Deformation And Crack Resistance Properties Of Concrete With Novel Expansive Agents

Mass concrete was used more and more widely with the increasing of the investment intransportation, water conservancy and other infrastructure. The problems of cracks in concrete havebecome more serious, and the function and durability of concrete will be affected. It is of greatsignificance to control concrete cracks and to take effective measures to prevent and reduce concretecracking. Adding expansive agents in concrete and designing the expansion volume, time and effectcan make the expansion properties of the expansive agents match to the shrinkage of concrete, whichis an effective method to resist and reduce shrinkage.In this paper, the deformation and crack resistance properties of conventional concrete andhydraulic concrete with four novel expansive agents and fly ash cured in different curing temperatureswere studied in details, and the expansion mechanism and microstructure of expansive agents werealso discussed. The main experimental contents and results show as follows:1The effects of the novel expansive agents and fly ash on the free and restricted deformation inconcretes were studied. The results showed that the expansion of the concrete increased with thecontent of the expansive agents. The expansive agents M3and M4displayed greater compensationeffect, and the expansion deformation increased uniformly, but M1and M2, whose expansion ishigher at late stage and did not increase uniformly. The free and restricted deformation curves ofconcrete mixed with the expansive agent were similar, but the restricted ones were more gently. Theexpansion rate of concrete mixed with the expansive agent was significantly accelerated as the curingtemperature increased, which was1.5~3times as the one at lower temperature for the same age period.Expansive agents M3and M4temperature-sensibility was higher at early stage, but for the expansiveagents M1and M2, it was higher at the late stage. The admixture of fly ash can significantly inhibitthe performance of the expansive agents.2The autoclave expansion ratio of concrete mixed with the expansive agents was studied. Theresults showed that the autoclave expansion ratio of concrete mixed with the expansive agentsincreased with the content of the expansive agents. The autoclave expansion ratio of concrete has theincreasing trend as the autoclave temperature or holding time increased. When the content of M2increased from6%to8%, the autoclave expansion rate of hydraulic concrete appeared more steeply,and the autoclave expansion ratio was as high as0.158%. As the content of M4in the conventionalconcrete increased to10%, the concrete did not appear unhealthy phenomenon. 3The crack-resistance properties of concrete with the expansive agents were performed throughthe ultimate tensile strain of mortar and the autogenous volume deformation of concrete. The resultsshowed that the ultimate tensile strain of mortar increased as the expansive agents were mixed in, andthe ultimate tensile strain of mortar did not increased obviously when the content was more than10%.The ultimate tensile strain of mortar increased uniformly as the curing temperature increased.Compositing with the expansive agents and fly ash, the ultimate tensile strain increased more easily.When the expansive agents were added, the autogenous volume deformation of concrete increasedwith the age in a logarithm law, and there was no excessive expansion and retraction. The autogenousvolume deformation became stable when the age is120d. Crack-resistance ability evaluation modelshowed that when the content of M4is8%or M2is6%, the concrete had better crack-resistanceproperties.4The size of crystals of hydrated expansive agents increased with the curing time. When thepaste was cured in water for180days, the hydration products were fiber-shaped crystals which wereabout3~5μm in length and0.3~0.5μm in width. Fly ash had its own special structure and particleshape, so the expansion effects of the expansion materials were greatly restrained.