Some Statistical Properties of Strength of Cement Paste and Mortar

Abstract

In the present paper, some statistical properties of the strength of cement paste and mortar are discussed in relation to their fracture process or failure mode. The variables chosen in the experiment are the kind and content of defect (air void or aggregate) in a specimen and the size of specimen.
The main results obtained are summarized as follows:
(1) The fracture process of cement paste and mortar becomes stabilized as the air or aggregate content increases.
(2) The larger the size of specimen is, cement paste and mortar show the more stable or ductile fracture process in the range of small size, but their fracture process transforms from ductile mode to brittle mode as the size of specimen becomes larger than a specific size.
(3) The statistical distribution of strength is closely related to the fracture process and the failure mode. The mean slope of the distribution curve of strength illustrated in the relation between ln(-ln(1-P)) and ln(F) increases as the fracture process is stabilized.
(4) The mean strength decreases with the increase of air content, and the rate of decrease of compressive strength is more significant than that of flexural strength.
(5) The aggregate plays the following two conflicting roles for the strength of mortar, i. e., the role as a defect which deteriorates the strength and the role as a crack-arrestor which improves the strength.
(6) The scale effect of the strength of mortar is more significant as the aggregate content becomes lower.