Browsing by Subject "flexural strength"

Now showing 1 - 2 of 2

Access status: Open Access ,
Microstructural, mechanical and pozzolanic characteristics of metakaolin-based geopolymer
(Wydawnictwa AGH, 2020) Abiodun, Yetunde Oyebolaji; Sadiq, Obanishola Muftau; Odeosun, Samson Oluropo
The use of cement contributes to global $CO_2$ emission and this leads to the depletion of ozone layer, causing global warming. The quest to reduce or eliminate this problem has resulted in the discovery of metakaolin-based geopolymer as an alternative to the use of cement in construction work. In this study, metakaolin obtained as a result of kaolin calcination from some deposits in Nigeria, Ogun (Imeko), Edo (Okpela), Ondo (Ifon) and Ekiti (Isan-Ekiti) were characterized and used to determine the compressive and flexural strength of metakaolin-based geopolymer concrete (Mk-GPC). Cubes of 150 x 150 x 150 mm were used for the compressive strength test and reinforced concrete beams of size 150 x 250 x 2160 mm were produced to test for flexural strength. A water-absorption test was also carried out on Mk-GPC and the effect of ball-milling was assessed on the strength properties. The results from the various tests showed that 800°C for 1 hour of calcination of kaolin gives best combination of performance properties due to the presence of amorphous silica in metakaolin. Mk-GPC gave higher compressive strength and at an early age than ordinary Portland cement (OPC) concrete. The water absorption capacities of Mk-GPC were higher than the control samples. In the flexural strength test, the reinforced beams failed in flexural-shear mode and the shear capacities at 28-, 56- and 90-day curing age of the beams were between 0.656 and 0.938 MPa for Mk-GPC beams and between 0.563 and 0.844 MPa for the control beams. The moment capacities for the beams were between 19.25 and 33.25 (x10$^{3}$ kgm$^{2}$/s$^{2}$) for Mk-GPC beams and were between 22.75 and 28.0 (x10$^{3}$ kgm$^{2}$/s$^{2}$) for the control beams. The study has revealed that metakaolin-based geopolymer can serve as an alternative to cement for sustainable construction in the Nigerian construction industry.
Access status: Open Access ,
Piaskowce modyfikowane związkami krzemoorganicznymi oraz zmiany ich porowatości i wytrzymałości na zginanie pod działaniem siły skupionej
(Wydawnictwa AGH, 2010) Rembiś, Marek
The sandstone samples representing 24 deposits localized in various geological regions of Poland were impregnated with liquid polymers, in which esters of the orthosilicic acid are active agents. Such preparations are commonly applied as stone strengtheners in conservation practices. The products of condensation of these polymers formed in the course of seasoning of the impregnated stone samples for 4 weeks have developed diversified microstructures. Their presence has lowered the porosity of the sandstones and changed the structure of the rock pore spaces. As a result, the sandstones have been strengthened as indicated by their values of the flexural strength under concentrated load. A distinct change of this parameter should be linked to exceeding of the threshold value of tetraetoxysilan oligomers concentration (percolation threshold) in the sandstones in question, mainly in their Liassic, Cretaceous and Istebna varieties. It has taken place in the samples with the porosity lowered at 41-66%. The percolation threshold has not been achieved in this part of the impregnated Magura, Krosno and Godula sandstones, in which their porosity has decreased at the value not exceeding 10%. In these cases, the value of the flexural strength under concentrated load remains at the same level as it was measured prior to impregnation.