Quality Assessment of Cement based on its dielectric parameters

Transcription

1 Quality Assessment of based on its dielectric parameters Dr. S.Arul Mary 1, S.Srimathi 2, S.Sudarsan Vakul 3 1 Associate Professor,Department of Civil Engineering, Thiagarajar College of Engineering, Madurai, INDIA Abstract: being the most important material in the construction field, is required to be free from adulterations and conform to the standard quality range. The conventional test methods yield only the basic properties of cement like fineness, soundness, setting time, consistency, specific gravity, etc. The need for an instant, reliable and economic method to classify cement based on its quality and composition can be served through Non-Destructive Evaluation of for its Dielectric Parameters, by the application of Microwaves. Therefore the determination of dielectric constant through Microwave Non- Destructive Evaluation is performed and the results obtained for Ordinary Portland of Grade 53 are discussed in this paper. This research extends to assessing the quality of cement based on the composition of cementitious sample, type of adulteration and the quantity of adulterant(s) in the sample. W ith the dielectric parameters known, contribution to the Quality Assurance/Quality Control area in identifying even minute deviation of cement from standards by means of a reliable technique is achieved and the subject shifts from probability to a possibility. Keywords : Quality of cement, testing, Non-Destructive Evaluation of I Introduction adulteration is basically the addition of non-cement material to cement. Where cement is supposed to help in bonding to attain strength in structures, adulterated cement will refuse to bind when mixed even in proper proportion. Adulteration in cement will lead to improper mortar formation, variation in setting time of cement and thereby question the quality of cement used. There have been few attempts in the past in quantifying the non-cement material present in large quantities of cement; however they were defective in some means. The conventional methods of testing the cement yield only the physical and chemical properties of cement and hence to determine the quality of cement for utilization, we need to carry out all of these tests. This requires a lot of time and effort and furthermore is not reliable. This can be overcome by Non-Destructive Evaluation of using Microwaves. It has been made possible to determine the dielectric parameters of many materials and composites by making use of the Material Measurement equipment of the Agilent Technologies. In this paper, this application has been extended to cementitious samples. The use of microwaves for testing and evaluating the performance of cement will be a great value addition to the existing practices of Non- Destructive Evaluation of materials. This method offers greater precision in characterization of materials by ensuring the quality of any huge quantity of cement required for construction. It is 28

2 aimed to serve the manufacturers, customers and quality assurance/quality control department so that sufficient quality of cement is maintained and adulteration can be minimized. II Adulteration in cement The common adulterants in cement include Fly ash, Coal, Carbonate additions, finely powdered slag and other materials resembling cement. These adulterants when present in cement are likely to cause weakening of structures. Concrete made from adulterated cement may withstand initial loads but is likely to collapse over time and under unusual loads, especially during hurricanes, typhoons, tsunamis, floods, etc. Ultimately the strength of concrete and in turn the structure is compromised. III Microwave application Microwave and its precise application becomes one of the widely used techniques in many areas of Engineering, owing to its high range of frequencies (300 MHz to 300 GHz). Microwaves are not hazardous and scatter less compared to acoustic waves. They have good spatial resolution and good penetration power in non-metallic materials. The technique based on application of microwaves is relatively cost effective and reliable compared to radioactive methods. This method can be used to prepare a data base of signatures that prescribes standard values of dielectric constants for pure cement and its mixtures that are in use in the field and for commonly adulterated cement mixtures. IV Literature Review Hasar. U.C(2009) [1] devised a simple and relatively inexpensive microwave set-up, which is suitable for industrial-based applications, constructed from discrete microwave components for ε r measurements of fresh cement-based materials by using amplitude-only reflection measurements from an open-ended waveguide probe at different frequencies. Kharkovsky. S.N [1] determined the microwave transmission and reflection properties measured from various sides of hardened mortar and concrete specimens with different water to cement ratios by Non-Destructive Testing of specimens at micro wave frequencies Free-Space method. K.Arunachalam et.al.(2006) identified that the permeability and permittivity were the useful microwave parameter to identify the density of the medium. Considering the possibilities of the application of microwaves to characterize cement based samples and their extension to determine the quality of cement, yet unexplored, this research focuses on capitalising on potential of microwaves and its usefulness in Non- Destructive evaluation of cement and cement mixtures for their standard. V Equipment for testing of cement under microwaves The Material Measurement Software of Agilent Technologies as shown in figure 1, based on a versatile network analyzer which measures the material s response to RF or microwave energy is capable of automating Complex Permittivity and Permeability measurements and determining the intrinsic electromagnetic properties of many dielectric and magnetic materials. It is proposed to extend the application of this setup to cement based samples to determine the dielectric constants of samples of different composition. The Coaxial airlines as shown in figure 1 are used as sample holders. The transmission line method works best for materials that can be precisely machined to fit inside the sample holder. It features an algorithm that corrects the effects of air gap between the sample and holder, considerably reducing the largest source of error with the transmission line 29

3 technique. A vector network analyzer is a test system that enables the performance of radio frequency (RF) and microwave devices to be characterized in terms of network scattering parameters or S parameters. The equipment under use prescribes a frequency range of 100 MHz to 325 GHz with an accuracy of 1.0 to 2.0 percentile. research is to estimate the quality of cement based specimens, in terms of scattering parameters (S parameters) permittivity and permeability that are unique for different compositions of samples. The cavity of the coaxial was coated with gold so that the readings obtained are only from the sample placed inside it. Fig. 1 Experimental Setup VI Experimental Evaluation In order to obtain accurate values of dielectric constants, samples were cast in specific dimensions to suit the cavity that is compatible with the equipment. The sample for testing is required to be a hollow cylinder with an outer diameter of 7mm, inner diameter of 3mm and a minimum height of 15mm. A die as shown in figure 3 made of mild steel and coated with arch chromium was designed to prepare cement samples with handling strength. Ordinary Portland of grade 53 was taken as the initial material and three samples were prepared to carry out the test since the IS code specifies the use of three specimens for experimental evaluations on cementitious material. A water to cement ratio of 0.35 was observed prior to casting and the samples were demoulded after the samples attained final setting time. Precision was observed in obtaining proper inner and outer surface in the samples as shown in figure 2. These samples were tested for dielectric parameters. The scope of this Fig. 2 Die and sample VII Results The material measurement software gave the pattern of dielectric constant value for the samples 30

4 over the frequency range of 100 MHz to 6 GHz. It can be seen from the graph in figure 3 that the dielectric constant value ranges from 6.00 to 7.00 and forms a constant pattern over the frequency range 0.56 GHz to 6GHz. It can also be seen from figure 4, 5, 6 and 7 that the reflection constant values (S 11r, S 11i, S 22r and S 22i ) are very close to zero. This confirms that the frequency range used is optimum. A comparative study on the values of S 12r and S 21r was performed and is represented in figure 8. It can be observed that the graphical pattern of both these values over the frequency range matches and thus ensure the reliability in testing methodology and the accuracy in the frequency range used. Fig. 5 Pattern of S 11i value for OPC Grade 53 Fig. 6 Pattern of S 22r value for OPC Grade 53 Fig. 3 Dielectric Constant of OPC Grade 53 Fig.7 Pattern of S 22i value for OPC Grade 53 Fig. 4 Pattern of S 11r value for OPC Grade 53 31

5 IX Conclusion Fig. 8 Comparison of S 12r and S 21r values for OPC Grade 53 VIII Discussions The application of microwaves in order to determine the dielectric parameters of cement has given way to standardize a reliable testing mechanis m to estimate the quality of cementitious materials. The observations made in this research yield the following methods of comparative testing of unknown samples: 1. The dielectric constant of OPC 53 Grade represents a signature pattern over the frequency range of 100 MHz to 6 GHz and is used to compare with the pattern represented by any unknown material. 2. A set of frequencies at regular intervals is chosen and the corresponding dielectric constant values are used to compare similar readings obtained from unknown material samples. 3. The frequency range at which the dielectric constant value is nearly same and forms a horizontal pattern is used to compare with the pattern or dielectric constant value obtained at that frequency range for unknown material samples. A reference has been set to test Ordinary Portland of Grade 53 based on its dielectric parameters by the application of microwaves through coaxial cavities. The research is the extension of the application of microwaves to cement based samples in characterizing them to different grades, compositions and adulteration levels. A minimum of three samples for each composition is mandatory in determining the S parameters which in turn provides signature and values of dielectric constants. Eventually a database of dielectric parameters shall specify to which grade or composition an unknown sample conforms to, by testing under microwaves. This shall be prescribed as a reliable ad economic method of quantifying adulterants and ensuring the quality standards of cement based materials. References [1] Hasar. U.C(2009), Permittivity Determination of Fresh -based Materials by an Open- Ended Wave Guide Probe using Amplitude-only Measurements, Progress In Electromagnetics Research, PIER 97, 27 43, [2] Kharkovsky. S.N, Hasar. U.C, Atis. C.D and Dover. S, Electro magnetic Properties of based materials over time at Microwave Frequencies. [3] Lawluvi. H, Kpeglo. D.O, Fammu. A, Deatanyah. P and Wotorchi. S.G,Arwui. C.C, Darko. D.O, Emi-Reynolds. G(2011), A Multivariate Statistical Approach to Detecting Adulteration of using Gamma Spectroscopy, International Journal of Science and Technology, ISSN , Volume 1 No

6 [4] SanjivK.Dhanjal(FCT), Lloyd Young(Ash Grove )and Peter Storer (FCT), Automatic Control of Quality using On-Line XRD. And itious Additions, International Centre for Diffraction Data 2004, Advances in X-ray Analysis, Volume 47. [5] Walenta. G andfüllmann.t(2006), Advances In Quantitative XRD Analysis For Clinker, s 33