MANUAL V/S MECHANICAL MIXING: ITS IMPACT ON CEMENT STRENGTHS 

Cement testing as per Indian standards IS: 4031, i.e., primarily determination of Normal Consistency of cements and subsequently gauging of cement mortar is  carried out manually and requires skill and experience for better accuracy, precision and reproducibility. In the changing times with less skilled manpower the manual methods result in issues of reliability and reproducibility

 At the authors’ lab, substantial test data were generated, so as to have comparison of cement mortar tests’ results for OPC, PPC & PSC gauged with manual and mechanical mixing (using Hobart mixer) & with normal consistency water being determined manually, as per BIS specifications. The paper discusses these results in details.

Detailed analysis of the available test data of different types of cements (OPC, PPC and PSC) indicated that although the testing was based on normal consistency water, the normal consistency is a function of the type of cement; and it was observed that OPC, PPC and PSC exhibited a clear consistent value of   W/C of 0.38, 0.43 and 0.41 respectively.

Further tests were conducted at authors’ labs to compare the tests results of the three varieties of Cement (OPC, PPC, PSC) tested using the fixed W/C ratios (0.38, 0.43 and 0.41 respectively) with mechanical mixing and gauged manually as per BIS guidelines. For some of the select cement samples the mortar tests were conducted at W/C ratio of 0.5 and mechanical mixing as used in European standards.

The paper discusses the comparison of the test data in details and finally concludes that the mechanical mixing has high reproducibility, reliability and precision. Another observation made is that taking a fixed W/C for OPC (0.38), PPC (0.43) and PSC (0.41) and with Mechanical mixing, the mortar results are comparable to test results of these cements tested as per IS 4031 methods. These observations could be useful from the angle of aligning BIS methods of testing with EN/ISO methods.

This paper was published and presented at the 15th NCCBM International Conference