Title:
Investigation of Bond in Unreinforced Interfaces for Partial- Depth Repairs and New Construction
Author(s):
Jeff West - Wiss, Janney, Elstner Associates, Inc.
Publication:
CRC
Volume:
Issue:
Appears on pages(s):
126
Keywords:
DOI:
Date:
2/24/2023
Abstract:
This project comprised two phases to investigate the bond of composite concrete-to-concrete interfaces. Phase 1 included 20 composite slabs with a series of direct shear and direct tensile bond tests. Within this phase, the use of the guillotine shear test method was explored while testing various interface surface preparations representative of repair and precast members. Phase 2 studied interface shear failure in composite beam specimens along with additional direct shear and direct tensile bond tests. Key observations from this research study are presented below. •The guillotine shear test appears to be an appropriate method to assess interface bond strength for composite concrete members (new construction and repairs). •The ratio of direct shear strengths obtained by the guillotine shear test and direct tensile strengths from pull-off tests are between 2.1 to 3.6. •The ratio of direct shear strengths obtained by the guillotine shear test and maximum horizontal shear strengths from flexural tests area are between 0.5 to 1.1. • Sound, tightly adhered concrete-to-concrete bond is dependent on many factors including moderate topping slump, good topping consolidation, and moderate substrate roughness. •Concrete-to-concrete bond strength is not consistently related to the degree of roughness measured by mean texture depth. •Average direct shear strength results ranged from 8 to 13 times greater than the nominal value of 80 psi specified by ACI 318-19 and ACI 562-19 for design of unreinforced interfaces for shear. •Maximum horizontal shear stresses at interface shear failure in beam tests were more than 13 times greater than the nominal value of 80 psi specified by ACI 318-19 and ACI 562-19 for design of unreinforced interfaces for shear.