STUDY ON BONDING PROPERTY OF POLYURETHANE CEMENT (PUC) TO STEEL BAR

The pull-out test of the bar and PUC is carried out in this paper, the effects of protective layer thickness, reinforcement anchorage length, diameter and shape of reinforcement on bonding properties were studied. The results show that the bond strength between reinforcement and PUC material increases with the increase of the thickness of the protective layer, but decreases with the increase of the anchorage length and diameter of reinforcement. The bond strength of bare round steel is significantly lower than that of ribbed steel, and the maximum bond strength is about 47.4% of ribbed steel. By analyzing the bond slip curve obtained from the pull-out test, the stress process of bond anchorage between reinforcement bar and PUC material is mainly summarized into three stages: the rising stage, the falling stage and the residual stage. The characteristics of the curve, the stress process and the failure mode of specimen at each stage are analyzed.

STUDY ON THE PROPERTIES OF POLYURETHANE-CEMENT COMPOSITE (PUC)

In order to study the properties of polyurethane cement composite (PUC) material, this paper has carried out the tests of compressive resistance, flexural resistance, axial tension, bonding and acid and alkali corrosion resistance of the material. The average compressive strength of the material is 59.3 MPa, the average flexural strength is 41.5 MPa, and the average axial tensile strength is 31.0 MPa. The bonding strength between the material and concrete in axial tension is 3.56 MPa, and that between the material and concrete in bending is 3.16 MPa. The failure interface of the two bond tests is not on the bond surface, indicating that the polyurethane cement composite (PUC) material has good bonding property. The chemical corrosion resistance test of polyurethane cement material showed no visible change on the surface of the material, indicating good chemical corrosion resistance.

Influence Factors and Prediction Model of Bond Strength of Tunnel Fireproof Coating under Freeze–Thaw Cycles

The freeze–thaw resistant performance of a tunnel fireproof coating (TFC) has an important impact on bonding property and durability. The influence of redispersible emulsion powder, polypropylene fiber and air-entraining agent on TFCs was studied. Transverse fundamental frequency and ultrasonic sound velocity were used to evaluate the damage degree of TFC, and the mechanism was revealed by SEM and pore structure. The results show that the most beneficial effect on bond strength of TFC is redispersible emulsion powder, followed by air-entraining agent, and then polypropylene fiber. After freeze–thaw cycles, the cumulative pore volume of micropores in the TFC increases obviously, while the porosity of macropores does not change significantly. A prediction model was proposed, which can calculate the bond strength from the damage degree of TFC under freeze–thaw cycles. The achievement can promote the application of TFC in cold regions.

Influence of Old Concrete Age, Interface Roughness and Freeze-Thawing Attack on New-to-Old Concrete Structure

The bonding surface structure generated by the repair of concrete structures has been paid more attention as a weak point. The effects of old concrete age, interface roughness, and freeze-thawing (F-T) attack on adhesive interface are comprehensively investigated. In this study, six kinds of interface roughness and five different old concrete age are designed. The interfacial bonding property is mainly evaluated by splitting tensile strength (fts). Fractal analysis was used to characterize the interface roughness using laser scanning data. In general, the fts increased with the increasing value of interface fractal dimension. The relationship between fts and fractal dimension value was further analyzed, considering the old concrete ages and the F-T cycles. The results show that the effect of roughness on the bonding property of new-to-old concrete is more significant than the age of old concrete, and the influence of the F-T cycles on the bonding surface is mainly reflected in the initial stage of the F-T deterioration process. The relative dynamic elasticity modulus decreased obviously under F-T cycles, especially for the specimens with low interface roughness. In combination with the results of two non-destructive methods (ultrasonic non-destructive test and relative dynamic elastic modulus test), the larger roughness and the smaller age of old concrete can improve the bond performance.

Harnessing reversible dry adhesion using shape memory polymer microparticles

Shape memory polymers can provide excellent bonding property because of their shape memory effects. This paper proposes an adhesive unit that is capable of repeatable smart adhesion and exhibits reversible adhesion under heating.

The bonding strength of polyamide-6 direct adhesion with anodized AA5754 aluminum alloy

With the application of hot-pressing technology, polyamide 6 (PA6) was successfully directly adhered to the aluminum alloy. The relationship between the bonding property and microstructures of PA6 and anodized AA5754 aluminum alloy hybrid were explored in the paper. The results showed that the honeycomb-like porous oxide film was prepared by anodic oxidation, which resulted in the decreased surface energy of the aluminum alloy, so that PA6 easily wetted on the aluminum alloy surface, and the maximum tensile shear strength and fracture work reached 8.24 MPa and 9.27 kJ m−2, respectively. Improved bonding strength was attributed to micro- and nanoscale honeycomb-like microstructures and large roughness on the anodized aluminum alloy surface.