The lower water content of roller-compacted concrete (RCC) coupled with climatic conditions (e.g., higher air temperature, increased wind speed, and lower relative humidity) and compaction delay factors (e.g., traffic delay, plant location, and paving speed) can significantly affect the in situ density and hardened properties of RCC pavements. In this study, a control RCC mix was batched and maintained at standard (21°C) and elevated (35°C) temperatures and then compacted at increasing delay times for up to 180 min. The elevated mix temperature and compaction delay times greater than 90 min prevented the RCC mix from achieving 98% of the initial wet density from the modified Proctor test. Two additional RCC mixes were batched to determine if they could maintain a longer compaction window, one containing a rheology-modifying and retarding admixture and the other incorporating saturated fine lightweight aggregates. The RCC with admixture was the most effective at maintaining moisture content, density, compressive strength, and fracture properties at all compaction delay times. For example, at 180 min of delay, the RCC mixture with admixture still maintained 98.2% of the initial wet density, 81% of the compressive strength, and approximately the same fracture toughness and energy. The addition of fine lightweight aggregates did not extend the compaction window relative to standard RCC mix. The gyratory compacted specimens were more sensitive to the effects of temperature and compaction delay on RCC mixes than the vibratory hammer prepared specimens.

Modern Roller-Compacted Concrete (RCC) pavements are being increasingly specified in the U.S. because of their construction expediency, material cost savings, and early opening to traffic. RCC mixture proportioning and adjustments are not as well understood as conventional concrete mixtures. The objective of this study is to provide guidance in selecting the initial RCC mixture proportions and adjustments as needed to achieve target properties. A statistically-based experimental design was developed to determine the combined effect of three independent, mixture variables on RCC properties: cementitious content, sand percentage, and fly ash dosage. Predictive response equations and contour plots were derived to predict moisture-density and strength based on the RCC mixture proportions and constituents. Significant increases in sand percentage in the RCC mixture was found to have a negative effect on density and strength of RCC.

The addition of macro-fibers to concrete slabs on ground have been shown to increase flexural capacity, fatigue resistance, reduce crack deterioration rates, and assist in shear transfer across joints and cracks. A laboratory study was performed to determine the benefits of macro-fibers in roller-compacted concrete (RCC) for pavements by measuring the change in RCCs mechanical properties and comparing it to conventional fiber-reinforced concrete for pavements. Six fiber types, four synthetic and two steel, with several fiber geometries were incorporated into RCC mixtures at two dosage levels (0.2% and 0.4% by volume). The addition of synthetic macro-fibers increased the maximum dry density (MDD) over the control RCC mix by reducing the internal friction between aggregates whereas steel fiber had a limited impact on the MDD of RCC. For several fiber types, the resultant RCC with fibers had a statistically significant increase in compressive and split tensile strength relative to the control RCC mix. The addition of fibers did not increase the flexural strength of RCC but did noticeably improve the post-peak and residual strength capacity of RCC. The increases in residual strength were dependent on the fiber type and geometry, similar to the behavior in conventional Portland cement concrete (PCC). The fracture properties of RCC with fibers based on disk-shaped compact tension (DCT) tests were shown to be similar or greater than PCC with fibers which indicates both RCC and PCC pavements, when properly constructed, will have similar fracture and fatigue resistance. (C) 2017 Elsevier Ltd. All rights reserved.

Roller-compacted concrete (RCC) pavements present three primary challenges relative to conventional concrete pavement: mixture design, structural design details, and construction process and verification. An investigation was initiated to reconcile the discrepancy between the field and laboratory properties of RCC pavements because of differences in laboratory mixture design procedures and field construction processes. Four RCC pavement projects in Illinois were selected for field coring along with sampling of RCC constituent materials for replication of the laboratory mixture design. Density measurements of field cores indicated that density decreased with depth into the pavement structure and the relative density at paving-lane joints could be as low as 80%. Statistical differences in compressive strength and fracture properties between field and laboratory samples were observed and result from differences in density. A 4% difference in density between field and laboratory samples resulted in an approximate 45% difference in compressive strength. The reduction in field RCC strength and fracture properties relative to the values obtained in the laboratory will result in decreased slab flexural capacity and field performance. Application of the gyratory compactor demonstrated that it can be used repeatedly to compact most RCC mixtures to similar target densities as the modified Proctor method and field-extracted cores. The gap between field and laboratory properties of RCC can be reduced by application of high-density pavers; improvement in mixture design procedure with the gyratory compaction method; a foundation layer beneath the RCC that is stiffer, thicker, or both; reduced RCC lift thicknesses to achieve specified density; or all of these.

This study addresses the feasibility of using coarse fractionated reclaimed asphalt pavement (FRAP), quarry by-products (QB), and macro-synthetic fibers in a cement-stabilized base course application that can be used for inverted pavements or simply as a stronger, more durable base course. The addition of macro-synthetic fibers is studied to add flexural ductility and resistance to crack propagation to the stabilized base course. The use of recycled and by-product aggregates that would otherwise be stockpiled, could improve the durability and permanence of the base course, and reduce surface course thicknesses. Laboratory characterization includes testing flexural toughness and fracture properties. Study results have confirmed more than sufficient mechanical properties are achieved relative to other stabilized base courses. Furthermore, the addition of fibers clearly increases the flexural capacity and fracture properties of the cement treated FRAP and quarry by-product base course mixes. While current pavement design procedures do not account for fracture properties or the effects of fibers (especially in cement stabilized base courses), it is clear that these parameters show trends that conventional strength testing (compressive and flexural) does not and therefore, they should be accounted for in design.

A laboratory study was conducted to demonstrate that sustainable cement-treated base courses can be achieved through the application of waste quarry by-products (QB) and fractionated reclaimed asphalt pavement (FRAP). Aggregate packing tests were performed on blends of QB and FRAP to determine an optimal blend that would minimize the void content of the aggregate structure while achieving acceptable strengths. The optimal aggregate packing proportions were found to be 70% QB with 30% FRAP. Modified Proctor samples were prepared to determine the moisture–density relationship with several cement contents (2% to 4% by total volume) on dolomite or FRAP coarse aggregate mixed with QB and 0.4% synthetic macrofibers. Mixture design performances were evaluated through strength (compression and split tension) and modulus tests. As expected, higher cement content increased both the strength and elastic modulus for all mixes tested. Mixtures containing virgin aggregates with QB yielded statistically greater elastic moduli than mixtures with FRAP and QB. Fibers did not have a statistical effect on strength or elastic modulus but did provide residual shear capacity across cracks. The QB and FRAP or virgin mixtures with 3% to 4% cement content exceeded the strengths for typical cement-stabilized base materials in the literature. The measured strength and elastic modulus properties show that QB, together with FRAP or virgin aggregates, can be successfully applied as a cement-treated foundation layer.

Roller-compacted concrete (RCC) is re-emerging as an alternative pavement type to asphalt concrete and even slip-form concrete pavements because of its rapid construction, early opening to traffic, and its economic benefit. The lower cement content of RCC requires careful selection of the aggregate structure to ensure adequate structural performance of the pavement. Recommended gradation bands have been proposed in the literature with few studies systematically investigating aggregate gradation effects on the fresh and hardened properties of RCC. A laboratory study was conducted to quantify the effects of aggregate gradation on the moisture-density relationships and the strength properties of RCC with low fines content. Low fines content RCC mixtures represent the direct application of existing concrete aggregates found in most ready-mixed concrete plants. Optimized moisturedensity relationships for nine RCC mixtures with different aggregate gradations and fixed cement content were determined using the modified Proctor test. The compressive and splitting tensile strengths were measured at 14 days and compared with a conventional concrete paving mixture.