CA1279663C - Method of preparing building materials - Google Patents

Method of preparing building materials

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Publication number
CA1279663C
CA1279663C CA000534388A CA534388A CA1279663C CA 1279663 C CA1279663 C CA 1279663C CA 000534388 A CA000534388 A CA 000534388A CA 534388 A CA534388 A CA 534388A CA 1279663 C CA1279663 C CA 1279663C
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Prior art keywords
slag
concrete
weight based
acidic
basic
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CA000534388A
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French (fr)
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Fredrik W.A. Kurz
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Individual
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    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02PCLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P40/00Technologies relating to the processing of minerals
    • Y02P40/10Production of cement, e.g. improving or optimising the production methods; Cement grinding

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  • Curing Cements, Concrete, And Artificial Stone (AREA)

Abstract

ABSTRACT
A method of making a building material by activation of latently hydraulic finely ground granulated basic blast-furnace slag to form a direct acting hydraulic binder is disclosed. The slag is mixed with water, sand and ballast material as well as with a combination of acidic and basic components.
The acidic components consist of phosphates, optionally in combination with strongly acting sulfates, and the basic components consist of oxides or other compounds of earth metals, optionally in combination with zinc.
Thereby, a concrete having great mechanical strength and high chemical resistance is obtained.

Description

lX79663 Port]and cement is generally considered as the best hydraulic binder, which only by addition of water hardens to form a rock-like material (concrete) within a few hours to obtain finally its ultimate strength within about one month. The effect is due mainly to chemical reactions between basic lime and silicic acid.
Analysis of Portland cement shows about 64 ~ CaO, 20 % SiO2, 2.5 % MgO, 6 % Al2O3 3.5 ~ Fe2O3 + FeO, 2 % K2O ~ Na2O, 1.5 % SO3. A disadvantage of cement is that not all lime is bound in the concrete and that a consistently appearing excess of unstable hydrate of lime which is formed towards the end of the hardening process, is relatively easily leached out by the action of water and carbon dioxide in the air, involving a danger of detrimental carboni~ation. Furthermore, the chemical resistance to acidic and basic attack is very limited. Also, the chemical resistance to acidic and basic attack is very limited.
Example: Destruction of concrete surfaces on roads by road salts or of concrete bridges by sea-water.
Risk of rust attack on steel reinforcement and great difficulties with glass fibre reinforce-ment.
To avoid the sometimes disturbing weaknessess of Portland cement, materials having a similar composition but with an enhancement of the components improving both the physical and the chemical resistance have long been sought. It was natural to experiment with finely ground granulated basic blast-furnace slag as it has just a high percentage of highly resistant substances. The analysis is as follows, varying with the source: about 30 to 40 ~ CaO, 35 to 40 % SiO2, 7 to 10 % MgO, 10 to 20 % Al2O3, 0.5 to 2 % Fe2O3 + EeO, 1 to 2 % K2O~Na2O, 0.5 to 3 % SO3. Compared to Portland cement, the lime content is only about ~, but SiO2 and ~l2O3 is about lX79663 double, and MgO almost 4 times higher. These substances, however, impart to sllicates the highest mechanlcal and chemical resistance, i.e. increased compressive and tensile strength and resistance to chemical action.
Blast furnace slag is obtained largely as a useless residual product in the manufacture of iron and steel and is present internationally in hundreds of millions of tons. "Granulated" generally means ! "subdivided", but in connection with slag it is commonly meant that the slag in a still red-hot state has been subjected to rapid cooling with water or with a combination of cold water and cold air, whereby the slag becomes vitreous and amorphous. In spite of the favorable chemical composition the finely ground granular blast-furnace slag is only "latently" hydraulic, i.e.
it does not bind directly after admixture with water.
The reason is that there is formed a dense gel rich in silicic acid, said gel enclosing the slag grains and preventing hydration. A condition for accomplishing activation is that this gel is broken. Thus, activators havea double task, they must first break down the gel and then react with the slag itself. }~owever, the gel formation also has a positive effect, since the gel pores are uniformly distributed, whereby a better resistance to frost is obtained than with capillary pores in Portland cement concrete.
Already toward the end of the nineteenth century attempts to activate blast-furnace slag were made. The oldest patent goes back to 1892 (Passow), wherein a mlxture of slag with Portland cement is recommended and wherein the free lime in the form Ca(OH)2 formed in the final stage of hydration functions as an activator.
Thereby, the reaction with sla~ occurs late and gives rise to a slow development of strength. Also the risk of shrinkage in cooling is rather great. This is the reason why the so-called slag cement is hardly used at present.

1'~79663 In addition to lime the activators known for a lony time (see H. K~hl, Zement-Chemie, Berlin 1951) are alkalies and sulfates. Hitherto, it was thouyht that activation with alkalies results in the highest strength values, but it results in a number of disadvantages. The lony-term strength is not satisfactory, and there are great risks of shrinkage, salt deposition and carbonatization. Setting occurs too quickly, in between 20 and 30 minutes, wherefore casting in a building site is not possible.
Use is limited to the manufacture of prefabricated concrete elements. Activation by alkalies also has the disadvantage that strong caustic NaOH is formed. Activation with lime or sulfates has the disadvantage of an inferior short-term strength and a risk of swelling. For all these known methods it is also difficult to control the rate of setting which is either too rapid or too slow.
With the prior art activating powders it was found that their admixture with slag powder during extended storage but also during transport will often result in some binding action. It is important to avoid this disadvantage in a novel activating system.
A much more reliable activation technique is obtained by the cooperation of acidic and basic components, the acidic substance consisting preferably of phosphates, optionally in combination with strongly acting sulfates, and the basic component of oxides of earth metals or optionally also zinc, and addition of water resulting in a hydraulic reaction.
According to the present invention there is provided a method of makiny a building material by activation of latently hydraulic finely ground granulated amorphous basic blast-furnace ~79663 slag to form a direct actlng hydraulic blnder, characterlzed by mixing the slag, water, sand and/or agyregate, wlth a combination of an acidic and a basic component, wherein the acidic component comprises a phosphate, and the basic component comprises an earth metal oxide to obtain a concrete of low calcium content and high mechanical strength and chemical resistance without high temperature heating. Preferably the earth metal oxide comprises MgO, A1203, TiO2, ZrO2, BaO and/or ZnO and the acid and basic components are of low calcium content.
Earth metals, apart from magnesium, are calcium, strontium, barium, aluminium, beryllium, gallium, indium, thallium, titanium and zirconium and the so-called rare earth metals. Most effective is magnesium oxide, which has the best improving effect on silicates, as it enhances the compression and tensile strengths and the elasticity, reduces shrinkage and results in a non 3a ~7~

~'~79663 hyyroscopic product. Normally MgO can be incorporated in silicates only by meltlng at a high temperature.
Together with phosphates, optionally in combination with sulfates, a hydraulically acting reaction is achieved with finely ground granulated basic blast-furnace slag. The best action is obtained with calcined magnesia (fired at about 1750C, whereby all water and carbon dioxide have been driven off). Less suitable are MgO containing minerals, e.g. dOlomite,which act more as fillers. ~he earth metal compounds are suitably employed in an amount of 0.3 to 3 % by weight, based on the dry concrete (i.e. slag + sand ~ aggregate) or 2 to 20 % by weight based on the slag.
The acidic components are suitably included in an amount of 0.3 to 6 ~ by weight, based on the dry concrete, or 2 to 40 % by weight based on the slag.
Furthermore, it was found that the reaction will be much more active if also a detergent or nitrate is added which reduces surface tension, disperses and prevents lump formation. The same effect will be achieved by taking a phosphate having detergent action, e.g. Na tripolyphosphate. MgO and phosphate per se do not react with slag and water, only in combination.
Sometimes it is advantageous with a cooperation of MgO with other earth metal compounds. A~03 has positive effectssimilar to those of MgO, improves the reactivity of the s]ag and its resistance to chlorides.
Titanium oxide imparts resistance to acidic actions, e.g.
in conta~inated air (sulfur deposition), and forms resistant crystals with silica gels. ZrO2 gives a reliable security against alkaline attack.
An example of a strongly acting sulfate is sodium bisulfate, Na~S04, which on account of its strongly acidic reaction is often used industrially instead of sulfuric acid.

1~79663 The hitherto known activators mostly bind too rapldly (ln the case of Port:Land cement too slowly), and no suitable control could be achieved. This is possible with the new method, either by addition of S surface-action reducing agents or fluxing (plasticizing) agents, e.g. lignosulfonate, melamine, naphthalene-formaldehyde, sodium gluconate or the like, or by plaster of Paris or anhydrite (about 3 %) or hy mixing different phosphates having different times of reaction.
Thus, it will be possible to obtain a binding agent which will harden within half an hour for prefabricated concrete elements, whereby more castings can be made per day, or it will be possible to increase the binding time to about 2.5 hours which will be necessary for casting or a building site.
By the addition of amorphous silicic acid, e.g. in the form of the filtered residual product from electrometallurgical processes (such as silicon ferrosilicon or silicon chrome manufacture), having an 20 SiO2 content between 75 and close to 100 % and usually a specific area of at least 20 m2/g, so called silica fume or silica, the compressive strength and density can be further improved, preferably in combination with plasticizing agents.
The amorphous silicic acid is suitably used in an amount of 0.6 to 2 % weight, based on the dry concrete or 4 to 15 % by weight, based on the slag.
The novel material is denser than concrete from Portland cement, is brighter in colour and lighter in weight. The new concrete can also be used as a plaster or porous or light-weiqht concrete, if a pore-forming agent or light-weiqht ballast of the type of perlite or vermiculite is added. Of course, it is possible to admix concrete aggregate,or steel,qlass, mineral or plastic fibres or fly ash. A combination with bitumen (asphalt) is possible.

'rhe advantage of the lmproved slag concrete according to the present invention as compared to common concrete from Portland cement is above all a higher compressive and tensi]e strength, as seen from the table below. This includes both a higher short~term strength which enables removal of moulds in building sites to be carried out after about 10 hours for wall mouldings and after about 16 hours for vault mouldings, which results in great savings, and also an increasing strength for several months, while conventional concrete reaches maximum values after about 2~ days.
The resistance to salt was tested at Chalmers Institute of Technology in Gothenburg for 4 months in a 30 % calcium chloride solution. No deterioration or cracking could be observed, as occurs in common concrete after a few weeks in highly concentrated calcium chloride solution.
Protection against attack by rust is achieved in common concrete by the free lime in the form of Ca(OH)2 formed in the final stages of hydration being deposited on the steel surfaces and protecting by its high pH the steel from oxidation by penetration of water, oxygen or CO2 from the air. I~owever, calcium hydroxide is an unstable substance which is dissolved by water and converted by CO2 (carbonatization). In the new concrete, MgO which has a higher pH than lime forms the rust protection. Calcined MgO is resistant to water, oxygen and CO2 and therefore more reliable than lime. In addition, the new concrete is much denser (less porous) and therefore makes more resistance to penetrating water, oxygen or CO2, which also results in an improved adherence to the steel reinforcement.
The stability of the high pl~ value in the new concrete was a]so checked at Chalmers Institute of Technology by means of a bath of phenolphthalein which is a pH

~27966~

indlcator. Permanent high pH is seen from unchanged red colour which i5 not the case with Portland cement concrete.
The combination of MgO and phosphate is hitherto known mostly from the manufacture of refractory ceramics but will also result in an improved fire-resistance of the activated blast-furnace slag. Usual concrete does not withstand temperatures higher than about 500C.
The reason for the sensitivity to high temperatures of Portland cement is substantially the presence of chemically bound water. The physically bound water (capillary water) is removed at about 105 C without any deleterious action. The chemically bound water is released later, but with cracking which will then result in decomposition. The unstable free lime Ca(OH)2 will be converted into CaO and H2O.
At the same time the liberated water will also attack the tri- and dicalcium silicates formed durina hydration which will be converted into unstab1e calcium silicate hydrate. In addition, the alpha phase of quartz (SiO2) present in the concrete will be converted into a different crystal form with increase in volume, which will also contribute to cracking (see R.K. Iler "Chemistry of Silicates"). In the combination of blast-furnace slag, phosphate and MgO there is no free lime and the SiO2 of the granulated slag is amorphous, wherefore these risks are not present. In uses where tem~eratures above 1000C can occur, it may be suitable to replace the stone material of aggregates which may expand in too high heat, by refractory ceramic materials which however is needed only exceptionally.
The new concrete may also be combined with bitumen (asphalt) in road pavings.

1~79663 As examples of the action of the novel combina-tion of activators with regard to compressive and tensile strenqths, reference may be made to the follcw-ing test results obtained with a mixture of 100 units of slag, 10 units of Na tripolyphosphate, 7.5 units of MgO, 353 units of sand and 40 units of water.

AgeCompressive strengthTensible strength MPa MPa 101 day6.2 1.2 3 days26.0 3-7 7 days40.9 6.3 28 days81.3 10.4 These va]ues are more advantageous than the corresponding values of Portland cement (after 28 days 49.0 and 7.9 MPa, respectively). By the additions ~entioned above, the tabled values can be further improved.
As compared to Portland cement concrete the novel concrete achieves the following advantages.
1. Higher mechanical resistance, i.e. higher compressive and tensile strengths.
2. Higher chemical resistance.
3. No carbonatization, i.e. precipitation of unbound lime, which may result in deterioration of the concrete.
4. No salt attack. A road paving will not be damaged by road salt. A higher life for concrete bridges.
A possibility of making resistant concrete boats.
5. Not alkaline in spite of pH 12. No unbound lime, wherefore reinforcement by glass fibres is possible. (If desired, a special type with æro2 may be manufactured).
6. Lighter than Portland cement concrete, structures may be made thinner.
7. The possibility of making thinner layers or thickness makes the construction cheaper, apart from the fact that slag is cheaper than Portland cement.

1'~79663 8. Much denser.
9. Thereby better adherence to steel reinforce-ment and protection against attack from rust on the steel reinforcement.
10. Higher refractoriness (fire resistance).
11. Resistance to frost.
12. Facilitates casting in cold weather.
13. The characteristics also enables it to be used in sealing compounds.
14. Better material than cement mortar for plastering.
15. Lower requirements for moist hardening of freshly cast concrete.
16. Similar to usual concrete, the new material may be rendered porous to o~tain a light-weight concrete which has qreat advantages as compared to traditional porous concrete a light-weight concrete, since the cell structure is mechanicall~ stronger and the new material is not hygroscopic.
17. Lighter colour.

Claims (15)

1. A method of making a building material by activation of latently hydraulic finely ground granulated amorphous basic blast-furnace slag to form a direct acting hydraulic binder, characterized by mixing the slag, water, sand and/or aggregate, with a combination of an acidic and a basic component, wherein the acidic component comprises a phosphate, and the basic component comprises an earth metal oxide to obtain a concrete of low calcium content and high mechanical strength and chemical resistance without high temperature heating.
2. A method according to claim 1 wherein acidic component further comprises a strongly acting sulfate and the basic component further comprises a compound of zinc.
3. A method according to claim 1, characterized by adding a surface-tension reducing agent.
4. A method according to claim 1, 2 or 3 wherein the earth metal oxide comprises MgO, Al2O3, TiO2, ZrO2, BaO and/or ZnO in an amount of 0.3 to 3 % by weight based on the dry concrete or 2 to 20 % by weight based on the slag.
5. A method according to claim 1, 2 or 3 wherein the acidic component comprises sodium tripolyphosphate in an amount of 0.3 to
6 % by weight based on the dry concrete or 2 to 40 % by weight based on the slag.

6. A method according to claim 1, 2 or 3 wherein the acidic component is sodium tripolyphosphate in admixture with a strongly acting sulfate in an amount of 0.3 to 6 % by weight based on the dry concrete or 2 to 40 % by weight based on the slag.
7. A method according to claim 1, 2 or 3 wherein the acidic component is sodium tripolyphosphate in admixture with a strongly acting sulfate in an amount of 0.3 to 6 % by weight based on the dry concrete or 2 to 40 % by weight based on the slag wherein the sulfate is NaHSO4.
8. A method according to claim 1, wherein the acid and basic components are of low calcium content.
9. A method according to claim 1, 2 or 3 characterized by adding a compound to control the setting time or a plasticizing agent.
10. A method according to claim 1, 2 or 3 characterized by adding plaster of Paris or anhydrite.
11. A method according to claim 1 characterized by adding amorphous silicic acid having a SiO2 content of from 75 % and up to almost 100 % and a specific area of at least 20 m2/g, in an amount of 0.6 to 2 % by weight of the dry concrete or 4 to 15 % by weight of the slag.
12. A method according to claim 11 wherein the amorphous silicic acid is a residual product from an electrometallurgical process.
13. A method according to claim 12 wherein the residual product is from the manufacture of silicon, ferrosilicon or chromium silicide.
14. A method according to claim 1, 2 or 3, characterized by adding concrete aggregate, steel, glass, mineral or plastic fiber reinforcement or a pore-forming agent or light-weight aggregate.
15. A method according to claim 1, 2 or 3 wherein the earth metal oxide comprises MgO.
CA000534388A 1987-04-10 1987-04-10 Method of preparing building materials Expired - Lifetime CA1279663C (en)

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Application Number Priority Date Filing Date Title
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Publications (1)

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CA1279663C true CA1279663C (en) 1991-01-29

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