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Grove Whitbed technical data
This technical data sheet was compiled by the Building Research Establishment (BRE) at the request of Albion Stone and is updated by Albion Stone to incorporate current test results. The 1,393 tests have been carried out in accordance with current European standards by the BRE on Albion Stone's behalf, or by other accredited testing houses. The work carried out by the BRE on this technical data sheet has been undertaken as a paid commission and does not represent an endorsement of the stone by the BRE.
A. Petrography
Macro Examination
This appeared to be a fine-grained sedimentary rock – probably limestone. Light creamy-white coloured matrix containing an abundance (>10%) of highly elongate light-grey (brownish-grey when weathered) coloured fossiliferous material. This material was orientated primarily in one direction which probably represented bedding. These fossiliferous clasts were observed up to 3mm in length. Voidage appeared modest and the fluorescent resin take up appeared high. This sample appeared to be a fairly uniform fine-grained material in which no bedding or linear features other than the fossiliferous material was apparent.
Microscopical examination
This limestone exhibited a moderately well compacted structure, which had moderate to poorly sorted appearance. No microcracking, linear or bedding related features other than the preferential orientation of the fossiliferous clastic material were observed. The clast to matrix ratio was approximately 90:10. Clast to matrix bond appeared good, with no separation cracks detected.
Clasts
These consisted of materials having a great range of sizes (3000µms down to <10µms). The larger fossiliferous material (>1mm) was elongate and was comprised primarily of Brachiopoda and Mollusc valves. Internally some of these clasts had open porosity now partially filled with secondary sparitic calcite. There was also evidence of conversion or replacement of the internal areas of some shells by large quartz crystals.
The finer (>1mm) material was also composed largely of fossiliferous materials including Brachiopoda and mollusc valves, along with bryozoa stems, algal material and colonial corals. However, the majority of this finer material was composed of micritised Ooliths, some of which were seeded with quartz sand grains and fossil debris. Other less abundant clastic constituents included lithoclasts (Oosparite/Oomicrite). The edges of the larger clasts and all of the finer material were composed of micrite size carbonate material. Worm action was observed on a pre-existing fossil shell fragment.
The clastic material was dominated by fossiliferous material with an almost equal amount of oolitic material also present. The fossiliferous clasts were more prominent in the coarse sized material.
Matrix
Though relatively rare, the matrix appeared to consist primarily of micrite-sized material. Some secondary sparite crystallisation had developed in some of the voidage and this partially filled some inter and intra-clastic voidage. Matrix material was felt to represent only a small component of the rock.
Voidage
This was felt to be in the range medium to high and was present largely at the finer <200µms size within individual voids. Occasional larger voids up to 4mm in length were found associated with a localised abundance of larger fossiliferous clasts and a lack of matrix material. The voidage was mainly inter-particle, but some partially filled intra-particle voidage and shelter voidage was detected. A visual estimation of the voidage, which was slightly patchy in appearance, ranged from 15 to 25%.
Composition
The clastic (ooliths and fossiliferous) material was composed of non-ferroan calcite. Micritic matrix material was composed of non-ferroan calcite. The relatively rare secondary sparite carbonate was composed of non-ferroan dolomite and non-ferroan calcite. Trace amounts of quartz sand grains, chert and silica associated with belemnite spins were detected but were felt to represent less than 1% of the total rock.
Classification
On the basis of the features described in this report, this rock would be classified as Oomicrite. However, it does contain an abundance of large fossiliferous material clasts.
B. Strength
1. Compression - BS EN 1926
Average: 49.79 from 76 tests
Lowest Expected Value 32.58 Mpa
Highest Expected Value 71.86 Mpa
2. Flexural Strength - BS EN 13161
Average: 7.65 from 66 tests
Lowest Expected Value 4.61 Mpa
Highest Expected Value 11.80 Mpa
C. Durability
1. Water Absorbtion BS EN 13755
Average: 5.07% from 195 tests
Lowest Expected Value 2.86%
Highest Expected Value 8.20%
2. Density BS EN 1936
Average: 2,234 kg/m³ from 301 tests
Lowest Expected Value 2095 kg/m³
Highest Expected Value 2378 kg/m³
3. Porosity BS EN 1936
Average: 17.02% from 288 tests
Lowest Expected Value 11.46%
Highest Expected Value 24.14%
4. Saturation Coefficient BS EN 1936
Average: 0.70 from 281 tests
Lowest Expected Value 0.60
Highest Expected Value 0.81
5. Salt Crystallisation
Average: 16.50% from 104 tests
Lowest Expected Value 1.10%
Highest Expected Value 100%
D. Abrasion & Slip Resistance
1. Abrasion Resistance – EN14157
Average: 24.48 from 9 tests
Lowest Expected Value 20.55
Highest Expected Value 28.99
2. Slip Resistance – TRRL Pendulum Test
Grit 60 (External Paving)
Wet Average 80
Lowest Expected Value 74
Highest Expected Value 86
Dry Average 95
Lowest Expected Value 91
Highest Expected Value 98
Internal Flooring
Independent Whitbed is suitable for all flooring applications up to semi-intensive use such as shops and offices with estimated visitor numbers of 5,000,000 with a service life without significant wear of 20 years. The slip resistance results of over 40 demonstrate that the stone will be safe in all applications.
Technical Summary
Prepared by: Dr T Yates, BRE (Building Research Establishment)
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 Bowers 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 very 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 the limited number of samples tested meet seem to meet these criteria. The crystallisation test results show the stone to be Class B-C which BRE Report 141 suggests is suitable for most uses including 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 >50 years). 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.
Revision 7 DECEMBER 2007
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