Kejin Wangkejinw@iastate.edu email >
PCC Engineer, CP Tech Center
About the research
A high-performance mortar (HPM) containing a large amount of industrial by-products such as fly ash, silica fume, and limestone fines was developed for rapid repair of concrete pavements. The HPM development included three major steps.
- Development of the mortar mixture proportion based on the optimal hydration of binder and particle packing of the mortar system. In this step of the study, all mortar materials were systematically proportioned, and the obtained mixtures were tested for flowability, rate of hydration, set time, and strength development. The optimal mixture proportion was then selected as the HPM, as it displayed good self-consolidating ability and achieved 1-day compressive strengths greater than 6,000 psi.
- Investigation of the mechanical properties of the new HPM, including compressive and flexural strength, elastic modulus, and slant shear and pull-off strengths of patch-substrate bonds tested at 1, 3, 7, and 28 days. In this step, the properties of the HPM were evaluated in comparison with those of a commercial repair material: the rapid-set concrete (RSC). Two types of substrates representing old concrete were used for patching repair. One was made of a typical pavement mixture (C-3WR-C20), and the other was a high-strength pavement concrete mixture (O-4WR).
- Investigation of the durability properties of the newly developed HPM compared to those of the RSC. Durability properties included cyclic freeze-thaw (F-T) resistance, permeability, and shrinkage behavior.
The results indicated that the newly developed HPM possesses excellent self-consolidating ability: highly flowable and non-segregating. Although there was delayed setting, the compressive strength of the HPM exceeded 6,000 psi at 1 day, approximately 25 percent higher than that of the RSC. At 28 days, the HPM reached 10,000 psi, while the RSC was about 7,000 psi. The HPM also displayed extremely low chloride permeability (18 coulombs) compared to the RSC (2,550 coulombs) and excellent F-T durability without the requirement for air entrainment. The F-T durability factor of HPM was kept around 100% throughout the standard F-T test, while the F-T durability factor of RSC reduced to 80% at the end of the F-T test. However, the HPM exhibited noticeably higher autogenous shrinkage and slightly lower free drying shrinkage than the C-3WR-C20 mixture, while the RSC had a little/no shrinkage during the 56-day test period. Addition of a small amount of micro-steel fibers (70 pcy) slightly reduced the shrinkage of the HPM.
Further studies on fatigue and shrinkage cracking behavior of the HPM are recommended.concrete
Iowa State University ($75,000.00)
Midwest Transportation Center
Contract Number: DTRT13-G-UTC37