GB2141421A

GB2141421A - Portland cement and method of manufacture thereof

Info

Publication number: GB2141421A
Application number: GB08316034A
Authority: GB
Inventors: Dr Hong Won Pyo
Original assignee: THAI HAN CO Ltd
Current assignee: THAI HAN CO Ltd
Priority date: 1983-04-08
Filing date: 1983-06-13
Publication date: 1984-12-19
Also published as: AU560840B2; GB8316034D0; IN167369B; GB2141421B; AU1329683A; CA1221389A

Abstract

Portland cement which is improved relative to ordinary Portland cement, in such properties as water proofness, compressive strength, durability, extended duration of storage and workability in concrete, is provided by coating an asphalt film on the surface of particles of cement powder and homogeneously mixing carbon black with or without addition of gypsum by requirement, or by addition of carbon black into ordinary Portland cement.

Description

SPECIFICATION Portland cement and method of manufacture thereof This invention relates to Portland cement and a method of manufacture thereof.

Prior proposals to improve ordinary Portland cement so far as concerns the extent to which it is waterproof, compressive strength, durability, duration of packing storage, etc. include the following: 1) U.S. Patent No. 1,134,573 relates to a method and means for producing an admixture by adding lime or bentonite to asphaltum oil or asphalt and mixing it with cement, water and aggregates to produce concrete or mortar.

2) U.S. Patent No. 1,772,999 relates to a process of producing an admixture by mixing diatomaceous earth or bentonite with mineral oil or animal oil, and coating Portland cement with it. It also relates to a method of production of the emulsion by mixing calcium aqueous solution, which is used as a setting accelerator for concrete, with asphalt dissolved crude oil and mixed with bentonite or Fuller's earth.

3) U.S. Patent No. 913,794 relates to a procedure for the manufacture of a waterproof cement by coating cement particles with the mixture obtained by admixing lime with an oleaginous substance without heating.

4) U.S. Patent No. 1,076,028 relates to a method of coating particles of a dry cement powder by passing them through a spray zone in which is present fatty acid soap or wax in a liquid state.

5) U.S. Patent No. 1,305,645 relates to a method of mixing cement with pitch powder pulverized to a granularity below 100 mesh.

The above proposals can be analysed as follows: A) By the above 1), it is quite possible that there may be partial leakage and that compressive strength, workability, duration of storage may not be preserved, because the hydrophobic admixture has to be mixed with the umimproved traditional cement in concreting without any technological proof.

B) By the above 2), any uniformity in quality can not be expected because the admixture is made of matural oil and mineral material which are so impure and weak in hardness as to decrease the strength and workability of the cement. There may be more cracks in concrete with the increase of the heat of hydration, on the other hand reinforced bars in concrete could become corroded by the corrosive property of calcium chloride.

C) By the above 3), workability and waterproofing strength in concrete may be decreased because no pore filler is used for the cement except wax and oleaginous substance with lime.

D) By the above 4), strength, waterproofing and workability in concrete may be decreased because the cement is coated while being forced through a spray zone.

E) By the above 5), there may be a decrease in workability, strength and waterproofing in the concrete because pitch has to be admixed with cement in concreting without any technological proof.

According to a first aspect of the invention there is provided a Portland cement comprising cement powder to which has been added carbon black.

According to a second aspect of the present invention there is provided a method of manufacturing Portland cement comprising the steps of providing a Portland cement dry powder, adding liquid or powdered asphalt to the powder, heating and agitating the cement/asphalt mixture in a range of from 100 to 180"C to form an asphalt film coated dry cement powder, cooling the coated powder to ambient temperature and agitating the cooled coated powder with carbon black to form a homogeneously mixed product, the proportions of the constituents being selected to yield a product which comprises from 0.1 to 5% by weight of asphalt and from 0.2 to 2% by weight of carbon black.

The second-mentioned step of the method of the invention serves to form thin films of hydro-phobic asphalt surrounding particles of ordinary Portland cement. The asphalt can be added with or without added gypsum.

A further step of the method comprises adding particles of carbon black, preferably of a diameter less than 60 millimicron, into the asphalt filmed cement powder, and to blend these into an homogeneous mixture.

Portland cement powder according to the invention can be used just like ordinary Portland cement in producing concrete or mortar, and it provides water-proofing in 28 days without utilizing the conventional water-proofing method. The asphalt has a hydro-phobic property and plasticity under heat. Furthermore, the asphalt substance changes character significantly at the softening point. It gains good fluidity above the softening point, but it loses fluidity and is transformed to an elastic solid state below the softening point.

This heat plasticity is primarily applied to create an asphalt film around particles of cement powder.

The asphalt is heated to a liquid state and it is added to the cement dry powder at the rate of 0.1-5 percent of the weight of cement. After blending this with the cement, the heat is kept between 1 OO"C - 180 C with agitation. In this way the liquid asphalt forms a very thin film around the particles of the cement dry powder.

The asphalt to be used here should have a softening point in a range of from 40" to 90"C. The asphalt should be straight asphalt, blown asphalt, or polymer added improved asphalt.

After the above process, particles of carbon black, preferably less than 60 millimicron in diamter, are added to the filmed cement particles and agitated into an homogeneous mixture. The concrete formed of this invented cement after curing is tight enough to be water-proof under water pressure as high as 15 kilograms per square centimeter after a certain period of curing. Other improved characteristics of the cement are as follows: First, in the conventional mixing of concrete or mortar using ordinary Portland cement, it is the rule to have much surplus water content compared with the necessary amount of water for hydration of cement, to enhance workability. This surplus water and the air entraining which necessarily occurs in concrete mixing produces a lot of pores during hydration and setting.When the pores are interconnected they give rise to undesirable leakage.

However, concrete made with cement according to the present invention improves the leakage problems.

Some of the pores are filled by the very thin asphalt film and the very fine carbon black (less than 60 mu in diameter). Leakage through the pore net is accordingly prevented due to the hydro-phobic asphalt and carbon black. This effect has been verified by a determination of porosity, which has demonstrated a relatively large porosity in the concerete of ordinary Portland cement and the much smaller porosity in the concrete of the present cement in terms of the number and diameter of developed pores. The above reasons illustrate the present cement's excellent effects on water-proofing even under water pressure as high as 15Kg/Cm.

Second, concrete or mortar made with ordinary Portland cement is prone to cracking, owing to the shrinkage and expansion by heat of hydration and variations of the surrounding temperatures under/after hardening. These cracks cause leakage. However, in the concrete or mortar made with the present cement, the innumerable lays of asphalt block out the water leakage through pores. When the temperature of the concrete rises, due to causes such as heat of hydration and changes in the surrounding temperature, the asphalt absorbs somewhat the heat of hydration and it softens.

When the temperature falls, the asphalt resumes its solid state. The role of the asphalt is to resist cracking.

The asphalt film itself interrupts the water's movement through the pores in the concrete. This results in much less cracking and accordingly enhances the water-proofing effects. Inspection of the hardened concrete by electronic microscope has shown the excellent results of the invented cement in preventing the cracks from interconnecting because the present cement is much better compared to the ordinary cement in terms of the number, and the length, of the cracks.

Third, conventional reinforced concrete made with ordinary Portland cement has a drawback. It creates a water pool beneath aggregate particles or the horizontal reinforcement bars due to the bleeding. This makes for more pores and cracking under the hydration. The present cement cuts down significantly on the bleeding, because the carbon black, finer than the cement powder, plays the role of dispersing agent, and the improved workability causes a smaller water-cement ratio compared with that of the ordinary Portland cement. These facts contribute to less bleeding.

Fourth, while in the mixing of concrete or mortar using ordinary Portland cement, it is very difficult to keep the low water-cement ratio due to poor workability, unless air entraining admixtures are used, the present cement is more workable. It contains carbon black which is very fine with a diameter less than 60 millimicron and very light in weight. (The specific gravity of cement and asphalt are about 3.2 and 1.8 respectively.) The carbon black acts as dispersing agent and it also has the characteristics of pigment. The properties of the carbon black improve workability. Accordingly, the present cement provides enhanced workability and stability of the water proof structure in the construction field. For example, tens of concrete specimens were made at various water-cement ratios ranging fom 60 to 45% with the various slumps ranging from 18 to 8 centimeters.No leakage was found from those specimens which were made of the present cement. Some of the specimens were moulded into three 24 hour stages and cured for 28 days at room temperature. The test results indicate no leakage under continuing pressure at 15 kilograms per square centimeter for a week.

We interpret these facts to show that the present Portland cement significantly improves workability and water tightness of concrete owing to the characteristics of the miro asphalt and carbon black. It also causes to join more firmly together the part of staged placement into a whole in the concrete.

Fifth, the compressive strength of the 28-day aged concrete made with the present cement is slightly weaker than that of the ordinary Portland cement by an amount of from 4 to 6 percent. However, after 40 days it has become stronger than ordinary Portland cement by an amount of about 15%. This is due to the phenomena that even though asphalt in the cement retards the setting by absorbing the heat of hydration in the early stage, the carbon black improves water tightness later.

Sixth, the durability of a reinforced concrete structure is closely related to neutralization of concrete material and corrosion of the included reinforcement bars. After setting, if the concrete loses its alkalinity by the action of the surface air or water which contains carbon dioxide (CO2) and sulphur dioxide (SO2) the concrete neutralizes. This causes the corrosion of the reinforcement bars and the destruction of the concrete.

The present cement has not only the predominant water-tightness but also an anti-corrosion effect relative to the reinforcement bars because the hydro-phobic asphalt film and chemically stable carbon black improve the watertightnes and protect the concrete from corrosion. Moreover, the asphalt in the concrete is softened by the heat of hydration and after reversion to the solid state it provides very close adherence around the bar. This also prevents the reinforcement bar from corrosion. Several tests show that the concrete with the present cement increases the strength of adhesion to the reinforcement bar by an amount of 30 percent compared with the ordinary Portland cement. The invented cement gives much better durability to the reinforced concrete structures.

Seventh, ordinary Portland cement is more absorbent of moisture and consequently problems arise in storage owing to water which results in hardening. But in the present cement particles are wrapped with a hydro-phobic asphalt film so that the cement can be stored for a longer period without solidification.

Eighth, additional water proofing processes are required for concrete structures made with ordinary Portland cement by the conventional method. The cost is high and the processes cannot always be used, especially in a pressured area. With the present cement there need be no leakage even under a high pressure of 15 kilograms per square centimeter, and no additional water-proofing work in concreting. Therefore, cement according to the invention can predominate in construction works including subways, tunnels, dams and substructures of buildings from the economical and technical point of view of water-proofing.

An experiment using ordinary conventional Portland cement and the present Portland cement of Examples 1 to 6 hereinbelow and of the same cement maker yielded the following results.

Item Compressive Strength Water Adhesive Permeability Strength of (after aging (after aging (after aging Reinforcement Cement for 28 days) for 40 days) for 28 days) Bar at 15Kg/Cm2 Conventional Portland cement 100% 100% 100% 100% Invented Portland cement according to 95-97% 100-120% 0% 110-150% the present invention The invention will now be further illustrated by the following Examples.

Example 1 This Portland cement consists of 99.6% of weight percent of dry powder of ordinary Portland cement clinker, 0.2% of asphalt (straight asphalt, blown asphalt, polymer added asphalt) of 40-90"C softening point and 0.2% of carbon black (less than 70 millimicron in diameter).

Example 2 This Portland cement consists of 97.5% of weight percent of dry powder of ordinary Portland cement clinker, % asphalt and 1.5% of carbon black.

Example 3 This Portland cement consists of 99% of weight percent of dry powder of ordinary Portland cement clinker, 0.5% of asphalt and 0.5% of carbon black.

Example 4 This Portland cement consists of 97.6% of weight percent of dry powder of ordinary Portland cement clinker, 2% of gypsum, 0.2% of asphalt, and 0.2% of carbon black.

Example 5 This Portland cement consists of 92:5% of weight percent of dry powder of ordinary Portland cement clinker, 5% of gypsum, 1% of asphalt, and 1.5% of carbon black.

Example 6 This Portland cement consists of 95.8% of wieght percent of dry powder of ordinary Portland cement clinker, 3% of gypsum, 0.5% of asphalt and 0.7% of carbon black.

Example 7 This Portland cement consists of 99.8% of weight percent of dry powder of ordinary Portland cement clinker and 0.2% of carbon black.

Example 8 This Portland cement consists of 98% of weight percent of dry powder of ordinary Portland cement clinker and 2% of carbon black.

Example 9 This Portland cement consists of 99% of weight percent of dry powder of ordinary Portland cement clinker and 1% of carbon black.

Example 10 This Portland cement consists of 97.8% of weight percent of dry powder of ordinary Portland cement clinker, 2% of gypsum, and 0.2% of carbon black.

Example 11 This Portland cement consists of 93% of weight percent of dry powder of ordinary Portland cement clinker, 5% gypsum and 2% of carbon black.

Example 12 This Portland cement consists of 96% of weight percent of dry powder of ordinary Portland cement clinker, 3% of gypsum and 0.6% of carbon black.

Example 13 The manufacturing process of a Portland cement with the compositions of Examples 1 to 3 was as follows: After getting a dry powder of clinker by pulverization, adding to it an asphalt of molten state or powder, heating and agitating it in a kettle with heating and agitation devices at between 100 - 150"C (straight asphalt 100 - 120 C, blown asphalt and polymer added asphalt 130 - 150"C) to get asphalt filmed cement powder, it was cooled down to room temperature with carbon black added and agitated to be homogeneously mixed.

Example 14 The manufacturing process of a Portland cement with the compositions of Examples 4 to 6 was as follows: a) After getting the asphalt filmed dry powder of the ordinary Portland cement clinker with the gypsum, with carbon black added and agitated to be homogeneously mixed by the process described in Example 13.

b) After getting the asphalt filed dry powder of the ordinary Portland cement clinker, with gypsum and carbon black added and agitated to be homogeneously mixed by the process described in Example 13.

Example 15 The manufacturing process of Portland cement with compositions of Examples 7 to 9 is as follows: After getting the dry powder of the ordinary Portland cement clinker, with carbon black added and agitated to be homogeneously mixed at room temperature.

Example 16 The manufacturing process of Portland cement with compositions of Examples 10 to 12 is as follows: After getting the dry powder of the ordinary Portland cement, with gypsum and carbon black added and agitated to be homogeneously mixed at room temperature.

Claims

1. A Portland cement comprising cement powder to which has been added carbon black.

2. A Portland cement comprising cement powder to which has been added asphalt and carbon black, the asphalt coating the particles of the cement powder, the proportion of asphalt in the cement being in a range of from 0.1 to 5% by weight and the proportion of carbon black in the cement being in a range of from 0.2 to 2.0% by weight.

3. A cement as claimed in claim 1 or 2 comprising from 2 to 5% by weight of gypsum.

4. A cement as claimed in claim 2 or 3 wherein the weight of asphalt is from 0.2 to 1%.

5. A cement as claimed in any one of the preceding claims wherein the weight of carbon black is from 0.2 to 1.5%.

6. A cement as claimed in either of claims 2 or 4 wherein the asphalt has a softening point at a temperature in a range of from 40 to 90"C.

7. A cement as claimed in any one of the preceding claims wherein the carbon black is present as particles of diameter less than 60 millimicron.

8. A cement substantially as described in any one of the foregoing Examples 1 to 12.

9. A method of manufacturing Portland cement comprising the steps of providing a Portland cement dry powder, adding liquid or powdered asphalt to the powder, heating and agitating the cementlasphalt mixture in a range of from 100 to 180into form an asphalt film coated dry cement powder, cooling the coated powder to ambient temperature and agitating the cooled coated powder with carbon black to form a homogeneously mixed product, the proportions of the constituents being selected to yield a product which comprises from 0.1 to 5% by weight of asphalt and from 0.2 to 2% by weight of carbon black.

10. A method according to claim 10 wherein the step of heating is in a range of from 100 to 150"C and the asphalt is selected to have a softening temperature in a range of from 40 to 90"C.

11. A method substantially as described in any one of the foregoing Examples 13 to 16.