Akademik Veri Yönetim Sistemi
JOURNAL OF MATERIALS IN CIVIL ENGINEERING, cilt.19, sa.8, ss.674-682, 2007 (SCI-Expanded, Scopus)
The results of early age reflection and transmission properties of young mortar samples with different water-to-cement ratios (w/c) changing between 0.40 and 0.60 with a 0.05 of increment are presented. Hourly nondestructive and noncontact measurements are conducted during 20-30 and 44-54 hours at X band (8-12 GHz) by free-space method. Two measurement systems are used for comparison and validation of measurements. One is a simple and relatively inexpensive (direct current volt meter and T-meter combination) and the other is expensive and complex in operation (Agilent Technologies power meter). A new approach (relative slope approach for reflection properties) is introduced to predict the history of the hydration process of young mortar samples. It is shown that the difference between the relative slopes of reflection properties of mortar samples with 0.40 and 0.45 w/c ratios is greater than that of other mortar samples whose w/c ratio difference is 0.05. This result shows that a mortar with a lower w/c ratio will gain hydration (and strength) quicker than the one with a higher w/c ratio (a nonlinear relationship between the degree of hydration and w/c ratios at early ages of curing). It is shown that a lower amplitude of transmission coefficient corresponds to the young mortar sample with a higher w/c ratio at early ages of curing. This is the opposite case for hardened cement samples. Therefore, early age transmission properties can be used to monitor the porosity level inside cement samples and this monitoring can be very useful for the quality enhancement of these samples. It is observed that the measurement results of both systems are almost the same (maximum 4% difference), and simple and relatively inexpensive system can be adapted for the detection of hydration, evaporation process, and porosity level detection inside cement samples at construction site.