It is well known that fresh concrete may be susceptible to plastic shrinkage cracking. Suchkinds of cracks may not endanger the present service ability of concrete structure butsignificantly impact its durability. There has been a great efforts devoted to this topic but thebehind mechanism is still far beyond understanding. In this paper, a modified restrained slabtest was developed which provided both base central restraint and around restraint. A mini-tensiometer was introduced and then the pore pressure (both at surface and bottom layer)could be monitored continuously till crack observed. The crack patterns, crack initiation timewere compared. Combining with high resolution laser displacement transducer the settlementand the water evaporation was continuously monitored. The tensile strength of the surfacelayer at crack initiation was measured. Four kinds of slurries were designed to investigate theparticle size, particle space and cement hydration on plastic shrinkage cracking. Thepreliminary comparative results provide possible quantitative explanations of the mechanismfor plastic shrinkage cracking of cement based materials.
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