Historic lime mortar: Basic analysis techniques

Dr Alan M Forster

Assistant Professor

Lime mortars: Analysis overview

• Visual

• Acid Dis aggregation

• Thin Section

• ESEM

Visual analysis

Process

-Optical microscopy (20x)

Information derived

- Identification of macro pore

structure

- Aggregate: type, shape & texture

Basic chemical analysis (acid digestion)

Process

- Sample placed in HCL (10%) : Consumption of lime binder

- dry, weigh and grade the aggregate

Information derived

- Approximate mix proportions: lime to aggregate ratio

- Approximate assessment of hydraulicity

Thin section (petrographic) analysis

Process

- Impregnate with resin

- Cut into a thin slice

- Examine under polarised light

Information derived

- Assessment of 2 dim pore structure

- Assessment of aggregate types

Non-hydraulic lime mortar

Hydraulic lime mortar

O.P.C mortar

X-Ray Diffraction (XRD)

Process

- Powder sample

-X-ray bombardment of sample

- Return information indicates

nature of crystalline material

Information derived

- Identification of hydraulic

components and aggregate

types

Incident electron

beam

Backscattered

primary electrons

Secondary electrons

X-rays

Light

Auger electrons

Inelastically

scattered electrons

Unscattered electrons

Absorbed

electrons

SPECIMEN

Environmental Scanning Electron Microscopy

Process

- no need to pre-treat the sample

- place on stage and carbon coat

Information derived

- identification of pore structure

- identification of individual components

- simultaneous EDX mapping

- can simulate environmental conditions: wetting / drying, freeze / thaw etc

Wetting characteristics: hydrophillic surfaces

Wetting characteristics: hydrophobic surfaces

Non-hydraulic lime mortar

Hydraulic lime mortar

Hydraulic lime mortar

Hydraulic lime mortar

Portland cement mortar

Portland cement mortar

Portland cement mortar

Building response to climate change

• PI for £150K EPSRC project “An assessment of binder leaching

in traditional mortars for mass masonry”

• Increased rainfall and solubility of binder

• Loss of structural integrity

Evidence of binder migration

Provenance – regional manufacture

• Researching materials produced from small scale burning

• Complexity of mortars greater than modern counterparts

• Influenced principally by; raw materials (limestones) composition,

calcination temperature, residence time

Experimental Lime

Kiln, Scotland

Experimental Lime

Kiln, Czech

Republic

Selected examples of published works

Conclusion