Abstract
Abstract Three nano-CaCO3 (NC) replacement levels of 1, 2, and 3% (by weight of cement) were utilized in autoclaved concrete. The accelerated carbonation depth and Coulomb electric fluxes of the hardened concrete were tested periodically at the ages of 28, 90, 180, and 300 days. In addition, X-ray diffraction, thermogravimetry, and mercury intrusion porosimetry were also performed to study changes in the hydration products of cement and microscopic pore structure of concrete under autoclave curing. Results indicated that a suitable level of NC replacement exerts filling and accelerating effects, promotes the generation of cement hydration products, reduces porosity, and refines the micropores of autoclaved concrete. These effects substantially enhanced the carbonation and chloride resistance of the autoclaved concrete and endowed the material with resistances approaching or exceeding that of standard cured concrete. Among the three NC replacement ratios, the 3% NC replacement was the optimal dosage for improving the long-term carbonation and chloride resistance of concrete.
Highlights
Three nano-CaCO3 (NC) replacement levels of 1, 2, and 3% were utilized in autoclaved concrete
To obtain the long-term durability behaviors of NC modified autoclaved concrete, specimens’ accelerated carbonation and Coulomb electric flux experiments were conducted at their ages of 28, 90, 180, and 300 d according to GB/T 50082-2009 (Standard for Test Methods of Longterm Performance and Durability of Ordinary Concrete)
To reduce errors usually occurred in autoclaved concrete specimens caused by solution overheating during the Coulomb electric flux experiment [6,11], the Coulomb charges of concrete were determined using an improved method of multiplying the initial charges of 30 min by 12 [28,32]
Summary
Abstract: Three nano-CaCO3 (NC) replacement levels of 1, 2, and 3% (by weight of cement) were utilized in autoclaved concrete. Results indicated that a suitable level of NC replacement exerts filling and accelerating effects, promotes the generation of cement hydration products, reduces porosity, and refines the micropores of autoclaved concrete. These effects substantially enhanced the carbonation and chloride resistance of the autoclaved concrete and endowed the material with resistances approaching or exceeding that of standard cured concrete. Shaikh and Supit [22] investigated the effects of NC on the mechanical and durability performance of concrete with a high volume of fly ash under room-temperature water curing; they found that a 1% NC replacement ratio results in remarkable improvements in the compressive strength, porosity, water sorptivity, chloride permeability, and chloride ion diffusivity of concrete. The scanning electronic microscopy (SEM) image of NC powder is shown in Figure 1, which is consistent with its particle size
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