vacuum-saturated (PVS) LWA. [7][8][9][10][11] Autogenous shrinkage, however, is not a concern at the w/cm used in bridge decks, which are typically greater than 0.42.Research using porous normalweight aggregates in combination with slag cement as a partial replacement for portland cement has demonstrated that the combination can significantly reduce shrinkage compared to concretes containing porous normalweight aggregate without slag or nonporous normalweight aggregate with slag. [12][13][14][15] In this study of concretes with a w/cm typical of that used in bridge decks and at which autogenous shrinkage should not occur, the use of PVS LWA as a partial replacement for normalweight aggregate is investigated to determine its effectiveness at reducing shrinkage both with and without slag cement. Control mixtures without LWA containing normalweight coarse aggregates with both low and high absorptions are also tested.Powers 16 observed that the length of curing has little effect on concrete shrinkage. His work was based, however, on cements that were not ground as finely as those currently in use. The effect of an increased curing period on drying shrinkage is included in this study. RESEARCH SIGNIFICANCEThis study demonstrates that a partial replacement of normalweight aggregate with PVS LWA will reduce drying shrinkage and that the effectiveness of the LWA is enhanced through the use of slag cement. This study also demonstrates the positive impact of extended curing on reducing shrinkage. Taken together, the results provide the basis for a combined strategy to reduce drying shrinkageand by extension, the cracking that accompanies it-in reinforced concrete bridge decks. ExPERIMENTAL INVESTIGATION MaterialsThe concretes in this study contained Type I/II portland cement, river-run sand and pea gravel, 3/4 in. (19 mm) maximum-size crushed granite (with an absorption of 0.71 to 0.76%) or limestone (with an absorption of 3.07%) coarse aggregate, a polycarboxylate-based high-range waterreducing admixture (HRWRA), and a tall oil (liquid rosin)-based air-entraining agent. The LWA was expanded shale. Because the concrete is intended for use in low-cracking mixtures with low paste contents, an intermediate-sized

The shrinkage of mixtures containing replacements of total aggregate with prewetted lightweight aggregate (LWA) (0, 8, and 10% by volume) and replacements of cement with Grade 100 slag cement (0 and 30% by volume) and silica fume (0, 3, and 6% by volume) is evaluated. The results show that internal curing provided by prewetted LWA reduces the tendency of the mixtures to develop shrinkage strains. Further reductions are observed as slag is added in conjunction with prewetted LWA and as silica fume is added in conjunction with the prewetted LWA and slag.

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