Table 2: Mixture design details

3.1.1 Concrete Mixtures

A summary of the mixtures design is provided in Table 2. The HES mixture was designed to meet standards provided by Pennsylvania Department of Transportation (PennDOT) for a 7-hr accelerated mix design whereas the conventional concrete mix was designed to meet PennDOT requirements for LLCP. Both mixes used Type I/II Portland cement with Type F fly ash. The coarse aggregates included #57 limestone and #8 sandstone, and the fine aggregate was concrete sand.

Table 2: Mixture design details

High Early Strength Mix Long-Life Conventional Paving Mix

Cement (lbs) 600

Pozzolan 1 (lbs) 150 Total Cementitious (lbs) 750 Coarse Aggregate 1 (lbs) 1309 Coarse aggregate 2 (lbs) 396 Total Coarse Aggregate (lbs) 1705

Fine Aggregate (lbs) 1158

Total Water (lbs) 236 W/C Ratio 0.315 Unit Weight (lbs/cu.ft) 142.93 477 134 611 1357 410

1767

1161 249 0.408 141.03

3.1.2 Laboratory and Field Testing

Three types of testing were conducted for this field study: conventional laboratory strength testing, maturity, and ultrasonic tomography. Laboratory testing was performed on cylinder and beam specimens to determine concrete strength in different ages. Maturity and ultrasonic data were collected on both the laboratory specimens and on the slabs in the field.

3.1.2.1 Laboratory Strength Testing

Compressive and flexural strength testing were performed (Figure 5). Cylinder and beam specimens were cast from concrete collected during the construction of slabs HES1 (HES) and C1.1 (LLCP). Standards ASTM C39, for compressive strength using 4 x 8-inch cylinders, and ASTM C78, for flexural strength using third-point loading, were applied (ASTM C39, 2015; ASTM C78, 2008). For the HES mix, compressive strength was estimated at 3, 5, 7, and 24 hours post construction. HES beams were only tested at 7 hours to determine the flexural strength at the suggested opening time. For the LLCP mix, both flexural and compressive

strength were computed from day 1 to day 28 after construction. Strength results are presented in Table 3 for compressive (f'c) and in Table 4 for flexural (MOR) strength.

PennDOT requires a conventional concrete mixture to reach a compressive strength of 3000 psi in 72 hours and 3750 psi in 28 days (Pub 408, 2021). LLCP mix was able to reach 3000 psi within the first 24 hours and far exceeded the 28-day requirement at 6219 psi. PennDOT also requires a HES mixture to reach 1200 psi in less than 7 hours (Zayed, 2018). The HES mix also met this requirement with a 7-hour strength of 2484 psi. Results show that both mixtures reach an average compressive strength of 3000 psi within the first 24 hours after construction indicating that both mixtures have a similar performance for this particular case study.

PennDOT does not have a minimum flexural strength to open to traffic. Several other states have flexural strength requirements for conventional concrete with opening strengths ranging from 400 to 750 psi (Ohio DOT Standards, 2019; TxDOT Standards, 2014; MnDOT Standards, 2013; NJDOT Standards, 2015). Within 7 days, the LLCP mix flexural strength was well over any state requirements at 819.3 psi. Five states that have HES specifications with flexural strength (California, Michigan, New Jersey, Ohio, and Texas) recommend opening strength ranging from 290 to 490 psi (Zayed, 2018; Ohio DOT Standards, 2019; TxDOT Standards, 2014; MnDOT Standards, 2013; NJDOT Standards, 2015). Results showed that at 7 hours, the recommended opening time for the HES mixture, the flexural strength was 360.9 psi, which falls into the suggested range based on other states’ policies.

(a) (b) HES

Figure 5: Conventional laboratory strength testing (a) compressive strength and (b) third-point loading for flexural strength