Experimental Study on the Chloride Diffusivity of Recycled Aggregate Concrete

2010 ◽  
Vol 168-170 ◽  
pp. 1404-1408
Author(s):  
He Ying Qin ◽  
Yan Lin Zhao ◽  
Bo Guang Luo ◽  
Yi Hu Chen
Keyword(s):  
Diffusion Coefficient ◽  
Fly Ash ◽  
Silica Fume ◽  
Recycled Aggregate Concrete ◽  
Recycled Aggregate ◽  
Chloride Diffusion ◽  
Partial Replacement ◽  
Chloride Diffusion Coefficient ◽  
Aggregate Concrete ◽  
Chloride Diffusivity

The study presented herein has been carried out in order to investigate the chloride diffusivity of recycled aggregate concrete (RAC). Meanwhile, the effect of the binder type, involving cement replacement materials such as, fly ash, slag and silica fume on the chloride diffusivity has also been investigated. For this purpose, RAC and concrete containing the different type of binders with w/b ratios of 0.35, 0.40, 0.45, 0.50, 0.55, and 0.60 were used. As a result, the chloride diffusion coefficient of RAC is higher than that of natural concrete and the partial replacement of cement with fly ash, slag and silica fume is effective in decrease in the chloride diffusion coefficient, measured by a rapid chloride conductivity test.

Diffusion of Multi-Ionic Species in Recycled Aggregate Concrete

2011 ◽  
Vol 477 ◽  
pp. 56-64 ◽  
Author(s):  
Nattapong Damrongwiriyanupap ◽  
Yu Chang Liang ◽  
Yun Ping Xi
Keyword(s):  
Diffusion Coefficient ◽  
Cement Paste ◽  
Recycled Aggregate Concrete ◽  
Phase Model ◽  
Recycled Aggregate ◽  
Chloride Diffusion ◽  
Chloride Diffusion Coefficient ◽  
Aggregate Concrete ◽  
Multi Scale ◽  
Multi Phase

In recent years, recycled aggregate concrete has been used in reinforced concrete structures. Concrete structures exposed to chloride environment often encountera premature deterioration due to corrosion of steel reinforcement. In order to avoid unplanned maintenances or repairs, it is necessary to develop a reliable prediction model for the chloride diffusion in concrete. The basic formulation of the transport theory will be presented first and then its application to Recycled Aggregate Concrete (RAC) will follow. Chloride diffusion in RAC is different from the diffusion in regular concrete, because the material parameters of RAC such as chloride diffusion coefficient are different from those of regular concrete. In this paper, a multi-scale and multi-phase model will be developed to characterize theinternal structure of the recycled aggregate with a layer of residual cement paste on the surface of natural aggregate and another layer of surface treatment material on the surface of the residual cement paste. The multi-scale and multi-phase model will also be used to characterize the chloride diffusion coefficient of RAC. The numerical analysis of the diffusion equations is performed by using finite element method.

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

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.

The Multiscale Spectral Stochastic Finite Element Method for Chloride Diffusion in Recycled Aggregate Concrete

2017 ◽  
Vol 15 (01) ◽  
pp. 1750078 ◽  
Author(s):  
Yuching Wu ◽  
Jianzhuang Xiao
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Digital Image ◽  
Recycled Aggregate Concrete ◽  
Recycled Aggregate ◽  
Chloride Diffusion ◽  
Stochastic Finite Element Method ◽  
Stochastic Finite Element ◽  
Aggregate Concrete ◽  
Chloride Diffusivity

In this study, the multiscale stochastic finite element method (MsSFEM) was developed based on a novel digital image kernel to make analysis for chloride diffusion in recycled aggregate concrete (RAC). It is significant to study the chloride diffusivity in RAC, because when RAC was applied in coastal areas, chloride-induced rebar corrosion became a common problem for concrete infrastructures. The MsSFEM was an efficient tool to examine the effect of microscopic randomness of RAC on the chloride diffusivity. Based on the proposed digital image kernel, the Karhunen–Loeve expansion and the polynomial chaos were used in the stochastic homogenization process. To investigate advantages and disadvantages of both generation and application of the proposed digital image kernel, it was compared with many other kernels. The comparisons were made between the method to develop the digital image kernel, which is called the pixel-matrix method, and other methods, and between the application of the kernel and various other kernels. It was shown that the proposed digital image kernel is superior to other kernels in many aspects.

The Influence of Mineral Admixtures on the Wear-Resisting Property of Recycled Aggregate Concrete

2013 ◽  
Vol 639-640 ◽  
pp. 417-422
Author(s):  
Wei Dong Chen ◽  
Jian Yin ◽  
Wei Min Song ◽  
Yi Chi
Keyword(s):  
Fly Ash ◽  
Flexural Strength ◽  
Silica Fume ◽  
Recycled Aggregate Concrete ◽  
Recycled Aggregate ◽  
Mineral Admixtures ◽  
Aggregate Concrete

It was tested the strength and wear value of recycled aggregate concrete mixing fly ash, slag, silica fume and double-mixture or three-mixture in deferent age. The results show that the wear value of recycled aggregate concrete mixing 30% fly ash is more than reference concrete at 3days, but can improve final wear-resisting property significantly. The wear value of recycled aggregate concrete mixing 30% double-mixture of fly ash and silica fume is much lower than reference concrete at 3days, and improve early wear-resisting property significantly. The flexural strength of the concrete is 4.26MPa at 3days, which can satisfy the traffic requirement. The wear value of recycled aggregate concrete mixing 30% three-mixture of fly ash, slag and silica fume is lower than reference concrete at 3days, but the declining rate is not significant. It investigates mechanics of double-mixture technique which improves wear-resisting property at the same time.

scholarly journals Influence of Bentonite on Mechanical and Durability Properties of High-Calcium Fly Ash Geopolymer Concrete with Natural and Recycled Aggregates

Materials ◽  
2021 ◽  
Vol 14 (24) ◽  
pp. 7790
Author(s):  
Rana Muhammad Waqas ◽  
Faheem Butt ◽  
Aamar Danish ◽  
Muwaffaq Alqurashi ◽  
Mohammad Ali Mosaberpanah ◽  
...  
Keyword(s):  
Fly Ash ◽  
Recycled Aggregate Concrete ◽  
Recycled Aggregate ◽  
Recycled Aggregates ◽  
Partial Replacement ◽  
Acid Attack ◽  
Aggregate Concrete ◽  
High Calcium ◽  
High Calcium Fly Ash ◽  
Strength And Durability

In this study, bentonite (a naturally occurring pozzolana) was incorporated as a partial replacement (up to 20%) for high-calcium fly ash (HCFA)-based geopolymeric natural aggregate concrete (GNAC) and geopolymeric recycled aggregate concrete (GRAC). The mechanical (compressive strength and splitting tensile strength), durability (chloride migration coefficient, water absorption, and acid attack resistance), and rheological properties (slump test, fresh density, and workability) were investigated. The results revealed that incorporation of bentonite (10 wt % with ordinary Portland cement) showed appreciable improvement in the strength and durability of both the GNAC and GRAC, though its effect is more significant for GRAC than the GNAC.

scholarly journals Effect of Mineral Admixtures on the Performance of Low-Quality Recycled Aggregate Concrete

Crystals ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 596
Author(s):  
Yasuhiro Dosho
Keyword(s):  
Blast Furnace ◽  
Fly Ash ◽  
Blast Furnace Slag ◽  
Recycled Aggregate Concrete ◽  
Recycled Aggregate ◽  
Mineral Admixtures ◽  
Structural Concrete ◽  
Aggregate Concrete ◽  
Granulated Blast Furnace Slag ◽  
Furnace Slag

To improve the application of low-quality aggregates in structural concrete, this study investigated the effect of multi-purpose mineral admixtures, such as fly ash and ground granulated blast-furnace slag, on the performance of concrete. Accordingly, the primary performance of low-quality recycled aggregate concrete could be improved by varying the replacement ratio of the recycled aggregate and using appropriate mineral admixtures such as fly ash and ground granulated blast-furnace slag. The results show the potential for the use of low-quality aggregate in structural concrete.

Recycling of Waste Concrete and Fly Ash for Recycled Aggregate Concrete: Fundamental Characteristics Evaluation

2009 ◽  
Vol 620-622 ◽  
pp. 255-258 ◽  
Author(s):  
Cheol Woo Park
Keyword(s):  
Fly Ash ◽  
Recycled Concrete ◽  
Recycled Aggregate Concrete ◽  
Recycled Aggregate ◽  
Experimental Program ◽  
Concrete Aggregate ◽  
Fine Aggregate ◽  
Recycled Concrete Aggregate ◽  
Aggregate Concrete ◽  
Waste Concrete

As the amount of waste concrete has been increased and recycling technique advances, this study investigates the applicability of recycled concrete aggregate for concrete structures. In addition fly ash, the industrial by-product, was considered in the concrete mix. Experimental program performed compressive strength and chloride penetration resistance tests with various replacement levels of fine recycled concrete aggregate and fly ash. In most case, the design strength, 40MPa, was obtained. It was known that the replacement of the fine aggregate with fine RCA may have greater influence on the strength development rather than the addition of fly ash. It is recommended that when complete coarse aggregate is replaced with RCA the fine RCA replacement should be less than 60%. The recycled aggregate concrete can achieve sufficient resistance to the chloride ion penetration and the resistance can be more effectively controlled by adding fly ash. It I finally conclude that the recycled concrete aggregate can be successfully used in the construction field and the recycling rate of waste concrete and flay ash should be increased without causing significant engineering problems.

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