Limestone

Portland Bowers Whitbed Limestone

Petrography Description (EN 12407:2001)

The rock was a grain supported oobiomicrite made up of predominantly rounded micritic ooliths showing concentric structure and ranging from 50 m to 300 m in diameter, numerous bioclasts up to 5 mm by 20 mm in size and sporadic irregular quartz grains 100 m nominal size. There was an apparent pressure adhesion of the grains and some matrix between between the ooliths and this results in occasional intergranular voids. Sporadically sparry calcite infilled or partially infilled intergranular spaces or replaced central parts of bioclastic debris.

The ooliths consisted of micritic calcite and the bioclasts generally exhibited original aragonitic texture.

The rock contained occasional voids 100 m nominal size. The micrite was also microporus with pores beyond the resolution of a transmitted light petrological microscope.

No deleterious constituents or features were observed.

Bowers Whitbed Limestone

STRENGTH	Compression - BS EN 1926
	Ambient Humidity Wet Dry	Actual Range: 36 to 72 Mpa Actual Range: 28 to 62 Mpa Actual Range:
	Flexural Strength - BS EN 13161
	Ambient Humidity Wet Dry	Actual Range: 7.7 to 8.8 Mpa Actual Range: 3.5 to 4.8 Mpa Actual Range:
	Modulus of Rupture
	Ambient Humidity Wet Dry	Actual Range: Actual Range: 4.0 to 7.8 Mpa Actual Range:
DURABILITY	Water Absorption - BS EN 13755	Actual Range: 3.9% to 7.4%
	Density - BS EN 1936	Actual Range: 2,123 to 2,376 kg/m³
	Porosity - BS EN 1936	Actual Range: 12.2% to 21.7%
	Saturation Coefficient - BS EN 1936	Actual Range: 0.70 to 0.89
	Salt Crystallisation	Actual Range: 17.7% to 45.3%
ABRASION & SLIP RESISTANCE	Abrasion Resistance – EN14157	Actual Range: 23.9 to 26.2
	Slip Resistance – TRRL Pendulum Test
	Grit 60 (External Paving)	Wet: 81 Dry: 72
	Grit 120 (Internal Flooring)	Wet: 44* Dry: 63*
	* - Testing carried out on geologically similar stone – Basebed from Bowers Quarry
	Internal Flooring
	Independent Basebed 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)
	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 Bowers 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 which BRE Report 141 suggests that it is suitable for plain walling and cladding. The results from the other tests suggest that the 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 >50years) then it may be desirable to use a more durable stone (e.g. Portland Whitbed). When using Bowers 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)

Terms & Conditions | Privacy Policy