Research on the Mechanism of Surfactant Warm Mix Asphalt Additive-Based on Molecular Dynamics Simulation

Warm mix asphalt (WMA) technology can bring certain environmental and technical benefits through reducing the temperature of production, paving, and compaction of mixture asphalt. Recent studies have shown that some WMA additives are able to reduce the temperature by increasing the lubricating properties of asphalt binder.-based on the tribological theory, this paper studied the mechanism of adsorbing and lubricating film of base asphalt and WMA on the surface of stone by molecular dynamics (MD) simulation method, and the effect of surfactant WMA additive on the lubrication performance of the shear friction system of “stone–asphalt–stone”. The model of base asphalt lubricating film, including saturates, aromatics, resin and asphaltene, as well as the model of warm mix asphalt lubricating film containing imidazoline-type surfactant WMA (IMDL WMA) additive molecule, were established. The shear friction system of “stone–asphalt–stone” of base asphalt and warm mix asphalt was built on the basis of an asphalt lubrication film model and representative calcite model. The results show that the addition of IMDL WMA additive can effectively improve the lubricity of asphalt, reduce the shear stress of asphalt lubricating film, and increase the stability of asphalt film. The temperature in the WMA lubricating film rises, while the adsorption energy on the stone surface decreases with the increase of shear rate, indicating that the higher the shear rate is, the more unfavorable it is for the WMA lubricating film to wrap on the stone surface. In addition, the shear stress of the WMA lubricating film decreased with increasing temperature, while the shear stress of the base asphalt lubricating film increased first and then decreased, demonstrating that the compactability of the asphalt mixture did not improve linearly with the increase of temperature.

Analysis of shear stress on marine piles using shear friction theory

The current research investigation is focused on estimating the theoretical capacity of a rehabilitated steel marine pile. The old steel pile can be rehabilitated by installing new concrete encasement (jacket). The new concrete jacket can be easily connected to the old steel pile using shear friction between old pile and new concrete jacket or additional mechanical or welded connection. The under-water welding process is a very expensive task and considerable saving can be realized by eliminating this process. A previous experimental investigation was conducted to evaluate the behaviour of the rehabilitated steel pile. The maximum load and the load-slip deformation data were recorded for all of the tested specimens. The test results indicated that the marine pile can be efficiently rehabilitated by installing a concrete jacket using shear friction principles or the bolted connection to avoid the expense of welding under-water. The theoretical study included the investigation of surface friction, shear friction mechanism and cohesion on the bond capacity. The effect of the bolted anchor on increasing the effective cross section of the rehabilitated pile is examined. After investigating the predicted values of various equations developed by various researchers, the shear friction mechanical model developed by CSA 1994 is recommended to be used as the most effective formula that can provide an accurate prediction for the rehabilitated pile capacity.

Analysis of shear stress on marine piles using shear friction theory

The current research investigation is focused on estimating the theoretical capacity of a rehabilitated steel marine pile. The old steel pile can be rehabilitated by installing new concrete encasement (jacket). The new concrete jacket can be easily connected to the old steel pile using shear friction between old pile and new concrete jacket or additional mechanical or welded connection. The under-water welding process is a very expensive task and considerable saving can be realized by eliminating this process. A previous experimental investigation was conducted to evaluate the behaviour of the rehabilitated steel pile. The maximum load and the load-slip deformation data were recorded for all of the tested specimens. The test results indicated that the marine pile can be efficiently rehabilitated by installing a concrete jacket using shear friction principles or the bolted connection to avoid the expense of welding under-water. The theoretical study included the investigation of surface friction, shear friction mechanism and cohesion on the bond capacity. The effect of the bolted anchor on increasing the effective cross section of the rehabilitated pile is examined. After investigating the predicted values of various equations developed by various researchers, the shear friction mechanical model developed by CSA 1994 is recommended to be used as the most effective formula that can provide an accurate prediction for the rehabilitated pile capacity.

Analytical Model of Two-Directional Cracking Shear-Friction Membrane for Finite Element Analysis of Reinforced Concrete

There are a multitude of existing material models for the finite element analysis of cracked reinforced concrete that provide reduced shear stiffness but do not limit shear strength. In addition, typical models are not based on the actual physical behavior of shear transfer across cracks by shear friction recognized in the ACI 318 Building Code. A shear-friction model was recently proposed that was able to capture the recognized cracked concrete behavior by limiting shear strength as a yielding function in the reinforcement across the crack. However, the proposed model was formulated only for the specific case of one-directional cracking parallel to the applied shear force. This study proposed and generalized an orthogonal-cracking shear-friction model for finite element use. This was necessary for handling the analysis of complex structures and nonproportional loading cases present in real design and testing situations. This generalized model was formulated as a total strain-based model using the approximation that crack strains are equal to total strains, using the proportional load vector, constant vertical load, and modified Newton–Raphson method to improve the model’s overall accuracy.