Blaxter Stone Specification

General
This large quarry, near Otterburn, Northumberland, has been worked since the 1890s and there are older workings nearby. There are good reserves of stone. The stone is available at depths of 1.2m on bed from a 6m face beneath about 2m of overburden. The quarry is currently operated by Dunhouse Quarry Co. Ltd.

Petrography 
Blaxter is from the Carboniferous Limestone of Lower Carboniferous age. It is a fine- to medium-grained stone, pale yellow-buff in colour, non-calcareous, slightly micaceous sandstone.

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. Carboniferous sandstone has been used extensively in many towns and cities in the UK. Blaxter has a long history of use and can be seen in many buildings in the north of England; it has also been used on a large number of restoration projects. Blaxter sandstone appears to be a durable stone that is not effected by acid rain or air pollution. However, the weight loss in the saturated sodium sulphate crystallisation test indicates a resistance to salt damage but the high weight loss in the harsher saturated sodium sulphate test indicates susceptibility to salt damage in harsh environments (for example in coastal locations or from de-icing salts). However, the freeze thaw results suggests that it may be susceptible to frost action in extreme conditions. Traditionally the sandstone has successfully been used in the northern climes of England and in Scotland without any adverse effect. The compressive and flexural strength of the stone is towards the lower end of the range for sandstone but is similar to some of the stronger limestones. The compressive strength indicates that the stone should be suitable for use in lightly trafficked areas.

Overall, Blaxter should be suitable for use in most aspects of construction including flooring, paving, load bearing masonry and cladding but caution should be used in areas where a long service life is needed and there are high salt concentrations.

Test Results – Blaxter Sandstone

Safety in Use
Slip Resistance (Note 1)

Wet 79

Values > 40 are considered safe.
Abrasion Resistance (Note 1)

Not Determined

Values <23.0 are considered suitable for use in heavily trafficked areas
Strength under load
1) Compression(Note 2)

55.1 MPa
(38 – 55 range)

Loaded perpendicular to the bedding plane ambient humidity

36 MPa

Loaded perpendicular to the bedding , wet (Note 5)        
2) Bending (Note 1)

3.1 MPa

Loaded perpendicular to the bedding plane ambient humidity

2.7 MPa

Loaded perpendicular to the bedding , wet (Note 5)

Not Determined

Loaded parallel to the bedding plane ambient humidity
Porosity and Water Absorption
1) Porosity (Note 3)

20.5%

2) Saturation Coefficient (Note 3)

0.63
(0.59 – 0.63 range)

3) Water Absorption

6.1 % (by wt)

4) Bulk specific gravity

2110kg/m3

Resistance to Frost 
Flexural strength after Freeze/Thaw Test (Note 1)

2.0 MPa

Loaded perpendicular to the bedding plane ambient humidity
Resistance to Salt
Sodium Sulphate Crystallisation Test (Note 3)

-0.70% Mean wt loss

Resistance to Acidity
Acid Immersion Test(Note 4)

Pass

(Test methods Note 1 = EN1341, Note 2 = En 1342, Note 3 = En 1341 /BRE 141,                   Note 4 = BRE 141, Note 5 = ASTM)