|FHWA > Engineering > Pavements > Concrete > High Performance Concrete Pavements: Project Summary > Chapter 32|
High Performance Concrete Pavements
(SLAG MIX #2)
(SLAG MIX #1)
|Portland cement quantity, lb/yd3 (kg/m3)||374 (222)||394 (234)||423 (251)|
|GGBFS quantity, lb/yd3 (kg/m3)||160 (95)||169 (100)||-|
|Class F fly ash quantity, lb/yd3 (kg/m3)||-||-||142 (84)|
|Pozzolan quantity, lb/yd3 (kg/m3)||30 percent||30 percent||25 percent|
|Course aggregate No.||357||57||57|
|Maximum top size, in (mm)||2 in (50 mm)||1 in (25 mm)||1 in (25 mm)|
|Course aggregate quantity, lb/yd3 (kg/m3)||1935 (1148)||1841 (1092)||1841 (1092)|
|Fine aggregate quantity, lb/yd3 (kg/m3)||1171 (695)||1217 (722)||1229 (729)|
|Water, lb/yd3 (kg/m3)||243 (144)||249 (148)||249 (148)|
|Water-to-cementitious materials ratio (w/cm)||0.45||0.44||0.44|
agent + retarder
agent + retarder
agent + retarder
Comparing the mix design of section 1 (the larger aggregate) with the mix designs for the other two sections, it is observed that the use of the larger aggregate did slightly reduce the required quantities of water and cementitious materials (Ozyildirim 2000).
Dowel bars were placed in baskets at the predetermined joint locations prior to the paving operations (Ozyildirim 2001). Transverse joints were cut initially 4.75 mm (0.19 in.) wide to a depth of one-third of the slab thickness (Ozyildirim 2001). A secondary cut was made 2 weeks later to establish the joint reservoir for the silicone sealant.
A water-based curing compound was used to cure the pavement, except that the appropriate materials could not be obtained during the placement of the westbound lanes (Ozyildirim 2001). Consequently, a white plastic sheeting was used to cure the pavement for 10 days (Ozyildirim 2001).
During construction, one outside slab in each of the three sections in the westbound lanes was instrumented to record strains, displacements, and temperatures in the slab (Ozyildirim 2000). Two vibrating wire strain gauges were placed in the middle of each slab, one 38 mm (1.5 in.) from the top of the slab and one 38 mm (1.5 in.) from the bottom of the slab (Ozyildirim 2000). Two additional vibrating wire strain gauges were tied to two stainless steel stakes and driven into the base (Ozyildirim 2001). The gauges were placed 2 m (6.5 ft) from the outside edge to avoid the vibrator of the paver (Ozyildirim 2001).
Two linear variable differential transformers (LVDTs) were installed in each of the slag concrete pavement sections to measure vertical displacements due to curling (Ozyildirim 2001). One LVDT was placed at the center of the slab and the other 280 mm (11 in.) from the joint (Ozyildirim 2001).
Type T thermocouples were placed at each location in the slab where the vibrating gauges were placed. The thermocouples were placed at 6 mm (0.25 in.), 76 mm (3 in.), 140 mm (5.5 in.), 203 mm (8 in.), and 273 mm (10.75 in.) above the base (Ozyildirim 2001). In addition, the vibrating wire gauges included thermistors that provide temperatures at the each location (Ozyildirim 2001).
Finally, 10 consecutive joints in each section were instrumented to monitor transverse joint movements (Ozyildirim 2001). Gauges were placed on either side of the joints 1 week after paving (Ozyildirim 2001).
During and immediately after construction, VDOT conducted an evaluation of the fresh and hardened concrete properties of each pavement section. Table 51 summarizes some of the selected concrete properties obtained from the monitoring. Both the fresh concrete properties and the hardened concrete properties generally met design requirements, but there was a noticeable difference in the properties of the mixtures between the westbound and eastbound lanes. Generally speaking, the westbound lanes had lower strengths and higher air contents than the eastbound lanes.
Comparisons of the different mixes show that the slag mixes (sections 1 and 2) have higher strengths than the fly ash mixes. Interestingly, the section 2 mixes had higher strengths than the section 1 mixes, even though the section 1 mixes had a larger coarse aggregate size.
The chloride ion permeability test measures the electrical conductance of a sample, and VDOT specifies a maximum of 3500 coulombs (Ozyildirim 2001). All of the mixtures exhibit permeabilities much less than that value, with the fly ash mixtures the lowest of all of the mixtures. All of the sections exhibited similar shrinkage values, with the section 1 mixture (containing the largest maximum coarse aggregate size) exhibiting the least amount of shrinkage.
The acceptance criteria for freeze-thaw data shown in Table 51 are a weight loss of 7 percent or less and a durability factor of 60 or more (Ozyildirim 2001). All mixtures complied with these requirements except the fly ash mixtures exceeded the allowable weight loss. However, this is a severe test and the fly ash mixtures are expected to perform satisfactorily in the field provided that they have adequate strength and an adequate air void system (Ozyildirim 2001).
|CONCRETE PROPERTY||SPECIMEN SIZE, IN.||SECTION 1|
(2-IN. AGG W/SLAG)
(1-IN. AGG W/SLAG)
(1 IN. AGG W/FLY ASH)
|Concrete temperature, °F||86.5||67||85.5||68||82||67|
|Unit weight, lb/yd3||145.6||144.2||147||145.6||147.6||143.8|
|28-day compressive strength, lbf/in2||6 x 12||5446||4530||5540||4625||4612||3920|
|28-day flexural strength, lbf/in2||6 x 6 x 20||704||670||783||685||-||-|
|Permeability, coulombs||4 x 4||1364||1774||1548||1672||680||1265|
|1-year shrinkage, %||6 x 6 x 200||0.041||0.052||0.044||0.059||-||-|
|Freeze-Thaw Data at 300 cycles (ASTM C 666, Procedure A, except air dried 1 week and 2% NaCl in test solution)|
|Weight loss, %||5.3||4||2.3||6||11.6||14.1|
Monitoring of the instrumented slabs was conducted during the first several weeks after construction, along with transverse joint movements. Generally, larger thermal gradients were observed for section 2, but all of the differences were really quite small (Ozyildirim 2001). Section 1 (larger aggregate) showed less curling than section 2, but again the differences were small (Ozyildirim 2001). Limited FWD testing showed nearly identical load transfer efficiencies of 85, 85, and 88 percent for section 1, 2, and 3, respectively (Ozyildirim 2001).
After 2 years and 6 months of service, respectively, both the westbound sections and the eastbound sections are in excellent condition, with no distress or scaling (Ozyildirim 2001). VDOT will continue monitoring the performance of these pavements and will produce a final report in 2004 (Ozyildirim 2000).
This project has illustrated that air-entrained paving concrete with satisfactory strength, low permeability, and volume stability can be prepared using concrete with Class F fly ash or slag, and with 25- and 50-mm (1- and 2-in.) maximum size aggregates (Ozyildirim 2000; Ozyildirim 2001). The larger maximum size aggregate is expected to provide better performance in the field, and it will be monitored over the next 5 years. Although the reduction in water and cement contents was minimal for the mix with the larger sized aggregate, the use of a more uniform combined grading is expected to reduce water and paste demands (Ozyildirim 2000; Ozyildirim 2001). The instrumentation did not provide any strong results regarding the relative performance of the different pavement sections (Ozyildirim 2000; Ozyildirim 2001).
No interim field testing results have been published, nor were they available for this update. However, an additional field evaluation will be conducted in the spring of 2004 that will include FWD and automated distress measurements. Results of these field reviews will be included in the final project report that is slated to be complete in August 2004.
Virginia Transportation Research Council
530 Edgemont Road
Charlottesville, VA 22903
Ozyildirim, C. 2000. Evaluation of High-Performance Concrete Pavement in Newport News, VA. Draft Interim Report. Virginia Transportation Research Council, Charlottesville.
---. 2001. "Evaluation of High-Performance Concrete Pavement in Newport News, VA." Preprint Paper 01-3173. 80th Annual Meeting of the Transportation Research Board, Washington, DC.
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