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IS 11315:1985 Part 1 is the Indian Standard (BIS) for methods of test for rocks - part 1: determination of water content, density, porosity and absorption. This standard specifies the laboratory test methods for determining the water content, density, porosity, and water absorption of rock samples. These are fundamental index properties used for the classification, characterization, and quality assessment of rock materials in civil and mining engineering projects.
Specifies methods for determining water content, density, porosity, and absorption of rock specimens.
Overview
Status
Current
Usage level
Specialized
Domain
Geotechnical — Surveying and Geotechnical Investigation
! Ensuring complete saturation is critical for accurate porosity results; vacuum saturation is highly recommended over simple immersion.
! The saturated-surface-dry (SSD) condition is a key step and requires skill to achieve correctly; a damp cloth is used to remove surface water without pulling water from the pores.
! The presence of micro-fractures, which may not be part of the intergranular pore space, can significantly influence absorption and porosity values.
ISRM (1979)International Society for Rock Mechanics (ISRM)
HighCurrent
Suggested Method for Determining Water Content, Porosity, Density, Absorption and Related Properties
Covers the same set of properties: water content, density, porosity, and absorption for rock materials.
ASTM D2216-19ASTM International, USA
HighCurrent
Standard Test Methods for Laboratory Determination of Water (Moisture) Content of Soil and Rock by Mass
Directly equivalent for the determination of water content, but does not cover density or porosity.
BS EN 1936:2006British Standards Institution (BSI), UK / European Committee for Standardization (CEN)
MediumCurrent
Natural stone test methods - Determination of real density and apparent density, and of total and open porosity
Covers density and porosity determination but uses more advanced methods like vacuum saturation.
BS EN 13755:2008British Standards Institution (BSI), UK / European Committee for Standardization (CEN)
HighCurrent
Natural stone test methods - Determination of water absorption at atmospheric pressure
Specifically covers the determination of water absorption, a key parameter in the IS code.
Key Differences
≠The saturation method in IS 11315 is a simple submersion in water for 72 hours, whereas standards like BS EN 1936 mandate vacuum saturation to determine open porosity, which is a more rigorous and complete method.
≠IS 11315 specifies a single oven drying temperature range of 105-110 °C. In contrast, BS EN 1936 allows for a lower temperature of 70 ± 5 °C for rocks that may be altered by higher heat.
≠IS 11315 is more flexible on specimen size, allowing lumps of 60 g or regular shapes with a minimum dimension of 40 mm. BS EN standards are stricter, requiring specific cube sizes (e.g., 50 mm or 70 mm) or cores of equivalent volume.
≠The IS code calculates 'porosity' based on water absorption from simple immersion, which effectively measures 'apparent porosity'. International standards like ISRM and BS EN are more explicit in distinguishing between 'apparent/open porosity' (from water intrusion) and 'total porosity' (which includes isolated pores).
Key Similarities
≈The fundamental principle and formula for calculating water content (mass of water divided by mass of dry solids) are identical across IS 11315, ASTM D2216, and ISRM methods.
≈All compared standards mandate drying the rock specimen in an oven until a 'constant mass' is achieved, ensuring all free moisture is removed before determining the dry mass.
≈The use of a desiccator for cooling oven-dried specimens before weighing is a standard procedural step in IS 11315 and all its international counterparts to prevent re-absorption of atmospheric moisture.
≈The concept of a 'Saturated Surface-Dry' (SSD) condition, achieved by wiping excess surface water from a saturated specimen, is a common requirement for determining saturated mass for both density and absorption calculations.
Parameter Comparison
Parameter
IS Value
International
Source
Oven Drying Temperature
105 °C to 110 °C
110 ± 5 °C; or 70 ± 5 °C for heat-sensitive stones
ASTM D2216 / BS EN 1936
Saturation Method for Porosity/Absorption
Simple immersion in water for 72 hours.
Vacuum saturation (e.g., pressure ≤ 2.0 kPa for 24 h).
BS EN 1936
Constant Mass Criterion (Drying)
Mass change < 0.1% after 4 hours of further drying.
Mass change < 0.1% between weighings at a 24-hour interval.
BS EN 1936
Minimum Specimen Mass (Irregular Lumps)
60 g
50 g
ISRM (1979)
Minimum Specimen Dimension (Regular Shape)
40 mm
50 mm (for cubes)
BS EN 1936
Cooling Method After Drying
In a desiccator over silica gel or calcium chloride.
In a desiccator.
ASTM D2216 / ISRM (1979)
⚠ Verify details from original standards before use
Key Values5
Quick Reference Values
Oven drying temperature105 to 110 °C
Minimum drying duration24 hours
Minimum specimen mass for water content50 g
Minimum saturation duration24 hours
Balance accuracy for weighing0.01% of specimen mass
Key Formulas
Water Content, w (%) = [(M_wet - M_dry) / M_dry] * 100
What is the standard oven temperature for drying rock specimens?+
The specimen shall be dried in an oven at a temperature of 105 to 110 °C for 24 hours or until constant mass is achieved (Clause 5.4).
How is porosity calculated according to this standard?+
Porosity (n) is determined from the masses of the saturated (M_sat), oven-dried (M_dry), and submerged (M_sub) specimen using the formula: n = [(M_sat - M_dry) / (M_sat - M_sub)] x 100 (Clause 7.5).
What is the difference between water content and water absorption?+
Water content is the amount of water present in the rock in its natural state, relative to its dry mass. Water absorption is the total amount of water the rock can hold when fully saturated, also relative to its dry mass.