The use of internal curing is a highly effective means of mitigating autogenous shrinkage in cement mortars (w/cm=0.35, 8 % silica fume). Two different sources of internal water supply are compared: 1) replacement of a portion of the sand by partially saturated lightweight fine aggregate and 2) the addition of superabsorbent polymer particles (SAP). At equal water addition rates, the SAP system is seen to be more efficient in reducing autogenous shrinkage at later ages, most likely due to a more homogeneous distribution of the extra curing water within the three-dimensional mortar microstructure. A comparison of the water distribution in the different systems, based on computer modeling and direct observation of two-dimensional cross sections, is given.

This paper presents the findings of a research project conducted at Georgia Tech that tested six pretensioned AASHTO Type II girders constructed using expanded slate lightweight concrete with design strengths of 8,000 and 10,000 psi (55.2 and 68.9 MPa). Actual strengths ranged from 8,790 to 11,010 psi (60.6 to 75.9 MPa). Each was prestressed using 0.6-inch (15.2-mm) diameter low relaxation strands tensioned to 75% of strand ultimate stress. External strain measurements showed transfer lengths of 21.9 inches (556 mm) and 15.6 inches (396 mm) for the 8,000 and 10,000 psi (55.2 and 68.9 MPa) concretes; these were 73 percent and 52 percent of the design values given by AASHTO 16' Edition. Three-point bending tests were conducted on each beam to determine development length characteristics. The distance from the beam end to the load point was varied from between 70 and 100 percent of the AASHTO specified development length. Strand slip was measured for each test. Results indicated that the development lengths were 91 inches (2.31 m) and 67 inches (1.70 m) for the 8,000 and 10,000 psi (55.2 and 68.9 MPa) concretes; these were 95 percent and 70 percent of the design development lengths given by AASHTO 16th Edition.

SP-218 This is a compilation of papers addressing “High-Performance Structural Lightweight Concrete” presented October 30, 2002 at the American Concrete Institute Fall Convention in Phoenix, Arizona. This symposium was sponsored by ACI Committee 213, Lightweight Aggregate and Concrete, to report on a wide range of global construction applications incorporating high-performance lightweight-aggregate concrete. This diverse symposium included papers that covered microstructural issues (autogenous shrinkage, internal curing), material and structural properties (transfer length, shear strength, seismic behavior), and applications in large civil structures (long-span balanced cantilever bridges, offshore platform, float-in navigational locks).

The Texas Department of Transportation sponsored Project 0-1852 at The University of Texas at Austin to determine the feasibility of using high-performance lightweight concrete in composite bridge girders and precast concrete deck panels. The scope of the research project included lightweight concrete mixture design development; full scale testing of TxDOT Type A (AASHTO Type I) girders with composite decks; an analytical design comparison of normal and lightweight concrete girders with various deck combinations; and an economic analysis. The purpose of this paper is to highlight some of the findings of this research to give engineers and designers a better understanding of high-performance lightweight concrete and its use in composite bridge systems. Some of the potential advantages of using lightweight concrete include lower loads on the substructure and foundation, lower crane capacities, increase in live load capacity, and lower shipping costs. However, lightweight concrete has unique features that must be considered during the design phase to insure a successful project. Some of these considerations include higher material costs and the higher elastic shortening losses that will result due to a lower modulus of elasticity.

Since more than 70 years ago, lightweight concrete has been used in the marine environment. Prime examples use are the ship Selma, grounded off Galveston; and several other ships of that age, laid up, still able to float. Over the last couple of decades, interest in the actual performance of marine lightweight concrete has grown, and in consequence several studies have been made, covering durability, mechanical properties and design procedures. Since other papers in the session will be concerned with many of the structures that have been placed in or near the sea, these objects are not central to the presentation — the same can be said for general questions like design procedures, long term mechanical properties and the like. The central issues of the paper are specifically related to the marine environment: durability — namely reinforcement corrosion — is briefly touched upon, and water absorption over time and at depth is given more attention. This paper is an opportunity to publish data gathered more than 10 years ago; used, but never made available generally.