Highway Concrete Technology Development and Testing Volume IIi: Field Evaluation of SHRP C-205 Test Sites (High Performance Concrete)

Chapter 1. Introduction

BACKGROUND

This research study, sponsored by the Federal Highway Administration (FHWA), summarizes the field performance of high-early-strength (HES) concrete patches constructed under Strategic Highway Research Program (SHRP) study C-205. ⁽¹⁾ HES is designed to develop the strength needed for opening in 12 to 24 Hours through:

• The use of Type III cement.
• High cement content.
• Low water to cement (w/c) ratio.
• Addition of nonchloride accelerator –calcium nitrite.

A high-range water reducer (HRWR) is used in the mixture to maintain workability at a low w/c ratio.

The test sections were constructed between June 1991 and July 1992 in five States that represent a wide variety of environmental and exposure conditions: Arkansas, Illinois, Nebraska, New York, and North Carolina. The basic configuration of the test sections consist of six 4.6-meter (m) (15-feet (ft)) full-depth patches made with HES. Three of the patches were insulated for more rapid strength gain, and three were uninsulated for normal curing. The test sections in Arkansas, Illinois, and Nebraska are of this basic configuration. In New York, only three insulated patches were placed.

More extensive testing was conducted at the North Carolina site. The North Carolina section consists of 55 m (180 ft) of U.S. 17 on both driving lane and passing lane. The experimental factors for the North Carolina sections include the following:

• Insulation–insulated and uninsulated.
• Aggregate type – crushed gravel and marine marl.
• HRWR type – naphthalene and melamine.

The SHRP-C-205 report discusses aspects such as HES mixture proportioning, mixing and curing, laboratory experiments, and field installations.⁽¹⁾ Laboratory tests were conducted on both fresh or plastic and hardened concrete (both laboratory-cured and field-cored samples). These tests included the determination of fresh concrete properties such as slump, air content, and unit weight, as well as the estimation of the strength, modulus, shrinkage, and freeze-thaw durability for hardened concrete.

SHRP C-205 sHowed that it is possible to produce HES concrete that will achieve its desired strength (35 megapascals (MPa) or 5000 pounds per square inch (psi) in 24 Hours) using conventional materials and equipment. However, more care is needed during batching, placing, and finishing than for normal concrete.

The monitoring of the SHRP C-205 test sections conducted under this project sHowed that HES concrete patches can perform adequately in the field with no extraordinary signs of durability-related distresses under a wide range of climatic conditions. However, because the study only spanned 7 years into the life of the patches, additional monitoring is needed to evaluate the long-term durability of these materials.

DESCRIPTION OF THE FIELD SECTIONS

High-performance concrete patches constructed at the following sites were monitored as part of this study:

1. I–88 eastbound (EB) near marker 88I-9406-3158 in Otsego County near Worcester, NY
2. U.S. 17 just north of Williamson, NC
3. I–57 about 16 kilometers (km) (10 miles (mi)) north of Effingham, IL
4. I–40 less than 8 km (5 mi) west of Forrest City, AR
5. U.S. 20 at mile marker 361 (Station 435) northwest of Norfolk, NE

Brief descriptions of each patch, highlighting the various section details and other relevant site information, are presented below. Most of the information in this section was obtained from the original SHRP report. ⁽¹⁾

New York

This installation was a full-depth patch constructed on Interstate 88, near the town of Worcester (about 82 km (50 mi) west of Albany). The patch is located in the eastbound passing lane near reference marker 88I-9406-3158. The patch was constructed on June 25, 1991. The original pavement was approximately 12 years old at the time the patch was built.

The patch is approximately 18.3 m (60 ft) long, 3.7 m (12 ft) wide, and 225 millimeters (mm) (9 inches (in.)) thick, with doweled joints placed at 6.1-m (20-ft) intervals. Epoxy-coated dowel bars were used, and the patch was provided with welded wire mesh reinforcement. The subbase consists of a 300-mm (12-in.) layer of sand, gravel, slag, and stone. The longitudinal joint with the adjacent lane was greased to act as a bond breaker. This patch was fully insulated to simulate properties of very-early-strength (VES) concrete.

The climatic exposure of the pavement can be described as wet-freeze. The annual average daily traffic (AADT) was approximately 6,200 vehicles with about 20 percent trucks.

Type III cement was used in constructing the patch, and the coarse aggregate was a crushed limestone. The admixtures used in the project included an HRWR, an air-entraining admixture (AEA), and calcium nitrite. The materials were batched in different proportions in the laboratory prior to field installation, and the optimum mix design was selected. However, modifications had to be made in the field to the predetermined quantities to adjust for acceptable fresh concrete properties such as slump and air content.

Table 1 contrasts the laboratory concrete mix proportions with the proportions batched onsite. The field mixture proportions satisfied the laboratory-specified values, with the exception of the amounts of water and HRWR added. The mix water in the laboratory seems higher than the field value. However, this is only an apparent discrepancy since the reported laboratory value was adjusted for free water in the aggregates and the calcium nitrate admixture, whereas the field value was not. The total amounts of water in both the laboratory and field were presumed to be the same if this discrepancy is accounted for. The discrepancy in the HRWR contents was noted in the original SHRP report.⁽¹⁾ In the field, the HRWR was reduced to decrease the total slump and air content in the mixture.

Table 1. Comparison of final laboratory and actual field concrete mix proportions for the New York site. ⁽¹⁾

North Carolina

The experimental placement is on U.S. 17 over the Roanoke River, just north of Willamston. The pavement was constructed between July and August of 1991.

The high-performance concrete pavement was approximately 55 m (180 ft) long and two lanes wide. It was unreinforced and jointed at 4.6-m (15-ft) intervals. However, dowel bars were placed only at the end of each day's placement, with a maximum of 36.6 m (120 ft) between doweled sections. The inside lane was placed first, and its construction was controlled tightly, with emphasis on testing and materials. The lane was placed in three different sections, each 18.3 m (60 ft) long. The outside lane concrete was placed using typical North Carolina Department of Transportation (NCDOT) batching and placement rates, also in three 18.3-m-long (60-ft-long) sections. Here the emphasis was to study the impact of routine construction metHods on variations in the product delivered. The minimum depth of the patches is 225 mm (9 in.). The pavement section was built on an asphalt base course.

To mimic the strength development of VES concrete, some of the sections were insulated by first covering them with plastic sheets and subsequently placing 25-mm-thick (1-inch-thick) rigid-foam building insulation on the slab. The insulation was removed after 6 Hours. The pavement can be described as being exposed to a mild marine environment.

Type III cement and two coarse aggregate types–crushed granite (CG) and marine marl (MM)–were used in preparing the concrete mixture. The CG aggregate is very hard and tough, whereas the MM is a relatively porous shell limestone. In addition, two different HRWRs were used, one with a melamine base and the other with a naphthalene base. Apart from this, AEA and calcium nitrite were used as admixtures. Taking into account the curing metHods employed (insulation versus no insulation) and the different admixtures and aggregates used, a total of eight unique combinations of test sections were built at the North Carolina site. All the mixtures contained the same nominal cement content and had approximately the same w/c ratio. The fine aggregates used in all the mixes were also the same.

Illinois

Two high-performance concrete experimental patches were constructed on Interstate 57, about 16 km (10 mi) north of Effingham. The patches were constructed in October 1991 and are situated in the outside lane of the northbound highway, separated by a distance of 305 m (1000 ft). The original pavement was approximately 24 years old when the patches were built.

The patches are 13.7 m (45 ft) long, 3.7 m (12 ft) wide, and 250 mm (10 in.) thick, with doweled joints placed at 4.6-m (15-ft) intervals. Epoxy-coated dowel bars were used at all transverse joints. Both patches were constructed with welded wire fabric. The patches were placed on the existing granular subbase. One of the patches was fully insulated; the other was not.

The pavement is situated in a wet-freeze environment. The average daily traffic (ADT) for this roadway is approximately 11,800 with approximately 22 percent trucks. Type III cement and limestone coarse aggregate were used in constructing the patch. The admixtures used in the project included an HRWR, an AEA, and calcium nitrite. The materials were batched in different proportions in the laboratory prior to field installation, and the optimum mix design was selected. However, modifications had to be made in the field to the predetermined quantities to adjust for acceptable fresh concrete properties such as slump and air content.

Table 2 contrasts laboratory concrete mix proportions with proportions batched onsite. The onsite proportions were computed by taking averages of quantities used to prepare batches for each of the six trucks that delivered the concrete to the patches. The field mixture proportions satisfied the laboratory-specified values, with the exception of the water content added to the mix. It is assumed that this discrepancy can be attributed to the fact that the field water content reported does not include the water contributed from the calcium nitrite and the aggregates. AltHough the water content in the field could not be determined for this site due to lack of information about the exact amount of water contributed to the mixture by the aggregate, it was presumed in the original SHRP study that the laboratory and field values match approximately. ⁽¹⁾

Table 2. Comparison of final laboratory and actual field concrete mix proportions for the Illinois site. ⁽¹⁾

Arkansas

The Arkansas installation is on Interstate 40, less than 8 km (5 mi) west of Forrest City. There are two patches in the passing lane of the westbound traffic near mile marker 237. The patches are separated by a distance of about 152 m (500 ft) and were built in November 1991. The original pavement was approximately 25 years old when the patches were built and was built on cement-treated subgrade.

The patches are 13.7 m (45 ft) long, 3.7 m (12 ft) wide, and 250 mm (10 in.) thick, with doweled transverse joints placed at 4.6 m (15 ft) intervals. One of the patches (the easternmost) was insulated with rigid foam insulation for about 3.5 Hours after the concrete had set.

The pavement is situated in a wet environment with potential for freeze-thaw cycling. The two-way AADT near the installation was approximately 19,890 vehicles with just over 47 percent trucks.

Type III cement was used in constructing the patch, and the coarse aggregate was limestone. The admixtures used in the project included an HRWR, an AEA, and calcium nitrite. The materials were batched in the laboratory in accordance with the original HES mix design prior to field installation.⁽¹⁾ With the exception of a minor modification to the quantity of AEA, the rest of the original HES mix design was adopted. This adjustment was necessitated to achieve the target air content. Table 3 presents a comparison of the laboratory concrete mix proportions with the proportions batched onsite. The onsite proportions were computed by taking averages of the quantities used to prepare batches for each of the six trucks that delivered the concrete to the patches.

Table 3. Comparison of final laboratory and actual field concrete mix proportions for the Arkansas site. ⁽¹⁾

Based on the field batching, the w/c ratio was 0.27, and the standard deviation was 0.002 between batches. The average entrained air content, slump, and unit weight were 4.6 percent, 183 mm (7.2 in.), and 2318 kg/m3 (143 lb/ft3), respectively.

Nebraska

Two high-performance concrete patches were built in Nebraska on the eastbound lane of U.S. Highway 20 between the towns of Osmond and Plainsview. The patches, constructed in July 1992, are the youngest of all the sections discussed in this report. The original concrete pavement was built in 1957 and consists of a 200-mm (4-in.) granular subbase resting on a silty clay subgrade.

The patches are 14.64 m (48 ft) long, 3.35 m (11 ft) wide, and 200 mm (8 in.) thick. They were built end to end. One patch was insulated during the construction for roughly 5.5 Hours after the concrete had set. Transverse joints were sawed at 4.9-m (16-ft) intervals within each patch, and epoxy-coated dowel bars were placed at all transverse joints.

The pavement is situated in a wet environment with a very high potential for freeze-thaw cycling. Approximately 1,500 vehicles per day with about 20 percent trucks constitute the traffic at the site.

Type III cement was used in constructing the patch, and the coarse aggregate was limestone. The admixtures used in the project included an HRWR, an AEA, and calcium nitrite. The materials batched in the laboratory were, for the most part, in accordance with the original HES mix design, but the coarse aggregate and fine aggregate contents were reversed to suit local practice.⁽¹⁾ This adjustment was necessitated to reduce the probability of alkali-silica reactivity (ASR) prevalent in the area.

Table 4 presents a comparison of the laboratory concrete mix proportions with the proportions batched onsite. The onsite proportions were computed by taking averages of quantities used to prepare batches for five of the six trucks that delivered the concrete to the patches. Data from one of the trucks was not used since the slab poured with the concrete mix from this truck was eventually replaced. It can be noted from the table that the field batching followed the laboratory specifications quite well.

Table 4. Comparison of final laboratory and actual field concrete mix proportions for the Nebraska site. ⁽¹⁾

SUMMARY OF SECTION PROPERTIES – EXPERIMENTAL DESIGN

Table 5 presents a summary of fresh concrete properties and important climatic indicators for each of the five experimental sites considered in this study. Mean values of the concrete w/c ratio, slump, air content, and unit weight are included in the table along with measures of variability of these properties within each site. The data presented in the table will be valuable in interpreting the long-term concrete performance data collected as part of this study and to draw important conclusions about the applicability of high-performance concrete as a patching material.

The data on the average number of freeze-thaw cycles and the average freezing index were not collected at the sites under consideration in this study. They were determined from the Long-Term Pavement Performance (LTPP) climatic database from a weather station closest to the site under consideration. Also, the freeze-thaw cycles reported were based on air temperature and not pavement temperature. The actual pavement freeze-thaw cycles will be lower than this value, the exact magnitude being a function of several other site and pavement variables. Regardless, since the same parameter was used for all the sites, these data sHould give a relative indication of the climatic conditions at each of the sites.

Table 5. Summary of materials, site factors, and fresh concrete properties for the SHRP C-205 sites.

Based on the freeze-thaw cycle information presented in table 5, the Nebraska and New York test pavements are in the harshest cold-weather climate, followed by Illinois, North Carolina, and Arkansas. The North Carolina section uses different coarse aggregates than the others. The mix proportions are relatively uniform (not all mix information is presented in the table), except for some variation in the w/c ratio. The factorial presented in the table forms a good basis for reasonable comparison of the durability of high-performance concrete.

OBJECTIVE AND SCOPE OF THE STUDY

The objective of this study was to perform long-term performance monitoring to verify the effectiveness of high-performance concrete patches constructed in the previously referenced SHRP study. The emphasis during this monitoring effort was on determining the durability and integrity of the concrete over time. The following work items were undertaken to realize the objective of the study:

• Collection of important site information such as weather conditions, traffic, use of deicers, and maintenance history of the pavement sections.

• Visual inspection using standard SHRP distress identification procedures to detect durability problems such as joint spalling and cracking.

• Obtaining pHotograph and video logs of each patch and the sections within each patch to record the progression of distress.

• Obtaining and testing cores for compressive strength, elastic modulus, rapid chloride permeability, and asphalt concrete (AC) impedance.

Visual inspections of the patches were to be performed once every year for a period of 5 years beginning in 1994. Cores were obtained from the field in alternate years instead of every year, as was intended in the original project plan.