A high cement content is often found in concrete mixture designs to achieve the unique fresh-state behavior requirements of three dimensional (3-D) printable concrete (3DPC) to ensure rapid stiffening of an extruded layer without collapsing under the stress applied by the following layers. Some materials with high water absorption, such as recycled concrete aggregates, have been incorporated in concrete mixture designs to minimize environmental impact; nevertheless, the fine powder fraction that remains from the recycled aggregate processing still poses a challenge. In the case of 3DCP, few studies are available regarding mixture designs using recycled concrete powder (RCP) for 3-D printing. In this context, this study presents the use of RCP as a filler to produce a printable mixture with low cement content. An RCP with 50 μm average particle size was obtained as a by-product from recycled concrete aggregate production. Portland cement pastes were produced with 0, 10, 20, 30, 40, and 50% of cement mass replacement by RCP to evaluate its effects on the hydration reaction, rheology, and compressive strength. It was found that the studied RCP replacement was not detrimental for the hydration reaction of portland cement during the initial hours, and at the same time, it was capable of modifying the rheological parameters of the paste proportionally to the packing density of its solid fraction. The obtained results indicated the viability of 3DCP with up to 50% cement replacement by RCP. It was concluded that RCP presents good potential for decreasing the cement consumption of 3DPC, which in turn could decrease its associated environmental impact while providing a destination for a by-product from recycled concrete aggregate production.

In this study, low-carbon ultra-high-performance concrete (UHPC) was designed by adding fly ash-based mineral admixtures (SD-FA). The improved Andreasen & Andersen model was used to obtain SD-FA, which was then used to replace part of UHPC cement, to achieve the effect of low-carbon emission reduction. The effects of the composition and dosage of cement-based materials, the water-cement ratio, the composition of sand, the steel fiber content, and the lime-sand ratio on the properties of UHPC were studied, and the design of the batches was optimized. On this basis, the performance changes were analyzed at the micro level. The results show that when the 1~3 grade fly ash content after screening treatment is quantitative, the densest stacking is theoretically reached. The SD-FA optimized design improves the bulk density of UHPC and realizes the dense microstructure of UHPC. Under the optimal mixing ratio, its processability is guaranteed and the mechanical properties are enhanced.

Although ultra-high-performance concrete (UHPC) is one of the promising materials for precast bridge girder applications due to its advanced properties and durability, its implementation in the precast industry is subject to several potential concerns. To support implementation, this paper presents the development of nonproprietary UHPC mixtures for precast, pretensioned UHPC bridge girder applications. The nonproprietary UHPC mixtures were developed using materials commonly available in the Texas precast industry with the additional requirement of obtaining a compressive strength of 12-14 ksi (83–97 MPa) within 24 hours without any heat treatment while maintaining current precast, pretensioned bridge girder fabrication practices. The fresh, hardened, and durability properties of both lab- and plant-made UHPC mixtures were investigated. The research results show that selected nonproprietary UHPC mixture developed in a lab setting can be successfully produced in a precast plant setting with comparable properties.

In light of the effort for decarbonization of the energy sector, it is believed that common geopolymer binding materials such as fly ash may eventually become scarce and new geological aluminosilicate materials should be explored as alternative binders in geopolymer concrete. A novel, tension-hardening geopolymer concrete (THGC) that incorporates high amounts of semi-reactive quarry wastes (metagabbro) as a precursor, and coarse quarry sand (granite) was developed in this study using geopolymer formulations. The material was optimized based on the particle packing theory and was characterized in terms of mechanical, physical, and durability properties (that is, compressive, tensile, and flexural resistance; Young’s modulus; Poisson’s ratio; absorption; drying shrinkage; abrasion; coefficient of thermal expansion; and chloride-ion penetration, sulfate, and salt-scaling resistance). The developed THGC, with an air-dry density of 1940 kg/m3 (121 lb/ft3), incorporates short steel fibers at a volume ratio of 2%, and is highly ductile in both uniaxial tension and compression (uniaxial tensile strain capacity of 0.6% at an 80% post-peak residual tensile strength). Using digital image correlation (DIC), multiple crack formation was observed in the strain-hardening phase of the tension response. In compression, the material maintained its integrity beyond the peak load, having attained 1.8% compressive strain at 80% postpeak residual strength, whereas upon further reduction to 50% residual strength, the sustained axial and lateral strains were 2.5% and 3.5%, respectively. The material exhibited low permeability to chloride ions and significant abrasion resistance due to the high contents of metagabbro powder and granite sand. The enhanced properties of the material, combined with the complete elimination of ordinary portland cement from the mixture, hold promise for the development of sustainable and resilient structural materials with low CO2 emissions, while also enabling the innovative disposal of wastes as active binding components.

Pervious concrete is a stormwater management practice used in the United States, Europe, China, Japan, and many other countries. Yet the design of pervious concrete mixtures to balance strength and permeability requires more research. Sphere packing models of pervious concrete were used in compressive strength testing simulations using the discrete element method with a cohesive contact law. First, three mixtures with varied water-cement ratios (w/c) and porosities were used for model development and validation. Next, an extensive database of simulated compressive strength and tested permeability was created, including 21 porosities at three w/c. Analysis of the database showed that for pavement applications where high permeability and strength are required, the advised porosity is 0.26 to 0.30, producing average strengths of 14.4, 11.1, and 7.7 MPa for w/c of 0.25, 0.30, and 0.35. The model can guide the mixture design to meet target performance metrics, save materials and maintenance costs, and extend the pavement life.