METHOD AND PLANT FOR THE PRODUCTION OF INJECTABLE CEMENT MIXTURES

Abstract: In a method for the production of a cement mixture for injection into fine gravel soils, porous or microfractured rocks and/or materials a commercial cement is reduced to fine grain size by milling to a required granulometry an aqueous suspension having a cement versus water ratio within the range from 0.25 to 2.5 by weight; before, during or after said milling step, at least one fluidifying additive is added to said suspension. The obtained milled mixture is finally injected into said soils or rocks.

Description: Method and plant for the production of injectable cement mixture The present invention concerns a method for the production of cement mixtures suitable to be used, thanks to their character stics of permeab l ty at low viscosities, in consolidation injections and/or in sealing fine grain soils or rocks and/or porous or m c ofractured materials. The present invention further concerns a plant for carrying-out the above mentioned method. The known methods at present used for the consolidation of sandy soils generally involve the injection of mixtures- based on sodium silicates. Such techniques, while foreseeing a setting time compatible with the duration of the operation and while giving good seal ng properties and mechanical cohesion .to the treated soi s, have the- drawback of creating a possible source of pollution of the groundwater due to the release of water-soluble chemical substances. The necessity haε therefore been identified to obtain injectable mixtures based on insoluble products which are suitable to give consistency to the soil, avoiding any risk of groundwater pollution. Cement iε an ideal product for this purpose, because it allows to obtain excellent consolidation results and, being insoluble, it does not affect the groundwater. However, it must be injected as a suspension, and the use of cement mixtures for injections iε thus limited bv the particle size of the commercially available cement, which, in addition to the aggregation phenomena of the cement particles dispersed in -water, prevents the penetration into fine all vional soils and microfractureri rocks or materials. Due to this grain size and aggregation phenomena, soil fracture problems arise during injections, resulting in formation of localised panels of cement, called "claquage", in εaid fractureε, without obtaining the reqLiired uniform and diffuse permeation of the soil by the cement mixture. If a cement mixture with very much smaller particle siz e were available, .it could be possible to inject the same into the soil with good penetration properties, even in fine sands, without the above entioned soil fracture effects. A known method for obtaining cement mixtures with suf iciently fine particle- size to be injected into the ground >.e.g. particles paεεing a 10 micron filter) provides for decanting a suspension of a commercially available cement into water to separate by settling the heaviest fraction, which iε about SOX of the total cement used, from the εupernatant εuεpeneion, which contains, the finest particles and can be uniformly injected into the soil . However this method iε a very expensive one, becaLiεe the actually used portion is onl / 20"/. of the whole cement mixture and it takes a long time to be carried-out, due to the time necessary for sufficient settling out to take place, and because it is a "batch" process. SB-A-4-3-1356, in the name of H. Ridley, discloses the preparation of a cement mortar by mi ling an aqueous mi,:tυre of cement and sand or other solids to a gel consistency. The obtained mixture is then sprayed on a surface '(e.g. the walls of a tunnel , on which it adheres because of its gelly consistency. Thiε mixture is clearly unsuitable for injecting purpose? . Accordi gly, an object of the present invention is to overcome the aboyementioned proble ε by providing a method which supplies an injectable cement mixture into fine granular soils and porous or icrof ractured rods or materialε using commercially available cement, quickly and without waste. A furthe- object of the present invention _= to provide a plant for the production of said cement mixture which can be injected within a short time into fine-gram εcαlε and rocks end /or porous or micro ractured materials. More specifically, the present invention concerns a method for the production of mixtures of cement or similar hydraulic binders to be injected into fine-grain soils and into porous or microfractured rocks or materials, characterised in milling to a required granulometry an aqueous suspension having a ratio of cement versus water within the range from 0,25 to 2,5 by weight; and un adding to said suspension, before, during or after said milling step, at leaεt one fluidifying additive. According to a preferred method, 0,5 to 7'A by weight of fluidifying additiveε are added to a cement mixture having a ratio of cement/water of 1.5 before the milling step. Moreover, the present invention concerns a plant for the production of injectable mixture of cement or si il r hydraulic binders, characterized in that it comprises a ball mill or similar milling means, for milling an aqueous suspension of commercially available cement; means, for adding to εaid suspension at least one fluidifying additive, before, during or after said milling step; and meanε for feeding εaid milling suspension to injection means. The invention vail now be described in more detai with reference to the attache drawings which a e given for illustrative and non-limitative purposes, and wherein: Fig 1 is a flow chart of a plant according to the invention: Fig 2 iε a schematic diagram of a. particular embodiment of a plant according to the invention, provided with a hydraulic particle εeparator/c aεεifier; Fig 3 is a graph comparing the particle size range of a commercially available cement before and after milling according to the invention; Fig 4 is a graph of the parti cl e size range in a medium- fine sand. According to present invention, a cement mixture suitable to be injected into fine-grain soils and porous or microfractured materials and/or rockε in order to obtain consolidation thereof iε prepared by reducing the particle ize of the commercial cement, i.e. cement normally available on the market, to a sufficiently low value by- milling to the reqLiired granulometry an aqueous suspension of said commercial cement having a ratio of cement versus water within the range from 0.25 to 2.5 by weight. A ratio of cement/water, by weight, of 2.5 resulted as the maximum ratio of a millable mixture, and mixtures having a cement/water ratio of less then 0.25 proved to be too diluted and brought to a self-grinding of the mill components. Mixtures having a high ratio of cement verεuε water, i.e. a C/W ratio higher than 0.5, are further diluted to the required concentration before the injecting step. Before, during or after εaid milling εtep at leaεt one fluidifying additive iε added to the suspension, in order to make the suspension injectable or, according to the preselected cement/water ratio, suitable to undergo the milling step.- too. Actually it was found that while suspensions with a cement/water ratio up to i.O >.w»'w> av be successfully milled without addition of fluidifving agents, suspensions having a higher ratio of cement vε water can be milled only if a suitable fluidifying additive iε added to the mixture before or during the milling step, to avoid the mill blocking. Mixtures, having a ratio higher than 1.5 are preferably treated with εaid additives before the milling step. Said additiveε are preferably added to the cement mixture in an amount within the range from 0,5 to 7V. by weight of the cement, according to the mixture characteristics and the particle average size. Any suitable agent can be used which wi l reduce flpeculation of the cement and involve "solvatation" thereof by any extension of the setting time, allowing the separ tion of the fine -from the coarse particles and the subsequent injection of tbe fines into the soil. For instance εuch additives could be chosen from the following groups of compounds: polynaphthalenεulphonic acid, pelyal ylεulphonic acid, polymethylmetacrvlic acid, polyphosphoric acid, their salts, such as sodium salts, el mine resins and mixtures thereof. A preferred additive is sodium poiynaphtalensulphonate. The method of the invention iε preferably carried out batchwiεe, by milling almost all the cement mixture that entered the mill to the deεi ed granulometry and feeding it to the injection means. More preferably, a claεεification/εeparation εtep iε carried out prior to the milling εtep to enhance the process efficiency. However it iε possible to carry out further cl ssification steps as disclosed hereinafter with reference to Fig 1, that shows a flow chart of a poεεibie plant for the production of such injectable cement i tureε according to the method of the present nvention. It should be noted that by "cement mixtures" is meant here both a simple εuεpension of cement or any eimilar hydraulic binders in water, and a more complex mixture in which, beεideε the binder, further mineral fillers, e.g. silicates or carbonates, are present. In the pref erred embodiment of Fig i the plant compriεeε a tank 1 or similar meanε for the preparation of a suspension of commercially available cement in water, preferably provided with a εtirrer to keep the cement in εuεpenεion, connected by a feeder line 2 to classification/separation means 3. Two run-off lines 4 and 5 exit from εaid ciaεεification/εeparation means 3. Line 4 takes the fine particle fraction (i.e. that with fine qrain size) to the injεctinq means .not shown). Line 5 takes the coarse particle fraction (i.e. that with coarse grain size) through suitable feeding meanε, e.g. a pump 6, to milling meanε 7. A line 8 is provided at the outlet of the milling - means 7 to connect the same to the classification/separation meanε 3. Preferably, the milling meanε 7 consists of a ball mill, with a plate agitator. An exit line 17 is connected with line S upstream a valve 19 to feed the milled mixture to the injecting meanε; a further valve 18 is provided to control with valve 19 the mixture flow through line 17 to the said injecting meanε. A valve 13 or similar controlling means is incorporated into the feeder line 2 at the outlet from tank 1, to regulate the flow of fresh mixture which enters the clasεifier/sepa ator 3, and a si ilar valve 14 is located on the fine particle fraction outlet line 4. In operation. a suspension of commercially available cement in water iε first prepared in tank 1. During this preparation or later in the course of feeding it through the feeder line 2 up to the classification/separation meanε 3, one or more deflocculant additiveε are added to the cement in water suspension to aεεiεt the following separation proceεε into fine and coarεe particle fractions and to extend the setting time of the cement. Suite obviously, if the suspension iε milled without claεεification the fluidifying additive may be added also during or after the milling εtep, aε above di scl osed . The mixture containing commercially available cement from tank 1 i s εent to the classification/separation means 3 where a continuous separation is carried-out into a fraction rich of fine particles -.the fines) and another one rich of large particles (the coa ses). At this point the fines mixture can be at least partially tapped and sent through line 4 to the injection means (not shown), while the coarse particle mixture iε taken and fed through line 5 to the milling means 7. Means 6 are shown in fig 1 for circulating the mixture through the plant, e.g. i n the form of a pump. The coarse mixture entering the milling means 7 iε milled along itε path through said means 7; at the outlet there iε a mixture whose percentage of fines depends on the size of the mill 7, the dwell time etc. Such a percentage is naturally the highest possible, but it iε not necessary that all the coarse mixture iε reduced to a fine particle mixture, in εo far as the milled mixture leaving meanε 7 is- recycled along the line S up to the classifier/separator 3, where it iε once again separated and clasεified together with the commercial cement suspension entering from tank 1. As previously mentioned, the supply of suspension from tank 1 to the classifie /separator 3, and the removal of the fine particle mixture from the latter along the line 4 are controlled by means of valve means 13 and 14 on the lines 2 and 4 respectively. This allows a choice of either a batch or εtepwiεe milling. In the case of the former, after a sufficient quantity of suspension iε prepared in the tank 1, this iε sent to the claεεifier/separator 3. Operating the mill feeding pump 6, the coarse particles are taken off and ε-ent to be completely milled to the required size and the milled mixture iε sent to the injecting means. In a εtepwise milling, the coarse particles are not immediately and completely milled aε required and the milled mixture is sent to the claεεifier/separator 3 for further separation. In this way the particle size iε progressively reduced until there are only fine particles. In both caεeε it iε possible to carry out a continuous milling; itε operation iε similar to those already described, but the flow along the line 2 iε regulated in εuch a way aε to constantly feed fresh suspension to the tank i, and at the same time tapping off the fines- from line 4 and/or the milled mixture through line 17. The preferred milling meanε for the- continuous- proceεε iε a ball mill, agitated by revolving plates-, in which the mixture to be milled enters- at the lower end and passes- up tnrouqh the mill. The balls-, which fill ail the free spaces, grind the particles of cement which are carri ed along by the flow of suspension aε obtained by the action of the feeding pump 6. The classification/separa ion meanε 3 could be any- suitable device for the separation the fines from the coarses in suspensions; e.g. a hydrocycione or a centrifuge could be used. In the preierred embodiment shown in Fig 2, a hydraulic cl ssifi r/separator 9 is used, where an ascending current having a predetermined flow rate allows to separate the fine particles from the larger ones, by making the fine particles to raise up toward the upper part of the classifier/separator 3, while the coarse particles remain on the floor of the cϊaεsifier/separator 9. Aε it can be seen from Fig 2, the diagram of the plant iε similar to that previously described with reference to Fig 1, and simil r components have been re-f rred to with the same reference numbers i n both figures. Aε already described, the classif er/separator of this plant consists of a cylindrical container or tank 9 where the suspension coming from tank 1 along l ne 2 and the mixture returning from mill 7 along line 8 are fed together along the common line 12 into the -lower part of the classifier/separator 9, and create, due to the controlled feeding of the mixture from tank i, an ascending current separating the fine particles- by running the εame toward the outlet line 4. Aε a result, the mixture portion in the lower part of the classifier/separator 9 is enriched of coarse particles; line 5 iε positioned to remove this larger particle fraction. Line 4, for tapping fine particles is positioned at a pre—selected higher level. corresponding to the suspension portion where fine particles only are present. To ensure uniform supply of coarεe particleε, the lower part of classifier/separator is provided with slow stirrer meanε 10. In the lower part of the cylindric container 9 there iε a run-off line 16, fitted with a valve 15, used for emptying the plant or for running off a batch operation. The feeding of the commercial cement suspension along line 2 results in the fluid, and the particleε entrained by it, rising at a linear speed through the claεεi ier/εeparator 9. By εuitably regulating the feed rate by meanε of valve 13, a rising speed may be chosen εuch aε not to raiεε the coarεe particles beyond a εafety level, and in any case not to the tapping line 4. Fig 3 shows in a graph the distribution of particle sizes in a commercially avail ble cement (Portland 525) (20) and in a mixture after milling according to the method of the invention (21), to be compared with the granulometry of the sample sand in fig. 4. Further particulars .of the method according to the invention will now be given with reference to the foilowinq exam 1eε. EXAMPLE i A plant as. disclosed Fi 2, is comprising: - a tank of fresh mixture 1 with a volume of 2 litres fitted with a regulation valve 13 on line 2, - a classifier/separator 9 with a volume of 0.65 litres, and an inner diameter of 0.046 m, fitted with a valve 14 on the outlet line 4, - a pump 6, - a microsphere and plate mill 7 having a volume of 0.50 litres. TWO litres of a 15"/. suspension of cement 525 ptl, to which sodium polynaphtalensuiphonate waε added aε previously disclosed were fed into the above plant. The suspension was fed from sai tank I to the classi ier/separator 9 along line 2 at a rate of 1.5 I/h. The stirrer 10 in the bottom of the classifier/separator 9, the pump 6 and mill 7 were switched on. Because of the flow-rate and the free cross-sec ion of the classifier/separator, the fluid rising εpeed waε of 1.67 cm/minute and 36 minutes after feeding began, the fine particle suspension started to flow through line 4. The level in tank 1 waε continuously topped up with fresh mixture and the run-off of line 4 was collected in a suitable container under stirring. In the course of the exper ent, which ran for 8 hours, 12 litres of suspension containing 2.00 kg of dry cement were fed into the system. At the end of the experiment, all the fraction tapped from head were collected together and homogenized. One part of εaid suspension was fed at a pressure of 0.5 atmospheres into a sample of fine sand with particle size of less- than 0.500 mm (Fig 45, suitably compacted in a rigid container. After 28 days cure said εample of conεoli dated sand was compression tested. 2 The average breaking load for the samples waε 9.3 kg/cm . Another part of said suspension was suitably dried and εent to a granulometry analysis in a mercury porosimeter (P0R0SIMETER SERIES 2000, CARLO ERBA STRϋπENTAZIO E) . The particle εize distribution of the cement iε shown in Table EXAMPLE 2 A plant of the type disclosed in Fig 2, comprises: - a tank of fresh suspension 1 with a volume of 2 li res fitted with a regul tion valve 1Z on line 2, - a classifier/separator 9 with a volume of 1.00 litres and an inner diameter of 0.063 , fitted with a regulation valve 14 on line 4, - a pump 6, - a rotating drum mill 7 having a volume of 10.00 litres, containing 5.00 litres of zirconium oxide microsphereε. Two litres of a 15% suspension of cement 525 ρtl, added with sodium polynaphtalensulphonate aε above disclosed were fed to tank 1 in εaid plant. Said suspension waε fed from said tank 1 along line 2 and the inner duct 12 to the claεεif ier /separator 9 at a rate of 3.0 1/h. The stirrer 10 in the lower part of the classifier/separator 9, the pump 6 and mill 7 were switched on. Considering the flow-rate and the free cross-section of the classifier/separator 9, the fluid rising speed was 1.67 cm/minute, and 60 minutes after feeding began the finished product started to flow through line 4. The level in tank 1 was continuously topped up with fresh- mixture and the run-off of line 4 waε collected in a suitable container under stirring. In the course of the ex eri ent, which ran for 8 hours. 24 litres of suspension containing 4.00 kg of dry cement were fed into the system. At the end of the experiment, all the fractions run off were collected together and homogeni ed. One p r cf sai d suepensior was irjεcted at a pressure of 0.5 atmospheres into a saff.ple of fine sand »suitably compacted in a rigid container), whose particle size distribution cur se is shown x r. Fig 4. After 23 da s cui-e εaid sample of compacted and consolidated sand waε compression tested. The average __. breakage load of the εampieε was 8.9 i-g.- ' cm . Another part of εaid suspension was suitably, dried and sent to granulometry analysis w th mercur- • po*-oε_ meter (POROSIMETER SERIES 2000, CARLO ΞRBA STRUMENTA2I0ME) . The particle size distribution of the obtained cement is shown in Table 1. EXAMPLE 3 A plant of the type illustrated in Fig 2, comcrriεeε: - a tani- of fresh mixture 1 with a o3u e of 2 litres, fitted with a regulation val e 13 on l ne I. - a classifier-'separator 9 with a volume of l. ^ litres. en inner diameter of 0.063 m, fitted with a valve 14 on the outlet line 4, - a pump 6. - a microεphere and ol te mill "* having a volume of 0,50 litres, A mixture volume equal to the ε stem dead volume, twc litres of 15"/. suspension of cement 525 ptl. to which was added sodium polynaphtalensul honate aε above di loεed, waε fed into tank 1 of said plant. Said suspension waε fed from said tank 1 along line 2 and the inner pipe 12 up to the classifier/separator 9 at a rate of 3.00 1/h. The εlow stirrer 10 in the lower part of the claεεifier/separator 9, the pump 6 and mill 7 were switched on. Consi deri ng the f l ow-rate and the free cross-secti on of the cl aεεi f i er /separator 9, the f l ui d ri si ng speed was of 1.67 cm/mi nute. Considering the volumes of the claεεifie /separator 9, the mill 7 and the connecting pipework, the supply waε shut off 40 minutes after feeding began and the process stooped. The mixture thus- obtained was run off through the drain valve 15, and collected in a suitable container. One part of said suspension was fed at a pressure 0.5 atmospheres into a sample of fine sand suitably compacted in a rigid container, whose particle size distribution curve is shown in Fig 4. After a 28 days cure, said sample of compacted sand waε compression tested. The average breaking load of the εa pleε was 9.7 kg/cm . Another part of εaid suspension waε suitably dried and sent to particle size analysis with a mercury porosi εter (POROSΣ ETER SERIES 2000, CARLO ERB STRUMENTA2I0NE). The particle εizε distribution of the obtained cement iε shown in Table 1. EXAMPLE 4 A plant according to fig.2 embodiment, comprises: - a fresh mixture tank 1 having a volume of 250 1 provided with a control valve 13 on line 2; - a secondary classifying tank 9 having a volume of 6001; provided with a stirrer and a tapping line 4 having a control valve 14 - a pump 6 - a microεprhere and plate mill 7 having a volume of 10 1. 250 1 of 525 ptl cement 66% suspension, with a ratio cement versus- water C/tø = 2, are prepared i tank 1 and treated with sodium poiynaphtalenesuiphonate aε previously diεcloεed. This- mixture is fed- to secondary tank 9 through line 2 a,nd successively through l ne 5 and pump 6 to mill 7 at a flow rate of 60 I/h. Mill 7 is started. Because of the free inner volume of mill 7 and of the flow rate of pump 6, three minutes after the feeding began, the milled suspension began to flow from the mill exit. The valve 18 is open and valve 19 iε cioεed to feed the mixture directly to the end use, where it may be uεed aε εuch or diluted prior to itε injection. In the meanwhile, fresh suspension iε continuously fed to tank 3 and operation of the plant iε continued. Globally, during the test which lasted 8 hours. 480 i of suspension containing 534.13 kg of dry cement were fed to the plant. Every hour, from the starting of the test, a sample of the cement flowing from the mill was taken and partially used to fill a steel cylinder with a 38.5 mm i.d. and 100 mm high. Another portion of εaid sample was diluted with water to a cement percent of 25% and was injected at a pressure of 0.5 at into a sample of sand having granulometry of less than 0.5 mm (fig.4), suitably compacted in a rigid container. A further portion of the suspension waε dried and sent to granulometric analysis aε previously disclosed. The particle size distribution is shown in Table 1. After 28 days cure the samples of suspension and of injected sand underwent a compression test. The averaαe 2 breakiπq load value waε 580 kq/c for the mixture sample 2 .. . and 30.3 kg/cm for the injected sand sample. EXAMPLE 5 In a plant aε diεcloεed in Example 4, 250 1 of a 50% suspension of 525 ptl cement (C/i-i ratio - 1) were prepared in tank 1 and added with a fluidifying agent aε previously diεcloεed. The plant waε operated aε discioεed in Example 4, and during the test, which lasted 8 hours, 480 I of suspension containing 363.12 kg of cement were fed to the plant. Samples were collected and treated as disclosed in Example 4. The average granulometry values of the resulting dried suspension are shown in Table 1. After 28 days cure the injected sand and mixture samples- underwent a compression test. The average- brea ino load n__, value was ISO kα/cm for the mixture samples and 27.3 2 kg/cm for the i njected sand samples. EXAMPLE 6 In a plant aε disclosed in Example 4, 250 1 of a 33% suspension of 525 ptl cement (C/tø ratio = 0.5) were prepared in tank 1 and treated with a fluidifying additive aε previously di closed. The suspension iε fed to the classifier 9 at a flow rate of 200 I/h. The stirrer 17, pump 6 and mill 7 are started. Because of the free cross section of classifier and the flow rate through it the fluid rising εpeed waε 1.67 cm/min. Because of the volumes of the classifier, the mill and the feeding lines, 65 minutes after starting the plant the end product flows- from output line 4. The level in tank i was- continuously topped up with fresh mixture and tha fractions flowing at 4 were collected. Durinα the test, which l sted 2 hou ε, 400 1 of suspension containing 174.00 kg of dry cement were fed to the plant. At the end of the experiment samples of the collected and homogeneized fractions- were injected and dried as disci o ed in Example 4: the resulting granul metry of the dried samples s shown i Table 1. After 28 day cure the compacted sand samples were subjected to a compression teεt. The average breaking load v axue w ε »5.9 K q / c It should be noted that, aε diεcloεed in previous examples-, mixtures obtained according to the invention are injectable in a sample of compacted and preεεed sand, having the granulometry shown in fig. 4, at very low pressures, namely at 1,5 atm or less (e.g. 0.5 at ). The cited sand granulometry iε characterizable as follows: max. diameter 0. 5 mm 60% 0. mm 10% 0 - .1 mm nominal . 5 uniformity coefficient U-2.23 permeability " less than 5 x 10 "" ** cm/see TABLE 1 Part±cle Commercial Cement Cement Cement Cement Cement Cement diameter Cement Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 (Micron) ( relative % ) 30.00- 20.00 0.85 0.74 0.69 0.62 0.82 0.61 0 .70 20.00- 14.00 2.20 0.75 0.69 0.93 0.41 0.63 0 .36 14.00- 10.00 17.67 0.75 0.80 0.55 0.83 0.62 0 .70 10.00- 8.00 11.93 0.75 1.41 0.55 0.82 0.62 0, .35 8.00- 6.00 18V55 1.50 1.71 1.24 0.83 1.25 0, .36 6.00- 4.30 16.33 7.59 1.77 3.11 7.15 5.68 2, . 15 4.30- 3.00 9.22 14.-82- 1.36 11.59 20.63 12.66 16, .67 3.00- 2.00 8.29 19.35 2.83 27.60 18.50 19.28 30, .44 2.00- 1.40 4173 13.99 3.46 19.08 16.34 10.07 15 , , 89 1.40- 1.00 2.48 11.67 8.42 11.18 8.73 7.82 9. , 31 1.00- 0.80 1.57 6.35 11.29 5.23 6.57 4.65 4 , , 61 0.80- 0.60 1.44 7.02 15.83 5.13 3.64 5.55 ' 4. , 87 0.60- 0.43 0.90 5.36 12.86 4.36 3.92 7.02, 4. , 41 0.43- 0.30 0.76 3.66 9.80 2.91 3.00 7.20 : 3. 83 0.30- 0.20 0.70 2.53 7.65 1.97 2.74 7.56 2. , 14 0.20- 0. 14 0.51 1.40 5.26 1.50 2.21 4.14 1. 43 0. 14- 0. 10 0.43 0.81 4.87 0.50 1.17 2.32 0. 91 0. 10- 0.08 0.30 0.40 2.55 0.34 0.54 0.97 0. 32 0.08- 0.06 0.42 0.25 2.63 0.74 0.56 0.81 0. 13 0.06- 0.04 0.57 0.16 2.56 0.20 0.38 0.52 0. 46 0.04- 0.03 0.15 0.15 1.58 0.17 0.01 0.10 0. 10

Claims: CLAWS 1. A method for the production of mixtures o cement or similar hydraulic binders to be injected nto fine-gram soils and. or into porous or mi rof ractured roc I- ε or materials, characteri ed in milling to a desired granulometry an aqueous suspension ha mg a ratio of cement versus water wi hin the range from 0.25 to 2.5 by weight; end _n adding to said suspension, before, during or after said milling step, at leasi one fluidifying 2. A method according to claim 1, characteri ed in adding to said mixture an amount of fluidifving additi es witn n the range from 0.5 to 7% of the cement weight. 3. A method according to claim 2, characterized in that said additive i chosen amongst the foil owing compounds: poi vnaphthaienesulpho ic acid, oo yaU' / inaothalenεuϊ honic acid, pol yiTieth l me c yl i c acid, ρol vphosphoric acid and their salts, mel mme resins, and mixtures I hereof. 4. A method according to claim 2, wner ^ n said additi es are added to a cement mixture having cement / water ratio higher than 1.5 before the cited milling step. 5. A method according to ciaif.. 2, characterized _n adding said addi ives to a susper.sicr ha/mg a cement »*water ratio lower than 1.0 after the milling step,, o. A method accordino to clan. 1, wherein milled suεpenεionε ha zing a cement -water ratio higher then 0.5 are futher diluted befor*? injection. 7. A method according to an/ ciaι»Tι from 1 to 7. wherein εaid injectable cement πu ;ture is at least partially classified prior- to the milling step and at least a part of the --eεuiting suspension of fine particles iε tapped to injection means. S. A method according to Claim 7 , characterized that it further co prisee the steps of: feeding εaid cement suspension m a controlled way to a classification/separation meanε to separate a suspension fraction containing fine particles from a suspension fraction containing coarse particles; feeding εaid suspension fraction containing coarse particles to milling means in order to reduce at least in part their particle size; returning the suspension e:ιting εaid milling means to said claεεif ication -'separation means; and repeating the above mentioned operations. -?. A method according to claim 7 or S where * n said εeperation between fine particle mixture and cosrsfc particle mixture iε carried-out by means of a hvdraulic cl aεεi f i er /separato . 10. A __.l_.-rit for the production cf an injectable m :ture of cement or similar hydraulic binders, c ha * - ct en ed in that it comprises: a bail mill or similar meanε for milling an aqueous suspension of commercially available cement; means for adding to εaid suspension at leaεt one flui ifying additive, before, during or after sai d milling step? and means for feeding said milled suspension to injection means. 11. A plant according to Cl im S, characterized i n that it further comprises: one or more tanks for the preparation of a εuεpenεion of commercially available cement in water; meanε for feeding εaid suspension in a controlled way to classification/separation means to separate a suspension fraction containing fine particles from a εuεpenεion fraction containing coarse particleε; means for feeding sai d coarεe particle fraction to said milling means: meanε for returning the milled mixture exiting said milling means to εaid classification/separation means. 12. A plant according to Claim 11 characteri ed in that it further comprises means for tapping at leaεt a part of said fine particleε εuεpenεion and sending it to injection meanε. 13. A method for consolidating fine—grain εoi1ε and/or porous or microfractured rocks or materials, characterized in injecting a cement mixture as obtainable accordinq to any claim from 1 to 9. 14. An injectable mixture as- obtained according to any claim from 1 to 9. 15. An injectable mixture according to claim 14, characterized in that it iε injectable at a preεsure of 1.5 atm or less into a sample of compacted εand having a granulometry characterizable aε follows-: max. diameter 0.5 mm 60% ' •■ 0.37 mm 10% " 0.16 mm nominal " 0.325 uniformity coefficient ϋ=2.23 permeability " less- than 5 x 10 "* - c /εec

Inventors: BALDUCCI AGOSTINO, BOSCO BRUNO, REBUSCINI CLAUDIO, BALDUCCI, AGOSTINO, BOSCO, BRUNO, REBUSCINI, CLAUDIO
Applicants: RODIO & C CONST G, ING. GIOVANNI RODIO & C. IMPRESA COSTRUZIONI SPECI
Application year: 1990
Main classification: B02C17
IPC codes: B02C17, B28C5, C04B7, C04B24, C04B28, C04B40, C09K17, E02D3