The Effect Of Raw Materials On Performace Of The Self Compacting Concrete

Self-Compacting Concrete is the top design of the fresh concrete, the meaning of which is that it can be evenly compacted only depends onself-weight without any external vibration in the process of pouring.Full machine-made sandis rarely used to prepare self-compacting concrete, especially in the highway engineering and the railway engineering. Instead, full river sand is commonlyusedin the present preparation.With the combination of technical requirements for the self-compacting concrete by full machine-made sand in Banan Motorway and Bashan Motorway Projects, this paper emphasizes the difficulties of preparingself-compacting concrete by full machine-made sand. Meanwhile, this thesis carries out anin-depth research into the coarse aggregate and the fine aggregate, which can affect the performance of the self-compacting concrete by full machine-made sand. Moreover, thickeners such as polypropylene fibers, thickening powder and xanthan gum are mixed to improve the performance of the self-compacting concrete. Accordingly, the study provides the following findings.(1)The sphericity and the shape index are commonly used as assessment method for the particle’s shape of the coarse aggregate by domestic scholars, and the calculation formula is α= Vg/Vs,0<α< 1. In the formula, Vg is the volume of coarseaggregateparticle,Vs is the volume of sphere which wrap the particle of aggregate, α is the sphericity of coarseaggregate’s particle, the grater the α is, the shape of the particle is more likely to be spherical; and the shape index of coarseaggregate’sparticle is I=ΣHαi·Pi, αj is the average sphericity of the sphericity interval (αi,αi+1), P; is the distribution rate of coarseaggregate’s particlewithin the interval (αi,αi+1).(2)By observing though stereo microscope,the writer puts forward two different methods of assessing the shape of the fine aggregate’s grain, namely the circularity and the spherical index. The calculation formula of circularity is Y=4S/πD2. In the formula, D represents the maximum diameter of the grain, S represents the projection area of the grain, and Y represents the circularity. The calculation formula of circularity is Z=K(?)/L (K=2(?)) In the formula, A is the projection area of the grain, L is the perimeter of the grain, and Z is the spherical index.(3)The particle of natural river land is relatively smooth and hasless angles. On the contrary, machine-made sand has more sharp angles which are caused by the various limiting factors. Therefore, the circularity and the spherical index of the machine-made sand are smaller than the natural river land’s.(4)If the fine aggregate is defined by the spherical index, the figure of calculation is relatively large (the average figure is approximately 0.9), which can’t well reflect the real particle shape of the fine aggregate. Furthermore, spherical indexes of fine aggregates withdifferent materials are closely approximate, which may fail to precisely define and distinguish the shape of grains. Therefore, it is more accurate to define the shapeof fine aggregate’sparticle by thecircularity rather than the spherical index.(5)Both the coarse aggregate and the fine aggregate can influence the mortar, ordinary concrete and self-compacting concrete, and the conclusions are as follows:the greater the aggregate’scircularity is, the particle is more likely to be spherical; the better the working performance of the freshmortar and the concrete, the higher their compressive strength is.(6)The incorporation of thickeners(polypropylene fibers, thickening powder and xanthan gum) will significantly affect the rheological property of fresh self-compacting concrete, namely an increase in the amount of admixture will lead to poor rheological property of fresh self-compacting concrete.