Zhuangzhuang Liu

Investigation on the Properties of Asphalt Mixtures Containing Antifreeze Fillers

AbstractTo investigate the properties of antifreeze asphalt mixtures (AFAC), the dense-graded and gap-graded asphalt mixtures, AC-13 and SMA-13, containing 2, 4, 5, 6, and 4 % by weight and 5, 6, 7, and 8 % by weight antifreeze filler, respectively, were used in this paper. In the experiments, Marshall, rutting, bending beam, and immersion Marshall tests were used to study the engineering performances of AFAC. In addition, a conductivity test was carried out to evaluate the salt releasing law under static state condition. Results show that the properties of AFAC are affected by the gradation composition and content of antifreeze filler. It is suggested that the content of antifreeze filler is 3∼6% by weight according to the Marshall test. The composition type of asphalt mixture is an important factor in AFAC because the durability of SMA-13 is worse than that of AC-13. Moreover, the salt releasing process is divided into three steps based on the conductivity test.

Temperature Characteristics of Porous Portland Cement Concrete during the Hot Summer Session

Pavement heats the near-surface air and affects the thermal comfort of the human body in hot summer. Because of a large amount of connected porosity of porous Portland cement concrete (PPCC), the thermal parameters of PPCC are much different from those of traditional Portland cement concrete (PCC). The temperature change characteristics of PPCC and the effects on surrounding environment are also different. A continuous 48-hour log of temperature of a PCC and five kinds of PPCC with different porosity were recorded in the open air in the hot summer. The air temperatures at different heights above concrete specimens were tested using self-made enclosed boxes to analyze the characteristics of near-surface air temperature. The output heat flux of different concrete specimens was calculated. The results show that the PPCC has higher temperature in the daytime and lower temperature in the nighttime and larger temperature gradient than the PCC. The air temperature above PPCC is lower than that of PCC after solar radiation going to zero at night. The total output heat flux of PPCC is slightly smaller in the daytime and significantly smaller at night than that of PCC. The results of tests and calculations indicate that PPCC contributes to the mitigation of heating effect of pavement on the near-surface air.

A laboratory study of Portland cement hydration under low temperatures

Portland cement hydration is related to mechanical properties, durability and sustainability of cement concretes, and also to the service level of building and structures. This paper will report an initial understanding of Portland cement hydration under low temperatures based on several laboratorial investigations (e.g. thermal gravity analysis /derivative thermogravimetry and X-ray diffraction). Mechanical behaviours and phase evolution are discussed in this report. Calculation based on Powers’ model in cement hydration was also utilised to analyse the Portland cement hydration process under low temperatures. Research shows that low temperature slows the hydration reaction rate and delays the initial setting time, as a result the mechanical behaviours are also influenced. The mechanical behaviours evolution was in great agreement with the calcium silicate hydrate fraction calculated by Powers model.

Effects of modifier content on high-modulus asphalt mixture and prediction of fatigue property using Weibull theory

High-modulus asphalt concrete (HMAC) is used widely in several countries; however, more investigations on the performance of HMAC are still needed. To investigate the effects of modifier content on the performance of HMAC and evaluate the fatigue property of HMAC, two kinds of HMACs containing 5%, 10%, and 15% of PR PLAST S® (PRS) and PR PLAST Module® (PRM) were analysed. The Marshall test, the wheel tracking test, the three-point bending test at −10°C, and the flexural beam fatigue test were conducted on these mixtures. The test results indicate that the PRS and the PRM remarkably improve the high-temperature performance of HMACs and slightly improve the resistance of HMACs to crack at low temperature; it is suggested that the contents of PRM and PRS be 10% by weight of asphalt binder, respectively, according to the results of Marshall test. The results of the flexural beam fatigue test can be fitted very well to the two-parameter Weibull function. The fatigue functions of the HMACs were determined. Compared with the original asphalt mixture, PRM and PRS improve the fatigue resistance of HMACs. Therefore, this paper could contribute to improving the design of HMACs and deepening the understanding of the performance characteristics of HMACs.

Kinetic and thermodynamic modeling of Portland cement hydration at low temperatures

Portland cement have to hydrate in cold climates in some particular conditions. Therefore, a better understanding of cement hydration under low temperatures would benefit the cement-based composites application. In this study, Portland cement was, therefore, kinetically and thermodynamically simulated based on a simple kinetics model and minimization of Gibbs free energy. The results of an evaluation indicate that Portland cement hydration impact factors include the water–cement ratio (w/c), temperature, and specific surface area, with the latter being an especially remarkable factor. Therefore, increasing the specific surface area to an appropriate level may be a solution to speed the delayed hydration due to low temperatures. Meanwhile, the w/c ratio is believed to be controlled under cold climates with consideration of durability. The thermodynamic calculation results suggest that low-temperature influences can be divided into three levels: irrevocable effects (<0xa0°C), recoverable effects (0–10xa0°C), and insignificant effects (10–20xa0°C). Portland cement was additionally measured via X-ray diffraction, thermal gravity analysis, and low-temperature nitrogen adsorption test in a laboratory and comparisons were drawn that validate the simulation result.

Determination of morphology characteristics of polymer-modified asphalt by a quantification parameters approach

Although microstructure is closely related to performance and is even considered decisively influential, this paper addresses the poorly understood morphology characteristics of styrene-butadiene-styrene (SBS). Eighteen groups of polymer-modified asphalt (PMA) were prepared with three binder sources, four SBS polymers and five modifier contents. Fluorescence microscope images and Fourier transform infrared (FTIR) spectroscopy were used to study the morphology characteristic and compositions. Fractal dimensions, average expansion diameter and FTIR peak area were proposed as the quantification parameters to describe the intricate morphology characteristics and functional groups. Expansion multiples of each polymer were deduced based on the principle of calculus variation. Furthermore, ANOVA was used to analyse the stability of the proposed quantification method. Results show that fractal dimensions can be used to characterise the microstructures and polymer swelling status of modified asphalt. For most SBS polymers in this study, the polymers swelled 6.12–8.38 times larger than their original particle size. The results indicated the potential for these quantification parameters to evaluate the PMA and its application for quality assurance.

Portland Cement Hydration Behavior at Low Temperatures: Views from Calculation and Experimental Study

Environmental condition affects the property of construction materials. This study gives an initial understanding of Portland cement hydration under low temperatures from the views of laboratory experiments (including electrical resistivity, degree of hydration (DoH), and maturity) as well as thermodynamic calculation. The hydrates of Portland cement at the given period were detected with X-ray diffraction (XRD), and their microstructure was observed by scanning electron microscope (SEM). Experiment result (i.e., DoH and electrical resistivity) indicated that the hydration of Portland cement was delayed by low temperature without hydration stopping at −5°C. Based on a basic kinetics model, the thermodynamic calculation predicted that the final hydrate differs in dependence on environmental temperatures. The mechanical behavior trend of Portland cement paste affected by low temperatures potentially is linked to the appearing of aluminate compounds and reduction of portlandite.