The Portland Cement Aggregate Bond: Influence of Surface Area of the Coarse Aggregate as a Function of Lithology

About the report:

Presented is a direct tensile test for measuring the bond of rock or mineral surfaces to portland cement paste, or for measuring the tensile strength of neat paste or of mortar specimens, devised using commercially available gripping devices and preparation equipment. The method of specimen preparation and testing permits the sample to be totally immersed in water throughout its entire history from casting to failure in the testing machine. The results of a series of bond tests on selected materials indicated the following relative order of bonding strength to cement paste: frosted glass, quartz, limestone, neat cement paste, dolomitic marble, and augite. Scanning electron micrographs representative of the minerals used in the bond tests are presented with the conclusion that the apparently smooth surfaces of the minerals have high roughness factors and possess many times the apparent surface area. The importance of the roughness factor in influencing the strength of the cement-aggregate bond is analyzed, and the differential capacity (an electrochemical) method for determining roughness factors is identified as the most promising technique available.

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