Research Of Cement Paste And Mortar Cracking Test Method

This paper mainly carried out two aspects: First, the evaluation of cement pasteand mortar shrinkage cracking test methods, second，plate of friction on cement pasteand mortar shrinkage and cracking. In the evaluation of shrinkage cracking testmethods, including both existing test equipment for research, but also to explore fornew evaluation methods.1) For the three evaluation methods of traditional ring method, foreign-squareinner-circle eccentric and non-eccentric constraint method, first, the three-dimensionalsolid elements of finite element simulation analysis is carried out, the results showthat in the cracked section the eccentric method stress is largest, non-eccentric methodfollowed by eccentric method but with little difference, the traditional ring method issmallest, the three kinds of specimen maximum stress points is seen on the inner edgeof the cracked section, the eccentric method specimen has a unique maximum stresssection. Secondly, taking cement paste and mortar as the research object, using thesethree methods to test shrinkage cracking, The results showed that the eccentric andnon-eccentric specimen cracking time difference between the two is very small butboth much shorter than the traditional ring cracking time, eccentric specimen canpredict the cracking position, proving that the reason of eccentric method shortencracking time lies not in the inner circle of eccentric, but rather the shape of thespecimen, the significance of the inner circle of eccentric is specifying the sectioncracking position.2) Using foreign-square inner-circle eccentric constraint method studied theinfluence of bottom friction on cement paste and mortar shrinkage cracking. Finiteelement simulation analysis shows: the stress on the designated cracking section,specimen with friction is larger than frictionless specimen; foreign-square inner-circleeccentric constraint method test results that: friction promote the shrinkage crackingof cement paste and mortar; as the water-cement ratio increases, the promotinginfluence has an enhanced tendency; the promoting influence has a universalapplicability; experimental study on shrinkage cracking should choose to keep thebottom; artificially increasing the base friction, can accelerate the specimen crackingand shorten test period.3) To imagine that double constraints to provide double shrinkage stress, we propose a double ring constraint test method. The results show that the cracking timeof the double ring specimens shortened a lot than the cracking time of traditional ringspecimens, longer than foreign-square inner-circle eccentric specimens, theconstraints of two inner steel columns did not make the specimen stress at the crackedsection to achieve the desired linear superposition, but appeared a certain stress losses.4) Through changing the shape of the test piece to change the stress state of thespecimen, we proposed an improved double ring constraint test method. The resultsshowed that this method can predict the position of the specimen cracking, can solvethe problem of traditional ring test method and the problem of inaccurate test results,but its cracking sensitivity is not as good as foreign-square inner-circle eccentricconstraint method, changing the shape of the specimen causing the stress of crackingsection is not conducive to the direction of crack.