Research On The Influences Of Micro Fines On Properties

Due to the shortage of natural sand resource as well as decline in quality and risein price, manufactured sand has found an increasingly wide application in industrialand civil engineering, water resources and hydropower engineering as well as roadsand bridges projects etc. so as to meet the growing demand of sand for construction.However, studies of micro fines on concrete properties mainly focused on the contentof micro fines, while ignoring the differences among micro fines. Thus further andmore systematic research on the impact of characteristics of micro fines onperformance of concrete is needed. It is important for theoretical research andpractical application to research the influence of micro fines’ characteristics onmanufactured sand concrete properties.By statistically analyzing main characteristic parameters of manufactured sandcollected from different areas, big differences were found among manufactured sandsamples in shape, grading, clay content, micro fines’ characteristics and content, thusthe accuracy and threshold value of the existing method for characterizing the claycontent is discussed. The study suggested that methylene blue value(MB value) ofdry-sieving micro fines together with powder content of manufactured sand couldn’tmeet with the actual clay content in the sand, while the MB value of manufacturedsand together with pass rate of2.36mm sieve and MB value of wet-sieving microfines together with powder content were better ways to reflect the clay content inmanufactured sand.The impacts of lithologic characters and fineness of pure micro fines, togetherwith type and content of clay mixed in micro fines on the MB value of micro fineswere studied. It is found that, as to pure micro fines, the increase of fineness has littleimpact on the MB value, while the difference in lithologic characters of micro fineaffected caused bigger difference in MB value, possibly due to the differences inmineral compositions and structures. The MB value of micro fines increased linearlywith the clay content, while the slope is determined by the type of clay. Comparedwith fineness and lithologic characters, clay content had more significant impact onMB value of micro fines.Properies of mortar, C30and C60manufactured sand concretes, includingworkability, compressive strength, durability, and volume stability, were also studiedwhen10%(by weight of sand) of micro fines of were added. The studies found thatfines and lithologic characters of micro fines affected the properties of concrete indifferent ways when the grades of strength were different. But all in all, fineness ofmicro fines has relatively smaller impact on properties of concrete when comparedwith lithologic characters, while MB value has the most significant impact onconcrete performances, especially the workability, frost resistance and volumestability of concrete. For C30manufactured sand concrete, the MB value of microfines should not surpass14, as to C60manufactured sand concrete, the MB value ofmicro fines should not exceed10, when the micro fines content of manufactured sandis10%by weight of sand. For flow state concrete or concrete with strict requirementson frost resistance, the amount of clay contained in micro fines should be controlled more strictly.If there is a comparatively high clay content in fine aggregates, the workabilityand frost resistance performance of concrete can be improved by adding someaddictives(for example, methylene blue) which can preferably adsorbed on the clay,thus improving the effect and adaptability of superplasticizer.