Requirements for Concrete Aggregate Conveying by Fine Stone Concrete Pump
2. Coarse aggregate
Pumped concrete can be made of pebbles, crushed stone or a combination of pebbles and crushed stone.
The pumpability of pebble aggregate concrete is good, followed by the mixture, and the crushed stone aggregate is poor.
Refer to the table below for the restrictions on the large particle size of coarse aggregate. Small diameter of the conveying pipe. Limited by the small diameter of the delivery pipeline. It is required that the large particle size of the pebbles should not exceed 1/3 of the caliber; the crushed stone should not exceed 1/4 of the caliber. A small amount of over-diameter aggregate is allowed to be mixed in. For example, in a 100mm diameter conveying pipe, a small amount of aggregate with a particle size of 50mm can pass through, but the proportion of this over-diameter aggregate should not exceed 1%, and they must be dispersed. of. Pumping concrete requires that the porosity of the coarse aggregate is as small as possible, and its gradation should be continuous and uniform, so as to obtain better pumpability with a small amount of cement and sand ratio. The gradation of coarse aggregates should meet the requirements of the table below. Gradation standard of coarse aggregate: the weight percentage of aggregate passing through each standard sieve in the range of various aggregate particle sizes Table Nominal size of sieve hole in particle size range (mm) (mm) 50 40 30 25 20 15 10 5 2.5 30 -5 100 100-95 75-40 35-10 10-0 5-0 25-5 100 100-90 90-60 50-20 10-0 5-0 20-5 100-90 100-90 (80-55 ) 55-20 10-0 5-0 The pumpability of concrete is very sensitive to the intermittent or uneven response of the aggregate gradation. A shortage of a certain component, or localized single coarse aggregate in the concrete, may cause a pumping blockage accident. The proportion of coarse aggregate in the total aggregate has a great influence on the pumpability of concrete, which is manifested in the change of pumping pressure and volumetric efficiency of concrete pump. In actual use, as long as the sand rate is well controlled, the amount of coarse aggregate will naturally be controlled.