Application of Large Prestress Strands in Precast/Prestressed Concrete Bridges

The objective of this research is to investigate the advantage of using large-diameter 0.7-inch (18 mm) strands in pretention applications. Large-diameter strands are advantageous in bridge construction due to the increased girders capacity required to sustain exponential increase in vehicle numbers, sizes, and weights. In this research, flexure capacity of girders fabricated using 0.7-inch (18 mm) diameter strands will be calculated and compared to bridge capacities constructed using smaller strands. Finally, two similar bridge sections will be designed using 0.6-inch (15 mm) and 0.7-inch (18 mm) diameter strands to quantify the structural advantages of increased strand diameter. The research findings showed that a smaller number of girders is required for bridge construction when larger strands are used. Four girders are required to design the bridge panel using high performance concrete and large diameter strands, as compared to 6 girders required when regular concrete mix designs and normal size strands are used. The advantages of large strands and high-performance concrete mixes include expedited construction, reduced project dead loads, and reduced demand for labor and equipment. Thus, large strands can partially contribute to the improvement of bridge conditions, minimize construction cost, and increase construction site safety

Developing high performance concrete for precast/prestressed concrete industry

High performance concrete (HPC) is a new class of concrete that has superior characteristics compared to conventional concrete. Despite of its superior characteristics, HPC is not widely used in local and international markets due to its high constituent materials cost. This paper presents the research done to develop economic HPC mixes using local materials and conventional mixing and curing techniques. HPC characteristics were attained using supplementary cementitious materials as silica fume and class C fly in partial replacement of Portland cement. Superplasticizers were used to maintain a high flowing ability using a low water-to-powder ratio. Concrete mixes were produced using a high energy mixer to maintain sufficient mix consistency. As a result, concrete mixes with 24 -h compressive strength of 70 MPa and 28-day strength of 105 MPa were produced. Concrete samples tested for expansion using accelerated mortar bar test (AMBT) showed that developed concrete is not susceptible to alkali-silica reaction. Improved characteristics can be used in improving the performance of concrete construction projects, reduce required maintenance, and increase construction projects life-span

Application of Supplementary Cementitious Materials in Precast Concrete Industry

Supplementary cementitious materials (SCMs) are increasingly incorporated into the concrete mix design. Silica fume, fly ash, and multi-wall carbon nanotubes are used to improve concrete mix properties. The objective of this chapter is to decipher the impact of different SCMs on the fresh and hardened concrete properties, including concrete flowing ability, initial strength, final strength, modulus of elasticity, and modulus of rupture. In addition, the impact of SCMs on mitigating the alkali-silica reactivity of concrete and increasing the hardened concrete long-term performance is investigated. Developed concrete mixes, incorporating SCMs, are used in fabricating different precast/prestressed bridge girders. The impact of improved concrete properties on precast girder performance in increased flexure, shear, and span-to-depth ratio significantly improves project sustainability and reduces the overall project life cycle cost

Additive Construction with Mobile Emplacement: Multifaceted Planetary Construction Materials Development

The National Aeronautics and Space Administration's Additive Construction with Mobile Emplacement (ACME) project is developing construction materials with which infrastructure elements, including habitats, will be additively constructed for planetary surface missions. These materials must meet requirements such as the ability to be produced from available in-situ resources to eliminate the cost of launching materials from Earth, the ability to be emplaced via three dimensional building techniques, the ability to resist aging in extreme environments including radiation and micrometeorite bombardment, and the ability to provide the necessary structural integrity for a given building. This paper reviews the constraints placed on such planetary construction materials and details the work of the ACME team in characterizing materials that could one day construct planetary surface structures on Mars or the Moon. Material compositions, compressive strength, and requirements for additive construction on planetary surfaces are discussed. Due to the multifunctional requirements of the material, an optimization is necessary to balance between the site-specific regolith composition, emplacement via additive construction techniques, and characteristics of the final structure

Development of High Performance Precast/Prestressed Bridge Girders

Demand continues to increase for bridges with long spans and shallow depths. Due to safety concerns, four-span overpasses are being replaced with two span overpasses to avoid placement of piers near the highway shoulders. In the meantime, the bridge profile is restricted due to existing businesses nearby. Thus, nearly the same superstructure depth must be used for double the span length. This dissertation focuses on topics aiming at providing precast prestressed concrete girders with the shallowest possible depth for a given span. It forms parts of larger projects conducted by the University of Nebraska for the Nebraska Department of Roads and for the Wire Reinforcement Institute. Specifically, the following issues were researched: (1) Use of 0.7 in. diameter Grade 270 ksi strands for pretensioning of precast concrete girders at a strand spacing of 2 inches by 2 inches. This arrangement gives nearly 190 percent of the prestressing with 0.5 in. diameter strands and nearly 135 percent with 0.6 in. strands. The research focuses on the required confinement steel to allow determination of transfer and development lengths according to current procedures in the AASHTO LRFD Bridge Design Specifications for smaller strands. (2) Develop a self consolidating concrete (SCC) mix, using Nebraska aggregates that will allow for a specified design strength at service of 15 ksi and a minimum strength at one day of 10 ksi, representing the demand at the time of release of the prestress to the concrete member. Prior to this study, standard concrete strength prevailing in Nebraska has been 8 ksi at service and 6.5 ksi at release. It was the goal of the research to keep the cost of materials as low as possible but not exceeding $250 per cubic yard, compared to the proprietary mixes that cost approximately four times this amount. (3) Use of 80 ksi welded wire reinforcement (WWR) as the auxiliary reinforcement for shear, web end splitting and flange confinement. This would result in higher quality product, less reinforcement congestion, about 25 percent savings in the steel materials, and considerable savings in girder fabrication costs. A combination of theoretical and experimental work has resulted in the following findings: (1) A shear friction model can be used to estimate the required amount of confinement of the bottom flange. (2) A reasonable reinforcement detail is needed, even with very heavily prestressed NU I girder bottom flange, to allow use of the current methods of estimating strands transfer and development lengths. (3) Two SCC mixes with materials costs less that$200 dollars per cubic yard and with the required strengths were able to be developed. The mixes exhibited excellent flowability and predictable engineering properties. (4) Grade 80 WWR was successfully used. Its shear resistance was theoretically predictable. It produced higher capacity than the Ultra High Performance steel fiber concrete demonstrated by the Federal Highway Administration, with much lower costs and conventionally predicable design strength. Advisors: George Morcous, Maher Tadro

Exploring the Potential of Smart Contracts in the Business Industry

In 2018, construction was responsible for more than 6 percent of global GDP, and this number is expected to rise to 14.7 percent by 2030. However, the construction sector is hampered by several obstacles that prevent it from evolving into a simpler, quicker, and more lucrative enterprise. Many of these hurdles may be overcome with the use of smart contract technology, which boasts advantages like increased security, accelerated processing, and transparent transactions throughout the whole construction sector. Insights into the application of "smart contracts" within the construction industry are explored in this study to determine the efficacy of this technology in the industry. The research makes use of a number of different approaches to arrive at findings that contribute to the scientific community. The value that "smart contracts" may bring to various facets of construction is discussed and analysed via the use of two case stud-ies and a survey. Prior to the case studies and survey chapters, a literature review and a chapter outlining blockchain and smart contracts and their applications in the construction industry are included. After years of study, a plethora of initiatives have been set in motion to bring the revolutionary blockchain technology to various segments of the construction industry. According to the findings, new software and hardware are being tested and deployed in the field. According to the results of the first case study, using the breakthrough technology, known as PLASMA, has the potential to drastically cut down on building projects' durations and budgets. In the second case study, it is obvious how the application of smart contract technology plays out in the real world. Payment automation on a building site using sensors and blockchain technology proved effective, with an error rate of under 5%. Finally, the poll found that over 70% of respondents think "smart contracts" technology would become commonplace in many facets of the construction industry