JP4518908B2 - Sulfuric acid resistant mixture - Google Patents

Description

  The present invention relates to a mixture of mortar, concrete or the like having high durability against sulfuric acid corrosion.

  Concrete structures such as pipes and sludge storage tanks provided in sewerage facilities gradually corrode from the inside because sulfate-reducing bacteria decompose hydrogen sulfide gas released from the raw water into the gas phase and produce sulfuric acid. To do. Moreover, the site | part corroded violently by the concentrated sulfuric acid shows strong acidity (for example, pH 1-3), and while it becomes a powder form, it also dissolves the reinforcing bar in concrete.

  Conventionally, various studies on durability of concrete against sulfuric acid corrosion (hereinafter referred to as “sulfuric acid resistance”) have been conducted. For example, Non-Patent Document 1 listed below includes four types of fine bones such as blast furnace slag granulated sand. As a result of immersing 8 kinds of mortar specimens made by combining 2 kinds of binder and 2 kinds of binders (cement) in sulfuric acid of pH 0.5, the relationship between the immersion period and the weight loss rate due to sulfuric acid erosion is described. Has been.

  According to this document, specimens using ordinary sand as fine aggregate and ordinary Portland cement as a binder have a weight loss rate of about 70% after 8 weeks of immersion in sulfuric acid, Specimens using blast furnace slag granulated sand as fine aggregate and blast furnace slag fine powder 70%, fly ash 20%, ordinary Portland cement 10% as binder, weight loss rate after 8 weeks of immersion in sulfuric acid Is about 40%. From this, it can be seen that if blast furnace slag granulated sand is used as the fine aggregate, the sulfuric acid resistance is higher than that of the concrete using the fine aggregate of ordinary sand and other materials.

Abstract of the 58th Cement Technology Conference 2004 ([81] Fundamental Study on Sulfate Erosion of Hardened Cement Using Various Aggregates / Kazumichi Shirasei, Faculty of Engineering, Chiba Institute of Technology, Graduate School of Engineering, The University of Tokyo Hirotomo Aoki, Kento Uomoto, Institute of Industrial Science, The University of Tokyo / May 25, 2004)

  However, the above document does not clarify the cause of the highest sulfuric acid resistance of mortar using blast furnace slag granulated sand as fine aggregate, and it is not intended to develop mortar and concrete having higher sulfuric acid resistance than before. Absent.

  An object of the present invention is to provide a mixture of mortar, concrete, or the like that has a higher resistance to sulfuric acid than before.

Sulfuric acid mixtures according to the invention, the binder hardens by reacting with water, and fine aggregate consisting of particles of sand, by mixing calcium oxide (CaO) which is used as part of the fine aggregate Become.

  In an embodiment of the present invention, the binder is cement, and water can be further mixed.

When a fine aggregate is used as the aggregate, calcium oxide can be mixed as a part of the fine aggregate. Preferably, the calcium oxide is mixed so that the total of the calcium oxide contained in the fine aggregate other than the calcium oxide in the fine aggregate is 59.3 % or less of the total weight of the fine aggregate. It is good.

  Moreover, blast furnace slag granulated sand can be used for the fine aggregate.

  According to the present invention, by mixing calcium oxide (CaO), it is possible to provide a material for making a mixture having higher sulfuric acid resistance than conventional mortar and the like that does not use calcium oxide. In this case, cement can be mixed as a binder. If cement is used as the binder and fine aggregate is used for the aggregate, it becomes a mortar material, or if both fine aggregate and coarse aggregate are used for the aggregate, it becomes a concrete material.

  Moreover, the solidified body of a mixture with high sulfuric acid resistance can be made by mixing water. For example, if fine aggregate is mixed, a solidified mortar with high sulfuric acid resistance can be made, and if both fine aggregate and coarse aggregate are mixed, a solidified solid with high sulfuric acid resistance can be made. it can.

Further, when calcium oxide is used as a part of the fine aggregate, the total of the calcium oxide and the calcium oxide contained in the fine aggregate other than the calcium oxide in the fine aggregate is the fine aggregate. By mixing so that the total weight is 59.3 % or less, it is possible to prevent the mixture from excessively expanding and cracking when solidified.

  Moreover, a mixture with higher sulfuric acid resistance can be made for fine aggregate by using blast furnace slag granulated sand.

  FIG.1 and FIG.2 shows the mixing | blending amount of the mortar of an Example, the mixing amount of a calcium oxide (CaO), and the chemical component content of the fine aggregate to be used. Mortar is a mixture of fine aggregates mainly composed of cement and solidified particles such as sand, which are hardened by hydration reaction with water. Fine aggregates are particles such as sand that pass through a 10 mm mesh screen and 85% by weight or more through a 5 mm mesh screen, and are used as materials for mortar and concrete.

The mortar of the example is made by mixing water, cement, and fine aggregate, and more specifically, solid or powdered calcium oxide is mixed as a part of the fine aggregate. Moreover, about the basic mixing | blending of each mortar, the ratio of the unit amount of water: cement: fine aggregate is 1: 1: 0.4. The unit amount is the weight of each material used when making 1 m ^{3 of} concrete.

  Furthermore, in the Examples, these mortars were classified into two types (FIGS. 1 and 2) based on the type of fine aggregate. Specifically, the mortar shown in FIG. 1 includes water “W”, ordinary Portland cement “NC”, ground granulated blast furnace slag “Sb” (sometimes called “blast furnace slag fine aggregate”), and calcium oxide “ The mortar in FIG. 2 is composed of water “W”, ordinary Portland cement “NC”, ordinary sand “Sn (sometimes called mixed sand)”, and calcium oxide “CaO”. It is made. Blast furnace slag granulated sand is, for example, particles made by finely pulverizing slag discharged from a blast furnace of a steel mill by quenching with water and granulating it.

  As a specific method for creating the mortar, for example, a general method based on JIS R 5201 can be employed. More specifically, the kneading is preferably carried out using a Hobart-type mortar mixer by a tabl mixing method in order to suppress bleeding in which solid particles settle in water. In the double mixing method, the water to be used is divided into primary water and secondary water, the primary water and cement are mixed once, then the secondary water is added and the cement paste is mixed to make the bleeding extremely small. Can do.

  In FIG. 1 and FIG. 2, among the names of each mortar such as “NCb-CaO * 1.1” described in the leftmost column, for example, the portion “* 1.1” is the amount of calcium oxide mixed and its It represents the total amount of calcium oxide contained in the entire mortar fine aggregate. Specifically, the mortar represented by “NCb—CaO * 1.1” (FIG. 1) contains calcium oxide in an amount 0.1 times the amount of calcium oxide originally contained in blast furnace slag granulated sand. This indicates that the amount of calcium oxide in the fine aggregate after mixing with calcium oxide is 1.1 times the amount of calcium oxide in ground granulated blast furnace slag before mixing. Furthermore, in the examples, since calcium oxide is used as a part of the fine aggregate, the composition of the mortar is “water: cement: fine aggregate = 1: 1: even after being mixed in the fine aggregate. The weight ratio of 0.4 "is maintained.

Next, a method for calculating the mixing amount of calcium oxide will be described. For example, in the mortar of “NCb—CaO * 1.1”, when the unit amount of blast furnace slag granulated sand is 843 kg / m ³ when calcium oxide is not mixed, the blast furnace slag granulated sand is originally 42.7% by weight. Therefore, the amount of calcium oxide in the unit amount of ground granulated blast furnace slag is 360 kg / m ³ . Here, simply adding 0.1 times the amount of calcium oxide in the ground granulated blast furnace slag (about 36 kg / m ³ ) increases the amount of fine aggregate itself to 879 kg / m ^3. The weight ratio of “water: cement: fine aggregate = 1: 1: 0.4” cannot be maintained. Accordingly, when recalculated so that the amount of fine aggregate becomes 843 kg / m ³ while maintaining the above weight ratio, the general composition of the fine aggregate is 808 kg / m ³ for ground granulated blast furnace slag and 34. ³ for calcium oxide. 5 kg / m ³ , and the fine aggregate contains about 45% by weight of calcium oxide. That is, it is understood that 34.5 kg / m ^{3 of} calcium oxide may be mixed when making a mortar of “NCb—CaO * 1.1”. For other mortars, the amount of calcium oxide mixed can be determined by the same calculation.

  On the other hand, the amount of calcium oxide that can be mixed into the fine aggregate becomes a problem. When calcium oxide is added as a material for mortar or concrete, it has a property of expanding when it is solidified. Therefore, if the mixing amount is too large, the mortar may be excessively expanded to cause cracks. Therefore, in the examples, when the appearance of each mortar (FIGS. 1 and 2) on the seventh day after kneading was observed, as shown in the figure, there were three “NCb-CaO * 2.0 to 8.0”. The mortar expanded and cracked and broke, making it unusable.

Therefore, based on this result, the total amount of calcium oxide and calcium oxide contained in the fine aggregate other than the calcium oxide in the fine aggregate is 59.3 % or less of the total weight of the fine aggregate. It can be said that it is preferable to use it. Specifically, when making the mortar “NCb-CaO” (FIG. 1) with a weight ratio of “water: cement: fine aggregate = 1: 1: 0.4”, the unit amount of fine aggregate is 843 kg. / M ³ , the total amount of calcium oxide is preferably 500 kg / m ³ (500/843 = 59.3%) or less.

  The greatest feature of the mortar of the example is that the sulfuric acid resistance of the mortar is improved by mixing an appropriate amount of solid or powdered calcium oxide. The sulfuric acid resistance can be judged based on, for example, the weight reduction rate when the mortar is immersed in a sulfuric acid solution for a predetermined period. The lower the weight reduction rate, that is, the lower the degree of sulfuric acid erosion, the higher the sulfuric acid resistance. It will be. The reason why the inventors of the present invention have reached the technical idea of adding calcium oxide will be described.

  As the sulfuric acid immersion test result described in Non-Patent Document 1 mentioned above, the mortar with the highest sulfuric acid resistance uses blast furnace slag granulated sand as a fine aggregate, but the inventors of the present invention also A sulfuric acid immersion test was conducted using a mortar specimen using fine granulated blast furnace slag sand, and similar results were obtained. Specifically, as shown in FIGS. 3 and 4, the weight reduction rate of the mortar made of blast furnace cement and blast furnace slag granulated sand becomes about 31% after 32 days from immersion in a 10% sulfuric acid solution. The result that sulfuric acid resistance is higher than any mortar is obtained. However, just by looking at the results, it is not possible to develop mortar or concrete having higher sulfuric acid resistance than before.

  Therefore, the inventors of the present invention further examined the results of the sulfuric acid immersion test using various blended mortars, and elucidated the cause of the highest sulfuric acid resistance when blast furnace slag granulated sand was used as fine aggregate. They started to develop a mixture of mortar and concrete with higher sulfuric acid resistance. The composition of the mortar used in the experiment is “cement: sand: water = 1: 1: 0.4”, and the components contained in the various materials used for preparing the mortar are shown in Table 1 below.

In this table, NC is ordinary Portland cement, BC is blast furnace cement type B, EC is eco-cement, fine aggregate n is ordinary sand, c is copper slag fine aggregate, f is ferronickel slag fine aggregate, b is Blast furnace slag granulated sand is shown. The value representing the chemical components and mineral components, shows the weight percent of each component in the case where the weight of all the chemical components or mineral components contained in the mortar of 1 m ³ and 100%, respectively. Further, F.A. M.M. Indicates the fineness modulus.

FIG. 5 shows the results of multiple regression analysis showing the relationship between the weight loss rate of mortar after 32 days of sulfuric acid immersion, the mineral component content of cement, and the chemical component content of fine aggregate. In this multiple regression analysis, the weight loss rate after 32 days of sulfuric acid immersion is used as an explanatory variable, and the explanatory variable is considered to contribute to C ₂ S and sulfuric acid resistance, which are considered to have relatively high chemical resistance from cement. C ₃ A was selected, and calcium oxide (CaO) and silica (SiO ₂ ) as main components were selected from the fine aggregates.

  As shown in the figure, the coefficient of determination was as high as 96.62%, and a correlation was observed between the contents of these four components in the mortar and the sulfuric acid resistance. Further, among the partial regression coefficients representing the influence of various components selected as explanatory variables on sulfuric acid resistance, the value related to CaO in the fine aggregate is a positive value, and the knowledge that CaO improves sulfuric acid resistance. Got. In other words, if CaO was added as a material for mortar or concrete, it was concluded that if it could be prevented from expanding and cracking during solidification, the sulfuric acid resistance was improved in proportion to the amount of mixing.

In order to verify the fact that sulfuric acid resistance is improved when calcium oxide is mixed, in the examples, the sulfuric acid resistance of each mortar was confirmed. Specifically, each mortar (FIGS. 1 and 2) was molded into 4 cm square (cutting, etc.) to prepare a specimen, and immersed in a 500 cm ³ sulfuric acid solution (for example, sulfuric acid concentration 10%), the weight reduction rate. It was confirmed. As a rule, the entire amount of the sulfuric acid solution was changed every week. The weight reduction rate is the weight measured after the specimen was immersed in a sulfuric acid solution for a certain period of time and then the part that easily peeled off was removed with a wire brush, and the surface of the specimen was dried, and before the specimen was immersed in sulfuric acid. It calculated | required based on the weight measured in the state. In addition, the mortar specimen “NCb-CaO * 2.0 to 8.0” which expanded and cracked in the solidified state is in a state where it cannot be used in the first place, so curing after solidification is not performed. The immersion test was not performed.

  In the case of the mortar “NCb-CaO” (FIG. 1), the sulfuric acid resistance of the mortars of the examples is based on the sulfuric acid resistance of the mortar “NCb” not mixed with calcium oxide. In the case of “CaO” (FIG. 2), the sulfuric acid resistance of the mortar “NCn” was used as a standard. Specifically, the mortar “NCb” has a weight reduction rate of 38.68% after 32 days of sulfuric acid immersion (FIG. 3), and the mortar “NCn” has a weight reduction rate of 32.68% after 32 days of sulfuric acid immersion. (FIGS. 3 and 4). And as a result of the sulfuric acid immersion test, the improvement of sulfuric acid resistance was confirmed about all the mortars.

Further, although the expansion agent contains calcium oxide, the unit amount is determined to be about 30 kg / m ^{3 in} order to prevent excessive expansion and cracking, and the expansion rate is controlled (for example, delayed). The chemical components of the fine aggregate shown in Table 1 are almost the same. Therefore, the swelling agent cannot be used in excess of the above-determined amount or used alone as calcium oxide. However, in practice, by using an appropriate amount of calcium oxide as a part of fine aggregate as in the example, it prevents cracking due to expansion during solidification, and more than mortar made by the conventional method. Mortar with high sulfuric acid resistance can be made.

  As mentioned above, although the mortar of an Example was demonstrated, also about the concrete made by further mixing a coarse aggregate, there can exist an effect of an improvement of sulfuric acid resistance similarly to the mortar of an Example. Furthermore, in the mortars of the examples, cement is used as the binder, but it is also possible to use a resin. For this resin, for example, an acrylic ester or a raw material (latex) of rubber can be used. More specifically, as the rubber, an SBR (styrene-butadiene rubber) type synthetic rubber obtained by copolymerizing styrene and butadiene in a ratio of about 1: 3 can be used.

  Moreover, although the mortar was illustrated as a sulfuric acid resistant mixture in the Example, the mixture of the state which mixed the binder which reacts with water and solidifies, the aggregate which consists of particle | grains, such as sand, and calcium oxide may be sufficient. This mixture is made of, for example, cement as a binder, fine aggregate or fine aggregate and coarse aggregate as an aggregate, and further mixed with water (for example, kneaded), thereby making it resistant to sulfuric acid. It becomes a material for making a mixture of high mortar and concrete.

The figure which shows the mixing | blending of specimen NCb, the mixing amount of a calcium oxide, the chemical component content of a fine aggregate, etc. The figure which shows the mixing | blending of specimen NCn, the mixing amount of a calcium oxide, the chemical component content of a fine aggregate, etc. The figure which shows the sulfuric acid immersion test result at the time of paying attention to the influence which a fine aggregate exerts on sulfuric acid resistance. The figure which shows the sulfuric acid immersion test result at the time of paying attention to the influence which cement has on sulfuric acid resistance. The figure which shows the result of the multiple regression analysis which shows the weight reduction rate of the mortar 32 days after sulfuric acid immersion, the mineral component content of cement, and the chemical component content of a fine aggregate.

Claims (5)

A sulfate-resistant mixture obtained by mixing a binder that hardens in response to water, a fine aggregate made of particles such as sand, and calcium oxide (CaO) used as a part of the fine aggregate .   2. The sulfuric acid resistant mixture according to claim 1, wherein the binder is cement.   The sulfuric acid resistant mixture according to claim 1 or 2, further comprising water. The sulfate-resistant mixture according to any one of claims 1 to 3 , wherein the calcium oxide is a sum of the calcium oxide contained in the fine aggregate other than the calcium oxide in the fine aggregate. A sulfuric acid-resistant mixture, which is mixed so that its weight is 59.3% or less. The sulfuric acid resistant mixture according to any one of claims 1 to 4 , wherein blast furnace slag granulated sand is used as the fine aggregate.

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