Abstract:As a natural modifier of asphalt, rock asphalt has been widely used to improve its thermal stability and aging resistance. However, the thermal cracking resistance of asphalt modified by rock asphalt is unsatisfactory. In order to improve the thermal cracking resistance in low temperature, two kinds of modifiers-styrene-butadiene rubber (SBR) and nano-CaCO 3 -were selected as the compound modifiers, and then implemented to improve the low-temperature performance of the binder. Then, compound asphalt modified by Buton rock asphalt (BRA) was chosen as the study subject. The thermal stability and aging resistance of asphalt modified by BRA, compound-modified asphalt by BRA/SBR, and compound-modified asphalt by BRA and nano-CaCO 3 were determined to identify whether the compound modifiers in the asphalt would have a negative effect on the thermal stability and aging resistance of the asphalt. The dynamic shear rheometer (DSR) test was employed to evaluate the thermal stability. The thin film oven test (TFOT) and pressure aging vessel (PAV) were adopted to determine the aging resistance. The viscoelastic characteristics of asphalt with and without modifiers were revealed to evaluate the low-temperature crack resistance of asphalt modified by compound modifiers. The bending beam rheometer (BBR) creep test was conducted in three test temperatures in order to determine the creep stiffness modulus of the BRA compound-modified asphalt. The viscoelastic model considering the damage caused by loading was established; then, the creep compliance and parameters of the viscoelastic damage model were implemented to evaluate the low-temperature performance of the compound-modified asphalt. The results show that the compound modifiers have little negative effects on the thermal stability and aging resistance of asphalt. The thermal crack resistance of the compound-modified asphalt by BRA/SBR was the best, followed by the compound-modified asphalt by BRA and nano-CaCO 3 within the three materials. The accuracy of forecasting the characteristics of compound-modified asphalt was improved by using the viscoelastic model and considering the damage effect.
The bearing plates used in plate load test for highway engineering are typically rigid. However, due to limitations in obtaining the accurate distribution of compressive stress at the bottom of the bearing plate, there is often a significant deviation between the measured subgrade resilient modulus and the actual condition. To address this issue, a flexible bearing plate can be used to test the subgrade and obtain a more accurate resilient modulus. In this study, we use variance and degree of mean deviation to quantitatively evaluate the distribution uniformity of compressive stress. To create a rigid-flexible bearing plate that is similar to a flexible bearing plate, we explore the combinatorial design of steel plates and rubber mats. We examine factors such as the thickness (10, 20, and 30 mm) of the steel plate, elastic modulus (5, 10, and 20 MPa) and thickness (10, 20, and 30 mm) of the rubber mat, friction coefficient (μ:0, 0,2, 0.4, 0.6, 0.8, ∞) between the bearing plate and subgrade, and the combined shape characteristics of the rubber mat and steel plate. To reduce friction between the rubber mat and subgrade, we use lubricant, and through our design process, we develop a flexible bearing plate with relatively uniform compressive stress. Our computations show that when μ = 0.05, the variance is 0.0001, and the degree of mean deviation is 0.0780. These results indicate that the distribution uniformity of the compressive stress is very close to the uniform distribution load, which meets the necessary accuracy requirements for engineering applications.
Novel shaped phase change plate was made of wheat straw impregnated with Na2SO4solution and water glass as cementing agent. The plate was subsequently inserted into the concrete bricks with rectangular holes, assembled as phase change bricks. The latent heat of phase change of the plate was measured by DSC, the microstructure of the plate was observed by SEM, and the performance of the plate was also measured. In addition, the heat insulating property of the brick was investigated. The results are as follows. The wheat straws can encapsulate 1.86 times Na2SO4•10H2O in mass,and the phase change heat of the plate is 113 J/g. The microstructure shows that the straws and hardened water glass play an encapsulating action for Na2SO4•10H2O. The weight loss of the plate was 1.8% after 30 times of phase change cycles. For the concrete bricks (size: 240×240×115 mm) inserted with phase change plates, when the heated surface temperature was 80 oC for 5 h or 8 h , the cold surface temperature increased by only 1.8 oC and 4.4 oC respetively ,that is, the temperature difference between the cold with hot surface was 63.7 oC and 61.1 oC. This study reflects that if the brick is used as walling material, interior temperature does not fluctuate, even in extreme heat summer. It has dramatically saving energy and the effect of improving inhabited environment.
Na2SO4 solution was impregnated into rice straws, then the straws impregnated with Na2SO4 was cemented using water glass and molded to shaped phase change plate. The plate was subsequently inserted into the concrete bricks with rectangular holes, assembled as phase change bricks. The latent heat of phase change of the plate was measured by DSC, the microstructure of the plate was observed by SEM, and the heat insulating property of the brick was investigated. The results are as follows. The rice straws can encapsulate 2 times Na2SO4•10H2O in mass and the phase change heat of the plate is 121 J/g. The microstructure shows that the rice straws and hardened water glass play an encapsulating action for the package of Na2SO4•10H2O. The weight loss of the plate was 0.9% after 30 times of phase change cycles. For the concrete bricks (size: 240×240×115 mm) inserted with phase change plates, when the heated surface temperature was 80 oC and the initial cold surface temperature was 14.5 oC, the needed time that the cold surface temperature rose to 25 oC was 17 h, which was 6.5 h and 9 h longer than the concrete bricks inserted with rice straw plates and the original concrete bricks, respectively. When the heating was maintained for 5 h and 8 h, the cold surface temperature increased by only 1.4 oC and 3.9 oC and the temperature difference between the cold surface and hot surface was 64.1 oC and 61.6 oC. This study provides a new way for the encapsulation of phase change materials and its application in construction.
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