Experimental Study On Pressure StrengthCurve Of Pumping Concrete By Rebound Test

Rebound method is widely used for testing concrete strength because it’s simple, convenient and cheap, also it won’t damage the structure of the specimen. Rebound method bases on the rebound strength curve which is mainly influenced by mix proportion, constituent materials, admixtures and curing conditions of the concrete. Recently, the preblend pumping concrete which is mixed with certain content of admixtures has occupied large percentage of concrete market. The admixtures change the formation and petrographic structure of cement hydration products, thus lead to the distinct errors when calculating concrete compressive strength using rebound strength curve of normal concrete. The thesis mainly focuses on the forming of the concrete rebound strength curve, analyzes the factors that affect the curves and then studies the laws of compressive strength as well as the rigidity, consequently gives a suggestion for enhancing the precision of rebound method. The establishment of concrete strength measuring curve in Lanzhou has a significant meaning for utilizing rebound method to test concrete compression strength.The establishment of concrete strength measuring curve includes samples preparations; laboratory test; models forming; data fitting; results analysis and practical assessment. Research indicates that when discussing the relations between compressive strength and rebound value of pumpcrete and normal concrete, discrepancies are found among them. What’s more, the content of fly ash and the constitution of coarse aggregate supposed to be the main factors which influence the errors. When the content of fly ash is over30%, the computative concrete rebound strength will be higher than that of authentic figure, whereas the impact of crushed graits is opposite. The effect of the fly ash and mineral powder on rebound value grows quickly at first (before90days curing), and slows down in the later stage (after90days curing). Fly ash blending causes "carbonization effect" together with "density effect" on surface rigidity of concrete. Besides,"carbonization effect" will become greater than "density effect" as the fly ash content exceeds30%, hence the surface rigidity will be higher than the relevant concrete compression strength. The distinctions of concrete materials and curing conditions between Lanzhou and other districts are determined to result in the greater compressive strength which calculated by rebound strength curve than that obtained by recommended standard strength curve.