Low-calcium silicate cement and preparation and hardening methods thereof

Abstract

A low-calcium silicate cement consists of calcium oxide, silica, alumina, and iron oxide. A preparation method of the low-calcium silicate cement consists of: subjecting raw materials to crushing, joint grinding and uniform mixing to obtain a low-calcium silicate cement raw meal; calcining the above low-calcium silicate cement raw meal at 1050-1300? C. for 30-90 min, and cooling to obtain low-calcium silicate cement clinker; and levigating the above low-calcium silicate cement clinker till a specific surface area is 400-500 m.sup.2/Kg, thereby obtaining a low-calcium silicate cement.

Claims

1. A preparation method of a low-calcium silicate cement, wherein raw materials consists of calcium carbonate that includes calcium oxide, a clay material that includes silica and alumina, and an iron oxide material that includes iron oxide; the low-calcium silicate cement comprising 50-60% of calcium oxide, 30-45% of silica, 2-7% of alumina, and 1-4% of iron oxide; wherein the preparation method comprising the following steps: i) crushing, grounding and uniformly mixing the raw materials to obtain a low-calcium silicate cement raw meal; ii) calcining the low-calcium silicate cement raw meal at 1050-1300? C. for 30-90 min, and cooling to obtain a low-calcium silicate cement clinker; iii) levigating the low-calcium silicate cement clinker till a specific surface area is 400-500 m.sup.2/Kg, thereby obtaining the low-calcium silicate cement.

2. The preparation method according to claim 1, characterized in that the crushing and grounding in the step i) makes the particle diameter of the raw materials be less than 10 mm.

3. The preparation method according to claim 1, characterized in that the levigating the low-calcium silicate cement clinker till a specific surface area is up to 300-350 m.sup.2/Kg in the step iii).

4. The preparation method according to claim 1, characterized in that the cooling in the step ii) is quick cooling or natural cooling.

Description

DESCRIPTION OF PREFERRED EMBODIMENTS

(1) The invention selects three kinds of raw materials, i.e., calcium carbonate essentially comprising calcium oxide, a clay material essentially comprising silica and alumina, and an iron oxide material essentially comprising iron oxide. The three raw materials, i.e., the calcium carbonate, the clay material and the iron oxide material can be natural minerals or industrial residues. Specific steps are as follows:

(2) Step 1: the three raw materials are subjected to crushing, joint grinding, and levigating till a specific surface area is up to 300-350 m.sup.2/Kg; the raw materials are uniformly mixed to obtain low-calcium silicate cement raw meal, with the goal of enabling mass proportions of the three raw material contained in the low-calcium silicate cement raw meal to meet the following requirements: 50-60% of calcium oxide, 30-45% of silica, 2-7% of alumina, and 1-4% of iron oxide, a sum being 100% based on the mass of oxides.

(3) Step 2: the low-calcium silicate cement raw meal is calcined at 1050-1300? C. for 30-90 min, where the calcining is conducted in a shaft kiln, a rotary kiln, or a tunnel kiln. After calcining, an essential mineral of the clinker, i.e., tricalcium disilicate is cooled to obtain low-calcium silicate cement clinker. A cooling method can be quick cooling (cooling by 200-300? C. per minute) or natural cooling.

(4) Step 3: the low-calcium silicate cement clinker is levigated till a specific surface area is 400-500 m.sup.2/Kg, thereby obtaining a low-calcium silicate cement.

(5) Step 4: a certain amount of water is added into the low-calcium silicate cement, with a mass ratio of the water to the solid (low-calcium silicate cement) of 0.1-0.3:1. The cement is compressed into a test block having a certain shape, and the test block reacts with 60? C.-150? C. CO.sub.2 or 60? C.-280? C. CO.sub.2-containing exhaust gas from industrial furnace for a certain time to obtain a hardened test block with a certain mechanical property.

(6) In comparison with the conventional silicate cement, in the foregoing process, the carbon dioxide emission reduces about 15%, the exhaust emission reduces about 25%, and the heat consumption in calcination reduces about 15%.

(7) Another embodiment in the foregoing process is to apply the CO.sub.2-containing gas produced during the calcination in step 2 to the hardening process of the cement in step 4, in which a total exhaust emission will reduce by no less than 40%.

(8) The invention will be described below in further details by several typical embodiments.

(9) Embodiment 1

(10) Limestone, clay and iron powder commonly used in current silicate cement-manufacturing plants were selected as raw materials, wherein a calcareous raw material was 1000 g, including 50% of calcium oxide; an argillaceous raw material was 600 g, including 68% of silica and 12% of alumina, respectively; an iron oxide raw material was 45 g, including 45% of iron oxide. The above-mentioned three raw materials were crushed respectively, so that the particle diameter was less than 10 mm, and then the raw materials are mixed, jointly ground, and levigated till a specific surface area was 300 m.sup.2/Kg, and are uniformly mixed to obtain low-calcium silicate cement raw meal. The raw meal contained 50% of calcium oxide, 41% of silica, 7% of alumina, and 2% of iron oxide, a sum being 100% based on the mass of oxides.

(11) The above low-calcium silicate cement raw meal was put in a rotary or shaft kiln and calcined at 1050? C. for 90 min, and then quick cooled in air with the temperature reduced at 200? C. per minute, thereby obtaining low-calcium silicate cement clinker.

(12) The above low-calcium silicate cement clinker was ground, and levigated till a specific surface area was 400 m.sup.2/Kg, thereby obtaining a low-calcium silicate cement.

(13) A certain amount of water was added into the above low-calcium silicate cement with a mass ratio of the water to the solid (hereinafter referred to as water-solid ratio) being 0.25, the cement was compressed into a test block of 2?2?2 cm, the test block was placed in an agitated reactor with introduced CO.sub.2 gas for carbonization at 60? C. for 1d, and the volume expansion ratio and compressive strength of the test block were 5.1% and 16.8 MPa, respectively. After the test block was carbonized at the same temperature for 3d, the volume expansion ratio and compressive strength of the test block were 8.3% and 24.7 MPa, respectively.

(14) Embodiment 2

(15) Limestone, clay and iron powder commonly used in the current silicate cement-manufacturing plants were selected as raw materials, wherein a calcareous raw material was 1200 g, including 50% of calcium oxide; an argillaceous raw material was 485 g, including 68% of silica and 12% of alumina, respectively; an iron oxide raw material was 55 g, including 45% of iron oxide. The above-mentioned three raw materials were crushed respectively, so that the particle diameter was less than 10 mm, and then the raw materials were mixed, jointly ground, and levigated till a specific surface area was 330 m.sup.2/Kg, and are uniformly mixed to obtain low-calcium silicate cement raw meal. The raw meal contained 60% of calcium oxide, 32% of silica, 5.5% of alumina, and 2.5% of iron oxide, a sum being 100% based on the mass of oxides.

(16) The above low-calcium silicate cement raw meal was put in a rotary or shaft kiln and calcined at 1100? C. for 60 min, and then quick cooled in water with the temperature reduced at 300? C. per minute, thereby obtaining low-calcium silicate cement clinker.

(17) The above low-calcium silicate cement clinker was ground, and levigated till a specific surface area was 450 m.sup.2/Kg, thereby obtaining a low-calcium silicate cement.

(18) A certain amount of water was added into the above low-calcium silicate cement with a water-solid mass ratio being 0.3, the cement was compressed into a test block of 2?2?2 cm, the test block was placed in an agitated reactor with introduced CO.sub.2 gas for carbonization at 90? C. for 1d, the compressive strength of the test block was 17.5 MPa, and after carbonization for 3d, the compressive strength of the test block was 28.2 MPa.

(19) Embodiment 3

(20) Limestone, clay and iron powder commonly used in the current silicate cement-manufacturing plants were selected as raw materials, wherein a calcareous raw material was 1000 g, including 50% of calcium oxide; an argillaceous raw material was 588 g, including 68% of silica and 12% of alumina, respectively; an iron oxide raw material was 66 g, including 45% of iron oxide. The above-mentioned three raw materials were crushed respectively, so that the particle diameter was less than 10 mm, and then the raw materials were mixed, jointly ground, and levigated till a specific surface area was 350 m.sup.2/Kg, and are uniformly mixed to obtain low-calcium silicate cement raw meal. The raw meal contained 50% of calcium oxide, 40% of silica, 7% of alumina, and 3% of iron oxide, a sum being 100% based on the mass of oxides.

(21) The above low-calcium silicate cement raw meal was put in a rotary or shaft kiln and calcined at 1150? C. for 30 min, and then subjected to natural cooling in air with the temperature reduced at 300? C. per minute, thereby obtaining low-calcium silicate cement clinker.

(22) The above low-calcium silicate cement clinker was ground, and levigated till a specific surface area was 500 m.sup.2/Kg, thereby obtaining a low-calcium silicate cement.

(23) A certain amount of water was added into the above low-calcium silicate cement with a water-solid mass ratio being 0.3, the cement was compressed into a test block of 2?2?2 cm, the test block was placed in an agitated reactor with introduced CO.sub.2 gas for carbonization at 120? C. for 1d, the compressive strength of the test block was 18.4 MPa, and after carbonization for 3d, the compressive strength of the test block was 32.7 MPa.

(24) Embodiment 4

(25) Limestone, clay and iron powder commonly used in the current silicate cement-manufacturing plants were selected as raw materials, wherein a calcareous raw material was 1100 g, including 50% of calcium oxide; an argillaceous raw material was 515 g, including 68% of silica and 12% of alumina, respectively; an iron oxide raw material was 88 g, including 45% of iron oxide. The above-mentioned three raw materials were crushed respectively, so that the particle diameter was less than 10 mm, and then the raw materials were mixed, jointly ground, and levigated till a specific surface area was 350 m.sup.2/Kg, and are uniformly mixed to obtain low-calcium silicate cement raw meal. The raw meal contained 55% of calcium oxide, 35% of silica, 6% of alumina, and 4% of iron oxide, a sum being 100% based on the mass of oxides.

(26) The above low-calcium silicate cement raw meal was put in a rotary or shaft kiln and calcined at 1300? C. for 30 min, and then subjected to natural cooling in air, thereby obtaining low-calcium silicate cement clinker.

(27) The above low-calcium silicate cement clinker was ground, and levigated till a specific surface area was 500 m.sup.2/Kg, thereby obtaining a low-calcium silicate cement.

(28) A certain amount of water was added into the above low-calcium silicate cement with a water-solid mass ratio being 0.3, the cement was compressed into a test block of 2?2?2 cm, the test block was placed in an agitated reactor with introduced CO.sub.2 gas for carbonization at 150? C. for 1d, the compressive strength of the test block was 19.1 MPa, and after carbonization for 3d, the compressive strength of the test block was 38.2 MPa.

(29) Embodiment 5

(30) Limestone, clay and iron powder commonly used in the current silicate cement-manufacturing plants were selected as raw materials, wherein a calcareous raw material was 1040 g, including 50% of calcium oxide; an argillaceous raw material was 605 g, including 68% of silica and of 12% alumina, respectively; an iron oxide raw material was 22 g, including 45% of iron oxide. The above-mentioned three raw materials were crushed respectively, so that the particle diameter was less than 10 mm, and then the raw materials were mixed, jointly ground, and levigated till a specific surface area was 350 m.sup.2/Kg, and are uniformly mixed to obtain low-calcium silicate cement raw meal. The raw meal contained 52% of calcium oxide, 40% of silica, 7% of alumina, and 1% of iron oxide, a sum being 100% based on the mass of oxides.

(31) The above low-calcium silicate cement raw meal was put in a rotary kiln or shaft kiln and calcined at 1300? C. for 30 min, and then subjected to natural cooling, thereby obtaining low-calcium silicate cement clinker.

(32) The above low-calcium silicate cement clinker was ground, and levigated till a specific surface area was 500 m.sup.2/Kg, thereby obtaining a low-calcium silicate cement.

(33) A certain amount of water was added into the above low-calcium silicate cement with a water-solid mass ratio being 0.3, the cement was compressed into a test block of 2?2?2 cm, the test block was placed in an agitated reactor with introduced CO.sub.2 gas for carbonization at 180? C. for 1d, the compressive strength of the test block was 20.4 MPa, and after carbonization for 3d, the compressive strength of the test block was 39.2 MPa.

(34) Embodiment 6

(35) Limestone, clay and iron powder commonly used in the current silicate cement-manufacturing plants were selected as raw materials, wherein a calcareous raw material was 1040 g, including 50% of calcium oxide; an argillaceous raw material was 605 g, including 68% of silica and 12% of alumina, respectively; an iron oxide raw material was 22 g, including 45% of iron oxide. The above-mentioned three raw materials were crushed respectively, so that the particle diameter was less than 10 mm, and then the raw materials were mixed, jointly ground, and levigated till a specific surface area was 350 m.sup.2/Kg, and are uniformly mixed to obtain low-calcium silicate cement raw meal. The raw meal contained 52% of calcium oxide, 40% of silica, 7% of alumina, and 1% of iron oxide, a sum being 100% based on the mass of oxides.

(36) The above low-calcium silicate cement raw meal was put in a rotary kiln or shaft kiln and calcined at 1300? C. for 30 min, and then subjected to natural cooling, thereby obtaining low-calcium silicate cement clinker.

(37) The above low-calcium silicate cement clinker was ground, and levigated till a specific surface area was 500 m.sup.2/Kg, thereby obtaining a low-calcium silicate cement.

(38) A certain amount of water was added into the above low-calcium silicate cement with a water-solid mass ratio being 0.1, the cement was compressed into a test block of 2?2?2 cm, the test block was placed in an agitated reactor with introduced CO.sub.2 gas for carbonization at 90? C. for 1d, the compressive strength of the test block was 16.5 MPa, and after carbonization for 3d, the compressive strength of the test block was 26.2 MPa.

(39) Embodiment 7

(40) Limestone, clay and iron powder commonly used in the current silicate cement-manufacturing plants were selected as raw materials, wherein a calcareous raw material was 1040 g, including 50% of calcium oxide; an argillaceous raw material was 605 g, including 68% of silica and 12% of alumina, respectively; an iron oxide raw material was 22 g, including 45% of iron oxide. The above-mentioned three raw materials were crushed respectively, so that the particle diameter was less than 10 mm, and then the raw materials were mixed, jointly ground, and levigated till a specific surface area was 350 m.sup.2/Kg, and are uniformly mixed to obtain low-calcium silicate cement raw meal. The raw meal contained 52% of calcium oxide, 40% of silica, 7% of alumina, and 1% of iron oxide, a sum being 100% based on the mass of oxides.

(41) The above low-calcium silicate cement raw meal was put in a rotary kiln or shaft kiln and calcined at 1300? C. for 30 min, and then subjected to natural cooling, thereby obtaining low-calcium silicate cement clinker.

(42) The above low-calcium silicate cement clinker was ground, and levigated till a specific surface area was 500 m.sup.2/Kg, thereby obtaining a low-calcium silicate cement.

(43) A certain amount of water was added into the above low-calcium silicate cement with a water-solid mass ratio being 0.15, the cement was compressed into a test block of 2?2?2 cm, the test block was placed in an agitated reactor with introduced CO.sub.2 gas for carbonization at 280? C. for 1d, the compressive strength of the test block was 28.5 MPa, and after carbonization for 3d, the compressive strength of the test block was 52.2 MPa.

(44) Embodiment 8

(45) Limestone, clay and iron powder commonly used in the current silicate cement-manufacturing plants were selected as raw materials, wherein a calcareous raw material was 1000 g, including 50% of calcium oxide; an argillaceous raw material was 600 g, including 68% of silica and 12% of alumina, respectively; an iron oxide raw material was 45 g, including 45% of iron oxide. The above-mentioned three raw materials were crushed respectively, so that the particle diameter was less than 10 mm, and then the raw materials are mixed, jointly ground, and levigated till a specific surface area was 300 m.sup.2/Kg, and are uniformly mixed to obtain low-calcium silicate cement raw meal. The raw meal contained 50% of calcium oxide, 41% of silica, 7% of alumina, and 2% of iron oxide, a sum being 100% based on the mass of oxides.

(46) The above low-calcium silicate cement raw meal was put in a rotary kiln or shaft kiln and calcined at 1050? C. for 90 min, and then quick cooled in air with the temperature reduced at 200? C. per minute, thereby obtaining low-calcium silicate cement clinker. Smoke generated in the calcining process had a temperature of about 200-280? C., wherein volume content of CO.sub.2 was about 20-30%.

(47) The above low-calcium silicate cement clinker was ground, and levigated till a specific surface area was 400 m.sup.2/Kg, thereby obtaining a low-calcium silicate cement.

(48) A certain amount of water was added to the above low-calcium silicate cement with a mass ratio of the water to the solid (hereinafter referred to as water-solid ratio) being 0.25, and the cement was compressed into a test block of 2?2?2 cm, the smoke discharged from the preheater at the kiln tail of the cement kiln in the preceding step was introduced into an agitated reactor in which the test block was placed, carbonizing was performed at 220? C. for 1d, and the volume expansion ratio and compressive strength of the test block were 5.3% and 19.2 MPa, respectively. After the test block was carbonized at the same temperature for 3d, the volume expansion ratio and compressive strength of the test block were 7.1% and 32.7 MPa, respectively.

(49) It can be seen from the aforementioned embodiments 1-8 that the invention can choose a low-calcium calcareous raw material to obtain low-calcium silicate clinker, and obtain an early-strength low-calcium silicate cement by a carbonization hardening method.