Fresh concrete pumping arrest investigation for thixotropy by a CFD modelling apporach

Concrete pumping operations determine construction speed, finishing quality, durability and even structural integrity. When pumping operations cannot be continued, most problems occur due to complex time-dependent transformations. This causes significant industrial costs (e.g. material and delay). Since time-dependent aspects are currently not fully understood and cannot be predicted, a way to quantify time-dependent aspects is needed. Therefore, we make an attempt by numerical simulation by comparing thixotropic cases with different pumping arresting times. After an introduction to fresh concrete rheology and numerical modelling, ten representative thixotropy cases are analysed. Despite some unresolved numerical instabilities, the numerical framework allows to estimate pumping pressure peaks after resting time. The results evaluate a thixotropy model, which is generally applicable for less thixotropic SCC’s. It is clear that flow re-initiation after rest in concrete pumping is poorly understood. Numerical simulation could be one approach for further analysis and is potentially important for practice. Future work such as simulation of concrete mixers, pressure increase after pumping arrest, formwork pressure decay and leakage are therefore recommended

State of the Art on Prediction of Concrete Pumping

Large scale constructions needs to estimate a possibility for pumping concrete. In this paper, the state of the art on prediction of concrete pumping including analytical and experimental works is presented. The existing methods to measure the rheological properties of slip layer (or called lubricating layer) are first introduced. Second, based on the rheological properties of slip layer and parent concrete, models to predict concrete pumping (flow rate, pumping pressure, and pumpable distance) are explained. Third, influencing factors on concrete pumping are discussed with the test results of various concrete mixes. Finally, future need for research on concrete pumping is suggested.ope

Krafla magma testbed (KMT): Engineering challenges of drilling into magma and extracting its energy

Preparations are underway for drilling well KMT-1 of the Krafla Magma Testbed at Krafla, Iceland to sample and instrument the margin of a rhyolite magma body. The project is driven by the need to understand magmatic systems, to improve volcano monitoring strategies, and to develop next-generation, high-enthalpy geothermal energy. The planned depth of the well is 2100 m with cemented casings to 2040 m and a 8 ½” open hole section for coring to 2010 m. The geology for KMT-1 is well known and the well will be located close to IDDP-1 where magma was unexpectedly intersected at 2102 m depth in 2009

Holocene Cyclic Records of Ice-Rafted Debris and Sea Ice Variations on the East Greenland and Northwest Iceland Margins

The dynamics of the Greenland Ice Sheet and drift of sea ice from the Arctic Ocean reaching Denmark Strait are poorly constrained. We present data on the provenance of Fe oxide detrital grains from two cores in the Denmark Strait area and compare the Fe grain source data with other environmental proxies in order to document the variations and potential periodicities in ice-rafted debris delivery during the Holocene. Based on their Fe grain geochemistry, the sediments can be traced to East Greenland sources and to more distal sites around the Arctic Basin. On the Holocene time scales of the two cores, sea ice biomarker (IP25) data, and quartz weight percent reveal positive associations with T°C and inverse associations with biogenic carbonate wt%. Trends in the data were obtained from Singular Spectrum Analysis (SSA), and residuals were tested for cyclicity. Trends on the environmental proxies explained between 15 and 90% of the variance. At both sites the primary Fe grain sources were from Greenland, but significant contributions were also noted from Banks Island and Svalbard. There is a prominent cyclicity of 800 yrs as well as other less prominent cycles for both Greenland and arctic sources. The Fe grain sources from Greenland and the circum-Arctic Ocean are in synchronization, suggesting that the forcings for these cycles are regional and not local ice sheet instabilities

The articles of faith of citizen aid actors - between dreams and realities

Over the years, established NGOs have been increasingly criticised for losing their role as transformational powers because of processes of (among others) professionalisation and bureaucratisation and, related to this, increased dependence on government funding. The organisational features of citizen aid are what distinguish them from established development organisations. Are the small and voluntary organisations run by citizens as a consequence and contrary to their established counterparts, not 'too close for comfort' and able to live up to the 'articles of faith' as distinguished by Tendler? This first chapter introduces the book, the two parts and the different chapters and authors. More importantly, it sets the stage by discussing the emergence of citizen aid particularly in the field of international cooperation and the many different ways they are related to other development actors, and bringing together the different names and concepts with which this phenomenon has been studied over the last decade and which are used in this book. All the research that has gone into private development organisations (mainly under the name of NGO studies) has provided little insight into broader groups of these NGOs and has been focused primarily on a few big organisations. In effect, we acknowledge the diversity in the sector but, in fact, know relatively little about that same diversity. This volume tackles that shortcoming of the existing literature. We study the rise of citizen aid as part of the changing aid architecture, with a clear folk to folk dimension, which includes aspects of solidarity and global citizenship. We discuss how the alternative nature of this actor, being small in scale and voluntary, determines their role as development actors

The founder-syndrome: Explaining the boundaries of financial expansion of small-scale development initiatives

Over the last couple of decades, private development initiatives (PDIs) have mushroomed across the globe. PDI support organisations have focused on strengthening PDIs in terms of capacities and finances. Surprisingly, this first longitudinal study of 200 Dutch PDIs, found that, despite these efforts, PDIs have not grown. This is explained through three hypotheses: the resource hypothesis, the professionalisation hypothesis and the founding syndrome hypothesis. It was found that while having additional members can contribute to growth, organisations with more budget at the start of the study saw their income decline. There is no proof that the professionalisation of PDIs has helped them grow; however, the evidence suggests that PDIs that are still run by their founder face substantial negative consequences. These findings are relevant for policy debate: if PDIs would like to be 'here to stay', more focus might be needed on succession planning instead of professionalisation