International Concrete Abstracts Portal

Workability after concrete placement is important in continuous flight auger (CFA) piles construction because the reinforcement cage needs to be placed within the concrete at the end of casting. During the rest phase, which can last 30 minutes, the restructuring of the concrete affects the penetration capacity of the reinforcement cage. An experimental investigation was carried out over a period of 30 minutes to compare the static and dynamic yield stress, measured using a rotational rheometer, with the shear stress interaction between the reinforcement cage and the concrete. Tests were performed using 10 mixtures in the laboratory. A viscosity-modifying admixture was used to promote the thixotropy effect. The study was completed with four mixtures on site. The results showed a good correlation between the concrete rheological properties and the capacity to sink the reinforcement cage into the concrete. A simple model is proposed to estimate the shear stress applied to the reinforcement cage. The time needed to reach the final depth was correlated with the plastic viscosity, while the shear stress of the cage and the final depth were connected to the concrete yield stress. The penetration cage test is an effective tool to optimize concrete mixture proportions for the construction of CFA piles.

This study investigated the friction shear behavior of concrete consisting of recycled aggregates and natural reinforced steel fibers. The concrete’s natural aggregates were 50% substituted for recycled ones. The addition of steel fibers was evaluated in two different percentages in volume: 0.5 and 1.0%. Thus, 27 non-cracked push-off specimens were produced. The recycled aggregates were separated into two groups according to the strength of the original concrete: Group 1 (15 to 20 MPa) and Group 2 (35 to 40 MPa). Data analysis showed that the concrete’s original strength and steel fiber percentage influenced the shear transfer capacity. Experimental data from natural concrete (NC) and high-strength concrete (HSC) with steel fibers tests performed using the push-off model and shear test methods were recompiled from the technical literature. Using models proposed by some researchers, it was concluded that both methods showed high dispersion in results.

Physical salt attack (PSA) is a potential deterioration mechanism in porous materials, including concrete, exposed to salt-laden environments. Damage occurs as salt crystals grow in the near-surface pores causing tensile stresses on the pore walls higher than the tensile capacity of concrete, which can lead to surface scaling similar in appearance to that of freezing-and-thawing damage. This paper compiles, synthesizes, and analyzes current knowledge/research on this topic in terms of the mechanisms of damage, test procedures, damage assessment methods, most influential factors, protection against PSA, and code/guideline provisions. Moreover, key aspects that require further investigation are highlighted, along with a proposed classification for the resistance of concrete to PSA and mitigation strategy.

The assessment of progressive degradation of bond between concrete and reinforcing steel is of great importance in evaluating the residual strength of the reinforced concrete (RC) structural members with corroded reinforcements. Simple empirical and analytical models are proposed to demonstrate the effect of reinforcement corrosion on the reduction of bond strength. The empirical models are proposed by considering a wide range of published experimental investigations related to the bond strength degradation as a result of reinforcement corrosion. An analytical model for bond strength of corroded reinforcement has been adopted in which the estimation of various bond strength parameters is proposed by the authors. These parameters include corrosion pressure due to expansive action of corrosion products, modeling of tensile behavior of cracked concrete, and adhesion and friction coefficient between the corroded bar and cracked concrete. The performance of the proposed empirical and analytical bond strength models is then investigated through their ability to reproduce the available experimental trends. It has been found that the proposed models are capable of providing the estimates of predicted bond strength of corroded reinforcement that are in reasonably good agreement with the experimentally observed values and are also in agreement with those of the other reported published data on analytical and empirical predictions.

Nitrite-based corrosion inhibitors are currently used in reinforced concrete to reduce the risk of corrosion of embedded steel due to chemical action. In the late 1970s, numerous studies were conducted to evaluate the corrosion-inhibiting properties of calcium nitrite. The mechanism of corrosion protection has been reported to be anodic inhibition. One of the calcium nitrite-based corrosion inhibitors, DCI, was marketed in 1979. It is used mainly in concrete exposed to seawater or in bridge decks where deicing salts are applied. Because calcium nitrite acts as a concrete accelerator, however, the rapid hydration of cement may cause larger crystals to be developed. This tends to increase the concrete permeability, especially at early ages. Four different concrete mixtures, with and without DCI, were evaluated using the rapid chloride permeability test after 33 days and 5 months of curing. The complex dielectric constant of these mixtures was also measured after 30 days of curing. The dielectric constant was measured using a parallel plate capacitor, operating at the frequency range of 0.1 to 40.1 MHz. The tested concrete mixtures are used to produce hollow precast concrete piles, and have a very low water-cement ratio (w/c). The mixtures were also rapid-cured in a steam room at 70 C for 4 h. It was found that mixtures with DCI have higher chloride permeability values than the mixtures without DCI. It was also found that the DCI mixtures have higher complex dielectric constants, especially the loss part. A least significant difference (LSD) statistical analysis was performed on the chloride permeability values and on the complex dielectric constant results. Significant differences between the means were obtained in each test method. This suggests that measuring the complex dielectric constant at low radio frequency could be related to the chloride permeability test.