Journal of Materials in Civil Engineering

Tests on steel hollow tubes of square and circular sections filled with foamed and lightweight aggregate concrete were conducted to investigate the contribution of these concretes to the strength of cross sections of composite members. Eight short column specimens filled with foamed and lightweight aggregate concrete, four specimens each, were tested under axial compression to calculate the squash load. Furthermore, eight simply supported short beams of similar sections, also four specimens for each concrete, were tested in bending to calculate the ultimate moment capacity. Unfilled steel sections of similar specimens were also tested and results were compared to those of filled sections. Theoretical values of squash loads and ultimate moment capacities for the test specimens are also included in this paper. The results of this investigation showed that the foamed concrete contribution to the squash load of composite sections is negligible while its contribution to the bending strength is quite significant. On the other hand, the contribution of lightweight aggregate concrete to the squash load and bending capacity is shown to be considerable.

Mixtures of liquid CaCl₂ and NaCl are being tested as prewetting deicers for better deicing and improved cost-effectiveness at the Minnesota Department of Transportation. However, the proper mixing ratio of CaCl₂ and NaCl needed to provide optimum deicing at various temperatures is not well known because of the lack of NaCl-CaCl₂-H₂O ternary-phase diagrams. The mixture of CaCl₂ and NaCl should be a liquid phase (solution) to be an effective prewet deicer at winter temperatures, and to prevent clogging of spray pumps. The phases of CaCl₂/NaCl mixtures vary with the ratio of CaCl₂/NaCl and with temperature. In this investigation, the ternary-phase diagrams of NaCl-CaCl₂-H₂O were constructed in terms of liquid phase at 22, 0, −15, and −28°C by determining the freezing temperatures and the solubilities of various CaCl₂/NaCl mixtures. The proper mixing concentrations of CaCl₂ and NaCl to be an effective prewet deicer at a certain temperature was determined from the ternary-phase diagrams.

A study of the mechanical behavior of wood members either reinforced or strengthened with fiber-reinforced plastic (FRP) materials in the form of sheets (laminates or fabrics) externally bonded to the shear-critical zones is presented in this paper. The analysis is described first for the (short-term) behavior of shear-reinforced wood members, followed by parametric studies to assess the effect of the type and amount of FRP reinforcement on the response of wood-FRP members. It is shown that the effectiveness of FRP reinforcement can be quite high, and that it is maximized when the fibers are placed in the longitudinal direction and the height of externally bonded sheets is just a little higher than a limiting value, beyond which FRP failure precedes wood failure. In the experimental part of the study, 21 wood beams designed to fail in shear are reinforced with carbon-FRP fabrics at various configurations and area fractions and tested to failure. The agreement between experiments and analysis, in terms of shear capacity, was found to be quite satisfactory.

The paper describes a novel method for determining the failure criterion of masonry in biaxial bending. The conventional failure theories are not applicable to masonry that exhibits both strength and stiffness orthotropies. The failure criterion has been established from a novel test described in this paper. It appears that the weaker direction cracks in flexure first, in many cases, and the load is then shed to the stronger direction. Final failure happens only after the stronger direction fails in flexure. The cracking and failure in biaxial bending is predicted by the equations given in this paper.

There is ample evidence based on uniaxial (unconfined) compression that asphalt concrete exhibits behavior that depends on the loading or straining rate. This paper describes the results of an experimental program aimed at investigating rate sensitivity of asphalt concrete in a more general stress state, namely, in triaxial (axisymmetric) compression. Laboratory compacted specimens were subjected to three loading histories: (1) constant load (static creep); (2) repeated constant load (repeated static creep); and (3) haversine load (dynamic creep). The creep and repeated creep test programs allowed for separating the hydrostatic and the deviatoric response, and the contribution of the elastic, viscous, and plastic properties in the overall response. The haversine tests concentrated on the deviatoric response, and were conducted to investigate the influence of load frequency and number of cycles. The creep results show small deviator-induced dilation that is nearly fully recoverable during the rest period, and which, in some applications, can be neglected or approximated by an elastic response. The deviatoric response, on the other hand, is not recoverable, and can be modeled as a sum of elastic, plastic, viscoelastic, and viscoplastic strains, all being linear functions of the deviator stress. Similar behavior was observed in repeated creep tests. The response to haversine loading can be separated into a response close to that observed in creep tests and, beyond initial transient response, into a linearly viscoelastic harmonic response. It was found that power laws accurately describe the time-dependent deviatoric strains.

Composites of concrete and polymers of various kinds are used in many applications. This paper briefly reviews the history of polymers in combination with cement as a building material, where the polymer is not in the form of fiber or mesh reinforcing, but in the form of a polymerized matrix comingled with the hydrated cement paste. The microstructure and properties of the composite polymer-modified concrete are described, and some current and possible future applications are mentioned. Several recently published articles and technical papers dealing with polymer-modified concrete are critically reviewed.

This research was carried out to evaluate the use of foundry sands on properties of flowable slurry. Two different flowable slurry mixtures were proportioned for strength levels in the 0.34–0.69 MPa (50–100 psi) range, at 28 days, using two different sources of foundry sand and two different sources of ASTM Class F fly ash. Flowable slurry mixtures containing fly ash, without any foundry sand, were used as reference mixtures for this investigation. For each reference mixture, additional mixtures incorporating clean and used foundry sands as a replacement for fly ash were also proportioned. These flowable mixtures made with and without foundry sand were evaluated for bleeding, depth of nail penetration, settlement, shrinkage, condition of set, etc. In general, bleed water increased with an increase in the added mix water or foundry sand content of the mixtures tested. The settlement decreased with a decrease in the slurry water content. All the test specimens showed no sign of shrinkage cracks. The depth of nail penetration decreased with increasing age or decreasing water content. Compressive strengths of the test mixtures were found to vary between 0.28 and 0.62 MPa (40–90 psi) at 28 days. The overall results showed that excavatable flowable slurry with desirable physical properties can be manufactured using foundry sand as a replacement for fly ash up to 85%.