A new test for combined Ca-leaching and sulphate resistance of cementitious materials

Limitations in the understanding of chemical key controls on concrete damaging mechanisms exacerbate predictions on the long-term performance and durability of cementitious materials. Therefore, the scope of the project “ASSpC Advanced and Sustainable Sprayed Concrete” is to obtain a better mechanistic understanding of the processes underlying deleterious chemical attacks. The herein presented alternative test, loosely following the regulations of the German Building Authority (DIBt) testing procedure (the so-called SVA test) for sulphate resistance, investigates the resistance of concrete mixes with high levels of limestone substitution (35%, 50% and 65%) against sulphate attack in a 10 g L-1 Na2SO4 solution at ambient temperature. Powdered samples were used in favour of prisms or drill cores to accelerate alteration reactions and to eliminate variations in microstructure or porosity. Based on throughout chemical and mineralogical characterisation of the experimental solutions and solid materials, we identified and traced several mineral reactions taking place in a chronological order: (1) dissolution of portlandite and Ca-leaching from C-S-H started immediately at the beginning of the experiments and provided the physicochemical conditions favourable for (2) the precipitation of massive calcite and ettringite during the advanced stage of chemical attack. Ongoing changes in the aqueous composition indicate that C-S-H dissolves incongruently and may be transformed into Si-bearing hydrogarnet. The amount of precipitated ettringite is apparently controlled by the availability of calcium, sulphate and aluminium and the precipitation rate correlates with the superplasticiser demand of the concrete mixes and with the pH of the solution during the nucleation and crystal growth stages, respectively. Our test allows distinguishing between competing reaction paths and kinetics and is capable to provide new insights into concrete damaging mechanisms in sulphate-loaded aqueous environments

A new test for combined Ca-leaching and sulphate resistance of cementitious materials

Limitations in the understanding of chemical key controls on concrete damaging mechanisms exacerbate predictions on the long-term performance and durability of cementitious materials. Therefore, the scope of the project “ASSpC Advanced and Sustainable Sprayed Concrete” is to obtain a better mechanistic understanding of the processes underlying deleterious chemical attacks. The herein presented alternative test, loosely following the regulations of the German Building Authority (DIBt) testing procedure (the so-called SVA test) for sulphate resistance, investigates the resistance of concrete mixes with high levels of limestone substitution (35%, 50% and 65%) against sulphate attack in a 10 g L-1 Na2SO4 solution at ambient temperature. Powdered samples were used in favour of prisms or drill cores to accelerate alteration reactions and to eliminate variations in microstructure or porosity. Based on throughout chemical and mineralogical characterisation of the experimental solutions and solid materials, we identified and traced several mineral reactions taking place in a chronological order: (1) dissolution of portlandite and Ca-leaching from C-S-H started immediately at the beginning of the experiments and provided the physicochemical conditions favourable for (2) the precipitation of massive calcite and ettringite during the advanced stage of chemical attack. Ongoing changes in the aqueous composition indicate that C-S-H dissolves incongruently and may be transformed into Si-bearing hydrogarnet. The amount of precipitated ettringite is apparently controlled by the availability of calcium, sulphate and aluminium and the precipitation rate correlates with the superplasticiser demand of the concrete mixes and with the pH of the solution during the nucleation and crystal growth stages, respectively. Our test allows distinguishing between competing reaction paths and kinetics and is capable to provide new insights into concrete damaging mechanisms in sulphate-loaded aqueous environments

The surgical safety checklist and patient outcomes after surgery: a prospective observational cohort study, systematic review and meta-analysis

© 2017 British Journal of Anaesthesia Background: The surgical safety checklist is widely used to improve the quality of perioperative care. However, clinicians continue to debate the clinical effectiveness of this tool. Methods: Prospective analysis of data from the International Surgical Outcomes Study (ISOS), an international observational study of elective in-patient surgery, accompanied by a systematic review and meta-analysis of published literature. The exposure was surgical safety checklist use. The primary outcome was in-hospital mortality and the secondary outcome was postoperative complications. In the ISOS cohort, a multivariable multi-level generalized linear model was used to test associations. To further contextualise these findings, we included the results from the ISOS cohort in a meta-analysis. Results are reported as odds ratios (OR) with 95% confidence intervals. Results: We included 44 814 patients from 497 hospitals in 27 countries in the ISOS analysis. There were 40 245 (89.8%) patients exposed to the checklist, whilst 7508 (16.8%) sustained ≥1 postoperative complications and 207 (0.5%) died before hospital discharge. Checklist exposure was associated with reduced mortality [odds ratio (OR) 0.49 (0.32–0.77); P\u3c0.01], but no difference in complication rates [OR 1.02 (0.88–1.19); P=0.75]. In a systematic review, we screened 3732 records and identified 11 eligible studies of 453 292 patients including the ISOS cohort. Checklist exposure was associated with both reduced postoperative mortality [OR 0.75 (0.62–0.92); P\u3c0.01; I2=87%] and reduced complication rates [OR 0.73 (0.61–0.88); P\u3c0.01; I2=89%). Conclusions: Patients exposed to a surgical safety checklist experience better postoperative outcomes, but this could simply reflect wider quality of care in hospitals where checklist use is routine