Jordans basebed

This technical data sheet is based on a format compiled by the Building Research Establishment (BRE) at the request of Albion Stone. The 102 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 (BRE reference: 231038/06/01/117)
The stone was off-white in colour and had a fine-grained texture. It effervesced with 10% hydrochloric acid indicating that it contained calsite. The clasts were often too fine to be identified in the macro examination, however there was a low abundance of elongate clasts that were up to 4mm in size that were considered to be mollusc shell fragments. There was some preferred alignment of elongate clasts, possibly denoting sedimentary bedding.

Microscopical Examination (BRE reference: 231039/06/01/117)
The Limestone was well sorted, well compacted (evident by concavo-convex contact at clast boundaries), and clasts supported. The clast to matrix ratio was visually estimated at 90:10. There was possibly some evidence of sedimentary bedding by the preferred alignment of elongate clasts.

Clasts
There were ooliths, which are visually estimated to account for 80% of the total stone. The ooliths were spherical in shape and ranged in size from 160 to 600µm, mean 400µm. The ooliths were composed of micritic carbonate and were seeded by sparitic and micritic carbonate, angular quartz (1 to 2%) and very occasional feldspar.

Elongate mollusc shell fragments (bivalves) were visually estimated to account for 10% of the stone. The mollusc shell fragments ranged in size from 300µm to 3mm and were composed of spartic carbonate with a micrite envelope. These showed some preferred orientation possibly denoting sedimentary bedding.

Quartz was visually estimated to account for 1 to 2% of stone. It was angular in shape and up to 250µm in size

Matrix
The matrix was visually estimated to account for 10% of the stone. The matrix was predominantly composed of euhedral shaped sparitic carbonate crystals which were present adjacent to open voidage space. Individual sparite crystals were up to 300µm in size. Micritic carbonate was also observed.

Voidage
There was a moderate abundance of open interparticle and intraparticle voidage space observed. The voids were visually estimated to account for 5 to 10% of the stone and they ranged in size from 40 to 500µm. The micritic carbonate present had a moderate capillary porosity.

Composition
The micritic and sparitic carbonate which made up the clastic and matrix components were composed of non-ferroan calsite. There was also 1 to 2% quartz present.

Classification
Based on the description given here this stone would be classified as a well sorted, well compacted, clast supported Oosparite Limestone.

Results Summary
The stone was classified as well as sorted, moderately compacted, clast supported Oosparite Limestone. The clasts were predominantly composed of ooliths, but the mollusc shell fragments and quartz were also present. The matrix was composed of sparitic carbonate and some micritic carbonate. There was a moderate abundance of open voidage space. There was some evidence of sedimentary bedding by the preferred alignment of elongate clasts.

B. Strength

1. Compression - BS EN 1926
Average: 41.15 Mpa from 26 tests
Lowest Expected Value 28.49 Mpa
Highest Expected Value 57.63 Mpa

2. Flexural Strength - BS EN 13161
Average: 6.46 Mpa from 52 tests
Lowest Expected Value 5.06Mpa
Highest Expected Value 8.11 Mpa

3. Breaking Load at Dowel Hole - BS EN 13364
Average: 4,329 N from 20 tests
Lowest Expected Value 3,795 N
Highest Expected Value 4,888 N

C. Durability

1. Water Absorbtion - BS EN 13755
Average: 6.40% from 6 tests
Lowest Expected Value 5.97%
Highest Expected Value 6.87%

2. Density - BS EN 1936
Average: 2,178 kg/m³ from 12 tests
Lowest Expected Value 2,122 kg/m³
Highest Expected Value 2,236 kg/m³

3. Porosity - BS EN 1936
Average: 19.08% from 16 tests
Lowest Expected Value 17.59%
Highest Expected Value 20.67%

4. Saturation Coefficient - BS EN 1936
Average: 0.73 from 10 tests
Lowest Expected Value 0.71
Highest Expected Value 0.76

Technical Summary

Prepared by: Prepared by: Dr T Yates, BRE (Building Research Establishment)Durability and Weathering

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 Basebed is traditionally acknowledged as being less durable than Whitbed but it has been used extensively where a faster rate of weathering is acceptable or where its working qualities were required. It is possible to compare the results for the Basebed Stone from Jordans Quarry to those collected from buildings, exposure trials and tests on quarry samples collected by BRE during the last 70 years. This shows that the stone compares well with the traditional view of Portland Basebed. Previous research at BRE has shown that Portland limestone which has a low saturation coefficient (>0.72), a high microporosity (>11.0 of the stone by volume) and an increased amount of micritic matrix will weather more rapidly than Whitbed when used on buildings. The results summarised on these sheets show that most of the samples tested are of this type. The crystallisation test results show the stone to be Class D -E which BRE Report 141 suggests that it is suitable for plain walling and cladding. The results from the other tests suggest that soundest stone may well perform better than this class in the current environment. Where more severe exposure conditions are expected, for example high concentrations of sulphur dioxide or severe frosts, or where a long life is required (for example >50 years) then it may be desirable to use a more durable stone (e.g. Jordans Whitbed). When using Jordans Basebed it is especially important that the detailing of the stonework is designed to offer the maximum protection to rainwater and rainwater runoff.

Based on current research it seems likely that the stone would weather at a rate of between 3 and 4 mm per 100 years but it could be greater in severe exposures or on the edges of stonework.

(Weathering rates are based on the BRE interpretation of historical data dating from 1932)

Revision 2 DECEMBER 2007