Peeling behavior and spalling resistance of CFRP sheets bonded to bent concrete surfaces

In this paper, the peeling behavior and the spalling resistance effect of carbon fiber reinforced polymer （CFRP） sheets externally bonded to bent concrete surfaces are firstly investigated experimentally. Twenty one curved specimens and seven plane specimens are studied in the paper, in which curved specimens with bonded CFRP sheets can simulate the concrete spalling in tunnel, culvert, arch bridge etc., whereas plane specimens with bonded CFRP sheets can simulate the concrete spalling in beam bridge, slab bridge and pedestrian bridge. Three kinds of curved specimens with different radii of curvature are chosen by referring to practical tunnel structures, and plane specimens are used for comparison with curved ones. A peeling load is applied on the FRP sheet by loading a circular steel tube placed into the central notch of beam to debond CFRP sheets from the bent concrete surface, meanwhile full-range load-deflection curves are recorded by a MTS 831.10 Elastomer Test System. Based on the experimental results, a theoretical analysis is also conducted for the specimens. Both theoretical and experimental results show that only two material parameters, the interfacial fracture energy of CFRP-concrete interface and the tensile stiffness of CFRP sheets, are needed for describing the interfacial spalling behavior. It is found that the radius of curvature has remarkable influence on peeling load-deflection curves. The test methods and test results given in the paper are helpful and available for reference to the designer of tunnel strengthening.

Domain adversarial training for classification of cracking in images of concrete surfaces

The development of automatic methods to recognize cracks in surfaces of concrete has been under focus in recent years,firstly through computer vision methods and more recently focusing on convolutional neural networks that are delivering promising results.Challenges are still persisting in crack recognition,namely due to the confusion added by the myriad of elements commonly found on concrete surfaces.The robustness of these methods would deal with these elements if access to correspondingly heterogeneous datasets was possible.Even so,this would be a cumbersome methodology,since training would be needed for each particular case and models would be case dependent.Thus,efforts from the scientific community are focusing on generalizing neural network models to achieve high per-formance in images from different domains,slightly different from those in which they were effectively trained.The generalization of networks can be achieved by domain adaptation techniques at the training stage.Domain adapta-tion enables finding a feature space in which features from both domains are invariant,and thus,classes become separable.The work presented here proposes the DA-Crack method,which is a domain adversarial training method,to generalize a neural network for recognizing cracks in images of concrete surfaces.The domain adversarial method uses a convolutional extractor followed by a classifier and a discriminator,and relies on two datasets:a source labeled dataset and a target unlabeled small dataset.The classifier is responsible for the classification of images randomly chosen,while the discriminator is dedicated to uncovering to which dataset each image belongs.Backpropagation from the discriminator reverses the gradient used to update the extractor.This enables fighting the convergence promoted by the updating backpropagated from the classifier,and thus generalizing the extractor enabling it for crack recognition of images from both source and target datasets.Results show that the DA-Crack training method improved accuracy in crack classification of images from the target dataset in 54 percentage points,while accuracy on the source dataset remains unaffected.

Influence of ＂Covercrete＂ Morphology on Durability Properties

Many leading experts agree on the importance of monitoring the ＂concrete skin＂ as the most loaded area affected by the external environment. Surfacing, concrete mixture composition and curing are of great importance for the concrete surface resistance. The paper introduces an experimental program focused on the monitoring of de-icing salts resistance, depending on surface roughness. Quantitative evaluation of the concrete surface was performed by using confocal laser scanning microscopy, which is the new generation of optical systems that are able to make all measurements in 3D resolution. These measurements are supplemented by results of mechanical and absorption tests.

Noise emission of concrete pavement surfaces produced by diamond grinding

In Germany, diamond grinding is frequently used to improve the evenness and skid resistance of concrete pavement surfaces. Since diamond grinding has been observed to affect tyre/pavement noise emission favourably, the relationship among surface texture, concrete composition and noise emission of concrete pavement surfaces has been sys- tematically investigated. The simulation program SPERoN was used in a parameter study to investigate the main factors which affect noise emission. Based on the results of the simulations, textured concrete surfaces were produced by using a laboratory grinding machine. As well as the composition of the concrete, the thickness and spacing of the diamond blades were varied. The ability of the textured surfaces to reduce noise emission was assessed from the texture characteristics and air flow resistance of textured surfaces measured in the laboratory. It was found that concrete composition and, in particular, the spacing of the blades affected the reduction in noise emission considerably. The noise emission behaviour of numerous road sections was also considered in field investigations. The pavement surfaces had been textured by diamond grinding during the last years or decades. The results show that diamond grinding is able to provide good, durable noise- reducing properties. Several new pavement sections were investigated using thicknesses and spacings of the blades similar to those used in the laboratory to optimize noise emission reduction. It is concluded that diamond grinding is a good alternative to exposed aggregate concrete for the production of low-noise pavement surfaces.

An examination of the mechanical interaction of drilling slurries at the soil-concrete contact

Evidence gained from previous field tests conducted on drilled shaft foundation shows that using drilling slurries to stabilize a borehole during the construction may influence the interfacial shear strength.This paper deals with an exhaustive study of the effects of drilling slurries at the contact between soil and concrete.This study involved adapting a simple shear apparatus and performing approximately 100 experimental tests on the interaction between two types of soils;clay and sandy clay and five specimens of concrete with different surface shapes.It also involved using bentonite and polymer slurries as an interface layer between soil and concrete.Results showed that an interface layer of bentonite slurry between clay and concrete decreases the interfacial shear strength by 23% and as an interface layer between sandy clay and concrete,bentonite increases interfacial shear strength by 10%.Using polymer slurry as an interface layer between clay and concrete decreases the interfacial shear strength by 17% while using it as an interface layer between sandy clay and concrete increases the interfacial shear strength by 10%.Furthermore,the data show that using bentonite and polymer slurry as an interface layer between clay and concrete decreases the sliding ratio by 50% to 60%,while increasing the sliding ratio by 44% to 56% when these are used as an interface layer between sandy clay and concrete.