Investigation Of Physical-mechanical Properties Research Articles

Investigation of Physical-Mechanical Properties and Microstructure of Mortars with Perlite and Thermal-Treated Materials.

This study aimed to obtain and characterize a mortar with perlite aggregate and thermal-treated materials that could substitute for Portland cement. First, the thermally treated materials were obtained by calcinating old Portland cement (OC-tt) and concrete demolition waste (CC-tt) at 550 °C, for 3 h. Second, plastic mortars with a perlite: cement volume ratio of 3:1 were prepared and tested for water absorption, mechanical strength, and thermal conductivity. The microstructure was also analyzed. Portland cement (R) was partially substituted with 10%, 30%, and 50% OC-tt. Thermal-treated materials negatively influenced the compressive and flexural strengths at 7 and 28 days. With an increase in the substitution percentage to 50%, the decrease in the compressive strength was 40% for OC-tt and 62.5% for CC-tt. The presence of 10% OC-tt/CC-tt positively influenced the water absorption. The thermal conductivity of the tested mortars was in the range of 0.37-0.48 W/m·K. SEM analysis shows the expanded perlite pores remained unbroken.

Investigation of Physical-Mechanical Properties and Structure of Layered Cermet Al–Al2O3–Al4C3

The layered cermet Al–Al2O3–Al4C3 was obtained by liquid-phase sintering under vacuum of powder blanks made of highly disperse PAP-2 industrial brand Al powder consisting of flaky particles of submicron thickness. The appearance of the liquid phase was associated with the formation of an Al/Al4C3 eutectic melt at 630°C as a result of the reaction of Al with its carbide. Lamellar nanoscale Al4C3 crystals separated upon cooling of the eutectic melt and acted as a disperse hardener in the Al matrix. An aluminum-oxide phase (δ-Al2O3) formed, increased the hardness of the cermet, and resulted from the reaction of Al with residual atmospheric oxygen during sintering at a pressure of 10–5 mm Hg in the furnace. The main properties of the obtained cermet were density 2.56 – 2.65 g/cm3, bending strength 300 – 500 MPa, and crack resistance 9 – 15 MPa·m1/2. A material of composition Al 80%, Al4C3 14%, and δ-Al2O3 6% retained a high bending strength (200 MPa) at 500°C.

Material Properties of Fibre-Cement and Fibre-Concrete Composites Used for Plated Components of Building Structures

ABSTRACTThe paper presents the brief information on particular results of experimental studies dealing with the problems of properties of materials based on fibre-cement and fibre-concrete composites, which are being recently developed, tested and verified, to use them in the plated components of load-carrying structures of building constructions. The problems mentioned are solved in the co-operation with the company of the Research Institute of Building Materials Inc. (“VUSTAH a.s.”) at Brno city in the Czech Republic. The attention is paid to two basic types of material: (i) fibre-cement composite used for the slab components intended for vertical or horizontal building or technology structures, such as permanent shuttering of bridges, timber floor structures and slab flooring, the wall cladding of buildings and formwork of components in manufacturing plants of the concrete units; (ii) glass-fibre-concrete composite mainly intended for the building façade claddings, but also for the objects of daily use. The experimental verification has been mainly oriented to the investigation of physical-mechanical properties, like as the tensile-bending strength, as well as the corresponding modulus of elasticity.

Investigation of Physical-Mechanical Properties and Structural Stability of the Nitrogen-Free and Nitrogen-Containing Austenitic Alloys of Fe-Cr-Mn System at Cryogenic Temperatures

Nitrogen effect on metastable state of Fe-Cr-Mn alloy at cryogenic temperature have been studied. Topograms were experimentally built showing distribution of mechanical characteristics at 77 K for the Fe-Cr-Mn and Fe-Cr-Mn-N system alloys (in the limits of 20-50% Mn and 0-15% Cr). Decreasing of maximal relative elongation, reduction and impact strength by 34, 23 and 50% respectively, was observed for the alloys doped with 0.15% N. With this, strength properties and stability of the γ-phase simultaneously increased. Area of maximal stability and impact strength broadens towards increasing of Mn and Cr content, as well. Nitrogen effect on decreasing of plasticity and impact strength properties in purely austenitic alloys at 77 K depends on Mn and Cr content. Obtained results allow us to plot the phase diagram of the investigated region of Fe-Cr-Mn system at cryogenic temperatures in quenched and tempered states before and after deformation and draw AB-line separating γ- and γ + δ + σ - phase region at 77 K.