CA1075455A - Soil treatment compositions - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

The invention relates to a method of aggregating sands to an appreciable depth so that they can be used, inter alia, for runways, roadways and the like, the method comprising applying a polymer emulsion to a body of sand in a large volume of water containing a stabiliser which ensures distribution of the polymer throughout a substantial depth and prevention of migration of the polymer as the water evaporates, thereby forming bonds between adjacent sand particles, and allowing the sand to dry.

Description

~ 754~5 This inven-tion relates to a me-thod of aggrega-ting sand and sandy soils. In -the specification which follows the term "sand" is intended to include sandy soils.

All methods known to the Applicant involving the treatmen-t of sands with polymeric compositions result in only a sur:Eace Eilm being formed. Special effects have been .
obtained by the use of two-component polymer systems or in situ freezing of the water in the sand, but these methods are very expensive.

It is an object of the present invention to provide a method oE aggregating sand in appreciable dep-th using a very dilute one-component composition.

It is a fur-ther object oE the invention to provide a method of aggregating sand which is very easy to apply.

According to the i.nvention a method for aggregating sands to a depth exceeding three centimetres includes the step of applying a polymer emulsion which has been stabilised with a colloid stabiliser in a volume of water at least thirty times by volume of the amount of polymer emulsion used, to a body of sand, whereby the polymer is dis-tributed through a depth exceeding three centimetres and does not migrate upwards as the water evaporates, thereby forming bonds between adjacent sand particles throughout the depth of sand treated.

In this specification the term "polymer emulsionll means either the product resulting from emulsion polymerisation '7S4Si5 or an emulsion of a polymer.

The colloid stabiliser may be a gum, cellulose, poly-vinylalcahol, and others normally used in polymer technology. Colloid stabilisers are distinguished from the surfactant.type of stabilisers in that the latter function by holding water shells to the polymer molecules by electrostatic forces, whereas the colloid stabilisers function by steric rather than ionic forces.

The amount of polymer required to eEfect satisfactory aggregation is surprisingly small and the ratio of dry polymer to sand can be less than 3:100. In fact, in many applications it can be as little as 0,2:100.

Sand may be aggregated to depths in excess of 3 cm, the upper limit of depth being governed by many factors, in-c~uding particle size of the sand, concentration of polymer, amount of water used and the like. The volume of water used to disperse the polymer emulsion is preferably greater than 5 litres per square metre area of the sand.
Either fresh or saline water may be used.

According further to the in~entlon the polymer emulsion and the water are simply applied to the surface of a sand area, but it will be appreciated that the polymer ; emulsion/water may be mixed with a quantity of sand and the mixture applied as a layer to a surface.

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On evaporation of the water from the ~and a consolldated load-bearing crust i~ formed which can be u3ed for roads, runways and the liXe. In ~act, tha crust is ~n some ways superlor to aggregates prepared from cement, S whlch fre~uently crack`and bxeak under varying cllmatic ~ondltlon~ and u~age because of its ln1exlbility. By virtue o~ the Rmall quan~itles of dry polymer us~d, the treatment of ~ands accordlng to the lnvention can be even less expen31ve than aggregation with cement.

In our co-pendlng South Afrlcan Patent Application ~o.74/8240 there wa~ described a method of treatlng sand or soll by applying a oomposi~lon including a polymer in an amount to provide from about 0,01 to about 0,5 parts of polymer ~o lOO parts of sand so ~hat the particles are rendered non-wetting and free flowing.
It is a further ob~ct of the present ln~ention o combine the two desirous propertles. Thus, accordlng fur~hex to the invention sand 15 rendered water-repellant and then treated wi~h mechanical mixing by ~he method . ac~ordlng to the present invention.

A~ mentioned above, ~he term "sand" includes sandy soil and it has been found that the inventlon works best in soils having le~s than 10 percent by wei~ht of clay having regard to the total inoxganlc fraction.

Mo~ polymer types may be used to carry out the pre~ent .. . ., .. . .. . _ . , _ _ .. . .. . . . . . ...

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~' -. . , ~o~s~ss invention ~ for example polyvinylacetate homopolymers, vinyl acetate-acrylic copolymers, acrylic-acrylic copoly~
mers and the like are all effective with the correct skabiliser system, which is easily established by simple trial and error. However, the following examples are given as a guide to the performing of the invention.

Example 1.
A 100 square metre area of very steep gold mine dump s~nd was sprayed with a diluted emulsion of externally-plasticised polyvinylacetate homopolymer emulsion.

The polyvinylacetate emulsion at 58~ solids content and a surface tension of 49 dynes per cm was diluted 30 times with water and then sprayed onto the sand at a rate of 10 litres per square metre. The metering was achieved by a venturi system at the exit end of the hose and mains water was used.

The sand was allowed to air dry and within 7 days a crust about 7 ceniimetres thick had formed. m is crust easily bore the weight of a heavy man and only with great difficulty could it be penetrated.

Example 2.

A flat area of reclaimed marine sand was sprayed with an externally plasticised polyvinylacetate homopolymer emulsion.

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~7S9~5 Saline water was pumped onto an area oE reclaimed marine sand at a rate of 150 - 300 litres per minu-te.
The 5~% sollds emulsion at a surface -tension oF 50 dynes per cm was bled into -the intake side of a cen-triEugal pump to give a final emulsion solids of 1 - 3%. The liquid was applied at approximately 25 litres per square metre. After 2 weeks' air drying a crust some 12 centimetres thick had formed which - supported the weight of a commercial vehicle driven across it.

E~ple 3.
An area of reclaimed marine sand was sprayed with ; fresh water containing 1% solids of a colloid stabilised polyvinylacetate homopolymer externally plasticised with a low level of dibutylphthalate. The 1% solids emulsion was applied at the rate of 20 litres per square metre. This was immediately followed by -the same emulsion but diluted less to give a high solids ; content and applied at a rate of 5 litres per square metre.
The whole area was lightly compacted and allowed to air dry. An effective aggregation to a depth of 15 cms was obtained.

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After 7 days~ drying a vehicle of approximately 3,000 kg was driven over the area without any ill effects to the aggregate. Because of the ~igher binder content in the wearing surface, little damage was caused by the tyre movement.

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In order to compare the efficacy of some colloid stabilizexs with those of surfactant stabilizers tested to date, emulsions con~aining completely or preclominantly vinyl acetate as monomer were polymerised using different stabilisers. The resulting emulsions were diluted with water to give a solid ~ontent of 1,0%. Marine sand (180 g) was slurried with 34 g of this diluted emulsion and then poured into a mould and compxessed slightly. The sand was dried at 50C
and the orce necessary to break the resulting aggregates was measured on a Richard ~upture Tester.

Results were as follows :-;
St-abiliser S~st~mMean Modulus of Ru~
(millibars) Surfactant (Dowfax 2Al) -(Trade Mark) 0 Cellulose (Matrosol)- Trade Mark (Hercules) 499 Polyvinyl alcohol 1598 Gums (gum acacia, gum arabic) 3103 m e colloid stabilised emulsions which include the celluloses, acrylics and gums have sand aggregating properties whereas the surfactant stabilised types so far tested have none.

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Emulsions containing as monomers vinyl acetate only, vinyl acetate-2 ethylhexylacrylate and methylmeth-acrylate-2 ethylhexylacrylate were manufactured using the same colloid stabiliser. m e methylmethacrylate~2 ethylhexylacrylate emulsion was also produced again but replacing the colloid stabiliser with a surfactant stabiliser. me resulting emulsions were diluted to 1,0% solids and 34 g of this was used to slurry 180 g of beach sand. ~his slurry was poured into moulds, dried at 50C and when dry the rupture strengths of the aggregated sand was measured on the Richards Rupture Tester.
Results were as follows :-Polyme~ pe Mean Modulus of Rupture (millibars) Vinyl acetate only 3734 Vinyl acetate-2 ethylhexylacrylate 1893 Methylmethacrylate-2 ethylhexyl-acrylate (colloid) 1699 Methylmethacrylate-2 ethylhexyl-acrylate (surfactant ~(Dowfax 2A1) (Trade Mark) 0 Irrespective of the monomers the colloid stabilised emulsions res;ulted in good sand aggregation.

Exam~le 6.
In order to reduce the effect of water on the strength ~ ~ .

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~075~55 of sand aggregated by -the techniques described in -this paten~, use was made of -the wa-ter repellency effect outlined in our previously referenced South African Patent 7~/8240.
In accordance with the ~rior patent, marine sand of particle size less -than 710 micron was made water repellent. This loose sand tl80 g) was mixed with some difficulty with (35,5 g) a 1% solids emulsion of a gum stabilised polyvinylacetate tPVAc)/homopolymer externally plasticised with dib~tylphthalate. The sand polymer slurry was poured into a stainless steem mould and dried at 55C~"for 17 hours. As a control ordinary marine sand was mixed with the same amount of the PVAc emulsion.

When dry the consolidated sand samples were sub~ected to the Richards Rupture test and their water uptakes measured after 17 hours submersion.
The results were as follows :-Polymer Type Modulus of Rup-ture Water Uptake in %
(millibars)(17 hours submersion) PVAc homopolymer (ordinary sand) 3633 21,0 PVAc homopolymer - (pretreated sand) 3989 6,4 - The pretreated sand has considerably increased the ';, g_ 5~55 waterproofing propertie~ of the PVAc-sand aggregate.

Example 7.
By ~che correct balance of emulRlon stabillsers lt wa~
poqsible in one polymer to achleve bo~h bond strength and water r~pellency ~as per our prior South African Patent 74/8240).

Marine ~and of partlcle slze less than 710 mlcron was mixed with a vinylacetate-vinyle~ter of versatic acid copolyn~r diluted to l~ solids ln the ratio o~ 180 g to 35,5 g. Thls ~mulslon was made using a blend of colloid and surfactant stabillsers. The resulting ~lurry wa~ cast into a mould and dried at 55C for 17 hours.

As contr~ls, a purely colloldal stabllised emulslon and s~parately a purely surfactant stabllised emulslon were included using the same grading o~ marine ~and and same welght to w~ight ratios.
Re3ult~ were a~ follow~ :-Stabill~er Type Modulu~ of Rupture Water U~taXe in %
(mlllibass) ~17 hours submers~o~
Colloid 352~ 24,1 Surfact~n~ 0 6,6 Colloid-Sur~actant blend 529 12 ,2 The collold stabilised ~ystem gave good stre~gth but poor Water repellency. In contra~t t~e surfactant , i4S5 stabilised system had no sand aggregating properties but excellent water repellency. The emulsion using a blend of Golloid and surfactant as stabilisers imparted intermediate aggregating and water repellency properties~

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Claims

1.
A method for aggregating sands to a depth exceeding three centimetres including the step of applying a polymer emulsion which has been stabilised with a colloid stabilser in a volume of water at least thirty times by volume the amount of polymer used, to a body of sand, and allowing to dry.

2.
The method of claim 1 in which the ratio of dry polymer to sand is less than 3:100 and in which the volume of the diluted polymer emulsion used exceeds 5 litres per square metre of sand.

3.
A method of aggregating sands to a depth exceeding 3 centimetres and also to form a waterproof aggregation, including the steps of first treating the sand particles with a composition including a polymer emulsion in an amount to provide between 0.1 and 0.5 parts of polymer to 100 parts of sand and then secondly applying a polymer emulsion which has been stabilised with a colloid stabiliser diluted in a volume of water at least thirty times the volume of the polymer emulsion used, and allowing to dry.