What is the primary purpose of petrographic examination of aggregates?

To identify rock types, mineral composition, and specifically to detect any deleterious or alkali-reactive minerals that could cause concrete deterioration.

Can petrographic analysis alone determine if an aggregate is definitively safe?

No, it is primarily used for screening. Suspect aggregates must be further evaluated using chemical or physical expansion tests as per IS 2386 Part 7.

What type of microscope is required for this standard?

Both a stereoscopic microscope (for examining coarse particles and surfaces) and a polarizing petrographic microscope (for thin sections) are required.

IS 2386 Part 8

: 1963

Methods of Test for Aggregates for Concrete - Part 8: Petrographic Examination

CurrentSpecializedTesting MethodMaterials Science · Aggregates and Sand

Download PDF BIS Portal Google

This part of IS 2386 outlines the procedures for the petrographic examination of concrete aggregates. It details methods to identify the mineralogical composition and physical characteristics of natural sand, gravel, and crushed stone to assess their suitability and screen for potentially reactive or deleterious minerals.

Describes methods for the petrographic examination of aggregates to identify mineral composition and potential deleterious constituents.

Quick Reference Values

Minimum sample weight for natural sand300 g

Fractionating sieves for sand analysis4.75mm, 2.36mm, 1.18mm, 600µm, 300µm, 150µm

Thickness of rock thin section for microscopic examination0.03 mm (approx)

Practical Notes

Petrographic examination is highly specialized and must be conducted by a qualified geologist or petrographer.

This test serves as an essential preliminary screening tool before performing time-consuming chemical or mortar-bar tests for Alkali-Aggregate Reactivity (IS 2386 Part 7).

Unrepresentative sampling is a common source of error; sampling must strictly follow IS 2430.