Journal of Materials in Civil Engineering

It has been claimed in the past that one of the main concerns regarding the use of galvanized reinforcement is a possible decrease of the rebar/concrete bond strength. The available results in the literature are contradictory to this. Besides, no long-term-study results have been found. In this paper, a series of tests is presented that compares the bond of deformed bare rebars with galvanized ones, exposed up to 10 years to a chloride environment in natural seawater (Mediterranean). In the case of galvanized rebars, the action of an H₂ inhibitor has been considered as well. The results show that galvanized rebars maintain bond characteristics throughout the test period, with values much higher than the minimum requirements. The addition of an H₂ inhibitor or the use of cements with a high alkali content has shown to be irrelevant in the long term.

In recent years, considerable research has been conducted in the construction of pavement layers incorporating foamed asphalt (FA). Development of improved foaming techniques has enabled both effective and economical stabilization of marginal quality pavement materials. This paper explores the ability of using FA to stabilize local sebkha soils to be used as a base or subbase material in asphalt structures under the relatively high temperature conditions in eastern Saudi Arabia. For the sake of relative performance and cost comparison, three types of treatment were used to stabilize the low quality sebkha soil: FA, emulsified asphalt, and sulfate-resisting (type V) portland cement. Marshall stability, indirect tensile, and unconfined compressive strength tests were performed to evaluate the properties of Marshall-prepared samples. Properly designed FA sebkha soil with as little as 2% cement displayed significant improvement in the strength properties, as compared with those of emulsified and cement-treated sebkha mixes. From cost perspectives, the FA-sebkha-2% cement mixture exhibited a superior rating as compared with the other stabilizing agents.

Studies have found that over 80% of total water ingress occurs at the brick/mortar interface and not through the brick unit or the mortar. The interface between the brick and mortar is influenced by the tensile bond strength between the two, which is highly affected by the applied load on the structure. However, numerous and often innovative laboratory testing techniques have been developed to assess water ingress under realistic weather conditions, but they consider only unstressed panels. One of the main objectives of this paper is to identify how crucial is the changing of loading direction and applied stress level on the formation of cracks and eventually on water ingress at the brick/mortar interfaces in masonry walls. The paper also presents some of the results from a research program carried out recently on stressed brickwork masonry, which shows that stressing has a fundamental and quantifiable effect on controlling water ingress.

This paper presents results of an extensive experimental parametric study of the mechanical response of various types of fiber-reinforced concrete tested under triaxial stress combinations. The objective of this study was to characterize the constitutive properties of these materials, with respect to fiber type and content, load path, condition at testing, and specimen size. A total of 250 tests were done on cylindrical specimens made of concretes with fiber contents (volumetric ratio): (1) steel microfiber, 1 and 2%; (2) mix of steel microfiber and long hooked steel fiber, 1 and 2%; (3) polypropylene fiber, 1.5 and 4%; and (4) mix of steel microfiber and polypropylene fiber, 2.5 and 5%. Triaxial stresses were applied either by hydraulic pressure or by means of passive confinement. In the latter procedure, lateral stress was provided by means of carbon fiber reinforced polymer jackets, wrapped to a fixed number of layers. Parameters of this component of the test program were (1) the number of wrap layers (one, two, or three); and (2) specimen size (two sizes were considered). Experimental results were used to quantify the relative influences induced by the various fiber additives and document the effectiveness of confinement provided by carbon fiber reinforced polymer wraps in comparison with actively applied lateral pressure. By mixing fibers of drastically different lengths, changes were effected both on the microstructure of the cement paste (by increasing its toughness) and on the macroscopic structure of concrete, thereby increasing the postpeak deformability and ductility of the material.

In recent years silica fume, a by-product in the production of metallic silicon or ferrosilicon, has gained acceptance for use as a mineral admixture in cementitious materials. The principal areas of application of silica fume include producing high strength concretes and improving concrete resistance to aggressive chemicals. A new application of silica fume for enhancing water resistance of cement and gypsum-cement materials is reported. As a characteristic of water resistance the wet/dry strength ratio of the material was used. The values of strength and the wet/dry strength ratio for hardened cement pastes of various ages, with water to cementitious material ratio varying from 0.33 to 0.50, were obtained. It is shown that, despite the low value at 3 days, the wet/dry strength ratio of cement-silica fume paste rises significantly after 28 days of water curing, achieving the value of pure portland cement paste having the same water to cementitious material ratio, and at 200 days exceeds it, approaching a value of 1. However, the most pronounced improvement of water resistance was fixed for the gypsum-cement materials with 5% addition of silica fume, where the value of the wet/dry strength ratio after 200 days of water immersion increased twice as much, compared with the ratio after 3 days of water immersion. The physical and chemical mechanisms of this improvement are discussed.

Modes of unrestrained free vibration of rectangular parallelepipeds are excited by impact and combined with solutions to the weak form of the equations of motion corresponding to the 3D equations of elasticity and periodic motion to provide estimates for the elastic constants of anisotropic materials. This method has been previously applied to isotropic materials based on analytic approximations for the relationship between elastic constants and resonant frequencies. The present approach extends this procedure to account for material anisotropy and variance in specimen dimension, and we apply this technique to several specimens of differing material type, constitution, and shape to compute various components of the elastic stiffness tensor. Our results are in very good agreement with those found by other techniques.

Knowledge of moisture storage capacity above the hygroscopic range is essential when calculating moisture, especially when different materials are to be connected. Generally, the storage capacity is represented by water retention curves, in which suction is plotted against the moisture content. In a number of laboratories in Europe and North America, the pressure plate and pressure membrane techniques are used to measure water retention curves. There are, however, various ways of carrying out such measurements. This paper compares two different methods of presaturating the specimens before testing, namely capillary and vacuum saturation. It also examines the effect of different beddings between the specimen and the ceramic plate. It is shown, as expected, that capillary and vacuum saturated specimens give differential results. Absorption tests clearly show that, for some materials, capillary saturation is a vague concept. For this reason, vacuum saturation is generally to be preferred. In the test with different beddings, no significant differences were found.

This paper presents a new mathematical relationship for representing the stress-strain behavior of structural steel at elevated temperatures. The relationship is constructed by fitting two versatile, continuous equations to experimental data. The first equation, a general stress-strain equation previously proposed by Poh, is used for characterizing the stress-strain data. The second equation is proposed in this paper. It is used for representing the variation of the stress-strain behavior with temperature. A simple two-stage procedure is used for fitting the equations to the experimental data. This gives a set of curve fitting coefficients that can be simply expressed in a matrix format. It is shown that the resulting relationship accurately represents the experimental data. Furthermore, since the relationship comprises only two equations and a coefficient matrix, it can be easily incorporated into computer analysis programs. It can also be readily used for establishing the properties of other steels.

The overall aim of this paper is to investigate the effect on pore structure of concretes exposed to hot and dry environments and made with combinations of portland cement, silica fume, and slag. Five different concrete mixes were cast and tested to investigate the role of different periods of water curing on the porosity and pore structure characteristics when exposed to two different hot/dry environments. The first environment was an indoor laboratory (23°C + 2°C and 70% relative humidity + 10%) and the other was the real outdoor environment in Dubai, representing a typical hot climate. Pore structure was evaluated by means of mercury intrusion porosimetry. The results indicated that longer water durations of water curing reduced porosity and pore sizes significantly. The influence of water curing was maximum in the case of slag mixes cured in the outdoor environment. Hot climates are seen to have adverse effects on the pore structure characteristics, especially when no water curing is involved. The properties of slag concrete were seen to be a function of duration of water curing. The properties of slag concrete mixes exposed to hot/dry environments without any water curing were very poor.

The compressive behavior of portland cement concrete with vitrified soil coarse aggregate is the focus of this paper. A total of 10 batches of concrete were examined at four different coarse aggregate volume fractions with three different combinations of vitrified and natural coarse aggregates. For comparison purposes, the ratios of cement, water, and fine aggregates were held constant. The stress-strain curves, modulus of elasticity, compressive strength, and Poisson's ratio are examined as a function of coarse aggregate content. Results show a decrease in compressive strength as the volume fraction of vitrified soil aggregate increased. Moduli of elasticity for concrete with vitrified soil aggregate are considerably higher than concrete with natural aggregate. The Hirsch-Dougill model is extended and applied to a three-phase material to predict the modulus of elasticity of concrete with natural and vitrified soil aggregates.