scholarly journals Prediction of the Interface Shear Strength between Ultra-High-Performance Concrete and Normal Concrete Using Artificial Neural Networks

Materials ◽  
2021 ◽  
Vol 14 (19) ◽  
pp. 5707
Author(s):  
Changqing Du ◽  
Xiaofan Liu ◽  
Yinying Liu ◽  
Teng Tong
Keyword(s):  
Bond Strength ◽  
High Performance ◽  
High Performance Concrete ◽  
Ann Model ◽  
Ultra High Performance Concrete ◽  
Shear Tests ◽  
Research Papers ◽  
Artificial Neural ◽  
Modified Formula ◽  
Slant Shear

The bond strength between ultra-high-performance concrete (UHPC) and normal-strength concrete (NC) plays an important role in governing the composite specimens’ overall behaviors. Unfortunately, there are still no widely accepted formulas targeting UHPC–NC interfacial strength, either in their specifications or in research papers. To this end, this study constructs an experimental database, consisting of 563 and 338 specimens for splitting and slant shear tests, respectively. Moreover, an additional 35 specimens for “improved” slant shear tests were performed, which could circumvent concrete crushing and trigger interfacial debonding. Additionally, for the first time in our tests, the effect of casting sequence on UHPC–NC bond strength was identified. Based on the database, an artificial neural network (ANN) model is proposed with the following inputs: namely, the normal stress perpendicular to the interface, the interface roughness, and the compressive strengths of the UHPC and NC materials. Based on the ANN analyses, the explicit expression of UHPC–NC bond strength is proposed, which significantly lowers the prediction error. To be fully compatible with the specifications, the conventional shear-friction formula is modified. By splitting the total force into adhesion and friction forces, the modified formula additionally takes the casting sequence into account. Although sacrificing accuracy to some extent compared to the ANN model, the modified formula relies on a solid physical basis and its accuracy is enhanced significantly compared to the existing formulas in specifications or research papers.

scholarly journals Effect of Elevated Temperature on the Bond Strength of Prestressing Reinforcement in UHPC

Materials ◽  
2020 ◽  
Vol 13 (21) ◽  
pp. 4990
Author(s):  
Petr Pokorný ◽  
Jiří Kolísko ◽  
David Čítek ◽  
Michaela Kostelecká
Keyword(s):  
Bond Strength ◽  
High Performance ◽  
Elevated Temperatures ◽  
High Performance Concrete ◽  
Future Research ◽  
Ultra High Performance Concrete ◽  
Negative Effect ◽  
Laboratory Investigations ◽  
Increasing Temperature ◽  
Positive Effect

The study explores the effect of elevated temperatures on the bond strength between prestressing reinforcement and ultra-high performance concrete (UHPC). Laboratory investigations reveal that the changes in bond strength correspond well with the changes in compressive strength of UHPC and their correlation can be mathematically described. Exposition of specimens to temperatures up to 200 °C does not reduce bond strength as a negative effect of increasing temperature is outweighed by the positive effect of thermal increase on the reactivity of silica fume in UHPC mixture. Above 200 °C, bond strength significantly reduces; for instance, a decrease by about 70% is observed at 800 °C. The decreases in compressive and bond strengths for temperatures above 400 °C are related to the changes of phase composition of UHPC matrix (as revealed by X-ray powder diffraction) and the changes in microstructure including the increase of porosity (verified by mercury intrusion porosimetry and observation of confocal microscopy) and development cracks detected by scanning electron microscopy. Future research should investigate the effect of relaxation of prestressing reinforcement with increasing temperature on bond strength reduction by numerical modelling.

Study on the transfer and anchorage length of steel strand in ultra high performance concrete material

2020 ◽  
Vol 10 (2) ◽  
pp. 153-164
Author(s):  
Hui Zheng ◽  
Dongdong Zhou ◽  
Xinfeng Yin ◽  
Lei Wang
Keyword(s):  
Bond Strength ◽  
High Performance ◽  
Failure Modes ◽  
High Performance Concrete ◽  
Protective Layer ◽  
Experimental Results ◽  
Ultra High Performance Concrete ◽  
Anchorage Length ◽  
Pull Out ◽  
Steel Strand

Ultra-high-performance concrete (UHPC) material, a new type of cement-based composite material, is usually employed in the bridge engineering. The transfer and anchorage length of steel strand in UHPC material is different from that in ordinary concrete; nevertheless, few design standards are found that how to anchor the transfer and anchoring length of steel strand in UHPC material under normal curing. Through central pull-out test under the different conditions of protective layer thickness and embedded length, the load-slip curves, failure modes, and bond strength of 36 UHPC material specimens under normal curing were studied. The experimental results showed that the ultimate bond stress between UHPC material and steel strand under natural curing conditions is 7.01∼11.68 MPa. When the compressive strength of cube was 157 MPa; the bond strength under natural curing was smaller than that under thermal curing; when the thickness of the protective layer of steel strand with a diameter of 15.2 mm is greater than 30 mm, it had a little influence on bond strength. The regression analysis of the test results based on the experimental results proves that the recommended formulas for the design of transfer length and anchorage length of steel strand in UHPC material were in great agreement with the results of published studies.

Study on Interfacial Properties of Ultra-High Performance Concrete Containing Steel Slag Powder and Fly Ash

2011 ◽  
Vol 194-196 ◽  
pp. 956-960 ◽  
Author(s):  
Yan Zhou Peng ◽  
Kai Chen ◽  
Shu Guang Hu
Keyword(s):  
Fly Ash ◽  
Bond Strength ◽  
High Performance ◽  
Steel Fiber ◽  
High Performance Concrete ◽  
Steel Slag ◽  
Interfacial Zone ◽  
Ultra High Performance Concrete ◽  
Slag Powder ◽  
Steel Slag Powder

The interfacial properties of reactive powder concretes (RPCs), other known as ultra-high performance concrete (UHPC), containing steel slag powder and ultra fine fly ash are studied in this paper. The microstrctural characterization of interfacial transition zones (ITZs), including the aggregate-cement paste interfacial zone and the steel fiber-paste interfacial zone, is investigated by SEM. The microhardness of the aggregate-paste ITZ and the steel slag-paste ITZ is studied and the bond strength of steel fiber in matrix is tested through fiber pullout tests. The results indicate that the microhardness of the steel slag-paste ITZ is slightly higher than that of the aggregate-paste ITZ, which implies the advantage of the substitution of quartz powder with steel slag powder in preparation of RPCs to some degrees. Moreover, the hardness of these two ITZs is higher than that of the hardened paste. A certain amount of hydration products has been observed exsiting on the surface of steel fiber by SEM and the bond strength of steel fiber-martix is up to 9.3MPa. These interfical properties are definitely critical to obtain high performance of UHPCs containing steel slag powder and fly ash.

scholarly journals Modified Formula for Designing Ultra-High-Performance Concrete with Experimental Verification

Materials ◽  
2020 ◽  
Vol 13 (20) ◽  
pp. 4518 ◽  
Author(s):  
Jarosław Siwiński ◽  
Anna Szcześniak ◽  
Adam Stolarski
Keyword(s):  
High Performance ◽  
High Performance Concrete ◽  
Experimental Studies ◽  
Ultra High Performance Concrete ◽  
Good Convergence ◽  
Fine Grained ◽  
Reinforcing Fibers ◽  
Proposed Modification ◽  
Modified Formula ◽  
Specimen Shape

The main purpose of the study was to propose a modification of Larrard’s formula for both the design and compressive-strength evaluation of ultra-high-performance concrete. The proposed modification consisted of the introduction of new parameters into the original formula that allowed it to consider the amount of binders and fine-grained aggregates, the amount of reinforcing fibers, the specimen shape and size, the curing time, and a reinterpretation of the water/cement ratio. The proposed modification was verified based on comparative analysis with the results of our own experimental studies and results taken from the literature. A very good convergence of these results was demonstrated, indicating the validity of the proposed modification.

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