A new method to improve the properties of recycled aggregate concrete: Composite addition of basalt fiber and nano-silica

In order to study the basic mechanical properties of basalt fiber reinforced recycled aggregate concrete, the concrete mix ratio, the length and the volume mixing ratio of chopped basalt fiber yarn are designed for changing factors. A total of 324 specimens have been completed for this investigation. The compressive strength, splitting tensile strength, elastic modulus and axial compressive strength of basalt fiber recycled concrete have carried on the experimental study and theoretical analysis as 81 specimens, respectively. In all specimens, coarse aggregate were replaced by recycled aggregate with a replacement rate of 100%. Experimental results show that the failure process and failure pattern of basalt fiber recycled concrete and ordinary concrete are similar; With the improvement of concrete strength grade; When the volume mixing ratio of chopped basalt fiber yarn is 0.2%, the mechanic performance can effectively improve, and the length of chopped basalt fiber has less effect on the mechanical indexes; The conversion relation between common concrete mechanics index is no longer suitable for basalt fiber recycled concrete, new conversion formulas for basalt fiber recycled concrete between the mechanics index were presented through fitting experimental data.

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Combined effects of nano-silica and silica fume on the mechanical behavior of recycled aggregate concrete

Nanotechnology Reviews ◽

10.1515/ntrev-2021-0058 ◽

2021 ◽

Vol 10 (1) ◽

pp. 819-838

Author(s):

Tang Yunchao ◽

Chen Zheng ◽

Feng Wanhui ◽

Nong Yumei ◽

Li Cong ◽

...

Keyword(s):

Silica Fume ◽

Structural Engineering ◽

Tensile Tests ◽

Cementitious Materials ◽

Recycled Aggregate Concrete ◽

Supplementary Cementitious Materials ◽

Recycled Aggregate ◽

Hydration Reaction ◽

Nano Silica ◽

Aggregate Concrete

Abstract Recycled aggregate concrete (RAC) is an environmentally friendly material. However, owing to inherent characteristics of the recycled aggregate (RA), it is difficult to promote and apply it in structural engineering. Silica fume (SF) and nano-silica (NS) have different characteristics as additives for RAC. It has been proven that adding SF only enhances the strength of RAC at a later stage, and NS can improve the early strength of RAC owing to its high pozzolanic activity. In this study, to further improve the properties of RAC, two types of additives were combined into RAC, which was named SF-NS-modified RAC (SSRAC). Compression and split tensile tests were conducted to analyze the mechanical properties of SSRAC at different curing ages. The results indicated that the combined addition of NS and SF improved the performance of RAC at early and later curing ages. Scanning electron microscopy and X-ray diffraction analyses were performed to explore the NS and SF mechanism. The results indicated that SF and NS in SSRAC had a good pozzolanic effect and underwent a secondary hydration reaction with calcium hydroxide to increase the production of calcium silicate hydrate, resulting in an increase in the properties of the interface transition zone. Finally, 6% SF and 2 or 3% NS are recommended as supplementary cementitious materials for RAC.

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