The invention relates to a composition for injecting soil, to a mortar comprising said composition and to uses thereof.

In the art of foundation the injection of soil means the pressurised introduc- tion of an injection agent into the soil. The introduced injection agent reacts with the soil as a result of which the properties of the soil are altered.

In the art such injection agents are also called"binding agents"as these agents form a bond ("react") with the soil, as a result of which soil strengthening or soil stabilisation is achieved. Below, the terms"injection agents"and"binding agents"will be used interchangeably.

Injection agents known from the state of the art are among others described in the article"Het chemisch injecteren van grond" ("Chemical injection of soil") by N. W. A. Broug, pages 1-10, published by"Bouw- centrum Rotterdam"from the Netherlands in 1970 in"Grondwerk, funderingen", Sfb (18), UDC 624.15.

In general the object of the injection of soil (with the injection agent/ binding agent) is increasing the (mechanical) strength and/or water imper- meability of the soil. By increasing the strength of the soil the bearing

capacity of the soil is improved (that means soil strengthening or soil stabilisation), which is of importance when the soil is used as foundation.

Soil stabilisation thus is particularly essential when a subsoil is too soft.

When for instance the subsoil of a dike is too soft, this may result in problems in case of dike improvement because this causes a higher load of the subsoil. Said load consists of pressure and/or bending or shearing.

The injection agent can be injected into the soil such that so-called injec- tion poles, injection plates, injection layers or injection blocks are formed for the foundation and/or water-retaining structure.

An advantage of increasing the strength of the soil by injecting it with an injection agent is among others that as a result of it a stronger foundation is obtained because for instance injection poles are formed in the soil at locations where in retrospect a foundation on steel appeared to be insuf- ficient.

A problem however is that the soil may contain acids, such as for example humic acids. Acidic groundwater flows and seepage water flows may be present and occur in the soil stabilised with the binding agent, which acidic flows can dissolve the binding agent and thus undermine the stability.

The object of the invention therefore, in addition to achieving soil strengthening or soil stabilisation, is particularly aimed at preventing or delaying as much as possible the attack on soil, which is among others used as foundation, by among others acids and salts, the object being the prolonging of the life span of the soil to be used as foundation.

According to the invention the above-mentioned object is achieved by injecting the soil with a composition, comprising a latent hydraulic substance and shell lime material.

Accordingly, the invention relates to a composition for injecting soil, comprising: (i) a latent hydraulic substance and (ii) shell lime material.

Examples of latent hydraulic substances are trass flour, fly ash, pozzolana, pozzolana earth, burnt sludge (for instance burnt dredge sludge) and silica fume. Silica fume is a very fine substance consisting of silicon dioxide.

Pozzolana is a general term and comprises both coarse and fine grains; pozzolana earth comprises only coarse grains. Siliceous earth is a technical synonym for pozzolana earth.

"Pozzolana"is furthermore also used as the general term instead of the general term"latent hydraulic substance". Preferably the latent hydraulic substance in the composition according to the invention is trass flour. In addition the composition according to the invention may also contain more than one latent hydraulic substance.

The shell lime material to be used in the composition according to the invention, has preferably been formed by burning shells in an oven, for instance at a burning temperature in the range of 900-1300°C, such as approximately 1100°C, and subsequently slaking the burnt shells with water, resulting in the formation of shell lime grains having cement-like properties.

When the shell lime material used in the composition according to the invention has been formed by burning shells in an oven, it is preferred that, after burning, a part of the burnt shells has been slaked with water and a part of the burnt shells has not been slaked with water.

When salt water shells are used it is preferred that the shells are washed with fresh water prior to burning, in order to remove the salts from the

shells.

The shell lime material prepared in the above-mentioned manner has a certain grain size (fine or coarse). Methods for obtaining a certain grain size for the shell lime material are generally known to the expert in this field.

Shell lime material having a fine grain size is usually also referred to as shell lime flour.

Preferably the shell lime material to be used in the composition according to the invention comprises various shell lime materials of different grain sizes, varying from fine to coarse. When after mixing the various com- ponents of the composition according to the invention it appears that the grains thus obtained are too coarse, the desired (fine) grain size can be adjusted by granulating.

The composition according to the invention preferably has a grain size according to"Blaine"in the range of 4000-10000, more preferably 5000- 9000 and most preferably 6000-8000 cm2/g. The grain size according to "Blaine"is a specific grain size, stated as the total external surface of all binding agent particles per gramme of binding agent. Said specific grain size is measured with"Blaine's apparatus"as among others described in NEN 3550. In general it holds good that the larger the grain size according to"Blaine"is, the smaller (and therefore the finer) the actual grain size is.

The relative quantity with respect to each other of the materials to be used in the composition according to the invention, as well as the relative quantity of the composition according to the invention with respect to the quantity of the soil to be injected, depend on the local conditions, the type of soil and the desired effective life span of the soil uses.

In a particular preferred embodiment the composition according to the invention comprises the following components:

(i) trass flour and (ii) slaked, burnt shell lime material.

In this embodiment the composition according to the invention preferably comprises 0.45-0. 85 part by weight, and more preferably 0.55-0. 75, of component (i); and 0.15-0. 55 part by weight, and more preferably 0.25- 0.45, of component (ii). The density (or bulk density) of this composition preferably is in the range of 400-1000 kgim3, and more preferably 600-800 kg/m3.

In another embodiment of the composition according to the invention, said composition more preferably comprises the following components: (i) trass flour and (ii) a mixture of (a) slaked, burnt shell lime material and (b) unslaked, burnt shell lime material.

In this embodiment the composition according to the invention preferably comprises 0.40-0. 80 part by weight, and more preferably 0.50-0. 70, of component (i); 0.10-0. 50 part by weight, and more preferably 0. 20-0. 40, of component (ii) (a) ; and 0.10-0. 50 part by weight, and more preferably 0. 20-0.40, of component (ii) (b). The density (or bulk density) of this com- position preferably is in the range of 400-1000 kgim3, and more preferably 600-800 kg/m3.

In the above-mentioned uses of binding agents (injection agents) in the art of foundation the binding agent is normally used in a mortar. In addition to the binding agent, the mortar then also contains another component, such as for instance sand. Instead of or in combination with sand so-called "sand substitutes"can be used, such as for instance rubble granulates, slags and the like. Hydraulic material (such as for instance cement) can also be added to the binding agent.

A known binding agent according to the state of the art is cement which, in combination with sand, forms the so-called cement mortar.

When a mortar is used in the invention, said mortar, which comprises the composition according to the invention, is injected into the soil.

Accordingly, the invention also relates to a mortar comprising the com- position according to the invention, as described above. Preferably the mortar according to the invention, in addition to the composition according to the invention, also comprises sand.

The invention furthermore relates to a use of the composition according to the invention or of a mortar, comprising the composition according to the invention, as injection agent or binding agent for injecting soil.

Such a use of the composition according to the invention leads to a higher density of the injected soil portions, such as soil columns and soil sur- faces/layers, as a result of which the attack on those soil portions by among others acids and salts, does not occur or substantially does not occur or occurs considerably delayed. As a result the maximum effective life span of the foundation soil portions is prolonged.

Due to the higher packing or density of the soil portion injected with the composition according to the invention, acids and salts originating from outside of said soil portion cannot or almost cannot penetrate into the soil particles composing the injected soil portion in question, and therefore cannot or almost cannot attack said particles.

An additional advantage of the composition according to the invention is that because the soil injected with it is less susceptible to attacks by acids and salts, the (mechanical) strength of said soil is increased which leads to an improvement of the foundation properties of the soil. Another ad-

vantage regards the higher water impermeability of the thus injected soil.

The composition according to the invention can suitably be used for injecting various types of soil, such as for instance peaty soil, clay soil and sand. The composition according to the invention is particularly suitable for the injection of peaty soil and clay soil. Also when there are soil layers of different compositions, such as peaty soil in combination with clay soil, the composition according to the invention can thus suitably be used.

Furthermore the composition according to the invention is suitable for the injection of soil from which dikes have been made. In case dikes are used as a sea defence it is of particular importance that the soil composing the dikes is protected from salts originating from the seawater.

For a description of the various possible uses of soil injected with the composition according to the invention, such as those uses wherein the injected soil is used as foundation material having improved bearing properties, the article discussed above, section 2, pages 2-5, is specifically referred to.

The components (i) and (ii) from the composition according to the invention may separately or jointly be injected into the soil. It is preferred to first mix these elements with each other prior to injecting the soil.

For a description of the various injection methods, such as for instance the "double-shot"method and the"single-shot"method, the article discussed above, page 7, is specifically referred to. Both aforementioned methods are also referred to as MIP- (mix-in-place) uses, wherein the soil to be injected is mixed in-situ with the injection agent by injection into the soil.

With regard to the technical measures that have to be carried out for introducing the injection agent into the soil, the article discussed above,

section 3.2, 3.3 and 4, pages 7-9, is specifically referred to.

Below the present invention, and its advantages, is further elucidated on the basis of the following examples, which do not limit the invention in any way.

Example 1 1. Introduction It is of great importance that the life span of for instance a soil pillar, stabilised with a binding agent (injection agent), is as long as possible.

"Life span"here means the period during which the soil pillar still produces a sufficient stabilisation of the (sub) soil.

The aforementioned life span is determined by on the one hand washing out of the binding agent and on the other hand chemical attack of the binding agent. Washing out of binding agents according to the state of the art or mortars comprising said binding agents (for instance cement mortar as mentioned above), in actual practice is almost negligible as these binding agents hydraulically almost fully tie off or seal off the mortar. The cement stone formed by the cement mortar is almost impenetrable. As a result of said tying off/sealing off a groundwater flow cannot flow through the mortar and therefore cannot wash out a binding agent.

However, in the long term the soil pillar may loose its stability because the binding agent chemically reacts with components from the groundwater flows, particularly with its acidic elements, as a result of which the binding agent dissolves. In this sense the life span of a soil pillar is predominantly determined by the following two factors: (A) the acid resistance of the mortar containing the binding agent and

(B) the magnitude of the groundwater flow through the pillar.

The acid resistance of the mortar (containing the binding agent) is deter- mined by the level of the concentration of the binding agent (in the mortar) in relation to the"specific acid binding value"of the binding agent. In this description said"specific acid binding value"is defined as follows : the quantity of acid (which acid reacts with the binding agent) wherein the binding agent looses its (stabilising) activity. Thus the higher the value for the"specific acid binding value"for the binding agent, the higher the acid resistance of said binding agent.

The loss of stabilising activity can be established because the compression strength and/or bending strength drops below a certain minimum, still acceptable limit value. A standard for the compression strength and bending strength is NEN 3835.

2. Test The present applicant carried out research wherein various mortars were compared to each other with regard to their effect on the life span of soil pillars stabilised with those mortars.

In addition to sand, the examined mortars comprised other binding agents.

The one binding agent is a binding agent according to the state of the art which is commercially available, and which below will be referred to as CEM I/32. 5 R binding agent. The other binding agent is a binding agent according to the invention. Said two binding agents were used together with (masonry) sand in a mortar.

The CEM I/32. 5 R binding agent consisted of Portland cement which is commercially available. It here regards Portland cement CEM I/32. 5 R according to NEN 3550. The composition and other characteristics thereof

are generally known. The CEM)/32. 5 R binding agent had a grain size according to"Blaine"of 3000 cm2/g.

The binding agent according to the invention used in this test was a finely granulated mixture comprising the following components: (i) 5 parts by volume (or 0.65 part by weight) of trass flour accor- ding to DIN 51034 and (ii) 4 parts by volume (or 0.35 part by weight) of slaked, burnt shell lime material according to NEN-EN 459.

The chemical composition and the other characteristics of said binding agent according to the invention are shown in Table 1.

Table 1 Chemical composition (in % (m/m) dry substance) Calcium hydroxide total (1) approximately 37 Calcium hydroxide; Ca (OH) 2 approximately 40 Calcium carbonate; CaC03 approximately 10 Magnesium oxide; MgO 1.0 Aluminium oxide; Ale03 9.4 Iron trioxide; Fe203 3.2 Silicon dioxide; SiO2 approximately 30 Sulphide; S032-0. 4 Potassium oxide; K20 2.1 Sodium oxide; Na20 1.2 Other characteristics Loss on calcining approximately 17 Bulk density (kg/m3) 675 25 Grain size according to"Blaine"approximately 7000 (cm2/g)

(1)"Calcium oxide total"means : the calculated content of the sum of calcium oxide present in the composing calcium compounds as calcium hydroxide, calcium carbonate, hydrated calcium sulphate, calcium silicates, etc.

From the aforementioned test it appeared that, under equal conditions, the relation between the compression strength and the bending strength on the one hand and the concentration of the binding agent in the soil to be stabilised on the other hand is a directly proportional relation. This means that the compression strength and the bending strength increase directly proportional to an increasing concentration of the binding agent in the soil.

The compression strength and the bending strength were measured in MPa (= 106 Pa) according to the standard NEN 3835. The test range for the compression strength was 0-15 Mpa and for the bending strength 0-7 Mpa. The concentration of the binding agent in the soil was stated in kg of binding agent/m3 of soil. Thus aforementioned directly proportional relation between the concentration of the binding agent in the soil and the comp- ression and bending strength can be stated in [Mpa/(kg/m3)].

A result of the aforementioned test was among others that with regard to the compression strength or bending strength, respectively, 13 or 7 parts by weight, respectively, of the binding agent according to the invention produced an equally large increase in the compression strength or bending strength, respectively, as 1 part by weight of the CEM l/32. 5 R binding agent. As a result of this, a higher concentration of the binding agent according to the invention will have to be present in the soil than of the CEM l/32. 5 R binding agent, in order to obtain an equal initial compression strength or bending strength in the soil to be stabilised.

In the test a concentration of the CEM I/32. 5 R binding agent of 3.5 kg/m3 of soil was used. Furthermore an approximately 7 times higher con- centration (25 kg/m3 of soil) or an approximately 13 times higher con-

centration (46 kg/m3 of soil) was used for the binding agent according to the invention, depending on whether an equal initial bending strength or an equal initial compression strength was desired. 1 m3 of soil was started from, having a weight of 1500 kg and a grain size according to"Blaine"of 500 cm2/g, the soil having no"specific acid binding value".

It is assumed that in both cases an equivalent to the grain size according to "Blaine"of 30000 cm2/g was realised due to gel formation: in case of the CEM I/32. 5 R binding agent for 100% and in case of the binding agent according to the invention for 70%.

From the research it appeared that the"specific acid binding value", as described above, of the binding agent according to the invention is a factor 5. 5 higher than that of the CEM I/32. 5 R binding agent.

Because a higher concentration in the soil of the binding agent according to the invention was necessary, as already discussed above, and because the binding agent according to the invention has a finer structure than the CEM I/32. 5 R binding agent (that means it has a larger grain size according to "laine"), the porosity of a soil pillar, stabilised with the binding agent according to the invention, was considerably lower. A lower porosity of a soil pillar implies that the rate of flow of acidic groundwater through said pillar is lower as a result of which in a same period less acid reacting with the binding agent is supplied, as a result of which the life span of the pillar is prolonged. For instance at a free porosity of 0.45 vol./vol. (that means the ratio of the pore volume to the total soil volume) in the soil, comprising the binding agent according to the invention, the flow-through resistance was a factor 6.3 higher than that in the soil comprising the CEM I/32. 5 R binding agent.

Based on the research it is concluded that the life span of a soil pillar, stabilised with the binding agent according to the invention, is longer than

that of a soil pillar stabilised with the CEM l/32. 5 R binding agent, due to the higher acid resistance of the binding agent according to the invention and due to the higher flow-through resistance of the mortar based on the binding agent according to the invention. It is estimated that the life span of the soil pillar, stabilised with the binding agent according to the inven- tion, is approximately 35 times longer (= 5.5 times higher acid resistance * 6. 3 times higher flow-through resistance) than that of the soil pillar stabilised with the CEM l/32. 5 R binding agent.

Example 2 In this example, in a manner similar as in example 1, various mortars were compared to each other with regard to their effect on the life span of soil pillars stabilised with those mortars.

In addition to sand, the examined mortars comprised other binding agents.

The one binding agent is a binding agent according to the state of the art which is commercially available, and which below will be referred to as CEM 1/32. 5 R binding agent. The other binding agent is a binding agent according to the invention. Said two binding agents were used together with (masonry) sand in a mortar.

The CEM I/32. 5 R binding agent is the same CEM I/32. 5 R binding agent as described in example 1.

The binding agent according to the invention used in this test was a finely granulated mixture comprising the following components: (i) 5 parts by volume (or 0.6 part by weight) of trass flour according to DIN 51034 and (ii) a mixture of (a) 3.5 parts by volume (or 0.3 part by weight) of slaked, burnt shell lime material according to NEN-EN 459 and (b) 0.5 part by volume (or 0.1 part by weight) of unslaked, burnt shell lime material.

The chemical composition and the other characteristics of said binding agent according to the invention are shown in Table 2.

Table 2

Chemical composition (in % (m/m) dry substance) Calcium hydroxide total (1) approximately 37 Calcium hydroxide; CaO approximately 10 Calcium hydroxide; Ca (OH) 2 approximately 35 Calcium carbonate; CaC03 approximately 10 Magnesium oxide; MgO 1.0 Aluminium oxide; Al203 9.4 Iron trioxide; Fe203 3.2 Silicon dioxide; Si02 approximately 30 Sulphide ; SO32-0. 4 Potassium oxide; K20 2.1 Sodium oxide; Na20 1.2 Other characteristics Loss on calcining approximately 16 Bulk density (kg/m3) 680 25 Grain size according to"Blaine"approximately 6500 (cm 2/g) (1) See note under Table 1.

The object of the test of this example was, just like in the test of example 1, aimed at the determination of the life span provided by a binding agent to soil or a soil pillar stabilised by a mortar based on said binding agent.

From a comparison of the results regarding the binding agent according to the invention of example 1 with the binding agent according to the inven- tion of this example, it appears that the binding agent according to the invention of this example provides a longer life span because both the acid resistance of said binding agent is higher and the flow-through resistance of the soil treated with said binding agent is higher.