A number of industrial products have been and are stilt used for earth stabilization for building purposes. These consist either of synthetic products, or of by-products, and may even be industrial wastes. Others in this category may be natural products, which require sophisticated processing.
Conditions of use
Conditions of use vary depending on each type of product. Manufacturers' recommendations must therefore be consulted. Certain products must be handled with care, eg acids. Others, such as amine quaternary derivates, which are intended to be used in very low concentrations, are difficult to mix m evenly. Finally, others, such as silicates and certain resins, for example, need to be prepared before use. These products are generally not very satisfactory from an economic point of view and their effectiveness is often doubtful. Some of these products have been known for a long time, while others have been abandoned. In general they are not widely used.
II. FIELD OF APPLICATION
List of products
The main "families" of products can be fisted as follows:
04 quaternary amine derivates
12 industrial wastes
13 to 17 various resins
These are products which Vary widely in nature, and a some of them are efficient only if used together with other stabilizing products. Soda, for example, is used as an additive to cement or lime. The use of these products often depends on their local avaitabitity.
The products are used for mass stabilization of materials but mainly of render mortars, given the fact that they often have a high unit cost which limits their extensive use. The most commonly used products are salts for mortars
and renders, which provoke colloidal reactions, modifying the characteristics of water and resulting in flocculation. But salts are incompatible with cement which restricts their use with cement-stabilized compressed earth blocks. Amine quartenary derivates can sometimes serve as a base for commercial products as a body mass or mortar stabilizer. They act as a binder or water-repellent, either directly or in conjunction with cement or bitumen. Silicates are fairly cheap and often available; they perform welt with sandy son's and have a waterproofing action.
Nature of products
Using acids always entails some degree of risk. Each type of acid gives a specific reaction. They modify the pH of the soils in which they are incorporated, resulting in flocculation, the effects of which are often reversible. Some acids act as catalysts to form insoluble phosphates. Hydrochloric acid (MCI) and nitric acid (HNO3) result in moderate stabilization. Hydrofluoric acid (HF) is very effective in all soils except those with high aluminium contents, inducing a reaction which brings about the formation of insoluble and strong silica fluorides. The effectiveness of sulphuric acid (H2SO4) is doubtful. If phosphoric acid (H3PO4) is incorporated, a hydration reaction is set off with the formation of phosphoric anhydride (P2O5) which reacts with clayey minerals, and the creation of an insoluble gel of aluminium and iron phosphates, which cement the grains together.
Sodas induce cementation by reacting with minerals which produce insoluble silicates and aluminates. Caustic soda (NaOH) acts as a dispersant by degrading the minerals by alkaline attack. The product reacts vigorously both with lateritic soils and with soils having a high aluminium content. The best strengths are obtained when an adequate curing period for the material is allowed. Caustic soda is not suitable for soils with a high montmorillonite content.
The following are also known to be used:
barium hydroxide: Ba(OH)2. 8H2O
calcium hydroxide: Ca(OH)2
potassium hydroxide: KOH.1/2H2O
Iithium hydroxide: LiOH. H2O
Salts acting on soils induce colloidal reactions, alter the characteristics of the water and lead to flocculation. By increasing the attraction between fine soil grains, salts help to create larger particles. This flocculation reaction leads to a reduction in density and an increase in OMC, in permeability and in strength, but also to a reduction in plasticity. Salts act on pore water and reduce the loss of water from the soil, slowing evaporation, and reducing water absorption. However, the effectiveness of treating soil with salt depends on the extent of moisture movements in the stabilized material. The treatment is not always lasting, as the salts can be leached out and dissolved when the material is moistened again. The quantity of salt required is approximately 0.5 to 396. Four main salts are used:
sodium chloride: flocculent and aid to compaction; effective in non-saline soils;
calcium chloride: impermeabilizing agent;
ferric chloride: powerful coagulant and flocculant;
aluminium chloride: electrolytic coagulant, electrochemical consolidation of soil.
Salts should never be used in conjunction with cement.
04 QUATERNARY AMINE DERIVATES
Some cationic quaternary amine compounds are used alone or occasionally as secondary additives to cement or bitumens in concentrations of 5 to 10% of the cationic exchange capacity of the clay fraction. They act as binders and water repellents. They require a sophisticated production process and they are difficult to mix with soil when only low concentrations are involved. These products are expensive and are not readily available. The most effective quaternary amine derivates are aromatic or aliphatic amines, and amine salts. These products are often effective in quantities as low as 0.5%. They form a water repellent film around the grains, which because of their tensile-active properties reduce capillary water absorption. These treatments are particularly suitable where capillary rise presents problems and may be suitable for foundations which are constantly exposed to moisture. The products may lose their effectiveness if they are immersed in water or if they are totally dried out over an extended period.
Sodium silicate is fairly cheap and available in many parts of the world. The quantity usually used is 5% and it has proved to be attractive for stabilizing sandy soils, clayey and silty sandy soils, soils rich in limonite (some laterites) in arid regions, and in general soils which lack cohesion. Sodium silicate also acts as an impermeabilizing agent, particularly where a surface treatment of the materials is required. A curing period of at least seven days is required if the effectiveness of the treatment is to be assured. The product is highly soluble but can be rendered insoluble by allowing it to react with slaked lime. Sodium silicate can be dissolved in water and is then known as "waterglass". Other silicates may be used such as potassium silicate and calcium silicate.
Stearates are salts or esters of the stearic acid contained in animal fats. They act as impermeabilizing agents. Aluminium and magnesium stearates as well as zinc stearate may be suitable.
Paraffins are a mixture of solid saturated hydrocarbons characterized by their inertness in the presence of chemical agents. They can be used as a compaction agent but must first be dissolved in a fatty medium.
Industrial waxes can be used as an aid to compaction. They are often added to other stabilizers.
Industrial or synthetic latex dissolved in water and added at the rate of 3 to 15% can give good results. These products are binders and impermeabilizing agents.
10 SYNTHETIC ADHESIVES
Synthetic glues with one or two components can be used. The one known to give very good and surprising results is the common polyvinyl acetate based white wood glue.
The use of between 0.1 and 0.2% of ionic detergent has no effect on strength but reduces water sensitivity by about 25%
12 INDUSTRIAL WASTES
Certain industrial wastes can be used for stabilizing soil.
SUMP OIL: This has no lasting effect, because it is washed off by rain. It is an impermeabilizing agent.
BLAST FURNACE SLAG: These are silica slags which can approach Portland cement in composition. They are usually finely ground and blended with Portland cement to produce Portland blast furnace cement, whereby the slag content can reach 80%.
LIGNIN AND LIGNOSULPHATES: These are by-products of the wood industry. Soluble in water they can be rendered insoluble by mixing with chrome salts (potassium or sodium bichromate) resulting in a thick gel, known as chromolignin. They are good waterproofing agents, but expensive.
MOLASSES: A product of the sugar industry, this improves compressive strength and reduces capillarity, A quatity of 5% is suitable for sandy and silty soils. Add lime for clayey soils.
POZZOLANAS: These are materials that contain silica and/or alumina, eg fly ash (from power generating stations), burnt clay (rejects from brick production) and rice husk ash. They are not cementitious themselves, but when finely ground end mixed with lime, the mixture will set and harden at ordinary temperatures in the presence of water, like cement.
OTHER PRODUCTS: Plastified sulphur sulphonates and siliconates (water repellents).
13 FURFURAL-BASED RESINS
Furfural is a toxic aldebyde found in grain alcohols and in the following materials: rice hulls, peanut shells, cotton seed, cane-trash, maize cobs and stalks and olive pits. It is present in percentages ranging from 10 to 20%.
FURFURAL ANILINE: A resin formed from furfural and aniline, which is a cyclic amine derived from benzene, and is nowadays obtained from coal. Mix 70% of aniline with 30% of furfural. The product is highly toxic and between 2 to 6% is adequate for soil stabilization. It makes grains water repellent by ionic exchange and cements them together by polymerization.
FURFURYL ALCOHOL: This is an organic compound derived from furfural. It polymerizes in the presence of certain catalysts giving rise to polymers with excellent mechanical properties. It improves both dry and wet mechanical strengths, and slows water absorption.
RESORCINOL-FURFURAL: This product is used in an aqueous solution catalyzed by soda in a basic medium. It is toxic and often very expensive.
FURFURAL-UREA AND PHENOL-FURFURAL: Stabilizers which have been tested alone or mixed with furfural aniline: disappointing results.
14 FORMALDEHYDE-BASED RESINS
Formaldehyde is a volatile liquid obtained by the oxidization of methyl alcohol. It is a toxic substance and its use should be limited to locations that are not often frequented by people or animals.
RESORCINOL-FORMALDEHYDE: This is a mixture of resorcinol, antiseptic phenol derived from benzene and formaldehyde. This yields a resin which acts by cementation and as a water repellent. Reduces water absorption.
PHENOL-FORMALDEHYDE: Results known to be satisfactory.
FORMALDEHYDE-UREA: The action of this compound is similar to that of furfural aniline.
CALCIUM-SULPHAMATE-FORMALDEHY DE: The results obtained have not been satisfactory.
MELAMINE-E;ORMALDEHYDE: Good results for dry strength, but a 50% loss of strength in a moist state.
15 RESINS BASED ON ACRYLIC COMPOUNDS
CALCIUM ACRYLATE: This water-soluble resin forms an insoluble gel with soil which is rubbery or stiff depending on the moisture content
ACRYLIC NITRATE: This resin is used for grouting. Cements and waterproofs. Acrylic amine nitrate, which is another derived compound has a similar action.
POLYACRYLAMINES: Cationic polymer.
16 UREA-BASED RESINS
DIMETHYLOL UREA: Gives the best known results for urea-based resins although wet strengths remain low.
17 POLYVINYL-BASED RESINS
POLYVINYLIC ALCOHOL: Non-ionic stabilizer which forms strong flexible films by the evaporation of the aqueous solution although it is soluble in water. Must be combined with natural oils or water repellents in order to be effective.
POLYVINYL ACETATE: This is the best product for sandy soils because it improves their cohesiveness. The product is completely destroyed if immersed in water.