Abstract
This study focuses on two separate investigations of the main aging mechanisms: alkali–silica reactivity (ASR) and the corrosion of reinforcing steel (rebar) concrete, both of which may result in a premature failure to meet the serviceability or strength requirements of a concrete structure. However, these processes occur very slowly, spanning decades. The impact of direct chemical additives to fresh concrete to accelerate ASR and the corrosion of reinforcing steel on the fresh and hardened properties of the ensuing material are investigated to inform the potential use of chemicals in large-scale studies. The deterioration of reinforced concrete (RC) is determined by means of expansion, cracking, bulk diffusivity and surface resistivity measurements, and compressive, split tensile and flexural strength tests. The results indicate that the addition of sodium hydroxide and calcium chloride can effectively accelerate the crack formation and propagation in concrete due to ASR and the corrosion of rebar, respectively. The ASR-induced cracks maintained a constant crack width from 0.05 mm to 0.1 mm over the measurement period regardless of the intensity of aging acceleration. Adding 4% chloride by weight of cement for accelerating rebar corrosion resulted in an average crack that was 82% larger than in the case of ASR accelerated with the addition of sodium hydroxide. The addition of alkali resulted in an increase in early-age (7-day) strength. At a total alkali loading of 2.98 kg/m3, 3.84 kg/m3 and 5.57 kg/m3, the 28-day compressive strength of concrete decreased by 3%, 10% and 24%, respectively. Similarly, a higher early-age strength and a lower later-age strength was observed for the concrete in the presence of corrosive calcium chloride. The results from this research are expected to inform future studies on the long-term performance of RC structures under accelerated ASR and corrosion.
Highlights
Aging in reinforced concrete (RC) structures occurs due to a combination of physical [1,2,3], thermal [4,5], chemical [6,7,8,9] and mechanical [10] effects
Pesavento et al [18] explained alkali–silica reactivity (ASR) as the reaction of the hydroxyl ion (OH− ) of the alkalis from hydraulic cement or other sources with the silanol groups (Si-O), and the breaking of the siloxane bonds of the silicon atom from the lattice [19], forming a hydrophilic alkali–silica gel consisting of silica, alkalis, water and other ions [18]
The results presented in this paper add to the existing datasets to improve the understanding of the ASR and corrosion degradation of concrete structures and how accelerated aging studies can be conducted with minimal influence on the concrete properties to represent the field conditions
Summary
Aging in reinforced concrete (RC) structures occurs due to a combination of physical [1,2,3], thermal [4,5], chemical [6,7,8,9] and mechanical [10] effects. The aging mechanisms may include cracking due to temperature variations [11], creep and shrinkage [12], the alkali–silica reactivity (ASR) of concrete [13,14,15] and the corrosion of reinforcing bars (rebar) [16,17] These effects may result in lower mechanical resistance and failure to meet serviceability or strength criteria in RC structures. Pesavento et al [18] explained ASR as the reaction of the hydroxyl ion (OH− ) of the alkalis (sodium and potassium) from hydraulic cement or other sources with the silanol groups (Si-O), and the breaking of the siloxane bonds of the silicon atom from the lattice [19], forming a hydrophilic alkali–silica gel consisting of silica, alkalis, water and other ions [18] The swelling of this gel generates stresses and osmotic pressure, and may result in in the cracking and failure of the concrete [20].
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