WO2008150039A1

WO2008150039A1 - Eco-friendly cold resistance substance composite with strength nature for concrete

Info

Publication number: WO2008150039A1
Application number: PCT/KR2007/002789
Authority: WO
Inventors: Hyung Guen Lee; Deug Hyun Ryu; Jun Young Jeon
Original assignee: Eugene Co., Ltd.
Priority date: 2007-06-08
Filing date: 2007-06-08
Publication date: 2008-12-11
Also published as: KR101360262B1; KR20100046006A

Abstract

Disclosed herein is an anti-freezing composition for concrete with high early strength. More specifically, the present invention relates an anti-freezing composition for concrete which prevents frost damage at early ages, provides an improved strength, and is environment -friendly by applying a liquid composition which comprises alkali metal or alkaline earth metal formate or acetate, chitosan, and water to cold weather concrete. The present inventors have found that, when alkali metal or alkali earth metal formates or acetates are properly combined and the combination is applied to a concrete, the concrete shows not only an anti-freezing property but also a high early strength property. Further, the present inventors have found that potassium acetate or potassium formate plays an important role in ant i -freezing, calcium formate is important for a high early strength, and the addition of chitosan is needed to prevent the salts from recrystallization and increase stability during storage. Thus, the concrete which comprises the combination of said components shows an improved anti-freezing and high early strength property. Further, the composition can further comprise calcium formate, potassium silicate, etc. as an essential component, and a fluidizer, a corrosion inhibitor, a pH controller, etc. as an additional component.

Description

[DESCRIPTION] [Invention Title]

ECO-FRIENDLY COLD RESISTANCE SUBSTANCE COMPOSITE WITH STRENGTH NATURE FOR CONCRETE [Technical Field]

The present invention relates to an anti-freezing composition for concrete with high early strength. More specifically, the present invention relates an anti-freezing composition for concrete which prevents frost damage at early ages, provides an improved strength, and is environment-friendly by applying a liquid composition which comprises alkali metal or alkaline earth metal formate or acetate, chitosan, and water to cold weather concrete. [Background Art]

Concrete curing is a work which maintains a temperature and humidity required at early stage in which hydration reaction progresses rapidly and protects the concrete until a required strength is obtained after placing the concrete so that the concrete is not deleteriously affected by heavy weight, impact, etc. The work has a considerable influence on the whole construction period and the durability of concrete, and thus needs sedulous attention to details. Under the condition that an average temperature for a day is below 4° C, the setting and hardening reaction is significantly delayed and the concrete may be frozen even during daytime as well as midnight and daybreak, and thus the work should be built of a cold weather concrete. For the construction of concrete during winter, a suitable measures should be taken for the material, combination, mixing, transporting, placing, vibrating, curing, form and early support so that the concrete is not frozen and has a required quality. If the temperature is 0 to 4° C, the construction of concrete during winter is carried out with a simple attention and thermal insulation. If the construction is carried out at the temperature of -3 to 0° C, it needs to heat water or water and aggregate together with some degree of thermal insulation. If the temperature is below -3° C, the construction of cold weather concrete should be carried out on a full scale, while raising the temperature of concrete by heating water and aggregate and, if desired, insulating the temperature or rapidly heating the concrete to keep the temperature required for the placed concrete. If the concrete is frozen at initial period of hardening, the chemical reaction of cement does not work well and subsequently, even if the concrete is cured at a proper temperature, it will have a harmful influence on the strength of concrete, the durability of concrete, the water tightness of concrete, etc. Thus, when the construction is carried out at a low temperature, the concrete should not be frozen at the initial stage of setting and hardening. After completing the concrete curing, the concrete should have a sufficient resistance against freezing and thawing process until the temperature of concrete is raised and a sufficient strength against the load which is expected at each step of the construction. Further, the concrete should have a strength, durability and water tightness required for the completed construction.

Chlorinated anti-freezing agents have been used for the construction at a low temperature. However, since the chlorinated anti- freezing agents have problems such as corrosion, etc., the currently used anti-freezing agent is non-chlorinated agents. A formalin condensate of sulphonated melamine or a formalin condensate of aromatic hydrocarbon sulphonic acid is used as a water reducing agent with an expectation that the condensate will improve the strength of concrete as much as water is reduced. However, at a low temperature, the effect on the amount of water per unit reduced by the water reducing agent is not high and, when the water reducing agent is used, the fluidity is reduced, which makes a difficulty in placing the concrete. Triethanolamine, thiocyanate, alkali or alkali earth metal sulphate, nitrate, nitrite, urea, etc. have some effect, but they bring about a reduction of basic performance of concrete. Since some of the above chemicals frequently induce rapid setting, it is difficult to keep the workability and transporting ability of concrete. For an organic anti-freezing agent, it was known that when the amount of the agent is increased, the initial strength of concrete is reduced. Particularly, for a lignin sulphonic acid-based anti-freezing agent, when the agent is used in a large amount of 1% or more, the setting of cement concrete is greatly retarded. When a polycarbonic acid-based high performance water reducing agent is used, the development of initial strength which should be taken within one day is retarded.

Therefore, there are still needs to provide an anti-freezing agent which maintains the anti-freezing property of the agent, even though the construction is carried out at a low temperature, and keeps the high early strength and workability of concrete. [Disclosure]

[Technical problem]

The present invention is directed to an agent that obviates the conventional problems disclosed above. An object of the present invention is to provide an anti-freezing composition for concrete which prevents frost damage during the construction at a low temperature, improves initial strength, and has a good workability. [Technical solution]

As a result of intensive study to resolve said problems, the present inventors have found that, when alkali metal or alkali earth metal formates or acetates are properly combined and the combination is applied to a concrete, the concrete shows not only an anti-freezing property but also a high early strength property. Further, the present inventors have found that potassium acetate or potassium formate plays an important role in anti-freezing, calcium formate is important for the high early strength, and the addition of chitosan is needed to prevent the salts from recrystallization and increase stability during storage. The concrete which comprises the combination of said components shows an improved anti-freezing and high early strength property.

Further, the composition can further comprise calcium formate, potassium silicate, etc. as an essential component, and a fluidizer, a corrosion inhibitor, etc. as an additional component.

More specifically, the present invention relates to a non- chlorinated anti-freezing composition for concrete, which comprises at least one of organic acid salts selected from the group consisting of alkali metal and alkaline earth metal formate and alkali metal and alkaline earth metal acetate, at least one of polysaccharides selected from the group consisting of chitin, chitosan and chitin-chitosan in which the acetyl group of chitin is partially removed, and water. The organic acid salts can be selected from the group consisting of potassium acetate, potassium formate, sodium acetate, sodium formate, calcium acetate, calcium formate, magnesium acetate, and magnesium formate. Preferably, the organic acid salts are potassium formate and calcium formate. The composition can comprise 10 to 50% by weight of potassium formate, 5 to 15% by weight of calcium formate, 0.01 to 5% by weight of chitosan, and the residual amount of water. The composition can further comprise calcium acetate. Preferably, calcium acetate can be comprised in an amount of 5 to 15% by weight. The composition can further comprise potassium silicate. Preferably, potassium silicate can be comprised in an amount of 2 to 10% by weight. The composition can further comprise a fluidizer, a corrosion inhibitor and a pH controller. Further, the composition can use potassium acetate or a mixture of potassium formate and potassium acetate instead of potassium formate. [Advantageous Effects]

The present composition does not comprise chlorides, which prevents concrete from corrosion. The components of the present composition are environment-friendly. The concrete curing by using the present composition can be accomplished in the severe cold area of -30° C to -40° C. When the concrete comprising the present composition is cured in the outside air at subzero temperature, since the present composition exerts a prominent freezing point depression, the conditions required for the concrete curing are maintained without any influence on the setting time (initial setting and final setting) and the change (of slump and air content) by time lapse, and thus the concrete is prevented from frost damage during the curing. Further, the present composition provides a superior early compressive strength and shows a prominent compressive strength development at long-term ages. Furthermore, the reduction of fluidity according to the addition of anti-freezing agent is not high, and thus workability is high. [Description of Drawings] FIG. 1 is a photograph showing a degree of recrystallization in an aqueous formate solution to which chitosan is added, compared with that in the aqueous formate solution which does not comprises chitosan. [Best Mode]

Hereinafter, the present invention will be described in further detail.

The present composition comprises at least one of organic acid salts selected from the group consisting of alkali metal and alkaline earth metal formate and alkali metal and alkaline earth metal acetate as an essential component. Further, the composition comprises at least one of polysaccharides selected from the group consisting of chitin, chitosan and chitin-chitosan in which the acetyl group of chitin is partially removed (hereinafter, referred to as "chitosan" ), which prevents the composition in the form of aqueous solution from recrystallization. In the composition of the present invention, chitosan eliminates the odor of the composition, prevents recrystallization, and is effective in o

adsorbing a small quantity of heavy metals. The organic acid salts can be selected from potassium acetate (PA), potassium formate (PF), sodium acetate, sodium formate, calcium acetate (CA), calcium formate (CF), magnesium acetate, and magnesium formate. Since the aqueous solution of said organic acid salts has an extremely low freezing point, it is vaguely predicted that when the solution is properly treated, the solution can be used as an agent for removing snow, anti-freezing, etc. However, actually the aqueous solutions show differences in their performances. Potassium formate is dissolved well in water, and thus the effect on the freezing temperature depression is considerable. In contrast, calcium formate is hardly dissolved in water, said effect is not high. But, when calcium formate is added to a composition for concrete, calcium formate contributes to the improvement of strength of concrete. The anti-freezing composition of the present invention comprises 10 to 50% by weight of potassium formate, 5 to 15% by weight of calcium formate, 0.01 to 5% by weight of chitosan, and the residual amount of water. If the amount of potassium formate is less than 10% by weight, the effect of freezing temperature depression is insignificant, and thus, when applied to a concrete, the effect required for anti-freezing can not be accomplished. If the amount of potassium formate is more than 50% by weight, it is difficult to dissolve such an amount of potassium formate in water. Calcium formate effects on the anti-freezing and, more importantly, when applied to a concrete, improves the strength of concrete. If calcium formate is less than 5% by weight, the improvement of strength is insignificant. If the amount of calcium formate is more than 15% by weight, it is difficult to dissolve such an amount of calcium formate in water. If the amount of chitosan is less than 0.01% by weight, the chitosan cannot play a role in preventing recrystallization. If the amount of chitosan is more than 5% by weight, the addition of chitosan increases the viscosity of liquid anti-freezing agent and, when the agent is mixed with concrete, it is difficult to disperse the agent to the concrete.

FIG. 1 is a photograph which shows a degree of recrystallization of the aqueous solution comprising potassium formate and calcium formate to which chitosan is added, compared with that of the aqueous solution which does not comprise chitosan. As shown in FIG. 1, recrystallization occurs in the aqueous solution to which chitosan is not added, but not in the aqueous solution to which chitosan is added. Forming a crystal in the anti-freezing composition considerably reduces the storage stability of the composition as well as the anti-freezing and high early strength of the composition. Further, since the formation of crystal makes the freezing point of the anti-freezing composition raised, it can be expected that the function of the anti-freezing agent will deteriorate. The composition of the present invention further comprises 5 to 15% by weight of calcium acetate and the residual amount of the composition is filled with water. When the calcium acetate is dissolved, since it competes with formate ions, the depression of freezing point is strengthened and the effect of anti-freezing is improved. Acetate ions are forced into competition with formate ions due to their similar ion size and, when they become close, the dipole effect between the particles increases and the colligative property is built up. Subsequently, the number of solutes per unit area is increased and the phenomenon of freezing point depression becomes more distinct. This is due to "the structure which is similar to molten matter, not solubilized matter in a solution," which can not be attributed to a simple mixing for an aqueous solution. In summary, the different organic acid salts become to take a structure which is similar to molten matter in a state of aqueous solution, and thus the colligative properties is built up. In an alternative phenomenon, the property of competitive hydrolysis of metal salts by anions in acetate and formate disturbs the development of solid crystals, which provides a mechanism lowering the freezing point of the composition considerably than that expected from the two substances. As a result, the competitive reaction of acetate and formate ions with water changes the crystalline structure of water and thus retards the tendency toward ice. If calcium acetate is less than 5% by weight, said effects are insignificant. If calcium acetate is more than 15% by weight, the amount of potassium formate to be dissolved in water should be reduced. However, in view of the fact that the freezing point depression of calcium acetate is less effective than that of potassium acetate, the addition of calcium acetate which exceeds 15% by weight can reduce the anti-freezing effect.

The combination of potassium silicate with alkali metal salts improves the anti-freezing effect. Potassium silicate is reacted with the steel frame of concrete, which enables the steel frame to have a superior rust preventive property, abrasion resistance and impact resistance and exert a prominent performance under the severe corrosive condition. Further, the combination shows a good initial workability and adhesion strength, and thus increases the binding strength of aggregate. The use of potassium silicate also improves the strength of the concrete, and reduces the amount of other components to be mixed with the present composition. The anti-freezing agent of the present invention can further comprise 2 to 10% by weight of potassium silicate with a residual amount of water. If the amount of potassium silicate is less than 2% by weight, the synergistic effect with the alkali metal salts is insignificant. If the amount of potassium silicate is more than 10% by weight, the amount of other organic acid salts used for the present composition is limited.

In the present composition, potassium acetate or a mixture of potassium acetate and potassium formate can be used instead of potassium formate. Since potassium acetate or potassium formate has a high solubility, they show a superior anti-freezing effect. Potassium acetate can be dissolved up to approximately 70% by weight. Thus, in case that a high anti-freezing is needed under the severe outside air condition, the amount of potassium acetate can be increased. But, since the high early strength of potassium acetate is lower than that of potassium formate, the use of potassium formate is preferred.

The present anti-freezing agent is prepared in the form of aqueous solution. The content of metal salts in the aqueous solution does not exceed approximately 60% by weight. Potassium acetate can be dissolved in the aqueous solution in an amount of about 50% by weight, when it is used as a single component. In case that chitosan is added to the solution, the content of the total metal salts is increased up to 60% by weight. If the total amount of metal salts is small, the effect of anti-freezing is decreased. If the amount is too large, it exceeds the range of dissolution in water. The preferred amount is about 35% by weight to 55 % by weight.

The fluidity of the anti-freezing agent can be lowered according to the increased amount of metal salts. However, the reduction of fluidity is insignificant. When the fluidity is lowered, a fluidizer can be added at the time of mixing with concrete with a caution that the addition of fluidizer can reduce the strength of concrete.

Preferably, the anti-freezing agent for concrete according to the present invention can further comprises a corrosion inhibitor. Typically, any corrosion inhibitors can be used without limitations so long as they can be used for the prevention of metal corrosion. Particularly, benzotriazole, sodium benzoate, sodium silicate, etc. is preferred. When benzotriazole is used, its amount is 0.05 to 0.5% by weight. When sodium benzoate is used, its amount is 0.05 to 1.5% by weight. When sodium silicate is used, its amount is 0.01 to 0.5% by weight. If the amount of corrosion inhibitor is small, the effect of it is insignificant. If the amount is too much, side effects due to the oxidation of corrosion inhibitor can be occurred.

Preferably, the anti-freezing agent for concrete according to the present invention can further comprises a pH controller, because a proper pH is required for the dissolution of each component in the composition. The pH controller can include triethanolamine, sodium hydroxide, potassium hydroxide, etc. The amount of the pH controller is preferably 0.05 t 0.3% by weight. The range can vary according to the component used in the composition. The components of anti-freezing composition for concrete according to the present invention are the materials which are close to the final step in the decomposition, and thus are environment-friendly. [Mode for Invention]

Hereinafter, the present invention is illustrated in detail with reference to the following examples. However, the scope of the present invention is not limited to these examples.

Example 1 (Comparative experiment with and without chitosan)

The elimination of the remaining odor of organic material (formic acid) and the inhibition of recrystallization were observed with an aqueous solution of 50% potassium formate to which chitosan (average molecular weight: 20,000, Deacetylation: 80%) was added in an amount of 0.5 by weight and with an aqueous solution of 50% potassium formate which does not contain chitosan. To measure the degree of inhibition of recrystallization, water in the two samples was left volatized at a room temperature in the air so as to derive the recrystallization. After 10 days, the occurrence of recystallization was determined. For the elimination of the remaining odor by chitosan, sensory evaluation for each sample was carried out by five. As a result, the sample which contains chitosan remarkably reduced the specific odor of formic acid, compared with the sample which does not comprise chitosan. As shown in FIG. 1, the addition of chitosan considerably improves the problem of the recrystallization of potassium formate, thereby enhancing the stability of a liquid composition. It is considered that the functional group of amine in chitosan molecules is chemically reacted with formate, which reduces the odor caused by the volatilization of formic acid and inhibits the recrystallization. [Table 1]

Example 2 (Freezing point of the anti-freezing agent and freezing point change according to the dilution of the agent)

The anti-freezing agent of the present invention has an effect of freezing point depression, and thus the concrete comprising the present agent can be hydrated under a lower temperature. The freezing point of the present composition was -65 to -55° C. The freezing point was measured as follows: 5Og of each sample was introduced into a deep freezer (manufacturer: Ilsinlab) and, while lowering the temperature up to -85° C, and the freezing point was observed. The result is shown in Table 2. [Table 2]

In case of 30% by weight of calcium chloride, the freezing point was - 36.6° C. In case of 50% by weight of ethylene glycol, the freezing point was -31.1° C. If a considerable amount of potassium acetate and potassium formate is dissolved, the effect of freezing point depression is maximized. When calcium formate is used as a single component, it is difficult to dissolve a large amount of calcium formate. In case of 12% by weight of calcium formate, the freezing point was -25.6° C. Considering the above, it is preferred that, while comprising potassium acetate and potassium formate as basic components, the anti-freezing agent further comprises the other organic acid salts. It is considered that the composition has a very low freezing point and thus can thoroughly fulfill its role as an anti-freezing agent for concrete. Therefore, it is seen that even if the weather condition is severe such as -30 to -40° C, concrete work can be carried out by using the anti- freezing agent for concrete according to the present invention.

The first composition and the last composition were used as a stock. After adding water to the stock solution, the freezing point of the diluted solution was measured. The result is shown in Table 3. [Table 3]

From the result, it is shown that the anti-freezing agent of the present invention has a low freezing point even if it is diluted, but ethylene glycol does not play a role in anti-freezing when it is diluted to some degree. Therefore, the anti-freezing agent of the present invention can prevent the concrete from freezing, even though the agent is diluted or a relatively small amount of the agent is used, and has a superior anti-freezing property.

Example 3 (Composition of anti-freezing agent)

The following anti-freezing compositions of the present invention were prepared. The unit is % by weight. [Table 4]

The metal salts were dissolved in water and chitosan was added to the solution. At 10 to 30° C, the solution was stirred at 100 to 1500 rpm. Each component was dissolved in water. Alternatively, all of the components were mixed at once and then stirred. When all of the components were mixed and stirred at once, the amount of total salts which are soluble was larger than that in the composition wherein the components of the composition were individually dissolved.

Example 4 (Application of the anti-freezing agent)

To test the performance of the anti-freezing agent of the present invention, the agent was add in an amount of 1%, 3%, and 15%, which was estimated for the severe condition, in relation to 1% of concrete binder, and then concrete and mortar tests were carried out. In order to compensate the change of fluidity which is caused by the increment in unit quantity due to the addition of anti-freezing agent, the amount of the anti-freezing agent added to the concrete or mortar was calibrated in relation to the total unit quantity.

A mortar test was carried out according to the method of testing a compressive strength of KS F 5105 hydraulic cement mortar. For a concrete, an initial fluidity and a change of the fluidity with elapsed time were measured. Further, a performance of cured concrete according to curing temperature was determined. A slump test was carried out according to the KS F 2402 air chamber pressure method. Air content was measured according to the KS F 2409 method.

The items evaluated are as follows: [Table 5]

In case of outside air curing at subzero temperature, considering the change of strength due to freezing, the compressive strength was measured after standing it at room temperature for 1 hour.

Measuring of hydration heat

The combinations for mortar and concrete to measure the heat of hydration are given below and the heat was tested at room temperature and -10° C. [Table 6]

Combination for mortar

OPC is a common Portland cement and W is water. The standard water reducing agent was added in an amount of 0.5A% in relation to OPC. The anti-freezing agent was applied in an amount of 3.0%. The standard represents a mortar which does not comprise the anti-freezing agent of the present invention. [Table 7]

Combination for concrete

BFS is a blast furnace slag, FA is fly ash, G is coarse aggregate, S is fine aggregate (sand), and AD is a standard water reducing agent. The anti-freezing agent was applied in an amount of 3.0% in relation to a binder.

The anti-freezing agents given in Example 3, that is, anti- freezing agent 1 to 9, were applied.

At room temperature, a rapid hydration reaction over all was shown and any special problems were not observed. At subzero temperature, the comparative combinations which comprise anti-freezing agent 2, 3, 5 and 9 showed a relatively rapid hydration in comparison with the standard which has no anti-freezing agent. The hydration reaction was rapidly carried out in case of anti-freezing agent 3. Ant-freezing agents 1, 7, and 8 showed a relatively rapid hydration reaction in comparison with the standard, but the speed of the combinations comprising the anti-freezing agents was slower than that of the other combination, wherein anti- freezing agent 1 was speeder than anti-freezing agents 7 and 8.

The rapid hydration rate indicates that the improvement of strength in early ages can be well accomplished. It is considered that when calcium formate is used, a good development of strength at early ages is accomplished. Also, it is seen that calcium acetate and potassium acetate can also improve the strength. When potassium formate and potassium acetate were used as a single component or their combinations was used, a sluggish improvement of strength at early ages was observed in comparison with the other combinations. Thus, it is seen that a combination of potassium formate or potassium acetate with the other material is preferred rather than the use of potassium and potassium acetate as a single component. Although the use of potassium formate as a single component is more effective in improving the strength at early ages than that of potassium acetate as a single component, upon considering the aspect of anti-freezing, it is possible to use their combinations.

Measurements of the flow of mortar and the strength according to curing [Table 8]

Combination of applied mortar

As a result of testing the flow of mortar, the addition of anti- freezing agent in an amount of 3% in relation to a binder had no influence all but on the fluidity. But, it is assumed that when a large amount of the anti-freezing agent is added to overcome an extreme condition, the anti-freezing agent may have an influence on the fluidity of mortar. [Table 9]

When anti-freezing agents 1, 7, and 8 were used, the strength at early ages was dropped. But, the remaining showed a good strength for the initial 3 days. When the anti-freezing agent which comprises calcium formate was used, it showed a similar or a superior strength in comparison with the standard even at long-time ages. This demonstrates that the anti-freezing agent can be used not only for the cold weather concrete but also as an agent for a high early strength in a standard curing.

The result of outside air curing at subzero temperature is given in Table 10. The result is obtained for 1% and 3% applications. The average temperature was -10° C. [Table 10]

When outside air curing was practiced at subzero temperature, the anti-freezing agent had an outstanding compressive strength in comparison with the standard. At long-time ages of 28 days, the anti-freezing agent showed a superior performance. It is seen that the anti-freezing agent of the present invention shows a superior effect of freezing point depression and prevents water involved in a hydration reaction from freezing, thereby permitting a good hydration reaction. For outside air curing at subzero temperature, according to the increased amount of anti- freezing agent, the properties of mortar were improved at early and longtime ages, and, even if the age is increased, the depression of compressive strength was not occurred in comparison with the standard. In the aspect of strength, when potassium acetate or potassium formate is combined with calcium formate, the effect of the combination was better than they are used as a single component. However, at an extremely low temperature, the amount of the anti-freezing agent used for anti-freezing or the amount of potassium acetate or potassium formate should be increased.

Measurement of the change according to concrete curing

The combinations of concrete are shown in Table 11. [Table 11]

The results of slump and air content of concrete are shown in Table 12. When the anti-freezing agent is 15% in terms of the quantity of concrete, the conversion rate of the anti-freezing agent in relation to the amount of a binder is 7.8%. The data is for anti-freezing agents 1, 3, and 5. [Table 12]

For initial fluidity, when 1% the anti-freezing agent in relation to the amount of the binder was added to the concrete, the change of initial water reducing rate was not high, but when the amount of anti- freezing agent is increased, the fluidity of concrete was decreased to some extent. When W*15%(B*7.8%) was applied on the assumption of a severe subzero temperature, the depression of fluidity was high. Therefore, when concrete curing is carried out at a severe subzero temperature, the addition of fluidizer is preferred. At a normal application, the change of slump is not high in comparison with the standard. For the change of slump with elapsed time, the change according to the increased amount of anti-freezing agent was increased to some extent. However, there is almost no difference from the standard.

The development of air content was decreased to some extent according to the increased amount of anti-freezing agent, but there is no large difference between them. For the change of slump by time lapse, when the anti-freezing agent is added, the range of change was some wide, but it is believed that such change has no influence on the change of physical properties. In conclusion, although the anti-freezing agent does not change the distinct depression of fluidity and physical properties, when the anti-freezing agent is used in a large amount on the assumption that a severe outside environmental condition is given, there is a possibility that the fluidity is disturbed, and thus it is preferred to add a fluidizer to the agent.

Measurement of the change of compressive strength of concrete

The compressive strength of hardened concrete was measured at a standard curing and a subzero outside air condition up to 28 days. When the measurement is carried out at a subzero outside air condition, in order to avoid the possibility to measure the strength of the frozen water, the strength of the concrete was determined after standing the concrete at room temperature for 1 hour. The mean outside temperature was -10 ^Q C, but it is seen that the surface temperature of concrete is lower than the mean outside temperature. For the standard concrete curing, all concrete to which the anti-freezing agent is added showed a superior strength up to 7 ages, but the depression of strength was somewhat observed at long-term ages.

In case of a subzero outside air curing, a superior strength development was observed over all ages, compared with the standard to which the anti-freezing agent was not added. Particularly, the strength development at early ages was remarkable. With an increase in the amount of anti-freezing agent, the strength development was increased. The strength for B*3% and W*15% anti-freezing agents at a subzero outside air curing is shown in Table 13. W*15% was for the assumption of an extremely low outside temperature. For a more extremely low temperature, the addition rate of anti-freezing agent may be increased. [Table 13]

In order to have a sufficient initial strength even at a severe subzero temperature, the amount of anti-freezing agent should be increased. In this case, the rate of increase in the strength of concrete is significantly high, compared with the standard. For concrete curing at subzero temperature, the strength was not depressed even at long-time ages.

Claims

[CLAIMS] [Claim 1]

A non-chlorinated anti-freezing composition for concrete, which comprises at least one of organic acid salts selected from the group consisting of alkali metal and alkaline earth metal formate and alkali metal and alkaline earth metal acetate, at least one of polysaccharides selected from the group consisting of chitin, chitosan and chitin- chitosan in which the acetyl group of chitin is partially removed, and water.

[Claim 2]

The non-chlorinated anti-freezing composition for concrete according to claim 1, wherein the organic acid salts are selected from the group consisting of potassium acetate, potassium formate, sodium acetate, sodium formate, calcium acetate, calcium formate, magnesium acetate, and magnesium formate.

[Claim 3]

The non-chlorinated anti-freezing composition for concrete according to claim 1, wherein the organic acid salts are potassium formate and calcium formate.

[Claim 4]

The non-chlorinated anti-freezing composition for concrete according to claim 3, wherein the composition comprises 10 to 50% by weight of potassium formate,

5 to 15% by weight of calcium formate, 0.01 to 5% by weight of chitosan, and the residual amount of water. [Claim 5]

The non-chlorinated anti-freezing composition for concrete according to claim 1, wherein the organic acid salts are potassium formate, calcium formate, and calcium acetate.

[Claim 6] The non-chlorinated anti-freezing composition for concrete according to claim 5, wherein the composition comprises 10 to 50% by weight of potassium formate, 5 to 15% by weight of calcium formate, 0.01 to 5% by weight of chitosan, 5 to 15% by weight of calcium acetate, and the residual amount of water.

[Claim 7]

The non-chlorinated anti-freezing composition for concrete according to claim 1, wherein the organic acid salts are potassium formate, calcium formate, and calcium acetate and further comprise potassium silicate.

[Claim 8]

The non-chlorinated anti-freezing composition for concrete according to claim 7, wherein the composition comprises 10 to 50% by weight of potassium formate, 5 to 15% by weight of calcium formate, 0.01 to 5% by weight of chitosan, 5 to 15% by weight of calcium acetate, 2 to 10% by weight of potassium silicate, and the residual amount of water.

[Claim 9]

The non-chlorinated anti-freezing composition for concrete according to any one of claims 3 to 8, wherein the potassium formate is replaced with potassium acetate or the potassium formate is a mixture of potassium formate and potassium acetate.

[Claim 10]

The non-chlorinated anti-freezing composition for concrete according to any one of claims 1 to 8, wherein the composition further comprises a fluidizer.

[Claim 11]

The non-chlorinated anti-freezing composition for concrete according to any one of claims 1 to 8, wherein the composition further comprises a corrosion inhibitor.

[Claim 12] The non-chlorinated anti-freezing composition for concrete according to claim 11, wherein the corrosion inhibitor is at least one selected from the group consisting of benzotriazole, sodium benzoate, and sodium silicate.

[Claim 13] The non-chlorinated anti-freezing composition for concrete according to any one of claims 1 to 8, wherein the composition further comprises a pH controller. [Claim 14]

The non-chlorinated anti-freezing composition for concrete according to claim 13, wherein the pH controller comprises at least one selected from the group consisting of triethanolamine, sodium hydroxide, and potassium hydroxide.