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Technical Data Sheet
Ham Hill Middle Bed Limestone
Ham Hill Stone Company Ltd
Compiled September 1997

This data sheet was compiled by the Building Research Establishment (BRE). Where possible, data collected in earlier surveys has been used to help interpret the test results. The data sheet was compiled in September 1997 using the results of tests carried out to the proposed European Standards. The work was carried out by BRE as part of a Partners in Technology Programme funded by the Department of the Environment and The Ham Hill Stone Company Ltd and does not represent an endorsement of the stone by BRE. 

General  

The Ham Hill Stone Company quarry is located on the summit of Ham Hill, close to the village of Stoke-sub-Hamdon on the edge of the Ham Hill Country Park. Stone has been quarried on Ham Hill for more than 500 years with the present quarry being reopened in 1984. The quarry's reserves have been measured at well over one million tonnes. 

Petrography 
1. Macroscopic 
The stone is a medium to coarse grained shelly limestone from the top of the Toarician Stage of the Upper Lias Age (Lower Jurassic Series ). The stone consists of a well cemented mass of shells, crystalline calcite and iron minerals wich gives it a distictive colour. 
2. Microscopic 
Ham Hill stone is classified as an allochemical rock consisting largely of fragments of Brachiopoda and Echinodermata. Although the stone is coarse-grained, thin laminae of finer-grained fragments do occur throughout the rock. The laminae tend to contain small concentrations of sand grains (grain diameter about 30 microns) and on occasions they can form features on a macro scale. Sand grains are also found throughtout the stone but at a low concentration. The original cement between the grains was probably sparry calcite but it now has a micritic fabric.  

In addition to calcite, the matrix contains relatively large quanitites of goethite (iron hydroxide). This takes the form of diffuse spheres of the mineral, up to about 20 microns across. It is this mineral that gives the stone its colour.  
(Based on Jefferson 1996) 

Expected Durability and Performance 
It is important that the results from the from individual tests are not viewed in isolation. They should be considered together and compared to the performance of the stone in existing buildings and other uses. Limestones from the Jurassic series have been used extensively in many towns and cities in the UK.  

Ham Hill limestone appears to be a durable stone that will weather well. In addition, the low weight lost in the sodium sulphate crystallisation test indicates good resistance to salt damage (for example in coastal locations or from rising salts); the stone is expected to have good frost resistance. The compressive strength of the stone is towards the lower end of the range for comparable limestone but the flexural strength is towards the upper end of the range. The abrasion resistance is seems quite low but the stone should be suitable for use in lightly trafficed areas.  

Overall, should be suitable for use in most aspects of construction including flooring, lightly trafficked paving, load bearing masonry and cladding including areas where a long service life is needed or where high salt concentrations are expected. 

Test Results - Ham Hill Middle Bed Limestone
 
Safety in Use
Slip Resistance (Note 1) 
76
Values > 40 are considered safe 
Abrasion Resistance(Note 1) 
30.6mm
Values <23.0 are considered suitable for use in heavily trafficked areas 
Strength under load 
1) Compression(Note 2) 
23.1 MPa
Loaded perpendicular to the bedding - ambient humidity 
Compression(Note 5) 
25.6 MPa 
17.2 MPa
38.6 MPa 
25.3 MPa
Loaded perpendicular dry 
Loaded perpendicular wet 
Loaded parallel dry 
Loaded parallel wet 
2) Bending (Note 1) 
8.2 MPa
Loaded perpendicular to the bedding - ambient humidity 
Bending(Note 5) 
7.1 MPa 
4.9 MPa
6.0 MPa
4.5 MPa
Loaded perpendicular dry 
Loaded perpendicular wet 
Loaded parallel dry 
Loaded parallel wet 
Porosity and Water Absorption 
1) Porosity (Note 3) 
23.5%
2) Saturation Coefficient (Note 3) 
0.70
3) Water Absorption
7.4% (by wt) 
6.3% (by wt)
4) Bulk specific gravity 
1970- 2104 kg/m3
Resistance to Frost 
Freeze/Thaw Test (Note 1) 
Not determined
Resistance to Salt 
Sodium Sulphate Crystallisation  
Test (Note 3) 
Mean: 9.0% wt loss

(Test methods Note 1 = prEN1341, Note 2 = prEN 1342, Note 3 = prEn 1341 /BRE 141, Note 4 = BRE 141, Note 5 = ASTM)
Tests were carried out at BRE in 1997 and by WSP Geotechnical and Environmental in 1996.

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