Shuanfa Chen

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.

Flame retardancy of asphalt mixtures and mortars containing composite flame-retardant materials

To investigate the flame retardancy of asphalt mixtures containing composite flame-retardant materials (M-FRs), four different asphalt mixtures were prepared: a reference asphalt mixture with common cellulous fibre and three mixtures with M-FRs of different compositions. The degradation of mechanical property and burning loss of asphalt binder during the burning process were introduced to evaluate the flame retardancy of asphalt mixtures. The results show that the residual dynamic stabilities of the asphalt mixtures containing M-FRs are 83.2%, 75.1% and 77.8%, respectively, which are greater than that of the asphalt mixture with cellulous fibre. After burning and freeze-thaw test, the split strength ratios of asphalt mixtures containing M-FRs show less attenuation than the common asphalt mixture, and the values are 80.2%, 72.3%, 84.4% and 69.4%. Moreover, the burning loss rates of asphalt binders are 22.0%, 8.2%, 8.5% and 12.8%, respectively. Besides, Limit Oxygen Index test, thermogravimetry and difference scanning calorimetry were used to analyse the flame retardancy and pyrolysis behaviour of M-FRs asphalt mortar. All the tests above prove that asphalt mixtures and mortars containing M-FRs have good flame retardancy.

Influence of thickeners on cement paste structure and performance of engineered cementitious composites

Hydroxypropyl methylcellulose (HPMC) and amphoteric polyacrylamide (ACPAM) were respectively used to prepare engineered cementitious composite (ECC) which exhibits strain-hardening behavior under uniaxial tension. The connections between cement paste structure and the performance of the composite in fresh and hardened state were investigated, aiming at achieving the desirable workability at a given solids concentration. The experimental results of viscosity and microstructure of cement pastes show that the intimate connections between flocculation groups lead to the growing increase in viscosity. The results of deformability and fiber dispersion demonstrate that fiber dispersion coefficient is a comprehensive index which can reflect the performance of deformability as well as uniformity. And the desirable fresh mixture can be achieved by optimizing the viscosity of cement paste. At last, the ductile strain-hardening performance of the ECC prepared with HPMC or ACPAM was investigated through uniaxial tensile test.

Dynamic mechanical characterizations and road performances of flame retardant asphalt mortars and concretes

To research the dynamic mechanical properties and road performances of flame retardant asphalt mortars and mixtures, four different asphalt mortars/mixtures were prepared: a reference group and three asphalt mortars/mixtures containing composite flame retardant materials (M-FRs) of different proportions. Temperature sweep, frequency sweep, repeated creep test, force ductility test and bending beam rheological test were carried out to research the dynamic mechanical properties of asphalt mortars containing M-FRs; wheel-tracking test, low-temperature bending test and freeze-thaw split test were used to study the road performances of asphalt mixtures containing M-FRs. The results show that high-temperature performances of the three flame retardant asphalt mortars improve greatly, while low-temperature cracking resistances decline. Both high-temperature performances and water stabilities of asphalt mixtures containing M-FRs are quite good and exceed the specification requirements. However, their low-temperature performances decline in different degrees. In summary, besides their good flame retardancy, the flame retardant asphalt mortars and mixtures also exhibit acceptable road performance.

Damage evolution model of strain hardening cementitious composites under the uniaxial stress state

The deformation and damage behaviors of strain hardening cementitious composites (SHCC) under the uniaxial stress state were investigated in this paper. Two ductile failure-based constitutive models were introduced to describe the uniaxial tension and compression properties of SHCC only using a few parameters. The computation method of model parameters was developed to ease the simulation procedures. Damage evolution of the SHCC was simulated by the formulation of continuum damage mechanics subsequently. The results show that the proposed models fit the stress-strain curves reasonably well, and the damage variables show different growth rules under uniaxial tension and compression. It is concluded that the proposed method can not only simply simulate the constitutive behavior of SHCC with the reasonable accuracy but also capture the characteristic of material degradation.

Fatigue Test of Composite Pavement on Stress Absorbing Layers for Reflective Cracking

To study the problem of reflective cracking in the composite pavement, the dynamic extension fatigue test device of the asphalt pavement for reflective cracking was developed. The large proportion size anti-cracking fatigue experiment was carried out to test the anti-cracking performance of the stress absorbing layers and to observe the expansion of reflective cracking, which can provide the important experimental data to determine the reasonable thickness of the stress absorbing layers. The results indicated that because of the stress absorbing layers established between Portland cement concrete base and asphalt pavement, the stress concentration in the cracks is reduced significantly, the reflective cracking propagation path is changed, and the service quality of the composite pavement is improved effectively. In order to compare the anti-cracking property of different pavement structures, the anti-cracking ratio R is proposed as the evaluation index. According to the test results and the material properties of the stress absorbing layers, the reasonable thickness of the stress absorbing layers is 2~3 cm.