Description

TAIL SEALS

TECHNICAL FIELD

The present invention concerns a tail seal compound (tail seal) for tunnelling machines, i.e. a sealing composition that is used to avoid the penetration of ground water and grout, injected behind the precast concrete segments inside mechanical tunnel boring machines during excavation.

The sealing composition of the present invention comprises blown oils, more than 30% by weight of a mineral charge and fibrous material. BACKGROUND ART

Sealing compositions are pumped to fill the gap occurring between tail brushes on the inside of the shield, to seal them and avoid ground water, grout or contaminants in general to enter.

They shall have excellent resistance against: - water wash-out

- mechanical wear and pressure

- flowing-off / extrusion

At the same time they have to show important features as:

- strong adhesive properties - high stability without fluid separation

- low toxicity and environmental compatibility

To further enhance their environmental compatibility, it is also highly desirable to have hydrocarbon free sealing compositions.

Known tail seals are usually made of a hydrophobic portion, a mineral charge, fibrous material and various additives and are in the form of sticky pastes.

Their maximum consistency is limited by the capacity of the pumping devices, that usually work by pressing out the mixture from its container.

The hydrophobic portion is responsible for adhesion to the metallic surface, for insulation from water leakage and its chemical structure strongly influences the rheology of the sealant.

To adequately perform its role, the hydrophobic portion normally represents at least 30% of the sealing composition.

The mineral charge is used as filler, its maximum concentration being limited

by the maximum final viscosity and consistency of the composition. The fibrous materials are usually added in small percentages (1 to 10% by weight) to improve the pastiness and lubricating characteristics of the sealing composition. Additives can be chosen among emulsifiers, gelling agents, viscosifiers, preservatives, corrosion inhibitors added alone or in combination. Among the patents concerning specific compositions useful as tail seals we cite: o US 5,478,385, describing sealing compositions comprising a hydrophobic portion, a lipophilic emulsifier and at least 20% water, in sufficient concentration to inhibit combustion of the composition; o FR 2 807 058, concerning a water reactive emergency sealing composition comprising a gelling or thickening agent; o JP 09-208943, describing seal tails that contain a synthetic pour point depressant, up to 60 wt% mineral charge and a biodegradable oil or grease or mixture thereof; in this publication, blown oil are not mentioned among the utilizable oils and greases and, although mineral charges like inorganic carbonate or sulfate are cited, in the examples desirable high levels of mineral charge are only obtained by using inorganic materials in the form of paste or talc (normally talc is commercially available with relatively small mean particle size, between 1 .5 and 37 microns and possesses lubricant properties). DISCLOSURE OF THE INVENTION

It has now been found that when blown oils are used as the hydrophobic portion of the sealant, the mineral charge can represent more than 30%, advantageously more than 45%, and up to 70% by weight of the total tail seal composition, without the need of pouring point depressants or emulsifying agents and without the need of using talc as the mineral charge. The result is an eco-compatible sealing composition that advantageously can be based on oxidized oils.

It is therefore a fundamental object of the present invention a tail seal comprising from 30 to 70% by weight of blown oils, from 30 to 70% by weight,

preferably from 45 to 70% by weight, of mineral charge and from 2 to 10% by weight of a fibrous material.

Blown oils are produced at elevated temperatures (60-250 ⁰ C), by blowing air through unsaturated oils; the oils polymerize by crosslinking through formation of peroxide bridges and C-C linkages.

Blown oils are also known as oxidized, thickened or oxidatively polymerized oils.

They can be produced from a wide range of animal or vegetable oils, for example from rape seed oil, castor oil, linseed oil, olive oil, soybean oil, palm oil, tall oil, fish oil, menhaden oil, herring oil, sardine oil, cod oil, liver oil, and mixture thereof.

Another convenient source of oils to be blown is the recovery of used oils.

Blown oils are generally manufactured to viscosity specifications.

For the realization of the present invention only blown oils having Brookfield ® viscosity RVT at 25°C, 20 rpm higher than 4,000 mPa*s can be used, preferably higher than 6,000 mPa*s, more preferably of at least 8,000 mPa*s.

According to a preferred embodiment of the invention the blown oils are blown used oils, obtained by air oxidation of waste oils and fats.

Preferably, the acidity number of the blown oils should not exceed 110 mg KOH/g.

The preferred amount of blown oils in the tail seals of the invention ranges from 40 to 50% by weight.

The mineral charge utilizable is a non fibrous mineral charge in the form of powder. Utilizable mineral charges are salts of multivalent cations, of natural or synthetic origin in the form of hydroxides, carbonates, sulphates, etc.

Preferred mineral charges are calcium carbonate, hydrated calcium sulphate, barium sulphate, the most preferred mineral charge being calcium carbonate.

The particle size of the mineral charge is not critical: for economical reasons it is therefore preferred to use mineral charges having mean particle size between 40 and 300 microns.

Cellulose fibres, preferably long length cellulose fibres, can advantageously be used as the fibrous material; also other non toxic fibrous materials having 1-5 mm length and 0.5-2 din fineness can be used.

The tail seals of the present invention can be prepared by mixing at room temperature its ingredients; preferably the mineral charge is first mixed with the blown oil, the fibrous material is added and mixing is continued until visual homogeneity is reached.

The sealant performances are not influenced by the operating temperature currently encountered by tunnel boring machine heads and generally in a range between 0 and 90 ⁰ C.

BRIEF DESCRIPTION OF THE DRAWINGS.

Fig. 1 represents the scheme of the equipment which is used to perform the slump test (see details in the Performance Testing section -Method 1 ).

Fig.2 represents the scheme of the equipment which is used to perform the water pressure test (see details in the Performance Testing section -Method

2).

EXAMPLES

Example 1

A tail seal is prepared having the following percentage composition by mass: 46% blown castor oil, with Brookfield ® viscosity RVT at 25°C, 20 rpm = 4,600 mPa*s

51% CaCO ₃

3% cellulose fibre

Preparation procedure: Blown oil and CaCO ₃ are mixed together at 25 ⁰ C to obtain an uniform, high viscosity but flowing liquid. At this point, fibres are slowly added to the mixture and mixed together to obtain a sticky, not flowing paste.

Example 2

Another tail seal is prepared having the following percentage composition by mass:

46% blown castor oil with Brookfield ® viscosity RVT at 25°C, 20 rpm = 8,000 mPa*s

50% CaCO ₃

3% long cellulose fibre

1 % short cellulose fibre

Preparation procedure is the same as in Example 1.

Example 3 Another tail seal is prepared having the following percentage composition by mass:

45% blown vegetable oil with Brookfield ® viscosity RVT at 25°C, 20 rpm

8,600 mPa-s

50% CaCO ₃ 5% cellulose fibre

Preparation procedure is the same as in Example 1.

PERFORMANCE TESTING.

Method 1. Slump test

Scope: the simple test characterizes the adhesion and slump of a tail seal, when it is in contact with metallic surfaces.

Method

Place the steel plate « A » horizontally. Spread the tail seal «B» on the steel plate to obtain an homogeneous layer of about 2-3 mm of thickness. Then place the upper steel plate « C » on the seal teal layer and put a load of 2 kg on top for 2 minutes. Take off the load and raise the support into a vertical position starting chronometer. Monitor the vertical movement of the 'upper plate' « C » and measure the time necessary to complete detachment of the plate. Sample temperature shall be 20 to 25 ⁰ C (unless differently requested).

The plates have dimension of 100 x 100 x 10 mm and their weight is approx. 800 g.

Analysis of the results

A detachment time of 40 seconds is considered the lowest acceptable limit; detachment times higher than 70 seconds are considered very good.

Method 2. Water Pressure test

Scope: the resistance of the tail seal to water pressure is measured forcing the product through a 1 mm mesh and measuring the amount of water or substance released. Method

The test is run with a fluid loss measure cell, that is a metal cylinder with a mesh at the bottom and an air inlet on the top. A 25 mm thick layer of tail seal is spread over the mesh. The part of the cell above the sealant is filled with water and an air pressure of 8 bar is applied. The amount of water released after 30 minutes under air pressure is measured. Analysis of the results.

An amount of released water of 10 ml is the highest acceptable limit; amounts of released water equal or lower than 3 ml are considered very good. The amounts of released water are reported in table 2. Table 2