Mineralogy and interfacial transition zone features of recycled aggregate concrete

At present, many modification methods have been proposed to improve the performance of recycled aggregate concrete (RAC). In this study, tests on the compressive strength and damping properties of modified RAC with the addition of different proportions of recycled coarse aggregate (RCA) (0, 50, 100%), rubber powder (10, 15, 20%), steel fibre (5, 7.5, 10%) and fly ash (15, 20, 5%) are carried out. To elucidate the effect of the modification method on the interfacial transition zone (ITZ) performance of RAC, model ITZ specimens are used for push-out tests. The results show that when the replacement rate of RCA reaches 100%, the loss factor of the RAC is 6.0% higher than that of natural aggregate concrete; however, the compressive strength of the RAC decreases by 22.6%. With the addition of 20% rubber powder, the damping capacity of the modified RAC increases by 213.7%, while the compressive strength of the modified RAC decreases by 47.5%. However, with the addition of steel fibre and fly ash, both the compressive strength and loss factor of the RAC specimens increase. With a steel fibre content of 10 wt%, the compressive strength and loss factor of the RAC increase by 21.9% and 15.2%, respectively. With a fly ash content of 25 wt%, the compressive strength and loss factor of the RAC increase by 8.6% and 6.9%, respectively. This demonstrates that steel fibre and fly ash are effective in improving both the damping properties and compressive strength of RAC, and steel fibre is more effective than fly ash. Two methods were used for modification of the RAC: reinforcing the RCA through impregnation with a 0.5% polyvinyl alcohol (PVA) emulsion and nano-SiO 2 solution, and strengthening the RAC integrally through the addition of fly ash as an admixture. Both of these techniques can improve the ITZ bond strength between the RAC and new mortar. Replacing 10% of the cement with fly ash in the new mortar is shown to be the best method to improve the ITZ strength.

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Performance evolution of the interfacial transition zone (ITZ) in recycled aggregate concrete under external sulfate attacks and dry-wet cycling

Construction and Building Materials ◽

10.1016/j.conbuildmat.2019.116938 ◽

2019 ◽

Vol 229 ◽

pp. 116938 ◽

Cited By ~ 9

Author(s):

Hongru Zhang ◽

Tao Ji ◽

Hui Liu

Keyword(s):

Transition Zone ◽

Interfacial Transition Zone ◽

Recycled Aggregate Concrete ◽

Recycled Aggregate ◽

Aggregate Concrete

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Microstructure and Finite Element Analysis of Recycled Aggregate Concrete

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.357-360.1383 ◽

2013 ◽

Vol 357-360 ◽

pp. 1383-1388 ◽

Cited By ~ 2

Author(s):

Hai Feng Yang ◽

Zhi Heng Deng ◽

Yue Feng Hu

Keyword(s):

Finite Element ◽

Transition Zone ◽

Weak Link ◽

Recycled Aggregate Concrete ◽

Interfacial Structure ◽

Recycled Aggregate ◽

Element Analysis ◽

Aggregate Concrete ◽

Finite Element Software ◽

Structure And Microstructure

In order to study the mechanistic differences between recycled aggregate concrete (RAC)and normal aggregate concrete(NAC), the magnifier and scanning electron microscope were used to observe the meso-interfacial structure and microstructure of interfacial transition zone morphology of the RAC respectively, and analysed differences between RAC and NAC; Secondly, the finite element software ABAQUS was used to simulation the simplified model of RAC. The above analysis results show that, there existe a transition zone in the interface, the aggregate-new mortar interface as well as the new-old mortar interface has been obvious cracks before loading, this part is the weak link of RAC ;After loading, the crack occurs first in the old interface, then appeared at the new interface, and then develop to the old mortar, finally, there formed a through crack.

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Chloride Diffusion Characteristics of the New Interface Transition Zone in Recycled Aggregate Concrete

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.261-263.104 ◽

2011 ◽

Vol 261-263 ◽

pp. 104-110

Author(s):

Hai Long Wang ◽

Jun Jie Wang ◽

Xiao Yan Sun ◽

Juan Cheng

Keyword(s):

Diffusion Coefficient ◽

Steady State ◽

Transition Zone ◽

Chloride Transport ◽

Recycled Aggregate Concrete ◽

Recycled Aggregate ◽

Chloride Diffusion ◽

Chloride Diffusion Coefficient ◽

Aggregate Concrete ◽

Phosphorous Slag

A three-part model (mortar, original concrete and ITZ) was established in this study to analyze the chloride coefficient of the new interfacial transition zone (ITZ) in recycled aggregate concrete (RAC). Based on this model, a formula for calculation was derived from the chloride transport characteristics in the steady state. Two types of RAC were used to study the properties of ITZ by steady-state migration test and Scanning Electron Microscope (SEM) method. The results indicate that the chloride diffusion coefficient of new ITZ in RAC is about 1 to 4 cm2/year, and that the addition of superfine phosphorous slag (PHS) not only reduces the chloride diffusion coefficient of mortar but also decreases the thickness and the chloride diffusion coefficient of new ITZ in RAC due to its pozzolanic reaction effect. The chloride permeability of mortar containing 20% PHS is only 1/5 of that in normal RAC. The chloride diffusion coefficient of ITZ in normal RAC is about 10 times greater than that of ordinary mortar. When modified with PHS and superplasticizer, the permeability of chloride in new ITZ is 3 to 7 times greater than that in the ordinary bulk cement paste. Furthermore, the mechanism and the effects of superfine phosphorous slag (PHS) on the resistivity of chloride permeation were discussed on basis of the experimental results and the images of SEM.

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