Ozkan Sengul

Electrical Resistivity Measurements for Quality Control During Concrete Construction

In severe environments, new concrete structure production increasingly uses chloride diffusivity requirements as a concrete durability performance-based specification. Chloride diffusivity testing is both elaborate and time-consuming, however, as a concrete quality control basis during concrete construction. Using the Nernst-Einstein equation as a basis, the given concretes electrical resistivity and chloride diffusivity relationship should therefore first be established. Then routine-based electrical resistivity measurement during concrete construction can indirectly control chloride diffusivity. There are several test methods for concrete electrical resistivity measurement. Such measurements may also be affected by several factors. An experimental program was carried out in order to provide more information about some of those factors, since, in regard to electrical resistivity during concrete construction, they may affect results and allow simple routine-based quality control procedures to be established. Primarily based on four-electrode (Wenner) electrical resistivity testing, the test program included different test specimen geometry and probe spacing. Some two-electrode measurements were also performed for comparison. Test results are primarily presented as relative resistivities that two different test methods obtained in order to describe various factor effects that resistivity may be affected by. That, for given testing conditions, Wenner-method obtained electrical resistivity differs from two-electrode method obtained resistivity is shown in the results. The authors conclude that, however, for a given concrete specimen type with given temperature and moisture conditions, a suitable and reliable test method for performance-based electrical resistivity quality control, and hence, concrete durability, during concrete construction appears to be the Wenner method.

Influence of Aggregate Type on Mechanical Behavior of Normal- and High-Strength Concretes

Effects of coarse aggregate type on the mechanical properties of both normal- and high-strength concretes (HSCs) were investigated under compressive loading. Basalt, sandstone, and Triassic and Devonian crushed limestone coarse aggregates were used in the concretes. For each coarse aggregate type, 6 concrete mixtures were made with the same portland cement and natural sand. Nominal slump, effective water-cement ratio, and cement content were kept constant in each concrete class. In all mixtures, the grading and maximum particle size were the same. Triassic limestone containing concrete had the highest compressive strength. However, in HSCs, the compressive strength of basalt containing concrete had the highest value. In HSCs, the hysteresis loops of Triassic and Devonian limestone concretes are generally narrower than those of basalt and sandstone concretes. It can be concluded that the irreversible energy up to prepeak stress in compression decreases significantly and the loop becomes narrower with an increase in compressive strength. The brittleness index increases substantially with the compressive strength of concrete.

Mechanical Properties and Rapid Chloride Permeability of Concrete With Ground Fly Ash

The objective of this study was to optimize the design of high-strength, high-volume fly ash concretes. Eight concrete mixtures were prepared using the same batch of ordinary portland cement (OPC) and ground low-lime fly ash. The aggregate grading used in the mixtures of concrete, water-binder ratio, and the maximum particle size of aggregate were kept constant in all concretes, however, the partial replacement of cement by fly ash was varied from 0% to 70% OPC concrete, in steps of 10%. The replacement was on a one-to-one weight basis. At 28 days, there was little reduction in compressive strength up to 40% cement replacement by ground fly ash; then a significant decrease was recorded for the further fly ash dosages. At 56 and 120 days, however, the compressive strength up to 40% cement replacement by fly ash was found to be almost identical to that of the no fly ash concrete, and for one year it was even higher. Beyond 40% replacement, the compressive strength decreased significantly. It was shown that the brittleness index increases substantially with increasing compressive strength of concrete. The results of the rapid chloride penetration tests revealed that high volume ground fly ash concrete had better resistance to the penetration of chloride ions. The mortar phases of these concretes were also prepared. As the dosage of fly ash increased, 2, 7, and 28-day compressive strengths of the mortars decreased. However, at later ages at 56, 120, and 365 days, nearly 40% cement replacement by ground fly ash, the compressive strength of mortar with fly ash was about equal to that of mortar without fly ash. The pozzolanic effectiveness ratio increased with increasing curing time and fly ash content.

Effect of Embedded Steel on Electrical Resistivity Measurements on Concrete Structures

Concrete electrical resistivity is a very important corrosion rate controlling factor for concrete structure embedded steel corrosion. Concrete electrical resistivity measurements are therefore normally important and integrated measurement components carried out during concrete structure condition surveying. It may not be easy to interpret resistivity measurement results, however, because the observed resistivity may be significantly affected by the embedded steel. An experimental investigation was performed to provide more information about how embedded steel affects concrete structure electrical resistivity measurements. This paper presents the experiments results. Four-electrode (Wenner) electrical resistivity testing formed the primary basis of the test program, and included different probe spacing and test specimens incorporating embedded steel. Testing was performed using two different directions relative to the embedded steel. There was also investigation of the effects that curing conditions and cover thickness have on resistivity. That observed concrete resistivity can be substantially affected by electrode spacing is shown in the results. For concrete structure electrical resistivity field measurements, that all measurements should be performed as far from all embedded steel as possible was confirmed by the investigation. If very dense reinforcement makes this an impossibility, the Wenner devices electrode spacing should be kept small, relative to cover depth.