ABSTRACT
A weighed sample of concrete is transferred to the elutriation column of the RAM. Fine material of 250μ m or less is raised as a suspension, sub-sampled (approx. 10% of original) and screened through a vibrating 150μ m sieve into a conditioning vessel in which the suspension is flocculated. The suspension then settles in a removable ‘constant volume vessel’ (CVV) which is brought to a constant volume state by the operation of siphons. The CVV is removed from the RAM and weighed. At the time of weighing, the CVV contains the separated fraction of fine material in a flocculated state plus supernatant water to give a reproducible total volume. The mass of flocculated fines weighs typically 120g. It consists of cement, of whichever type used, any additional/replacement materials and silt, clay and fines (passing 150μ m) from the 0aggregates; all in the same proportions, by mass, as contained in the original concrete sample. The mass of cementitious material and fine sand (‘silt’) in the original suspension is determined by reference to a calibration chart. The chart is previously established from tests on the components of the concrete typical of, or preferably precisely the same as, those to be used. The cement content is then determined by making a subtraction, silt correction, for the fines contributed by the aggregate.
