Study On The Properties Of Concrete With Manufactured Sand And Its Mix Proportion

With the increasing development of construction engineering in China, the consumption of concrete is accordingly increased, which results in a growing shortage of natural sand resources, consequently an increasing contradiction between supply of sand and demand for construction. Thus, it becomes an inevitable trend for the concrete industry to partially or fully replace the natural sands with manufactured sands as fine aggregate in concrete. However, the manufactured sands are generally more angular or square torque and have rougher surface texture than natural sand particles, which cause the concrete with manufactured sand more prone to bleeding or segregation. By testing the basic properties of five selected kinds of sands, which mainly include the particle morphology, particle size distribution, the apparent density, bulk density, void ratio, fine powder content and the slump of sand heap, the overall characteristics of manufactured sands were revealed. The properties of concrete are closely related to the characteristics of manufactured sands. Through testing and analyzing performance of concrete, the influence law of sand characteristics on properties of concrete is revealed. The other main objective of this research to discuss the crushed way and silt content of manufactured sands on the workability, mechanical properties and drying shrinkage performance of concrete. In order to provide some guidance for promoting the manufactured sands applied in the concrete, mix proportion of manufactured sands concrete was optimal improved with statistical methods, and a reasonable sand ratio range of concrete with manufactured sands was provided, combined with the characteristics of the manufactured sands. The major achieved results by this study are as follows:The characterization of sand particle morphology was tested with the method of digital image and fine aggregate angularity, the testing results are not completely consistent, but there is a good correlation, the flow time grows with the particle surface roughness, the uncompacted void content is small if particles approximate to spherical. The distribution characteristics of manufactured sand shows "many on both sides, a gap in the middle", and the apparent density of natural sand is lower than manufactured sand, the apparent density of rolling sand is the largest. Particle shape and angularity of sand can be better represented by the slump state.Manufactured sand is affected by crushing process to produce a fine aggregate which is generally more angular, sharp edged, higher limestone fines content, where the surface roughness of rolling sand is the largest, which yield the highest 28 d compressive strength; the higher limestone fines content of vertical impact sand result in the 28 d splitting tensile strength of concrete is the highest. High percentages of micro fines produce concrete with manufactured sand of lower workability and bigger drying shrinkage rate.Through a large amount of data statistical analysis, the relationship of 28 d compressive strength with cement water ratio of concrete with manufactured sand was concluded, that is 0.465 0.308 f_ce = C/W-. When the water cement ratio is 0.6, fineness modulus of manufactured sand is between 2.5 and 2.8, gravel size is 5 to 25 mm, the reasonable sand ratio is in 41⁴5%; when water cement ratio is 0.5, the fineness modulus of manufactured sand is small, the reasonable sand ratio is 40⁴3%; when the water cement ratio is 0.32 to 0.35, the reasonable sand ratio is 40⁴2%; water-cement ratio is during 0.3 and 0.32, with a sand is not too coarse, the reasonable sand ratio is 36⁴0%. The water of concrete with manufactured sand can be chosen in terms of the upper limit of natural sand concrete or calculated according to the bulk density of concrete.