Effect of mix design on restrained shrinkage of concrete

The impetus for this research came from a project that involved the reconstruction of Twelve bridge decks in Tabriz, East Azerbaijan, IRAN that was completed in the summer of 2009. Shortly after construction was completed, shrinkage cracks were observed on 8 of the 12 bridge decks. Such cracking can cause long term durability problems by facilitating chemical ingress and moisture penetration that may aggravate problems such as alkali-silica reaction and corrosion of the reinforcing steel [1]. Shrinkage cracks can also increase deterioration caused by cyclic loadings. Any of these problems can decrease the service life of a bridge deck [1]. The mixture used in the bridge decks had a w/c+p ratio of 0.33 and contained 26.2% fly ash (Class F). Although the mixture was not intended to be a high performance concrete (HPC) mixture, it did have characteristics similar to HPC mixtures. As the use of HPC becomes more common, studies on the effect of pozzolanic materials and the ability of admixtures to reduce concrete shrinkage are needed to ensure durability of the structures. This paper presents results from an experimental study conducted to determine how certain mixture proportion parameters influence concrete shrinkage. In particular, the free shrinkage of concrete mixtures with varying amounts of fly ash, shrinkage reducing admixture (SRA), expansive cement, and fibers were studied

The Weil pairing and the Hilbert symbol

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/46247/1/208_2005_Article_BF01444229.pd

Pulse velocity assessment of early age creep of concrete

Creep of concrete can have damaging effects by inducing deformations that may contribute or eventually lead to cracks, which influence concrete durability, steel reinforcement exposure to corrosion, and aesthetic damage to architectural buildings. This research investigated the early age creep deformation in concrete samples made with normal, lightweight (Lytag), recycled concrete, and recycled asphalt aggregates using ultrasonic pulse velocity measurements. Creep was achieved by applying a load corresponding to 30% of the strength of concrete to 100 × 250 mm prisms. The compressive load was applied from 24 h after mixing and up to 27 days. The results and analysis of measurements obtained for stress development, specific creep (creep strain per unit stress), and ultrasonic pulse velocity measured up to 27 days after load application are presented. Empirical models that allow the assessment of creep of concrete using ultrasonic pulse velocity measurements are also presented. Early age specific creep is higher for recycled asphalt aggregate than Lytag aggregate and recycled concrete aggregate concretes, which are higher than gravel concrete. Measurements of ultrasonic pulse velocity could be used to determine creep but further work to refine this technique is required

The Syrian Involvement in Lebanon : An analysis of the role of Lebanon in Syrian regime security from Ta'if to the death of Hafiz al-Asad.

This study analyzes the Syrian involvement in Lebanon following the end of the Lebanese civil war in 1989/90 and until the death of Syrian President Hafiz al-Asad, which marked the end of an era. I argue that Lebanon's geo-strategic position, not Syria's ideological orientation, has been central in explaining the Syrian involvement since the Syrian intervention in 1976, and especially in the 1990s. I further argue that Syrian foreign and security policy has been mainly driven by concerns for regime stability and security. I have defined security broadly to encompass concerns by the Asad-regime to ward off threats to 1) the legitimacy of the rule of the Asad-regime (political security), 2)military threats from mainly Israel (military security), and 3) threats to the allocative political economy (economic security). I also very briefly discuss the importance of water. In all these sectors of security, Lebanon has had a pivotal role. Thus, mainly security concerns, not 'Greater-Syria' ambitions have defined Syria's involvement in Lebanon in the 1990s

The First Dry Tree Semisubmersible Drilling and Production Platform Sold

Abstract This paper discusses the Octabuoy®, which is the first semisubmersible drilling and production platform for dry tree field developments that has been sold and is being built. Its design, which is based on proven semisubmersible technology, has been validated theoretically and by extensive model testing, features excellent motions characteristics, and has been integrated by select major and independent operators as part of their tool kits. The platform meets oil and gas industry needs:For dry tree field developments in diverse environments, from benign to harsh, particularly when large topside loads carrying capacity and deepwater applications are needed.For a real alternative to other dry tree platforms in operation today.Suitability for fabrication, installation, and integration for field developments in Gulf of Mexico (GOM), North Sea, Brazil, West Africa, and Far East. The paper describes the platform's design, components, and performance characteristics. It summarizes the results of theoretical analyses and testing programs that validate its suitability for all environments including Brazilian metocean conditions. It also addresses its cost-effectiveness and flexibility regarding fabrication, installation, and integration. The platform's hull profile minimizes first order motions, parametric motions and, ultimately, fatigue problems in risers, moorings, and platform structure. Extensive model testing—including seakeeping, wind tunnel, towing, Vortex Induced Motions, and comparative tests—has validated the platform's performance. Test results have also confirmed analytical calculations, including hydrodynamic, mooring, and riser analyses. The platform features flexible topside designs and a very favorable topside-to-hull weight ratio. It accommodates conventional top-tensioned riser systems with manageable stroke ranges and steel catenary risers. It can be fabricated at shipyards worldwide using conventional shipbuilding methods and can be installed by floatover, heavy lift, or quayside. The platform can be relocated at the end of field life, thereby amortizing platform costs over multiple fields, and it can store oil in its hull. This paper summarizes the platform's value and key contribution to the oil and gas industry: It meets a need as the industry moves further offshore and into deeper waters, and it does so cost-effectively. Introduction The Octabuoy drilling and production platform is the first dry tree semisubmersible platform to be sold. One Octabuoy was sold to ATP Oil and Gas (ATP) in 2008 for deployment on ATP's Cheviot field in the UK sector of the North Sea. The Octabuoy is a deep-draft semisubmersible platform that was engineered and designed specifically to serve as a floating production unit with excellent motions performance for dry tree field developments. The Octabuoy concept evolved from three decades of semisubmersible platform experience, and it is based on proven principles and technology. Suitable for use in both benign and the harshest of environmental conditions, the Octabuoy can accommodate both production facilities and complete drilling or workover rig packages. Its design allows for flexibility of fabrication, installation, and integration methods and the possibility of relocation to multiple fields. </jats:sec