Papers by Keyword: Weathering

Abstract: The paper addresses the use of laser ultrasonic structuroscopy to study how weathering affects the internal structure of rocks used for facing buildings. For 1,250 hours rock samples were subjected to 150 cycles of freezing (at-20°C) and thawing in water (at +20°C) to determine their frost resistance. Also, moistened every 30 minutes, rock samples were exposed to thermal and ultraviolet radiation for 480 hours to determine their weather resistance. The frequency-dependent phase velocity and attenuation coefficient of longitudinal ultrasonic pulses in the samples were measured. It is found that the rock samples are most seriously damaged when exposed to sharp changes in temperature. As a result of freeze-thaw processes, the velocity of elastic waves decreases by 10% on average, and the attenuation coefficient increases by a factor of 1.5 in the range of 300kHz-500kHz and more than 3 times in the range of 1.0MHz-1.5MHz. The coefficient of the relative power of “structural” noise (K parameter) is introduced to characterize the degree of degradation of rock samples. The parameter K is defined as the ratio of the power of noise component in the spectrum of scattered waves to the power of reference signal. It is shown that the parameter K increases almost by a factor of 10 as a result of various weathering processes.

Abstract: In recent years, Wood Plastic Composite (WPC) has found widespread applications in the field of construction, decoration and furniture. In this work, the effect of weathering on the mechanical properties of WPC made from high density polyethylene (HDPE) and rice straw particles (RS) has been studied. Different loading of composite (20, 35 and 50% RS) were tested. Polyethylene wax (PE-wax) and UV-stabilizer were also added to assess their effect on the WPC composite.

Abstract: The occurrence of corrosion on glass surfaces results from the reaction between sodium in glass surfaces and water in the atmosphere under a certain condition. This reaction is promoted at high difference of humidity and temperature between a daytime and a nighttime especially in a rainy season. Glass surface treatments, for example by solutions, can improve the hydrolytic resistance. In the previous study, it was found that using 5wt% of alum gave the best effect to increase this property. The aim of this study was to examine the effect of closed and unclosed glass bottles during storage in a warehouse to the hydrolytic resistance. After treatment by 5wt% of alum, the amount of Na leached from the inner surfaces of glass bottles under simulated condition was determined. The weathering chamber was used to simulate the condition of a rainy season in Thailand with conditions set up and run in cycle. At first, the condition under the relative humidity (RH) value of 60 at 32°C was run for 12 hours, and then followed by RH of 80 at 25°C for 12 hours. The cycle was continued in the period of 8, 14, 21, 28, 53 days. After that the quantity of leached Na which is the conversion of hydrolytic property was analyzed by Flame-Atomic Absorption Spectrometry (FAAS). The results showed that the amount of Na leached from the untreated bottles was higher than the treated bottles around 5 times. It was also found that the quantity of leached Na from the untreated and closed bottles was raised with increasing time after 30 days while the untreated and opened bottles gave a rather constant result.

Abstract: In general, wood-polymer composites are vulnerable to weathering factors such as UV radiation, moisture, freeze-thaw action. Weathering can cause discoloration, chalking, dimensional change, and loss of mechanical properties of wood-polymer composites. This comparative study was focused on weatherability of wood–polypropylene composites made with and without pigments. Two types of inorganic pigments were applied: carbon black master-batch and synthetic iron oxide. Wood-polypropylene composite made without pigment was used as a reference. Also, composites prepared with addition of wollastonite were tested. The composite samples were exposed to outdoor weathering and in a parallel the accelerated UV weathering was conducted in xenon weathering chamber for the 2000 hours. The colour change was estimated by spectrophotometric method, and the change of Charpy impact strength after weathering was determined. The surface morphology was studied with scanning electron microscopy (SEM). The addition of pigments decreased the lightness of non-weathered composites. The change of lightness and total colour change of weathered composites were affected a lot by type of pigment and method of weathering. As, expected wood-polypropylene composite made with carbon black showed the best results in colour stability of composites exposed to weathering. SEM showed that accelerated weathering in the xenon chamber caused more significant changes in the morphology of the polymer surface layer of the composites than outdoor weathering. Charpy impact strength of all studied composites was found to retain after 2000 hours of outdoor weathering, although accelerated weathering caused significant reduction of Charpy impact strength of these composites.

Abstract: This research encompasses structural behavior of FRP-RC beams under fatigue and different conditioning. Twelve beams were designed, casted, and after 28 days, subjected to pre-cracking. This pre-cracking was designed to simulate the expected flexure cracks in service and to enhance the effects of subsequent exposure. The beams were then exposed to one of the following four conditions: control (indoor lab environment), immersion in alkaline solution, cyclic immersion in alkali solution (Wet and Dry or W&D condition), and outdoor exposure (local Montreal climate) for 14 month .Two potentiometers installed after pre-cracking at the mid-span for flexural crack and at the shear span and after every 50-100 thousands cycles crack mouth opening displacement (CMOD) measured .Deflection of the mid-span recorded at the same time and degradation of crack, and deflection versus number of cycles and life-span prediction with considering service limit state (SLS) elaborated in this research.

Abstract: To study the weathered characteristics of silty mudstone in Hunan province, china, mineral analysis, softening test, disintegrability test, and weathering rate test are used. The test results show that with the increasing of weathering degree, the content of clay minerals increase from 34.1% to 57.2%, the content of quartz decrease from 58.6% to 38.7%. The content increasing ratio of Fe₂O₃ and Al₂O₃ are 52% and 44% respectively, the content decreasing ratio of K₂O is 52%. From lightly weathered rock to completely weathered rock, the decreasing ratio of dry density is 20%, the increasing ratio of water absorption is 40%, the increasing ratio of porosity is 190% nearly and the decreasing ratio of natural compressive strength is 84%. For strongly weathered silty mudstone, the softening coefficients of the first dry-wet cycle, the second cycle and the third cycle are 30%, 54% and 72% respectively. So when silty mudstone weathered further, the content of primary minerals decrease and the content of secondary minerals increase. The weak activity chemical composition increase and the strong activity chemical composition decrease. Weathering cause the mechanical properties of rock become worse. Repeated dry-wet cycle can accelerate the softening of rock. The larger the exposure area of rock is, the quicker the rock weathered.

Abstract: An assessment of subsurface profile of a study area at Nusajaya. Johor was conducted using 2D resistivity method. The aims of the study are to determine the subsurface profile hence contouring the appearance of outcrop by 2D resistivity imaging. Subsurface structure can be delineated based on the physical and chemical parameter which is apparent resistivity of the medium. A survey line of 80m and minimum 2m electrode spacing was adopted using Pole-dipole array. Data acquisition on the survey line was completed and processed by using Res2Dinv software. The inversion model resistivity shows sandstone contains iron mineral (30-250 ohm-m) and weathered sandstone (500-1000 ohm-m). The lower part of the layer represents sandstone and siltstone exhibit high resistivity values of 1500-5000 ohm-m. The range from 30-1000 ohm-m correspond to the grade IV and V of sandstone in the actual profile. Meanwhile, the high range of the resistivity value matched the material with weathering grade II and III in ground mass. The deterioration of most physical properties was associated with the increase number of weathering grade.

Abstract: Outdoor applications of wood-plastic composites (WPCs) have raised question about the durability of such materials. WPCs are vulnerable to weathering factors such as UV radiation, moisture and freeze-thaw action. Weathering can cause discoloration, chalking, dimensional changes and loss of mechanical properties.This comparative study examines the effects of increased moisture content and artificial weathering on the properties of wood-plastic composites. Five commercial wood-plastic composite products from five different manufacturers were chosen and their water absorption, thickness swelling, impact strength and resistance to artificial weathering analyzed. An in-house manufactured wood-polypropylene composite with carbon black pigment was used as a reference product. In addition to quantitative investigation of material properties, the measured values were also compared with the values ​​reported by the manufacturers.The composite samples were exposed to accelerated weathering in a xenon weathering chamber for 500 hours. The color change was estimated by spectrophotometer method. The weathering resulted in no significant color fading of the composites. After weathering, the general trend was a minor decrease in impact strength. Also the water absorption and thickness swelling of commercial WPC products remained on a low level.

Abstract: Porous construction materials such as masonry constituents are notoriously affected by weathering, pollutants attack and damp transport with manifest consequences on the masonry visible appearance and its mechanical reliability. Water transport mechanisms inside such materials as well as the chemical reactions and phase changes occurring in salt at varying combinations of temperature and humidity content have been previously studied. Nevertheless the investigation of damp and salts degradation processes since their appearance in real structural elements and the monitoring over time of their evolution is a problem never completely investigated...

Abstract: The aim of the contribution is to present the results of research focused on cement mineralogical composition changes and their influence on physical-mechanical properties of sandstones. Three types of Czech sandstones were tested during this experiment Hořice, Kocběře and Božanov. The sandstone samples were treated in the climatic chamber in order to simulate weathering processes that are typical for winter period in Prague. The influence of road salts was also taken into consideration. For the purposes of mineralogical changes determination the sandstone cement was separated and subsequently analyzed using X-Ray diffraction a DTA/TG analysis. The physical-mechanical properties such as e.g. uniaxial compressive strength, water absorption and open porosity were determined before and after the climatic treatment to enable evaluation of the influence of weathering processes.