International Concrete Abstracts Portal

Ground-glass pozzolan has recently been considered a supplementary cementitious material by Canadian (CSA A3000) and American (ASTM C1866/C1866M) standards, but limited studies have been done on ground-glass use on-site. So, in this study, several sidewalk projects were performed by the SAQ Industrial Chair at the University of Sherbrooke from 2014 to 2017 on fields with different proportions of ground glass (that is, 10, 15, and 20%) in different conditions considered in such a cold climatic region. Sidewalks are a nonstructural plain concrete element that are among the most exposed to chloride and freezing and thawing in saturated conditions of municipal infrastructures. Coring campaigns were carried out on these concretes after several years of exposure (between 5 and 8 years). The results of core samples extracted from the sites were compared to the laboratory-cured samples taken during the casting. These laboratory concrete mixtures were tested for fresh, hardened (compressive strength), and durability (freezing and thawing, scaling resistance, chloride-ion penetrability, electrical resistivity, and drying shrinkage) properties (up to 1 year). The results show that ground-glass concrete performs very well at all cement replacements in all manners in terms of long-term performance. Besides that, using ground-glass pozzolan in field projects also decreases the carbon footprint and environmental and glass disposal problems.

The U.S. National Ocean Service estimates 95,741 miles (154,080 km) of shoreline in the United States, where 163 miles per year are hardened by bulkheads and riprap. These shoreline protection techniques are costly and require frequent maintenance. Different agencies are examining “nature-based” solutions that combine vegetation with traditional concrete. Digital construction, advanced manufacturing, and innovative cementitious composites have also been proposed as potential means to lower material use, cost, and environmental impact. This paper presents a novel advanced manufacturing technique using a reactive-diffusion morphological process, called “dry-forming,” to three-dimensionally (3-D) printed concrete structures of various shapes, sizes, and complexities with standard concrete mixtures. This technology has reduced 60% of material use, enhanced local habitats, and increased the resiliency of the shoreline to sea level rise. The widespread use of this technology would increase the resiliency of coastal communities, protect aquatic life, and protect waterfront public and private real estate investments.

The early-age material parameters of three-dimensional (3-D)-printable concrete defined under the umbrella of printability, namely, pumpability, extrudability, buildability, and the “printability window/open time,” are subjective measures. The need to correlate and successively substitute these subjective measures with objective and accepted material properties, such as tensile strength, shear strength, and compressive strength, is paramount. This study validates new testing methodologies to quantify the tensile and shear strengths of printable fiber-reinforced concretes still in their fresh state. A tailored mixture with high sulfoaluminate cement and nonstructural basalt fibers has been assumed as a reference. The relation between the previously mentioned parameters and rheological parameters, such as yield strength obtained through International Center for Aggregates Research (ICAR) rheometer tests, is also explored. Furthermore, in an attempt to pave the way and contribute toward a better understanding of the mechanical properties of 3-D-printed concrete, to be further transferred into design procedures, a comparative study analyzing the work of fracture per unit crack width in three-point bending has been performed on printed and companion nominally identical monolithically cast specimens, investigating the effects of printing directions, position in the printed circuit, and specimen slenderness (length to depth) ratio.

Ultra-high-performance concrete (UHPC) is a cementitious concrete material known for its sustained post-cracking tensile performance. Various specimen geometries and different test approaches have been used to establish the tensile characteristics of UHPC. Intending to standardize a direct tension test method, this paper independently evaluates a procedure developed by the Federal Highway Administration (FHWA), which has been adopted into AASHTO T 397. To verify the reliability and repeatability of the test method, 216 tensile specimens were cast from three different UHPC types with fiber-volume fractions of 1, 2, and 3% and tested at six laboratories. The measured responses were characterized for different phases of the tensile behavior and analyzed to understand the scatter in the test data. It was found that testing can be executed with a 60 to 70% success rate with carefully prepared samples and some modifications to the proposed test method. The test results show an increase in both the tensile strength and multicracking phase with an increase in fiber-volume fraction, but the crack straining phase depends primarily on the type of UHPC. Using the test data, average and characteristic tensile responses were established, which are intended, respectively, for analysis and design purposes.

The atmospheric purification capacity of concrete has not beenadequately investigated. This study examines the feasibility ofusing sustainable foam-concrete granules as a porous materialfor reducing air pollutants in concrete. To enable the removal of nitrogen oxide (NOx) and sulfur oxide (SOx) using titanium dioxide (TiO2) nanoparticles, foam concrete was crushed into granules with porosity exceeding 30%. Ordinary portland cement (OPC), fly ash (FA), and slag cement were used as source cementitious materials. OPC was replaced with 0 to 40% FA and 0 or 40% slag cement by weight. Test results indicate that 30% FA and unit cementitious materials content exceeding 500 kg/m3 (31.2 lb/ft3) are optimal for replacing cement and foam-concrete granules, respectively. Considering the particle-size distribution and specific surface area, 6 to 13 mm (0.24 to 0.51 in.) and 6 to 9 mm (0.24 to 0.35 in.), were selected as optimal granule sizes. The coating procedures yielded improved SOx and NOx removal, with the removal rates reaching 83.8 and 45% using granules of 6 to 9 mm (0.24 to 0.35 in.), respectively. Consequently, the foam-concrete granules coated with TiO2 nanoparticles are promising in developing porous concrete with the reduction capability of air pollutants.