METHOD FOR THE STABILIZATION OF MARINE CLAYS

Abstract

The present invention relates to a new method for stabilising marine clays such as sediments, marine sediments, or dredging muds by using mussel shell powder and cement, their use and a respective product. A properly treated milled shell powder is mixed with a cement in order to obtain a solid composition of powders, which is subsequently mixed with the marine clay to obtain a product that can be used in the building industry.

Claims

1. A method for stabilizing marine clays comprising the following steps: a. heating mussel shells at a temperature ranging from 90? C. to 140? C., below than the mussel shell calcination temperature; b. milling the heated mussel shells up to obtaining a powder having an appropriate particles size; c. mixing the milled shell powder obtained in step b) with a cement, said cement being present in a quantity ranging from 15% to 50% by weight as referred to the total weight of cement and powder, in order to obtain a solid composition of powders; d. obtaining a final product by mixing the solid composition of powders obtained in step c) with marine clays, wherein said marine clays sediments are used in their natural state in terms of content of water and are characterized by a negative consistency index, said consistency index being an index that defines material consistency and being calculated by using the following formula:
CI=(w.sub.L?w)/PI where w is the water content, w.sub.L the liquid limit, and PI is the plasticity index, representing the range of water content values internally to which a soil is in the plastic status, said plasticity index being calculated on the basis of the difference between said w.sub.L the liquid limit and the plastic limit w.sub.P, and wherein said solid composition of powders is present in a percentage from 2% to 20% by weight as referred to the weight of the final product.

2. The method according to claim 1, wherein the marine clays are a sediment, a marine sediment, or a dredging mud.

3. The method according to claim 1 wherein the marine clay has at least 50% of the particles size having a diameter of less than 75 ?m.

4. The method according to claim 1, wherein the shells used are of the type Mytilus galloprovincialis.

5. The method according to claim 1, wherein the mussel shells are ground to a particle size of less than 300 ?m.

6. The method according to claim 1, wherein the cement according to step c) is selected amongst a type I cement and a type III cement according to the UNI EN 197-1(2011) standard.

7. The method according to claim 1, wherein the solid composition of powders ranges from 8 to 16% by weight as referred to the weight of the final product.

8. A product obtained in accordance with the method according to claim 1.

9. The product of claim 8, wherein the final product is used directly in situ for preparing a road subgrade.

10. The product of claim 8, wherein the final product is used for manufacturing ex-situ a prefabricated product selected from the group consisting of: a self-locking outdoor eco-block, artificial breakwater against wave motion, and a boulder for building a quay.

11. The method of claim 1, wherein the mussel shells are heated at a temperature of 105? C.

12. The method according to claim 5, wherein the mussel shells are ground to a particle size between 60 ?m and 100 ?m.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0050] The invention will be described here below with reference to a number of examples which are provided for exemplary, non-limitative purposes as illustrated in the attached figure.

[0051] FIG. 1 summarily describes the steps of the method according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0052] Whereas the invention is susceptible of various alternative modifications, some preferred embodiments will be described below in details. However, it is understood that there is no intention of limiting the invention to the specific embodiment here illustrated, but, on the contrary, the invention is meant to cover all modifications and equivalents that fall within the scope of the invention as set forth in the claims. The individual steps of the process are indicated in the process flowchart illustrated in FIG. 1.

[0053] In the process flowchart of FIG. 1, mussel shells are treated at a temperature lower than the calcination one, in order to eliminate most organic substances that might be present in the shells 101.

[0054] At the end of the thermal treatment, the heated mussel shells are milled up to obtaining a powder having an appropriate particles size distribution 102.

[0055] The powder obtained from the properly milled shells is mixed with a cement, preferably according to the UNI EN 197-1 (2011) standard in a proportion ranging from 15% to 50% by weight as referred to the total weight of the cement and of the powder in order to obtain a solid composition of powders 103.

[0056] Finally, the solid composition of powders is mixed with marine clays characterized by a negative consistency index CI<0, wherein said solid composition is present in a proportion from 2% to 20% by weight as referred to the total weight of the final product 104.

[0057] The present invention features numerous particularly important advantages.

[0058] First of all, the thermal treatment 101 is performed at temperatures well below than the calcination one (500? C.), namely from 90? C. to 140? C., preferably 105? C., because advantage is taken from the chemical activation potentials deriving from the addition of marine clays in which the fine fraction is predominant.

[0059] Secondly, it is not necessary to add water to obtain the final product in the marine clays-cement mixing step because use is made of sea water already present in the sediments. The final product is easy to obtain because the sediments are used in their natural state in terms of content of water and salts in the interstitial fluid and natural organic substance.

[0060] In this regard, here follows a calculation of the water content (w) of the natural sediment obtained by weighing before and after drying:

[00004]$w\left(\%\right)=\left(\left[\mathrm{humid}\mathrm{sample}\mathrm{weight}\left(\mathrm{gr}\right)-\mathrm{dry}\mathrm{sample}\mathrm{weight}\left(\mathrm{gr}\right)\right]\right)/\left(\mathrm{dry}\mathrm{sample}\mathrm{weight}\left(\mathrm{gr}\right)\right)?100\left(w\mathrm{sediment}=74\%\right)$

[0061] This water content has been subsequently used to calculate the addition of binder, as described in the examples below.

[0062] The following Table 1 shows the main physical-chemical characteristics of the sea water used in the present invention:

TABLE-US-00001 TABLE 1 Conductivity Salinity Chlorides Sulphates PH (?S/cm) (ppt) (mg/l) (mg/l) 9.21 50.4 33.17 6750 2810

[0063] Concerning the mineralogic characterisation of the sediment used in the present invention. this one is shown in Table 2 below.

TABLE-US-00002 TABLE 2 Sediment Mineral (% by mass) error Quartz 17.4 0.3 Microcline 2.0 0.2 Orthoclase 2.0 0.3 K-Feldspar group 4.0 0.5 Albite 6.2 0.3 Plagioclase group 6.2 0.3 Calcite 23.8 0.6 Aragonite 3.1 0.2 Dolomite/Ankerite 3.1 0.2 Alite 2.2 0.1 Pyrite 1.1 0.1 Rutile 0.4 0.1 Anatase 0.6 0.1 Amorphous 12.7 1.2 Tot. Non-clay 74.7 Kaolinite 3.6 0.5 Kaolinite group 3.6 0.5 Muscovite 2M1 7.8 0.3 Mica (bi-octahedral) 7.6 0.3 Smectite (bi-octahedral) 10.1 1.5 Chloride (tri-octahedral 4.0 0.3 Tot. Clay/phyllosilicate 25.3 Tot. identified 100.0

[0064] Concerning the treatment of mussel shells, these ones have been taken from mussel farmers in Taranto and have been submitted to a cleaning and milling treatment.

[0065] In particular, 1 kg of mussel shells have been washed in hot water (40? C. for 10 minutes). Then they have been put in an aluminium tray and inserted into an oven in order to submit them to a thermal treatment at 105? C. for 48 hours.

[0066] At the end of the thermal treatment, they have been taken off from the oven and milled in a Retsch crusher for 15 minutes. They have subsequently been sieved thus obtaining a particles size distribution characterised by D.sub.50=6.32 mm and Cu=2.213, where: [0067] D.sub.50 is the diameter corresponding to 50% of passing and Cu is a coefficient that assesses the uniformity of a sample in terms of grain size distribution and is defined as: Cu=D.sub.60/D.sub.10, where D.sub.60 is the diameter corresponding to 60% of passing and D.sub.10 is the diameter corresponding to 10% of passing.

[0068] In all examples described below, the cements used are cements according to the EN 197.1 (2011) standard marketed by Italcementi?.

[0069] A particularly significant aspect is in that the marine clays mixed with mussel shell powder present a synergetic effect in the presence of cement.

[0070] The cement mixed with mussel shell powder only presents a remarkable decrement of mechanical strengths as referred to cement as such, and the cement mixed with the solid mussel shell powder/marine clay composition behaves better in terms of mechanical strengths as compared to the cement only mixed with marine clays only.

EXAMPLE 1 (REFERENCE) TESTS IN STANDARD MORTAR

[0071] Mussel shells treated as described above have been used in replacement of Portland cement for producing standard mortars (25% by weight as referred to the total weight of the components). The standard mortar has been prepared according to the indications on composition, sample preparation, and curing, as set forth in the UNI EN196-1, 2016 standard.

[0072] The results of the mechanical tests have been compared to those of the Portland cement (CEM I) used as a standard, as detailed in tables 3 and 4 below.

TABLE-US-00003 TABLE 3 Standard mortar with CEM I Weight Rc A Rc B Rc Average Rf Seasoning (g) (MPa) (MPa) (MPa) (MPa) 7 days 577.70 55.39 55.91 55.65 10.06 28 days 578.30 64.65 64.45 64.55 9.10
where Rc stands for compressive strength and Rf stands for flexural strength.

TABLE-US-00004 TABLE 4 Standard mortar with CEM I and mussel shell flour (25%) Weight Rc A Rc B Rc Average Rf Seasoning (g) (MPa) (MPa) (MPa) (MPa) 7 days 495.80 25.50 26.88 26.19 4.62 28 days 500.70 27.18 27.87 27.52 4.73

[0073] As it can be noted from a comparison between the data relevant to Tables 3 and 4, the addition of mussel shell powder to CEM I drastically reduces the mechanical strength of the standard mortar.

EXAMPLE 2 (INVENTION)

[0074] Stabilisation of marine clay in the form a marine sediment with a quantity of binder equal to 8% as compared to the sediment. By binder we mean a solid cement (6%) and mussel shell powder (2%) composition.

[0075] Approximately 1 kg (=P.sub.tot) of marine sediment coming from a fill-in basin in the port of Taranto has been taken and mixed in its natural status (water content, w, equal to 74% measured as described above in the description) in a mechanical mixer for 10 minutes at a speed of 285 RPM.

[0076] The mussel shell powder has been prepared as described above in the description.

[0077] A quantity corresponding to 2% as referred to the weight of the dry sediment has been weighed.

[0078] In details:

[00005]$\mathrm{Weight}\mathrm{calculation}\left(\mathrm{dry}\right)\mathrm{Ps}=P_{tot}/\left(1+w\right)=1000/\left(1+0.74\right)=574.7g$$\mathrm{Quantity}\mathrm{of}\mathrm{mussel}\mathrm{shell}\mathrm{powder}=P_s*2/100=11.49g$

[0079] A quantity corresponding to 6% of Portland cement 52.5 R type I has been weighed, the percentage having been calculated as referred to the weight of the dry sediment (P.sub.s).

[0080] In details:

[00006]$\mathrm{Weight}\mathrm{calculation}\left(\mathrm{dry}\right)P_s=P_{\mathrm{tot}}/\left(1+w\right)=1000/\left(1+0.74\right)=574.7g$$\mathrm{Quantity}\mathrm{of}\mathrm{cement}=P_s*6/100=34.48g$

[0081] The two powders, cement and shell, have been joined, first between each other and subsequently mixed with the sediment. Thus, the material has been mixed for 5 minutes at a speed of 140 RPM. The same procedure has been repeated for comparison purposes, by using the Portland cement 52.5 R type I at 8% by weight as referred to the sediment.

[0082] The results of the product, in terms of mechanical strengths after 28 days of curing, are shown in Table 5.

[0083] IC is the consistency index, an index that assesses the consistency of a product calculated as described in the text, and R_Cu (kPa) is the undrained shear strength, i.e. the maximum tangential tension that can be applied to the soil before a breakage occurs in terms of total tensions.

TABLE-US-00005 TABLE 5 Geo-stabilised product CI R C.sub.U (kPa) CEM I 52.5R_6% + 2%_mussels 0.64 147.5 CEM I 52.5R_8% (comparison) 0.59 100

[0084] As it can be noted from the data shown in Table 5, a partial replacement of CEM I with a mussel shell powder increments the value for the consistency index, CI, as well as the undrained shear strength of the mixture, thus resulting in an overall improvement of its mechanical characteristics.

EXAMPLE 3 (INVENTION)

[0085] A marine clay stabilisation has been performed in the form of marine sediment to obtain a product as described in the example 2, but using a cement type III 42.5 N instead of cement type I 52.5R. The results after 28-day of curing are shown in Table 6.

TABLE-US-00006 TABLE 6 Geo-stabilized product CI R CU(kPa) CEM III 42.5N_6% + 2%_mussels 0.65 173.5 CEM III 42.5N_8% (comparison) 0.61 165.6

[0086] As it can be noted from the data of Table 6, a partial replacement of CEM III with mussel shell powder increments the value for the consistency index, CI, as well as the undrained shear strength of the mixture, thus resulting in an overall improvement of its mechanical characteristics.

EXAMPLE 4 (INVENTION)

[0087] Marine clay stabilisation in the form of marine sediment with a quantity of binder equal to 16% as reference to the sediment. By binder, we mean a solid cement (12%) and mussel shell powder (4%) composition.

[0088] Approximately 1 kg (=P.sub.tot) of marine sediment coming from a fill-in basin in port of Taranto has been taken and mixed in its natural status (water content, w, equal to 74% measured as described above) in a mechanical mixer for 10 minutes at a speed of 285 RPM.

[0089] The mussel shell powder has been prepared as described above.

[0090] A quantity corresponding to 4% by weight as referred to the dry weight of the sediment has been weighed. In details:

[00007]$\mathrm{Weight}\mathrm{calculation}\left(\mathrm{dry}\right)P_s=P_{tot}/\left(1+w\right)=1000/\left(1+0.74\right)=574.7g$$\mathrm{Quantity}\mathrm{of}\mathrm{mussel}\mathrm{shell}\mathrm{powder}=P_s*4/100=22.99g$

[0091] A quantity corresponding to 12% of Portland cement 52.5 R type I has been weighed, as a percentage calculated as referred to the dry weight of the sediment (P.sub.s).

[0092] In details:

[00008]$\mathrm{Weight}\mathrm{calculation}\left(\mathrm{dry}\right)P_s=P_{tot}/\left(1+w\right)=1000/\left(1+0.74\right)=574.7g$$\mathrm{Quantity}\mathrm{of}\mathrm{cement}=P_s*12/100=68.96g$

[0093] The two powders, cement and shell, have been joined, first between each other and subsequently mixed with the sediment. Thus, the material has been mixed for 5 minutes at a speed of 140 RPM. For comparison purposes, the procedure has been repeated by using Portland cement 52.5 5 R type I at 16% by weight as referred to the sediment.

[0094] The results after 28 days of seasoning are shown in Table 7.

TABLE-US-00007 TABLE 7 Geo-stabilised product CI R_C.sub.U(kPa) CEM I 52.5R_12% + 4%_mussels 1.25 557 CEM I 52.5R_16% (comparison) 1.22 511.33

[0095] The data of Table 7 show that a partial replacement of CEM I with mussel shell powder increments the value for the consistency index, CI, as well as the undrained shear strength of the mixture, thus resulting in an overall improvement of its mechanical characteristics.

EXAMPLE 5 (INVENTION)

[0096] A marine clay stabilisation has been performed in the form of marine sediment to obtain a product as described in example 6, but using a cement type III 42.5 N instead of a cement type I 52.5R. The results after 28 days of curing are shown in Table 8.

TABLE-US-00008 TABLE 8 Geo-stabilized product CI R C.sub.U(kPa) CEM III 42.5N_12% + 4%_mussels 1.19 545 CEM III 42.5N_16% (comparison) 1.16 540.5

[0097] The data of Table 8 show that the partial replacement of CEM III with mussel shell powder increments the value for the consistency index, CI, as well as the undrained shear strength of the mixture, thus resulting in an overall improvement of its mechanical characteristics.

EXAMPLE 6 (COMPARISON)

[0098] An attempt has been made to stabilise the marine clay with a quantity of powders equally shared between cement and mussel shell powder (50/50).

[0099] Approximately 1 kg (=P.sub.tot) of marine sediment coming from a fill-in basin in port of Taranto has been taken and mixed in its natural state (water content, w, equal to 74% measured as described above) in a mechanical mixer for 10 minutes at a speed of 285 RPM.

[0100] The mussel shell powder has been prepared as described above.

[0101] A quantity corresponding to 4% as referred to the dry weight of the sediment has been weighed.

[0102] In details:

[00009]$\mathrm{Weight}\mathrm{calculation}\left(\mathrm{dry}\right)P_s=P_{\mathrm{tot}}/\left(1+w\right)=1000/\left(1+0.74\right)=574.7g$$\mathrm{Quantity}\mathrm{of}\mathrm{mussel}\mathrm{shell}\mathrm{powder}=P_s*4/100=22.98g$

[0103] A quantity corresponding to 4% of Portland cement 52.5 R type I has been weighed, as a percentage calculated as referred to the dry weight of the sediment (P.sub.s).

[0104] In details:

[00010]$\mathrm{Weight}\mathrm{calculation}\left(\mathrm{dry}\right)P_s=P_{\mathrm{tot}}/\left(1+w\right)=1000/\left(1+0.74\right)=574.7g$$\mathrm{Quantity}\mathrm{of}\mathrm{cement}=P_s*4/100=22.98g$

[0105] The two powders, cement and shell, have been joined, first between each other and subsequently mixed with the sediment. Thus, the material has been mixed for 5 minutes at a speed of 140 RPM. The results of the product after 28 days of curing are shown in Table 9.

[0106] IC is the consistency index, an index that assesses the consistency of a product calculated as described in the text, and R_ C.sub.u (kPa) is the undrained shear strength, i.e. the maximum tangential tension that can be applied to a soil before breakage takes place in terms of total tensions.

TABLE-US-00009 TABLE 9 CI R C.sub.U (kPa) CEM I 52.5R_4% + 4%_mussels 0.46 28.5 CEM I 52.5R_8% (comparison) 0.59 100