JP2001316145A - Admixture for hydraulic composition consisting of chaff ash and its application - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an admixture for a hydraulic composition with early development of strength, resistance to permeation of chloride ion and a controlled alkali-aggregate reaction. SOLUTION: The admixture consists of a chaff ash with the following properties: specific surface area (BET) is 20-200 m2/g, preferably 50-200 m2/g, ignition loss is <=5%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydraulic composition admixture composed of rice husk ash having a specific surface area within a certain range, a hydraulic composition containing the admixture, and a concrete or concrete product thereof.

[0002]

2. Description of the Related Art Reinforced concrete structures have long been considered to have a semi-permanent life. However, concrete structures due to early neutralization, salt damage, frost damage, alkali-aggregate reaction, etc. in recent decades have been considered. The phenomenon of early deterioration of steel has become apparent, and its durability has recently been questioned. Salt damage is a phenomenon in which concrete reinforcement corrodes due to the effects of salt contained in seawater and concrete aggregate.In the civil engineering and construction field, along with alkali-aggregate reaction and carbonation, deterioration of concrete structures is a major factor. It has been attributed. As a method of preventing this salt damage, thorough washing of aggregates such as sea sand, and control of the chloride ion content of chemical admixtures and kneading water ensure that the total amount of chloride in concrete is within the regulation value (0.30 kg / m ³ or less).

[0003]

Although the possibility of chloride ions being mixed is reduced by such management, measures against intrusion of chloride ions from the outside have been insufficient. In particular, when sodium chloride is used as a structure near the coast or as an anti-icing agent, corrosion of reinforcing steel due to intrusion of chloride ions is inevitable. As one of the countermeasures, there has been proposed a method of adding a pozzolan to densify a concrete structure to suppress the intrusion of chloride ions (Japanese Patent Laid-Open No. 3-40946). It takes a long time to react with the hydrate, and as a result, it has not been used much because the initial age strength is low and the construction period is long.

On the other hand, since rice husk ash contains a large amount of silica and has a high pozzolanic activity, attempts have been made to utilize it as a cement admixture. For example,
The Journal of Concrete Engineering (1993, Vol. 15, No. 1) entitled "Highly active rice ash production method and properties of concrete using it" and "Basic properties of mortar mixed with rice husk ash" The relationship between the amount of concrete mixed with rice husk ash in ordinary Portland cement and its compressive strength has been reported. However, all of these reports mainly examine the mixing amount of the rice husk ash and the production (firing) method, and there is almost no study on the effect on chloride ions or the effect on the specific surface area.

According to the present invention, the rice husk ash can be used as a suitable pozzolanic admixture by examining the effect on the compressive strength and chloride ion of concrete and the effect of its specific surface area. That is, according to the study of the present inventors, rice husk ash has a specific surface area within a certain range and a material outside this range has a remarkable difference in expression of initial strength, resistance to chloride ion penetration, and the like. Was found to work. The present invention utilizes a specific range of rice husk ash as an admixture for hydraulic compositions based on such findings.

In recent years, it has been difficult to completely eliminate the use of reactive aggregates due to a shortage of aggregate resources. The present invention also makes it possible to use reactive aggregates, since cracks due to the aggregate reaction can be prevented.

[0007]

That is, the present invention relates to (1) an admixture for hydraulic composition, which comprises rice husk ash having a specific surface area (BET) of 20 to ²⁰⁰ m ² / g. The admixture preferably has (2) a specific surface area (BET) of 50 to 200.
It is an admixture for hydraulic composition composed of rice husk ash having m ² / g and a loss on ignition of 5% or less. Further, the present invention provides (3) the above (1)
Or (2) a hydraulic composition comprising the rice hull ash admixture, (4) a concrete or concrete product produced by the hydraulic composition of (3).

The mortar or concrete using the admixture of rice husk ash according to the present invention has improved initial strength development and excellent resistance to chloride ion penetration. Further, it has a high effect of suppressing the alkali-aggregate reaction, and is excellent in acid resistance and abrasion resistance.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on embodiments. The admixture of the present invention is made of rice husk ash having a specific surface area within a certain range. When rice husks are burned at an appropriate temperature of about 600 ° C., rice husk ash having high pozzolanic activity is obtained. The properties of the rice husk ash are greatly affected by the pozzolan activity, the amount of unburned carbon, and the like. That is, if the combustion temperature is too high, minerals such as cristobalite are generated, and the pozzolan activity is reduced. When the combustion temperature is too low or the combustion time is too short, the unburned carbon increases. When rice husk ash is mixed with concrete or mortar, if the pozzolan activity of the rice husk ash is low, the strength of concrete or the like cannot be sufficiently increased. On the other hand, if the amount of unburned carbon is large, the AE water reducing agent, the water reducing agent and the like are adsorbed, and the effect of these admixtures is reduced, which is not preferable.

The admixture of the present invention has a specific surface area (BET specific surface area) measured by the BET method of from 20 m ² / g to ²⁰⁰ m ² / g.
g of rice husk ash with a low unburned carbon content. Rice husk ash having a specific surface area of 20 m ² / g or more has a high pozzolanic activity and rapidly reacts with a hydraulic substance to increase the initial strength. Incidentally, those having a specific surface area exceeds 200 meters ² / g because production is difficult, it is appropriate chaff ash specific surface area of practically 20 to 200 m ² / g. Preferably, the specific surface area is 50 m ² / g or more and the ignition loss is 5% or less. As shown in the examples, rice husk ash having a specific surface area and loss on ignition within the above ranges, when mixed with concrete or mortar, has excellent initial strength and resistance to chloride ion penetration and alkali aggregate. The effect of suppressing the reaction is high, and the effect of being excellent in acid resistance and abrasion resistance can be obtained. A specific surface area of 50 m ² / g or more, preferably 130m ² /
This effect is particularly excellent when the ignition loss is 2 g or less and the ignition loss is 2% or less. Such rice husk ash can be obtained, for example, by a production method proposed by the present inventors (Japanese Patent Application Laid-Open No. H11-141825).

[0011]

EXAMPLES The following experiments were conducted using the admixture of the present invention and the admixture of the comparative example. Table 1 shows the cement and admixture used in the test. Each of the rice husk ash used in the present invention has a large specific surface area and a small ignition loss as compared with the rice husk ash of the comparative example. This ignition loss has a correlation with the unburned carbon amount, and the smaller the ignition loss is, the smaller the unburned carbon amount is. Ignition loss is to standard (J
It is measured based on IS A 6201).

[0012]

[Table 1]

Example 1 (Strength development test) Using the admixture of rice husk ash according to the present invention and the admixture of the comparative example, a mortar was prepared according to the composition shown in Table 2, and formed into a columnar shape (φ50 × 100 mm). The specimen was prepared. This specimen was cured in wet air (20 ° C., 85% RH) for one day, and then cured in water (20 ° C.), and its compressive strength was measured at 3, 7, and 28 days of age. The average compressive strength was obtained by measuring four specimens of each specimen for each material age. The results are shown in Table 2 and FIG. The sample (No.A1 to A3) mixed with rice husk ash having a specific surface area of 133.5 m ² / g has compressive strength of 100 N / mm ² or more at 28 days of age, and is much more compact than other samples. High strength. Samples (No. A4 to A6) mixed with rice husk ash having a specific surface area of 53 m ² / g also show relatively high compressive strength. On the other hand, the compressive strength of the sample (No. B2 to B4) containing rice husk ash having a specific surface area of 20 m ² / g or less and ignition loss of 5% or more was obtained by blending silica fume (SF) or blast furnace slag (GFS) (N
o.B5 ~ B10), the compressive strength of 3 days old is lower than plain mortar (No.B1) which does not contain admixture,
Most of the compressive strengths at the age of 28 days were 90 N / mm ² units.

The specific surface areas of the rice husk ash (RHA4) and silica fume of the comparative examples are all 20 m ² / g or less, and it takes time for the pozzolan reaction to proceed. Therefore, the 3-day-old strength is lower than that of plain mortar (No. B1). This tendency is common to conventional pozzolans.Concrete mixed with conventional pozzolans generally has low initial strength, and the long-term age strength becomes higher than plain concrete after the age has passed and the pozzolanic reaction has progressed. .

On the other hand, the compressive strength of the concrete containing rice husk ash of the present invention is higher than that of plain concrete containing no admixture even at 3 days of age, and is higher than that of concrete mixed with other admixtures at all ages. High compressive strength. This is because, in the present invention, since the specific surface area of the rice husk ash is large, the pozzolanic reaction between the silica and the cement hydrate in the rice husk ash rapidly progresses from the initial age to produce calcium silicate hydrate. This is because the cured body structure becomes dense and has a high compressive strength.

[0016]

[Table 2]

Example 2 (Chloride ion permeability test) Using the admixture composed of rice husk ash according to the present invention and the admixture of the comparative example, a mortar was prepared according to the composition shown in Table 3, and a specimen for measuring compressive strength was prepared. (φ50 × 100 mm) and a test specimen (φ100 × 200 mm) for measuring the accumulated passing electric charge. After curing these specimens for 1 day in wet air (20 ° C, 85% RH),
℃) Curing was performed, and the compressive strength and the accumulated amount of electricity passed were measured for the ages 7 and 28. The specimen for measuring the quantity of electricity was divided into two parts at about the center one day before the age of the test material, and the cut surface was polished into a disk shape (φ100 × 50 mm). The specimen was kept in a vacuum vessel (reduced pressure to 1 mmHg) for 3 hours while immersed in water, then returned to atmospheric pressure, and kept in water until the test material age. The measurement of the amount of accumulated passing electricity is based on the U.S. standard test (AASHTO T
25912) [RCPT: Rapid Chloride Permeability Test]
It went according to. First, both end faces (φ100m
m) with an electrode cell (approximately 500 cm ³ ), the anode cell is filled with an aqueous sodium hydroxide solution (0.3N concentration) and the cathode cell is filled with an aqueous sodium chloride solution (3.0% concentration), ) Was applied, and the current value from the start of energization to the lapse of 6 hours was recorded every 30 minutes to calculate the integrated amount of passing electricity. This quantity of electricity is 2 per age for each specimen.
An average value was obtained by measuring each of the test specimens. Table 4 shows the results.
It was shown to. The cumulative amount of passing electricity increases as the ion mobility in the concrete (mortar) increases, and therefore, the chloride ion hardly permeates the concrete (mortar) as the cumulative passing amount of electricity decreases.

Regarding the compressive strength of the mortar, the samples (Nos. A20 to A28) containing rice husk ash (RHA1 to RHA3) having a specific surface area of 50 to 133.5 m ² / g were all higher in compressibility than plain mortar. Although showing the strength, the samples (No. B21 to B23) using rice husk ash (RHA4) having a specific surface area of 20 m ² / g or less have a lower compressive strength at 7 days of age than plain mortar.
The mortar using this rice hull ash (RHA4) has a compressive strength of 28 days of age, but the increase in rice husk ash admixture rate is only slight, but the rice husk ash (RHA1 to RHA3) with a large specific surface area is used. In the mortar, a large increase in strength was observed in proportion to the mixing ratio of rice husk ash.

Regardless of the material age and the type of rice husk ash, the cumulative amount of electricity passed is smaller in mortars mixed with rice husk ash than in plain mortars. There is a tendency for the amount of electricity to decrease. The cumulative amount of electricity passing through the mortar mixed with rice husk ash becomes particularly small when rice husk ash (RHA1) having a large specific surface area is used. When the mixing ratio of rice husk ash is 1% (No.A2
Mortar using rice husk ash (RHA4) with small specific surface area
In (No.B21 to B23), although not significantly different from the accumulated passing electricity of plain mortar, those using the rice husk ash (RHA1) of the present invention having a large specific surface area have a significantly reduced accumulated passing electricity, It shows high resistance to chloride ion penetration.

As described above, the mortar and concrete mixed with the rice husk ash having a large specific surface area have high resistance to chloride ion penetration and exhibit excellent strength development because of the rice hull ash contained therein. Amorphous silica reacts more quickly with cement hydrate than silica contained in rice husk ash with a small specific surface area to produce calcium silicate hydrate, and mortar to densify the cement cement structure. This is because it becomes difficult for chloride ions to penetrate therein.

[0021]

[Table 3]

[0022]

[Table 4]

Example 3 (Chloride ion permeability test 2) Concrete (No. B30, A30, A31) having the composition shown in Table 5 was formed into a block (100 × 100 × 200 mm), which was wet for one day. Sky
After curing at (20 ° C., 85% RH), it was cured in water for 27 days, and further air-dried (20 ° C., 65% RH) for one week. Two sides (100 ×
(200 mm) were coated with epoxy resin. This was immersed in a saturated sodium chloride aqueous solution at 20 ° C. for 26 weeks, then cut by a dry cutter to a thickness of 1 cm from the surface not coated with the epoxy resin, and crushed to obtain a sample, which was subjected to a predetermined potentiometric titration method (JCI The total chloride ion content in concrete was measured by -SC4 [potential difference titration method using chloride ion-selective electrode of [Method for analyzing salt content in hardened concrete]). The results are shown in Table 6 and FIGS.

Regardless of the mixing ratio of rice husk ash, the amount of chloride ions in concrete mixed with rice husk ash is much smaller than that of concrete not mixed with rice husk ash. In the concrete (No.B30) which does not mix rice husk ash, the amount of chloride ion in the portion 1.5 cm from the surface is about 0.16%, but in the concrete (No.A30, A31) which mixes rice husk ash, 1.5c
The amount of chloride ions in the m part is 0.024% and 0.02%, respectively.
0%. This value is below the rust limit value (0.025%), which is generally said to cause corrosion of reinforcing steel. In addition, 0.5cm from the surface
Table 6 shows the chloride ion diffusion coefficient obtained by the diffusion equation based on the total chloride ion amount in the 1.5 cm portion.
It was shown to. As is clear from the results, the chloride ion diffusion coefficient of concrete mixed with the rice husk ash of the present invention is as follows:
Although this is not mixed, it is almost halved with respect to the diffusion coefficient.

Further, concrete (B3
(A32) (B32, A33) was molded into a block (100 × 100 × 200 mm), which was cured for 1 day in moist air (20 ° C., 85% RH).
Cured in water for 7 days, air-dried for 1 week (20 ℃, 65% RH)
Cured. During this air-drying curing, four sides except for two sides (100 × 200 mm) which were in contact with the side of the concrete form were coated with an epoxy resin. Put this in a 20% aqueous sodium chloride solution
13 days of repetition of the dry / humidity test with one cycle consisting of immersion for 20 days and drying for 4 days at 20 ° C. and 50% relative humidity.
(91 days), cut with a dry cutter from the surface not coated with epoxy resin to a thickness of 1 cm, pulverized into a sample, and the total chloride ion in the concrete was measured by the above measurement method (JCI-SC4). The amount was measured. The results are summarized in Table 6.

Regardless of the water binder ratio, the total chloride ion content of the rice husk ash-mixed concrete of the present invention is smaller than that of concrete not mixed with it. In addition, the diffusion coefficient of chloride ions in the case where the rice husk ash of the present invention is mixed is small, and the diffusion coefficient of the concrete having a water binder ratio of 0.53 is reduced to half that in the case where the rice husk ash is not mixed. Thus, the concrete mixed with the rice husk ash of the present invention has a greater effect of suppressing chloride ion penetration than the comparative example. Moreover, the mortar and concrete mixed with the rice husk ash of the present invention have a particularly high compressive strength at the initial age compared to the comparative example.

[0027]

[Table 5]

[0028]

[Table 6]

Example 4 (Alkali-aggregate reaction)
The reaction between (Na ⁺ , K ⁺ ) and the amorphous silica in the reactive aggregate generates alkaline silica gel, and the gel absorbs water to cause expansion. The following test was conducted for this alkali aggregate reaction. Using crushed Pyrex (registered trademark) glass as the reactive aggregate, blending the admixture shown in Table 7 with mortar (formulation specified in JIS A 5308, Appendix 8)
Was adjusted, and the rate of change in mortar bar length was measured according to a predetermined measurement method (JIS A 5308, Appendix 8). Table 7 shows the results.
And FIG. In addition, the prescribed measurement method (JIS A 5308,
Annex 7: The alkali concentration reduction amount (Rc) and the dissolved silica amount (Sc) of the Pyrex glass measured by the alkali silica reaction test of aggregate (chemical method) were each 132 mmo.
l / l and 1918 mmol / l, and Rc ≦ Sc, the aggregate was determined to be not harmful (harmful).

Plain mortar without admixture (No.B4
0) The length change rate increases rapidly with the passage of the age of the measured material, and shows a 0.50% expansion at the age of 6 months. On the other hand, the length change rate of the mortar mixed with the admixture is smaller than that of the plain mortar. Plain mortar has the largest length change rate of 6 months, No.B41 (RHA4: 10
%), No.B44 (blast furnace slurries: 50%), No.B42 (RHA4: 20%), No.
B43 (silica fume: 10%), No.A42 (RHA2: 10%), No.A40 (RHA1:
10%), No.A43 (RHA2: 20%), and No.A41 (RHA1: 20%) in this order. In particular, No.A41 (RHA1: 20%) and No.A43 (RH
(A2: 20%) mortar shows almost no change in length until the age of 6 months, showing a remarkable inhibitory effect on the alkali-aggregate reaction. By the way, according to the above measuring method (JIS A 5308, Appendix 8), when the expansion rate of the mortar bar exceeds 0.10% at the age of 6 months, it is determined that the used aggregate is not harmless.

The admixture of the admixture of the present invention (RHA1, RHA2) has a low mortar expansion coefficient even when an aggregate determined to be not harmful by the above-mentioned measurement method (chemical method) is used, and a material age of 6 Less than the judgment value (JIS: 0.10%) in months. So far, the effect of inhibiting the alkali-aggregate reaction due to the incorporation of pozzolan has been reported.

The reason why rice husk ash having a large specific surface area exhibits the above-mentioned excellent inhibitory effect on alkali-aggregate reaction as compared with other pozzolans is considered as follows. Silica is formed by a network structure of siloxane bonds (Si-O-Si bonds), and the surface of the particles has a large number of silanol groups (Si-OH groups) generated by breaking siloxane bonds. Therefore, the fact that the specific surface area is large means that siloxane bonds in silica
(Si-O-Si bonds) are small and silanol groups (Si-OH groups) are large. Therefore, many hydrogen ions of silanol groups
Since (H ⁺ ) is replaced by many alkali ions, the effect of reducing the amount of alkali that reacts with the aggregate increases.
In addition, siloxane bonds of silica are cleaved by alkali ions, and alkali silicate gels (Si-ONa, Si-OK
Etc.), but in rice husk ash with a large specific surface area, a large number of alkali ions are bonded to silanol groups as described above, so the alkali-silica molar ratio (R ₂ O / SiO ₂ : R is an alkali metal) It becomes a high gel. This gel has a low degree of polymerization because a large number of alkali ions are bonded to the ends of the molecular structure. Even if the amount of such a gel is large, its expandability upon absorbing water is relatively low, so that the mortar or concrete containing the gel has a low expansion coefficient.

[0033]

[Table 7]

Example 5 (Acid resistance test) A mortar having the composition shown in Table 8 was prepared and a mortar having a columnar shape (φ50 × 100 ) was prepared.
mm) to give a specimen, which was humid air (20 ° C, 85
% RH) After curing, water curing (20 ℃) until the age of 28 days
Then, the mass reduction rate of the specimen when immersed in 2% hydrochloric acid at 20 ° C. for 26 weeks was measured every week. During the measurement, the eroded portion was removed with a wire brush, and the test solution was replaced with a new one every week. The results are shown in Table 8 and FIG. Regardless of the formulation, the weight of the mortar tends to decrease over the immersion period. Regardless of the water binder ratio, the mass reduction rate of plain mortar (No. B50, B51) was the largest during all the immersion periods, and the mass reduction rate tended to decrease as the rice husk ash mixing ratio increased. Specifically, plain mortar (No.B50: water binder ratio
0.30) (No. B51: water binder ratio 0.40), the mass reduction rate during the immersion period of 26 weeks is about 73% and about 84%, respectively. On the other hand, the mortar mixed with the rice husk ash (No. A50 to A53) has a mass reduction rate of 1/3 or less of the value of the plain mortar during the immersion period of 26 weeks, indicating remarkable acid resistance. Mortar mixed with rice husk ash has excellent resistance to hydrochloric acid because calcium hydroxide in mortar is consumed by the pozzolanic reaction of rice husk ash, and calcium silicate water is chemically more stable than calcium hydroxide. This is because a hydrate is generated.

Example 6 (Abrasion Resistance Test) A mortar similar to that in Example 5 was subjected to a rubbing test in accordance with the standard (ASTM C418). Specifically, a mortar was formed into a test specimen (40 × 40 × 160 mm), and after curing was performed in the same manner as in Example 5, one surface (40 × 160 mm) that was in contact with the side of the formwork was applied. Place a shield plate with an opening (φ 28.7 mm), keep the distance between the injection nozzle and the specimen at 76 ± 2.5 mm, and send silica sand (particle size 0.6 to 08) from the injection nozzle toward the opening.
5 mm, 600 ± 25 g) is sprayed at a predetermined pressure (414 ± 1 KPa) for 1 minute, the oiled clay is filled in the worn part and the volume is measured,
The abrasion loss due to the silica sand collision was determined. The measurement was performed at nine locations for one specimen, and the average value was determined. The results are shown in Table 8. Regardless of the water binder ratio, the incorporation of rice husk ash slightly reduces the amount of mortar abrasion. Specifically, the abrasion loss of the mortar mixed with rice husk ash with respect to the abrasion loss of the plain mortar is 0.30 relative to the water binder.
In this case, the mortar is about 90%, and when the water binder ratio is 0.40, it is about 83%.

The husk ash used in Examples 5 and 6 has a specific surface area of about 110 m ² / g and a loss on ignition of about 1.8%, but the loss on ignition is less than 2%. By mixing rice husk ash having a specific surface area of about 100 m ² / g or more with mortar or concrete, acid resistance and abrasion resistance can be enhanced.

[0037]

[Table 8]

[0038]

As described above, the admixture for hydraulic composition of the present invention is composed of rice husk ash having a specific surface area in a specific range. According to this admixture, the admixture is less than conventional silica fume or blast furnace slag. It has good initial strength of mortar and concrete, and has remarkable resistance to chloride ion penetration. Further, those containing the admixture of the present invention have a high effect of suppressing the alkali-aggregate reaction and are excellent in acid resistance and abrasion resistance.

[Brief description of the drawings]

FIG. 1 is a graph showing the results of Example 1.

FIG. 2 is a graph showing the results of Example 3.

FIG. 3 is a graph showing the results of Example 3.

FIG. 4 is a graph showing the results of Example 4.

FIG. 5 is a graph showing the results of Example 5.

Claims (4)

[Claims] 1. An admixture for hydraulic composition comprising rice husk ash having a specific surface area (BET) of 20 to ²⁰⁰ m ² / g. 2. The admixture for hydraulic compositions according to claim 1, comprising rice husk ash having a specific surface area (BET) of 50 to ²⁰⁰ m ² / g and a loss on ignition of 5% or less. 3. A hydraulic composition comprising the rice hull ash admixture of claim 1 or 2. 4. A concrete or concrete product made with the hydraulic composition of claim 3.