This article reports on research into the use of solid alkalis (Na 2 CO 3 and K 2 CO 3 ) as activators to obtain hybrid cement (cement whose hydration generates a mix of C-A-S-H and (N,C)-A-S-H gels) from a blend of 20% cl ınker + 40% blast furnace slag + 40% metakaolin. More specifically, the study aimed to determine the effect of activator dosage (5 and 8 wt%) and type of alkaline cation (Na + or K + ) on the 2-and 28-d mechanical strength of the end materials. The findings showed that the highest mechanical strength values were obtained with 5% Na 2 CO 3 . According to the XRD, NMR, and SEM/EDX analyses conducted on the reaction products, the alkalinity and solubilized chemical species generated by adding 5% Na 2 CO 3 to the system yielded a mix of (N,C)-A-S-H and C-A-S-H cementitious gels as the main reaction products. The secondary reaction products included metastable (3CaOÁAl 2 O 3 ÁCaCO 3 Á 11H 2 O-type) carboaluminates that evolved into the calcite or vaterite forms of calcium carbonate. When K 2 CO 3 was used (instead of Na 2 CO 3 ), a (3CaOÁAl 2 O 3 Á0.5Ca(OH) 2 Á0.5CaCO 3 Á 11H 2 O-type) hemicarboaluminate also formed. The study also revealed that Na + favors coagulation/precipitation more effectively than K + , generating gels with a wider range of Q n species.
The aim of this study was to investigate the deterioration of concrete sewers and identify responsible factors; this investigation was a part of an ongoing asset evaluation for Rennes (France). The sewer studied was a 300 mm spun concrete pipe laid in 1992. Core samples (D 28 mm, L 40 mm) were taken from different areas of a pipe (invert, crown and side wall) and analysed to quantify the condition of the concrete and the extent of damage to the internal and external surface of the pipe. Physical and mechanical properties of the material were characterised. The depassivation of the concrete was measured by testing with a phenolphthalein solution. The study showed that in this particular case the external corrosion was extensive with minimal internal corrosion.It is proposed that the corrosion was possibly linked to the use of a contaminated backfill or organic acids in the ground water. Recommendations are proposed concerning the direction of future research.
In this paper, a new technique is proposed to confine concrete columns using GFRPprefabricated bonded shells and a shrinkage-compensating cement mortar. The confinement is performed with three identical shells, each of which contains two stepped lap joints at their ends. The main advantage of this technique is that the shells can be directly assembled on site by structural bonding to cover any column shape. The gap between the shells and the column is filled with shrinkage-compensating cement mortar. To evaluate the efficiency of this technique, several concrete specimens were confined, instrumented and tested under monotonic compression. To simulate the actual strengthening conditions, the load was directly applied on the concrete crosssection. The results show clearly the benefits of an efficient confinement in terms of a noticeable increase in the axial strength and ductility where the stress-strain curves are characterised by a third softening phase and the failure mode which spread over the whole length of the shells.
L'étude porte sur la récupération du collapse de bois d'Eucalyptus camaldulensis Dehn provenant de la station de Beghla (Algérie), qui occupe une superficie voisine de 500 hectares. Le matériel végétal est constitué de trois arbres dont six barrettes radiales ont été extraites (soit deux barrettes par arbre, représentant le haut et le bas). Une première analyse densitométrique a été effectuée à l'état sec à l'air, puis les éprouvettes ont été reconditionnées, séchées jusqu'à l'humidité initiale, puis soumises à une seconde analyse densitométrique. Le reconditionnement a permis de réduire le collapse dans une large mesure. Les profils obtenus avant et après reconditionnement ont été comparés. La perte de densité relative provoquée par le traitement a été utilisée comme indicateur du collapse. Les résultats montrent que l'indicateur varie en sens inverse de la densité entre éprouvettes et dans le cerne mais décroît sensiblement avec la densité dans l'aubier.
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