Study On The Preparation Technology Of Dry-Mixed Reactive Powder Concrete

Reactive powder concrete(RPC)is an ultra-high performance cementitious material with excellent mechanical properties and durability.The preparation of RPC usually uses highquality quartz sand,and its cement dosage is often high,which not only further expands the cost of raw materials,but also runs counter to the low-carbon development direction of cementitious materials in the future.Therefore,in order to clarify the technical advantages of limestone machine-made sand for the preparation of RPC,develop a dry-mixed RPC with excellent performance and low carbon.Based on the principle of the tightest accumulation,this project conducts experimental research on the gradation of fine aggregates.By adjusting the mix ratio parameters of RPC,the influence of cementitious material composition on the early working properties and later mechanical properties of RPC under multi-factor mechanism was studied.The influence level of each factor was quantitatively evaluated by using the gray correlation method,and the mixing ratio of dry-mixed RPC was further optimized,and a set of multi-performance grade limestone machine-made sand dry-mixed RPC preparation technology was formed.The main conclusions are as follows:(1)The gradation optimization of limestone machine-made sand,river sand and molybdenum tailings sand was carried out through the tight bulk density test,and it was found that the cubic compressive strength of the RPC prepared by the graded optimized fine aggregate was significantly improved.The mechanical properties of limestone machine-made sand RPC are the best,and its 28 d compressive strength meets the strength grade requirements of R120,followed by river sand RPC,and the compressive strength of molybdenum tailings sand RPC is relatively low,but after grading optimization,the compressive strength at the age of 28 d can meet the strength grade requirements of R100.In addition,with the increase of the maximum particle size of sand,the compressive strength of RPC showed a trend of first increasing and then decreasing,and 2.36mm>1.18mm>4.75 mm.Therefore,the best dry-mixed RPC can be obtained by using limestone machine-made sand with a maximum particle size of 2.36 mm and optimized gradation(2)By adjusting the parameters of the mixing ratio appropriately,it is found that the parameters including sand-to-binder ratio(the ratio of sand to binder dosage),water-to-binder ratio(the ratio of water to binder dosage),and water-to-cement ratio(the ratio of water to cement dosage)have a significant impact on RPC performance,among which the lower the sand-to-binder ratio,the better the RPC fluidity,but when the sand-to-binder ratio is less than1.3,the increase of RPC folding and compressive strength is no longer obvious,or even decreases;The lower the water-to-binder ratio,the worse the fluidity of RPC,and the opposite of mechanical properties;The water-to-cement ratio had little effect on the fluidity of RPC,but when the water-to-cement was relatively high,the intensity in the early stage of RPC was relatively low,but the intensity increase in the later stage was large.When the steel fiber content is high,the fluidity of the new RPC decreases significantly,but the mechanical properties are significantly improved.Silica fume can significantly improve the compressive and flexural strength of RPC,but its content should be 8-15%;Compared with single fly ash or slag powder,the combination of the two is more favorable to the working and mechanical properties of RPC,and there is an optimal ratio.Limestone powder can not only improve the fluidity of freshly mixed RPC,but also significantly reduce the viscosity of RPC mixture,but the mechanical properties of RPC should be controlled when the content is high,so the amount of limestone powder in higher performance grade RPC should be controlled.(3)The influence relationship between RPC extension,compressive strength,flexural strength and various factors was analyzed by gray correlation degree,and the threshold of drymixed RPC was divided.Through the mechanical properties and durability of dry-mixed RPC prepared with different performance grades,it is found that the compressive strength of the drymixed RPC at the age of 90 d can reach up to 155 MPa,and the flexural strength is much higher than the corresponding value specified in the standard,and it also has excellent durability.The test results of SEM also verify the excellent comprehensive performance of dry-blend RPC from the microscopic level.