International Concrete Abstracts Portal

Carbon dioxide emissions from cement production pose major environmental concerns. This study investigates the combined incorporation of glass powder (GP) as a partial cement replacement and dog hair (DH) as a natural fiber reinforcement in cement paste. GP was incorporated with replacement levels of 5%, 10%, and 15%, whereas DH was incorporated with dosages of 0.25% and 0.5% by weight of cement. Both fresh and hardened properties were evaluated for a duration of up to 90 days. GP enhanced workability, increasing mini-slump by approximately 21% at 15% GP, whereas DH with 0.25% reduced workability by up to 6%. At 90 days, compressive strength improved by 26.6%, 17.6%, and 16.5% for GP5, GP10, and GP15, respectively. Flexural strength was improved by a maximum of 8.9% with the addition of DH. The porosity of all the modified mixes was reduced to a minimum of 20.4% in the GP15-0.25DH mix compared to the control mix of 28.0%. Sustainability analysis showed CO₂ emission reductions ranging from 4.06% to 16.07%, and material cost decreased to a maximum of 15.95% for GP15. These results clearly show the potential of GP and DH to enhance performance while improving economic and environmental sustainability.

The calculation of the nominal flexural strength of concrete members prestressed with hybrid (i.e., a combination of bonded and unbonded (steel and/or carbon fiber reinforced polymer (CFRP)) tendons is dependent on determining the stress in the unbonded prestressed reinforcement. Current provisions in the ACI CODE-318-25 are only applicable to members with either unbonded or bonded steel tendons. Additionally, while ACI PRC-440.4R-04 is adopted for unbonded CFRP tendons, neither ACI provisions address the use of hybrid tendons. This paper presents a closed-form analytical solution for the stress at ultimate derived based on the Modified Deformation-Based Approach (MDBA) that is applicable to beams prestressed with unbonded, hybrid (steel or FRP), external with deviators or internal tendons, with and without non-prestressed reinforcement. An assessment of its accuracy and applicability in calculating the nominal flexural strength is examined using a large database of 330 beams and slabs (prestressed with steel and/or CFRP tendons) compiled from test results by the authors as well as those available in the literature. Results predicted by the proposed approach exhibited excellent accuracy when compared to those predicted using ACI CODE-318 or ACI PRC-440 stress equations. They also show that the approach is universally applicable to any combination of bonded and/or unbonded (steel and/or CFRP) tendons, span-to-depth ratio, as well as loading applications.

To improve the ductility of fiber-reinforced polymer reinforced concrete structures, the hybrid reinforcement with glass fiber-reinforced polymer (GFRP) and stainless steel (SS) is selected in this paper. Nine seawater sea sand concrete beams were designed and tested. The effects of concrete strength, effective reinforcement ratio ρ₂, and reinforcement type in the tensile zone on the flexural behavior of the beams were analyzed. The test results show that with the same concrete strength and the same effective reinforcement ratio ρ₂, the ductility of hybrid reinforced beams is higher than GFRP reinforced beams; the comparison of mid-span deflection of the GFRP bars and hybrid reinforced beams are not only depend on the reinforcement type, but also depend on the total stiffness of reinforcement before SS bars yield in the tensile zone and whether the SS bars are yielding in the tensile zone. Meanwhile, theoretical analysis was conducted for cracking moment, ultimate flexural load-carrying capacity, and mid-span deflections. A new ultimate flexural load-carrying calculation equation was proposed, which predicted the experimental values in good agreement.

To promote the application of fiber-reinforced polymer (FRP) bars reinforced ultra-high-performance seawater sea-sand concrete (FRP-UHPSSC) structures in marine construction, four-point static bending tests were carried out on 16 FRP-UHPSSC beams with different reinforcement ratios, height of cross-section, and type of FRP bars to investigate the ultimate load-carrying capacity, the midspan deflection, and the failure modes of the beams. The experimental results show that all the test beams are brittle failures, and the failure mode of the beams is shear failure when the ratio of the actual reinforcement ratio to the balanced one is higher than 2.73. Increasing the reinforcement ratio and the beam section height both improve the bending moment at ultimate load and the flexural stiffness at the service limit state. The Steel-FRP composite bars (SFCB) reinforced UHPSSC beams have the maximal bending moment at ultimate load, and the basalt fiber reinforced polymer (BFRP) bar reinforced UHPSSC beams have the optimal ductility. The deviation of ultimate bending moment and midspan deflection obtained by the proposed calculation method is reduced from 7.5 to 2.8%, and from 15 to 3%, respectively, compared with current specifications for FRP-reinforced concrete structures.

Ultra-high-performance concrete (UHPC) is composed of a high volume fraction of binder and steel fibers, and a very low water content, resulting in enhanced strength and ductility along with higher cost and environmental impacts. This study develops a UHPC mixture amenable for three-dimensional (3-D) printing, with 30% of cement (by mass) replaced with a combination of replacement materials. The proportioned UHPC mixture with 1.5% fiber volume fraction demonstrates 28-day compressive strengths of >120 MPa (17.4 kip), and limited anisotropy when tested in the three orthogonal directions. Furthermore, 3-D-printed layered composites are developed where UHPC (with and without fiber reinforcement) and conventional concrete layers are synergistically used in appropriate locations of the beam to achieve mechanical performance that is comparable to 3-D-printed UHPC sections. Such manufacturing flexibility offered by 3-D printing allows conserving resources and attaining desirable economic and environmental outcomes, as is shown using life cycle and techno-economic analyses (LCA/TEA). Experimental and theoretical analyses of load-carrying capacity and preliminary LCA/TEA show that >50% of the fiber-reinforced UHPC beam volume (in the compression zone) can be replaced with conventional concrete, resulting in only a <20% reduction in peak load-carrying capacity, but >35% reduction in cost and >20% reduction in CO2 emissions. These findings show that targeted layering of different materials through 3-D printing enables the development and construction of 3-D-printed performance-equivalent structural members with lower cost and environmental impacts.