Hybrid Interfacial Transition Zone between Wet-On-Wet Casted Concrete-Microstructure and Mechanical Properties

Area of Science:

• Civil Engineering
• Materials Science
• Construction Technology

Background:

• Hybrid concrete elements offer reduced Portland cement usage by tailoring properties to specific structural and durability needs.
• Common hybrid element production methods include wet-on-hard and wet-on-wet casting.
• The wet-on-wet method, typically used for overlays, is investigated here for vertical and horizontal elements.

Purpose of the Study:

• To investigate the bond behavior and micro-properties at the wet-on-wet casting interface between ultra-high-performance concrete (UHPC) and normal strength concrete.
• To evaluate the feasibility of the wet-on-wet method for producing hybrid vertical and horizontal structural elements.
• To analyze the characteristics of the interfacial transition zone formed between dissimilar concrete types.

Main Methods:

• Application of the wet-on-wet casting technique for both vertical and horizontal hybrid concrete elements.
• Microscopic analysis of the interfacial transition zone (ITZ) between UHPC and normal strength concrete.
• Assessment of porosity, phase composition, and mechanical properties (flexural and compressive strength) of the hybrid elements.

Main Results:

• Formation of a hybrid interfacial transition zone with combined properties of both UHPC and normal strength concrete.
• Gradual changes in porosity and phase composition within the ITZ.
• Absence of microcracking or delamination at the interface, despite differential shrinkage between the concrete types.
• Ultimate flexural and compressive strengths of the hybrid elements were comparable to or exceeded those of the stronger constituent concrete.

Conclusions:

• The wet-on-wet casting method is effective for producing defect-free hybrid concrete elements combining UHPC and normal strength concrete.
• The developed hybrid ITZ exhibits favorable microstructural and mechanical properties.
• This approach allows for optimized material usage and enhanced performance in structural applications.