International Concrete Abstracts Portal

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).

An experimental program was planned and executed to demonstrate the feasibility of using lightweight high performance concrete (LWHPC) bridge beams and decks. The prestressed American Association of State Highway and Transportation Officials (AASHTO) beams were designed for a minimum 28-day compressive strength of 8,000 psi (55 MPa) and the deck concrete for 4,000 psi (27.6 MPa). The maximum permeability was 1500 coulombs for the beam and 2500 coulombs for the deck concrete. The density was less than 120lb/ft3 (1920 kg/m3). This program was a necessary prelude to an LWHPC demonstration bridge built over the Chickahominy River on Route 106 at the Charles City County New Kent County line in Virginia.

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.

This paper outlines the testing program developed for the Raftsundet Bridge, the first bridge in Norway that utilized pumping for placement of lightweight concrete. It reports the results from parallel testing of both normalweight and lightweight concrete performed during construction of this bridge. This paper also presents a discussion of the economics of using high performance lightweight concrete on the Rugsund Bridge. It also describes the Sundoy Bridge, the second bridge in Norway to utilize pumping for lightweight concrete placement. These projects confirm that high strength lightweight concrete is an economical, efficient construction material for long span bridges. While lightweight concrete may cost more per cubic yard than normalweight concrete, the structure may cost less as a result of reduced dead weight and lower foundation costs (1).

This work is part of a much larger program to evaluate high performance concrete mixtures that can be used successfully in hot dry climates. In this research magnetic resonance imaging (MRI) was used to measure the effectiveness of extending the moist curing period by incorporating some saturated lightweight aggregates into a concrete mixture being placed in hot dry climatic conditions. A series of concrete mixtures were prepared and moist cured for either 0, 0.5, 1 or 3 days, or by using a curing compound, followed by air drying at 38°C and 40% relative humidity. To accomplish this, 11% by volume of the total aggregate content was replaced with lightweight aggregate. Type I white portland cement and quartz aggregate plus the lightweight aggregate were all selected for their low iron content to minimize adversely affecting the MRI measurements. The concrete mixtures were low strength concrete (W/C=0.60), self-consolidating concrete (W/C=0.33 containing 30% fly ash), and high strength concrete (W/ C=0.30 containing 8% silica fume). Specimens prepared with these mixtures were cast in triplicate. After curing, the specimens were dried in one direction in an environmental chamber at 38°C and 40% relative humidity. As the specimens were drying, magnetic resonance imaging was used to determine the evaporable water distribution. After the drying period, the specimens were conditioned in an oven at 105°C and water absorption tests were undertaken to determine their sorptivity. The profiles obtained during drying indicated a reduced moisture loss with increasing length of moist curing. Also the use of saturated lightweight aggregate does not eliminate the need to provide some external moist curing for a reduced period of time. The results from water uptake experiments indicated that the addition of lightweight aggregate particles substantially increases the sorptivity in low strength concrete while it has only a marginal effect in both self-consolidating and high strength concrete, when compared to the same concrete mixtures containing only normal-weight aggregate.