Journal of Materials in Civil Engineering

The fire damage inflicted upon Kuwaiti structures following the August 2, 1990, Iraqi occupation left behind many types of structural damage. This study includes a field assessment of the damaged structures where an investigation of 222 buildings was conducted. The field investigation concentrates on damage to commercial buildings, apartment buildings, residential houses, and public buildings, whereas the data obtained by other agencies cover all types of structures. The fire-damaged Kuwaiti structures demonstrate building-material behavior when subjected to severe temperatures. Technical data on material behavior was documented to show the changes in material properties under actual field conditions for other scientists to benefit from the Kuwaiti experience. The inspected structures showed fire damage ranging from heavy smoke to major destruction, such as distortion, buckling, and collapse of structural steel frames, disintegration of reinforced concrete, yielding of steel reinforcements within concrete (causing large deflections), and buckling of structural elements, as well as damage to a variety of interior elements. The different effects resulted in reduction in the integrity and strength of the affected Kuwaiti structures.

This paper is concerned with the determination of the modulus of elasticity of concrete at very early ages by means of a nondestructive method. The method covers measurements of the dynamic resonance frequency on concrete prisms with fast Fourier transform (FFT) analyzer. At a known resonance frequency the dynamic E-modulus and the damping coefficient can be calculated. Based entirely on the dynamic test results a simple empirical formula is suggested for prediction of the static modulus of elasticity. Application of the prediction formula for two concrete mixtures showed consistency and good agreement with the static test results. The advantage of the dynamic procedure is that the method enables measurement of progressive changes in the stiffness of the concrete without damaging the specimen, and it gives high quality and consistency in the test results relative to the static method.

A study was carried out to investigate the cyclic behavior of steel-fiber cement-mortar overlaid concrete beams at various stress levels. Two different volume fractions of steel fibers were selected for the present study. The concrete-beam specimens used in this study were tested simply supported with a point load at midspan. Two different types of bonding conditions were studied. The deterioration in the flexural rigidity of the test specimens after being subjected to a predetermined number of load cycles was evaluated. The test specimens were subjected to 100,000 cycles of loading under a maximum load of 45, 55, and 65% of the ultimate static load. Static loading tests to failure after 100,000 cycles of applied load showed that some of the beams loaded up to 65% of ultimate static failure strength failed by partial or complete delamination of the overlay. The results of the experimental tests are summarized and discussed in this paper.

An experimental program was conducted to study the effect of chloride contamination of portland cement concrete (PCC) on its complex permittivity over low radio frequencies (RF) range (0.1–40.1 MHz). Two types of aggregate (quartzite and limestone) were used to prepare the PCC mixes at a water to cement ratio (w/c) of 0.45. Two methods were used to induce chlorides into PCC: partial immersion in NaCl solution (6% by weight) and the addition of NaCl to the PCC mixing water. For the NaCl addition to the mixing water, three levels of chloride content were used. Dielectric measurements were taken for PCC specimens during the 28-day curing period and continued for six months. Powder PCC samples were collected periodically to estimate the chloride content in the PCC specimens. Results showed that complex permittivity of PCC specimens (immersed in NaCl solution) quantitatively increased as the chloride content increased, until quantitatively 75% of the chloride content estimated theoretical saturation volume. Aggregate type and frequency also show a significant effect on the measured dielectric constant.

The sulfate resistance of concrete pavers was determined using a method based on ASTM C 1012. Specimens were submerged in a 5% sodium sulfate solution for a period of one year. Length change and loss in mass were determined. Effect of mixture proportions on sulfate resistance, and relationships between expansion, mixture proportions, and concrete bulk properties are presented and analyzed. In addition, the expansion of the test specimens is compared to proposed acceptance limits found in the literature. Test results showed that the concrete pavers had excellent sulfate resistance, even above that expected when using moderate sulfate-resisting ASTM C 150 type II cement. Sulfate resistance was found to be directly related to the aggregate-cement ratio of the mixture and bulk properties of the concrete. The continued expansion measured throughout the experiment and the absence of any visual signs of softening appear to indicate that the principal factor in the sulfate attack was the in-situ formation of ettringite.

The severity of marine environments varies depending on location and has a major bearing on the durability performance of marine structures. A series of concrete specimens was cast, was exposed to four marine environments for two years, and the effect of marine exposure was estimated from chloride ingress levels. Two marine sites in South Africa were chosen, being either sheltered or exposed to severe wave action. At each site, concrete was placed in the tidal and spray zones. Results from this work indicated that concrete in the tidal zone exposed to heavy wave action had significantly higher chloride levels than concrete sheltered from wave action. When predicting the potential durability of marine concrete, allowance must be made for the severity of exposure together with material properties since both factors determine long-term durability performance. The results also have implications for laboratory simulations of marine exposure under relatively stagnant conditions.

Results of failure of cylinders under the uniaxial compression are reported. Cylinders of three different diameters (37.5, 75, and 150 mm) were tested. For all the cylinders, the height to diameter ratio was h/d= 2. The cylinders were made of microconcrete with maximum aggregate size 4.76 mm and the compressive strength (${\mathit{f}}_{\mathit{c}}^{\prime }$) of concrete was found between 34 and 48 MPa depending on the size of specimens. The concrete mix proportions of water:cement:aggregate:silica fume:superplasticizer were 0.3:1:4:0.1:0.08. The results reveal the existence of a significant size effect that can be approximately described by the size effect law previously proposed by Bažant. The experiments indicate that larger specimens tend to fail in a more brittle manner, while smaller specimens tend to fail in a less brittle or more plastic failure.