Single Fiber Reflectance Spectroscopy for the Monitoring of Cement Paste

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.

Optical fiber sensors for monitoring cement paste carbonation

“…Single fiber reflectance spectroscopy [9] was used to monitor the changing color of cement paste due to the carbonation process. Figure 1 (a) displays the setup used for this purpose.…”

“…Light is reflected at the fiber tip, depending on the refractive index and color of the cement paste, and is transported into a spectrometer. Previously this setup was used to monitor the rate of water ingress to estimate the capillary coefficient of the cement paste and, hence, its durability [9]. This was possible, because the higher refractive index of water relative to air would decrease the reflectance of light at the fiber tip.…”

“…Some of them are alkali-silica reactions [5], ion chloride ingress [6], freeze and thaw [7] and carbonation [8]. All these mechanisms are influenced or require water to occur, which denotes the importance of its monitoring in concrete [9]. And all these mechanisms produce cracks on concrete, which will further expose these structures to further deterioration.…”