Zhi Ge

Coupled Navier–Stokes Phase-Field Model to Evaluate the Microscopic Phase Separation in Asphalt Binder under Thermal Loading

AbstractThe evolution of asphalt microstructures under thermal loading has always been a critical issue for pavement engineers. Previous researches show that phase separation will greatly affect the mechanical performance of asphalt at microscale. To analyze this important phenomenon, the conserved phase-field model is coupled with the Navier–Stokes equation to simulate the phase kinetics in this paper. The asphalt is chemically simplified to a quaternary system consisting of four chemical components: asphaltene, resin, oil, and wax. The coupled Navier–Stokes phase-field system is solved in a unified finite element framework in COMSOL software. It is observed that phase separation has a significant influence on the thermal stress distribution. Moreover, stress concentration is observed at the interfaces between different phases, which may result in microcracks. This conclusion is validated by atomic-force microscopy (AFM) experiment results.

Mixed-Mode I–II Cracking Characterization of Mortar Using Phase-Field Method

AbstractThere have been many studies on mortar single-mode cracking behavior under tensile loading, however, the mixed-mode cracking is still not fully understood. In this paper, the mortar Mixed-M...

Mechanical Properties of Mortar with Recycled Clay-Brick-Powder

Replacing cement with recycled clay-brick-powder could reduce carbon dioxide (CO2) emission, enhance conservation of natural resources, and decrease the cost of waste disposal sites. This paper studied the effect of recycled brick-powder on mortar mechanical properties, including flow, compressive strength, and flexural strength. Three level of cement replacement ratio (10%, 20%, and 30%) and four different average particle size of clay-brick-powder (0.3mm, 0.1mm, 0.06mm, and 0.04mm) were considered. Total 13 mixes, including one normal cement mortar as reference, were tested. The water/cement ratio (W/C) and sand ratio were kept constant for all mixes. Testing results showed that recycled clay-brick-powder could be used as partial replacement of cement in mortar without reducing its properties. Compared with normal cement mortar, samples with 10% of 0.1mm and 0.06mm clay-brick-powder had similar or even higher mechanical properties. The effect of clay-brick-powder on the flow and compressive strength depended on its replacement level and average particle size. Generally, compressive strength decreased as the replacement level and average particle size increased. However, mortar with and without clay-brick-powder had similar flexural strength.

Properties of self-consolidating concrete containing nano-CaCO3

This paper studied the effect of nano-CaCO3 on workability, strength development, and pore structures of cement paste and self-consolidating concrete. The effects of dosage and size of nano-CaCO3 were considered. For the workability, slump flow (total spread and T50 time), L-box, and V-funnel tests were conducted. The compressive strength was tested at 1, 7, and 28u2009days for concrete and 1 and 7u2009days for cement paste. The pore structure, including pore size distribution and volume, was measured using nitrogen adsorption method. The results show that the addition of nano-CaCO3 reduced the setting times. Concrete with a low content of nano-CaCO3 (≤2.5%) had satisfactory workability. No segregation was observed for all concrete specimens. The addition of nano-CaCO3 increased the compressive strength of the concrete and paste. The compressive strength decreased as the particle size increased. The addition of nano-CaCO3 reduced the average pore diameter. XRD test showed no new hydration products.

The Properties of Concrete with Recycled Clay-Brick-Powder

This paper studied the splitting tensile strength of concrete containing partial clay-brick-powder. Four variables, water to cementitious material ratio (W/CM), sand ratio, cement replacement ratio, and the average particle size of clay-brick-powder were determined to analyze the affected factors on the properties of the concrete. The orthogonal experimental design table L16 (45) was adopted to study the significance sequence of the variables. Total 17 type mixes, including one normal cement concrete as reference, were tested. Experiment results showed that recycled clay-brick-powder could be used as partial replacement of cement in concrete. The splitting tensile strength of samples with clay-brick-powder ranged from 2 to 4MPa.

Properties of self-consolidating concrete with recycled clay-brick-powder replacing cementitious material

Clay brick is becoming a major demolition waste and causing environmental contamination in China. Recycling of wasted clay brick could conserve natural resources and preserve land from waste filling. In this research, recycled clay-brick-powder (CBP) was used to partially replace Portland cement (PC) and fly ash (FA) in self-consolidating concrete (SCC) mix. The effects of dosage of CBP on the workability, strength, and shrinkage of SCC were investigated. Test results show that partially replacing cementitious material with CBP can reduce the workability of SCC. Compared with the reference concrete, specimens with CBP had higher 28-day and 56-day strength. The specimens containing 1% CBP had the highest compressive strength. Meanwhile, the replacement of CBP to PC and FA could also reduce the shrinkage of the SCC due to the internal curing effect. Based on scanning electron microscope investigation, specimen with CBP had less pores than the specimen without CBP and improved the microstructure of concrete. Hence, CBP had positive effects on the mechanical and physical properties of SCC.

Prediction of Pavement Concrete Strength Development, Joint Sawing, and Opening Time Using FEMLAB

AbstractThis paper describes a new model using Finite Element Modeling Laboratory (FEMLAB). The model can be used to predict pavement strength development and consequently the pavement joint-sawing and opening times. The strength prediction was based on the temperature history of the concrete pavement, which was determined by the rate of heat generation and the heat exchange between the pavement and the environment. Pavement joint-sawing and opening times were defined as the times when concrete strength reached 4.3 and 24.1xa0MPa (megapascals), respectively. Using this model, the effects of weather conditions, fly ash and slag replacement, concrete placement time and temperature, and pavement thickness on concrete strength, joint-sawing time, and pavement opening time were evaluated. Results showed that weather conditions and the use of fly ash and slag had a significant effect on strength development, joint-sawing time, and pavement opening time. Based on the prediction, this model can be used to optimize ...

Mechanical Properties of Concrete with Recycled Clay-Brick-Powder

This paper studied the mechanical properties of concrete with cement partially replaced by recycled clay-brick-powder. Four variables (water/cement ratio, sand ratio, replacement level and average particle size of clay-brick-powder) were considered. Each variable had four levels. By using the orthogonal experimental design method, total 17 mixes, including one normal cement concrete as reference, were tested. Experiment results showed that recycled clay-brick-powder could be used as partial replacement of cement in concrete without reducing its properties. The strength was not significantly reduced with cement replacement level up to 25%. The elastic modulus was lower compared with cement concrete.

Flexural Properties of ECC-Concrete Composite Beam

Rebar corrosion-induced durability issue is a major concern for bridges. The ECC cover was employed to prevent the intrusion of the corrosive agent. This paper studied the flexural behavior of ECC-concrete composite beam. The effects of bonding at the interface and fiber mesh reinforcement on the flexural properties and cracking pattern were investigated. The strain distribution and midspan deflection were evaluated. Test results show that the bonded composite beam had a higher loading capacity. But the unbonded composite beam showed better postcrack energy absorption capacity with higher midspan deflection. The fiber mesh reinforcement could further improve the flexural properties regardless of the bonding condition. The strain at the bottom of the unbonded beam was much smaller than that of the bonded beam. The penetrated cracks were observed at the ECC layer of the bonded composited beam.

Mechanical Property and Electromagnetic Interference Shielding Effectiveness of Mortar Produced with Radiation-Proof Cloths

AbstractThis paper explores a new way to recycle wasted radiation-proof cloths and produced a cost-effective material for electromagnetic shielding. Chopped fiber (CF), produced from radiation-proo...