Samples

The mixture proportions of the samples prepared for this experiment were designed to yield a moderate range of transport properties and are based upon mixture proportions from previous experiments [30]. The wide range of transport properties were achieved through variations in water-cement ratio (w/c), cement replacement by pozzolanic mineral admixtures, aggregate gradation and volume fraction, and dosage of high range water reducing admixture (HRWRA). The cement was ASTM Type 1; the chemical composition is given in Table 1. The pozzolanic mineral admixture was silica fume in slurry form. The aggregate type was natural silica and two gradations were used: silica sand conforming to the ASTM C 778 Graded Sand designation; and a "micro" concrete aggregate composed of natural silica sand. The gradation for the "micro" concrete aggregate, based upon a report by Fuller[31], is shown in Table 2. The HRWRA was a 40 % (by mass) aqueous solution of naphtalene-sulfonate. The mixture proportions of the samples used in this experiment are shown in Table 3.

Table 1: Chemical composition of the Type 1 cement used in this experiment.

Oxide	Mass %
Calcium	63.73
Silica	21.63
Aluminum	4.27
Iron	3.02
Sulfur	2.69
Magnesium	2.26
Free Lime	0.75
Potassium	0.51
Sodium	0.21

Table 2: Specification for "Micro" concrete aggregate proportions. Designation C 778 indicates conformity to specification ASTM C 778

Designation	Particle Size (µm)	Mass Fraction (%)
S15 1	2360-600	37
C 778 (20-30)	850-600	19
C 778 (Graded Sand)	600-300	19
F95 1	300-200	25

¹Product of U.S. Silica Company (Ottawa, IL).

Table 3: Sample mixture proportions. Relevant quantities are the sand gradation, the sand:cement ratio S/C, the water:cementitious materials ratio w/(c+s), cement mass replacement by silica, HRWRA dosage with respect to cement mass, and the air content as measured using a procedure based upon the specification ASTM C 185.

Sample	Sand Gradation	S/C	w/(c+s)	Silica %	HRWR %	Air %
A	-	-	0.30	-	-	53.7
B	-	-	0.45	-	-	11.3
C	C 778	2.75	0.60	-	-	4.2
D	C 778	2.02	0.36	-	0.09	6.7
E	Micro	1.41	0.29	-	0.40	1.2
F	Micro	2.02	0.36	-	0.09	2.0
G	C 778	2.75	0.49	10	0.40	8.5
H	Micro	2.02	0.36	10	0.40	2.1
I	-	-	0.25	-	-	2.6
J	C 778	2.75	0.49	-	-	8.6
K	C 778	1.40	0.29	-	0.40	4.2
L	Micro	2.75	0.49	-	-	3.9
M	Micro	2.02	0.49	-	0.09	0.1

Note: Designation C 778 refers to a product conforming to the specification for Graded Sand in specification ASTM C 778.

The mixtures were prepared according to the procedures in ASTM C 109. The samples were cast in 100 mm diameter and 200 mm long cylindrical molds, covered, and stored in a 100% relative humidity chamber. At 24 hours of age, the specimens were removed from the molds and stored in a saturated calcium hydroxide bath until they were tested (50-80 days). Although no temperature controls were used, the laboratory temperature could be characterized by the interval 20± 2 º C.

Each specimen was prepared for testing according to the specifications of ASTM C 1202. A single cylinder mold was cast from each mixture and two specimens, one specimen 50 mm long (ASTM C 1202) and the other 100 mm long, taken from the middle 150 mm of the cylinder, were tested. The purpose of using two specimen lengths was to verify the validity of the conductivity measurement techniques. Conductivity, an intrinsic property, is independent of specimen geometry and size. A reliable technique for determining specimen conductivity should obtain equivalent results from replicate specimens with different lengths.