Study on surface degradation of LCFA-GGBF geopolymers by partial water absorption and silane impregnation techniques

When the pore solution becomes supersaturated in Portland cement hardened bodies due to evaporation of moisture, temperature change and so on, salts dissolved in the pore solution precipitate and the surface whitening (efflorescence) and surface roughening may occur. Similar phenomena also occur in hardened geopolymer (GP) (Fig.1). Formation process and resultant minerals are different from those of Portland cement and there are a few studies on GP so far on these events. In this paper, efflorescence and surface roughening were studied using low calcium coal fly ash (LCFA) / ground granulated blast furnace-slag (GGBS) type GP. Primarily, these phenomena were studied by partial water immersion technique (Fig.2). Subsequently, surface impregnation technique by a silane was performed and effective results were obtained as follows: (1) Since efflorescence and surface roughening were promoted in the refrigerator rather than in the constant temperature room (20°C, 60%RH), deterioration of the surface layer of GP is more likely to proceed as the temperature and humidity are lower. In addition, repetition of temperature change promotes deterioration of the surface layer. (2) Efflorescence and surface roughening of GP impairs not only aesthetic appearance of the structure but also sometimes lowers proof stress, so certain measures are necessary. (3) Efflorescence and surface roughening of GP can be suppressed by increasing the GGBS substitution rate (Fig.3). (4) Adjustment of the concentration of alkaline solution may suppress efflorescence and surface roughening. (5) The silane-based surface impregnating material for OPC concrete has the effect of reducing the rate of efflorescence and surface roughening of GP. Please click Additional Files below to see the full abstract

Testing superabsorbent polymer (SAP) sorption properties prior to implementation in concrete: results of a RILEM Round-Robin Test

This article presents the results of a round-robin test performed by 13 international research groups in the framework of the activities of the RILEM Technical Committee 260 RSC "Recommendations for use of superabsorbent polymers in concrete construction''. Two commercially available superabsorbent polymers (SAP) with different chemical compositions and gradings were tested in terms of their kinetics of absorption in different media; demineralized water, cement filtrate solution with a particular cement distributed to every participant and a local cement chosen by the participant. Two absorption test methods were considered; the tea-bag method and the filtration method. The absorption capacity was evaluated as a function of time. The results showed correspondence in behaviour of the SAPs among all participants, but also between the two test methods, even though high scatter was observed at early minutes of testing after immersion. The tea-bag method proved to be more practical in terms of time dependent study, whereby the filtration method showed less variation in the absorption capacity after 24 h. However, absorption followed by intrinsic, ionmediated desorption of a specific SAP sample in the course of time was not detected by the filtration method. This SAP-specific characteristic was only displayed by the tea-bag method. This demonstrates the practical applicability of both test methods, each one having their own strengths and weaknesses at distinct testing times

Utility of intraoral stents in external beam radiotherapy for head and neck cancer

AimThis study aimed to assess the utility and stability of intraoral stent during intensity-modulated radiation therapy (IMRT).BackgroundThe benefits of intraoral stents in radiotherapy are unclear.Materials and methodsWe analyzed 386 setup errors in 12 patients who received IMRT for head and neck cancers without intraoral stents (intraoral stent [−]) and 183 setup errors in 6 patients who received IMRT with intraoral stents (intraoral stent [+]). All patients were matched according to the immobilization method (masks and boards). Setup errors were measured as the distance from the initial setup based on the marking on the skin and mask to the corrected position based on bone matching on cone beam computed tomography.ResultsThe mean interfractional setup errors in the right–left, craniocaudal, anterior–posterior (AP), and three-dimensional (3D) directions were −0.33, 0.08, −0.25, and 2.75[[ce:hsp sp="0.25"/]]mm in the intraoral stent (−) group and −0.37, 0.24, −0.63, and 2.42[[ce:hsp sp="0.25"/]]mm in the intraoral stent (+) group, respectively (P[[ce:hsp sp="0.25"/]]=[[ce:hsp sp="0.25"/]]0.50, 0.65, 0.01, and 0.02, respectively). The systematic errors for the same directions were 0.89, 1.46, 1.15, and 0.88[[ce:hsp sp="0.25"/]]mm in the intraoral stent (−) group and 0.62, 1.69, 0.68, and 0.56[[ce:hsp sp="0.25"/]]mm in the intraoral stents (+) group, respectively. The random errors were 1.43, 1.43, 1.44, and 1.22[[ce:hsp sp="0.25"/]]mm in the intraoral stent (−) group and 1.06, 1.11, 1.05, and 0.92[[ce:hsp sp="0.25"/]]mm in the intraoral stents (+) group, respectively.ConclusionSetup errors can be significantly reduced in the AP and 3D-directions by using intraoral stents

Effect of superabsorbent polymers (SAP) on the freeze–thaw resistance of concrete: results of a RILEM interlaboratory study

info:eu-repo/semantics/publishe

Effect of internal curing by using superabsorbent polymers (SAP) on autogenous shrinkage and other properties of a high-performance fine-grained concrete: results of a RILEM round-robin test

The article presents the results of a round-robin test performed by 13 international research groups (representing fifteen institutions) in the framework of the activities of the RILEM Technical Committee 225-SAP "Applications of Superabsorbent Polymers in Concrete Construction". Two commercially available SAP materials were used for internal curing of a high-performance, fine-grained concrete in combination with the addition of extra water. The concrete had the same mix composition in all laboratories involved but was composed of local materials. All found a considerable decrease in autogenous shrinkage attributable to internal curing. Also, with regard to the shrinkage-mitigating effect of both particular SAP materials, the results were consistent. This demonstrates that internal curing using SAP is a robust approach, working independently of some variations in the concretes' raw materials, production process, or measuring technique. Furthermore, the effects of internal curing on other properties of concrete in its fresh and hardened states were investigated. These are consistent as well and expand considerably the existing data basis on properties of concrete materials containing SAP. \ua9 2013 RILEM.Peer reviewed: YesNRC publication: Ye