Abstract
Cold weather drastically shortens the construction season in northern regions. Low ambient temperatures are known to have detrimental impacts on the reactivity and hardened performance of cementitious materials. This study therefore aims to assess the combined impacts of calcium silicate hydrate (C–S–H) seeds, binary chloride-free antifreeze admixture (i.e., urea and calcium nitrate), and short-period precuring at room temperature (23 ± 1 °C) on ordinary Portland cement (OPC) paste-cured at −10 °C. The heat of hydration, setting time, compressive strength, freezing point, frozen water amount, hydration products precipitation rate, water absorption, and permeable porosity were investigated experimentally. The best results in terms of compressive strength, degree of hydration, water absorption, and permeable porosity were obtained when C–S–H seeds, antifreeze admixture, and precuring were combined due to their mutual impacts. In the absence of room-temperature precuring, C–S–H seeds additive and antifreeze admixture showed negligible acceleration impacts on compressive strength development of subzero-cured paste. The incorporation of seeds and antifreeze admixture decreased the freezing points of the binders and thus protected the admixed binders against frost damage, and their effects were more obvious when combined with a few hours of precuring. The compressive strength of 28 d-old OPC paste modified by C–S–H seeds and antifreeze admixture and treated with precuring developed rapidly at −10 °C, gaining 96% (75.1 MPa) of that measured in control paste cured at room temperature (78 MPa), with comparable durability properties and a significant reduction of energy consumption and CO2 emissions.
Highlights
Urbanization and infrastructure development are constantly increasing worldwide
Heat of hydration The inclusion of calcium silicate hydrate (C–S–H) seeds and/or antifreeze admixture accelerated the hydration rate of the binders according to the hydration heat measurement
Tp were 9 h (6.6 mW/g), 8.6 h (7.3 mW/g), 7.1 h (7.4 mW/g), 6.4 h (8 mW/g), and 6 h (8.2 mW/g) in C0, C0.5, C2, C4, and C6, respectively. This shows that the maximum reduction (≈33.3%) in the induction phase period was gained by the addition of 6 wt% of C–S–H seeds, while the minimum (≈4.4%) was calculated at low seed dosages (i.e., 0.5 wt%) in comparison with C0
Summary
The harsh cold weather significantly shortens construction and maintenance seasons because of its detrimental impacts on cementitious materials’ quality This slows down infrastructure developments and construction schedules in those areas. Several measures, including antifreeze admixtures, thermal systems, heated raw materials, and special cement types (e.g., rapid-hardening cement and calcium sulphoaluminate cement) have been employed in winter construction activities, especially when the ambient temperature is < 5 ◦C [1,10,12,13,14,15,16,17] These measures aim to protect the fresh concrete against freezing during its plastic and hard ening states, as well as accelerating the early hydration reaction of the cement. The usage of antifreeze admixtures in cold weather concreting works is the most economical and applicable option [9,15]
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