Abstract
To better understand the synergistic effects of combined fibers on mechanical properties and durability of recycled aggregate concrete (RAC), different types of fibers with various lengths and mass ratios were adopted in this study. Experimental investigations were conducted to study the 28-day compressive strength and strength loss after exposed to salt-solution freeze–thaw cycles and the coupled action of mechanical loading and salt-solution freeze–thaw cycles. The microstructure was also characterized to evaluate the mechanism of this synergistic effect. To determine the effectiveness of the combined fibers on improving the mechanical properties and durability of RAC, the synergistic coefficient was proposed and applied for various combinations of fibers. The results indicate that the incorporation of fibers slightly decreased the 28-day compressive strength of RAC, but combining different sizes and types of fibers can mitigate this negative effect. Moreover, the incorporation of fibers greatly improves the freeze–thaw resistance of RAC. The combining different fibers exhibited a synergistic effect on the enhancement in properties of RAC, which could not be predicted with only one simplistic rule of fibre mixtures. In addition, microstructural characterization shows that the bonding strength of the interfacial transition zone (ITZ) between the fiber and cement matrix is mainly determined by the chemical bonding force which is due to the hydration reaction between fiber surface and cement matrix.
Highlights
A lot of investigations have been conducted worldwide on the mechanical properties, durability, and structural performance of recycled aggregate concrete (RAC) in realizing the sustainable development of the construction industry (Xiao et al 2012; Behera et al 2014; Safiuddin et al 2013; Hu et al 2019; Tang et al 2020a; Tam et al.Lei et al Int J Concr Struct Mater (2020) 14:372020)
Most of these results indicated that RAC is less durable than natural aggregate concrete (NAC), and the durability decreases with increases in replacement ratios (Abbas et al 2009; Yildirin et al 2015; Bogas et al 2016)
5 Conclusions Based on the investigations on the synergistic effects of hybrid polypropylene and glass fibers on the mechanical properties and durability of RAC in this study, the following conclusions can be drawn up: 1. Incorporating fibers reduces the compressive strength of RAC to a certain extent, but combining different sizes of fibers and different types of fibers can reduce this negative effect and greatly improve the freeze–thaw resistance and durability
Summary
A lot of investigations have been conducted worldwide on the mechanical properties, durability, and structural performance of recycled aggregate concrete (RAC) in realizing the sustainable development of the construction industry (Xiao et al 2012; Behera et al 2014; Safiuddin et al 2013; Hu et al 2019; Tang et al 2020a; Tam et al.Lei et al Int J Concr Struct Mater (2020) 14:372020). RAC generally has a compressive strength that is 10–30% lower than that of NAC (Rahal 2007; Tabsh and Abdelfatah 2009; Poon et al 2004b). Ravindrarajah et al (1987) reported that the splitting tensile strength of RAC was 10% lower than that of NAC. Tabsh and Abdelfatah (2009) reported that splitting tensile strength of concrete made with 100% RCA 10% was reduced by 25%–35% Most of these results indicated that RAC is less durable than NAC, and the durability decreases with increases in replacement ratios (Abbas et al 2009; Yildirin et al 2015; Bogas et al 2016). Many remedial measures for improving the mechanical properties and durability of RAC have been proposed (Li et al 2017b; Shi et al 2016; Dimitriou et al 2018; Tang et al 2020b)
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