Construction and Materials Best Practices for Concrete Sidewalks: Phase II - Long-Term Performance and Hot Weather Placement Effects

This report summarizes the investigation of construction practices and materials to develop durable concrete sidewalks which can resist scaling damage caused by exposure to freezing environment and deicer application. Over 16 months, a field study accompanied by laboratory testing was conducted to identify factors that affect the performance and durability of sidewalks. The variables considered for the study are concrete mix design, placement and finishing practices, curing methods, and deicer application. The placement of the sidewalks took place in late July 2021, to investigate the impact of hot weather concreting practices on the performance of sidewalks. Forty-eight sidewalk panels were placed behind Robert Brack Structural Engineering Laboratory at University of Massachusetts Amherst (UMass). During the sidewalk placement, cylinders and rectangular prisms were placed for laboratory testing. Thirty-two rectangular prisms were subjected to same curing method as the corresponding sidewalks for scaling resistance test in laboratory via BNQ NQ 2621-900. The results of this study indicate that mixture design formulation, curing method, de-icing method, and temperature based concreting practices impact the performance of scaling in concrete sidewalks. Recommendations incorporating these variables are presented in this report with accompanying testing standards and procedures

Ultra-High-Performance Concrete Reinforced with Multi-Scale Hybrid Fibers and Its Durability-Related Properties

Due to its excellent mechanical properties, dense microstructure, low permeability, ease of placement and volume stability, ultra-high performance concrete (UHPC) is considered the next-generation structural concrete and is increasingly used in transportation infrastructure. While previous research efforts generated valuable results, to achieve the desired performance, UHPC needs to be well formulated with precise and optimized quantities of cementitious materials, fillers, fine aggregate, water, chemical admixtures, and fibers. In addition, the mixture design of UHPC and its correlation with the performance evolution under different curing conditions remain unclear, and there exist critical significant gaps in understanding the efficiency of fibers and mixture design on the properties of UHPC, especially the mechanical and durability-related performance. Massachusetts Department of Transportation (MassDOT) is exploring multiple infrastructure applications that can incorporate UHPC, including joints, overlays, repairs, rehabilitation, and bridge beam fabrication. This project aims to develop UHPC mix design formulations that can be implemented at ready-mix batching plants or precast/prestressed concrete fabrication facilities by identifying and maximizing the roles of fibers and additives in enhancing mechanical and durability-related properties. Four fiber-reinforced mixes and seven UHPC mixes with different fibers were investigated and a UHPC mix for large-scale batching and field applications was recommended

Revised Load Rating Procedures for Deteriorated Prestressed Concrete Beams

The first prestressed concrete bridge in the United States was built in the early 1950s. Since then, several typical sections have been developed for use in bridge construction including I-beams, deck slabs, box beams, double tees, etc. In bridges under aggressive environments, corrosion deterioration of prestressing strands and stirrups has occurred creating challenges associated with determining the strength of deteriorated existing bridge sections. The MassDOT LRFD Bridge Manual includes provisions to estimate strength of corrosion deteriorated prestressed concrete box beams allowing engineers to calculate the load rating of these types of bridges. The provisions are based on the observed condition of the bridge, particularly with regard to estimates of strand area reductions to estimate residual strength. In bridges with adjacent box beams or deck slabs, corroded reinforcement is difficult to identify because only the top and bottom surfaces of the superstructure elements are accessible. The goals of this research are to evaluate the existing strength calculation procedures and to provide recommendations on how to properly evaluate the reduction in strand area based on the observed condition of the bottom surface of the prestressed box or deck beams

Observations About the Seismic Response of RC Buildings in Mexico City

Over 2000 buildings were surveyed by members of the Colegio de Ingenieros (CICM) and Sociedad Mexicana de Ingenieria Estructural (SMIE) in Mexico City following the Puebla-Morelos Earthquake of 2017. This inventory of surveyed buildings included nearly 40 collapses and over 600 buildings deemed to have structural damage. Correlation of damage with peak ground acceleration (PGA), peak ground velocity (PGV), predominant spectral period, building location, and building properties including height, estimated stiffness, and presence of walls or retrofits was investigated for the surveyed buildings. The evidence available suggests that (1) ground motion intensity (PGV) drove the occurrence of damage and (2) buildings with more infill and stiff retrofit systems did better than other buildings

Construction and Materials Best Practices for Concrete Sidewalks: Phase II \u2013 Long-Term Performance and Hot-Weather Placement Effects

This report summarizes the investigation of construction practices and materials to develop durable concrete sidewalks which can resist scaling damage caused by exposure to freezing environment and deicer application. Over 16 months, a field study accompanied by laboratory testing was conducted to identify factors that affect the performance and durability of sidewalks. The variables considered for the study are concrete mix design, placement and finishing practices, curing methods, and deicer application. The placement of the sidewalks took place in late July 2021, to investigate the impact of hot weather concreting practices on the performance of sidewalks. Forty-eight sidewalk panels were placed behind Robert Brack Structural Engineering Laboratory at University of Massachusetts Amherst (UMass). During the sidewalk placement, cylinders and rectangular prisms were placed for laboratory testing. Thirty-two rectangular prisms were subjected to same curing method as the corresponding sidewalks for scaling resistance test in laboratory via BNQ NQ 2621-900. The results of this study indicate that mixture design formulation, curing method, de-icing method, and temperature based concreting practices impact the performance of scaling in concrete sidewalks. Recommendations incorporating these variables are presented in this report with accompanying testing standards and procedures

Rationale, study design, and analysis plan of the Alveolar Recruitment for ARDS Trial (ART): Study protocol for a randomized controlled trial

Background: Acute respiratory distress syndrome (ARDS) is associated with high in-hospital mortality. Alveolar recruitment followed by ventilation at optimal titrated PEEP may reduce ventilator-induced lung injury and improve oxygenation in patients with ARDS, but the effects on mortality and other clinical outcomes remain unknown. This article reports the rationale, study design, and analysis plan of the Alveolar Recruitment for ARDS Trial (ART). Methods/Design: ART is a pragmatic, multicenter, randomized (concealed), controlled trial, which aims to determine if maximum stepwise alveolar recruitment associated with PEEP titration is able to increase 28-day survival in patients with ARDS compared to conventional treatment (ARDSNet strategy). We will enroll adult patients with ARDS of less than 72 h duration. The intervention group will receive an alveolar recruitment maneuver, with stepwise increases of PEEP achieving 45 cmH(2)O and peak pressure of 60 cmH2O, followed by ventilation with optimal PEEP titrated according to the static compliance of the respiratory system. In the control group, mechanical ventilation will follow a conventional protocol (ARDSNet). In both groups, we will use controlled volume mode with low tidal volumes (4 to 6 mL/kg of predicted body weight) and targeting plateau pressure <= 30 cmH2O. The primary outcome is 28-day survival, and the secondary outcomes are: length of ICU stay; length of hospital stay; pneumothorax requiring chest tube during first 7 days; barotrauma during first 7 days; mechanical ventilation-free days from days 1 to 28; ICU, in-hospital, and 6-month survival. ART is an event-guided trial planned to last until 520 events (deaths within 28 days) are observed. These events allow detection of a hazard ratio of 0.75, with 90% power and two-tailed type I error of 5%. All analysis will follow the intention-to-treat principle. Discussion: If the ART strategy with maximum recruitment and PEEP titration improves 28-day survival, this will represent a notable advance to the care of ARDS patients. Conversely, if the ART strategy is similar or inferior to the current evidence-based strategy (ARDSNet), this should also change current practice as many institutions routinely employ recruitment maneuvers and set PEEP levels according to some titration method.Hospital do Coracao (HCor) as part of the Program 'Hospitais de Excelencia a Servico do SUS (PROADI-SUS)'Brazilian Ministry of Healt

Assessment of carbon capture, utilization and storage for gasendal

In order to meet the goals set in the Paris Agreement and the stringent CO2 emission level targets set in Sweden, there is an urgent need to increase the amount of CO2 utilization and storage. This thesis presents a techno-economic analysis of CO2 liquefaction and the synthesis of electro-methanol (e-MeOH) as a CO2 utilization pathway for captured CO2 from Gasendal, a biogas upgrading plant. The processes are implemented and simulated in Aspen Plus to extract important parameters and calculate capital and operational costs as key performance indicators. The results show that liquefaction costs 34 €/tonCO2 for Gasendal, which is approximately 80% higher than shown in other studies. However, when increasing the plant size to 1M tonCO2/year, the cost decreases to 10 €/tonCO2. In terms of heat recovery potential, the plant could only provide heat to district heating, but the amount is too small considering no close pipelines. On the other hand, e-methanol synthesis costs amounted to 1387 €/tonMeOH, with about 91% of expenses attributed to alkaline water electrolysis for hydrogen generation. Given that electrolysis costs pose a limitation and do not decrease with the scale of the plant in this study, the overall cost of e-methanol synthesis remains unaffected by the plant’s capacity. Regarding heat recovery, the process is able to supply 98% of its heating demand and reduce the natural gas consumption in the existing process at Gasendal by around 43%

Structural Engineering

•Introduction to Structural Engineering • •Forces in Structures • •Structural Systems • •Civil Engineering Materials • •Some Definitions of Important Structural Propertie

Construction and Materials Best Practice for Concrete Sidewalks

This report summarizes an 18-month effort to investigate best practices to incorporate into the materials and construction of concrete sidewalks to mitigate surface scaling damage induced by freeze-thaw cycles in the presence of deicing chemicals. The study involved an in-situ experimental study accompanied by laboratory testing and quantitative analyses to determine key factors that impact sidewalk performance and durability. The primary variables considered in the study were concrete mixture design (aggregate/paste optimization, air content, and cementitious material replacements), workmanship (delivery, placement, finishing, curing), and deicing treatment. The collective effort involved participants from construction companies, a concrete producer, academia, testing laboratories, and the Massachusetts Dept. of Transportation (MassDOT). Fifty-four unique sidewalk panels were placed adjacent to the Hopkinton, MA, MassDOT Research and Materials Laboratory. Collectively, the results indicate that sidewalk performance can be controlled though a combination of optimized mix design formulation, proper pre-placement, placement, finishing, curing, cold and hot weather concreting practices, contractor quality control, and department acceptance. Recommendations based on findings and in combination with referenced standards are provided, covering the range of variables studied in this researc

Forces and Stresses Generated During Rigging Operations

Rigging is one of the most dangerous aspects of arboriculture, yet there are no robust studies of the forces and stresses generated during rigging. Compounding the inherent danger of rigging is the structurally-deficient condition of many trees that are removed using rigging. Red pines (Pinus resinosa Ait.) (n = 13) were removed using conventional techniques, and forces at the block and in the rope were measured as the top, and four subsequent pieces were rigged with a block and Port-A-Wrap. Stress in the trunk at breast height was calculated from strain measurements and each tree’s modulus of elasticity. Multiple regression was used to determine which independent variables (mass of piece, fall distance and fall ratio, notch angle and depth) best predicted forces. Tops and pieces exhibited different relationships with mass, which was the best predictor of force at the block and tension in the rope. Other variables were not as important and exhibited counter-intuitive relationships with forces. There were few differences in stress generated when removing tops and pieces, which appeared to be due to greater deflection higher in the trunk when tops were removed