International Concrete Abstracts Portal

Zinc anodes are an effective and economical method to prevent and control the corrosion of steel bars. They supply the bars with cathodic current, which can provide corrosion protection at low current densities in the range of 0.2 to 2 mA/m2. The efficacy of zinc anodes is affected by the resistivity of concrete or cementitious repair material in which these anodes are embedded. Limited data is available on the maximum electrical resistivity of repair materials/concretes beyond which zinc anodes cannot properly function to prevent corrosion. In this study, concrete slabs were cast to simulate partial- and full-depth repair configurations. Key variables included resistivity and anode position. Resistivity of the repair section varied from 10,000 to 50,000 Ω-cm, with three anode positions: 25, 100, and 250 mm in the repair section. Analysis of data shows the effectiveness of anodes at controlling corrosion, even in repair concrete with high resistivity.

Jointed plain concrete pavement (JPCP) repair slabs experience high incidences of early-age cracking due to high temperature rise and increased autogenous shrinkage of high-early-strength (HES) concrete mixtures. This paper presents an investigation to evaluate early-age cracking mitigation strategies of JPCP repair slabs. Finite element analyses were performed to understand the effects of physical phenomena leading to early-age cracking in JPCP repair slabs. While the analyses indicate the importance of concrete hydration kinetics and viscoelastic behavior on the early-age stress development in slabs, concrete moisture loss to the base was found to be the most significant phenomenon. Numerical modeling of concrete slabs was found to be useful in predicting the stress development in advance of costly field trials. Therefore, the proposed modeling approach can be applied to evaluate the performance of concrete mixtures prior to slab placement and thus improve and economize the current rigid pavement maintenance practices.

This paper investigates the influence of concrete porosity on durability of the bond between fiber-reinforced polymer (FRP) and concrete. Twenty-four slab specimens were cast using three different concrete mixtures with water-cementitious materials ratios (w/cm) of 0.53, 0.41, and 0.21, representing high, medium, and low porosities, respectiviely. The slabs were preconditioned by oven-drying and two commercially used carbon fiber-reinforced polymer (CFRP) materials bonded to surfaces that had been sand-blasted to provide a concrete surface profile (CSP) 3 rating. Repaired specimens were submerged in 30°C (86°F) potable water for 15 weeks and residual bond was evaluated through pulloff tests. Results showed 1 to 3% bond reduction in the high-porosity, low-strength concrete compared to a reduction in excess of 20% in its low-porosity, higher-strength counterpart. The likely reason for the better performance was deeper epoxy penetration into the more porous concrete substrate. Findings suggest that surface preparation and installation methods that allow epoxy to penetrate deeper into low-porosity, high-strength concrete can result in increased durability under moisture exposure.

This paper presents an experimental study on the seismic performance of reinforced concrete (RC) perimeter interior special moment frames (SMFs) that use high-performance fiber-reinforced concrete (HPFRC) in joint and beam plastic hinge regions. This research evaluates the feasibility of using both HPFRC joint and beams as major sources of energy dissipation in an effort to reduce overall damage and repair cost after earthquakes and to provide ease of construction for beam-column connections. A balanced damage concept was used so the energy dissipation was shared by the joint and beam plastic hinges, thereby preventing severe damage from occurring to the beams. This concept together with the mechanical properties provided by HPFRC, including high shear and bond strength, reduce the need of placing a large number of transverse reinforcement in the joint and beam plastic hinge regions. A full-scale HPFRC slab-beam-column (SBC) subassemblage designed with this concept was tested under large displacement reversals. This specimen used a small amount of transverse reinforcement (approximately 20% of that used in a typical RC joint) in the joint and no transverse reinforcement in the beam plastic hinge regions, thus significantly enhancing the constructability. A counterpart conventional RC specimen compliant with ACI 318-14 was tested under the same loading protocol. Both specimens showed stable hysteretic responses up to 3.5% column drift ratio without significant strength degradation, which meets the collapse prevention structural performance according to the criteria given in ACI 374. Experimental results show that the damage in the HPFRC specimen was distributed in both joint and beam ends, whereas the conventional RC specimen had severe damage concentrated in the beam plastic hinging regions. This research proves the feasibility of using ductile HPFRC joint to dissipate seismic energy, thereby balancing the damage between the joint and beams.

Jointed plain concrete pavement (JPCP) replacement slabs can experience early-age cracking from early-age volume change. These slabs are often made of high-early-strength (HES) concrete characterized by high cement content and low water-cement ratio (w/c), which can result in large temperature rise and high levels of autogenous shrinkage, and ultimately an elevated cracking potential. This study investigated the effects of reduced paste content and base restraint minimization on reducing concrete early-age cracking potential. The effect of each of these measures was evaluated in place by measuring the stress and temperature development in concrete test slabs instrumented with concrete stressmeters and thermocouples. Calorimetry studies and mechanical properties testing were used with modeling software to assess field trends. The findings indicated that it is possible to achieve higher strengths and lower stresses with low-paste mixtures. Changes in concrete stress during the first 24 hours after placement, due to moisture loss to the base, were seen in slabs with polyethylene sheet or geotextile fabric underneath the slab.