Papers by Keyword: Mass Change

Abstract: This study investigated the resistance of garnet fiber concrete (hereinafter, GFC) to magnesium sulfate. GFC was fabricated in various mix ratios using GA, nylon (Ny), polypropylene (PP), and others. Plain concrete without GA was also fabricated for comparison with GFC. The test pieces were soaked in 10% magnesium sulfate for up to 210 days to test their compressive strengths, sulfate deterioration factors (SDFs), and mass losses. It was observed from the test results that the compressive strength test pieces mixed with GA and Ny, which perform the pozzolanic reaction, had excellent performances under the influence of sulfate. The plain concrete underwent greater mass loss compared to the GFC test pieces. The test results showed that the GFC mixed with 10% GA and Ny was more resistant to magnesium sulfate than the GFC with PP.

Abstract: This paper investigates the sulfate resistance of blended cements produced by replacing 10, 20, and 30% of sulfate resisting cement (SRC) with Algerian natural pozzolan. Ordinary and blended cement mortar specimens were cast and immersed in a 5% sodium sulfate solution for 3 years. The sulfate resistance of mortars was evaluated by visual examination, compressive strength, mass change and diffraction (XRD), which was used to identify the degradation products formed by sulfate attack.The test results demonstrated that the sulfate resisting cement incorporating 10% of natural pozzolan was less susceptible to sulfate attack. In addition to improved performance, the results promise the production of a sustainable building material with environmental and economic benefits due to the reduced amount of overly-high-energy-consuming cement used and the potential reduction of the cost of sulfate resisting cement.

Abstract: This paper presents the study on mortar specimens exposed to three kinds of Na2SO4 solution(0.5%,5%and10%)and different drying-wetting cycles(20,30,40and75). Influence of cycle number and solution concentration on mechanical behavior, mass and appearance of mortar specimen was analysis. The results show that surface of specimen in 5% and 10% solution shows obvious desizing, sandiness and some crack at 75 drying-wetting cycles. In different solution concentration, mass of specimen shows a trend to increase firstly then decrease lately. The increasing and declining separately of specimen mass are more obvious in high concentration solution. In three kinds concentration of solution, peak stress and modulus of elasticity of specimen show the same trend to increase in early erosion stage and decrease in late erosion stage. Change rate of mechanical behavior of specimen in high concentration solution is larger than that of in low concentration solution at early and later stage separately. On the contrary, peak strain show a trend to decline firstly then increase lately.

Abstract: Sulfate attack is one of several chemical and physical mechanisms of concrete deterioration. In actual situation, concrete structures always suffer from the coupled effects of multifactor such as wet-dry cycle and sulfate attack when exposed to tidal area or groundwater level change environment. Partial replacement of cement with mineral admixture is one of the efficient methods for improving concrete resistance against sulfate attack. In this regard, the resistance of concrete with fly ash and slag to sulfate attack was investigated by wet-dry cycle method. The degree of sulfate attack on specimens after different cycles was observed using scanning electron microscopy. The results of compressive strength and percentage of compressive strength evolution factor at various cycling times show an increase in the sulfate resistance of concrete with 60% of fly ash and slag than that only with 40% fly ash. The microstructural study indicates that the primary cause of deterioration of concrete under wet-dry cycle condition is swelling of the sulfate crystal rather chemical attack.

Abstract: Change in mass and gas concentration during oxidation of carbon matrix composite added with B4C and SiC particles as an inhibiter for oxidation were measured continuously and accurately using a thermogravimetric analyzer, a couple of zirconia type oxygen sensors and infrared CO-CO2 gas analyzer. Total amount of oxygen consumed, the amount of oxygen consumed for matrix carbon oxidation, the amount of oxygen incorporated in CO and CO2 gases, total oxygen consumption rate during oxidation of the composite were obtained. The amount of glass phase formed from the inhibiter and the amount of matrix carbon oxidized could be estimated from calculation of a mole balance between the total oxygen consumption and the amount of oxygen incorporated in CO and CO2 gases. Oxidation behavior and oxidation mechanism of the C-B4C-SiC composites were clarified.