Managing the Heat Release of Calcium Sulfoaluminate Cement by Modifying the Ye'elimite Content.

Nowadays, calcium sulfoaluminate cement (CSA) is garnering a large amount of attention worldwide and is being promoted as a sustainable alternative to Portland cement for specific applications. This study aimed to control the heat release of CSA cement paste by choosing the appropriate composition. For this purpose, different calcium sulfoaluminate clinkers with up to 75 wt. % of ye'elimite were synthetized. Then, a reactivity study on the synthesized clinkers was conducted while varying the amount of gypsum added. The heat of hydration was measured by isothermal calorimetry. The influence of the ye'elimite content on the heat release and on the compressive strength was investigated. According to the findings, the amount of ye'elimite in the cement has a direct relationship with the heat release. The heat release as well as the mechanical performance increase with the increase in the ye'elimite content in the CSA cement. An equation allowing the prediction of the total heat release after 24 h is provided. Such data can be of particular interest to consultants aiming at the reduction of thermal cracking in massive concrete.

The use of calcium sulfo-aluminate cement as an alternative to Portland Cement for the recycling of municipal solid waste incineration bottom ash in mortar.

Municipal solid waste incineration generates large quantities of bottom ash that should be recycled. Current use of municipal solid waste incineration bottom ash (MSWI-BA) in cementitious materials is mostly in Ordinary Portland Cement (OPC). This paper considers using MSWI-BA as sand substitution in Calcium Sulfoaluminate Cement (CSA) as an alternative to OPC. A comparison between OPC and CSA mortars containing 0-2 mm MSWI-BA is conducted. The MSWI-BA used was treated to remove the ferrous and non-ferrous metals in order to obtain a better mineral fraction. Different percentages (0%, 25%, 50%, 75%, and 100%) of standard sand were substituted by MSWI-BA based on equivalent volume. Experimental results showed that the compressive strength and porosity of the CSA mortars were superior to OPC after substitution at 1, 7, 28, and 90 days. The compressive strength of OPC mortars with 25% substitution decreased by 40% compared to 11% for CSA mortars at 90 days. This is due to the difference in pH between the two cement pastes as OPC in contact with the MSWI-BA leads to a reaction with the aluminum content which releases hydrogen gas, increases the porosity, and decreases the compressive strength.

Risk assessment of asbestos-cement roof sheets in Chekka, North Lebanon.

Asbestos-cement was manufactured and used in Lebanon since the early 1950s. Corrugated rooftops of asbestos-cement were mostly spread within residential areas throughout the country. These rooftops are subject to weathering factors which are known to increase friability and risk of hazardous fiber release. This study aimed at assessing the asbestos-cement rooftop friability and the possible emerging risks in the urban-industrial city of Chekka, North Lebanon. The evaluation of the asbestos-cement included two field assessment algorithms and a standardized pull-up test. Hazard of fiber emissions was assessed by a pull-up test method, whereas vulnerability was determined by a level of interaction between people and the rooftops. Geographic object-based image analysis was used to map hazard, vulnerability, and risk of asbestos rooftops in the study area. The field algorithms classified most rooftops in a bad state compared with the pull-up test which ranked most of them as good. The X-ray diffraction analysis showed the presence of serpentine and amphibole fibers, except for crocidolite, in some rooftop samples. Hazard, vulnerability, and risk maps of the sampled area showed how hazard potential was amplified by vulnerability of population to possible fiber emission.

Stabilization of ZnCl2-containing wastes using calcium sulfoaluminate cement: leaching behaviour of the solidified waste form, mechanisms of zinc retention.

To assess the potential of calcium sulfoaluminate cement to solidify and stabilize wastes containing high amounts of soluble zinc chloride (a strong inhibitor of Portland cement hydration), a simulated cemented waste form was submitted to leaching by pure water at a fixed pH of 7 for three months, according to a test designed to understand the degradation processes of cement pastes. Leaching was controlled by diffusion. The zinc concentration in the leachates always remained below the detection limit (2 µmol/L), showing the excellent confining properties of the cement matrix. At the end of the experiment, the solid sample exhibited three zones which were accurately characterized: (i) a highly porous and friable surface layer, (ii) a less porous intermediate zone in which several precipitation and dissolution fronts occurred, and (iii) the sound core. Ettringite was a good tracer for degradation. The good retention of zinc by the cement matrix was mainly attributed to the precipitation of a hydrated and well crystallized phase with platelet morphology (which may belong to the layered double hydroxide family) at early age (≤ 1 day), and to chemisorption onto aluminum hydroxide at later age.

Influence of bacteria on lanthanide and actinide transfer from specific soil components (humus, soil minerals and vitrified municipal solid waste incinerator bottom ash) to corn plants: Sr-Nd isotope evidence.

Experiments have been performed to test the stability of vitrified municipal solid waste (MSW) incinerator bottom ash under the presence of bacteria (Pseudomonas aeruginosa) and plants (corn). The substratum used for the plant growth was a humus-rich soil mixed with vitrified waste. For the first time, information on the stability of waste glasses in the presence of bacteria and plants is given. Results show that inoculated plant samples contained always about two times higher lanthanide and actinide element concentrations. Bacteria support the element transfer since plants growing in inoculated environment developed a smaller root system but have higher trace element concentrations. Compared with the substratum, plants are light rare earth element (LREE) enriched. The vitrified bottom ash has to some extent been corroded by bacteria and plant activities as indicated by the presence of Nd (REE) and Sr from the vitrified waste in the plants. (87)Sr/(86)Sr and (143)Nd/(144)Nd isotope ratios of plants and soil components allow the identification of the corroded soil components and confirm that bacteria accelerate the assimilation of elements from the vitrified bottom ash. These findings are of importance for landfill disposal scenarios, and similar experiments should be performed in order to better constrain the processes of microbially mediated alteration of the MSW glasses in the biosphere.