GB2459778A - Controlling strength development of cementitious materials - Google Patents

Controlling strength development of cementitious materials Download PDF

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Publication number
GB2459778A
GB2459778A GB0907909A GB0907909A GB2459778A GB 2459778 A GB2459778 A GB 2459778A GB 0907909 A GB0907909 A GB 0907909A GB 0907909 A GB0907909 A GB 0907909A GB 2459778 A GB2459778 A GB 2459778A
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Prior art keywords
akermanite
ca2mgsi2o7
present
mortar
gehienite
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GB0907909D0 (en
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Gary Hunt
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Cenin Ltd
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Cenin Ltd
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    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B28/00—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements
    • C04B28/02—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements containing hydraulic cements other than calcium sulfates
    • C04B28/08—Slag cements
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B28/00—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements
    • C04B28/02—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements containing hydraulic cements other than calcium sulfates
    • C04B28/04—Portland cements
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B28/00—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements
    • C04B28/02—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements containing hydraulic cements other than calcium sulfates
    • C04B28/08—Slag cements
    • C04B28/082—Steelmaking slags; Converter slags
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B7/00—Hydraulic cements
    • C04B7/14—Cements containing slag
    • C04B7/147—Metallurgical slag
    • C04B7/153—Mixtures thereof with other inorganic cementitious materials or other activators
    • C04B7/17—Mixtures thereof with other inorganic cementitious materials or other activators with calcium oxide containing activators
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B7/00—Hydraulic cements
    • C04B7/14—Cements containing slag
    • C04B7/147—Metallurgical slag
    • C04B7/153—Mixtures thereof with other inorganic cementitious materials or other activators
    • C04B7/17—Mixtures thereof with other inorganic cementitious materials or other activators with calcium oxide containing activators
    • C04B7/19—Portland cements
    • Y—GENERAL 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
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
    • Y02W30/00—Technologies for solid waste management
    • Y02W30/50—Reuse, recycling or recovery technologies
    • Y02W30/91—Use of waste materials as fillers for mortars or concrete

Abstract

A method of controlling the strength development and setting time of cement, mortar or concrete is disclosed which comprises varying the total combined amount of Ca 2 MgSi 2 O 7 (akermanite) and Ca 2 Al 2 Si0 7 (gehlenite) present in dependence upon the desired strength characteristics and/or setting times. The process relies on varying blends of paper ash, weathered blast furnace slag with the possible addition of free MgO, CaO and calcium silicates. Also disclosed are mortar and concrete products.

Description

LOW CARBON CEMENT COMPOSITION
Background to the invention
The present invention relates to a method of controlling the strength development and/or setting times of cement, mortar and concrete and/or concrete products produced by such a method.
By cement we mean hydrated cementitious material, by mortar we mean a hydrated mixture of cementitious material and sand, and by concrete we mean a hydrated mixture of cementitious material, sand and a coarser aggregate.
Portland cement (PC), as a cementitious material, is well established and widely used in industry. Portland cement provides a strong and durable component in concrete/mortar.
The main constituents of PC include Portland cement clinker (a hydraulic material which consists of two-thirds by weight calcium silicates ((CaO)3SiO2(CaO)2SiO2), the remainder being calcium aluminates (CaO3Al2O3) and calcium ferro-aluminate (CaO4A12O3Fe2O3 (and other oxides), and minor additional constituents. Minor constituents of up to 5 % can be added and the cement is still classed as PC. After the addition of materials such as Ground Granulated Blast Furnace Slag (GGBS), Pulverised Fuel Ash (PFA) etc, the resultant cement is classed as a composite cement.
However, PC has the disadvantage that its production is a high energy intensive process that creates significant environmental damage due to the high level of carbon dioxide produced. Furthermore, PC has a further disadvantage of being the most expensive component of concrete and mortar.
Industrial wastes and raw materials are, in general considered to be an increasingly serious environmental problem. At present, many of these raw materials are dumped to landfill. Some of these industrial waste and by-products contain elements that are common to those found in cements and cement replacements.
GGBS, a significant constituent of composite cements, as mentioned above, is an example of a raw material which is recycled rather than being dumped to landfill.
As well as PC being expensive, concrete made from hydrated PC and composite cements has limitations in terms of setting times and strength development.
Another raw material which has the same chemical composition as GGBS is Weathered Blast Furnace Slag (WBFS). However, despite the two components having the same chemical composition they do not form the same compounds during the hydration process. WBFS typically contains significant levels of magnesium oxide (MgO). As MgO forms periclase in cement clinker which in turn can cause cracking in concrete, WBFS is not considered to be a raw material used in the production of concrete and is not used with Portland cement in composite cements. However, during the hydration of a cementitious composition including GGBS, periclase does not commonly result and so GGBS is considered to be a useful raw material in the cement production industry.
There is therefore a need to identify an alternative to PC and composite cements with more controllable setting times and strength development.
Summary of the Invention
The present invention seeks to address the problems of the prior art.
Accordingly, a first aspect of the present invention comprises a method of controlling the strength development of cement, mortar or concrete comprising a varying the amount of Ca2MgSi2O7 (akermanite) and Ca2A12SiO7 (gehienite) present in dependence upon the desired strength characteristics of the cement, mortar or concrete.
It is the combined total amount of akermanite and gehienite present that determines the strength characteristics of the cement, mortar or concrete.
A further aspect of the present invention is a method of controlling the setting time of cement, mortar or concrete comprising varying the amount of Ca2MgSi2O7 (akermanite) and Ca2A12SiO7 (gehlenite) present in dependence upon the desired setting time.
Akermanite and gehienite are preferably present in the cementitious material prior to hydration. However, akermanite and/or gehienite may also be formed during the hydration process if sufficient free lime and free magnesium oxide present or released from the hydrating materials. In addition, Silica must be present to allow akermanite and/or gehlenite to form during the hydration process.
It has been identified that the setting time and the strength development characteristics of cementitious materials after hydration can be controlled in dependence upon the levels of Ca2MgSi2O7 (akermanite) and Ca2AJ2SiO7 (gehlenite) present in the cementitious material during the curing process.
By increasing or decreasing the amount of Ca2MgSi2O7 (akermanite) present in the hydrated cementitious composition, it is possible to control the strength development and setting times to achieve higher early and late concrete strengths than would otherwise be obtained using conventional composite cements such as, but not limited to, PC/GOBS.
A
In one embodiment, the combined amount of Ca2MgSi2O7 (akermanite) and Ca2Al2SiO7 (gehienite) present in the concrete is up to around 20% by weight.
Preferably, Ca2MgSi2O7 (akermanite) and Ca2A12SiO7 (gehlenite) are present in the concrete in an amount of up to around 15% by weight. More preferably, Ca2MgSi2O7 (akermanite) and Ca2A12SiO7 (gehlenite) are present in the concrete an amount in range of around 8 to 12 % by weight. It will be appreciated that it is the combined amounts of akermanite and gehlenite that are being referred to.
In one embodiment, the Ca2MgSi2O7 (akermanite) and Ca2A12SiO7 (gehlenite) are derived at least in part from WBFS. When WBFS is present in the cementitious material, WBFS undergoes a chemical reaction on hydration in the presence of free lime and calcium silicates to produce and increased total amount of Ca2MgSi2O7 (akermanite) and Ca2A12SiO7 (gehlenite). The controlled presence of Ca2MgSi2O7 (akermanite) and Ca2AI2SiO7 (gehlenite) in the hydrated cementitious material may result in reduced setting times and faster strength development in the concrete.
Finding a commercial use for WBFS is particularly advantageous as it is available in abundance, and provides a useful way to recycle the waste by-product of another industrial process.
Ca2MgSi2O7 (akermanite) and Ca2AI2SiO7 (gehienite) are from the melilite group of compounds and is typically found in dolomite and limestone rocks, and is also found in iron and steel slags such as, but not limited to, WBFS. However, Ca2MgSi2O7 (akermanite) and Ca2Al2SiO7 (gehlenite) are not present in GGBS.
The calcium and silica phases are well known and commonplace in composite PC cements and other composite cements.
It is not desirable to add MgO to conventional cementitious compositions (e.g. containing GGBS) prior to hydration as hydration of the cementitious material will lead to the formation of periclase in the cement clinker potentially resulting in extremely detrimental cracking of the resultant concrete.
However, when MgO is added to a cementitious material containing WBFS rather than GGBS, the calcium and silica phases of the cementitious material combine with the MgO in the WBFS to further form Ca2MgSi2O7 (akermanite) and Ca2Al2SiO7 (gehlenite). This chemical reaction does not occur on hydration of a cementitious composition containing GGBS.
In one embodiment, the total combined level of Ca2MgSi2O7 (akermanite) and Ca2Al2SiO7 (gehlenite) may be varied in dependence upon the amount of WBFS present in the cementitious composition at the time of hydration.
Preferably, the method further comprises providing a source of MgO. By adding additional MgO to the cementitious composition prior to hydration, more Ca2MgSi2O7 (akermanite) and Ca2Al2SiO7 (gehienite) are produced during the hydration step in the presence of free lime and calcium silicate.
Preferably, MgO is present in the concrete in an amount in the range of around 3 to 7 % by weight.
Preferably, the MgO is derived at least in part from WBFS, which typically contains MgO in an amount of around 8 to 12% by weight. However, it is to be appreciated that the amount of MgO could be greater depending on the source of slag as the composition can vary between countries and steel and iron plants.
In a further embodiment, the MgO which combines with the calcium and silica phases of the WBFS is derived at least in part from paper ash. Many types of paper ash contain akermanite and free lime, and the inclusion of such paper ash as a
S I I
component in the cementitious composition prior to hydration assists in the formation of Ca2MgSi2O7 (akermanite) and Ca2A12SiO7 (gehienite) post hydration.
It is preferred, but not essential, that the hydration of the cementitious composition is carried Out substantially in the absence of granulated slag.
The method of the present invention may further comprise providing a source of free GaO.
The method of the present invention may further comprise providing a source of free calcium silicates.
A further aspect of the present invention provides a cement, mortar or concrete composition comprising Ca2MgSi2O7 (akermanite) and Ca2A12SiO7 (gehlenite).
Preferably, concrete containing the Ca2MgSi2O7 (akermanite) and Ca2AI2SiO7 (gehlenite) is produced using a method in accordance with a first aspect of the present invention.
It is preferred that the Ca2MgSi2O7 (akermanite) and Ca2AI2SiO7 (gehienite) are present in the cement, mortar or concrete in a combined total amount of up to 15 %. However, more preferably Ca2MgSi2O7 (akermanite) and Ca2A12SiO7 (gehlenite) are present in a combined total amount in the range of around 8 to 12 %.
A further aspect of the present invention provides a mortar composition comprising Ca2MgSi2O7 (akermanite) and Ca2A12SiO7 (gehienite).
Preferably, mortar containing the Ca2MgSi2O7 (akermanite) and Ca2AI2SiO7 (gehlenite) is produced using a method in accordance with a first aspect of the present invention. a * I
It is preferred that the Ca2MgSi2O7 (akermanite) and Ca2AI2SiO7 (gehienite) are present in the mortar in a combined total amount of up to 15 %. However, more preferably Ca2MgSi2O7 (akermanite) and Ca2AI2SiO7 (gehienite) are present in the concrete in a combined total amount in the range of around 8 to 12 %.
A further aspect of the present invention provides a cementitious composition comprising WBFS and optionally an additional source of MgO. For example, MgO may be added directly, or MgO may be provided by including paper ash or any other suitable source of MgO in the cementitious composition.
A further aspect of the present invention provides a cementitious composition comprising a hydrated blend of paper ash and weathered blast furnace slag.
Brief Description of the Drawings
Embodiments of the invention will now be described, by way of example only, and with reference to the accompanying figures, in which: Figure 1 is a graph illustrating mortar strength development over 28 days with 12 % by total weight of akermanite and gehlenite present; Figure 2 is a graph illustrating mortar strength development over 28 days with 15 % by total weight of akermanite and gehlenite present; Figure 3 is a graph illustrating mortar strength development over 84 days in the presence of various amounts of MgO; Figure 4 is a graph illustrating mortar strength development over 84 days in the presence of different grades of MgO; and Figure 5 is a graph illustrating the composition changes of Portland cement over a 24 hour period.
Figures 6 -10 are graphs of composition changes in cement pastes: Figure 6 is a graph illustrating the composition changes of a standard cement composition for a composite blend formed from Portland cement and GGBS; Figure 7 is a graph illustrating the composition changes of a standard cement composition for RM1, a composite blend formed from Portland cement and Cenin; Figure 8 is a graph illustrating the composition changes of a standard cement composition for RM3, a composite blend formed from Portland cement and Cenin; Figure 9 is a graph illustrating the composition changes of a standard cement composition for BL1 (Blend 1), a composite blend formed from Portland cement and Cenin Grade 2 with a ratio of 70% paper ash: 30% WBFS; Figure 10 is a graph illustrating the composition changes of a standard cement composition for BL2 (Blend 2), a composite blend formed from Portland cement and Cenin Grade 2 with a ratio of 30% paper ash: 70% WBFS; Figure 11 is a graph illustrating the heat of hydration for PC (C3), GGBS (C7), Bli (Blend 1) and Bl2 (Blend 2); Figure 12 is a graph illustrating the initial setting times for PC (C3), GGBS (C7), Bil (Blend 1) and B12 (Blend 2); Figure 13 is a table and graphs illustrating the composition changes of the blend 30% SDP and 70% C3' over time; Figure 14 is a table and graphs illustrating the composition changes of the blend 30% WCP and 70% C3' over time; Figure 15 is a table and graphs illustrating the composition changes of the blend 30% PFA and 70% C3' over time; and Figure 16 is a table and graphs illustrating the composition changes of the blend 30% C7 and 70% C3' over time.
Detailed Description of the invention
1. Preparation of paper-ash and \VBFS components of cementitious materials Waste paper-ash comes from combined heat and power (CHP) systems and so is already dry prior to being milled. WBFS is heated to remove surface moisture prior to the milling process.
WBFS and waste paper-ash are then milled to less than 75 tm (and preferably less than 40 pm). The milling of each component is typically carried Out separately.
However, it is envisaged that the two components could be combined prior to milling and the two components milled together to increase the efficiency of the milling process.
The two components are then in a condition to be blended with any selected additional components to be included in the cementitious material prior to hydration, such components to include magnesium, calcium and silica oxides or materials containing them.
The additional components may also be added prior to milling.
2. Components formed post-hydration The main components that form during the hydration process are listed below.
These compounds are mainly formed during the first 24 hours after initiation of hydration, with further changes in the property of the cement observable over time.
Elements present in trace amounts Sodium Na20 Potassium K2-O Phosphorus P2-05 Zinc Zn-0 Vanadium V2-05 Manganese Mn-0 Chromium Cr2-03 Lead Pbo Barium BaO Nickel Ni Copper Cu Arsenic As Rubidium Rb Strontium Sr Yttrium V Zirconium Zr Cadmium Cd Mercury Hg Molybdenum Mo Antimony Sb Selenium Se Common compounds in Portland Cement: Name Label Chemical formula Tricalcium silicate C3S 3CaO.Si02 Dicalcium silicate C2S 2CaO.Si02 Tricalcium aluminate C3A 3CaO.A1203 Tetracalcium aluminoferrite C4AF 4CaO.A1203. Fe203.
Calcite CaCO3 Additional compounds in composite PC/GBBS cement: Name Label Chemical formula Arcanite K2S04 In WBFS, the following extra phase has been introduced: Name Label Chemical formula Akermanite Ca2MgSi2O7 Gehlenite Ca2A12SiO7 At the start of the hydration stage, the C3S is present in a high percentage and the Calcite is present in a low percentage. However, this rapidly changes as the C3S is changed to Calcite.
The following table shows the phase changes in PC and composite GGBS and WBFS cements: Table 1 Showing phase changes in Portland Cenient (PC) and composite cements (GGBS & Cenin) using Reitveld analysis Typical phase amounts present from 6-24 hours from the initiation of hydration (%) Phases present PC GGBS Cenin 3CaO.Si02 20-25 10-25 10-25 2CaO.Si02 10-15 0.9-15 0.3-5 3CaOA12O3 4-5 3.5-6 4-15 4CaOA12O3.Fe203. 3.5-4.5 1.5-2.5 0.5-3.5 CaCO3 40-55 40-50 25-40 K2S04 0 10-15 5-20 Ca2MgSi2O7 and 0 0 12-16 Ca2A12S1O7 The table above shows that the akermanite and gehienite phase appears to partly replace the C2S and calcite phases during hydration. This is endorsed by the fact that the magnesium oxide is partially combining with the calcium and silica oxides to form akermanite.
The following table shows the typical chemical compositions of PC, and various WBFSs and paper ashes: Table 2 Typical chemical composition of PC, Blast Furnace Slag's and Paper Ashes Blast Furnace ___________ Slag's ____________________________________ Paper PC GGBS W/Slag Granular Ashes POWDER PELLETS XRF C3 C-7 RM3 RM12 RMJ RM6 RMI3 CaO (%) 64.278 36.922 36.543 37304 43.424 62.061 54.78 Si02 (%) 20.894 35.443 36.627 33.953 32.836 11.156 24.057 Al203 (%) 4.146 13.633 13.123 13.167 12.367 6.66 11.667 Fe203 (%) 2.96 0.241 2.339 0.801 1.655 0.624 0.702 MgO (%) 1.27 11.866 12.323 9.78 6.942 2.279 6.865 Ti02 (%) 0.465 0.707 0.746 0.698 0.433 0.579 0.326 Trace Elements Na20 (%) 0.26 0.264 0.241 0.283 0.445 0.446 0.193 K20 (%) 0.549 0.531 0.54 0.615 1.182 0.608 0.266 P205 (%) 0.154 0.004 0.023 0.009 0.343 1.095 0.186 ZnO (%) 0.009263 -0.00015 0.004619 0.000162 0.061118 0.043675 0.010844 V205 (%) 0.01 0872 0.004784 0,004338 0.005606 0.004963 0.002071 0.002321 MnO (%) 0.0404 0.4479 0.5575 0,4045 0.0841 0.0359 0.0273 Cr203 (%) 0.009515 0.002616 0.005846 0.002119 0.022186 0.008506 0.017685 PbO (%) 0.002822 0.000366 0.000668 0.000463 0.037239 0.008898 0.00391 BaO (%) 0.018713 0.100631 0.135153 0.12813 0.044392 0.037503 0.022118 XRF* -X-ray fluorescence C-3 -Portland Cement C-7 -GGBS sample RM3 -WBFS sample RM12 GBS sample RMI -Paper ash sample RM6 -Paper ash sample RM13 -Paper ash sample Paper ash is a waste product from the paper industry and comprises burned sludge optionally with wood and/or plastics. Please note that RM1, RM6 & RM13 are different sources of paper ash. RMI is a mixture of paper and wood with a free lime content of around 7%. RM6 is a mixture of paper ash and plastics with both free lime and high chloride present. RM13 is paper sludge and has a free lime content of around 30%. Chloride is present in all materials with RM 6 having a particularly high chloride content.
3. Effect of % of combined akermanite and gehlenite content on the strength development over 28 days Four different blends (C3, C3 Aug, Bli and C7) were prepared: 1. C3 (Portland Cement sample 1); 2. C3 (Portland Cement sample 2); 3. Bli (Blend 1) -composite PC and Cenin Grade 2 with a 70%:30% ratio of paper ash:weathered slag; and 4. C7 (GGBS).
Blend 1 is a composite blend of Portland cement and Cenin Grade 2 with a 70%:30% ratio of paper ash:weathered slag. Blend 2 is a composite Portland Cement and Cenin Grade 2 with 30% paper ash:70% WBFS.
POWDER PELLETS _XRF* Bli (Blend 1) Bl2 (Blend 2) CaO (%) 38.4 39.84 Si02 (%) 35.10 31.90 A1203 (%) 12.10 11.91 Fe203 (%) 1.33 1.53 MgO (%) 5.44 6.68 T102 (%) 0.41 0.50 Trace Elements Na20 (%) 0.34 0.24 K20 (%) 0,72 0.58 P205 (%) 0.21 0.13 ZnO (%) 0.0184 0.0100 V205 (%) 0.0053 0.0075 MnO (%) 0.26 0.47 Cr203 (%) 0.0214 0.0133 PbO (%) 0.0051 0.0029 BaO (%) 0.0506 0.0796 Bli (Blend 1) has akermanite and gehlenite present in the blend in a total combined amount of 12 % by weight, B12 (Blend 2) has akermanite and gehienite in the blend in a total combined amount of 15 % by weight. The strength development of the mortar was tested over a period of 28 days.
The akermanite and gehienite level is manipulated by changing the ratio between the paper ash and the WBFS. It can also be manipulated by adding free MgO and/or free CaD.
The results are shown in figures 1 and 2.
By comparing the results shown in figures 1 and 2, it is demonstrated that Bli (having akermanite and gehlenite present in a total combined amount of 12 % by weight) is superior in strength after 28 days compared to B12 (having akermanite and gehienite present in a total combined amount of 15 % by weight). Thus, it appears that there is an optimum amount of MgO which can be included in the blend containing WBFS and still provided strength development benefits. In addition, free CaO is provided from the paper ash. There must be a reaction in order to form compounds of calcium, silica & magnesium oxides that create the akermanite when a composite with PC. This is how the total percentage of akermanite and gehienite present is manipulated.
4. Effect on cement compressive strength of varying the amount of MgO present in the blend Blend R23A was prepared including MgO at various replacement levels i.e. 5%, 10%, 15% and 25%, and the compressive strength of mortar prepared from the blends measure over 84 days from hydration. RM23A is derived from a dolomitic limestone quarry and therefore contains a higher level of MgO than the other samples mentioned previously. The compressive strength of concrete prepared using conventional Portland cement was also measured over 84 days as a control.
The compressive strength of the mortar is tested by producing mortar prisms and testing to European standard EN: 196 The results are shown in figure 3.
At a 5% replacement level of MgO in the blend the compression strength development is equal to or greater than that of the Portland cement control.
However, if the replacement level of MgO in the blend is increased this appears to be detrimental to the strength development of the mortar. When the mortar is mixed with aggregate to produce concrete and the compressive strength of the concrete tested over time, the concrete is observed to be marginally stronger than comparable mortar under experimental conditions. However, the observed concrete strength can be influenced at least in part by the type and shape of the aggregate used.
5. Effect on cement compressive strength of using different grades of MgO in the blend prior to hydration Various blends (RM23A, RM23B, RM23C, RM23D, RM23E and RM23F) were prepared using various grades of MgO. The MgO in RM23A was prepared from Dolomite and sea water. The MgO in the remaining blends was prepared from limestone and sea water. The various blends used vary in production time and cost as shown below: List of blends in order of increasing production time and cost: RM23A; RM23B; RM23C; RM23D; RM23E; RM23F The compressive strength of mortar produced using each of the blends mentioned above was measured over a period of 84 days. The mortar composition includes 95% PC and 5% MgO.
The results are shown in figure 4.
It can be seen that concrete produced from RM23A is far superior to that produced from the other blends with respect to compressive strength development over 84 days.
The compounds akermanite and gehienite can be found in both weathered slag and paper ash (although there is significantly more akermanite and gehienite present in weathered slag). There is also free lime present in paper ash which is not detected after the hydration process has begun. Therefore, it is likely that the free lime becomes bound with another compound, the most likely candidates being the akermanite and gehienite.
6. Composition changes of Portland cement over a 24 hour period Portland cement was prepared and the levels of various components monitored over a period of 24 hours following initiation of hydration. The results are shown below:
Table 3
______________________________ Ohr 6hr l2hr l8hr 24hr C3S Tricalcium Silicate 45.7 26.1 25.2 24.9 23.7 C2S Dicalcium Silicate 18.4 14.4 11.7 11.8 12.4 C3A -Tricalcium Aluminate 7.7 5.7 4.7 4.5 5 C4AF Tetracalcium Aluminoferrite 7.9 4.3 4.1 3.7 4.1 CaCO3 Calcite 6.1 43.9 51.5 51.9 51.8 K2S04 Arcanite 0 0 0 0 0 Ca2MgSi2O7 Akermanite and CaA12SiO7 Gehienite 0 0 0 0 0 Figure 5 shows the above results in line-graph form.
7. Composition changes of a standard cement composition for a composite blend formed from Portland cement and GGBS A composite blend was prepared from Portland cement and C7 (the composite blend having a 75:25% ratio of PC:GGBS) and the levels of various components monitored over a period of 24 hours following initiation of hydration. The results are shown below: Table 4 _______ _______ _______ _______________________________ 6hr l2hr l8hr 24hr C3S Tricalcium Silicate 22.4 13 12.9 21.1 C2S Dicalcium Silicate 0.9 13 10.7 0.8 C3A -Tricalcium Aluminate 5.1 3.6 4.2 5.7 C4AF Tetracalcium Aluminoferrite 2.2 1.5 1.8 2.2 CaCO3 Calcite 42.8 44.5 46.5 47.3 K2S04 Arcanite 14.9 14.5 12.5 11.8 Ca2MgSi2O7 Akermanite and CaAl2SiO7 Gehlenite 0 0 0 0 Figure 6 shows the above results in line-graph form.
8. Composition changs of a composite blend formed from Portland cement and RM1 (paper ash) A composite blend was prepared from Portland cement and RM1 (the composite blend having a 75:25% ratio of PC:RM1) and the levels of various components monitored over a period of 24 hours following initiation of hydration. The results are shown below: Table 5 ________ ________ ________ ________ ________ ______________________________ Ohr 6hr l2hr l8hr 24hr C3S Tricalcium Silicate 35.3 9.4 9 9.1 8.3 C2S Dicalcium Silicate 19.1 12.3 10.1 11.1 9.9 C3A -Tricalcium Aluminate 9.8 4.4 5.1 5.7 5.1 C4AFTetracalcium Aluminoferrite 6.5 1.3 1.2 0.6 1.3 CaCO3 Calcite 9.6 37.1 38.1 37.7 38.7 K2S04 Arcanite 0.4 25.1 26.5 26.4 25.9 Ca2MgSi2O7 Akermanite and CaA12SiO7 Gehlenite 11.1 5.7 5.8 5.7 6.2 21) Figure 7 shows the above results in line-graph form.
9. Composition changes of a standard composite blend formed from Portland cement and RM3 (WBFS) A composite blend was prepared from Portland cement and RM3 (the composite blend having a 75:25% ratio of PC:RM3) and the levels of various components monitored over a period of 24 hours following initiation of hydration. The results are shown below: Table 6 _______ _______ _______ _______ _______ ______________________________ Ohr 6hr l2hr l8hr 24hr C3S Tricalcium Silicate 30.9 14.6 13.5 13.6 13.8 C2S Dicalcium Silicate 19.1 9.9 10.6 9.2 8.6 C3A -Tricalcium Aluminate 6.6 4 3.7 3.5 3.5 C4AF Tetracalcium Aluminoferrite 5.6 1.7 2.2 1.8 2 CaCO3 Calcite 6.9 41.3 41.1 41.8 44.2 K2S04 Arcanite 0.9 10.9 12.1 13.1 10.6 Ca2MgSi2O7 Akermanite and CaA12SiO7 Gehienite 20.3 12.2 12.1 12.4 12.6 Figure 8 shows the above results in line-graph form.
10. Composition changes of a composite blend formed from Portland cement and Bil (Blend 1) A composite blend was prepared from Portland cement and Bli (the composite blend having a 75:25% ratio of PC:Bl. Bil has a 70:30% ratio of paper ash:weathered slag) and the levels of various components monitored over a period of 24 hours following initiation of hydration. The results are shown below:
Table 7:
______________________________ Ohr 6hr l2hr l8hr 24hr C3S Tricalcium Silicate 31 21 21 23 23 C2S Dicalcium Silicate 18 12 18 10 7 C3A -Tricalcium Aluminate 3 3 3 3 3 C4AF Tetracalcium Aluminoferrite 5 5 5 5 5 CaCO3 Calcite 25 33 33 32 33 K2S04 Arcanite 2 6 6 6 7 Ca2MgSi2O7 Akermanite and CaA12SiO7 Gehienite 10 12 12 12 12 Figure 9 shows the above results in line-graph form. It is clear from the graph that the C3 and C2 phases are similar to that of Portland cement except that the calcite is present in a reduced amount and arcanite, akermanite and gehlenite are now present.
11. Composition changes of a composite blend formed from Portland cement and Bl2 (Blend 2) A composite blend was prepared from Portland cement and B12 (the composite blend having a 75:25% ratio of PC:Bl2. B12 having a 70:30% ratio of weathered slag:paper ash) and the levels of various components monitored over a period of 24 hours following initiation of hydration. The results are shown below: Table 8: _______ _______ _______ _______ _______ _______________________________ Ohr 6hr l2hr l8hr 24hr C3S Tricalcium Silicate 28 17 19 17 19 C2S Dicalcium Silicate 19 13 12 13 14 C3A -Tricalcium Aluminate 2 2 3 2 2 C4AF Tetracalcium Aluminoferrite 4 2 5 5 5 CaCO3 Calcite 20 37 31 34 31 K2S04 Arcanite 0 10 10 1 1 11 Ca2MgSi2O7 Akermanite and CaAI2SiO7 Gehienite 15 15 16 16 16 Figure 10 shows the above results in line-graph form. From the graph it can be seen that the C3 and C2 phases are much close and the level of arcanite is similar to a PC/GOBS composite. However, the combined level of akermanite and gehlenite is higher.
It can be seen (from section 3 above) that Blend 1 (Bli) has the best strength development and therefore Blend 1 has the most desirable composition.
The data shown in figures 9 and 10 was obtained from X-ray diffusion using Bruker software which is semi-quantitative, all other data was obtained from X-ray diffusion using Panalytical software using Reitveld refinement analysis and is quantitative.
12. The effect of the Heat of Hydration on setting times of mortar Graph 11 shows the heat of hydration that occurs during hydration of C3 (PC), C7 (GGBS), Bli (Blend 1) and Bl2 (Blend 2).
C3 -Portland Cement C7 -GGBS Bli -Bli has a 70:30% ratio of paper ash:weathered slag B12 -has a 70:30% ratio of weathered slag:paper ash C7 composite blend: 75%PC;25%GGBS(C7) Bli composite blend: 75%PC;25% Bli Bl2 composite blend: 75%PC;25% B12 It can be seen from the graph that although all samples exhibited a peak of heat during the initial stages of hydration, the Bli composite blend and the Bl2 composite blend exhibited a lower rate of heat production when compared with the C3 composite blend Portland Cement and the C7 composite blend.
Graph 12 shows the initial settings times of the samples Bli composite blend, B12 composite blend, C3 composite blend and C7 composite blend and it is clear that the setting times of Bil composite blend and B12 composite blend are significantly lower than those of C3 and C7 composite blend.
Thus, it would appear that the lower the Heat of Hydration, the shorter the setting time of the mortar.
It was observed thatl2 % total combined akermanite and gehienite gives a shorter setting time than 15%.
Typical Chemical Composition of SDP (semi-dry product) and WCP (wet-cast product) using XRF (X-ray fluorescence
______ SOP WCP
Calcium CaO % Pellet 51.074 46.431 Silica Si02 % Pellet 27.217 30.475 Alumina A1203 % Pellet 12.695 11.875 Iron Fe203 % Pellet 0.727 1.046 Magnesium MgO % Pellet 7.179 7.242 Titanium 1102 % Pellet 0.479 0.535 Sodium Na20 % Pellet 0.223 0.271 Potassium K20 % Pellet 0.339 0.723 Phosphorus P205 % Pellet 0.168 0.218 Zinc ZnO % Pellet 0.0107 0.0400 Vanadium V205 % Pellet 0.0043 0.0051 Manganese MnO % Pellet 0.1721 0.1930 Chromium Cr203 % Pellet 0.0147 0.0160 Lead PbO % Pellet 0.0043 0.0218 Barium BaO % Pellet 0.0536 0.0632 Zinc Zn ppm Pellet 86 321 Vanadium V ppm Pellet 24 29 Manganese Mn ppm Pellet 1332 1494 Chromium Cr ppm Pellet 101 109 Lead Pb ppm Pellet 40 203 Barium Ba ppm Pellet 480 566 Nickel Ni ppm Pellet 25 25 Copper Cu ppm Pellet 229 252 Rubidium Rb ppm Pellet 24 31 Strontium Sr ppm -Pellet 824 759 Zirconium Zr ppm Pellet 277 257 Antimony Sb ppm Pellet 7 9 Molybdenum Mo ppm Pellet 4 6 Arsenic AS ppm Pellet 4 28 Yttrium Y ppm Pellet 28 29 Sulphate SO3 % Pellet 0.6736 0.89 Sulphur S % Pellet 0.2694 0.36 Chloride CI % Pellet 0.0092 0.03 Loss on Ignition LOIxrf % XRF ________ ________ Na20 equivalent XRF 0.446 0.747 Changes in respective amounts of akermanite and gehienite over time: The following blends were prepared and hydrated, and the composition of the resultant material monitored over the course of 28 days.
1. 30% SDP and 70% C3; 2. 30% WCP and 70% C3; 3. 30% PFA and 70% C3; and 4. 30% C7 and 70% C3.
The results are shown in figures 13 to 16.
This shows that over time, the levels of akermanite and gehienite remain relatively constant in the blend 1 (30% SDP and 70% C3) whereas in blend 2 (30% WCP and 70% C3) the amounts of akermanite and gehlenite change dramatically with time.
In blend 2 it can be seen that the level of akermanite decreases and the level of gehienite increases over time.
In blend 3 (30% PFA and 70% C3) it is shown that arcanite is present in PFA in very limited quantities and decreases over time. In blend 4 (30% C7 and 70% C3) some variation can be seen over time in the amount of arcanite present, however, 2.S the levels of akermanite and gehlenite do not vary as dramatically as observed with blend 2.
Although aspects of the invention have been described with reference to the embodiment shown in the accompanying drawings, it is to be understood that the invention is not limited to the precise embodiment shown and that various changes and modifications may be effected without further inventive skill and effort.

Claims (36)

  1. CLAIMS1. A method of controlling the strength development of cement, mortar or concrete comprising varying the amount of CazMgSi2O7 (akermanite) and Ca2A12SiO7 (gehlenite) present in dependence upon the desired strength characteristics of the cement, mortar or concrete.
  2. 2. A method of controlling the setting time of cement, mortar or concrete comprising varying the amount of Ca2MgSi2O7 (akermanite) and Ca2A12SiO7 (gehienite) present in dependence upon the desired strength characteristics.
  3. 3. A method according to Claim 1 or Claim 2, wherein the amount of Ca2MgSi2O7 (akermanite) and Ca2AI2SiO7 (gehienite) are present in a total amount of up to around 20 %.
  4. 4. A method according to Claim 3, wherein the amount of Ca2MgSi2O7 (akermanite) and Ca2A12SiO7 (gehienite) are present in a total amount of up to around 15%.
  5. 5. A method according to any preceding Claim, wherein Ca2MgSi2O7 (akermanite) and Ca2Al2SiO7 (gehlenite) are present in a total amount in the range of around 8 to 12 %.
  6. 6. A method according to any preceding Claim wherein the Ca2MgSi2O7 (akermanite) and/or Ca2A12SiO7 (gehienite) are derived at least in part from weathered blast furnace slag.
  7. 7. A method according to any precediiig Claim, wherein the level of Ca2MgSi2O7 (akermanite) and/or Ca2AI2SiO7 (gehienite) is varied in dependence upon the amount of weathered blast furnace slag used.
  8. 8. A method according to Claim 2 wherein the method further comprises providing a source of MgO.
  9. 9. A method according to Claim 5, wherein MgO is present in an amount in the range of around 3 to 7 %.
  10. 10. A method according to Claim 6, wherein the MgO is derived at least in part from weathered slag.
  11. 11. A method according to Claim 6 or Claim 7, wherein the MgO is derived at least in part from paper ash.
  12. 12. A method according to any preceding Claim, wherein the method further comprises providing a source of free CaO.
  13. 13. A method according to any preceding Claim, wherein the method further comprises providing a source of free calcium silicates.
  14. 14. A method according to any preceding Claim carried out substantially in the absence of granulated slag.
  15. 15. Mortar produced by the method of any one of claims 1 to 9, wherein Ca2MgSi2O7 (akermanite) and Ca2AI2SiO7 (gehlenite) are present in the mortar composition.
  16. 16. Mortar according to Claim 11, wherein Ca2MgSi2O7 (akermanite) and Ca2A2SiO7 (gehienite) are present in the mortar in a total amount of up to 15%.
  17. 17. Mortar according to Claim 12, wherein Ca2MgSi2O7 (akermanite) and Ca2Al2SiO7 (gehienite) are present in the mortar in a total amount in the range of around 8 to 12 %.
  18. 18. Mortar according to any one of Claim s 11 to 13, further comprising MgO.
  19. 19. Mortar according to Claim 14, wherein MgO is present in an amount in the range of around 3 to 7 %.
  20. 20. Cement produced by the method of any one of claims 1 to 9, wherein Ca2MgSi2O7 (akermanite) and Ca2AI2SiO7 (gehienite) are present in the mortar composition.
  21. 21. Cement according to Claim 11, wherein Ca2MgSi2O7(akermanite) and Ca2A12SiO7 (gehlenite) are present in the mortar in a total amount of up to 15%.
  22. 22. Cement according to Claim 12, wherein Ca2MgSi2O7 (akermanite) and Ca2A12SiO7 (gehlenite) are present in the mortar in a total amount in the range of around 8 to 12 %.
  23. 23. Cement according to any one of Claim s 11 to 13, further comprising MgO.
  24. 24. Cement according to Claim 14, wherein MgO is present in an amount in the range of around 3 to 7 %.
  25. 25. Concrete produced by the method of any one of claims 1 to 9, wherein Ca2MgSi2O7 (akermanite) and Ca2AI2SiO7 (gehienite) are present in the concrete composition.S
  26. 26. Concrete according to Claim 11, wherein Ca2MgSi2O7 (akermanite) and Ca2A12SiO7 (gehienite) are present in the cement in a total amount of up to 15%.
  27. 27. Concrete according to Claim 12, wherein Ca2MgSi2O7 (akermanite) and Ca2A12SiO7 (gehienite) are present in the concrete a total amount in the range of around 8 to 12 %.
  28. 28. Concrete according to any one of Claim s 11 to 13, further comprising MgO.
  29. 29. Concrete according to Claim 14, wherein MgO is present in an amount in the range of around 3 to 7 %.
  30. 30. A cementitious composition comprising Ca2MgSi2O7 (akermanite) and Ca2A12SiO7 (gehienite).
  31. 31. A cementitious composition comprising Ca2MgSi2O7 (akermanite) and Ca2A12SiO7 (gehienite) in a total amount of up to 15 % by weight.
  32. 32. A cementitious composition according to Claim 17 comprising Ca2MgSi2O7 (akermanite) and Ca2Al2SiO7 (gehienite) in a total amount of between 8 and 12 % by weight.
  33. 33. A cementitious composition comprising a hydrated blend of paper ash and weathered blast furnace slag.
  34. 34. A method substantially as hereinbefore described and with reference to the accompanying figures.
  35. 35. Cement, mortar or concrete substantially as hereinbefore described and with reference to the accompanying figures.
  36. 36. A cementitious composition substantially as hereinbefore described and with reference to the accompanying figures.
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EP1325897A1 (en) * 2000-09-13 2003-07-09 Denki Kagaku Kogyo Kabushiki Kaisha Cement composition
US20070095255A1 (en) * 2005-10-28 2007-05-03 Abbate William V Blended cement composition

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GB2401104B (en) * 2003-04-29 2007-08-29 Gary Hunt Cementitious material

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EP1325897A1 (en) * 2000-09-13 2003-07-09 Denki Kagaku Kogyo Kabushiki Kaisha Cement composition
US20070095255A1 (en) * 2005-10-28 2007-05-03 Abbate William V Blended cement composition

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