Mixture Property

Medium and coarse grained aggregate Fine–grained, i.e. Clays and chalks (Rc typically ~ 1MPa.)
Strength Rc > 3MPa Rit > -0.2/0.25MPa
Immersed Strength Rimm > 80% Rimm > 80%
Frost Heave Limits Test not necessary if compliance with above Aim for no heave but pragmatically <2 or 3 mm
SO4 and S Limits Limits not usually necessary Yes limits required – refer to BP/16

Rc denotes compressive strength.

Rit denotes indirect tensile strength.

Rimm denotes the ratio of the strength of the specimens cured unprotected in water after an initial period of sealed curing, to the strength of the specimens cured totally in sealed conditions.

It should be noted, that these recommendations apply to all HBM irrespective of the frost susceptibility of the aggregate or soil in the unbound state.


Capillary Absorption Test

UK Materials Asian Materials
Fresh wet density – kg/m3 1950 1940
28 day sealed cube strength – N/mm2 2.4 2.6
28 day immersed cured cube strength – N/mm2 2.0 2.25
Capillary absorption – mg/mm2 0.05 0.37
Cat cube strength from D specimens – N/mm2 2.45 1.8

The very rigorous Capillary Absorption Test (CAT) is used to assess the weathering performance for pre-cast concrete cast stone durability specifies a maximum CAT value of 1 mg/mm2

Comparative results for different "concretes" are given below.

Material/Type Age Average Density – kg/mm2 CAT – mg/mm2
Limestone Rock 18 million years 2400 0.3 & 0.52
Cast Stone 28 Days 1990 0.19 & 0.30
CIC ecoProactive™ 28 Days 1950 0.05 & 0.37

This test method was used in view of the fact that both pre-cast stone which is instantly de mouldable and HBM are produced from similar consistency mixes requiring machine compaction to achieve the desired close finish and durable performance.