Alkali–silica reactions (ASR): Literature review on parameters influencing laboratory performance testing

Utilisation of potentially alkali–silica reactive aggregates requires reliable performance tests to evaluate the alkali–silica reactivity of various aggregate combinations, including their alkali threshold dependence on binder type. Several such performance tests have been used worldwide for more than 15 years, but none of the methods have proven to be reliable for use with all aggregate types and all binders. One of the objectives of RILEM TC 219-ACS (2007–2012) is to develop and validate one or more of such performance tests. Several parameters may influence the results obtained in an accelerated performance test compared to the field behaviour. Based on a state of the art literature review, this paper discusses which parameters must be considered to be able to develop reliable ASR performance testing methods and provides some tentative recommendations. The internal humidity in the test specimens, the extent of alkali leaching and the storage temperature are of particular importanceACKNOWLEDGEMENT. We greatly acknowledge all RILEM TC 219-ACS members and the TC Chairman and Secretary. We are particularly thankful to the authors that took part in the literature survey report performed within the task group “Performance testing”, in which has formed the basis for this review paper. The authors would also like to acknowledge COIN, the COncrete INnovation centre (www.coinweb.no) for the financial support to the PhD study of the principle author.acceptedVersio

Trapped-Ion Quantum Logic Utilizing Position-Dependent ac Stark Shifts

We present a scheme utilizing position-dependent ac Stark shifts for doing quantum logic with trapped ions. By a proper choice of direction, position and size, as well as power and frequency of a far-off-resonant Gaussian laser beam, specific ac Stark shifts can be assigned to the individual ions, making them distinguishable in frequency-space. In contrast to previous all-optical based quantum gates with trapped ions, the present scheme enables individual addressing of single ions and selective addressing of any pair of ions for two-ion quantum gates, without using tightly focused laser beams. Furthermore, the decoherence rate due to off-resonant excitations can be made negligible as compared with other sources of decoherence.Comment: 5 pages, 4 figures. Submitted to Physical Review Letter

Field-Induced Two-Step Phase Transitions in the Singlet Ground State Triangular Antiferromagnet CsFeBr3_3

The ground state of the stacked triangular antiferromagnet CsFeBr$_3$ is a spin singlet due to the large single ion anisotropy $D(S^z)^2$. The field-induced magnetic ordering in this compound was investigated by the magnetic susceptibility, the magnetization process and specific heat measurements for an external field parallel to the $c$-axis. Unexpectedly, two phase transitions were observed in the magnetic field $H$ higher than 3 T. The phase diagram for temperature versus magnetic field was obtained. The mechanism leading to the successive phase transitions is discussed.Comment: 8 pages, 9 figures, 10 eps files, jpsj styl

Signatures of intrinsic Li depletion and Li-Na anti-correlation in the metal-poor globular cluster NGC6397

To alleviate the discrepancy between the prediction of the primordial lithium abundance in the universe and the abundances observed in Pop II dwarfs and subgiant stars, it has been suggested that the stars observable today have undergone photospheric depletion of Li. To constrain the nature of such depletion, we conduct a homogeneous analysis of a very large sample of stars in the metal-poor globular cluster NGC6397, covering well all evolutionary phases from below the main sequence turn-off to high up the red giant branch. Non-LTE Li abundances or abundance upper limits are obtained for all stars, and for a size-able sub-set of the targets also Na abundances are obtained. The sodium abundances are used to distinguish stars formed out of pristine material from stars formed out of material affected by pollution from a previous generation of more massive stars. The dwarfs, turn-off, and early subgiant stars form a thin abundance plateau, disrupted in the middle of the subgiant branch by the lithium dilution caused by the first dredge-up. A second steep abundance drop is seen at the red giant branch bump. The turn-off stars are more lithium-poor, by up to 0.1 dex, than subgiants that have not yet undergone dredge-up. In addition, hotter dwarfs are slightly more lithium-poor than cooler dwarfs, which may be a signature of the so-called Li dip in the cluster, commonly seen among PopI stars. A considerably large spread in Na abundance confirms that NGC6397 has suffered from intra-cluster pollution in its infancy and a limited number of Na-enhanced and Li-deficient stars strongly contribute to form a significant anti-correlation between the abundances of Na and Li. The inferred Li abundances are compared to predictions from stellar structure models including atomic diffusion and ad-hoc turbulence below the convection zone.Comment: 13 pages, 11 figures, accepted by A&A, minor language corrections and some references change

11th International Conference on Modern Building Materials, Structures and Techniques, MBMST 2013

The experience of ASR and ASR testing varies substantially across Europe and outside. Several testing procedures exist but are not always linked to service life records. Also, the European concrete standard on this issue refers to regulations valid in place of use. An attempt to provide a complete set of design and assessment tools is explained in this paper, whereby concrete performance testing is one key element but must be regarded exactly as that, i.e. one step only within a framework of additional requirements and still linked to regional experience. The performance testing concept development is briefly explained in order to display opportunities and limitations. Performance in the sense of combining constituents for concrete prims expansion testing has been adopted in some countries, e.g. in Norway and, hence, providing a tool set for flexible concrete design regulations. Implicitly, several investigations on fly ash quality scatter and processing have been performed. Evidence of the fly ash mitigation effect is provided, but also strong indications supporting performance enhancement when supplied as a composite cement, compared to that of a concrete mixer blend.Acknowledgements. The progress of the RILEM testing procedures would not have been possible without the active support of the RILEM TC 219 chairman Philip Nixon and secretary Ian Sims, who also jointly chaired the EU “PARTNER” project. We also thank them for allowing the use of yet non-published data.publishedVersio