Aggregate testing results, Cainozoic of north-east Scotland

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Merritt, J W, Auton, C A, Connell, E R, Hall, A M, and Peacock, J D. 2003. Cainozoic geology and landscape evolution of north-east Scotland. Memoir of the British Geological Survey, sheets 66E, 67, 76E, 77, 86E, 87W, 87E, 95, 96W, 96E and 97 (Scotland).

Contributors: J F Aitken, D F Ball, D Gould, J D Hansom, R Holmes, R M W Musson and M A Paul.

Aggregate testing results across the district[edit]

The strength and durability of aggregates from the district have been measured by a series of mechanical and physical tests. These were conducted in accordance with BS 812 (British Standards Institution, 1975), on the 10 to 14 mm gravel fraction taken from composite samples collected in each area of assessment. The tests included measurement of aggregate impact value (AIV), aggregate crushing value (ACV), ten per cent fines value, relative density (on both an oven-dried and surface dried basis), water absorption and measured concrete drying shrinkage. Aggregate impact value residue (AIVR) and aggregate crushing value residue (ACVR), as defined by Ramsay (1965) and Ramsay et al. (1973, 1974) were also calculated. Inferred concrete drying shrinkage values (which provide a crude estimate of concrete drying shrinkage) were determined, using the relationship between water absorption of gravel and concrete drying shrinkage established by Edwards (1970). The test results are summarised in the table below and discussed more fully in each Mineral Assessment Report.

Summary results of mechanical and physical testing of naturally occurring gravels from north-east Scotland
Test Garmouth MAR 41 Peterhead MAR 58 Ellon MAR 76 Aberdeen MAR 146 Inverurie Stonehaven MAR 148 Strachan Auchenblae Catterline Mar 149 Combined mean
Aggregate Impact Value 71(1) (11-18)(2) 23 (16-38) 22 (14-31) 28 (22-34) 25 (17-32) 27 (19-31) 24 (11-38)
Aggregate Impact Value Residue - - - 35 (29-43) 35 (26-52) 33 (26-41) 34 (26-52)
Aggregate Crushing Value 19 (13-20) - - - 20 (16-24) - 2 (13-24)
Aggregate Crushing Value Residue - - - - 39 (34-48) - 39 (34-48)
Ten percent Fines Value - 190 (95-270) 170 (120-280) 170 (120-230) - 150 (95-240) 170 (95-280)
Relative Density (oven dried basis) 2.57 (2.53-2.60) 2.50 (2.45-2.54) 2.59 (2.51-2.63) 2.58 (2.52-2.62) 2.55 (2.51-2.62) 2.53 (2.44-2.63) 2.55 (2.44-2.63)
Relative Density (surface dried basis) 2.60 (2.57-2.62) 2.56 (2.51-2.59) 2.63 (2.58-2.66) 2.62 (2.56-2.67) 2.60 (2.56-2.68) 2.59 (2.53-2.73) 2.60 (2.51-2.73)
Apparent Relative Density 2.65 (2.64-2.66) 2.66 (2.60-2.76) 2.71 (2.64-2.75) 2.67 (2.62-2.70) 2.69 (2.62-2.82) 2.69 (2.59-2.99) 2.68 (2.59-2.99)
Water Absorption (%) 1.1 (0.7-1.6) 2.1 (1.7-2.4) 1.8 (0.9-2.9) 1.3 (0.8-1.6) 2.0 (1.1-2.9) 2.2 (0.9-4.8) 1.8 (0.7-4.8)
Inferred Drying Shrinkage(3) (concrete) (%) 0.054 (0.044-0.063) 0.071 (0.064-0.077) 0.066 (0.048-0.088) 0.056 (0.046-0.063) 0.070 (0.052-0.088) 0.075 (0.047-0.126) 0.065 (0.044-0.126)
Measured Drying Shrinkage (concrete) (%) - - - 0.048 (0.039-0.054) 0.049 (0.040-0.065) 0.055 (0.040-0.073) 0.051 (0.039-0.073)
(1) Averaged results; these are listed fully in each of the six Mineral Assessment Reports.

(2) Figures in parentheses refer to the range of results. (3) It is emphasised that the ‘inferred’ drying shrinkage values quoted for concrete are obtained indirectly. They are probably anomalously high.

The AIV and water absorption results from the Garmouth assessment are the lowest from any aggregates tested during the assessments in north-east Scotland and suggest that these gravels are particularly durable. In general, the other mechanical and physical tests also show a smaller variation (range) of results than from any other assessment area and suggest that the resources are relatively homogeneous. The Garmouth results are probably representative of the sands and gravels in the lower Spey valley and reflect their high content of psammite and fresh granite clasts.

The results from the Ellon and Peterhead assessment areas are similar, but the AIV and water absorption results are higher than those from the Garmouth area, probably reflecting the higher proportion of nondurable rock types present in the gravels in the eastern parts of the district. The AIV figures are also higher than those obtained by Edwards (1970) from several gravel samples from north-east Scotland. However, they are comparable to values quoted by Edwards for ‘glacial mainly granite’ gravels in the district. Overall, most of the other testing results given in the table above also suggest aggregates of poorer strength and much greater water absorption than inferred by Edwards. A probable explanation for these disparities is that Edwards tested processed samples from stockpiles at working pits, whereas most of the samples tested during the assessment studies also included unprocessed material, collected from boreholes and trial pits.

The mechanical and physical testing results from aggregates in the Aberdeen assessment area indicate that they are generally significantly weaker than those from the Ellon and Peterhead areas. The range of values is also more restricted, suggesting relatively homogeneous gravel resources within the Aberdeen assessment area as a whole. Apparent relative density values are comparable to those from all of the other assessments, but the low water absorption values are comparable to those from gravels in the Garmouth area. As the gravels from Garmouth and Aberdeen are both mainly composed of granitic and psammitic clasts, the relative weakness of the Aberdeen material may reflect the derivation of many of the granite clasts from weathered bedrock.

The testing results from the Inverurie–Stonehaven and Strachan–Auchenblae–Catterline assessment areas are similar to those from Aberdeen, though they both have higher water absorption values. These higher values are thought to reflect the presence of highly weathered volcanic clasts and porous clasts of mudstone and sandstone within the gravels of the Drumlithie Sand and Gravel Formation in Strathmore.

Despite the variations recorded across the district the test results indicate that much of the coarse aggregate appears suitable for use in concrete. Nearly all of the measured concrete drying shrinkage values for aggregates from Aberdeen, Inverurie–Stonehaven and Strachan–Auchenblae–Catterline areas are below 0.065 per cent, suggesting that the aggregate is suitable for inclusion in concrete for ‘most applications’ (Building Research Establishment, 1968; Smith and Collis, 1993). The lower AIV figures and comparable water absorption figures from the Garmouth, Peterhead and Ellon assessments indicate that coarse aggregate from these areas is also probably suitable for more specific types of concrete. This conclusion is supported by the inferred concrete drying shrinkage figures, which, although anomalously high when compared with actual measurements (see table above), are generally below 0.085 per cent. Hence, most aggregate from the district is at least suitable for making general purpose concrete.


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