|M.Sc Student||Kovalchuk Kogan Tatiana|
|Subject||Development of Methods for Real Time Estimation of|
Cement Contents in Concrete
|Department||Department of Chemistry||Supervisors||Professor Israel Schechter|
|Professor Emeritus Izhack Oref|
|Full Thesis text|
Concrete is one of the most used materials in modern building technologies. The compressive strength of concrete is the most important property for quality control in concrete production and construction. Hence, knowing the potential concrete strength at the earliest time after concrete pouring, especially in a few hours, can be beneficial if necessary remedy or adjustments are required. Cement is an important ingredient in concrete and the ultimate strength of concrete in later years is related to water/cement ratio (w/c), thus it is important to know its amount in concrete.
Currently, methods that are used for testing the strength of concrete are mechanical. The results are obtained only after a long period of time (28days). In addition, those tests can be conducted only after the concrete has been solidified. There are no useful and short methods for prediction the concrete strength in early state.
The present research is focused on developing new methods for estimating cement content in concrete, which generate near on-line results and can be applied even at the plastic state of concrete. Those methods used fluorescence spectroscopy.
The new methods are based on fluorescence spectroscopy of two kinds. Direct analysis: native fluorescence of analyte was measured, and indirect analysis: indicator fluorescence was converted to the amout of cement in the concrete. All methods have shortened the test time to few days and some of them to a few hours. New methods are: characterization of cement powder and concrete plate’s surface, marker extraction methods and experiments with plastic concrete.
In the direct method of cement powder characterization, calibration curves for cement amounts in the sample were obtained. The analysis time was 4 hours for each cement types.
In surface investigation, a dependence of fluorescence markers for cement on its concentration in concrete was shown. The extraction methods of cement markers from concrete have shown a strong linear dependence of fluorescence signal on the indicator percent in concrete. Extraction methods also show a dependence of fluorescence intensity on stirring time of the concrete sample. Calibration curves for cement concentration in concrete were derived using the proposed new extraction methods. An extraction method with glass filter can shorten a test time from 28 days to one hour.
Although all the methods require previous experimental correlations and depend on the kind of used cement, it can indicate cement concentration in concrete sample in short period of time. Also a brief test can be made for evaluating the w/c ratio.