Microstructural analysis of recycled aggregate concrete produced from two-stage mixing approach

With a rising tide of adoption of recycled aggregate (RA) for construction, investigation on ways to improve the quality of RA has been overwhelming. The adoption of RA brings benefits including savings in the limited landfill spaces and the use of natural resources. However, the poorer quality of RA often limits its utilization to low grade applications such as sub-grade activities, filling materials and low grade concrete. The major reason that affects the quality of RA is the large amount of cement mortar remains on the surface of the aggregate, resulting in higher porosity, water absorption rates and thus a weaker interfacial zone between new cement mortar and aggregates, which weakens the strength and mechanical performance of concrete made from RA. This paper attempts to study three pre-soaking treatment approaches; namely ReMortarHCl, ReMortarH2SO4 and ReMortarH3PO4 in reducing the mortar attached to RA. The results show that the behaviour of RA has improved with reduction in water absorption, without simultaneous exceeding the limits of chloride and sulphate compositions after the treatment. This work has also compared the compressive strength, flexural strength and modulus of elasticity of concrete made from the approaches, which shows marked improvements in quality when compared with those using traditional approaches.

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Removal of cement mortar remains from recycled aggregate using pre-soaking approaches

Diversifying two-stage mixing approach (TSMA) for recycled aggregate concrete: TSMAs and TSMAsc

As more than 50% construction and demolition (CD and (ii) the deformation and permeability of RAC can be enhanced when adopting TSMA. Therefore, it demonstrates that TSMA can help to improve the durability of RAC, on top of the previously verified strength improvement, and thus opening up wider applications of RAC.

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Assessment of durability of recycled aggregate concrete produced by two-stage mixing approach

The advantages of fiber-reinforced polymer (FRP)-strengthening have been shown time and again during the last decade. Several thousand structures retrofitted with FRPs exist worldwide. There are various reasons why the retrofit is needed, but it is not uncommon for the demands on the structure to change with time, as buildings and civil structures usually have a very long life. The structures may have to eventually carry larger loads or fulfill new standards. In extreme cases, a structure may need repair due to an accident or to errors made during the design or construction phases, and must therefore be strengthened before it can be used. Different methods to retrofit with FRPs also exist, such as bonding of plates or sheets, with their use of epoxy as the bonding agent being the commonality. Epoxy provides very good bond to concrete and is durable and resistant to most environments in the building industry. However, epoxy may also create problems in the working environment, needs a minimum application te...

Mineral-Based Bonding of Carbon FRP to Strengthen Concrete Structures

The weak transition zone between new and old concrete controls many properties of repaired concrete. The transition zone between aggregates and cement pastes of normal concrete has been studied by a number of researchers. But to date, there is little information available about the interfacial zone between new and old concrete. In this paper, major properties of the transition zone between new and old concrete with different binders were studied by using both scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The bond strength was also investigated. The test results show that the binder is a vital factor, which affects the morphology (size and shape), mineralogy and the microstructure of the transition zone in repaired concrete.

Transition zone studies of new-to-old concrete with different binders

A way for improving interfacial transition zone between concrete substrate and repair materials

Enhanced low-field magnetocaloric effect in Nb and Al co-substituted EuTiO3 compounds

The short-term and long-term flexural properties of 18 concrete beams were experimentally investigated with an emphasis placed on the influence of the unbonded interface between repair materials and concrete substrate. These beams were divided into four different series: normally repaired beams, unbonded repaired beams (by using a layer of plastic membrane between new and old concrete), unrepaired beams (with exposed reinforcement), and control beams. The short-term loading test results showed that the ultimate moment capacity of the unbonded repaired beams was slightly lower than that of the control beams. Great decreases in stiffness and ductility were observed in the unbonded repaired beams compared with the reference beams. The long-term loading test results suggest that most of the deflection caused by the unbonded slip between new and old concrete was completed within one day after loading.

Huicai Xie

Papers

Transition zone studies of new-to-old concrete with different binders

A way for improving interfacial transition zone between concrete substrate and repair materials

Enhanced low-field magnetocaloric effect in Nb and Al co-substituted EuTiO3 compounds

Flexural Behavior of Reinforced Concrete Beams with Unbonded Repair Patch

Enhanced magnetocaloric effect from Zn substitution in perovskite Eu(Ti,Zn)O3 compounds