KR20020004915A - Crack retardant mixture for cement mortar and cement mortar by using it for heating floor(on-dol) - Google Patents

Abstract

PURPOSE: Provided are a shrinkage reducer for cement mortar which has high compression strength, prevents initial cracking and enables a differential mixing according to season, and a cement mortar for hot floor(ondol)-plastering prepared therewith. CONSTITUTION: The shrinkage reducer is formed by adding blast slag powder and fly ashes, being less than 50wt.%(based on the fly ashes) each, to ashes obtained by burning a mixture of 30-70% of lime stone(5mm in size) and 30-70% of petroleum coke at 850deg.C. The cement mortar contains 70-80wt.% of cement, 15-30wt.% of prepared shrinkage reducer and sand more than 2.8 in fineness modulus(FM), where the ratio of the raw materials comprising shrinkage reducer and cement to sand is 1 : 2.5-3.

Description

Shrink reducer for cement mortar and cement mortar for plastering using ondol {{Crack retardant mixture for cement mortar and cement mortar by using it for heating floor (on-dol)}

The present invention relates to a shrinkage reducing material used in a housing floor and the like, and more specifically, to a cement mortar using the same, and more particularly, to a shrinkage reducing material and a cement mortar using the reducing material. will be.

As the construction of houses increased quantitatively and the houses became higher and larger, the mechanized construction of cement mortar pumped and plastered on the floor became common. Mechanized construction is a situation in which excessive water is added for the convenience of pump pumping, serious cracking occurs after construction.

These cracks are caused by shrinkage during cement condensation and are most affected by the composition of cement, the powder of cement, the amount of water, and the like. In order to prevent shrinkage cracking of cement, it is known to use an expansion cement that can expand to a degree that compensates for dry shrinkage.

K, S, M and O types are developed and used in the United States, Japan, etc., and they are used in cement as (3CaO · Al ₂ O ₃ · CaSO ₄ ) · CaO · CaSO ₄ , (3CaO · Al ₂ O ₃ ) And one of CaSO ₄ , CaO, or CaSO ₄ are mixed in an appropriate amount to secure the expandability of the cement. The expansion cement expands by (1) absorbing moisture in the process of forming Ettringite (3CaO.3CaSO ₄ .32H2O) and expanding, or (2) CaO added is expanded while forming crystals of calcium hydroxide. It is known to become.

By the way, the expansion cement known so far is difficult to apply as a cement mortar for finishing the floor of the general housing complex. Therefore, a technique for mixing and using shrinkage reducing materials which fundamentally block the cause of cracking by chemically introducing expansion force corresponding to the amount of shrinkage of cement mortar to compensate for shrinkage has been generalized.

A representative example thereof is a shrinkage reduction mortar for ondol finishing plastering proposed in Patent No. 148438 developed by the present inventor. This mortar has an excellent effect on crack prevention even in moist mortar. However, this shrinkage reduction mortar is difficult to obtain sufficient plastering time due to the shortening of the initial setting time, the initial crack may occur, and the 28-day compressive strength expression is late, and the differential mixing due to the seasonal characteristics is difficult. Disadvantages of shrinkage reduction mortar are believed to be due to the following causes.

(1) initial crack

Combustion materials in which petroleum coke is mixed with limestone powder are mainly composed of CaO, CaSO ₄ , SiO ₂ , and Al ₂ O ₃ , and an example thereof is shown in Table 1 below.

Chemical composition (% by weight) CaO SiO ₂ Al ₂ O ₃ Fe ₂ O ₃ MgO SO ₃ K ₂ O Na ₂ O ₃ Test Methods 59.3 2.45 0.45 0.33 1.42 22.6 0.18 0.19 KSL5120-90I.C.P. analysis Powder level (mm) 1.18 or higher 1.18-0.6 0.6 to 0.25 0.25-0.177 0.177 to 0.125 0.125 to 0.105 0.105-0.075 Less than 0.075 2.1% 5.8% 24.6% 16.7% 17.2% 7.5% 9.8% 16.3%

As can be seen in Table 1, the petroleum coke combustor has a low powdery density, and it is estimated that the surface crackiness is lowered due to the phenomenon of the fine particles floating on the surface (latency phenomenon), so that early cracking occurs especially in the summer season.

In addition, the shrinkage reducing material contains a lot of CaO, the initial heat setting time is shortened by the high heat of hydration of CaO to ensure a sufficient plastering time (a plastering time of 4 hours 30 minutes is required at least about four times) As such, it was analyzed that an initial crack occurred.

(2) 28-day intensity expression rate

Gypsum contained in petroleum coke combustors caused coagulation delay, resulting in about 70% strength development on 28 days.

(3) Seasonal Characteristics

As such, shrinkage reduction mortar for plastering ondol is mainly composed of petroleum coke combustor and cement, so it is not possible to control the initial setting time of mortar during summer and winter, especially in summer when delay of initial setting time is required. There is a disadvantage of falling characteristics.

The present invention was devised in a series of studies to improve the shortcomings of shrinkage reduction mortar made from petroleum coke combustors, the initial crack does not occur, as well as the high expression rate of 28 days compressive strength and seasonal characteristics According to the present invention, a shrinkage reducing material capable of differential blending and a composition of cement mortar for plastering ondol finishing using the reducing material are proposed.

1 is a graph showing the change in length according to the composition of the shrinkage reducing material.

The shrinkage reducing material of the present invention for achieving the above object is formed by further mixing the blast furnace slag powder and coal ash within 50% by weight at room temperature, respectively, with respect to the combustion material mixed with limestone and petroleum coke.

In addition, the cement mortar for plastering ondol finishing of the present invention,

(a) cement: 70-85 wt%

(b) The raw material which mix | blended 15-30 weight% of said shrinkage reducing materials is comprised from the sand of granulation rate (F.M) 2.8 or more.

Hereinafter, the present invention will be described in detail.

[Reduction Reduction Material]

In the petroleum coke combustor used in the present invention, when limestone and petroleum coke are combusted in a fluidized bed combustion boiler or lime kiln, almost all of the petroleum coke is combusted, and the sulfides contained in the petroleum coke are lime (CaO). It is made by forming ash while combining with the component. The combustor usually occurs when a mixture of 30 to 70% by weight of limestone and 30 to 70% of petroleum coke is combusted at a high temperature (about 800 to 900 ° C.). The petroleum coke is a heavy oil in a hydrocracking unit of the petroleum refining process. Use the residue from the extraction of diesel oil from Bunker C oil.

In the present invention (1) blast furnace slag powder, to improve the initial crack, 28-day strength expression, seasonal characteristics generated when using petroleum coke combustor mixed with limestone as a cement mortar for ondol finishing 2) It is characterized by blending coal ash at the proper mixing ratio.

(1) blast furnace slag powder

In the present invention, the blast furnace slag powder can be effectively used as an admixture for reducing shrinkage, but in the present invention, the blast furnace slag contains CaO component, but there is no heat of hydration, and appropriately delays the setting time, thereby ensuring sufficient plastering time in the summer. It is also effective in preventing cracks.

In the present invention, the blast furnace slag powder is added to the shrinkage reducing material 10 to 30% by weight, which is less delayed effect of the setting time when the blast furnace slag powder is less than 10%, the surface powder also exceeds 30% by weight This is because is lowered, which is disadvantageous for the initial cracking.

The chemical composition and properties of the blast furnace slag powder used in the present invention are shown in Table 2.

division Chemical composition (% by weight) Constellation SiO ₂ Al ₂ O ₃ CaO MgO SO ₃ Fe ₂ O ₃ lg-loss importance Specific surface area 33.22 14.59 43.74 4.64 2.42 0.33 1.02 2.92 4448

(2) fly ash

Coal ash in the present invention serves to prevent the initial crack by reducing the heat of hydration of the petroleum coke combustion material. In addition, it improves the fluidity of mortar to play a role as a water reducing material. Coal ash is preferably blended 10 to 20%, which is less effective when the coal ash is less than 10%, and reduces the expandability of the shrinkage reducing material when it exceeds 20%.

[Cement mortar]

Cement mortar of the present invention

(a) cement: 70-85 wt%

(b) For raw materials produced by mixing petroleum coke with limestone, blast-furnace slag powder and coal ash are blended within 50% by weight at room temperature, respectively, and are composed of sand having a granulation rate (F.M) of 2.8 or more.

Here, the shrinkage reducing material is preferably mixed with cement in a mixing ratio of 15 to 30% by weight, because less than 15% by weight of the expansion effect is less than 30% and may overexpand.

In addition, although the mixing ratio of the raw material and sand which consist of a shrinkage reducing material and cement is a conventional method, it is usually 1: 2.5-3. Importantly, the granulation rate of sand is set to 2.8 or higher, in order to prevent the initial cracking by increasing the mortar powder when cement mortar is applied.

Cement mortar of the present invention can be added to the air entrainer, water reducing agent, thickener in the usual way to facilitate pump pressure and finishing plastering.

Hereinafter, the present invention will be described in detail through examples.

Example 1

50kg of shrinkage reducing materials, which are composed of petroleum coke combustor, blast furnace slag powder and coal ash (Dangjin Thermal Power Plant) as shown in Table 3, were mixed 50kg per ton of dry mortar (15 ~ 16% of unit quantity), and the setting time was measured. 4 and shown in FIG. 1 by measuring the rate of change in length. The granulation rate of sand was 2.8.

division Petroleum coke combustion material Blast Furnace Slag Powder Coal ash One 100 - - 2 80 10 10 3 70 20 10 4 60 30 10 5 50 30 20

division One 2 3 4 5 Condensation time (hours: minutes) 5:05 5:15 5:30 5:55 6:10

As shown in Table 4, it was found that the condensation time was generally delayed when blast furnace slag powder and coal ash were mixed rather than 100% of petroleum coke combustor as a shrinkage reducing material.

Example 2

5-25% of the shrinkage reducing agent having the composition of Table 5 in cement was mixed with sand to make mortar, and the physical properties of the mortar were measured and shown in Table 6.

The change of length of mortar was made by specimen and the change of length according to drying condition and age was measured, and the mixing amount of mortar kneading was determined by expressing 100 ± 5% of flow rate prescribed in KSL 5220 cement-based dry mortar with general mortar. It was.

material Binder (Cement + Shrinkage Reducing Material) Sand (dry sand) water Compounding cost 280 720 155

Addition amount of binder weight reduction material (wt%) Flowchart (%) Air volume (%) Compressive strength (kgf / ㎠) Length change (× 10 ^-5 ) 7 days 28 days 7 days 28 days 5% 97 13.8 170 235 240 -270 10% 95 14.2 164 230 410 -230 20% 93 14.5 152 220 490 75 25% 91 14.7 145 195 580 105 General mortar (cement + sand) 100 13.0 170 250 -410 -920

Mortar containing 10% shrinkage reducing material showed almost no change in length, so it was expected to produce the desired crack prevention effect, but in actual construction, cracking appeared and 20-25% of shrinkage reducing material with expansion effect was included. Cracks did not appear when. This is believed to be due to the expansion of the shrinkage reducing material compensated for the shrinkage of the cement during the drying process.

Whether or not cracking is caused by dry shrinkage after placing the shrinkage reducing material of the present invention prepared according to the above embodiment on the floor and living room (33 equilibrium) of the apartment under construction by mixing the cement mortar and the ready-mixed concrete company Was observed. Since mortar finishes the floor finishing work by pressing the trowel four or five times after pouring for 1-2 hours, there was little occurrence of plastic shrinkage cracking. After curing for 2 months, there was no dry shrinkage crack on each floor of the ondol, so heating was run for 1 month after covering some households with monolium and cardboard to observe the change after heating. As a result, there was no discoloration of monolium and a sheet of paper, but a crack occurred rarely. It was found to be caused by the lack of mortar in the cracked area and the lack of coating thickness of the heating pipe (within 15mm of coating thickness). As a result of the in-site casting, the shrinkage reducing material according to the present invention showed little cracking and had an effect of suppressing dry shrinkage cracking of mortar for ondol finishing.

As described above, in the present invention, the initial crack does not occur, as well as the 28-day compressive strength expression rate is high, and has a useful effect that can provide a cement mortar exhibiting excellent properties for the ondol finisher by differentiating according to seasonal characteristics.

Claims (2)

A shrinkage reducing material for cement mortar obtained by baking a mixture of 30 to 70% of limestone and 30 to 70% of petroleum coke pulverized within 5 mm at a temperature of about 800 to 900 ° C. Shrinkage reducing material for cement mortar formed by further mixing the blast furnace slag powder and coal ash within 50% by weight at room temperature with respect to the shrinkage reducing material of claim 1 (a) 70 to 80% by weight of cement, (b) Cement mortar for ondol finishing plaster, which is composed of sand having a granulation ratio of 2.8 or more in a raw material containing 15 to 30% by weight of the shrinkage reducing material according to (2).