Mechanical properties and microstructure of nano-SiO₂ and basalt-fiber-reinforced recycled aggregate concrete

Abstract

In this study, nano-SiO2 (NS) and basalt fiber (BF) were used to improve the quality of recycled aggregate concrete (RAC). The crushing value, water absorption, and apparent density of NS-modified recycled coarse aggregate (RA) were determined, and the effects of BF with different contents and lengths on the slump, compressive strength, splitting tensile strength, and flexural strength of RAC and BF-reinforced RAC containing NS-modified RA were analyzed. Finally, the filling effect of NS, the toughening and crack resistance mechanism of BF, and the micro-composite effect between NS and BF were analyzed based on scanning electron microscope (SEM) and energy-dispersive detector (EDS) measurement. The results show that the optimum modified concentration of NS solution is 2%, the content of BF is the main factor affecting the mechanical properties of concrete, and the optimum length and content of BF are 12 mm and 0.2%, respectively. For BF-reinforced RAC containing NS-modified RA, the 28 day compressive strength, splitting tensile strength, and flexural strength of RAC increase by 34.28, 40.55 and 54.5%, respectively. Based on SEM and EDS measuring, NS can react with Ca(OH)2 crystal to form flocculent C–S–H gel, which makes RAC compact and enhances the bonding properties of the interfacial transition zone (ITZ) between BF and the matrix.

Mechanical Properties and Durability of Geopolymer Recycled Aggregate Concrete: A Review

“…This is due to the cracks that tend to form in the aggregate during the manufacturing process of RA and the presence of porous mortar attached to the aggregate [ 63 ]. In order to improve the high-water absorption and porosity defects of GPRAC, significant results can be achieved by using several methods; these include surface modification of RCA [ 76 ], reduction of the aggregate/ash ratio, and appropriate increase in the amount of fine aggregates [ 77 ]. MK also plays a filling role because of the fine particles, making the matrix and interfacial transition zone (ITZ) denser.…”

Effect of Recycled Aggregate and Slag as Substitutes for Natural Aggregate and Cement on the Properties of Concrete: A Review

“…The RA extracted from waste concrete that is subsequently crushed and sieved by a grinder is generally composed of 65%-70% natural coarse and fine aggregates and 30%-35% old cement paste [15]. Owing to the presence of the old cement mortar, the aggregate has high water absorption and porosity and low density, thereby resulting in a low compressive strength [69][70][71]. Owing to the high absorption of the RA, the water-cement ratio around the aggregates decreases significantly; the incomplete hydration around these aggregates and the higher porosity of the RA increase the stress in the RAC around these aggregates, thereby reducing its strength [72].…”

Macro-Mesoscale Mechanical Properties of Basalt-Polyvinyl Alcohol Hybrid Fiber-Reinforced Low-Heat Portland Cement Concrete

“…According to the available research results, the design principles of concrete cubic compressive, tensile, and flexural resistance can be used when the fiber content is low. This method is approximately the same as the design method for the plain concrete mix proportion [ 39 ]. According to the experience of fiber-reinforced concrete mix proportion design combined with the mix proportion design method in ACI 211.1 [ 40 ], the preliminary mix proportion design of concrete was carried out.…”