CS263391B1 - Method of production of concrete mixture - Google Patents

Abstract

In today's practice, the turbochargers are added to the concrete mixer, along with the mixing water, for the concrete mixer to the concrete mixer before being emptied on site. According to the invention, a substantial higher fluidity is achieved or a lower dose of the additive can be used by the addition of a fluidizer 10 to 300 seconds after addition of the mixing water or a portion thereof. At the same time, the swelling effect is not rapidly lost, but is maintained for the time required to transport and process the mixture.

Description

The invention relates to a method of producing a concrete mixture with the addition of a draining agent.

To improve the workability of the concrete mixture, additives are used that reduce the viscosity of the cement paste and, as a result, increase the fluidity of the concrete mixture. These additives are referred to as plasticizers or deliquescent agents or superplasticizers. The most well-known substances with this effect are ligninsulfonates, condensates of formaldehyde with sulfonated naphthalene, phenol, melamine, but also other substances and their combinations with each other.

In current practice, these additives are added to the mixing water dosed into the mixer during the production of the concrete mixture in accordance with the generally known recommendations (see example Ha Sborník US1 Rationalization of the production of concrete mixtures by means of chemical additives to concrete, 1984, p. 10 from a professional seminar, the expert guarantor of which was TAZUS Praha in cooperation with the Ministry of the Czech Republic).

In the case of ready-mixed concrete with a long delivery distance and therefore a long transport time, they are sometimes added at the place of depositing the concrete mixture before emptying the truck mixer. The team aims to eliminate the loss of workability, which occurs relatively quickly during the distribution of plasticized concrete. However, the liquefaction effect of admixtures added a long time after mixing the concrete mixture is less (see Superplasticizing Admixtures in Concrete, Report of a Joint Working Party of the Cement Admixtures Associacion and the Cement and Concrete Association, 1976, p. 16).

Surprisingly, it has now been found that the trickling effect of the addition of additives can be increased up to several times if the additive is not added in the existing way with the mixing water during the production of the concrete mixture, but only after the addition of the mixing water or part of it, no sooner than 10 seconds and optimally 60 to 180 seconds after the addition of the mixing water to the cement or cement and aggregate. Further extension of this time no longer has a positive effect and the effectiveness decreases for times over 300 seconds.

According to the invention, a plasticized or fluid concrete mixture is produced by first bringing the cement into contact with the mixing water or a part of it, and only then, in a time not shorter than 10 seconds and not longer than 300 seconds, optimally after 60 to 180 seconds, an additive with a trickling effect is added.

The increase in effect achieved according to the invention is evident from the examples of execution. A mixture of Portland cement and standard sand with a w/c of 0.45 was produced, to which a different amount of draining agent was added at different times from the moment of mixing water addition. The fluidity after the preparation of the mixture was determined, as well as the repeated fluidity of the same mixture, matured after another 20 minutes had passed. Fluidity was measured in a standard way by spilling the mixture on a streak table. In the tables, the achieved flow is expressed in % of the value of the spillage of the mixture without the additive.

Example 1

Flowing of the mixture with the addition of ligninsulfonate

Additive added 0.15% 0.30% 0.45%

after adding water after production after production after production sec immediately ¹ zaa/20* immediately in 20' immediately . in 20 0 11 6 21 2 35 8 30 22 10 30 32 120 30 30 44 48 53 61 360 25 23 42 59 41 48 15 minutes 0 1 23 26 32 32

It is clear from the results that with the method according to the invention it is possible to: Add a 3x smaller amount of draining agent for the same flow.

Achieve up to 3 times more flow at low dose, 2 times more at medium dose and 50% more at high dose.

While when the additive is added to water, the trickling effect is quickly lost with time, according to the invention it was the same after 20 minutes and, with higher doses, even higher than immediately after mixing. This is important because the concrete mix compacts after a certain time has passed since it was made. At the same time, the results show that a very short as well as a very long time between the addition of water and the additive is not suitable and the desired effect is not achieved.

The same conclusions follow from another example.

Example 2

Flowing of the mixture with the addition of naphthalene condensate

Additive added -t e,i5r%< 0.30 % 0.45 % after adding water after production

sec immediately in 20' immediately in 20' immediately in 20' 0 6 3 24 25 30 21 27 40 74 46 60 36 26 52 42 83 78 180 48 34 75 57 79 81 360 34 30 33 12 57 59 15 minutes 25 26 15 10 41 43

Example 3

Flowing of the mixture with the addition of melamine condensate

Additive added after water addition sec 0.15% 0.30% after production immediately in 20' 0.45% immediately in 20' immediately in 20' 0 13 4 18 13 31 ³⁰ 18 8 58 47 60 32 20 76 180 57 47 126 360 46 50 15 minutes 46 40

It is clear from the results in the examples that this is a highly effective and technically undemanding method. It is natural that the achieved effect also depends on the composition of the concrete mixture and its components, and thus in specific cases it can be higher or lower. The optimal time must be determined experimentally for a specific mixture, while it is also influenced by other production factors - such as the capacity of the concrete mixer and the specified mixing time due to these potential causes. The addition of the additive, for example, up to 180 seconds after the addition of the mixing water can be used without changing the mixing time in the mixer, for example, by adding the additive after this time to the automixer. Addition times in tens of seconds directly into the concrete mixer.

Similar to the production of concrete mixes, the method according to the invention can be used in the production of mortar and injection mixes, cement bentonite mixes and other cement-based building materials, flowed in the fresh state with the addition of flowable additives.

Claims (1)

OBJECT OF THE INVENTION Process for producing a concrete mixture with the addition of a flowing additive characterized in that the additive is added 10 to 300 seconds expediently 30 to 180 seconds after the addition of the mixing water or part thereof.