JPH0637316B2 - Admixture for mortar and concrete - Google Patents

Description

TECHNICAL FIELD The present invention relates to an admixture for mortar / concrete, which improves watertightness and initial curing and has a rust preventive effect.

[Prior art]

Conventionally used as a waterproofing admixture for mortar and concrete are chloride-based, sodium silicate-based, siliceous powder-based, zirconium compounds as inorganic materials,
There are many types of organic materials such as fatty acid, paraffin emulsion, asphalt emulsion, resin emulsion, and water-soluble resin, each of which has its own characteristics.Most of these are ideal for hydration reaction in mortar and concrete. Since its properties are exhibited only when the mortar / concrete is in an insufficiently hydrated state, there is a drawback that it cannot sufficiently exhibit its performance. A technique described in Japanese Patent Publication No. 53-33970 is proposed in which a water reducing agent and a nitrite are added to mortar or concrete to accelerate the hardening thereof.

On the other hand, chloride-based (mainly calcium chloride-based) accelerators promote the rusting of reinforcing bars by destroying the stable ferrous hydroxide film in an alkaline environment due to the deflocculating action of chloride ions. It is known that, and in recent years it is unavoidable to use sea sand from the bottom of fine aggregate, so similar rusting can be seen with the salt content that adheres,
As a countermeasure against this, it is already known that the above-mentioned nitrite is effective, and for example, there is a technique described in JP-B-52-24530 in which a lignin sulfonate and triethanolamine are added thereto.

In addition to the above-mentioned characteristics, the technology disclosed in Japanese Patent Application Laid-Open No. 57-22146 is known to further increase the strength, and the technology disclosed in Japanese Patent Publication No. 58-43349 is known to enhance the watertightness.

[Problems to be solved by the invention]

As mentioned above, various improvements have been made to the admixture for mortar and concrete from a diversified point of view. First, for salinity, the water reduction promotion specified in JIS A6204 "Chemical admixture for concrete" Almost no chlorine-free type (no chlorine-based raw material is used in the production of the admixture) is present in the admixture or the AE water-reduction accelerator, and the salt content in the admixture is in an uncontrolled state.

Also, the salt content in fine aggregate used for concrete is regulated by the Japan Society of Civil Engineers and the Institute of Architecture, but the cleaning of sea sand is not sufficient, and the salt content in concrete is mixed more than expected when analyzed after placing. Things have been reported. The Architectural Institute recommends the use of rust preventives when sea sand is used,
Since the admixture is expensive, it is rarely used in private buildings, and it is not necessarily satisfactory in terms of rust prevention effect. We used a non-chlorinated AE water reduction accelerator. In some cases, the initial hardenability and watertightness of concrete were not sufficient.

The problem to be solved by the present invention is exactly at this point, and the inventor, as a result of diligent studies, promotes the hydration reaction of cement without containing any chloride-based raw material,
Admixture for mortar / concrete that not only enhances the watertightness and initial hardening of mortar / concrete, but also has sufficient rust preventive hardening against 0.1 to 0.3% by weight of salt normally contained in sea sand. We were able to provide the drug for the first time.

[Means for solving problems]

Thus, the newly developed rust preventive mortar of the present invention
The admixture for concrete is obtained by uniformly mixing silicate, sodium hydroxide, nitrate, nitrite, water reducing agent, alkanolamine and tributyl phosphate.

Specific examples of each of these components include sodium silicate as a silicate, sodium nitrate and / or calcium nitrate as a nitrate, and one of sodium nitrite, calcium nitrite and potassium nitrite as a nitrite. As mentioned above, as the water reducing agent, one or more of naphthalene sulfonic acid formaldehyde condensate, sulfonated melamine formaldehyde condensate, lignin sulfonate and polyhydroxy compound, and as the alkanolamine, mono and / or di And / or triethanolamine and the like, and the surfactant includes neutralized vinsol resin and / or polyglycol ether of aliphatic alcohol alkylphenol and / or sulfuric acid and / or phosphoric acid ester of these polyglycol ethers. These components are used in the following ways. That is, silicate 1 to 45 parts by weight, preferably 18 to 28 parts by weight, sodium hydroxide 1 to 15 parts by weight, preferably 3 to 11 parts by weight, nitrate 5 to 25 parts by weight, preferably 13 to 17 parts by weight, nitrite 5 to 45 parts by weight. Parts by weight preferably 25 to 35 parts by weight water reducing agent 15 to 35 parts by weight preferably 20 to 30 parts by weight alkanolamine 0.3 to 3 parts by weight preferably 1 to 2 parts by weight tributyl phosphate 0.5 to 5 parts by weight preferably 2 to 3 parts by weight as an essential component, and usually a surface active agent 0 to 20 parts by weight, preferably 2 to 10 parts by weight, water 20 to 160 parts by weight, preferably 60 to 120 parts by weight to obtain a uniform aqueous solution. However, the amount of the admixture (aqueous solution) used is preferably about 2% by weight with respect to the weight of cement in the mortar or concrete.

[Action]

In the present invention, silicate functions as a waterproofing agent and watertightness-imparting agent, nitrate and alkanolamine function as a curing accelerator, and nitrite functions as a rust preventive agent. Further, the water reducing agent also acts as a waterproofing agent, a watertightness imparting agent and a curing accelerator, and also as a secondary rust preventive agent, and the alkanolamine alone has a curing acceleration action, but in the present invention,
Its function is further enhanced by the combined use with other components.
Tributyl phosphate has an antifoaming action, and the action is utilized in the present invention. Details of these properties and actions are as follows.

First, the water-tightness is enhanced and waterproofed largely by the addition of silicate, but the water-reducing agent disperses cement to diminish the unit water amount, and the breathing water amount decreases to reduce the amount of water supply and increase the water-tightness.

This is also proved from the comparison of the water permeability test of the silicate alone and the silicate + water reducing agent in Table-1 and the comparison of the breathing test of the silicate alone and the silicate + water reducing agent in Table-2. Has been done.

Next, the enhancement of the initial curing is accelerated by the nitrate to accelerate the initial setting and accelerated by the silicate, the water-reducing agent and the alkanolamine, but the nitrite is also increased by the silicate, the water-reducing agent and the alkanolamine. It is intended to enhance the initial hardening of mortar and concrete by the synergistic effect of the combined use of the above. This is also proved from the results of the comparative test of the compressive strength of concrete when the types of chemicals shown in Table 3 are changed.

Furthermore, the mechanism of action of the rust preventive agent on the reinforcing bars in concrete is classified into three types: (1) anode reaction suppression rust preventive agent, (2) cathode reaction suppressive rust preventive agent, and (3) adsorption rust preventive agent. However, nitrite corresponds to (1) an anodic reaction-inhibiting rust preventive agent, which promotes the formation of a passive film on the reinforcing bars, neutralizes the concrete, and destroys the film destroyed by chlorine. Although it plays a role of repair, etc., the rust preventive effect is not sufficient with nitrite alone, and increasing the water tightness of concrete by the water reducing agent further enhances the rust preventive effect. This is also proved by the observation results of rust in the mortar when the types of chemicals shown in Table 4 are changed.

The actions of the individual components of the present invention are as described above, and some of their properties are already known. However, the present invention does not simply utilize them as they are, but it is possible to use them in combination. The feature of the present invention lies in the fact that the mutual and synergistic effects thus obtained are confirmed and utilized.

〔Example〕

 Next, the present invention will be described with reference to examples.

As each of the above components, sodium silicate, sodium hydroxide, sodium nitrate, sodium nitrite, sodium lignin sulfonate, triethanolamine and tributyl phosphate admixture prepared by adding a surfactant and water thereto ( Aqueous solution) was added so as to be 2% by weight of the weight of the cement, and subjected to the following various tests.

(1) Setting and stability test of cement paste The setting and stability test was carried out according to JIS R5201. The results are shown in Table-5.

(2) Mixture of concrete and compressive strength test results are shown in Table-6.

(3) The results of water permeability test are shown in Table-7.

(4) The results of the water absorption test are shown in Table-8.

(5) Observation of rust in mortar Mixing of mortar: cement: sand: water = 1: 2.5: 0.
6 Salt content in sand: converted to NaCl Mold mortar in a 4 x 4 x 16 cm mold, and bury a polished steel rod in the center. After 24 hours, the steel rod was deformed and exposed outdoors for 6 months. Then, the steel rod was taken out from the specimen, and the rusting state was visually observed.

The results are shown in Table-9.

(6) Observation of rust in concrete The results are shown in Table-10.

(7) Observation of water permeability and rust Mixing of mortar: cement: sand: water = 1: 3: 0.56 However, water is an aqueous solution of 1.6% NaCl (NaC to sand).
The amount of 1 corresponds to about 0.3%) Mortar was molded into a φ15 × 4 cm mold to prepare a water permeability test specimen. JIS A1
After demolding according to 404, water pressure was applied for 1 hour at 3 kgf / cm ² . Mold the mortar into a 4 x 4 x 16 cm mold,
A φ5 × 100 mm polished steel rod is embedded in the center. 48
The mold was removed after a lapse of time, and after 12 months of outdoor exposure, the steel rod was taken out and the rusting state was visually observed.

The results are shown in Table-11.

[Effect of the invention] As can be seen from the above test results, when the admixture of the present invention is added to cement, there is no significant change in the setting time first, but cracks due to expansion, warpage, etc. do not occur and normal curing occurs. (See setting and stability test above). Then, the compressive strength of concrete increases, and especially the initial strength increases remarkably (see the concrete mix and compressive strength test above).

Further, the water permeability and the water absorption are greatly reduced, and the effect is great particularly in the case of dry air curing (see the above water permeability and water absorption test).

Furthermore, even when rust is observed in the mortar, no rust is generated under the above-mentioned conditions, so that it shows a very excellent rust preventive effect (see the above observation of rust). Thus, the admixture of the present invention can be added to the mortar by adding only 2% by weight.
It is very useful because it can modify concrete.

Claims (1)

[Claims] 1. A rust preventive mortar-concrete admixture comprising silicate, sodium hydroxide, nitrate, nitrite, water reducing agent, alkanolamine and tributyl phosphate.