Rajesh, M; Geetha, K; Sheeba, M; Radhakrishnan, P; Vallabhan, C P G; Nampoori, V P N(Elsevier, May , 2006)
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Abstract:
A simple, effective and inexpensive fiber optic sensor for investigating the setting characteristics of various grades of cement is described. A finite length of unsheathed multimode optical fiber laid inside the cement mix, is subjected to stress during the setting process. The microbends created on the fiber due to this stress directly influence the intensity of light propagating through the fiber. Continuous monitoring of such variations in the light output transmitted through the fiber gives a clear measure of the setting characteristics of the cement mix, thus providing a simple and elegant technique of great practical importance in the field of civil engineering. The smart fiber optic sensor described above can be incorporated into a building during the construction process itself so that continuous monitoring of the deterioration process for the entire life time of the building can be carried out.
Deepa, Nair G; Alex, Fraaij; Adri, Klaassen A K; Arno, Kentgens P M(Elsevier, 2008)
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Abstract:
Various factors determine the applicability of rice husk ash (RHA) as a pozzolanic material. The amount and accessibility of reactive sites is
thought to be a key factor. A structural study of RHA samples in relation to their reactivity has been performed; Silica in RHA formed by burning
rice husk in a laboratory furnace under continuous supply of air have been characterized as a function of incineration temperature, time and
cooling regime. The characterization methods included chemical analyses, conductivity measurements, microscopic analysis, X-ray diffraction
(XRD) and 29Si magic-angle spinning (MAS) nuclear magnetic resonance (NMR). In line with earlier observations, the analyses show that the
highest amounts of amorphous silica occur in samples burnt in the range of 500 °C–700 °C. The 29Si NMR data allow direct identification of the
reactive silanol sites in the RHA samples. De-convolution of the NMR spectra clearly shows that the quickly cooled RHA resulting from burning
rice husk for 12 h at 500 °C has the highest amount of silanol groups. This sample also induced the largest drop in conductivity when added to a
saturated calcium hydroxide solution giving an indication of its reactivity towards lime. Therefore, this RHA is the favorable sample to be used as
pozzolanic cement additive