Study On The Effect Of Lithology And Gradation Of Manufactured Sand On Concrete Performance

As a result of the large-scale infrastructure construction in the past twenty years,natural sand resources,as one of the raw materials of concrete,have been depleted in many places.Under such a background,China is rapidly entering the new era of engineering construction using the manufactured sand and stone.Compared with natural sand,manufactured sand has various lithology and different characteristics.Moreover,the particle size distribution is partial?region,and the intermediate particles are less,and the porosity is large,and the shape is not smooth,and the content of stone powder or mud powder is high.Because of the lack of understanding and clear manufactured sand and its reasonable gradation,it is easy to cause a series of problems such as poor workability of fresh concrete,low strength of concrete after hardening,and short service life due to poor durability,which seriously restricts the popularization and application of manufactured sand.In this paper,the lithology and gradation of the manufactured sand are studied.The main contents and results are as follows.(1)The effect of different lithology and content of stone powder on the yield stress,plastic viscosity and lagging ring area of cement paste were studied under the condition of basically uniform particle size distribution.The results show that the rheological curve of cement slurry made from stone powder and cement instead of cement conforms to the Bingham model.On the whole,with the increase of the amount of stone powder,the yield stress and plastic viscosity of tuff,granite and gneiss increase,and the yield stress and plastic viscosity of andesite,limestone and quartzite are reduced.The curves of the area of the hysteresis loops of the 6 stone powder groups first increased and then decreases,but the inflection point is different.These effects may be mainly caused by the water absorption rate of stone powder,the particle morphology of stone powder,the absorbability of limestone powder additives and surface energy of stone powder.(2)Under the condition of the same gradation and grain shape,six kinds of common lithologic manufactured sand were selected to study the influence of lithology on the performance of mortar and concrete.The results show that the influence of different lithologic manufactured sand on the workability of adhesive sand and concrete is more related to the texture of sand surface,the adsorbability of stone powder and water absorption,and the calcareous manufactured sand is better than the siliceous manufactured sand on the whole.The granite manufactured sand,tuff manufactured sand and gneiss manufactured sand with great adsorbability of stone powder and uneven surface texture have great influence on the workability of the mortar and concrete,and the adaptability to the admixtures is poor.The surface texture of the manufactured sand,the adsorbability and water absorption of the stone powder can affect the strength of the mortar and the concrete and the carbonization resistance of the concrete,but the effect is not significant.(3)Gneiss manufactured sand with high adsorption is selected as the test material.On the basis of an initial gradation,reaching the same flow degree,the content of 0-0.15 mm is adjusted according to 0%,3%,6%,9%,12%,and the content of 0.15-0.3mm is adjusted according to the 5%,8%,11%,14% and 17% of the sifter to study the effect of different particle sizes on the performance of mortar.Through the analysis of the test data of the rubber sand group,3 groups of sand gradations with better state are selected to prepare the concrete with a strength grade of C30 and C50 respectively,and their workability,splitting tensile strength,compressive strength and carbonization resistance are measured.The test results show that the amount of admixture increases,and the flexural strength of the mortar and the splitting tensile strength of the concrete are reduced,while the compressive strength of the mortar and concrete increases first and then decreases,and it has an influence on the carbonization depth of the concrete but is not significant with the increase of the fine particle size.The smaller the particle size is,the more significant the effect of content change on the performance of mortar and concrete is.