210 TESTS ON CEMENT 



must be well protected, as exposure to heat, cold, dampness, 

 or any other abnormal condition may seriously affect the 

 results. 



PURPOSE AND CLASSIFICATION OF TESTS 



In order that a mortar or a concrete made with cement 

 shall give good results in actual construction it must possess 

 two important properties, namely, strength and durability. 

 The primary purpose of cement testing, therefore, is to deter- 

 mine whether any particular shipment of cement possesses 

 sufficient strength and durability to admit of its use in 

 construction. 



A determination of the quality of cement necessitates the 

 employment of several tests, which may be classified as 

 primary tests and secondary tests. The former tests, which 

 include tests for soundness and tensile strength, are made to 

 give directly a measure of the essential qualities of strength 

 and durability. Unfortunately, neither of these tests is 

 capable of being made with precision. Therefore, the second- 

 ary tests, which include tests to determine the time of setting, 

 the fineness, the specific gravity, and the chemical analysis, 

 are made to obtain additional information in regard to the 

 character of the material. However, with the possible 

 exception of the test of time of setting, the secondary tests 

 have but little importance and only indicate by their results 

 indirectly the properties of the material. 



PRIMARY TESTS 



TESTS FOR SOUNDNESS 



Soundness may be defined as the property of cement that 

 tends to withstand any forces that may operate to destroy 

 or disintegrate it. This property of soundness, or, as it is 

 sometimes called, constancy of volume, is the most important 

 requisite of a good cement. 



The most common cause of unsoundness in Portland 

 cement is an excess of free or uncombined lime, which 

 crystallizes with great increase of volume, and thus breaks 

 up and destroys the bond of the cement. This excess of lime 



