JPH0512295B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to concrete admixtures that are mainly used for concrete, mortar, and cement, and in particular, concrete admixtures used to improve the mechanical strength and waterproofness of concrete, mortar, etc. This is a proposal regarding its manufacturing method. Such concrete admixtures are used in addition to concrete, as well as mortar and cement, to impart or improve desired properties. Among them, waterproof admixtures (hereinafter simply referred to as "waterproofing agents")
By promoting the hydration reaction of cement,
Cement gel is used as a material that has the function of blocking water absorption and permeation in mortar and concrete by filling voids and forming a water-impermeable or water-repellent layer or membrane inside mortar or concrete. [Prior Art] Conventionally, the waterproofing agents used include naturally occurring pozzolanic substances such as clay and clay, fly ash produced as a by-product in thermal power plants, fine particulate silica hume produced as a by-product during the production of ferrosilicon, and calcium chloride. , sodium silicate, higher fatty acids, liquid paraffin (paraffin emulsion), water-soluble polymers, etc. were used. [Problem to be solved by the invention] Among the above-mentioned mixtures that reduce water permeability that have been conventionally used, naturally occurring pozzolanic materials such as white clay and slate are natural products, so they do not have physical properties. However, since there are many variations in chemical properties, the effect when added to mortar or concrete is inconsistent, so there was a problem in that properties had to be tested before use. There are even examples of this, such as when the properties of the same mine change slightly when the mining area changes slightly. In addition, in the case of the fly ash, the reaction rate is slow and it takes several months for the effect to become apparent.On the other hand, the silica hume has excellent performance as a waterproofing agent, but has problems such as a scarcity of supply sources and a high price. It was hot. Furthermore, in the case of calcium chloride, sodium silicate, etc., although they exhibit waterproof properties, they are expensive and have the problem of lowering the strength of mortar and concrete. The present invention aims to overcome the problems of conventional waterproofing agents as described above, and is particularly effective in improving the mechanical strength and water impermeability of mortar and concrete, and is also effective in preventing alkaline aggregate reactions. The purpose is to provide an effective concrete admixture. [Means for solving the problem] The above objectives will be reliably achieved by adopting means that have the following points as their main points. That is, the present invention
A coating layer of silicic acid sol and/or silicic acid gel obtained by neutralizing an alkali silicate with an acid is provided on the surface of a silicic acid-containing substance containing soluble silica, and We propose a concrete admixture made by adhering fine particulate silicic acid to the surface. [Function] The "silicic acid-containing substance containing soluble silica" which is the main component of the admixture of the present invention is a pozzolanic natural mineral such as white clay, clay, fly ash, silica-containing slag, etc., and the particle size when used is an average particle size. Preferably 1 in diameter
It is about ~100μm. Normally, natural minerals can be used as is, but they may be crushed if necessary. In some cases, amorphous high silica (containing a large amount of soluble silica) is preferable. This is because so-called high-silica admixtures with a high silica content increase the strength and water resistance of concrete. The reason for this is that the amorphous silica (soluble silica) contained in this admixture causes free CaO in the concrete.
This creates a stable, insoluble substance called lCaO・mSiO ₂・nH ₂ O (called a polazon reaction), which strongly bonds between concrete particles, resulting in an increase in strength, and this stable substance
It is thought that water impermeability increases because by reducing the voids caused by breathing after water has drained out, concrete becomes denser and fills the voids. However, this porazon reaction is very slow with naturally occurring amorphous silica, fly ash, and silica found in mine slag, and a certain temperature and long time are required for complete reaction, so improvements are desired. On the other hand, if alkali silicate (sodium silicate), which is used as a waterproofing agent, is mixed into concrete,
The Na ₂ O part in sodium silicate (mNa ₂ O・nSiO ₂ ) replaces CaO, creating insoluble mCaO・nSiO ₂ , which liberates alkali, causing an alkali aggregate reaction and causing the concrete to collapse. , undesirable for use in concrete. Therefore, the present inventors conducted research to solve the above-mentioned bottlenecks of the silicic acid substance and sodium silicate, and found that alkali silicate can be neutralized with an inorganic acid (e.g. sulfuric acid, hydrochloric acid, etc.) or an organic acid. The active sol or gel silica is prepared in advance or subsequently, and this is coated on the surface of natural porazone-based materials, fly ash, or slag, and then white carbon, silica fume, etc. are coated on the surface. Fine particles (approximately 10~
They discovered that good results could be obtained by sprinkling amorphous silicic acid (20 μm). It was also found that concrete obtained by adding the admixture thus obtained has greater strength and excellent water impermeability than concrete that does not have amorphous silica attached. Sols and gels produced in the neutralization process of alkali silicate are composed of colloidal particles, and the surfaces of these colloidal particles have a large amount of silanol groups (-Si
−OH). Therefore, when the surface of a silica-containing substance such as porazone is coated with this sol or gel, the surface is activated. In addition, such silanol groups can be heated (especially
If the temperature exceeds 200℃, a dehydration reaction will occur, forming siloxane bonds (Si-O
-Si), so it is desirable to perform the drying process at 200°C or lower. In short, the present invention is characterized in that a coating layer of silicic acid sol and/or gel is formed on the surface of a silica-containing substance containing soluble silica, and amorphous silica is further adhered to the surface. However, as a coating agent (prepared in advance) for forming the above-mentioned coating layer, an alkali silicate neutralized with an inorganic or organic acid such as sulfuric acid, hydrochloric acid, nitric acid, or phosphoric acid is used. The pH of the coating agent neutralized as described above is about 9 to 4 (9: sol 7 gel: 4)
shall be. Further, the concentration of this coating agent should be set to a silica sol suitable for coating, taking into account the next surface coating, but even with silica gel, the surface can be coated sufficiently uniformly by using a mixer. Please note that the drying of the product after this coating depends on the surface condition.
It is desirable to dry at a temperature below 200℃. In addition to the method described above, such surface coating may be carried out by first mixing a predetermined amount of alkali silicate with a silica-containing substance, and then neutralizing it by adding the same acid as above, and using it as a concrete admixture. It has the same effect. In the present invention, the mixing ratio of alkali silicate and silica-containing substance is considered as follows. In other words, when the amount of alkali silicate is less than 0.1wt%, it has no effect on the silica-containing substance, while when it is 40wt%
Above this amount, the effect of addition becomes limited and becomes expensive.
When applied to cement, approximately 20wt% is appropriate as the upper limit of addition amount. [Example] As an example of the present invention, first, JIS No. 3 water glass was added to natural silicate clay (total silica: 71.5%, soluble silica: 47.3%, average particle size: 10 μm) with 10 times the amount of water. The gel obtained by diluting and neutralizing with sulfuric acid to pH 7 was mixed with 2.5 parts (sample A) and 5 parts (sample B) of water glass per 100 parts of the above clay,
It was dried at 100°C and crushed to obtain a sample. Next, JIS diluted 10 times with water to 100 parts of white clay.
3 glass with water glass etc. 2.5 parts (sample C) and
5.0 parts (sample D) were mixed, and sulfuric acid (10% sulfuric acid) necessary to neutralize the pH to 7 was added and mixed, followed by drying and crushing to obtain a sample. Samples E and F are samples in which fly ash (total silica 58.6%, soluble silica 33.7%, average particle size 23 μm) is used instead of the silicate clay. 90.7% soluble silica, 72.4% soluble silica, average particle size 0.3 μm) were added and mixed as Samples G, H, and I (products of the present invention), respectively, and Samples J and I were obtained by adding silica hume to Sample E, respectively. K and L (products of the present invention). Furthermore, regarding the prior art, an example using untreated silicate clay is designated as M, and an example using untreated fly ash is designated as N. For each of the above samples (A to N) shown in Table 1, test results are shown in Table 2 regarding the compressive strength and water permeability when added to mortar according to the JIS A1404 test method for cement waterproofing agents for construction. . As can be seen from this table, for example, in Test No. 9, compared to the conventional product Test No. 15, the compressive strength after 6 months was 26 kgf/cm ² higher, and the water permeability was 26 kgf/cm 2 higher. It has also dropped by 6g,
The admixture of the present invention showed better results in both strength and waterproofness. Moreover, it was found that both strength and water permeability were excellent when compared with Samples A to F.

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〔Effect of the invention〕

As explained above, according to the present invention, when the obtained admixture is applied to concrete, first, the amorphous silica attached to the surface and the coated active silica undergo a porazon reaction, which improves strength and water permeability. In addition, the silica-containing material that forms the core reacts over a long period of time, making it possible to obtain concrete that is strong and water-resistant from short to long term.

Claims (1)

[Claims] 1. A concrete admixture that has a coating layer of silicic acid sol and/or silicic acid gel on the surface of a silicic acid-containing substance containing soluble silica, and further has fine particulate silicic acid adhered to the surface of the coating layer. .