MECHANICAL PROPERTIES OF GYPSUM BOARD AT ELEVATED TEMPERATURES
Gypsum board is a common fire barrier used in house and general building construction. Recently, evaluation of the collapses of the World Trade Center Towers highlighted the potential role and failure of gypsum board in containing the fires and resisting damage. The use of gypsum board as primary fire protection of light-flame wood or steel construction is ubiquitous. Yet knowledge of the common engineering mechanical properties of this construction product is nearly nonexistent. Gypsum board is used in a prescriptive manner with little or no rational design. Summarized here are the results of a study examining the mechanical properties of Type X gypsum board at elevated temperatures. These properties are needed to contemplate the engineering design of gypsum board fire barriers. Tests were undertaken with a small oven within a test machine measuring mass loss, shrinkage, bending strength and modulus of elasticity at elevated temperatures to 400°C. The research showsthat shrinkage and calcination of the gypsum board appear complete between 20 to 30 minutes of exposure at a uniform 400°C. Only after complete calcination, where all moisture is driven off, does the bending strength approach 0. Strength appeared to decrease linearly with increasing temperature. Mass loss and modulus of elasticity exhibited similar trends with the greatest decreases occurring from 100°C to 200°C followed by more gradual decrease to 400°C. The surface paper plays significant stiffening and strengthening roles up to 60 minutes at temperatures as high as 200°C.
Physical and mechanical properties of gypsum particleboard reinforced with Portland cement
High thickness swelling, high water absorption and low mechanical properties of gypsum particleboard limit its utilization in building construction. Gypsum particleboard reinforced with Portland cement could result in a product with higher mechanical properties and an acceptable resistance to moisture. Physical and mechanical properties of gypsum-cement particleboards were analyzed for specimens previously conditioned at 20 °C and 60% relative humidity and then soaked in water for 24 hours. The results showed that Portland cement incorporation increased the mechanical resistance of the boards. In the dry state, Portland cement addition generated a modulus of rupture increase ratio of 53% and an internal bond strength increase ratio of 206%. Higher increase ratios were obtained after 24 hours water soaking. An increase ratio of 642% was obtained for the modulus of rupture and 97% for hardness. Furthermore, the addition of Portland cement resulted in a reduction ratio of 21% for water absorption after 2 hours water soaking and 26% after 24 hours water soaking. Moreover, reduction ratios of 43% and 61% in thickness swelling and 33% and 46% in linear variation were observed after 2 and 24 hours water soaking. It can be concluded that Portland cement is a suitable reinforcing material for improving the performance of gypsum particleboard.ZusammenfassungGroße Dickenquellung, hohe Wasseraufnahme und schlechte mechanische Eigenschaften gipsgebundener Spanplatten schränken deren Verwendung im Bauwesen ein. Gipsgebundene Spanplatten verstärkt mit Portlandzement könnten ein Produkt mit höheren mechanischen Eigenschaften und akzeptabler Feuchtebeständigkeit ergeben. Untersucht wurden die physikalischen und mechanischen Eigenschaften von mit Zement verstärkten Gipsspanplatten anhand von Prüfkörpern, die bei 20 °C und 60% rel. Lf. klimatisiert worden waren und anschließend für 24 Stunden in Wasser gelagert wurden. Die Ergebnisse zeigten, dass die mechanischen Eigenschaften der Platten durch Zugabe von Portlandzement verbessert wurden. Durch Zugabe von Portlandzement wurde die Biegefestigkeit im trockenen Zustand um 53% und die Querzugfestigkeit um 206% erhöht. Nach 24-stündiger Wasserlagerung erhöhten sich die Werte prozentual noch stärker. Die Biegefestigkeit nahm um 642% zu und die Härte um 97%. Des Weiteren verringerte sich durch Zugabe von Portlandzement die Wasseraufnahme nach 2-stündiger Wasserlagerung um 21% und nach 24-stündiger Wasserlagerung um 26%. Außerdem wurden nach 2- und 24-stündiger Wasserlagerung eine Abnahme der Dickenquellung um 43% bzw. 61% und der Quellung in Plattenebene um 33 bzw. 46% beobachtet. Daraus kann geschlossen werden, dass die Zugabe von Portlandzement geeignet ist, die Eigenschaften gipsgebundener Spanplatten zu verbessern.
Neotectonic rotations in the Orava-Nowy Targ Intramontane Basin (Western Carpathians): An integrated palaeomagnetic and fractured clasts study
Abstract The objectives of this contribution are: (1) to promote the application of fractured clasts analysis in conglomerates for regional stress reconstructions and (2) to advance reconstruction of the Western Carpathians structural development. Our results show that the Neogene fill of the Orava-Nowy Targ Intramontane Basin underwent CCW rotation of about 30°. We infer that the rotation terminated after 8 Ma and was related to shift along NW-SE to NNW-SSE trending faults at the NE termination of the sinistral Mur-Žilina Fault Zone. Our results show that, fractured clasts analysis can be good tool for regional tectonic reconstructions. The tool is especially useful when other tectonic tools are scarce or absent. Results of our palaeomagnetic study and fractured clasts analysis verify and supplement each others. In the studied case, palaeomagnetic results allow to distinguish between regional stress field rotation and rotation of the Orava-Nowy Targ Basin Neogene fill, whereas, results of fractured clast analysis help to constrain the age of rotation.