Influence of Raw Material on Concrete Pumping Ability
(1) Cement and Gelling System
The stone in the concrete mixture itself is not liquid. It must be driven by evenly dispersed in the cement slurry to move forward. The resistance of the stone moving with the slurry is related to the filling of the slurry in the mixture.
Cement variety, fineness, mineral composition and admixture affect differently to the water demand, the ability to maintain fluidity, bleeding water characteristics, viscosity of the concretes with the same liquidity. That is the main factor affecting the pumping ability of the concrete.
(2) The Aggregate
The aggregate occupies the largest volume, and its characteristics have a great impact on the pumping ability of the mixture, including gradation, particle shape, surface state, maximum particle size, water absorption energy, etc.
The gap rate of the graded aggregate is small. Under the same pulp volume, better pumping ability can be obtained.
However, in the slurry-rich mixture, the effect of grading is significantly reduced. In aggregate grading, the medium particle content of 0.3-10mm significantly affects the pumping ability.
If the content is too much, that is, the stone is fine, the sand is coarse, it is very easy to lead to mixing rough, loose, poor fluidity, large friction resistance and poor pumping.
If the content is too little, that is, the stone is coarse, the sand is fine, it is very easy to increase the admixture and water consumption, make the cohesion of the mixture poor and the segregation occur.
The fluidity of the concrete mixture is fulfilled by filling the gap between the sand and the gravel, and then the surplus cement slurry layer covering the aggregate surface.
The change of sand rate will change the total surface area and voidage of the aggregate, so it has obvious influence on the compatibility, fluidity and viscosity of the mixture, especially in the case of sand with large angular coefficient and large water absorption rate, the influence is obvious.
Under the condition of a certain mortar volume, the sand rate is too large, the total surface area of the aggregate increases, the mortar layer between the aggregate is thinner, the fluidity is poor, and the mixture is dry and thick.
Sand rate is too small and sand is not enough to fill the gap between the coarse aggregate, needing additional mortar supplement.
The coating layer on aggregate surface becomes thinner, and the friction resistance between the stones increases, which reduces the fluidity of the mixture, seriously affects the cohesion and water retention of the mixture, and makes the coarse aggregate segregation, slurry loss and even collapse.
Therefore, the aggregate with large water absorption rate should be wet for construction, but in the areas with high frost resistance requirements, the water absorption rate of the aggregate should be limited.
Due to the needs of pumping process, in order to meet the appropriate slurry content and liquidity, the water consumption of pumping concrete is usually large, and from the concrete performance, it is necessary to control the water glue ratio, the effect of admixture to solve the contradiction: reduce water consumption, improve workability, increase the fluidity of the slurry.
The effect of admixture in pumping concrete is reflected in the following aspects:
Reducing water consumption, increasing fluidity, improving accessibility, improving the viscosity of concrete due to the reduce the friction resistance of mixture, extending the setting time to adapt to the construction operation, reducing the loss of slump and improving the loss od slurry fluidity.
(4) Water and Fine Powder
Water is the contact phase between the components of concrete mixing materials. It is also the key medium of pumping pressure transmission, dominate the whole process of concrete pumping, but the water consumption is too much, excessive dilution of slurry is not conducive to pumping and adverse to the strength and durability of concrete.
(5) Pump Type Selection and Site Construction
High strength concrete ultra-high pumping is a systematic engineering, the equipment should have high reliability and super strong pumping capacity.
Ultra-high pressure concrete, due to the high pressure of concrete, is easy to leak, leading to concrete segregation, pipe plugging and many other problems. It must solve many problems such as the sealing of ultra-high pressure pipeline, ultra-high pressure concrete pumping construction process and residual concrete treatment and water washing in the pipeline.
In the selection of equipment, the pumping capacity (maximum outlet pressure), ultra-high pressure pipeline sealing, pipe diameter, pipe material and reliability should be considered.
The site construction is mainly divided into pipeline layout, pump pipe fixing, setting horizontal buffer layer, high pressure pipe connection, pipeline cleaning, etc.