Patent Application
20170174572
The present invention relates to a cement compound. The invention also relates to a method for producing such a cement compound. More in particular, the present invention relates to a cement compound comprising at least a reactive glass compound, an alkaline activator and a filler, and optionally additives, said reactive glass compound comprising at least 35 wt % CaO, at least 25 wt % SiO2 and at least 10 wt % Al2O3, and optionally also other oxides.
Such a cement compound and a method for preparing it is known per se from NL1001242, which document relates to the preparation of a cement raw material by melting waste products with an inorganic component under reducing conditions so that zinc is volatilised and the iron oxide fraction in the slag is kept between 0.5 and 10% m/mm at temperatures above the melting temperature of the produced slag, the slag compound containing calcium oxide (CaO), aluminium oxide (Al2O3) and silicon dioxide (SiO2) as its main components, plus a maximum of 25% m/m other oxides and sulphides, optionally adjusting the composition by adding mineral raw materials, shock-cooling the produced slag to obtain an amorphous glassy mass, grinding it and using it as cement in a mixture containing activator and/or gypsum or plaster. Portland cement or calcium is used as the activator, while the gypsum is to be regarded as calcium sulphate.
Known from the German Offenlegungsschrift DE 26 11 889 is a method for preparing binders by using for example blast-furnace slag, the blast-furnace slag being melted under oxidising conditions together with calcium in a weight ratio of 60-90% blast-furnace slag and 40-10% calcium, after which the melt is cooled so that finally the granulate is ground together with 3-8 wt % gypsum, relative to the total amount, where the gypsum is to be regarded as calcium sulphate.
Cement is a binder that, by reacting with water, acts as a binder for mortar and concrete, fibre-reinforced products and other applications requiring long-term binding. Known types of cement consist largely of calcium silicate and, when mixed with water, form a plastic mass that can be easily applied to materials. Cement subsequently hardens in a chemical reaction, with its compressive strength increasing with time until the hardening is complete. In the hardening the material becomes less porous.
Various types of cement have been standardised according to EN 197; they are referred to as CEM I to CEM V, having Portland cement clinker concentrations between 95% (CEM I) and 5% (CEM III/C), the rest being supplemented with blast-furnace slag, pozzolana and/or inert fillers. Portland cement clinker is made from marl limestone.
Cements are classified according to EN 197 on the basis of the compressive strength measured after a period of 28 days (32.5 MPa; 42.5 MPa and 52.5 MPa), the classes varying from cement with a low initial strength after 2 days (slow-hardening cement) to cement with a high initial strength after 2 days (fast-hardening cement). Cements with a high initial strength are needed for the production of, say, prefab concrete elements.
One aspect of Portland cement is that large amounts of CO2 are released during its production, partly as a result of heating to high temperatures, but mostly because the raw material—limestone—has to be calcined, which means that the addition of heat causes the original mineral CaCO3 to separate into CaO and CO2.
Portland cements are suitable for general use, but are less suitable for applications in which the concrete product comes into contact with acids. In such applications the concrete will have a shorter life. Secondary raw materials are waste materials, for example waste produced in industrial processes such as blast-furnace slag and fly ash, whose composition makes them suitable for the production of cement. Primary raw materials are purer than secondary raw materials, as a result of which cement compounds based on primary raw materials are more reproducible.
An alternative for Portland cement are alkali-activated cements, also known as geopolymers. They are based on a reactive solid substance that hardens under the influence of an alkaline activator.
One aspect of known alkali-activated cements or geopolymers is that it is difficult to realise a constant quality because of the varying quality and composition of the raw materials. This is a problem in particular when secondary raw materials are used.
Another aspect of the present invention is to provide a cement compound that exhibits a rapid increase in strength and, in particular, has a high initial strength.
The present invention hence provides a cement compound comprising at least a reactive glass compound, an alkaline activator and a filler, and optionally additives, said reactive glass compound comprising at least 35 wt % CaO, at least 25 wt % SiO2 and at least 10 wt % Al2O3, and optionally other oxides, characterised in that the reactive glass compound is obtained from one or more secondary raw materials, the cement compound comprising: at least 10 wt % reactive glass compound;
at least 10 wt % filler;
at least 1 wt % alkaline activator, and
optionally additives, said wt % being based on the total weight of said cement compound and the alkaline activator comprising one or more parts selected from the group consisting of sodium or potassium salts of sulphate, carbonate, phosphate, silicate, oxalate, formiate, lactate, sodium hydroxide and potassium hydroxide, CEM I, Portland cement clinker, belite clinker and calcium sulphoaluminate clinker.
The present inventors have found that a good initial strength is obtained with such a cement compound, in particular in combination with a compressive strength after 28 days' hardening of at least 30 MPa measured according to EN197.
The quality of the present cement compound is reproducible, in spite of the fact that secondary raw materials are used for the reactive glass compound. The cement compound has a relatively high initial strength, making it particularly suitable for use in the production of prefab concrete elements. The reactive glass compound is produced separately for the production of the cement compound. The glass compound is obtained largely or entirely from secondary raw materials, but may optionally consist of a mixture comprising relatively small amounts of primary raw materials or purified raw material. The reactive glass compound is the compound which, after the addition of alkaline activator and water, undergoes a chemical reaction that results in the hardening of the cement. The filler may affect chemical, physical and mechanical properties of the cement either before or after the hardening, but it is not essential for the hardening process.
The term “alkaline activator” is understood to mean substances that activate or initiate the hardening process of the reactive glass compound after it has been mixed with water. If the alkaline activator is omitted, the hardening process under the influence of water will proceed much slower, resulting in a lower compressive strength measured after 28 days.
The cement compound according to the present application comprises at least 10 wt % reactive glass compound; at least 10 wt % filler; at least 1 wt % alkaline activator and optionally additives, said wt % being based on the total weight of said cement compound.
The present cement compound preferably comprises 30-70 wt % reactive glass compound; 30-70 wt % filler; 3-20 wt % alkaline activator and optionally 0.5-10 wt % additives, said wt % being based on the total weight of said cement compound.
After hardening for 28 days the cement compound should preferably have a compressive strength of at least 32.5 MPa (according to EN197). EN197 is the European standard for cement in which e.g. the specifications of different strength classes are defined for cement, e.g. implemented by the Dutch Standardisation Institute NEN. Here use is made of version NEN-EN 197-1:2011 (Cement—Part 1: Composition, specifications and conformity criteria for common cements).
It is advantageous for the reactive glass compound to comprise 35-50 wt % CaO, 25-45 wt % SiO2 and 10-25 wt % Al2O3, and optionally other oxides, preferably 40-45 wt % CaO, 28-35 wt % SiO2 and 13-20 wt % Al2O3, said wt % being based on the total weight of said reactive glass compound.
It is favourable for the weight of the one or more secondary raw materials from which the reactive glass compound is obtained to be at least half of the total mass of the glass compound. That way effective use is made of the secondary raw materials and savings are realised on relatively expensive primary raw materials. The one or more secondary raw materials are preferably selected from the group consisting of:
ashes (fly ash and soil ash) released in the combustion of coal (e.g. pit coal or brown coal), wood, biomass, rice waste, paper sludge, waste;
substances released in the recycling of concrete and concrete products, cement-bound fibre plates, glass wool, rockwool;
filter substances from rock processing, cement production or lime production;
residual substances from the metal industry, in particular slag, more in particular blast-furnace slag;
residual substances from the paper industry;
residual substances from the purification of (drinking or sewage) water;
thermally treated soil or sludge;
residual substances from the recovery of primary raw materials such as bauxite, brick clay and corundum;
or mixtures thereof.
The alkaline activator in the present cement compound may hence be selected from the group consisting of sodium or potassium salts of sulphate, carbonate, phosphate, silicate, oxalate, formiate, lactate, sodium hydroxide and potassium hydroxide, CEM I, Portland cement clinker, belite clinker and calcium sulphoaluminate clinker, or a combination hereof. These activators can be well mixed and ensure relatively fast hardening of the cement after it has been mixed with water.
In a preferred embodiment the alkaline activator is used in a combination of at least two alkaline activators, which combinations are selected from the group consisting of Na2CO3 and Ca(OH)2; Na2CO3 and CEM I; Na2CO3 and Ba(OH)2; Na2CO3 and belite cement; K2CO3 and Ca(OH)2; K2CO3 and CEM I; K2CO3 and Ba(OH)2; K2CO3 and belite cement; Na2SO4 and Ca(OH)2; Na2SO4 and CEM I; Na2SO4 and Ba(OH)2; Na2SO4 and belite cement; K2SO4 and Ca(OH)2; K2SO4 and CEM I; K2SO4 and Ba(OH)2; K2SO4 and belite cement; NaOH and sodium silicate; KOH and sodium silicate; NaOH and potassium silicate; KOH and potassium silicate; Na3PO4 and Ca(OH)2; K3PO4 and Ca(OH)2; Na3PO4 and Ba(OH)2; K3PO4 and Ba(OH)2; sodium oxalate and Ca(OH)2; potassium oxalate and Ca(OH)2; sodium oxalate and Ba(OH)2; potassium oxalate and Ba(OH)2.
In particular, it is preferable for the alkaline activator to be selected from at least one of Na2CO3, K2CO3, Na2SO4 and K2SO4 in combination with at least one of Ca(OH)2, CEM I, Ba(OH)2 and belite cement, or for the alkaline activator to be selected from at least one of NaOH and KOH in combination with at least one of sodium silicate and potassium silicate.
The additive is preferably selected from the group consisting of Ca(OH)2, Ba(OH)2, CaCl2; BaCl2, polyphosphate and tartrate, or combinations thereof.
The filler is preferably selected from the group consisting of filter substances: fly ash, in particular pulverised coal fly ash; microsilica; crushing waste and stone powder; thermally activated clay or sludge; residual substances from the metal industry, in particular slag, more in particular blast-furnace slag, and pozzolana, or a combination hereof.
The filler and the one or more secondary raw materials preferably derive from the same source. This makes it logistically easier to produce cement and reduces the number of quality inspections and chemical analyses of the ingredients to be used.
The present invention also provides a method for the production of a cement compound, which cement compound comprises at least a reactive glass compound, an alkaline activator and a filler, and optionally additives, said reactive glass compound comprising at least 35 wt % CaO, at least 25 wt % SiO2 and at least 10 wt % Al2O3, and optionally other oxides, which method comprises
characterised in that step i) comprises a number of sub-steps:
a) providing one or more raw materials, comprising primarily secondary raw materials;
b) thermally treating the one or more raw materials to obtain a reactive glass compound;
c) optionally calcining the raw materials;
in which in step a) optionally one or more corrective substances are added to the raw materials, the alkaline activator comprising one or more parts selected from the group consisting of sodium or potassium salts of sulphate, carbonate, phosphate, silicate, oxalate, formiate, lactate, sodium hydroxide and potassium hydroxide, CEM I, Portland cement clinker, belite clinker and calcium sulphoaluminate clinker, after which step ii) is carried out.
This method makes it possible to produce a cement compound of reproducible quality, in spite of the use of secondary raw materials.
The raw materials may be supplied in different forms; it may be advantageous to pretreat them, for example through grinding, granulation, compression or pelleting.
Various known melt aggregates can be used for the heating in sub-steps a), b) or c), optionally in combination with a preheater and/or a calciner. In the glass industry, natural gas or petroleum oil is usually used as fuel for the heating facilities, in combination with air or pure oxygen. It may be necessary to granulate the raw materials, depending on the type of furnace used.
During the optional calcining prior to the melting, fuel is added to the raw materials, causing the temperature to rise to 800° C. CO2 is then released, in particular in the chemical conversion of calcium carbonate to calcium oxide. This process step calls for a relatively large amount of energy, and it depends on the raw materials whether calcining is necessary.
The thermal treatment according to step b) involves preheating to 600-800° C. This is optionally followed by calcining. The temperature is then raised to above the composition's melting point, for example to 1200-1500° C., after which the molten glass can be collected from the furnace in a liquid form for further processing.
The molten glass is first cooled to a solid substance. This may take place in the open air or with the aid of water or other cooling agents. The cooling rate has an influence on the properties of the glass ultimately obtained. The solidified reactive glass compound can then be processed, for example by grinding, to obtain a granule size that can be better handled and dosed. The reactive glass compound can subsequently be mixed with the other ingredients of the cement compound.
The one or more corrective substances are preferably selected from the group comprising calcium oxides, calcium carbonates, silicon oxides and aluminium oxides. These corrective substances make it relatively simple to obtain the desired composition.
Preferably solid fuel, in particular organic solid fuel, more in particular brown coal, pit coal or biomass, is used as the fuel for carrying out step i). Surprisingly, such fuels prove to perform satisfactorily as a source of heat for the process.
In a preferred embodiment the thermal treatment in sub-step b) is concluded with the thermal quenching of the reactive glass compound. ‘Thermal quenching’ is understood to mean the forced cooling of the glass compound formed in sub-step b), for example by introducing the glass compound into a colder medium (water, air). Fast cooling results in a higher percentage of glassy character. By quenching, the temperature of liquid glass with a temperature of above 1000° C. can for example be lowered to less than 100° C. within a few minutes. Preferably, the obtained glassy character is 60 wt %, based on the total reactive glass compound, more preferably more than 96 wt %.
The invention also comprises a method for processing a cement compound according to the invention, comprising mixing the cement compound with water, in which the alkaline activator is optionally added only after the mixing of the reactive glass compound, the filler and optional additives. This makes it easier to realise the hardening under controlled conditions. Such a method can be facilitated by packing the alkaline activator separate from the other ingredients, for example in a separate compartment of the packaging, or a separate sub-packaging.
The separate packing also makes the cement compound less susceptible to unintentional exposure to water during transport or storage. Packing the entire compound in a single packaging on the contrary implies the advantage that the alkaline activator will in that case already be effectively mixed with the other ingredients for a homogeneous hardening.
The invention will now be elucidated with reference to the following non-limitative examples.
A number of glass compounds for use in a cement compound were produced on the basis of the method described here.
Two different mixtures of fly ash and limestone were produced, as shown in Table 1. On the basis of the element analysis of the fly ash, 5.9 wt % aluminium oxide was added to the second batch as a corrective substance. The percentages are based on the total glass compound.
The compound was processed into glass according to the invention. The raw materials were ground into granules and mixed. In a first step the mixture was preheated and calcined to 800° C. in a preheater and calciner. In a subsequent step the mixture was further heated to 1450° C., resulting in a molten glass. The molten glass mixture was quickly cooled in water or air (quenched). X-ray diffraction showed that the reactive glass obtained had around 98% glass character. Table 2 shows the composition of the obtained glass on the basis of X-Ray Fluorescence analysis (XRF). XRF is a well-known method for the analysis of solid substances, and was used according to NEN-EN 15309:2007, “Characterisation of waste and soil—Determination of elemental composition by X-ray fluorescence”. The method for determining the glass content is described in for example T. Westphal, T. Füllmann, H. Pöllmann, Rietveld quantification of amorphous portions an internal standard—mathematical consequences of the experimental approach, Powder Diffract. 24 (2009) 239-243. The measurements were carried out using a Seifert XRD 3003 TT, with ZnO as the internal standard reference.
The ratio of the mass of the secondary raw material (fly ash in this case) and the glass mass was 0.63 in the case of batch g1 and 0.50 in the case of batch g2.
The same method was used to prepare some more batches, whose results are presented in table 3. The chemical composition was determined with the aid of XRF, the average particle size with the aid of laser granulometry using an HORIBA LA-300 Particle Analyzer in water. Laser granulometry is a well-known method for determining average particle sizes.
The following cement compounds were prepared on the basis of the glass compounds described above.
Cement compound c1 was prepared using 44 wt % glass compound g5, 44 wt % fly ash as filler and a combination of 7% Na2CO3 and 5% Ca(OH)2 as alkaline activator. Other additives could optionally be added to this compound. In 3 tests mortars were prepared using the cement in different cement/water ratios. The water/cement (w/c) ratios were 0.5, 0.45 and 0.4, respectively, with 0.05 wt % tartaric acid, based on the cement, being added to the water for the last batch. The compressive strength of the cement was then measured at different times for 28 days according to EN196, using a press suitable for that purpose.
Cement compound c2 was prepared using 49 wt % glass compound g5, 49 wt % fly ash and 3% NaOH as the activator. Filler and other additives could optionally be added to this compound. This cement compound was mixed 1:1 with water.
In example 3 a number of cement compounds according to NL1001242 were prepared and compared with cement compounds according to the present invention.
The following Table 4 shows the compounds of examples 1-4 according to NL1001242.
Compounds were prepared for examples 2 and 4 of NL1001242, i.e. compounds 728 and 730, so as to be able to determine the initial strength, which values in NL1001242 are not mentioned for examples 2 and 4 of NL1001242. The results are shown in Table 5.
Surprisingly, it was found that good compressive strengths can be obtained even with 50% of the employed slag and replacement of it with less reactive or non-reactive filler (here fly ash), as shown in Table 6.
The following Table 7 shows the influence of the replacement of slag/glass by a mixture of slag/glass and fly ash.
In Table 8 the present inventors find that surprising results can be obtained when sodium sulphate is used as the sulphate component instead of calcium sulphate. The initial strength can be more than doubled.
Table 9 shows that replacement of sodium sulphate by calcium sulphate lowers both the initial strength and the final strength. The compound values specified for examples 713 and 726 correspond to one another as far as the oxidic analysis is concerned. The same holds for examples 715 and 727.
The present inventors also concluded (see Table 10) that the strength development can be geared to the strength development required in the application by using other sulphate/clinker ratios.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2012959 | Jun 2014 | NL | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/NL2015/050410 | 6/5/2015 | WO | 00 |
