Laterite Soils and Their Stabilization

Home , Laterite, Parent material, Parent rock

7. McLeod, Norman W., "A Cana• sium on Load Tests of Bearing Capacity dian Investigation of Load Testing of Soils, ASTM Special Technical Pub• Applied to Pavement Design," Sympo• lication No. 79, p. 83.

LATERITE SOILS AND THEIR STABILIZATION

Hans F. Winterkorn and E. C. Chandrasekharan Winterkorn Road Research Institute, Princeton, New Jersey

Synopsis Origin, occurrence, and correct identification of latente rock and soil are briefly discussed. The peculiar properties of latente soils are outlined and suggested methods of dealing with them are indicated. Results are reported of experimental studies on four latente soils and one intrazonal non-laterite soil, with special attention to their susceptibility to stabilization. The latter varied over a wide range Of the stabilizers used, Portland cement gave best results m some cases and aniline-furfural (2:1) m others. The presence of organic matter seems to play a detrimental role m many cases. The possible use of "oiled earth" properly fortified with anti-oxidants and bactericidal substances for low-cost roads in latente areas is briefly discussed

Of the important groups of the trop• From a purely scientific point of ical and subtropical soils of the world, view, the peculiar engineering prop• the laterite soils occupy a unique place, erties of laterite soils as extreme in regard to both their extensive oc• products of soil genesis call for an currence and peculiar properties. They extensive investigation and possible are widely distributed in such areas as elucidation, not only for their own India, Indonesia, Indo-China, Malaya, sake but also for a better understanding Burma, Western Australia, Mada• of the properties of less extreme soil gascar, Central Africa, the Guianas, types. The present work is confined Brazil, and Cuba (Fig. 1). From a to the engineering characteristics of world-wide political and economical these soils, especially those of impor• point of view^ study of these soils is of tance in low-cost road construction. vital interest because: (1) they nor• The development of the science of mally possess good tilth and excellent soil stabilization has given a scientific drainability, with plenty of solar energy footing to an understanding, though as and water available; with an adequate yet more or less qualitative, of soil supply of fertilizers they are capable behavior in highway and airport struc• of excellent yields and may well be tures (31). Most of the available in• destined to contribute in a major degree formation, however, pertains to soils to the food supply of the world; and (2) of the temperate zones. That soils of a great need exists for a suitable net• the different climatic zones vary ex• work of low-cost roads m these areas tensively in th6ir properties is well- already in their present under-develop• known. The necessity for a possible ed condition and even more so if their special approach to the study of the proper agricultural development is to tropical and subtropical soils has been proceed. emphasized by many authors (13, 27, 32, 33).

'See Point IV of the Truman Program, and PREVIOUS INVESTIGATIONS the British plans for assisting in the eco• nomic development of Southeastern Asia and Ever since the word laterite was of Africa. introduced, first in geology and later 11 in pedology, there has been a sea of the term bauxite came to be used only for controversy over its correct nomen• commercial alummum ores. Campbell clature and identification. Laterite (4) in 1917 called a material laterite owes its origin to the Latin word later only if it contained uncombmed alumina meaning "brick," and was first dis• in the form of the hydroxide. cussed in 1807 by Buchanan (3) purely In 1926 Harrassowitz (14) first on its field-occurrence: "It is one of characterized laterites as red soils the most valuable materials for build• enriched on the surface with oxides of ing. It is full of cavities and pores, and iron and aluminum. According to him contains a large quantity of iron in the the European red beds are of fossil form of red and yellow ochres. In the laterite origin. Marbut's (21) "normal" mass, while excludedfrom the air, it is laterites are those formed under the so soft that any iron instrument cuts influence of good drainage free from the it, and IS dug up in square masses with action of high ground water. He calls a pick-ax, and immediately cut mto the ground-water laterites the soils falling shape wanted with a trowel or a knife. within Fermor's first group. Mohr (23) It soon after becomes hard as brick, and believes that the laterite crust is the resists the air and water much better result of eluviation followed by erosion. than any brick I have known in India. . . He mentions five stages in the full de• The most proper name would be Lat• velopment of a typical laterite, viz. , erite from Lateritis. " * fresh ash soil, tarapan (juvenile soil), In 1911, Fermor (9), in a most brownish yellow lixivium, red lixivium, explanatory paper, defines laterite as and laterite. Periodic variation of being formed by a process which causes ground-water level (descent and ascent) the superficial decomposition of the appears to be a most important factor parent rock, removal in solution of in laterite formation. combined silica, lime, magnesia, soda and potash, and accumulation of LATERITIC SOILS hydrated iron, aluminum, titanium, and rarely, manganese. The latter were One of the important reasons for the termed by him "lateritic constituents. " confusion regarding the correct iden• A residual rock with 90 percent or tification of laterites is the large area more of lateritic constituents is termed of the tropical and subtropical zones a true laterite. This true laterite is to involved and the different degrees of be distinguished from the lesser groups, laterization encountered in the various viz., lithomargic laterites and lateritic parts. Martm and Doyne (21) used the lithomarges with 50 to 90 percent and silica-alumina ratio as a classification 25 to 50 percent of lateritic constituents criterion: respectively. The controversy over the identification of bauxite as a variety of Soil Type Si02/Al203 laterite was answered by Clark (7) in 1916 to the effect that there is no di• Laterite soil 1. 33 or less viding line between bauxites and later• Lateritic soil 1.33 - 2.00 ites - one shades into the other. Later, Non-lateritic soil 2. 00 and over

'This term used by Buchanan, meaning literally "brick disease", throws a peculiar The Si02/Al203 rather than the light on the problem whether "laterite" Si02/R203 ratio was employed for ana• refers primarily to the use of the material lytical reasons since iron may some• in construction or to its bnck-hke appear• times be in the form of ferrous oxide. ance. In several Indian dialects laterite is This leads to the paradox that formal- called "brick-stone" (itica cullu), in the istically the presence of iron is non• Tamil language it is called shun cull or "itch-stone" because its surface appearance essential for a soil to be termed laterite; resembles certain cutaneous disorders. The this, of course, is in direct contradic• Latin-derived English term happens to cover tion to the original definition of Buchanan both appearance and function. and overlooks the important role which 12 iron oxides play in the rock named later- (4) Non-accumulation of organic matter ite by him. Moreover, the presence of (5) Distinctive red color. iron in laterite soils is one of the most important factors that influence their B^ Characterization of the residual engineering properties. It certainly is weathering product "laterite". more appropriate to employ as class• ification criterion the silica sesquioxide (1) A tropical climate subject to alter• ratio: nations of dry or wet seasons or monsoons. Soil Type S1O2/R2O3 (2) A level, or very gently sloping, elevated land surface which is not Laterite soil 1. 33 or less subject to appreciable mechanical Lateritic soil 1.33 - 2.00 erosion (abrasion by ram and wind) Non-lateritic soil 2.00 and over (3) The chemical and mineralogicalcom-

a .^UrlU and XaUTillc SoiU (AFTER BOL'SHOI SOVETSKI ATLAS MIRA: JOFFE)

Figure 1. Distribution of Laterite and Lateritic Soils in the World.

It should be useful at this point to position of the exposed rocks to be juxtapose the presently accepted char• suitable for a supply of the lateritic acterization of lateritic and laterite constituents, alumina and ferric soils and the conditions stipulated in the oxide. revised theory of C. S. Fox for the (4) The texture of the rock to be (or tropical residual weathering product rapidly become during weathering) "laterite" (12, 19). sufficiently porous for the entry of percolating water, so that the condi• A^ Characterization of lateritic and tions for chemical action will be at laterite soils- a maximum. (5) The infiltrating water to remain in (1) Disintegration and decomposition of the interstices of the rock for long the parent material in the direction of periods annually, 1. e. , during the the end products of weathering. wet monsoon, but eventually to drain (2) Release and removal of silica. away in the dry period thus givmg (3) Separation of sesquioxides and fixa• maximum play to chemical erosion tion in the profile. (6) The infiltrating water to contain 13

either an acid or alkaline substance external manifestations of the gran- with which to react on the rock com• ulometry and the inherent affinity of ponents as well as to constitute an the individual particles or aggregates electrolyte and allow electro-kinetic to one another under different conditions phenomena to operate. of moisture and mechanical stress. (7) These annual processes to be in Consequently, the nature, mechanical operation for at least a geological strength, and the permanency of ce• epoch of roughly a million years mentation in these soils must be under• stood. This comparison shows that it is The granulating effect of organic relatively easy for a rock to become material is well known. However, the a lateritic or laterite soil, but that the resulting aggregations are usually soft chances to become a "laterite" are and friable, rather than mechanically severely restricted. strong. It is felt that the organic mat• The general acceptance of absence ter in laterite soils may be more im• of organic matter due to intense bio• portant for cementation because of its logic and inorganic oxidation assumed reducing effect giving the iron greater for the red soils of tropical areas has mobility than for its specific cementing been questioned by some authors who or water-repellmg power. Baver (1) testify to high organic content of some makes the following statement concern• of these soils. Joffe (19) states that ing organic matter and cementation in a red soil with organic content either laterite soils: is an immature specimen of laterite or "The only group of soils in which a falls in a category between laterites and correlation has not been observed be• podsols. This explanation, however, tween organic matter and aggregation is hardly touches the nucleus of the prob• the lateritic soils, where dehydrated ox• lem or organic matter in laterite soils. ides of alumina and iron are responsi• ble for stable aggregate formation. " PROPERTIES OF LATERITE SOILS In connection with the problem of organic matter it is of interest that the As has been excellently dealt with previously discussed Hawaiian clay elsewhere (13), laterite soils in their which exhibited such unique consistency natural state are granular in structure properties contained about 20 percent and are possessed of low plasticity and of organic matter (15). excellent drainability. In this state The existing situation indicates a they can carry heavy loadings. When great need for a fundamental study of remolded in the presence of water they the structure of laterite soils with often become clayey and plastic to the special emphasis on the actual type depth disturbed (34). An extraordinary and amount of organic matter present influence of the change in the natural including the role of micro-organisms moisture content on the plasticity and (1, 13, 28, 34). An integral part of density characteristics of a certain such a study must be concerned with Hawaiian lateritic clay of volcanic swell and shrinkage properties, with origin has been reported; depending cracking patterns, as related to the upon the natural moisture content, the degree of laterization and to the type plasticity mdex of this clay varied from and amount of organic matter, as well 245 to zero (13). Thus, it is easy to as with the effects of remolding (13, see that the conventional subgrade soil 27, 28) and of prevailing moisture test results may not at all reveal the conditions. true characteristics of members of the laterite soil group. PROBLEMS IN SUBGRADE COMPACTION AND POSSIBLE METHODS OF APPROACH GRANULAR SOIL STABILIZATION

Plasticity, density, and structural The engineering soil problems en• characteristics of soils are only the countered in laterite areas as related 14

to the nature of the soil material as well With respect to compaction, both m as to the environmental conditions have the laboratory and in the field, the been thoroughly studied and ably pre• task IS to search for and adopt suitable sented by Wooltorton (33). He was the mixing and compaction methods that first to point out the importance of would not destroy the granular structure swelling and shrinking for tropical soils and yet yield sufficient density. which by many "temperate-zone soil In the field extra care is needed if scientists" were believed to possess heavy machinery is employed. Ex• great volume constancy. His work perience has shown that primitive combined with concepts normally em• manual compaction of certain laterite ployed in Portland cement concrete soils has yeilded better airfields than design led to Winterkorn's work on compaction of the same soils with volume relationships in soil stabiliza• standard heavy-compaction machinery tion (27). Application of the volume and procedure. principle leads, for granular stabiliza• So far consideration has been given tion of laterite soils, to clay contents mainly to the problems encountered in greater than those given by the ASTM the engineermg use of laterite soils. Standard specifications. Obviously, This might give the impression that all the latter represent a specific solution laterites and laterite soils give trouble. of the general problem; but being This IS far from the truth. The phys• specific they are applicable only for the ical and chemical properties of the average illite clay soils and for the group of materials encountered range average climatic conditions of the from excellent to poor for engineering United States. purposes. The problem is one of Specifically, Wooltorton (34) sug• recognizing the good, eliminating the gested: For no over-all swelling of a poor, and improving the intermediate coarse granular system: Plastic Index ones. This is well stated in a recent X Fines Content > Volume of voids a- paper by Christophe (6) treating spe• vailable between granular aggregates to cifically with the utilization of African accomodate swellmg, or a modification laterites as road construction materials. thereof when some swelling is permis• Many of Christophe's statements are sible. In place of the plastic mdex, so pertinent from a road building as shrinkage volumes may be employed as well as from a scientific point of view indicators of suitability of the binder that they are given in the following as portion, viz. , (a) liquid limit-shrinkage abstracted from the original French. limit, where exposure conditions permit slakmg, or (b) field moisture equiva• The term laterite is applied to any rock colored lent-shrinkage limit where environ• red to dark maroon which is either in the harden• ing or m the decomposition stage as a result of mental conditions do not favor slaking. environmental variations. Laterites range from It is necessary to caution here that friable soils to hard rock similarly as lime stone the fines content as determined by the may range from marl to marble The use of laterites must be preceeded by a study of their ordinary standard method of mechan• properties. ical analysis for soils may be greatly The silty parts of the foundation soils must misleading; well developed laterite be eliminated. In granular soil stabilization soils with their granular structure are higher amounts of lateritic clays than of other clays are allowed The pH influences the clay not easily dispersed by the common content as determmed by sedimentation analysis. dispersing agents. Secondly, the con• The interpretation of sedimentation curves re• sistency limits may show large varia• quires great care. The strength of compacted tions in particular cases, depending laterites may go up to 2,000 kg per sq. cm. and higher upon the moisture content of the sample At the Ivory Coast a very excellent laterite and the extent to which it was remolded rock IS found of strength properties comparable during the tests. Special tests or to those of medium porphyry In equatorial Africa modifications of the standard tests may and especially at L'Oubangui-Chari pudding stones have to be developed to serve as indices predominate In Togo amorphous laterites a- bound, in the Haute Volta strong lateritic gravels for the plasticity and swelling character - are found. In the Sudan, under the present istics that form the basis for proper dry climate, hills of laterite rock are eroded design. 15 to a considerable extent. In laterite soils one soil-stabilizer specimens of Proctor can always find more or less rock-like aggre• gations. density, moist or dry curing for 7 The affinity of hard laterite to asphaltic bitu• days, exposure to four cycles of freez• men IS good, similar to the affinity of bitumen ing and thawing*, four cycles of wettmg to Basalt and lava, but the presence of silt hinders and drying*, and 7 days immersion in the proper contact between the hard laterite and bitumen Laterite used in bituminous construc• water, respectively, with subsequent tion should not contain too much loam or clay determination of the compressive Design must be based on the results of preced• strength in a Carver hydraulic press. ing tests Pougnaud, chief engineer of Abidjan, The susceptibility to stabilization is has treated laterite by impregnation and subse• rated on the basis of compressive quent surface treatment The oldest job is 13 years old and still in good condition. Treatment strength values, combined with a qual• with cut-backs yeilds good results if it is thor• itative judgment of the nature of failure oughly mixed with the soil Improvement of etc. granulometry is recommended to obtam greatest strength. This can be done by breaking amorphous laterite down to sand size The expense of this STABILIZERS USED is compensated by the resulbng smaller bitumen requirements, for the base and surface treatment. The stabilizers used and the nomen• Laterite clays make excellent binders for stabilized soil roads. In the case of soils com• clature employed are given in the rel• posed of pisoliths (lateritic gravel) and fines, evant tables of results of the stabiliza• compaction alone is sufficient, and results in tion tests. Only Portland cement, MC- bearing values of 60 or more. Hydrocarbon 3 cut-back, and aniline-furfural (2:1) binders have good adhesion to laterite rocks Excellent bitummous concrete has been made with were used with the Havana and Catalina such rock. Amorphous laterites should be com• soils while these and a variety of other minuted and well-mixed in order to obtain a stabilizers were employed with the homogeneous material. Compact laterite rocks Matanzas soil. The tests with the Nipe Jiave sufficient strength to be used as a construc• soil were confined to the respective tion material for highways as broken stone, gravel, etc. However, it is indispensable to soil-cement system. The data reported judiciously choose the borough pit. for the Guinea soil were obtained during an investigation undertaken for Portu• The statements by Chnstophe ob• guese Guinea, which had as object the viously refer to actual "laterite" or utilization of local low-cost vegetable material coming very close to it. The materials in low-cost road and air• e}q)eriments described in the following drome construction. The common deal with the more troublesome laterite stabilizers, Portland cement and as• - lateritic and non-lateritic soils oc- phaltic cut-backs, had been employed curing in tropical regions. originally only for purposes of com• parison; however, the failure of these EXPERIMENTAL INVESTIGATION materials to stabilize the soil in question prompted a search for the underlaying reasons. Five soils, two laterite, two later• itic and one non-lateritic, were em• ployed in the experimental investiga• PREPARATION OF THE SPECIMENS tion (Table 1). The latter was concerned with: (1) physical and physico-chemical Soil (passmg through No. 10 sieve) tests and (2) stabilization tests with was mixed with predetermined quan• external additives. tities of water and stabilizer in a Hobart Consistency limit and thermal anal• mixer and compacted m a Dietert ysis tests were made on all materials. machine. Solid stabilizers such as The Matanzas soil was studied m great• 'Freezing and thawing: 4 cycles, each cycle er detail, with respect to mechanical consisting of 8 hours of freezing and 15 analysis. Proctor compaction, perme• hours of thawing. ability, base exchange capacity, etc. Only a limited number of tests were *Wetting and drying: 4 cycles, each cycle performed on the other soils. consisting of 3 hours of wetting and 20 hours The stabilization tests consisted of of drying. preparation of 2-by 2-m. cylindrical 16

TABLF 1

DESCBIPTIOS' OF THE SOILS USED FOR EXPERIMENTAL INVESTIGATIONS

Organic Clay Minora Soi] Name Profile Matter Paren t from Therma Gi ven Description of the Soil Characteristics Presen t Materla1 Analysis

Matan203 Dark red, we11 granule- A2 horizon 0 15 Yes Lime Hydrated ted 1aterite soiI from to 1 10 ft (rather Rock Halloysite Cuba below ground high) (coco') with some 1 evel gibbsite

Havana^ Ashy gray, clayey tro• horizon 0 50 Yes Lime Mixture of pical soil from Cuba to 2 75 ft (rather Rock 1111te and (Probably similar to below ground 1 ow) (coco') mentmori110 the *'C*' horizon soil level ni te of the Matanzaa series)

Cata1ina Yellowish-red later- B and C hori• Yes Andesi- Kaolinite itic soil from Puerto zons 1-5 ft (rather tic tuff Rico, not well granu• below ground low) & tuffa- lated level ceous shal e

Guinea Light red, sandy later- Yes Kaolinite itic soil from Guinea (very -- Africa high)

Nipe Dark red, well granu• B2 horizon-- Yes Serpen• Kaolinite lated laterite soil 2 to 5 ft (rather tine wi th from Puerto Rico below ground low) Rock gibbsite level

Contains more than 50 percent CaCOj

Portland cement and lime were first Best specimens were obtained by mixed dry with the soil; subsequently, employing the lowest speed of the mixer water in an amount calculated to satisfy and molding the specimens when the mix the moisture requirement of the soil presenteda very loose granular appear• and the hydration needs of the stabilizer ance with uniform moisture distribution. was added. In the case of semi-solid Observations of the behavior of the and liquid stabilizers, the concept of laterite and lateritic soils in the prep• optimum liquid content was used. The aration of specimens with a large reported percentages of the stabilizers number of stabilizers brought out the are based on the dry weight of the soil. importance of avoiding over-mixing, The preparation of soil-cement not only for soil-cement, but also for specimens at the standard optimum the other systems. Excessive mixing moisture content m the earlier attempts destroys the desirable granular struc• posed a problem due to the fact that the ture of the soil. However, with bitumi• soil-water-cement system presented a nous materials the dispersion was poor rather sticky consistency, hardly con• and did not improve significantly, even ducive to obtaining well defined sam• with continuous and intimate mixing. ples. A close observation of the mixing The non-lateritic Havana soil alone process showed the existence of a showed a uniform mix with the bitu• gradual change of the mix from the minous stabilizer. granular texture to a rather sticky Aniline and furfural were added consistency. This was much pronounced separately in the respective order to with an increase in the speed and time the soil-water system and the mixing of mixing. contmued after the addition of each. 17

TABLE 2

PHYSICAL CHARACTERISTICS OF THE MATAflZAS SOIL

A Granulation Characteristics

1 Dry Sieve Analysis Characterizing Natural Granulations

Sieve No. Percentage Paasing (by weight of total)

4 77 1 10 59 1 40 23 95 200 2 50

2 Aggregate Analysis in an Elutriator

Sue of Aggregates Percentage by Weight

> 0.1 mm 84 45 0 1 - 0 05 mn 7 85 0 05 - 0 02 mm 3 73 < 0.02 mm 3 97

Mechanical Analysis on Soil Passing No 200 Sieve, Sedimentation Method

Size and Description Without After After Removal ' of Particles Treatment Treatment of Fe and Al Oxides

Sand >SCl fl 6 9 31 4 37 4 Coarse silt S/i - 50/1 28 3 61 97 38 64 Fine silt 5^ - 2/Ll 12 8 3 17 15 30 Clay < 2 51 9 3 46 9 59

B Consistency Limits

Fresh Soil Moisture Soil air-dried for a long time Content 20.5 Percent (Moisture Content 4 7 Percent)

Description With With of test Remolded Minimum Remolded Minimum Handling Handling

Liquid limit 53 0 46 2 52 6 45.9 Plastic limit 31 2 31 2 32 1 32 1 Plasticity Index 21 8 15 0 20 5 13 8 Shrinkage Limit 20 8 31 5 20 32 26 8

Other Tests In Water In tetrahydronephtholene 1 Specific gravity 2 90 2 94 2 Compaction tests Proctor Modified AASHO

Optimum moisture 30 % 25 5 % content

Maximum dry density 88 95.25 in lb per cu ft

Permeability coefficient from consolidation test at 4 8 tons per sq ft 3 x 10"^ cm per sec

^Jeffries " Rapid Method for the Removal of Free Iron Oxides in Soil Prior to Petrographic Analysis " Proc Soil Science .Society of America 211-212 (1946) 18

to set with moist curing for 7 and 14 days, respectively. All the other specimens were im• mersed in water for 7 days before testing for compressive strength.

MAT>SNZAa SOIL

UNTQCATCB COMPRESSIVE STRENGTH TESTS

On completion of the exposure tests the compressive strength tests were performed at room temperature and the nature of failure noted.

PHYSICAL AND PHYSICO-CHEMICAL PROPERTIES

t^C^ TBCATCD The results of the tests are given in Tables 2, 3, and 4.

HAVANA SOIL

UNTOZATCD

CATALINA SOIL

TE¥PCBATWC - Ka.C Figure 2. Differential Thermal Curves of -200 Fractions of the Soils. SUINCA soil, CURING a TfiCATED

All the Portland cement and lime specimens were moist cured. One- half of the number of specimens con- tainmg organic cementing or water• proofing agents were moist cured, the other half were dry cured the same procedure was followed with the sodium- silicate specimens.

EXPOSURES NIPE SOIL M^Cl TOCATED Separate sets of the lime and Port• land-cement specimens were subjected to the three kmds of exposure tests TCMPCRATXIRC - DCO.C. mentioned previously. The only ex• Figure 3. Differentia] Hiermal Curves of ception was the Guinea soil which failed -200 Fractions of the Soils. 19

MATANZAS SOIL the effect of remolding on its consist• ency properties was made. The change The results of the sieve analysis in the initial moisture content did not and aggregate analysis signify a very affect the values to any significant high degree of stable aggregation of extent. On the other hand, the role the primary particles of the soil in its played by the structure is indicated natural condition. clearly by the increase of the plasticity No proper dispersion could be ob• mdex by 40 to 50 percent in the case of tained employing agents such as sodium the remolded soil, as compared with silicate, sodium hydroxide, sodium the value obtained when structural carbonate, ammonium hydroxide, or a disturbance due to the test itself was mixture of sodium hydroxide and sodium held at a minimum. oxalate. The other tests conducted on this soil show a high specific gravity of CONSISTENCY LIMITS 2. 94, high permeability of 3 x 10 cm per sec. , a low affinity for water, and A study of the effect of change in the a low base exchange capacity of 6. 6 initial moisture content of the soil and me per 100 grams. The thermal curve

TABLE 3

PHYSICO-CHEMICAL PROPERTIES OF THE MATANZAS SOIL

1 Hygroscopicity at 25 C 22 4 5 7 2 8

2 pH value of soil-water slurry (1 1) 6 30

3 Base exchange capacity by conducto- metric titration 6 6 m e 100 gms

4 Carbon content by combustion analysis 2 0 Percent

5 Clay mineral from thermal curve Hydrated helloysite with some gibbsite

TABLE 4

A Physical and Physico-Chemical Characteristics of Havana, Catalina, Guinea and Nipe Soils Name of No Soil L L P L P I S L. Clay Mineral From Thermal Curve

1 Havana 62 2 36 7 25 5 26.5 Combination of illite and montmorillonite (non- lateritic)

2 Catalina 72 0 53 7 18 3 25 9 Kaolinite (lateritic)

3 Guinea Kaolinite (lateritic)

4 Nipe 48 3 38 0 10 3 25.7 Kaolinite with some gibbsite (laterite)

B. Results of Additional Tests on the (Aiinea Soil

1 Wet Sieve Analysis Passing Sieve No Percent by Weight

4 100 10 95 40 38 200 12

2 Maximum dry density of Proctor Compaction 113 5 lb. per cu ft

3 Optimum moisture 10 3 Percent 20

shows presence of gibbsite in an essen• 14 percent. Further increase to 16 tially hydrated halloysite, the presence and 18 percent did not improve the of gibbsite probably indicating a fairly strength values appreciably. It is high degree of laterization (Fig. 2, even possible that a lesser quantity of Table 3). cement (12 to 14 percent) may show satisfactory stability characteristics. HAVANA, CATALINA, NIPE AND Stabilization with lime was a total GUINEA SOILS failure; in fact, decreasing values of compressive strength accompany in• The limited number of tests per• crease in lime content. It is possible formed on these soils shows reduced that for lime stabilization a longer values of plasticity indices with higher period must be allowed for the carbon- degrees of laterization as seen from ation of the calcium hydroxide. Fur• the thermal curves. The Guinea soil thermore, if a soil contains acid or• had only 12 percent passing the No. 200 ganic matter, lime may stimulate the sieve, and an optimum moisture content growth of bacteria with detrimental of 10. 3 percent. action on mechanical resistance of the The thermal analysis shows the system. Havana soil to contain a combination of The dry-cured specimens failedcom- lUite and montmoriUonite clay min• pletely while the moist cured ones show• erals, which are typical for non-later- ed very poor compressive strengths. ite soils. The Catalina and the Guinea It IS, of course, realized that field soils show typical kaolinite clay mm- performance of a soil-bitumen system erals indicative of their lateritic char• cannot be judged correctly from com• acter. The Nipe soil shows kaolinite pressive strength values alone; how• with gibbsite, the latter an indicator of ever, such data are important for a higher degree of laterization (Figs. comparison of relative effectiveness. 2 and 3). The complete failure in one case and the very poor strength values obtained SUSCEPTIBILITY TO STABILIZATION ui the other, show the ineffectiveness WITH ADDITIVES of the bituminous stabilizer used or the method adopted. A number of mvestigators have Of the dry cured specimens, those reported good stability characteristics containing 10 percent of tar alone with• of systems of red and yellow soils stood the immersion exposure, but stabilized with Portland cement in showed rather poor strength. The moist amounts as low as 6 to 10 percent (5, cured specimens showed fairly satis• 30). Studies have revealed that soils factory values. Though in general, with high iron and aluminum contents stabilization with tar alone may not be are easily stabilized by means of bi• adequate, treatment with the latter tuminous materials and by silicate of resulted in distinctly better stability soda, the latter to be supplemented characteristics than treatment with with' a waterproofing agent (20, 29). corresponding quantities of MC-3 cut• The results of the present series of back. stabilization tests are given in Tables Both the dry cured and moist cured 5, 6, 7, 8, and 9. In the following specimens showed satisfactory values, discussion, only the most significant though a feeble tendency for slaking was features are pointed out. noticed during immersion of the dry- cured specimens. This, however, did MATANZAS SOIL (TABLE 5) not significantly affect the strength characteristics. The poor results, Fairly good compressive strength amounting practically to total failures values were obtained at comparatively with the use of the other stabilizers high percentages of cement. Steady and listed in Table 5 do not warrant sep• optimum strength conditions seemed to arate or detailed discussion. Note• be reached around a cement content of worthy tendencies, if any, are brought 21

TABLE 5

RESULTS OF THE STABILIZATION TESTS WITH MATANZAS SOIL

Type of exposures F-T 4 cycles of freezing and thawing W-D: 4 -cycles of wetting and drying IMM 7 days immersion in water

Description of Percent Compressive Soil-Stabilizer of Strength Specimens Stabilizer in P S I Remarks

I Inorganic Stabilizers

(a) Portland cement

moist cured 258 14 481 F-T Shear failures 16 506 18 550

8 132 14 296 W-D Shear failures 16 299 18 314 J

8 150 14 313 IMM Shear failures 16 351 18 354 J

(b) Lime - moist cured 14 F-T Crumbly shear failures 16 18

14 Slaked end failed on W-D 16 wetting for the second 18 cycle

14 IMM Crumbly sheer failures 16 18

Note All compressive strength values liated in the following parts of Table 5 were obtained after 7 days immersion of the specimens in water

(c) Silicate of sods (N-Brand 40 % Concentrated Solution) dry cured- Stabiliser added directly to soil Stabilizer added in an y aqueous medium

Silicate of soda

moist cured 12 Stabilizer added directly ]• to aoi1 Stabilizer added in an aqueous medium 22

TABLE 5 (Cont'd)

Description of Percent Compressive Soil-Stabiliier of Strength Specimens StabiUier in P S I . Remarks

II Organic Stabilizers

(a) MC-3 cut-back - dry cured £ -- Swelled, cracked and failed 8 -- 10 --

MC-3 cut-back - moist cured 6 10 After exposure all specimens 8 12 5 - were wet but did not show 10 13 failure

(b) Tar BT-6 - dry cured 6 Both 6 and 8 percent samples 8 } swelled, cracked and failed Cracked slightly and showed 10 8 } some compressive strength Tar RT-6 - moist cured 6 30 Plastic failures 8 33 10 33

Aniline-furfural (2 1) - moist cured 2 46 3' Crumbly shear 3 52. [) - 4 70 3

(d) Resins* (abietic acid) - Considerable slaking was dry cured 0.5 17. noticed in all cases. The 0 75 18 1 percent specimens were of 1 00 7 poor mold

Hesins (abietic acid) - moist cured 0 5 8 Crumbled 0 75 8 1.0 14

(e) Abietic salt Resin 321 - dry cured 0 5 0 All the specimens slaked 0 75 3 considerably 1 0 5

Abietic salt Resin 321 - moist cured 0 5 11 Crumbled 0 75 11 1.0 10 23

TABLE 5 (Cont'd)

Description of Percent Compressive Soil-Stabilizer of Strength Specimens Stabilizer in P.S.I Remarks

III Bitumen and Admixtures

(a) cut-back MC-3 + 10% gasoline -

dry cured 8 Slaked and failed

moist cured 8 Plastic failure

(b) 8% cut-back MC-3 + 10% kerosene + 0 8% aniline-furfural (2 1) - dry cured 0

moist cured 35 Crumbly shear failure

dry cured Specimens slaked considerably in both cases moist cured

(d) 8% tar RT-6 +0.8% anlllne-furfural 2 1- Specimens slaked completely dry cured and failed

moist cured* 30> Plastic failure forward. susceptibility to stabilization with Silicate of soda was a complete Portland cement, and a rather satisfac• failure in immersion for both dry and tory one with aniline-furfural; the moist cured specimens. Both abietic general results are, however, quite acid and abietic salt (Resin 321) showed below the level that would normally very poor strength values. The addition be expected of this well developed of gasoline as a dispersing aid for the laterite soil. MC-3 treatment gave no improvement. However, definite improvement resulted from the addition of a small percent• HAVANA SOIL (TABLE 6) age of aniline-furfural to the MC-3. Further addition of pentachlorophenol in The specimens failed almost com• the combination gives even better pletely in the wetting and drying tests results. These observations are in with Portland cement. In the other Ime with previous fmdings on the m- exposures, the specimens showed fluence of these activators. The addi• relatively poor strength values consid- tion of anilme-furfural to the RT-6, ermg the high percentages of cement however, did not show any marked employed. change in the strength values. In view The stabilization with the MC -3 was of the excellent compatibility of anilme- a total failure for both moist cured and furfural with coke-oven pitch, the dry cured specimens. The fact that observed behavior with the RT-6 may moist cured samples with 6 percent of be due to the character of the cutting cut-back were relatively more stable oil. than those with 8 and 10 percent is note• The results obtained with soil of the worthy. The soil contained a consider• Matanzas series show a fairly good able amount of lime. 24

Only the moist cured samples with• difficulty in stabilization with the con• stood the exposure tests, with aniline- ventional stabilizers. furfural showing better strength values than the cut-back MC-3. Optimum CATALINA SOIL (TABLE 7) performance possible with this resin was not achieved, however, since the The specimens failed completely in calcium carbonate in the soil neutraliz• wettmg and drying in the Portland ed the acid catalyst and slowed down cement test and gave extremely poor the setting and hardening time of the values in freezmg and thawing. They resin. This is illustrated by the fact did better, though still poorly, in the that the lesser percentage of aniline- immersion test. It is significant that furfural, viz. , 3 percent gave better in the supposedly semi-rigid or rigid results than 4 percent. In the meantime, system of soil-cement, the specimens methodology has been developed to with as much as 16 percent of cement successfully stabilize calcium carbon• exhibited plastic failures. This brings ate-containing soils with aniline-fur• home the fact, observed separately on fural resin. pure soil-water specimens, that par• The Havana soil with its illitic and tially developed lateritic soils may montmoriUonitic clay mineral and high have a greater water affinity and con• calcium content presents extreme sequently more pronounced swellmg

TABLE 6

RESULTS OF STABILIZATION TESTS wmi HAVANA SOIL

Description of Percent Compressive Soil-Stabiliier of Strength Specimens Stabilizer in P S I Remarks

I Portland cement moist cured 114 • F-T Shear failures 131 - 164.

0} Failed on second wett&ng W-D 12 Failed on second wetting «> 16 70 J- Considerable slaking was noticed 128 • IMM Shear failures 175 - 182.

II Cut-bock MC-3 - 0 • dry cured 6 Swelled, cracked and IMM 0 . 8 failed within one day 0_ 10 of immersion

Cut-back MC-3 - 5" The 6 percent samples were moist cured 6 IMM 0 - 8 definitely better than the 0 . 10 8 and 10 percent ones by both appearance and strength III Aniline-furfural (2 1) dry cured Cracked and failed after 1 day IMM • > Cracked and failed after three days

Anil ine-furfural (2 1) moist cured* 30 y Plastic failure IMM 19" 20 Crumbly shear failure 25

TABLE 7

RESULTS OF STABILIZATION TESTS WITH CATALINA SOIL

Description of Percent Compressive Soil-Stabilizer of Strength Specimens Stabilizer in P S I. Remarks

I Portland cement moist cured o" F-T Plastic failures 12 3 - 16 25. Slaked and failed on 03- second wetting 12 Slaked and failed on second wetting but less W-D fast 16 Slaked and failed on third wetting

r Plastic failures IMM 12 0 - 16 0

II Cut-bsck MC-3 dry cured 6 0. • Swelled, cracked end failed IMM 8 0' Swelled, cracked and failed 10 0. • but retained the shape, showed no strength

Cut-back MC-3 moist cured 33 Plastic failures, cracks IMM 33 commenced with a pressure 10 40 of 10 to 20 psi

III Aniline-furfural (2 1) - dry cured 3 97 IMM Crumbly shear failures 4 68 5 143

Aniline-furfural (2 1) - moist cured 3 lay Plastic failure IMM 4 70' Plastic to crumbly shesr 90 and shrinkage characteristics than than the moist cured ones for any soil normally expected in view of the kao- with any organic stabilizer. The nature linite type of clay contained in such of failure of the moist-cured specimens soils. was crumbly shear. The strength and The dry-cured specimens failed water-resistance obtained with 3 per• completely with MC-3 cut-back. The cent of stabilizer were sufficiently good moist-cured specimens showed fairly to suggest lowering of the stabilizer good compressive strength for such quantity to 2 percent. The good values plastic systems. obtained here have an added significance The results obtained with anilme- because of the poor showing with this furfural are m sharp contrast to those soil of the other stabilizers, even at obtamed with Portland cement and high percentages. MC-3. Excellent compressive strength was exhibited by both the dry- and GUINEA SOIL (TABLE 8) moist-cured specimens. The dry- cured specimens, for the first time, The size composition as well as showed better strength characteristics the lateritic character of the soil under 26 investigation would indicate that it The low cohesion of this soil makes could be easily stabilized by means of it imperative that the organic stabi• any of the conventional materials, lizers possess cementing in addition to Portland cement, asphalt and tar. waterproofing properties. The proto-

TABLE 8

RESULTS OF STABILIZATION TESTS ON GUINEA SOIL (23)

Precent of Compressive Strength of the Soil-Cement Specimens

Portland Without

Cement additive 10% CaClj' 2% Hydrous AlClj" 2% Hydrous AljCSO^jj'

A' After 7 days curing

22 40 6 4 19 25 9 1 12 7 10 29 12 7 19

B Afttr 14 days curing

6 9 6 27 8 8 24 10 12 8 30

Percentage based on weight of Portland cement

TABLE 9

RESULTS OF STABILIZATION TESTS ON NIPE SOIL

Description of Moisture Soil-Stabilizer Content Compressive Specimen During Strength Mold ing in P S I Remarks

Portland cement used 8% - Moist cured

F-T 23 4° 27 5 W-D 23 4 77 IMM 23.4 53 3 Samples were bruised F-T 27 0 - 2 during molding W-D 27 0 77 0 IMM 27.0 Samples were bruised F-T 30.0 33 3' during molding W-D 30 0 43 0 IMM 30 0 43.3

Optimum moisture content as of Proctor

The results obtained with Portland type of a stabilized system to be achiev• cement were quite disappointing be• ed with this type of soil is "sand- cause the cement failed to set and bitumen" (8). harden. This condition was not helped The real problem in the stabilization by the admixture of calcium chloride of this specific soil was the presence as suggested by the Portland Cement of organic matter ranging in size from Association, nor by the admixture of easily recognizable fractions of peanut aluminum chloride or alummum sulfate. shells and roots to colloidal dimensions 27 and viable matter ranging from seeds of laterite and lateritic soils may vary to microbes. over a wide range from excellent to The seeds sprouted lustily in the poor. As a general rule, this suscep• soil-cement specimens; the microbes tibility increases with increasing de• proved to be especially active in the gree of laterization as evidenced by the immersion test and provided visual silica-sesquioxide ratio. This con• and kakodylic evidence of their ex• firms conclusions drawn from previous istence by reducing the red, iron-oxide work performed on temperate zone color of the soil to a dirty bluish-green soils in which iron and aluminum ions and by polluting the atmosphere. Sub• had been substituted for the exchange sequently, some oil-treated specimens ions of the natural soils. were immersed in water contained in (2) In the absence of the analytical an iron bath well covered with rust. data required for calculation of the The microbes not only changed the color S1O2/R2O3 ratio, clay-type determina• of the soil but, in addition, so thorough• tion by differential thermal analysis ly reduced and dissolved the rust of the may be used as an index to the degree bath that the latter showed a clean and of laterization. Highly laterized sam• shiny metal surface after the seven day ples contain aluminum and iron oxides, immersion test. possessing typical thermal curves, in The problem of the organic matter addition to the Kaolinite mineral which could be overcome by chemically ster• possesses a silica-sesquioxide ratio ilizing makro- and microbial agents of 2. present in the soil. The relative pro• (3) Soils possessmg a low degree of portion of organic matter in the fraction laterization may possess more pro• passing the No. 200 sieve can be glean• nounced swell and shrinkage character• ed from a comparison of the thermal istics than normally expected of red curves obtained on the unoxidized and lateritic clay soils. oxidized soil fraction. (4) Fairly high quantities of organic matter may be present m red tropical NIPE SOIL (TABLE 9) and subtropical soils. This organic matter, especially if biologically active, The tests with this soil were con• may prevent a soil from properly cerned mamly with the influence of responding to stabilizing treatment, mixing moisture on the properties of even though the soil be granulometncally soil-cement. The results are not well suited for such treatment. In such conclusive; but there is a tendency for cases, chemical sterilization preced• a decrease in strength with increase m ing or simultaneous with the stabiliza• moisture content at constant com- tion IS indicated. pactive effort. The data do not permit It may be appropriate to append a decision as to whether this apparent few considerations to this paper. De• effect IS a primary one of the moisture, pending upon environment, parent rock or a secondary one either caused by and time, soil forming processes may, easier destruction of structure during in the tropical and subtropical zones, mixing at higher moisture contents or produce materials ranging from hard by a resulting change of the density of laterite "rock" to non-laterite soils the specimens. See reference (30). similar to those found in temperate regions. CONCLUSIONS From the point of view of road use, either as an aggregate, or as a binder, The work described and documented or as a material to be treated with in this paper was concerned with a cementing or waterproofing agents, limited number of tests on a limited the material becomes more favorable number of soil systems. Despite these the farther it has progressed on the way limitations, the following conclusions to laterization. This indicates that the of general importance could be drawn: greatest problem in the road use of (1) The susceptibility to stabilization laterite soils arises from the effecton 28

the soil systems of the severity of Very special acknowledgment is due climate, especially the desiccation to F. L. D. Wooltorton for his close followed by the monsoon, rather than cooperation and very valuable advise from the inherent soil properties which with respect to tropical soils and trop• at the worst come to resemble more and ical road problems. more those of soils from the temperate regions. REFERENCES It stands to reason that granular soil stabilization has been more widely 1. Baver, L. D. , "Soil Physics," employed in laterite areas than the John Wiley and Sons, Inc. , New York, other stabilization methods. Granular 1948. stabilized soils suffer most from cli• 2. Besairie, Henri, "Les Soils de matic severity especially from long Madagascar," Recherches Sur le Sol desiccation periods. This is true not (Bodenkundliche Forschungen) Soil Re• only for tropical climate but also for search, Bol/Bd V, No. 3, International our own gravel roads in the great Society of Soil Science, 1937. plains and for the more frigid climate 3. Buchanan, Hamilton, "Journey of Argentine Patagonia, as judged from from Madras Through the Countries of the wind erosion m these areas. Mysore, Kanara, and Malabar," 1, 2, Considering these general facts, and and 3. London, 1807. also the specific properties of most 4. Campbell, J. M. , "Laterite: soils in the tropic regions, i. e., Its Origin, Structure and Minerals," cementation and structure which are The Minmg Magazine 17, 67-77, 120- best left undisturbed, it would appear 128, 171-179, 220-229, 1917. that the most promising method for 5. Catton, Miles D. , "Research low-cost road construction is "earth on Physical Relations of Soil and Soil- oiling" as described in the Current Cement Mixtures," Proc. Highway Road Problems Bulletin on "Soil Bi- Research Board, 21, 821-855, 1941. tummous Roads." Of course, the oil 6. Christophe, L. "Les Later- to be employed - and it may be any ites et leur Utilization Comme Materiau type of oil, asphaltic, pyrogenous from de Construction des Routes," Rev. coal, vegetable or animal origin, or any Gen. des Routes et des Aerodromes, other, must be well fortified with anti• Pans, France, No. 212, 38-50, Sep• oxidant and with bactericidal additives. tember, 1949. 7. Clarke, F. W. , "The Data of ACKNOWLEDGMENTS Geochemistry," U. S. Geological Sur• vey, Bulletin 616, 3rd Edition, 1916. A portion of this work represents 8. "Current Road Problems," No. material submitted by E. C. Chandras- 12, Soil Bituminous Roads, Highway ekharan m partial fulfillment of the Research Board, Washington, D. C. , requirements for the degree of Master 1946. of Science in Civil Engmeermg at 9. Fermor, L. L. , "What is Princeton University. Laterite," Geological Magazine, N. S. The major portion of this experi• Decade V, VIH, 454-462, 507-516, mental investigation was performed, 559-566, 191L however, by Chandrasekharan as holder 10. Fox, Cyril S. , "Buchanan's of the Indian Fellowship for the year Laterites of Malabar and Kanara," 1950-51 of the Winterkorn Road Re• Records of the Geological Survey of search Institute. This fellowship was India, LXIX, Part 4, 1935-36. established as a private implementation 11. Fox, Cyril S. , "The Bauxite of Point IV of the Truman program. and Aluminous Laterite Occurrences Acknowledgments are due to the of India," Memiors of the Geological Public Works Administration of Cuba, Survey of India, XLIX, Part I. the Soil Conservation Service of Puerto 12. Fox, Cyril S., "Laterite," Rico, and the Governor of Portuguese Encyclopedia Britanica, 13, 740, 1950. Guinea for supplying the soils in• 13. Fruhauf, Bedrich, "A Study vestigated. of Lateritic Soils," and Discussion by 29

Willis, E. A., Proc. Highway Research 26. Warth, H. and Warth, F. J., Board, 579-593, 1946. "The Composition of Indian Laterite," 14. Harrassowitz, H., "Laterite," Geological Magazine, Decade IV, V, Fortschrite der Geologie und Palaeon- 154-159, 1903. tologie 4, 253-566, 1926. 27. Wmterkorn, H. F. and Dutta 15. Hirashima, K. B. , "Highway Choudhury, A. N. , "Importance of E^^erience with ThixotTopic Volcanic Volume Relationship in Soil Stabiliza• Clay," and Discussion by Willis, E. A. , tion, " Proc. Highway Research Board, Proc. Highway Research Board, 481- 553-560, 1949. 496, 1948. 28. Wmterkorn, H. F. and Tsche- 16. Holland, T. H., "On the Con• botarioff, G. P., "Sensitivity of Clay stitution, Origin and Dehydration of to Remolding and its Possible Causes," Laterite," Geological Magazine, Decade Proc. Highway Research Board, 435- IV, X, 59, 1903. 442, 1947. 17. Humbert, R. P. , "The Genesis 29. Winterkorn, H. F. and Eckert, of Laterite," Soil Science, 65, 281- G. W., "Physico-chemical Factors of 290, 1948. Importance in Bituminous Soil Stabiliza• 18. Imperial Bureau of Soil Science, tion," Proc. Association of Asphalt "Laterite and Laterite Soils," Technical Paving Technologists, 11, 204-257, Communication No. 24, 1-30, 1932. 1940. 19. Joffe, J. S., "Pedology, " 30. Winterkorn, H. F. , Gibbs, H. Pedology Publications, New Brunswick, F., and Fehrman, R. G., "Surface New Jersey, 1949. Chemical Factors of Importance in the 20. Mamfort, R. C., "A Laboratory Hardening of Soils by Means of Portland Study of the Effectiveness of Various Cement," Proc. Highway Research Chemicals as Soil Stabilizing Agents," Board, 1942. Technical Development Note No. 40, 31. Winterkorn, H. F. , "Soil Sta• U. S. Civil Aeronautics Administration, bilization, " Proc. Second International Washmgton, D. C. , 1945. Conference on Soil Mechanics and 21. Marbut, C. F., "Morphology of Foundation Engineering, 5, 209-214, Laterites," Proc. and Papers, Second Rotterdam, 1948. International Congress, Soil Science, 32. Wooltorton, F. L. D., "Re• 5, 72-80, 1932. lation Between Plastic Index and the 22. Martin, F. J. and Doyne, H. Percentage of Fines in Granular Soil C., "Laterite and Laterite Soils in Stabilization," Proc. Highway Research Sierra Leone," Journal of Agricultural Board, 479-490, 1947. Science, 17, 530-547, 1927. 33. Wooltorton, F. L. D. , "Report 23. Mohr, E. C. J. , "Soils of to the Government of Burma on Low Equatorial Regions," Edward Brothers, Cost Roads," Government Printing and Ann Arbor, Michigan, 1944. Stationery, Rangoon, Burma, 1948. 24. Pendleton, R. L., "Laterite 34. Unpublished data: Wooltorton, and its Uses in Thailand and Cam• F. L. D. , in Private Communications bodia," Geogr. Rev. 31, 172-202. to Winterkorn, H. F. 25. Pendleton, R. L. and Sharas- 35. Unpublished data: "Report to uvana, S., "Analyses of Some Siamese the Portuguese Government on Sug• Laterites," Soil Science, 62, 423-440, gested Soil Stabilization for Airport in 1946. Guinea, Africa," 1947.