General
The entrance to the quarry is in Grove Road. The quarry was formerly known as Convicts Quarry and following a period of abandonment work restarted in 1982. There are good reserves of stone.

Petrography
The stone is an open textured oolitic limestone from the Portlandian formation (Jurassic). The stone is formed from micrite (fine grained calcium carbonate) ooids with a small quantity of micrite occurring as matrix. The shell fragments are elongated to rounded and are typically about 5 mm across. The stone generally appears to be moderately compacted although the degree of compaction is variable. Most of the areas exhibit a fairly high intergranular porosity with interlinking of adjacent pores. In some areas ooids are fused or are surrounded by a sparse carbonate matrix. (Examination carried out by Stangers 05/07/91)

Expected Durability and Performance
It is important that the results from the sodium sulphate crystallisation tests are not viewed in isolation. They should be considered with the results from the porosity and water absorption tests and the performance of the stone in existing buildings. Stone from the Portland Whitbed is traditionally acknowledged as generally being a very durable building stone and it has been used extensively in many towns and cities in the UK. Comparing the results for the Whitbed Stone from Independent Quarry to those collected from buildings, exposure trials and tests on quarry samples collected by BRE during the last 70 years shows that this stone compares well with the traditional view of Portland Whitbed. Previous research at BRE has shown that Portland limestone which has a low saturation coefficient (<0.72), a low microporosity (<11.0 of the stone by volume) and an open oolitic structure generally performs well over long periods when used on buildings. The results summarised on these sheets show that most of the samples tested meet these criteria. The crystallisation test results show the stone to be Class C - D which BRE Report 141 suggests is suitable for most uses. Where exposure conditions are to be more severe, for example high concentrations of sulphur dioxide or severe frosts, or where a long life is required (for example >50years) then the best stone should be selected. In all cases it is important that the detailing of the stonework is designed to offer the maximum protection from rainwater and rainwater runoff. Based on current research it seems likely that the stone would weather at a rate of between 1 and 2 mm per 100 years but it could be greater in severe exposures.

Test Results - Portland Independent Whit Bed Limestone

Safety in Use
Slip Resistance (Note 1)	Wet: 78	Range 76 - 83.Values > 40 are considered safe
Abrasion Resistance(Note 1)	25.1	Range 23.3-26.8Values <23.0 are considered suitable for use in heavily trafficked areas
Strength under load
1) Compression(Note 2)	51 MPa	Range 35 - 68Loaded perpendicular to the bedding - ambient humidity
2) Bending (Note 1)	7.6 Mpa	Range 7.6 - 8.5Loaded perpendicular to the bedding - ambient humidity
Porosity and Water Absorption
1) Porosity (Note 3)	19.6%	Range 17.0 - 20.9%
2) Saturation Coefficient (Note 3)	0.64	Range 0.56 - 0.69
3) Water Absorption	5.2% (by wt)
4) Bulk specific gravity	2218 kg/m3
Resistance to Frost
Freeze/Thaw Test (Note 1)	Not determined
Resistance to Salt
Sodium Sulphate Crystallisation Test (Note 3)	Mean: 16.2%  wt loss	Range 0.1 - 33.3

(Test methods Note 1 = prEn1341, Note 2 = prEN 1342, Note 3 = prEN 1341 /BRE 141, Note 4 = BRE 141)

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