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.

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.

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.

Fly ashes that do not meet the ASTM C618 specifications areconsidered “off-spec” and are not used as supplementary cementitious materials (SCMs). In this research, four off-spec fly ashes (OFAs) were sourced from different parts of the United States and the characteristics of these OFA concretes were measured to compare their performance with that of the mixtures containing 0% OFA. The first objective of this study is to assess the influence of OFA reactivity and replacement levels on concrete characteristics. The second objective is to assess the influence of constituent material characteristics such as shape and size of coarse aggregate, fineness modulus of fine aggregate, and cementitious content of the concrete mixture on the fresh and hardened characteristics of concretes containing OFAs. Results indicate that at sufficient degrees of reactivity and replacement levels, OFAs can provide characteristics comparable to that of conventional ordinary portlandcement (OPC) concrete while improving the consistency of theconcrete. Findings from sensitivity analysis reveal that the degree of reactivity (DoR) of the OFA has a high influence on the hardened characteristics of concrete. Finally, the life cycle assessment of concrete mixtures containing OFAs indicate that greenhouse gas emissions can be reduced up to 45% when compared to conventional mixtures.

Most concrete service life models are designed for uncrackedconditions, and the effect of microcracks on such models has not been as well researched. A service life model for concrete structures that takes into account microcracking is presented. A unique feature of this model is that its input parameters can be determined using only nondestructive methods, thus allowing it to be used when samples for laboratory tests cannot be extracted— for example, in in-service or critical infrastructure. The model was developed for low water-cementitious materials ratio (w/cm) concrete mixtures and validated on full-scale prestressed concrete girders. The results showed that the presence of a large number of microcracks could cause a loss in the remaining service life of concrete structures, even if individual microcracks did not cause asignificant impact.