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If the amount of sulfate within the mix design for concrete is not balanced, ettringite formation which first controls solidification continues while the concrete is hardening. Ettringite forms by reaction of sulfate contained in the cement or in some admixture with calcium aluminate (C3A) as cement component. The “late primary ettringite formation” promotes an increase in volume within the hardened concrete leading to cracks. To analyze the effect of substituting part of ordinary Portland cement (OPC) by a treated brown coal fly ash mortar bars were tested according to ASTM C452. This test method was originally developed to extrapolate from the internal to external sulfate attack and is based on the idea that by testing a concrete mixture containing sulfate the process of deterioration is accelerated because it does not have to diffuse into the concrete before reaction first. In addition to the samples prescribed in ASTM C452 further samples in the size of the German SVA procedure were tested also designed for accessing the external sulfate resistance. The results show that while the replacement of 25 % of cement by brown coal fly ash leads to length changes around the limit defined by ASTM, the substitution of 50 % cement exceeded the limit by a multiple. The progress of expansion is the very similar for the two geometries tested. In-situ XRD measurements confirmed that while for pastes made of OPC the formation of ettringite is completed after 20 hours, this is not true for the mixtures containing the brown coal fly ash.
In a different study the effect of hydrothermal treatment on the phase composition of ultra-high-performance concrete was analyzed. The results show that the sulfate and aluminate resulting from the decomposition of ettringite are bound into new phases.
If this binding is permanent this might allow the larger use of sulfate bearing raw materials.
The presentation will discuss the difference between EU and US standards for the determination of explosion (flammability) limits and limiting oxygen concentration. Small differences observed in measured values can be traced back to the different test apparatuses and criteria. The discrepancies can be much greater in the case of limiting oxygen concentration because of the high amount of inert gases and the corresponding low laminar burning velocities. The paper describes some examples and the influence of the chosen criteria on the results. The European and US standards use the criteria of flame propagation in open test vessels and of pressure rise in closed ones. The examples discussed show that flame propagation is still possible at very small pressure rise values, as observed much below the pressure rise criterion of usual standards. However, flame propagation in a process plant can cause an accident or explosion and must be avoided. Therefore, the flame propagation criterion is recommended to be used in chemical safety engineering. The European safety database CHEMSAFE contains expert-evaluated safety data for cases where the determination method and criteria are known. Flammability characteristics based on the pressure rise criterion may suffice in certain cases, e.g. for explosion protection in closed vessels without any connecting pipes.
IGUS is the International Group of Experts on the Explosion Risks of Unstable Substances. IGUS was established in 1962 with the objective to harmonize test methods used by different countries to identify and quantify the explosive properties of unstable materials. Over the years, IGUS has continued to offer scientists, who are advisers to their governments, and others, a forum to exchange data and information. The Energetic and Oxidizing Substances (EOS) working group as a sub-group of IGUS is dealing with test methods, Classification and safety aspects relating to organic peroxides, self-reactive substances and other energetic substances, fertilizers, ammonium nitrate and oxidizers.
The EOS working group holds an annual meeting alternating between Europe, the United States and Japan. The 2011 meeting took place from the 27th to the 29th of April 2011 at the Madison Hotel in Washington, D. C. The meeting was hosted by the Organic Peroxide Producers Safety Division (OPPSD) of the Society of Plastics Industry, Inc. (SPI). This was the fourth EOS meeting held in the USA since 1994. Of particular importance is the fact that 39 colleagues from authorities, universities, research institutes and industries attended the meeting. The delegates came from USA, Canada, China, France, The Netherlands, Norway, Sweden, Italy, Japan, United Kingdom and Germany. This confirms the breadth and scope of this forum and the value the participants associate with being able to contact other colleagues from around the world enabling the effective exchange of scientific results and discussion on the wide-ranging Problems concerning energetic and oxidizing materials.