Abstract
Reinforced concrete structures are an essential part of our modern society, and monitoring their structural health is of paramount importance. Early detection of decay allows for the reduction of repair costs and, more importantly, the prevention of catastrophic failure. For this purpose, a single fiber reflectance spectrometer was embedded in cement paste samples for the monitoring of water at the fiber tip through its sensitivity to changes in the refractive index. It monitored the curing of samples with different water-to-cement ratios (w/c), between 0.45 and 0.60, measuring the water exhaust during the hardening of the cement paste. It also measured the capillary coefficient from cement paste samples of 0.50, 0.55 and 0.60 w/c: 0.668 ± 0.002 mm/√h, 1.771 ± 0.052 mm/√h and 6.360 ± 0.269 mm/√h, respectively. The capillary coefficient values agree with gravimetric measurements of sorptivity and are further confirmed through porosity measurements made with a scanning electron microscope. Thus, single fiber reflectance spectroscopy can be a gateway to inexpensively measure the entire life cycle of cement, from its curing until its eventual decay, assessing, in situ, its durability through the capillary coefficient.
Highlights
Accepted: 1 November 2021Reinforced concrete has been a go-to for infrastructure and housing projects in the last century and is paramount for our developed society
The capillary coefficient values agree with gravimetric measurements of sorptivity and are further confirmed through porosity measurements made with a scanning electron microscope
The dissolution of cement grains occurs in a brief exothermic reaction, during which the formation of ettringite restricts the further dissolution of cement grains
Summary
Accepted: 1 November 2021Reinforced concrete has been a go-to for infrastructure and housing projects in the last century and is paramount for our developed society. The properties of concrete are established early on during the hydration of cement and depend on the water-to-cement ratio (w/c), the type of cement used, the added aggregates or pozzolans and the curing methods employed [3,4]. Cement advances to the phase of hydration—dormancy This lasts between two to four hours, whilst water begins to be saturated with calcium and hydroxide ions. This triggers the formation of calcium–silicate–hydrate (C-S-H) and calcium hydroxide (CH) in an exothermic reaction, causing the cement to become stiffer—hardening. These hydration products, C-S-H and CH, begin to limit the dissolution of cement, which lowers its temperature—cooling. Over time undissolved cement continues to hydrate, leading to its densification
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