A test procedure was developed to evaluate the effect of different techniques to limit settlement cracking over reinforcing steel with low concrete cover. Various specimen configurations and methods of finishing and curing were investigated. It was found that a clear cover of 1-1/8 in. (29 mm) over a No. 6 (No. 19) bar and covering the specimens after placement with sloped hard plastic enclosed in plastic sheeting provided a suitable method for obtaining clearly visible settlement cracks for concrete with slumps ranging from under 2 in. (50 mm) to over 8 in. (205 mm). The test specimen was then used to evaluate the effectiveness of a rheology-modifying admixture and four types of synthetic fibers on settlement cracking. Eighty-eight concrete batches were tested for mixtures with a cement paste (cement and water) content of 27 percent by volume and a water-cement ratio (w/c) of 0.45. The results show that the addition of the rheology-modifying admixture or fibers greatly reduces settlement cracking over reinforcing steel with low concrete cover.

The inconsistent supply of fly ash and relatively high cost of slag as supplementary cementitious materials (SCMs) in the Northeastern United States is of concern to the concrete industry. Fly ash is a by-product from coal-burning plants that are shutting down or converting to natural gas, and slag is a residue from steel production mainly outside of the United States. With the goal of contributing significantly to the implementation of sustainable high performance concrete, this study focuses on the evaluation of mixture designs using recycled post-consumer glass as SCM for concrete, for three mixtures with 20, 30, and 40% glass pozzolan as cement replacements, as well as two other comparable mixtures with 30% fly ash and 40% slag. Following laboratory characterizations for fresh and hardened properties, the mixtures with 20 and 40% glass pozzolan were selected for implementation in a sidewalk project in Queens, NY. The field work involved evaluations of mixture production, placement, finishing, curing, compressive strength, and development of maturity curves from data loggers in concrete. This study offers great potential for benefitting the concrete and glass recycling industries.

With adoption of winter maintenance strategies that typically include incorporation of aggressive deicer chemicals, pavement surfaces in cold regions are exposed to the risk of scaling damage. Reduced ride quality due to surface deterioration can eventually lead into a variety of maintenance and repair programs. Such pavement preservation programs impose significant charges to the owner agencies, while raising concerns regarding the safety issues associated with work zone areas. The present study addresses the correlation between surface hardness and concrete hardened properties. Moreover, factors that influence the concrete performance with respect to surface-abrasion resistance (hardness) were investigated. Of special interest was the relationship between surface hardness and concrete salt-scaling performance. An extensive investigation was carried out to assess the effects of various mixture proportions, curing regimes, and finishing times on surface hardness of the concrete specimens. In addition, compressive strength, depth-sensing indentation (DSI), and salt scaling tests were used to evaluate the correlation between concrete surface hardness and performance. A scaling quality classification table using abrasion mass loss values was developed. The results reflect further understanding of the relationship between abrasion resistance and salt scaling resistance that can cause defects when more than two cycles of abrasion testing are applied.

An experimental investigation of the effect of the wait time between finishing of the concrete surface and application of the curing compound on concrete scaling resistance was conducted. Test variables included type of curing compound, wait time, cementitious material, and type of coarse aggregate. The results indicate that the influence of timing of curing compound application on the scaling resistance of concrete can be significant and depends on the selected compound and characteristics of the concrete mixture. In actual practice, other factors such as temperature, relative humidity, and wind speed also likely come into play. For the linseed oil- and acrylic-based curing compounds, scaling resistance improved with an increase in wait time. The poly-alpha-methylstyrene-based curing compound was generally insensitive to wait time. Increasing wait time for the wax-based curing compound did not consistently yield improved scaling resistance.

A pilot-scale field investigation was conducted through which: 1) a refined ultra-high-performance concrete (UHPC) mixture was prepared in a ready mixed concrete plant; 2) a large reinforced UHPC block was constructed through placement, consolidation, and finishing of UHPC; and 3) a commonly available concrete curing (insulating) blanket was applied for field thermal curing of the UHPC block using the exothermic heat of hydration of the cementitious binder in UHPC. Monitoring of the reinforced UHPC block temperature over time confirmed the development of a reasonably uniform temperature and a viable temperature time history, which suited thermal curing of UHPC without any heat input. In-place nondestructive inspection of the reinforced UHPC structure pointed at timely setting and strength development, leading to achievement of ultra-high-performance status. Specimens were cored from the large reinforced concrete block and subjected to laboratory testing. The experimental results indicated that the field thermal curing was more effective than the laboratory thermal curing considered in the project, and that the pilot-scale production of the UHPC mixture produced compressive strengths approaching 170 MPa (24.7 ksi).