- Open Access
Evaluation on the Mechanical Performance of Low-Quality Recycled Aggregate Through Interface Enhancement Between Cement Matrix and Coarse Aggregate by Surface Modification Technology
© The Author(s) 2016
- Received: 1 September 2015
- Accepted: 20 December 2015
- Published: 20 January 2016
In this study, a quantitative review was performed on the mechanical performance, permeation resistance of concrete, and durability of surface-modified coarse aggregates (SMCA) produced using low-quality recycled coarse aggregates, the surface of which was modified using a fine inorganic powder. The shear bond strength was first measured experimentally and the interface between the SMCA and the cement matrix was observed with field-emission scanning electron microscopy. The results showed that a reinforcement of the interfacial transition zone (ITZ), a weak part of the concrete, by coating the surface of the original coarse aggregate with surface-modification material, can help suppress the occurrence of microcracks and improve the mechanical performance of the aggregate. Also, the use of low-quality recycled coarse aggregates, the surfaces of which were modified using inorganic materials, resulted in improved strength, permeability, and durability of concrete. These results are thought to be due to the enhanced adhesion between the recycled coarse aggregates and the cement matrix, which resulted from the improved ITZ in the interface between a coarse aggregate and the cement matrix.
- surface-modification technology
- interfacial transition zone (ITZ)
- low-quality recycled coarse aggregate
- interface strength
In this study, crushed-stone coarse aggregates, whose surfaces had been modified, were used to fabricate the concrete specimens. The bonding performance was assessed and the interface was observed with microscopy. The resulting improvement in the concrete’s mechanical performance and the applicability of the surface-modification technology to low-quality recycled aggregates with low density and large water absorption ratio was determined. Moreover, the effects of surface modification on low-quality recycled aggregates, which are mainly used as a sub-base course material, were examined, and their effects on the mechanical and permeation resistance of the water and deterioration factor into the concrete and durability performance of concrete were reviewed.
3.1 Overview of the Experiment
3.2 Experimental Method
Composition of SMCP.
C × 100
Composition of mortar.
Unit weight (kg/m3)
4.5 ± 1.5
Experimental factors and conditions.
Cutting specimen of crushed hard sandstone (standard density: 2.66 g/cm3; water absorption ratio: 0.70 %)
Normal strength, W/C = 55 %
30°, 45°, 60°
3.3 Compressive- and Tensile-Shear Bond
3.4 Microscopic Observation of the Interface Between Each Aggregate and the Cement Matrix
4 Effects of Surface Modification on the Mechanical Characteristics of Low-Quality Recycled Aggregates
In Sect. 3, the results of examining the bonding performance of the simulated concrete fabricated by performing surface modification on crushed stone coarse aggregate and observing the specimens microscopically showed that it was possible to improve the mechanical performance (improvement of ITZ) of concrete through surface modification. Also, based on the results, it is deemed possible to enhance the mechanical performance of concrete and improve the interface enhancement between cement matrix and low-quality recycled coarse aggregate (LRCA) through surface modification (Xiao 2013). Thus, in this section, an experiment was conducted, according to Japanese Industrial Standards (JIS), for the purpose of reviewing the permeability and durability performance (drying shrinkage, neutralization, freezing-thawing) and mechanical performance of concrete by examining the effect of surface modification on improving the adhesion quality of recycled aggregate.
Type and quality of coarse aggregates.
Standard density (g/cm3)
Water absorption ratio (%)
Composition of modification paste (based on 1 kg of original coarse aggregates) (Choi et al. 2014a).
Table flow (mm)
C × 100
C × 1.9 (b*)
4.2 Composition of Concrete
Composition of concrete.
Unit weight (kg/m3)
180 ± 25
4.5 ± 1.5
C × 0.5(a*)
C × 0.5(a*)
Slump and air content of each type of concrete.
Air content (%)
4.3 Results and Discussion
4.3.1 Mechanical Characteristics
The modification treatment of the surface of adhesive paste consist of a porous causes densification on the surface of recycled coarse aggregates, resulting in higher density and lower absorption ratio compared to low-quality recycled aggregates as shown in Sect. 4.1. On the other hand, large amounts of adhesive paste are present in the low-quality recycled coarse aggregates (Fig. 10) and modified aggregates used in this study, and due to the large sizes of internal pores compared to general coarse aggregates, there may be an increased possibility of penetration of water and harmful substances into the concrete from the external environment. In other words, the progressive penetration of deterioration factors such as water, CO2 gas and chloride ions (Cl−) into the concrete increases permeability, which is highly associated with durability. This in turn accelerates deterioration of concrete and as a consequence, there are concerns of fatal damage to the concrete structure concerned (Jacobsen 1996; Wang et al. 1997; Khatri and Sirivivatnanon 1997). Accordingly, after fabricating concrete using low-quality recycled coarse aggregates and modified coarse aggregates, the water and air permeability coefficients of each specimen were measured and the correlations between the water and air permeability coefficients and compressive strength were analyzed as a means to determine the water tightness and air tightness of each concrete specimen.
When the W/C ratio was 55 %, the improvements in the shear bond strength were confirmed to be due to the SMCP coating, and the ITZ was densified by the admixtures (inorganic materials). The FE-SEM results confirmed that the interface between the SMCA and the cement matrix was denser and ITZ was strengthened with a high level of calcium–silicate–hydrate by the surface modification.
The use of low-quality recycled coarse aggregates (LRCA), the surfaces of which were modified with inorganic materials, resulted in improved strength, permeability, and durability of concrete. These improvements are thought to be due to the enhanced adhesion between recycled coarse aggregate and cement matrices resulting from the improved ITZ that existed in the interface between the coarse aggregate and the cement matrix.
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