CBR Test

(California Bearing Ratio)


The EL-Quarto SSS CBR TEST: 2012

Soils in group A-6 are typically lean clays, and those in group A-7 are typically highly plastic clays. Within groups containing fines, one may calculate a group index to further evaluate relative quality and supporting value of a material as sub-grade.


When any tests are performed in order to observe the effect of EL-SSS treatment it is essential that identical tests be done on un-treated and treated soil so that comparisons may be made. It is further essential that the soil be tested with proper application rate in terms of millilitres of EL-SSS per square meter.

Prior to attempting any laboratory testing when investigating the effects of EL-SSS, it is essential to be fully aware of the following important facts:

  • EL-SSS is not a cement, which develops an early strength after application, increases when more cement is added.
  •  The distribution of EL-SSS within the soil is slightly slower in the initial stages and as time lapses (normally 5 to 7 days on site) curing is needed for soil strength maturation.
  • Too much EL-SSS is not beneficial and proven counterproductive.
  • The quantity of EL-SSS added is equal to 10ml (two teaspoons) per m² x 150mm of soil.
    This translates to a ration of 1: 250 water.

Dilution of the EL-SSS with water prior to application is essential. As the quantity of EL-SSS added to a m²x 0.15m of soil is only 10ml (two teaspoons), for a laboratory sample the quantity is extremely small. Furthermore, as EL-SSS needs a maturation time to become effective, two important operations are to be performed prior to initiating any tests of the soil:

  •  The EL-SSS must be properly diluted prior to delivery to the laboratory.
  • The treated soil must be in a plastic bag and given a time for maturation to take place.

If these two operations are not undertaken when testing the treated soil, the effects of the treatment will not be reflected/ observed positively. 

The soil sample shall be of sufficient size to enable all the proposed tests (in duplicate or triplicate) to be properly prepared with due allowance for the tests to be performed on treated as well as un-treated soils simultaneously. 

It should be noted that the procedures sited below are to be construed as “Standard Procedures” in respect of the date of this directive. These procedures may be amended locally if necessary to suit local conditions and which may then be termed “Local Procedures”. 


The EL-SSS solution for treating one half of the total soil (1/2m2 x 0.15m) is prepared by adding 5 ml of EL-SSS to 1 500ml of pure potable water.


The full soil quantity required to perform all the anticipated tests shall be riffled to obtain two lots of equal samples for any tests proposed; one to be prepared as treated and one as untreated soil.

To the untreated soil, add sufficient pure water to bring the moisture content to approximately equal to anticipated Proctor Optimum Moisture Content (OMC).

To the soil to be treated at a ratio of 5ml of EL-SSS diluted with 1500ml of water for ½ m² x 0.15m thick layer of dry soil together with more pure water to bring the moisture to 1 to 2 % above OMC, the same applies to the untreated soil (this extra moisture enhances the maturation process).

The moist soil, both treated and un-treated, shall now be placed in plastic bags and allowed to mature (cure) for 24 hours, after which it should be removed from the plastic bags and exposed to normal laboratory conditions for the remainder of the curing or maturation period of 96 hours.

The soil now exposed to normal lab conditions is cured for a further 96 hours. (If the soil is very plastic the 96 hours of curing may be extended to 144 hours). After the lapse of half of this curing period, a portion of the soil may be used to determine the maximum Proctor density and OMC.

Drying out of the material may occur during this curing period and additional (undiluted) pure water may be added to keep the moisture as close to OMC as possible.

Moulding of the soil for CBR testing or, after drying, sieving for other tests may now proceed. Care must be taken to ensure that both the treated and untreated samples be given the same treatment of moisture and curing, except for adding of the DILUTED solution is omitted for the un-treated sample.


The success of the soil stabilisation depends on the following defining factors:

  • Ideally the soil to be 3tabilizer should be at least 6 to10% of material finer than 0.425mm to 0.075 mm. Particle sizes should range from sub 0.002 mm (fines) to about 40 mm (gravel).
  • The presence of fine particles is essential as the EL-SSS product reacts solely with the fine particles. In some instances, it may be necessary to add finer material to improve the particle size distribution (envelope grading envelope).
  • The dosage of EL-SSS stabiliser, application recommendations, as well as application tolerance (technical references) rate will always be provided by the manufacturer.
  • The application of the stabiliser should be undertaken in an easily controlled manner.
  • Both under and over dosing may result in poor performance of the final product.
  • In addition, the EL-SSS product is a compaction aid too, on other words strength gain should be immediate. However, as mentioned previously, improvement is derived from evaporation and a secondary compaction means, such as traffic, may proof to be beneficial. It is therefore suggested that test procedures and methodologies should be modified to reflect field conditions.

There is further evidence that suggests that laboratory tests do not represent field (on site insitu) performance. Due to this, discussions identified by professional practitioners suggest and identified that at times, laboratory tests results in non-performance of the product. However, field trials have proven differently and positively. Therefore, it is recommended that further work be considered to design appropriate testing conditions. These could include:

  • Sealing the sides of the samples to prevent lateral movement of moisture, but permitting water to evaporate from the top of the sample.
  • It could also include application cyclic load to specimen confined in a mould simulating secondary compaction.
  • Curing temperature and humidity should also reflect field (on-site) conditions.

The additional testing described above will require intricate equipment and test procedures. 

In view of the difficulty in performing these laboratory tests, it is strongly suggested for the Laboratory simulate field conditions in order to identify the stabiliser as favourable. In addition, it is recommended that any changes in moisture content, CBR be measured over at least a wet and a dry season respectively.


The group or family of A-7 soils in particular (high compressibility clays, silty clays and high-volume change clays) are problematic or challenging materials to be treated and tested in the laboratory. Many technicians may not find satisfactory results when conducting tests in a laboratory environment. Studies have identified that these types of materials (soils) can be positively treated with EL-SSS. Furthermore, these soils can be confidently utilized (successfully) as a road bed (in-situ) or as a sub-base layer/s, in the construction of roads, railway lines and other projects requiring soil strengths (CBR). It has been further identified and observed that such materials do not tolerate mechanical intervention, and a soft engineering approach or a soft manipulation should be adopted in order to achieve the required positive results. 


Case Study 1

When preparing A-7 type of materials for a road bed or a sub-base layer, it is important NOT to excavate (box cut), NOT to rip and mix.

The preparation consists of a light scarification, no deeper than 50mm.

Spray-on the first application of diluted EL-SSS, only one or two passes up and down onto the light scarified area/surface. 

WHEN NECESSARY – Place a layer of approximately 3…5cm thick of coarser aggregate (river sand or small stone or any other gravel material available within close surrounding areas) onto the A-7 material, spread it evenly.

Spray-on the second application of diluted EL-SSS, and, as soon as the surface is fairly dry, then apply the third/last application of diluted EL-SSS.

Compact at adequate moisture content. 

Spray water for maturation once a day for the next 7 days in the absence of rain. 

If applicable: The next layer may be placed immediately on the compacted surface (immediate if need arises. In this case maturation watering for 7 days will not be required as evaporation is minimum).

Case Study 2

Cut and fill: Similar application process as identified in case study 1 above.
When in doubt, please do contact our technical team.