No abstract

Background: The tensile strength of the plain concrete is weak. Thus, fibres are embedded in concrete to improve its ductility. However, pulling out steel fibres from concrete structures is one of the most encountered issues in the fiber-reinforced concrete, which hinders using their maximum capacities. Objectives: Thus, closed steel fibres (square shape) were incorporated into concrete mixes to evaluate their impacts against the pulling-out effects and assess the feasibility of applying Closed Steel Fibres (CSFs) on the fresh and hardened concrete properties. Hooked end and straight steel fibres were also investigated for comparison. Methods: The utilized steel fibres were incorporated with lengths of 20, 30, and 40 mm, and volume fractions of 0.25%, 0.50%, and 0.75%. Silica Fume (SF) was involved in the fibre-reinforced concrete mixtures at 7% of the cement weight. Results: Paper outcomes stated that the inclusion of steel fibres involved different impacts on the concrete compressive strength depending on the applied fibre geometries and content. Conclusion: CSFs exhibited better performance against the pulling-out effect from the surrounding concrete structure than those of hooked end and straight steel fibres. However, the addition of CSFs has increased the concrete permeability due to their poor space-filling capacity.

Generally, low calcium fly ash concretes (FFACs) subjected to ambient temperatures exhibit low initial strengths. Thus, FFACs require higher temperatures to improve the monomer dissolutions, but that increases the energy consumption. Thus, this paper aims to evaluate the influence of the incorporation of different dosages of silica fume (SF) and metakaolin (MK) on the green and hardened properties of FFACs cured at room temperature of 21 ˚C. Slump and air content tests were applied to evaluate the green characteristics of the designed geopolymer concrete mixes (GPCMs). The hardened properties of FFACs were assessed in terms of compressive, flexural, and splitting tensile strengths at different curing ages. Outcomes revealed that the slump and air content of GPCMs declined with improving SF or MK percentages. The 28 days flexural, compressive, and splitting tensile strengths of FFACs manufactured with the optimum dosages of 20% MK and 10% SF cured at 21 ˚C were evidently higher than those of FFACs (100 % FFA) subjected to curing temperatures ranging from 10-to-50 ˚C. Also, the strength enhancement of MK was relatively comparable to those of SF with less requirement for superplasticizers.