KR19990053112A - Cement mortar composition for crack prevention - Google Patents

Abstract

The present invention relates to a cement mortar composition for crack prevention. Recently, the mechanized construction of cement mortar for plastering floors is becoming more common due to the necessity of shortening air and reducing labor costs. However, the high flow mortar of about 220mm flow is required for mechanized construction, which increases the water-cement ratio of the mortar and causes dry shrinkage cracking. It is a cause of complaints caused by defects. Since the cracks caused by dry shrinkage are closely related to the unit quantity of mortar, it is necessary to manufacture the mortar with the minimum unit quantity within the range to secure the required compressive strength and workability, and also to the mortar manufactured with the minimum unit quantity. Cracks from dry and plastic shrinkage occur, which is solved by adding quicklime or expandable CSA. To the cement mortar with a water-cement ratio of 50 to 60% and a cement-to-grain aggregate ratio of 1: 2 to 1: 4, quicklime (CaO) is added 4 to 6% of the cement weight, or expandable CSA (Calcium Sulfa Aluminate) is added to the cement weight of 5 The expansion pressure generated when the added quicklime or expandable CSA reacts with water to produce an expandable compound by adding -10% is used as a dry shrinkage compensation mechanism. A high performance water reducing agent or a high fluidizing agent may also be added to the composition to reduce the water-cement ratio.

Description

Cement mortar composition for crack prevention

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows the relationship between the addition amount of quicklime (CaO) and the rate of change of the mortar length.

2 is a view showing the relationship between the amount of expansion of expandable CSA (Calcium Sulfa Aluminate) and the mortar length change rate.

[Field of Invention]

The present invention relates to a cement mortar composition for crack prevention. More specifically, the present invention relates to a cement mortar composition capable of preventing initial dry shrinkage cracking and plastic shrinkage cracking occurring in the mortar after constructing a floor plastering mortar.

[Background of invention]

Recently, mechanized construction of cement mortar for plastering floors is becoming common in construction projects due to air shortening and labor cost reduction. The mechanized construction methods include the method of manufacturing, transporting and placing mortar in the ready-mixed concrete plant as in the conventional concrete construction, and the method of mixing, transporting, and pouring mortar in the field, and the construction efficiency is superior to that of conventional hand beams. It is a popular method.

However, in order to mechanized construction in the field requires a high flow mortar without impairing the mortar, there is a problem that the water cement ratio of the mortar is increased, the initial dry shrinkage cracking and plastic shrinkage cracking for a long time. These cracks are often overlooked as a minor problem confined to non-structuring plaster mortars, but their role as covering mortars that protect the durability and structural properties of concrete over time and deteriorate, causing condensation, leakage, and moisture release to bury the floor, tile or carpet. This causes problems such as breakage and aesthetic damage due to the advancement of cracks and surface finishes.

In particular, in the case of a multi-family house, defects such as cracks in the floor mortar generate a group complaint, which causes a large cost burden such as reconstruction after complete dismantling, distrust of the quality of the whole building, damage to the image of the contractor, and deterioration of reliability. .

In order to control the cracking of the bottom mortar, a method of reducing the amount of unit cement, a method of adding a surfactant to reduce the unit quantity, a method of increasing the tensile strength of cement mortar by mixing fiber reinforcement, an appropriate expanding agent or Desulfurization gypsum is used to compensate for shrinkage.

However, if the amount of unit cement is reduced, the strength and workability are lowered, and thus there is a limit to the reduction. In the case of using the fiber reinforcement material, the polypropylene fiber has a problem of dispersibility of fiber and low tensile strength of the fiber itself, and thus the tensile reinforcing effect cannot be obtained. Due to the addition of the frictional resistance of the pressure feed pipe increases when pump pumping, there is a problem that the workability is deteriorated. The method of adding desulfurized gypsum is difficult to control because the degree of expansion obtained according to the temperature at the time of construction or the reactivity of the desulfurized gypsum is uneven, and it is difficult to measure crack expansion because it has infinite hygroscopicity by physical external force after curing.

Unlike concrete, where manufacturing, construction, and quality control methods are established, floor plastering mortars do not have specially defined quality control methods, and there is a great variation in the quality due to unique manufacturing and quality control methods for each company or site. It is showing a problem.

Therefore, the present inventors can easily and economically obtain dry shrinkage compensatory effect and plastic shrinkage complementation by slowly generating an expandable compound by reacting with cement, and have a permanent mortar composition for plastering flooring that does not adversely affect workability. Developed.

[Purpose of invention]

It is an object of the present invention to provide a cement mortar composition capable of preventing initial dry shrinkage cracking and plastic shrinkage cracking.

[Summary of invention]

The present invention relates to a cement mortar composition for crack prevention. Recently, due to the need for shortening the air and reducing labor costs, the mechanized construction of mortar for floor plastering has become common. However, the high flow mortar of about 220mm to 280mm is required for mechanized construction. And plastic shrinkage cracking. In order to prevent such dry shrinkage and plastic shrinkage cracking, quicklime (CaO) or expandable Calcium Sulfa Aluminate (CSA) is added to the mortar, and the expanded pressure generated at this time as the added quicklime or expandable CSA reacts with water to generate expandable compounds. By using to prevent the cracks caused by dry shrinkage and plastic shrinkage. The quicklime or expandability is obtained by adding 4-6% of the quicklime or 4-10% of the cement weight of the cement, or 5-10% of the cement weight to the cement mortar with a cement-grain aggregate ratio of 1: 2 to 1: 4 and a water-cement ratio of 50 to 60%. Compensate for dry and plastic shrinkage by expansion pressure due to chemical reaction of CSA and water.

Detailed Description of the Invention

The present invention relates to a cement mortar composition for plastering floors that can prevent cracking caused by dry shrinkage and plastic shrinkage. The present invention is composed of cement, fine aggregate, water and quicklime (CaO) or expandable calcium sulfa aluminate (CSA). A water reducing agent can also be added as needed. In the cement mortar having a water-cement ratio of 50 to 60% and a cement-to-grain aggregate ratio of 1: 2 to 1: 4, quicklime is added 4 to 6% of the cement weight or expandable CSA 5 to 10% of the cement weight. Cement mortar compositions for plastering floors should be free of cracks, but more importantly they should ensure the required compressive strength and proper workability. Compressive strength is generally used more than 210kg / cm ² 28 days strength, workability requires about 220mm flow for mechanized construction. In order to manufacture the high-mobility mortar as described above, the unit quantity is increased and the cracks caused by dry shrinkage and plastic shrinkage are closely related to the unit quantity of cement mortar. It is necessary to produce mortar in a unit quantity of. However, cracks due to dry shrinkage and plastic shrinkage occur even in the mortar prepared with the minimum unit quantity, thereby preventing the occurrence of cracking by compensating for dry shrinkage and plastic shrinkage by expansion of quicklime or chemical reaction of expandable CSA. . That is, by mixing quicklime or expandable CSA in cement mortar for plastering floor, it is possible to prevent cracking due to dry shrinkage and plastic shrinkage due to the expansion of calcium hydrate obtained by the quicklime or expandable CSA reacting with water.

When the water-cement ratio is 50% or less, it is difficult to secure required fluidity, and when the water-cement ratio is 60% or more, the compressive strength is lowered. When the cement-grain aggregate ratio is also less than 1: 2, the amount of unit cement increases, resulting in increased dry shrinkage and plastic shrinkage. Therefore, the water-cement ratio is about 50-60%, and the cement-grain aggregate ratio is 1: 2-1: 4. In addition, an appropriate amount of a high performance water reducing agent or a high fluidizing agent may be used to reduce the water-cement ratio.

Quicklime is the formation of fine crystalline calcium hydroxide after hydration, and the expansion pressure generated at this time is used as the shrinkage compensator, and the expansion compensator of the expandable CSA is the swelling property of ettringite, in which crystals of hydrate are formed as acicular gypsum. By using it, the composition component was adjusted in order to make generation of ettringite easier than anhydrous gypsum system.

EXAMPLE

EXAMPLE 1, 2, 3

Three cases in which quicklime was mixed with 2%, 4% and 6% of cement weight in mortar with water-cement ratio 55% and cement-grain aggregate ratio l: 2.5 were tested. The effect of dry shrinkage compensation with the addition of quicklime was evaluated by measuring the change in the length of mortar specimens, and the change in length at 3, 4, 5, 6, 8, 10, 17, 24, 31, and 38 days of the specimen. It was.

The specimens were prepared using a double mold of size 25.4 × 25.4 × 285.7mm according to the test method for mortar length change of KS F 2424. The specimen placed in the mold was cured for 24 hours in a constant temperature and humidity chamber of 20 ° C and 95% RH, and demolded to measure the initial length using a length change meter. After the measurement, the specimen was placed in a constant temperature and humidity chamber of 20 ° C and 60% RH again. The change in length was measured at a predetermined age.

In this example, quicklime produced by Jangja Co., Ltd. was used, and the properties of cement and quicklime used are shown in Tables 1 and 2.

[Table 1 Physical and chemical properties of cement]

TABLE 2 Chemical Properties of Quicklime

EXAMPLE 4, 5, 6

Same as Examples 1, 2, and 3, except that an expandable CSA was used as the expanding agent and the expandable CSA was incorporated in 5%, 10% and 15% of the cement weight. In the present embodiment, a CSA-based expanding agent manufactured by Japan Electrochemical Co., Ltd. was used, and the physical properties of quicklime are shown in Table 3.

TABLE 3 Chemical Properties of Expandable CSA

Comparative Example 1

In order to compare the degree of cracking with cement mortar, which was conventionally constructed, mortar specimens having a water-cement ratio of 55% and a cement-grain aggregate ratio of 1: 2.5 were prepared, and the rate of change in length was measured in Examples 1 to 6. Is the same as

The experimental results of the length change are shown in Table 4. In Table 4, in Examples 1 to 6 and Comparative Example 1, the rate of change in specimen length was increased with increasing age, and about 50% of the total shrinkage occurred until age 7, and the shrinkage became gentle after 17 days. Long-term convergence tends to converge.

Figure 1 shows the rate of change in specimen length when quicklime is added, and the dry shrinkage decreases as the amount of quicklime is increased. However, the addition amount of quicklime 4% and 6% does not show a big difference, it is estimated that the addition amount of quicklime is about 4-6%.

Figure 2 shows the rate of change of specimen length when adding expandable CSA, and shrinkage decreases with the addition of expandable CSA. Therefore, it is judged that the addition amount of expandable CSA is about 5 to 10%.

Table 4 Length Change Experiment Results

Claims (3)

It is composed of cement, fine aggregate, quicklime (CaO), and water, the weight ratio of the cement and the fine aggregate is 1: 2 to 1: 4, the weight of the water is 50 to 60% of the weight of the cement, the weight of the quicklime The crack prevention cement mortar composition, characterized in that 4 to 6% of the weight of the cement. Cement, fine aggregate, expandable Calcium Sulfa Aluminate (CSA), and water, the weight ratio of the cement and the fine aggregate is 1: 2 to 1: 4, the weight of the water is 50 to 60% of the weight of the cement, The weight of the expandable CSA is 5 to 10% of the weight of the cement, characterized in that the cement mortar composition for preventing cracks. The method of claim 1 or claim 2, wherein the cement mortar composition for preventing cracks, characterized in that the addition of a high performance water reducing agent or a high fluidizing agent to the cement mortar composition.