The objectives of this lab were:
1) Determine the bulk unit weight and percentage of air voids in the rodded coarse
aggregate sample
2) Evaluate the gradation of the fine aggregate sample and determine its fineness modulus
3) Determine the bulk specific gravity, the bulk specific gravity saturated surface-dry
(SSD), the apparent specific gravity, and the percent absorption of the coarse aggregate
4) Calculate the fine aggregate angularity (FAA) of the fine aggregate sample
5) Evaluate unexpected errors and determine possible causes
Theoretical Information/Literature Review:
Aggregates are individual particles usually containing crushed rocks, sand, and gravel
that are used as underlying materials. Aggregates are used to create a stable and sound base for
roadways and to create foundations for buildings. Aggregates have many important properties
used in portland cement and asphalt, in particular, such as angularity, elongation, particle size,
toughness, abrasion resistance, and soundness.
The scope of this lab was limited to such
aggregate properties as particle size and gradation, bulk specific gravity and absorption, bulk
density, percentage of voids, and fine aggregate angularity.
Bulk Unit Weight and Void Percentage
Bulk unit weight, or bulk density, measures the weight of an aggregate per unit volume.
By knowing bulk unit weight one can determine the percentage of voids when looking at
portland cement, which can help determine how much binder will be needed and how dense the
blend will be.
According to ASTM C29 procedure,
Bulk unit weight is the weight of aggregate
divided by the volume of the container in which it was measured (Materials for Civil and
Construction Engineers, 2011). The equation for bulk unit weight is below, in Equation 1:
(1)
where M is the bulk unit weight of the aggregate in g/cm
3
, G is the weight of the dry aggregate
sample in grams, T is the weight of the measure in grams, and V is the volume of the container in
cm
3
.
In order to determine the percentage of air voids in a mixture or blend of aggregates the
bulk dry specific gravity must be known. Equation 2, below, shows how to determine the
percentage voids between aggregates.
%
(2)
where P is the percentage of voids in the aggregate sample, S is the bulk specific gravity of the
aggregate, and M is the bulk unit weight of the aggregate in g/cm
3
, and W is the unit weight of
water in g/cm
3
.
2