Synthesis of sodium waterglass from white rice husk ash as an activator to produce metakaolin-based geopolymer cements
JOURNAL OF BUILDING ENGINEERING
Authors: Tchakoute, Herve Kouamo; Ruescher, Claus Henning; Kong, Sakeo; Ranjbar, Navid
Abstract
Rice husk from source in Cameroon was leached in HCI (5 M) to remove the most of metallic ingredients and then calcined at 600 degrees C in order to produce white rice husk ash. This white ash were applied for producing sodium waterglass with different molar ratios SiO2/Na2O (0.31; 0.47; 0.62; 0.78; 0.93; 1.09 and 1.25) and then used to synthesize metakaolin-based geopolymer cements. The obtained white rice husk ash shows the loss of crystalline mineral and reveals high amorphous silica with quartz as impurity. Geopolymers GPi (i varying from 1 to 7) were obtained using different synthesis sodium waterglass (NWG) with a mass ratio NWG/MK = 0.87. It could be observed that the 28 days compressive strength (4/5/7/9/32/ 34/36 MPa) increase with increasing the molar ratios SiO2/Na2O defined in this work in the course GP1/GP2/GP3/GP4/GP5/GP6/GP7. The micrographs show the formation of more geopolymer gels when the molar ratios SiO2/Na2O in alkaline activators are between 0.93 and 1.25. Sodium waterglass from white rice husk ash proved to be an effective alkaline activator in geopolymers preparation. It can be concluded that it is possible to replace quartz sand and sodium carbonate which is responsible to greenhouse gas emitted during the production of commercial sodium silicate solution by using rice husk as silica sources. (C) 2016 Elsevier Ltd. All rights reserved.
Which high-risk HPV assays fulfil criteria for use in primary cervical cancer screening?
CLINICAL MICROBIOLOGY AND INFECTION
Authors: Arbyn, M.; Snijders, P. J. F.; Meijer, C. J. L. M.; Berkhof, J.; Cuschieri, K.; Kocjan, B. J.; Poljak, M.
Abstract
Several countries are in the process of switching to high-risk human papillomavirus (hrHPV) testing for cervical cancer screening. Given the multitude of available tests, validated assays which assure high-quality screening need to be identified. A systematic review was conducted to answer the question which hrHPV tests fulfil the criteria defined by an international expert team in 2009, based on reproducibility and relative sensitivity and specificity compared to Hybrid Capture-2 or GP5+16+ PCR enzyme immunoassay. These latter two hrHPV DNA assays were validated in large randomized trials and cohorts with a follow-up duration of 8 years or more. Eligible studies citing the 2009 guideline were retrieved from Scopus (http://www.scopus.com) and from a meta-analysis assessing the relative accuracy of new hrHPV assays versus the standard comparator tests to detect high-grade cervical intraepithelial neoplasia or cancer in primary screening. The cobas 4800 HPV test and Abbott RealTime High Risk HPV test were consistently validated in two and three studies, respectively, whereas the PapilloCheck HPV-screening test, BD Onclarity HPV assay and the HPV-Risk assay were validated each in one study. Other tests which partially fulfil the 2009 guidelines are the following Cervista HPV HR Test, GP5+/6+ PCR-LMNX, an in-house E6/E7 RT quantitative PCR and MALDI-TOF (matrix-assisted laser desorption-ionization time-of-flight). The APTIMA HPV assay targeting E6/E7 mRNA of hrHPV was also fully validated. However, the cross-sectional equivalency criteria of the 2009 guidelines were set up for HPV DNA assays. Demonstration of a low risk of CIN3+ after a negative APTIMA test over a longer period is awaited to inform us about its utility in cervical cancer screening at 5-year or longer intervals. Clinical Microbiology and Infection 2015 European Society of Clinical Microbiology and Infectious Diseases. Published by Elsevier Ltd. All rights reserved.