DE2634189A1 - Consolidating sub-structure of roads or runways - by adding binder contg. hydrophobic cement and lime, and compacting - Google Patents

Abstract

Earth or soil consisting of fine or mixed grain sizes is consolidated for use as the substructure for roads, etc., where a binder is mixed with the soil, followed by compaction. The binder is a mixt. of (a) a hydrophobic, hydraulic material; and (b) a non-hydrophobic, non-hydraulic material. Material (a) is pref. a hydrophobic cement, or milled, roasted oil shale, whereas(b) is fine CaO or Ca(OH)2. The binder pref. contains by wt. 50-80%, esp. 55-75% (a), with 20-50%, esp. 25-45% (b). If treated oil shale is used, alumina can be added to bond the anhydrite in the shale, esp. using 25% alumina w.r.t. the wt. fo anhydrite; alternatively, the alumina addn. may be achieved by adding a cement. Used under roads or airport runways etc. Apart from producing the required load carrying ability, six to eight hours elapse before the start of setting, so adequate time is available for proper compaction.

Description

Patent application

Methods and binders for consolidating soils The invention relates to a method and a binding agent for the consolidation of the subsoil for Roads or the like forming fine and mixed-grain soils, with in the soil Binder incorporated and the soil mixed with the binder compacted will. Fine-grained soils are understood to mean soils in which a proportion of at least 40% by weight has a grain size smaller than 0.06 mm and below mixed-grain Soils those in which the proportion with the grain size of less than 0.06 mm between 5 and 40% by weight.

When building roads, runways or the like. is towards it make sure that the soil lying under e.g. the road structure can withstand the loads that from the weight of the road surface, from the traffic and from the changing weather conditions can arise without inadmissible deformations. Soils that have low water contents have, are normally so far load-bearing that the loads mentioned increase do not lead to impermissible deformations. There, however, the vast majority the Soils cannot be connected to groundwater through capillary forces it can be assumed that such soils always have a water content which requires sufficient load-bearing capacity. On the contrary, if there is a larger water supply from the subsoil, or when the groundwater level rises, a water content develops can set in the soil, which largely eliminates the load-bearing capacity of the soil. Furthermore, the effects of frost in the zero degree Celsius limit form Ice lenses in the ground, which are mainly caused by the fact that from the subsoil an unlimited supply of water is possible and that at a certain point if there is sufficient heat dissipation, a zero degree isotherm is formed in its area the water fed in by the capillarity freezes. Such ice lenses can take on considerable thicknesses and lead to an uplift of the carriageway body. The actual Damage to the road surface occurs in spring when the ice lenses melt the water enriched in this ice lens into the neighboring zones of the soil penetrates, completely saturates these zones and at this saturation the load-bearing capacity of the soil completely abolishes. The road surface is in such places by the Load with heavy vehicles and the lack of load-bearing capacity of the floor resulting groundbreak destroyed. So-called frost breaks form.

Since both the changes in the carrying capacity, as well as the changes in the structure of the soil through ice lens formation ultimately from a water migration are usually those pending under a planned road structure Soils, if they are in the area of the groundwater or in the area of penetration from above Frost are treated in such a way that primarily water migration reduced and their carrying capacity is increased.

For such extensive changes in the properties of soils mainly hydraulic binders (highly hydraulic lime, cement) or non-hydraulic Binder (burnt and slaked limes) used, cf.

11Technical regulations for the consolidation of soils "(TVV 74 - Forschungsgesellschaft f.d. Straßenwesen e.V., Cologne).

In the case of the subsequently consolidated soil, the binders used have various functions. The hydraulic binders, for example, mainly act in the way that soil particles are attached to each other by layers of binding agent or mortar be cemented. Here, the soil particles are in practice by milling of the soil formed with special tillers. After milling or during the When milling, certain amounts of binding agent (depending on the nature of the soil, approx. 3 - 1o%) sprinkled on the ground, worked in with the tiller and the ground afterwards compacted after incorporation with suitable rollers. The soils treated in this way win In the course of time an increased load-bearing capacity, which e.g. by testing the compressive strength can be followed on suitable test specimens. The method of soil consolidation described with hydraulic binders, e.g. cement, has the disadvantage that, since e.g. Cements have relatively short setting times (approx. 1.5 - 2.5 hours until the start of setting), the operations required for the introduction of the binder and the compaction in this time must be ended because with the start of solidification the workability such soil-cement mixes is significantly reduced and therefore towards the end of the Perfect compaction is no longer possible.

However, it is known that one of the most important factors for a successful soil consolidation the perfect compaction of the soil mixture and is binder. Without such compaction there can be no adequate bearing capacity can be obtained. Also the cause of the reduction in the load-bearing capacity of the soils, namely the water migration is not reduced to an acceptable level.

Attempts have been made to use a wide variety of water-repellent, i.e. water-repellent additives to cements prevent water migration despite the often inadequate To reduce the compactability of the soil. However, neither is this the problem the too short processing time of the cement, as well as that of the sufficient prevention the water migration has been solved. There was no shortage of laboratory tests where it should be demonstrated that soils consolidated with such cements absorb practically no water. However, when the test specimen was manufactured, since these test specimens could be produced in a short time due to their small dimensions, the problem only seemingly solved. In practice, the lack of compressibility remains but maintained.

Another way of influencing the structure of the soil exists when using non-hydraulic binders such as white fine lime or Hydrated lime for the restructuring of soils. These limes cause after milling restructuring of the soil so that it rests on the surfaces of the soil parts Sedentary Blkali ions, which have a great ability to bind water, through Clcium ions with a lower water-binding capacity can be exchanged.

This exchange and with it the restructuring and the crumbling of the soil go very quickly, so that after a short processing time a A very loose structure of the soil is achieved, which is also a much more intensive one Mixing of the binder with the soil is guaranteed as if cement is used which, since the restructuring of the soil is not going on so quickly, only adheres to the outside of the soil particles.

The treatment of the soil with white fine lime or hydrated lime is also done as with the treatment of the soil with cement, completed by compaction, whereupon the hardening takes place.

When using such a soil consolidation with lime, only in the lime reacts with soil particles for very long periods of time by the formation of calcium silicate and calcium aluminate to a certain increase the load-bearing capacity of the soil. In short, when treating the soil with Lime has a relatively longer processing time compared to treatment with cement (approx.

24 hours), the stable load-bearing capacity of the floor is guaranteed however, on the other hand, only achieved after much longer periods of time (several months).

It has been tried to add water repellants to lime as well, the insufficient reduction in water migration in the case of soil consolidation To improve lime. It has been shown, however, that when Walke at her Manufacture to be made hydrophobic, each particle of this Walke with a hydrophobic Shell surrounds, whereby the reactivity of the lime with those on the surface of the alkali ions sitting in the soil particles was greatly reduced. This was the Incorporation of the lime is extremely valuable, as is the restructuring of the Soil. Since the Water migration has not been sustainably reduced, there was also no perfect frost resistance of the soil in such treatment processes to achieve with hydrophobized limes.

Attempts have also been made to combine the advantages of both methods to connect by first restructuring the soils with white fine lime or hydrated lime, in order to subsequently solidify them permanently with hydraulic binders such as cement. These attempts are both technically and economically veiled. In technical For example, it took time to incorporate cement after pretreating the floor with white fine lime or hydrated lime, as well as the perfect compaction of this soil always longer than the latitude allowed in the setting time of the cement0 In addition, the process was called into economic question because two Operations and a considerable amount of binder in most cases the application failed this procedure. Usually it was more economical then, the upcoming ones Remove the soil and replace it with a frost-proof material. It is on this one Note that the above mainly refers to fine-grained Cover floors.

Coarse-grained soils, such as sand, are more advantageous with hydraulic ones Solidified binders. It is not very useful to use white fine lime or hydrated lime to be used because the specific surface of coarse grains is smaller than that of fine grains Grains and because the reactivity of fine-grained soils is generally essential is higher.

l Since, however, in most cases under the roadways to be built If fine-grained soils are present, the object of the invention is to provide a method to create the type mentioned, which makes it possible to use a suitable binder using only one work step in sufficient time To carry out soil consolidation which is stable in space, i.e. which there is no significant migration of water in the soils and which are caused by frost no ice lens formation occurs, which later affects the load-bearing capacity of the soil represents.

It has now been shown, surprisingly, that this task while avoiding all the disadvantages listed above can be solved if you use the method of the type mentioned according to the invention in such a way that a from a mixture of a hydrophobized, hydraulic component with a non hydrophobized, non-hydraulic component existing binder is used will.

This method achieves that as a result of the used special binder 6 to 8 hours pass before the start of solidification, so that enough time is available to compact the soil mixed with the binding agent stands.

This causes water to migrate in the soil that has been consolidated in this way and effectively prevents ice lens formation as well as good soil integrity achieved.

Another proposal is that as hydrophobized, hydraulic Component hydrophobized cement is used.

It is advisable to use Portland cement clinker before or during the To add a water repellent to the grinding and render this water repellent Cement then the non-hydrophobic, non-hydraulic component, e.g. 3. Fine white lime or add hydrated lime. In this way, the Reaction speed of the Portland cement clinker once through the hydrophobizing additive and further by the fact that it is only one component of the binder used and thus only represents a small proportion of the total amount of binder much of its adverse properties taken while by the addition on white fine lime or hydrated lime the restructuring effect of the binding agent in Interfering is very pronounced and, viewed overall, much less The need for binding agents arises as if the soil was treated with fine white lime or hydrated lime and then a treatment with Portland cement clinker at different times was made.

Another variant of the method is characterized in that Ground water-repellent tempered as a hydrophobized, hydraulic component Oil shale burn is used.

Here, too, can be used as a non-hydrophobic + non-hydraulic component Fine white lime or hydrated lime can be used. The aforementioned tempered oil slate burns can e.g. be obtained from the incineration of oil shale in fluidized bed furnaces, whereby the combustion residue is largely eliminated by suitable process management active silicic acid, active clay, highly burnt anhydrite and burnt lime consists.

The presence of anhydrite occurs when the binder is incorporated a formation of ettringite in the soil by the fact that the non-hydrophobic, non-hydraulic component of the binder (lime), reactive clay and anhydride react with each other. Apart from the fact that every: molecule of ettringite, for example 32 molecules of water binds and thus reduces the water content in water-rich Soils also carry the crystal needles that occur during ettringite formation to reinforce the soil.

These resulting needles grow especially when through a sufficiently high lime content of the binder a sufficient restructuring of the Soil has taken place in all directions into the soil and thus increase considerably the cohesion of these soils.

In the event that the oil shale burnup used does not naturally occur Contains enough aluminum compounds to remove the one formed during the firing process To bind anhydrite to ettringite, there is one embodiment according to the invention binder used in that the hydrophobized hydraulic component Representative oil shale burn-up reactive onekde to bind the in the oil shale burn-up contained anhydrite is added. The addition of reactive clay can thereby amounting to about 25 weight of the anhydrite and by cement or also by Blast furnace slag, hydraulic lime and the like. Be formed.

When the method according to the invention is carried out, hardening occurs of the binder used largely take place in that the in the binder existing lime reacts with active silicic acid and active clay, whereby these Reactions, as they are among less reactive components than those in the cement in front of them walk, proceed relatively slowly. The load capacities or strengths achieved of the soil, however, after about 28 days, are just as high as that which one at dor Hardening only gets with cement. In this way you can achieve a longer one Processing time, during which you can work in the material properly and can compress and during which there is no need to worry, even in the event of breakdowns in the construction process is that certain places are not sufficiently solidified because of the occurrence of the BrBtarrona could become, In addition, it is also recommended for use from oil slate burn-off, the latter during the grinding process with a hydrophobing agent, e.g. to move fatty acids, fatty amines, silicones, etc. When you think of the ground Binder later not hydrophobized white fine lime or not hydrophobized Adding hydrated lime is the restructuring effect of white fine lime or des Hydrated lime is much cheaper than using both substances together during the Hydrophobic grinding process. Even in those cases in which the binder has certain If quantities of Portland cement clinker are ground in, it has proven to be beneficial proven, the oil shale burn-off formed by combustion residues of the oil shale, to grind the clinker and the water repellent together and this mixture later add the required amount of non-hydrophobized white fine lime or hydrated lime.

In practice, the composition of the binder or

the amount of binder to be used is determined by produces test specimens with the soils and binders in question, which according to 28 days of storage are exposed to twelve freeze-thaw cycles. Here the specimens are placed on a water-absorbent felt during thawing, so that they can absorb water. Test specimens that absorb water show measurable elongations after the freeze-thaw cycles. On the other hand, it's the other way around possible to make the floors water-repellent as far as possible with the added binding agent, that one practically abolishes the capillarity of the soil and in contrast to the capillary Soils that absorb water get those that give off water through capillary depression. It is beneficial set the type and amount of binding agent so that that no broken debris, but also no excessive water release, resp.

there is no excessive shrinkage of the soil.

With regard to the composition of the binder, it is proposed that that the proportion of the hydrophobized hydraulic component is 50 to 80% by weight and the proportion of the non-hydrophobic, non-hydraulic component 20 to 50% by weight of the mixture. In many cases, the proportion of the hydrophobized hydraulic component 55 to 75% by weight and the proportion of the non-hydrophobic, non-hydraulic component be 25 to 45% by weight of the mixture.

The following examples show with reference to FIGS. 1 to 4, how a Soil on the addition of different types and amounts of binding agents by changing the Volume expansion or

-contraction reacts. All volume changes were after 1 2 times Frost-permanent cycles measured.

In Fig. 1 is the influence of the known addition of Portland cement and applied by hydrophobized Portland cement to the change in volume of the soil. As can be seen, the hydrophobization of the cement leads to a lower level of water repellency Stretching or expansion of the soil. However, it can still be seen that from one Addition of about 7 ffi binder does not significantly change the expansion is to be determined. It can be seen that the hydrophobized cement is better for the soil It confers properties as cement that has not been hydrophobized, but it does so with both Binders exceeded the maximum permitted expansion of 1% of the soil.

Fig. 2 shows the action of the same binders on the soil, if this has been treated beforehand with 3% fine white lime, as is known. Here can the maximum permitted elongation of 1% 0 can be achieved with both binders, with non-hydrophobized cement, however, only with a 10% addition, with hydrophobized cement Cement with 6% additive.

Fig. 3 shows the influence of binders according to the invention, and with a hydrophobized cement with the addition of 25 or 50% hydrated lime. These binders are in an amount of 7 ffi with the hydrophobized cement 25% hydrated lime, or 5.8% in the case of a hydrophobized cement with 50 ffi hydrated lime can be added to achieve an elongation of less than 1,560. So it is with these binders succeeded in keeping the elongation to the prescribed level of 1%, which was achieved with a smaller amount of binder, than when using conventional binders.

Fig. 4 shows the expansion of floors, which according to the invention with Oil shale burn was treated, once with 25% and once with 50% Hydrated lime. Here, the maximum elongations are achieved with an even smaller amount of binder fell below, namely with 5.5% with the addition of 25% hydrated lime and with 4.8% with an addition of 50% hydrated lime.

The processing of the slate binder on the construction site provides significant advantages in that the processing time, i.e. the time between Milling and compacting is much longer than the processing time when doing it alone Application of portland cements. As a result, in practice, the one according to the invention binders used Soil improvement far better Properties than that performed with Portland cements alone.

Expectations:

Claims (9)

Claims method of consolidation of the subsoil for roads Od. Like. Fine-grained and mixed-grained soils, with binders in the soil incorporated and the soil mixed with the binder is compacted, thereby characterized in that one of a mixture of a hydrophobized, hydraulic Component with a non-hydrophobic, non-hydraulic component Binder is used. 2. The method according to claim 1, characterized in that the hydrophobized, hydraulic component hydrophobized cement is used. 3. The method according to claim 1, characterized in that the hydrophobized, hydraulic component of tempered, ground, hydrophobized oil shale burn is used. 4. The method according to any one of claims 1 to 3, characterized in that that as a non-hydrophobic, non-hydraulic component, white fine lime or hydrated lime is used. 5. Binder for carrying out the method according to one of the claims t to 4, characterized in that the proportion of the hydrophobized, hydraulic Component 50 to 80% by weight and the proportion of the non-hydrophobic, not hydraulic component 2O to So% by weight of the mixture. 6. Binder according to claim 5, characterized in that the proportion of the hydrophobized, hydraulic component 55 to 75% by weight and the proportion the non-hydrophobic, non-hydraulic component 25 to 45% by weight of the Mixture amounts. 7. Binder according to claim 5 or 6, characterized in that the oil shale burn-up used according to claim 3 reactive alumina for binding of the anhydrite contained in the oil shale burn-off is added. 8. Binder according to claim 7, characterized in that the additive of reactive alumina is 25% by weight of the anhydride. 9. Binder according to claim 6 and / or 7, characterized in that that the addition of reactive clay is formed by cement.