Experimental

Cement mortars with a water-cement mass ratio (w/c) of 0.40 were prepared using Cement and Concrete Reference Laboratory (CCRL) proficiency cement sample 140¹⁶ and a blend of four sands. Complete mixture proportions are provided in Table 2. The mortars were prepared in an epicyclic mixer (one internal rotating shaft contained within a larger shaft that also rotates), with the cement and water first being mixed together for 30 s on low speed. Then, all of the sands were added during the course of an additional 30 s of low speed mixing. After mixing for 30 s more on medium speed, the sides of the mixing bowl were scraped down and the mixture was allowed to set for 90 s, before 1 min of final mixing on medium speed. The mortars were immediately cast into 5 in (127 mm) by 7 in (178 mm) plastic photographic trays to a depth of about 5/8 in (16 mm). The trays were weighed and immediately placed in an environmental chamber maintained at 23 ºC (73.4 ºF) and 50 % RH. About 920 g (2 lb.) of mortar were placed in each tray. At various times after mixing, the trays with the mortars were weighed once again, and then sprayed with a solution of either distilled water, a solution containing 10 % of a commercially-available SRA by mass fraction, or a solution containing 20 % SRA. A spray bottle was used in an attempt to apply a uniform layer of the solution to the top surface of the mortars. The mass of the trays was determined immediately after applying the solution and periodically over the course of the subsequent drying exposure. Typically, 10 g (0.35 oz.) of solution was applied to each mortar in this one-time application. The time of application of the "curing" solutions was varied between 1 h and 3 h after the initial casting to monitor the influence of this variable on the subsequent evaporative water loss and achieved degree of hydration. Degrees of hydration were estimated using loss-on-ignition (LOI) analysis, correcting for the LOIs of the cement powder and the four sands used in the mortar mixtures. Based on a propagation of error analysis, the estimated uncertainty in the calculated degree of hydration was 0.01.¹⁷ In a separate casting, three small cuvettes, 10 mm x 10 mm x 40 mm, were filled with the mortar and about 0.2 g (0.007 oz.) of the curing solutions were immediately added to the top of each cuvette. After 6 d curing at 23 ºC and 55 % RH, the specimens were removed from each cuvette, broken in half, and the evaporable and non-evaporable water contents of the top and bottom sections of each specimen were determined by heating in an oven at 105 ºC overnight, followed by heating in a furnace at 1000 ºC for 4 h.