JPS6256343A - Accelerator for cement - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to an quick setting agent for cement.

(Conventional technology and problems) In recent years, a new tunnel construction method, the NATM construction method, has become established, and the amount of shotcrete construction is increasing. It is essential to add a quick setting agent for cement to this shotcrete, and known quick setting agents include alkali aluminates and alkali carbonates. For example, a powder quick-setting agent whose main component is a powder mixture of sodium aluminate and soda carbonate, a liquid quick-set agent whose main component is a mixed aqueous solution of potassium aluminate and potassium carbonate, and the like are commercially available. In the case of the song title, when spraying mortar or concrete, a quick-setting agent is mixed into the mixture of cement and aggregate, and while it is supplied by a dry sprayer, it is combined with pumped water from another system near the nozzle tip. Up until now, it was pumped in the form of powder and fluid, which generated dust that harmed the working environment, caused uneven mixing with the quick-setting agent, and caused reactions between the moisture contained in the aggregate, the cement, and the quick-set agent. Since there is a risk of clogging the system path, strict management of materials, etc. is required. In the latter case, since it is a liquid, it is free from the above-mentioned drawbacks, but there was a desire for an additive that would be effective in further improving the rapid setting performance.

However, aqueous solutions of alkali aluminates are chemically unstable and aluminum hydroxide crystals tend to precipitate during storage. To prevent this, gluconic acid or its salts, tartaric acid or its salts, etc. are added as stabilizers. USP 2
, 345, 134) is often performed.

In such cases, there is a problem in that when other quick-setting agents are added, the performance as a stabilizer for the alkali aluminate or, incidentally, the performance as a fast-setting agent is often impaired.

(Objective of the Invention) The present inventors have conducted various studies in order to take advantage of the advantages of a liquid quick-setting agent and still improve its quick-setting performance, and as a result, have arrived at the present invention. The first object of the present invention is to provide a compounded agent that further improves the quick-setting performance of an alkali aluminate-alkali carbonate liquid quick-setting agent even in the presence of a stabilizer that prevents precipitation of aluminum hydroxide. be.

(Structure of the Invention) The present invention is a quick-setting agent for cement, characterized in that an alkali tetraborate salt is blended into an aqueous solution containing an alkali aluminate and an alkali carbonate as main components.

Examples of the alkali aluminates and alkali carbonates include lithium salts, sodium salts, and potassium salts, and potassium salts are preferred from the viewpoint of solubility and viscosity. The mixing ratio of alkali aluminate and alkali carbonate to water is, for example, 10 to 20 potassium aluminate to potassium oxide.
It is desirable to adjust the weight of aluminum oxide to 5 to 15 weight percent and the potassium carbonate to 15 to 30 weight percent in order to improve rapid setting performance and workability.

The above-mentioned alkali tetraborate salt is a lithium salt.

There are sodium salts, potassium salts, etc., but since the quick-setting agent is a highly concentrated alkali salt, the effect remains the same no matter which one is added. Therefore, from the economic point of view, sodium tetraborate decahydrate, which is commercially available as borax, is desirable.

The blending ratio of the alkali tetraborate salt is preferably 0.1 to 5% by weight, preferably 0.5 to 3% by weight as a hydrate, based on the aqueous solution. When the weight ratio exceeds 5%, the rapid setting performance decreases.

If necessary, such as when long-term storage is required, the quick-setting agent of the present invention may contain stabilizers such as the aforementioned gluconic acids and tartaric acids without impairing quick-setting performance.

The product of the present invention can be used by dissolving it in advance in the mixing water for shotcrete, by press-mixing it into the mixing water using a pump, or by injecting only the quick-setting agent into the nozzle tip. In normal spraying work, the amount used is 1 to 10% by weight, preferably 4 to 6% by weight, based on the cement gap.

J'3 The cement used in the present invention is preferably Portland cement, but blast furnace cement, silica cement,
It is also used in mixed cements such as fly ash.

The present invention will be specifically explained below with reference to Examples.
is based on weight.

Example 1 Potassium aluminate (2013% in aqueous solution).

Solution A is an aqueous solution containing ΔR2O (39%), potassium carbonate 25%, and sodium gluconate 0.2%.

A liquid quick-setting agent was prepared by adding 0 to 3% of powder sand to this liquid A.

In order to compare the quick setting performance of this liquid quick setting agent, the
Helland cement 2,000 (1, river sand 6,000 (
IN-, M, 2,6. Surface water rate: 5%), water to cement: 45%, liquid quick setting agent: 4 to 6% to cement.
Mix it for about 15 seconds, then quickly pack it into the mold, 19
Broctor Penetration Resistance Test (ASTM C403)
-631'), and the time from the start (500 PS I) to the end (4000 PS I) was measured. The results are shown in Table-1 and Table-2. Note that the test was conducted at 20°C.

Table-1 (accelerating agent added to ejected cement ratio 4%) Table-2 (accelerating agent added ii to cement ratio 6%) Example 2 Created by adding 1% borax to liquid A in Example 1. In order to examine the effect of liquid quick-setting agent on compressive strength, J.I.
A strength test was conducted on SK5201-9 cement.

Ordinary Portland cement eoog, river sand 1800g (
F, M, 2.6. Mix 45% water to cement, 6% liquid quick-setting agent to cement, mix for about 10 seconds, and then quickly mix 4x4x16. Packed into a double formwork, and after demolding, the temperature was 20℃ and the humidity was 90%.
I was cured with In addition, tests were also conducted using only liquid A and when no quick-setting agent was added. The results are shown in Table-3.

Pressure) In the middle of m, compare -.

As described above, the product of the present invention has been tested for strength even in setting tests (1111'm), which was the most important test for rapid setting in the Song Dynasty.
- 6 hours), and had a clearly remarkable rapid setting performance compared to the case where only the Δ solution was mixed.

Note that when the quick setting agents of the present invention of Examples 1 and 2 were left at room temperature for 3 months, no precipitation of crystals such as aluminum hydroxide was observed.

(Effect of the invention) The quick-setting agent for cement of the present invention has higher quick-setting properties than the conventional liquid quick-setting agent, so it is possible to reduce the amount added to cement, making it economical. 11, and has particularly high initial strength, so it is particularly effectively used in the Pootom construction method. Also, since it contains a stabilizer, it can be stored for a long period of time without changing its performance.

Claims (1)

[Claims] A quick-setting agent for cement, characterized by blending an alkali tetraborate salt into an aqueous solution containing alkali aluminate and alkali carbonate as main components.