Cement, Mortar and Concrete: Composition and Forensic Analysis

The three materials are a hierarchy, not three alternatives. Cement is the binder powder. Mortar is cement plus fine sand plus water, used to lay bricks and finish walls. Concrete is cement plus fine and coarse aggregate plus water plus optional admixtures, used as the structural matrix of buildings.

Portland cement (Aspdin 1824). Joseph Aspdin's 1824 patent describes burning a slurry of limestone and clay to a hard mass, grinding it, and selling it as "Portland cement" because the set mortar looked like Portland stone from Dorset. Modern Indian cement plants run essentially the same process at industrial scale.

Raw materials. A typical kiln feed is about 80 percent limestone (CaCO3, source of CaO), 15 percent clay or shale (source of SiO2, Al2O3, Fe2O3), small amounts of iron ore to balance the ferrite phase, and about 5 percent gypsum (CaSO4.2H2O) added after burning to control setting time.

Dry-process kiln (~1450°C). In the dry process used by most modern Indian plants, the raw meal is preheated in cyclone towers, calcined at about 900°C (CaCO3 to CaO + CO2), then sintered in a rotary kiln at around 1450°C. The product, clinker, is cooled, ground with gypsum, and bagged as cement.

Mortar. The site mix is one part cement, four to six parts sand, water to a workable consistency. Lime mortar (older buildings, conservation work) replaces some or all of the cement with hydrated lime.

Concrete. IS 456:2000 fixes design mixes by characteristic strength at 28 days in MPa. The common nominal mixes a candidate should memorise:M10(1:3:6, 10 MPa, levelling course),M15(1:2:4, 15 MPa, mass concrete),M20(1:1.5:3, 20 MPa, workhorse RCC),M25(1:1:2, 25 MPa, slabs and columns). Anything beyond M25 is design mix only, proportioned per IS 10262.

The four clinker phases and their hydration behaviour are the foundation of all forensic interpretation of cement fragments.

Hydration products. Water on ground clinker gives four products on overlapping timescales:

1. Ettringite (AFt)in the first minutes to hours. C3A plus gypsum plus water gives needle-shaped 3CaO.Al2O3.3CaSO4.32H2O. Gypsum is there precisely to slow C3A; without it the cement flash-sets in seconds.
2. C-S-H gel over hours to weeks. Alite and belite hydrate to amorphous calcium silicate hydrate, the actual glue holding concrete together. XRD shows it as a broad hump.
3. Portlandite, Ca(OH)2 as a by-product of silicate hydration. Hexagonal plates, sharp XRD peaks, dehydrates at about 450°C on TGA. Portlandite gives fresh concrete its pH around 12 to 13, which protects rebar from rust.
4. Monosulphate (AFm)after a day or so, as remaining C3A reacts with the early ettringite and gives plate-like calcium monosulphoaluminate.

BIS publishes a standard for every commercial cement type sold in India, and the IS number is frequently the starting point for forensic source identification.

A forensic lab asked to identify the cement type in a debris fragment starts from these distinctions. Fly-ash spheres on SEM point to PPC. Angular slag particles point to PSC. Very low C3A on XRD and SEM-EDX points to SRC. White, low-iron material with no ferrite phase is white cement.

Cement and concrete enter casework in four distinct fact patterns.

Building collapses. Cores from collapsed structures are tested to check whether the as-built mix met the design grade. The Mumbra building collapse near Thane in April 2013 killed 74 people and the investigation flagged substandard concrete and unauthorised additional floors. The Kanpur housing collapse (2018)and Greater Noida structural failures (2023)followed the same script: cores extracted, compressive strength tested at a NABL lab, mix design and W/C ratio reconstructed by petrographic thin section, and the result compared against the contractor's design submittal. Charges typically include BNS Section 109 (attempt to murder) when negligence amounts to dolus, and BNS Section 115 (voluntarily causing hurt).

Burglary and forced entry. A burglar drilling or chiselling through a wall picks up mortar and cement fragments on tools and clothing. Stereomicroscopy plus XRD can link a recovered tool or shoe to a particular wall by matching aggregate type, mortar composition and cement clinker fingerprint.

Explosion debris. A blast against a concrete structure produces fine cement particles which embed in clothing, hair and victim wounds. Recovery of these particles helps reconstruct the seat-of-blast and is read alongside chemical residue work covered in the investigation of explosion and arson casesexaminers bullet.

Concreted-body disposals. A recurring case type involves disposal of human remains inside a freshly cast concrete pillar, tank or slab. Forensic work covers the age of the concrete (carbonation depth, portlandite content, ettringite versus monosulphate ratio), the source of the cement, and the link to materials at the suspect's possession.

A fragment received in a sealed exhibit packet runs through a standard sequence at CFSL Chandigarh, the National Council for Cement and Building Materials (NCCBM) at Ballabhgarh, and state SFSL trace-evidence divisions.

1. Stereomicroscopy
2. Petrographic thin section (ASTM C856)
3. X-ray diffraction (XRD)
4. SEM-EDX
5. FTIR / ATR-FTIR
6. TGA (thermogravimetry)
7. XRF (bulk composition)

A report under Bharatiya Sakshya Adhiniyam Section 39carries findings into court. Institutional anchors to recall: CFSL Chandigarh for central forensic work, NCCBM Ballabhgarh as the BIS-recognised cement R&D body, state SFSLs for routine casework, CPWD and PWD as the construction authorities under whom most public-works tests are commissioned, BIS for the IS standards themselves, and the National Building Code 2016 as the master design and construction document.