicated that a 15 wt‰ addition ratio with 12 mm UHMWPE fiber significantly enhanced performance, with an average impact number improvement of 5527 % under a 50 Joule impact energy, compared to the benchmark specimens. The study concludes that incorporating UHMWPE fiber into concrete significantly boosts its static and dynamic performance.

Predictive etiological classification of acute ischemic stroke through interpretable machine learning algorithms: a multicenter, prospective cohort study

BackgroundThe prognosis, recurrence rates, and secondary prevention strategies varied significantly among different subtypes of acute ischemic stroke (AIS). Machine learning (ML) techniques can uncover intricate, non-linear relationships within medical data, enabling the identification of factors associated with etiological classification. However, there is currently a lack of research utilizing ML algorithms for predicting AIS etiology.ObjectiveWe aimed to use interpretable ML algorithms to develop AIS etiology prediction models, identify critical factors in etiology classification, and enhance existing clinical categorization.MethodsThis study involved patients with the Third China National Stroke Registry (CNSR-III). Nine models, which included Natural Gradient Boosting (NGBoost), Categorical Boosting (CatBoost), Extreme Gradient Boosting (XGBoost), Random Forest (RF), Light Gradient Boosting Machine (LGBM), Gradient Boosting Decision Tree (GBDT), Adaptive Boosting (AdaBoost), Support Vector Machine (SVM), and logistic regression (LR), were employed to predict large artery atherosclerosis (LAA), small vessel occlusion (SVO), and cardioembolism (CE) using an 80:20 randomly split training and test set. We designed an SFS-XGB with 10-fold cross-validation for feature selection. The primary evaluation metrics for the models included the area under the receiver operating characteristic curve (AUC) for discrimination and the Brier score (or calibration plots) for calibration.ResultsA total of 5,213 patients were included, comprising 2,471 (47.4%) with LAA, 2,153 (41.3%) with SVO, and 589 (11.3%) with CE. In both LAA and SVO models, the AUC values of the ML models were significantly higher than that of the LR model (P < 0.001). The optimal model for predicting SVO (AUC [RF model] = 0.932) outperformed the optimal LAA model (AUC [NGB model] = 0.917) and the optimal CE model (AUC [LGBM model] = 0.846). Each model displayed relatively satisfactory calibration. Further analysis showed that the optimal CE model could identify potential CE patients in the undetermined etiology (SUE) group, accounting for 1,900 out of 4,156 (45.7%).ConclusionsThe ML algorithm effectively classified patients with LAA, SVO, and CE, demonstrating superior classification performance compared to the LR model. The optimal ML model can identify potential CE patients among SUE patients. These newly identified predictive factors may complement the existing etiological classification system, enabling clinicians to promptly categorize stroke patients’ etiology and initiate optimal strategies for secondary prevention.

Investigation on dynamic splitting mechanical properties of weakly cemented siltstone based on digital image correlation method and FracPaQ algorithm

Soft strata composed of weakly cemented rock are frequently subjected to dynamic loads in underground energy mining engineering, yet the dynamic mechanical properties of these materials remain insufficiently explored. In this study, dynamic splitting tests were conducted on Brazilian disc specimens of weakly cemented siltstone to assess their dynamic mechanical and failure characteristics. The findings revealed that both dynamic strength and dissipated energy increased under higher stress rates. A dynamic splitting strength model for weakly cemented siltstone was subsequently developed based on the incubation time criterion. Additionally, the digital image correlation technology was employed to analyze strain variations during the initiation of the main crack, and the quantitative analysis of the fragmentation process indicated that average opening rates increased with rising stress rates. The FracPaQ algorithm was also applied to further characterize fracture patterns under varying stress rates, demonstrating that the Gaussian function accurately represented the relationship between deflection angles and fracture trace lengths. These research outcomes can provide essential mechanical parameters and a theoretical foundation for the safety assessment of weakly cemented rock strata in coal mining.

A strategy for the improvement of the bonding performance of 3D-printed concrete interlayer interfaces

3D-printed concrete, as an intelligent building technology, has enormous potential in construction. However, the weak bond interfaces between two adjacent layers of concrete are still a well-known problem affecting the mechanical properties of printed structures, with reduced interlayer shear and tensile properties. The reinforcement method of inserting steel bars in vertically printed layers is crucial and requires research and exploration of suitable methods, as well as finding the optimal reinforcement scheme that satisfies the interlayer interface when facing different loads. This study proposes a method of interlayer reinforcement by vertically laying steel fibers between layers, and investigates the effects of steel fiber offset, deployment density, and cross-sectional area on interlayer bonding strength. The strengthening effect of steel fiber on interlayer shear and tensile strength was tested through shear and splitting tests. Microscopic numerical models are used to study the evolution process of interlayer cracking. The correlation between different steel fiber variables and interlayer bonding strength was studied using a Generalized Grey Relational Analysis (GGRA). The results showed that the shear strength and tensile strength of the interlayer interface could be improved by 256.32 % and 353.61 %, respectively, through a reasonable fiber layout scheme. It is recommended to lay steel fibers with small offsets. When the interlayer interface is subjected to shear loads, priority should be given to increasing the cross-sectional area. When the interlayer interface is subjected to tensile loads, the deployment density should be increased first to achieve the best improvement in interlayer strength.

Rubber concrete reinforced with macro fibers recycled from waste GFRP composites: Mechanical properties and environmental impact analysis

With the rapid growth of the automotive industry, a huge amount of tires have been produced, which inevitably led to the accumulation of scrap tires. A typical disposal routine is using scrap tires as a partial substitute for fine aggregate in concrete, producing so-called rubber concrete. However, the detrimental effects of rubber particles on concrete properties have been identified, which, to some content, hinders their broader application. The discrete fiber addition is shown to be effective in minimizing this detrimental effect, and this paper has therefore attempted to introduce macro fiber produced from waste glass fiber reinforced polymer (GFRP) into the rubber concrete system. Three series of specimens for compression, splitting, and flexural testing were tested. The test variables include concrete type (i.e., normal concrete, rubber concrete, and modified rubber concrete); and macro fiber content (i.e., 0–2 %). In addition, the inverse analysis is performed to transform the flexural test response into the tensile constitutive law of the fiber-reinforced concrete (FRC). The test results revealed macro fibers have little effect on the compressive strength of normal concrete and rubber concrete and a detrimental effect on that of modified rubber concrete. Incorporated fibers notably improve the splitting and flexural performance of normal concrete and rubber concrete. In addition, the cost and environmental impact analysis revealed that the addition of recycling products increases the concrete cost and results in a maximum reduction of carbon emissions by 17.3 % and embodied energy emissions by 80 %.

Improving erosion resistance of calcareous sand slope with zinc sulfate solution

Loose and uncemented calcareous sand slopes are prone to collapse under rainstorm erosion. In order to improve the erosion resistance stability of slopes, it is crucial to enhance the erosion resistance of calcareous sand. In this study, a new method of cementing calcareous sand with zinc sulfate solution (ZSS) is proposed. The ZSS reinforcement technique can effectively cement calcareous sand, enhance the mechanical properties and help reduce erosion on calcareous sand slopes. A series of laboratory experiments were conducted, including uniaxial compression tests, Brazilian splitting tests, surface penetration tests, microscopic tests, and rainfall scouring tests. The test results show that the uniaxial compressive strength of calcareous sand achieved 8.3 MPa reinforced with ZSS. Microscopic analyses revealed the mechanism of reinforcement, discovering the formation of environmentally friendly compounds such as ZnCO3 and CaSO4·2 H2O between calcareous sand particles, which enhanced the soil mechanical properties. The calcareous sand slope reinforced with ZSS forms a hard shell on the slope surface, which effectively improves the erosion resistance of the slope. After being reinforced with a ZSS concentration of 1.0 mol/L, the slope remained stable after 20 min of scouring at a rainfall intensity of 80 mm/h. This method provides a quick solution for reinforcing calcareous sand slopes and holds promising potential for practical engineering applications.

Utilising integrated bio-behavioural surveillance (IBBS) to investigate declining hepatitis C antibody prevalence among people who inject drugs in the Australian Needle and Syringe Program Survey

BackgroundPrevalence of hepatitis C virus (HCV) antibody (Ab) on dried blood spot (DBS) samples in the Australian Needle and Syringe Program Survey (ANSPS) decreased nationally from 57 % in 2015 to 32 % in 2022. We aimed to investigate potential explanations for this decline. MethodsChanges in DBS HCV Ab prevalence were investigated by redefining positive cases as those with those with either a positive HCV Ab test result or a self-reported history of ever having HCV treatment (modified prevalence), examining HCV Ab prevalence by birth and age cohorts, and assessing trends in key risk behaviours. ResultsOverall prevalence of DBS HCV Ab declined rapidly and significantly from 57 % in 2015 to 32 % in 2022 (p < 0.001) however modified HCV Ab prevalence remained stable over time (85 % and 88 % in 2015 and 2022, respectively, p = 0.357). The proportion of participants with negative HCV Ab and self-reported HCV infection increased from 20 % in 1995 to 40 % in 2022 (p < 0.001) and the proportion with negative HCV Ab and lifetime HCV treatment increased from 3 % in 1999 to 67 % in 2022 (p < 0.001). We also observed a decreasing trend in DBS HCV Ab prevalence in all birth and age cohorts with a noticeable acceleration in the decline commensurate with the advent of HCV DAA treatment. A long-term decreasing trend was also observed for key risk behaviours (p < 0.001) however the short-term trend was not significant for recent receptive syringe sharing. ConclusionThe temporal decline in HCV Ab prevalence appears related to reduced sensitivity of DBS HCV Ab detection with viral clearance following treatment. Since 2016, HCV treatment uptake has increased markedly including among people who inject drugs. In this context, continuing to monitor HCV Ab prevalence by DBS testing is problematic, with a shift to surveillance of active infection the most relevant to guide policy and practice in this setting.

Quality Management In Ready-Mix Concrete Production In Zambia

The construction industry, a significant contributor to global economies, is projected to yield substantial economic output by 2030 of around $135 trillion. Central to construction is concrete, a widely used material. Ready-mix concrete (RMC), a specialised form of concrete, is gaining prominence due to its rapid setting and superior quality. In Zambia, the increasing demand for RMC highlights the need for stringent quality management to hedge potential structural risks. This study aimed to determine the quality management in ready-mix concrete production in Zambia. Employing a parallel convergent mixed-methods research design to achieve the objectives, qualitative data was collected through semi-structured interviews and desk study and quantitative data was gathered through a structured questionnaire and an observation checklist. The findings of the study reveal that while guidelines exist, adherence varies. Regulatory bodies for standards, engineering and construction play pivotal roles in overseeing RMC quality. However, their execution faces inconsistencies and challenges due to limited resources and a lack of sense of responsibility. Quality control practices were investigated unveiling variations in forward, immediate, and retrospective control phases. Notable trends in proper storage and equipment calibration showed a commitment to precision. Immediate control practices, encompassing sampling and non-compliance management, demonstrated both positive aspects and areas for improvement. Retrospective control showed commitment to comprehensive strength testing and minimal towards split cylinder testing and on-site slump evaluation. In the realm of quality assurance (QA), RMC facilities show substantial adherence to documented QA standard operating procedures and thorough raw material inspections. However, deficiencies in batching and mixing practices and limited adoption of modern weighing systems require improvement. The study recommends creating an industry association for collaboration, enhancing standardised practices, introducing third-party quality audits, and proposing compulsory RMC standards to boost progress in the Zambian RMC industry. Key Words: Quality Management, Ready Mix Concrete, Observation, Desk Study, Zambia.

Mechanical properties and failure mechanism of 3D printing ultra-high performance concrete

Steel fiber reinforced 3D printing ultra-high performance concrete (3DP-UHPC) is prepared and experimentally studied. The effects of steel fiber content and various interlayer reinforcing materials on compressive, flexural, and splitting tensile properties are investigated, supplemented by Digital Image Correlation (DIC) technique for crack propagation analysis. Fabricated 3DP-UHPC specimens exhibited compressive strengths exceeding 160 MPa, with a peak at 205.2 MPa. Incremental increases in steel fiber content slightly enhanced compressive strength, whereas the addition of interlayer reinforcing materials, textile/steel wire mesh (SWM), reduced it due to altered interlayer bonding characteristics. The incorporation of textile/SWM significantly improved the flexural performance, enhancing energy absorption capacity and toughness. Specimens reinforced with SWM exhibited excellent flexural performance, with their flexural strength and ultimate deflection reaching 110.9 % and 192.5 % respectively of those before reinforcement. The splitting test revealed typical fractures along the interfaces between printed layers, with higher splitting strength obtained in the bottom layers. In specimens reinforced with carbon textile, glass textile, and SWM, the splitting strengths were more than double those of the subsequent layers. These insights contribute to a deeper understanding of 3DP-UHPC, paving the way for optimized use of reinforcing materials to improve structural integrity and performance.