Influence On Performance Of High-flowing Concrete By Admixture And Maximum Dosage Determined

With the development of concrete technique, high-flowing concrete has been widelyapplied with its good workability and durability, mineral admixture has become one of thenecessary raw materials of high-flowing concrete. The current specification for mixproportion design of ordinary concrete stipulates the maximum dosage of mineraladmixture in concrete: Employing ordinary Portland cement,when the water-binder ratioless than or equal to0.4, maximum dosage of fly ash and powder slag are35%and55%respectively;when the water-binder ratio greater than0.4, maximum dosage of fly ash andpowder slag are30%and45%respectively.As a new type of mineral admixture, range ofdosage of grounded fluidized bed coal slag has not been stipulated.This paper employ flyash, powder slag and grounded fluidized bed coal slag as mineral admixture ofhigh-flowing concrete respectively,influence on workability of concretemixture,compressive strength,anti-carbonization and anti-chloride ion penetration ofhardened concrete is studied by the dosage of different admixture and water-binder ratio,atthe same time,the relationship between the compressive strength of28d of high-flowingconcrete with different mineral admixture and binder-water ratio is analyzed.Hoping toprovide basis for definition of different range of water-binder ratio, the maximum dosageof admixture in the different range of water-binder ratio and the calculation of water-binderratio.The main conclusions are as follows:(1) When the dosage of fly ash increases from30%to40%with the water-binder ratio0.4,the workability of concrete mixture are almost the same,all meet the requirements ofhigh-flowing concrete, compressive strength of28d is in C40strength grade, theaccelerated carbonation depth of28d only increases by0.9mm, the electric flux of concreteincrease slightly but belong to the same level.Therefore,the maximum dosage of fly ash is40%.(2) When the dosage of powder slag increases from45%to60%with thewater-binder ratio0.4,the workability of concrete mixture are almost the same,all meet therequirements of high-flowing concrete, the compressive strength of28d is in C40strengthgrade, the accelerated carbonation depth of28d only increases by1.1mm, the anti-chlorideion penetration meet the role of the environment50years F level,and belong to lowpermeability concrete level. Therefore,the maximum dosage of powder slag is60%.(3) When the dosage of grounded fluidized bed coal slag are35%,40%,45%and 50%with the water-binder ratio0.4, the workability of concrete mixture are almost thesame,all meet the requirements of high-flowing concrete, the compressive strength of28ddecreases with the increasing of the dosage of grounded fluidized bed coal slag, theaccelerated carbonation depth of28d increases with the increasing of the dosage ofgrounded fluidized bed coal slag and is up to5.5mm, the electric flux of concrete belong tolow permeability concrete level. Therefore,the maximum dosage of grounded fluidized bedcoal slag is60%.(4) When the dosage of mineral admixture is fixed, the compressive strength of28d ofhigh-flowing concrete decreases with the increasing of water-binder ratio,according to thesignificance:①water-binder ratio is divided into four range to set the the maximum dosageof fly ash;②water-binder ratio is divided into five range to set the the maximum dosage ofpowder slag;③water-binder ratio is divided into three range to set the the maximumdosage of grounded fluidized bed coal slag.(5) When the dosage of mineral admixture is fixed, the accelerated carbonation depthof28d of high-flowing concrete increases with the increasing of water-binderratio,according to the significance:①water-binder ratio is divided into two range to set thethe maximum dosage of fly ash;②water-binder ratio is divided into three range to set thethe maximum dosage of powder slag;③water-binder ratio is divided into two range to setthe the maximum dosage of grounded fluidized bed coal slag.(6)Compared with the regression coefficient of current specification,the linearregression coefficient between compressive strength of28d of high-flowing concrete withfly ash, powder slag and grounded fluidized bed coal slag respectively and binder-waterratio have deviation,lead to the average difference between actual water-binder ratio andwater-binder ratio calculated by current specification are0.03,-0.11and0.03;When thethree mineral admixture combine togerher,the linear regression coefficient of compressivestrength of28d of high-flowing concrete and binder-water ratio are almost the same withthe regression coefficient of current specification.