The problem of mixing amount of liquid accelerator in application

Accelerating agent is mainly used for shotcrete. The appropriate dosage of accelerating agent refers to the economic dosage when concrete sets fast, early strength high, shrinkage deformation small and other properties basically meet certain requirements.

The dosage of alkali liquid accelerating agent is generally 4%~6%, the dosage of alkali liquid accelerating agent is generally 6%~8% 

The mixing amount of accelerating agent depends on the injection location, rock face state, solidification time specified by the injection method, early strength and 28d strength of shotcrete, and the temperature of the operation site.The effect of shotcrete should be considered comprehensively from two aspects of time and space, combined with the dynamic properties of shotcrete and surrounding rock, so as to determine the optimal solidification time of shotcrete and the optimal dosage of accelerating agent.If the accelerating agent exceeds the dosage, the solidification time will increase, and the concrete strength will decrease more seriously in the later stage.

1.The influence of dosage on properties of fast setting concrete

With the increase of the accelerator dosage, the setting time is shortened, but the strength loss is increased, the shrinkage value is increased, so in the case of meeting the requirements of the setting time (generally 2~10min), the dosage should be less than or equal to no alkali liquid accelerator and liquid alkali accelerator advantages and disadvantages are opposite

Determined the type of accelerator after the next step focus on the accelerator dosage is the general principle of the dosage is the smaller the better the dosage is small means that cement compatibility is good, good economic benefit; Large amount of cement means poor compatibility, poor economic benefit with good compatibility of cement to choose accelerator, with small amount of accelerator to choose cement this process can be completed in the site laboratory, and finally do cost-effective analysis, the best economic benefit combination of cement and accelerator

2.The influence of temperature on accelerator dosage

The temperature mixing water temperature is high, the setting speed is fast, the accelerating dosage is small, such as GQ-SN03 type alkali free liquid accelerating agent in the production of 425 ordinary Portland cement in a cement factory in Shandong, the appropriate dosage is 2% when the temperature is 25, 2.5% when the temperature is 20, and 3% when the temperature is 15. Different kinds of cement produced by different factories also have different dosage of accelerating The general content of slag cement is higher than that of ordinary Portland cement.

The temperature is 20 as the standard, the temperature drops 5, increase the dosage of 0.5% or more, the temperature rises 5, reduce the dosage of 0.5% or so have alkali liquid accelerating agent because of its dosage adjustable range is small, in winter construction is often difficult to control, often appear concrete does not set phenomenon No alkali liquid accelerating agent only as the temperature drops to increase the dosage is easy to control, increase the dosage will not appear concrete does not condense down the phenomenon

3.The influence of construction position on the accelerator dosage

The mixing amount of the top arch is larger than that of the slope wall. For example, GQ-SN04, the mixing amount of the top arch is 4%~6% and that of the slope wall is 2.5~3%.

4.The influence of the time from mixing to spraying on the content of accelerating agent

The longer the time from concrete mixing to spraying, the greater the amount of accelerator. It has been proved that the time from concrete mixing to spraying is 30 minutes, and the amount of accelerator increases by 20%. 60 minutes, accelerating agent dosage increased 35%; 90 minutes, the accelerating agent dosage increased by 60%; 120 minutes, accelerating dosage increased 100%, therefore, as far as possible to shorten the mixing of concrete to use time, rapid use of mixing good concrete is the key to save the accelerating agent, but also to prevent concrete to fall down one of the most effective methods.

 The presence of alkali liquid accelerator optimal dosage control well, injection effect is good, the springback is small, high strength Increase or decrease the best dosage of 0.5% is not favorable to the development of sprayed concrete, instead affects the injection effect and quality. 

 In case of poor cement adaptation, add content has the effect not beautiful, memory foam, low intensity, and won’t appear the phenomenon of alkali-free accelerating agent is Is the ideal construction method of concrete from the new mix to one-off injection construction completed, but the current domestic haven’t the construction methods and equipment

 In conclusion, in the sprayed concrete engineering construction process, must according to the construction site reasonable use, appropriate adjustments accelerator dosage, pays special attention to the whole process of quality control points, to guarantee the final quality shotcrete construction

Post time: Aug-21-2021