Comparison Of Expansive Agent And Crumb Rubber In Crack Resistance Of Mortar Specimens By Restrained Shrinkage Tests

Shrinkage will take place when a cementitious material undergoes hardening process,which will lead to material cracking and eventually the structural failure.Therefore,shrinkage and cracking becomes one of criteria in evaluating the structural durability,and a large amount of resource has been invested into reducing shrinkage and raising anti-cracking ability.Many methods have been developed and one of them is the additive called “expansive agent”.Adding this agent into cementitious material will result in the shrinkage reduction,and it has the history of over half century.Crumb rubber is made by shredding old car tires.During last 10 year or so,a large amount of resources has been invested into studying the effect of adding crumb rubber into cementitious materials,and one major finding is that it will reduce material cracking.Now,there are two additives: expansive agent and crumb rubber,available for controlling of cracking with different mechanisms with the former being the shrinkage reduction and the latter being the brittleness reduction.This thesis proposes to compare those two additives in the regard to cracking property,which is a study that has not been reported in public literature so far.The thesis puts forward a cement mortar as a base material proposition,and upon that a well-round proposition with expansive agent and crumb rubber is presented.There are two types of test methods on shrinkage,one is non-destructive,and the other is destructive.Only destructive tests can achieve the purpose of evaluating and comparing cracking resistance for expansive agent and crumb rubber.Therefore,the latter is adopted with other tests on strength index,which is considered to be essential material property.As such,the thesis takes three material propositions: 1.CM0(ordinary cement mortar);2.RM20(crumb rubber mortar);3.EM10(expansive agent mortar),five tests are planed: 1.Fluidity Test or Flow Test;2.Compressive Strength Test;3.Flexural Strength Test;4.Restrained Ring Shrinkage Test and 5.Restrained externally squared eccentric ring shrinkage test.4 and 5 tests are destructive method.The experimental results show that as far as cracking time is concerned,EMP10 exceeds RM20.The strength reduction is less for EMP10 than RM20 in against CM0.But it is also noted that EMP10 somewhat declines in strength as it gets aged.It appears that more studies are needed for evaluating and comparing expansive agent and crumb rubber for their overall effects on cementitious materials.The 4th test,e.g.restrained ring shrinkage test,enjoys many benefits and widely accepted.But this test method lacks of identifying crack position and shows the large scattering of measured cracking time.This thesis conducts the 5th method,an improved restrained shrinkage test named externally squared eccentric ring test developed by Han Zhu in Tianjin University of China which provides the predetermined cracking position and shortened cracking time,resulting in the enhancement for measuring of restrained shrinkage behavior of the intended material.It is the first time that this thesis employs Zhu's method in evaluating and comparing CM0?RM20,EPM10.