Methods of test for soils, Part 38: Compaction control test (Hilf method)
1976 Edition

The sand equivalent test quantifies the proportion of clay-like or plastic fines relative to sand in granular soils and fine aggregates passing the 4.75 mm IS sieve. It serves as an indicator of the material’s cleanliness and quality by measuring undesirable fine particles, assisting engineers in evaluating soil suitability for construction applications. This rapid assessment complements more detailed soil investigations but does not replace them.

Preparation begins by dissolving 480.4 grams of calcium chloride in 2 liters of distilled water, followed by cooling and filtration. Subsequently, 2179 grams of technical-grade glycerine and 49.7 grams of formaldehyde are added to the filtered solution. The mixture is then diluted to a total volume of 4 liters, forming the stock solution. To prepare the working solution, 90 milliliters of this stock is diluted to 4 liters with distilled or demineralized water. Tap water may be used only if testing confirms it does not affect results. Approximately 100 ± 2 milliliters of the working solution is used per test to ensure consistent accuracy.

The apparatus includes a sand equivalent shaker (mechanical or manual) for sample agitation lasting 45 ± 1 seconds; a siphon assembly comprising copper and rubber tubes such as a 5 mm diameter by 410 mm long siphon tube, a 3 mm internal diameter by 1220 mm long siphon hose, a 3 mm ID blow hose, a 5 mm diameter blow tube, and a two-hole rubber stopper fitting a 4-liter bottle; an irrigator tube made of stainless steel; a clamp pinchcock; a transparent acrylic graduated tube (38 mm outer diameter, 450 mm length) with a base; and a weighted foot assembly including a nylon sand reading indicator, a brass rod, a cold-rolled steel weight, a corrosion-resistant roll pin, a brass foot, and a solid rubber stopper for the graduated cylinder.

Drying the soil specimens at 105 ± 5°C until constant weight is crucial for obtaining accurate sand equivalent values. Moisture present in undried samples can reduce the measured sand equivalent by affecting the dispersion and suspension of clay fines. While testing undried samples is permissible for rapid checks, if results fall below the specified minimum, retesting with dried specimens is mandatory. This process ensures more reliable and consistent assessment of clay fines in the material.

To achieve precise and repeatable results, specimens must be dried to a constant mass at 105 ± 5°C and cooled to room temperature before testing. The sample is then placed in the test cylinder and agitated using a mechanical shaker for 45 ± 1 seconds. If initial dried specimen results do not meet the minimum requirements, two additional tests should be conducted on dried specimens from the same sample. Strict adherence to drying, shaking duration, and repetition protocols minimizes variability and ensures dependable sand equivalent values.