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

Effect of near-fault ground motion with pulse signal on dynamic response of dam-reservoir-foundation systems

U ovom radu cilj je utvrditi učinke impulsnih pomaka tla uslijed bliskih potresa na dinamički odgovor gravitacijskih brana uključujući i interakciju brana – akumulacija – temelj na različite pristupe modeliranju akumulacije kao što su Westergaardov, Lagrangeov i Eulerov pristup. Kao studija slučaja, betonska gravitacijska brana Sarıyar smještena na rijeci Sakarya, 120 km sjeveroistočno od Ankare, odabrana je za istraživanje učinaka impulsnog pomaka tla uslijed bliskog potresa na odziv brane. Prvo su izložena glavna načela i osnovna formulacija pristupa. Zatim su uspostavljeni modeli brane s konačnim elementima uzimajući u obzir interakciju brana-akumulacija-temelj, pomoću računalnog programa ANSYS., sve da bi se odredio strukturni odgovor brane pod utjecajem impulsnog pomaka tla. Linearne privremene analize provedene su korištenjem Taiwan Chi-Chi 1999. i Imperial Valley 1979. koji prikazuju prividne impulse brzine kao reprezentativne za bliske potrese. Na kraju analize uspoređene su dinamičke karakteristike sve kako bi se demonstrirali modeli učinaka domene fluida i učinaka impulsnog signala.This paper aimed to determine the effects of a pulse signal of near-fault ground motion on the dynamic response of gravity dams, including dam-reservoir-foundation interaction, using different reservoir modelling approaches such as Westergaard, Lagrange, and Euler. As a case study, a Sarıyar concrete gravity dam located on the Sakarya River, 120 km northeast of Ankara, was considered for investigating the near-fault ground-motion pulse effects on dam responses. First, the main principles and basic formulations of these approaches were presented. Then, finite element models of the dam were realized considering dam-reservoir-foundation interaction using ANSYS software. To determine the structural response of the dam under pulse effects of the near-fault ground motion, linear transient analyses were performed using the 1999 Taiwan Chi-Chi and 1979 Imperial Valley ground motions, which display apparent velocity pulses as representative of the near-fault earthquakes. Subsequently, the dynamic characteristics were compared to demonstrate the models of the fluid domain effects and pulse signal effects