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The presence of low-quality coarse aggregates and exposure to aggressive conditions are the two major problems with the durability of concrete. Therefore, an alternative concrete with enhanced properties to prevent fluid and ionic mobility compared to conventional concrete is needed. This study investigated the effects of main mix parameters on the transport characteristics and corrosion behavior of ultra-high performance fiber-reinforced concrete (UHPFRC). A set of 27 UHPFRC mixtures with different combinations of w/b ratio, cement, and silica fume contents, based on a 33-factorial experiment design, were prepared and tested for water permeability, chloride penetrability, electrical resistivity, chloride profile, and corrosion current density. The results showed that UHPFRC mixtures exhibited excellent durability properties characterized by negligible water penetration (< 15 mm), negligible and very low chloride permeability when the w/b ratio was 0.15 (< 100 Coulombs) and up to 0.2 (< 300 Coulombs), respectively, and very low chloride concentrations at the rebar level (0.03–0.18 wt.%). All resistivity values were within the range of 26.7–78.8 kΩ cm (> 20 kΩ cm) and pH values were 12.41–13.01, indicating the implausible likelihood of corrosion in the UHPFRC mixtures. This was confirmed through the corrosion current density measurements of reinforced UHPFRC specimens after 450 days of chloride exposure, which were below the critical limit for the corrosion initiation of reinforcing steel. Finally, the experimental data were statistically analyzed and fitted for all the listed tests, and models were developed for them using the regression analysis such that regression coefficients were within 0.90–0.99. [ABSTRACT FROM AUTHOR]

Silica fume (SF), an ultra-fine pozzolanic material that is a by-product of industrial processes, is essentially used as mineral filler in the manufacture of ultra-high-performance concrete (UHPC) at a high dosage. However, its high cost can be a significant barrier to UHPC production, particularly in areas where local sources are not available. The aim of this study is to investigate the feasibility of partially replacing SF with two other pozzolanic waste materials, fly ash (FA) and natural pozzolan (NP), for UHPC production. Six different mixes of UHPC were designed, produced and tested initially for workability and compressive strength, considering different constitutions of FA and NP to partially substitute SF. Based on fulfilling the minimum requirements of flow and compressive strength of a UHPC mix, three UHPC mixes, including the control mix with SF alone, were considered for a detailed assessment of their performance in terms of strength, shrinkage, and durability characteristics, including resistance against reinforcement corrosion. Results reveal that both pozzolanic waste materials can be used to replace SF up to 60% to produce UHPC mixes without compromising strength and durability. The outcome of this study would help in reducing the consumption of SF and produce UHPC by utilizing FA and NP as partial replacements of SF when SF is not available locally as a waste material. [ABSTRACT FROM AUTHOR]

The resin-sand mixture was proposed to be used as the surface course, and cement permeable concrete was used as the base course; such two kinds of materials were combined to prepare water-permeable brick with a composite structure. The compressive strength, flexural strength, and permeability were studied by using adjusting the contents of carbon fiber, quartz powder, cement, sand, and surfactant. The study shows that the hydrophilicity of the resin-sand mixture can be improved after any amount of resin is replaced by quartz powder; by using the surfactant, the interface energy of the particles can be reduced so that the water permeability of the surface course can be promoted effectively. However, the mechanical properties of the surface course were negatively affected by the surfactant. With the optimal process consideration in the experiments, the properties about compressive strength, flexural strength, and permeability of the composite permeable brick can meet the requirements of the specifications of resin-sand based water permeable brick JGT 376–2012 (compressive strength was higher than 35 MPa, the flexural strength exceeded 5.19 MPa, and the average permeability coefficient was higher than 2.3×10−2 cm/s). There are no obvious pores on the surface course and only water molecules can pass through it, therefore, the surface of the permeable brick cannot be blocked up by solid substances, and the permeability of such permeable brick can be improved effectively in this way. [ABSTRACT FROM AUTHOR]