Development of a simulation dump truck dynamics model to estimate loads acting on its carrier and load platform when loading and dumping bulk loads

It is important for mining dump trucks to minimize the weight of the carrier and the load platform while maintaining a sufficient level of their rigidness and strength. This requirement significantly affects the weight of the transported material, the cost of transportation and, consequently, the economic efficiency of mining operations. Processes of loading and dumping of bulk loads, which is transported by dump trucks, make a significant contribution to reducing the service life of the carrier. Therefore, proper consideration of the bulk load dynamics is an important and relevant task. Contemporary systems for calculating the dynamics of solids allow for joint modeling with applications designed to calculate the dispersed body dynamics. This approach helps to obtain adequate loads in the pivots and force links of the model, to analyze the loading of the load platform, to asses the durability of the dump truck elements, to define the geometry of the load platform. In order to perform the simulation, it is required to develop a mathematical model of a dump truck, including all its key elements and subsystems, a model of the bulk load, and a model of the load platform. The purpose of the study is to develop a mathematical model of a mine dump truck to determine the loads in the pivots and force links connected to the carrier and the load platform for the strength calculations and durability analysis. The calculations are made with the combined use of the solids dynamics calculation system and the application to calculate the dynamics of dispersed bodies.

Properties of Shotcrete According to Accelerator Types and Mixing Ratios

Shotcrete should be attached to the ground and should have stable strength for a long-term. It should develop strength earlier for rapid work. Therefore, in this study, three types of accelerators—aluminate, cement mineral, and alkali-free—were selected and mixed to secure the initial strength. Depending on the type and mixing rate of each accelerator, slump, air amount, and compressive strength were used to evaluate the basic properties, boiling water absorption test, and chloride ion penetration resistance to conduct durability analysis. The mixing of aluminate-based and cement-mineral-based accelerators was effective in improving the initial strength, and alkali-free accelerator was effective in improving the long-term strength. The mixture to which accelerators were not mixed showed the highest water-tightness.

A Methodology to Evaluate Long Term Durability of Dam Concrete Due to Calcium Leaching through Microscopic Tests and Numerical Analysis

Hydropower dams are subjected to soft water penetration during their service lives. Concrete deterioration due to calcium leaching will decrease the durability of concrete and affect dam safety. The long-term performance of concrete dams due to calcium leaching should be evaluated and predicted accurately to complete reinforcement work in a timely manner. In this paper, a methodology that combined microscopic tests and numerical analysis to evaluate the long-term performance of dam concrete due to calcium leaching is proposed. The current state of concrete is evaluated by analyzing the components of sediments and seepage water through microscopic and spectroscopic tests, such as X-ray photoelectron spectroscopy, scanning electron microscopy, and inductively coupled plasma mass spectrometry. The long-term degradation of concrete was predicted by utilizing a multi-scale model of calcium leaching, which considered the micro-pore structure of cement hydrates flux with time. The simulated results using this calcium leaching model showed a good agreement with other experiments. Finally, a real case study including field inspection was performed and the long-term durability of dam concrete was predicted through microscopic tests and finite element analysis method. It implies that the proposed method could provide calculation and theoretical basis for the durability analysis of concrete dams due to calcium leaching.

Sequential Analysis of Binding and Neutralizing Antibody in COVID-19 Convalescent Patients at 14 Months After SARS-CoV-2 Infection

Durability of SARS-CoV-2 Spike antibody responses after infection provides information relevant to understanding protection against COVID-19 in humans. We report the results of a sequential evaluation of anti-SARS-CoV-2 antibodies in convalescent patients with a median follow-up of 14 months (range 12.4-15.4) post first symptom onset. We report persistence of antibodies for all four specificities tested [Spike, Spike Receptor Binding Domain (Spike-RBD), Nucleocapsid, Nucleocapsid RNA Binding Domain (N-RBD)]. Anti-Spike antibodies persist better than anti-Nucleocapsid antibodies. The durability analysis supports a bi-phasic antibody decay with longer half-lives of antibodies after 6 months and antibody persistence for up to 14 months. Patients infected with the Wuhan (WA1) strain maintained strong cross-reactive recognition of Alpha and Delta Spike-RBD but significantly reduced binding to Beta and Mu Spike-RBD. Sixty percent of convalescent patients with detectable WA1-specific NAb also showed strong neutralization of the Delta variant, the prevalent strain of the present pandemic. These data show that convalescent patients maintain functional antibody responses for more than one year after infection, suggesting a strong long-lasting response after symptomatic disease that may offer a prolonged protection against re-infection. One patient from this cohort showed strong increase of both Spike and Nucleocapsid antibodies at 14 months post-infection indicating SARS-CoV-2 re-exposure. These antibodies showed stronger cross-reactivity to a panel of Spike-RBD including Beta, Delta and Mu and neutralization of a panel of Spike variants including Beta and Gamma. This patient provides an example of strong anti-Spike recall immunity able to control infection at an asymptomatic level. Together, the antibodies from SARS-CoV-2 convalescent patients persist over 14 months and continue to maintain cross-reactivity to the current variants of concern and show strong functional properties.

Durability assessment of concretes reinforced with steel and synthetic fibers in Colombia

In recent years, the use of steel fibers has increased in Colombia, optimizing structure designs, quality specifications and mechanical behavior. However, the concrete durability and resistance to aggressive environments such as sulfates and chlorides are not commonly evaluated. This paper includes results of durability analysis for 21 MPa compressive strength concretes reinforces with steel and synthetic fibers. Performance parameters measured during tests include sulfate resistance, chlorides penetration, and carbonation according to technical standards. The Variables of experimental program were fiber type and fiber dosage. Dosages for synthetic fibers were 1.5 kg/m3, 3.0 kg/m3 and 5.0 kg/m3, and for steel fibers were 5.0 kg/m3, 9.0 kg/m3 and 18 kg/m3. Results of the study were used to propose recommendations for reducing concrete deterioration when exposed to these aggressive environments and for extending the durability service life.