Renjuan Sun

Properties of self-consolidating concrete containing nano-CaCO3

This paper studied the effect of nano-CaCO3 on workability, strength development, and pore structures of cement paste and self-consolidating concrete. The effects of dosage and size of nano-CaCO3 were considered. For the workability, slump flow (total spread and T50 time), L-box, and V-funnel tests were conducted. The compressive strength was tested at 1, 7, and 28 days for concrete and 1 and 7 days for cement paste. The pore structure, including pore size distribution and volume, was measured using nitrogen adsorption method. The results show that the addition of nano-CaCO3 reduced the setting times. Concrete with a low content of nano-CaCO3 (≤2.5%) had satisfactory workability. No segregation was observed for all concrete specimens. The addition of nano-CaCO3 increased the compressive strength of the concrete and paste. The compressive strength decreased as the particle size increased. The addition of nano-CaCO3 reduced the average pore diameter. XRD test showed no new hydration products.

Properties of self-consolidating concrete with recycled clay-brick-powder replacing cementitious material

Clay brick is becoming a major demolition waste and causing environmental contamination in China. Recycling of wasted clay brick could conserve natural resources and preserve land from waste filling. In this research, recycled clay-brick-powder (CBP) was used to partially replace Portland cement (PC) and fly ash (FA) in self-consolidating concrete (SCC) mix. The effects of dosage of CBP on the workability, strength, and shrinkage of SCC were investigated. Test results show that partially replacing cementitious material with CBP can reduce the workability of SCC. Compared with the reference concrete, specimens with CBP had higher 28-day and 56-day strength. The specimens containing 1% CBP had the highest compressive strength. Meanwhile, the replacement of CBP to PC and FA could also reduce the shrinkage of the SCC due to the internal curing effect. Based on scanning electron microscope investigation, specimen with CBP had less pores than the specimen without CBP and improved the microstructure of concrete. Hence, CBP had positive effects on the mechanical and physical properties of SCC.

Flexural Properties of ECC-Concrete Composite Beam

Rebar corrosion-induced durability issue is a major concern for bridges. The ECC cover was employed to prevent the intrusion of the corrosive agent. This paper studied the flexural behavior of ECC-concrete composite beam. The effects of bonding at the interface and fiber mesh reinforcement on the flexural properties and cracking pattern were investigated. The strain distribution and midspan deflection were evaluated. Test results show that the bonded composite beam had a higher loading capacity. But the unbonded composite beam showed better postcrack energy absorption capacity with higher midspan deflection. The fiber mesh reinforcement could further improve the flexural properties regardless of the bonding condition. The strain at the bottom of the unbonded beam was much smaller than that of the bonded beam. The penetrated cracks were observed at the ECC layer of the bonded composited beam.